Monographs in Aerospace History Number 40—Journey Into Space Research 35

CHAPTER 5 Space Simulation Studies

In the period before the start of the

space program, the division to which I

was assigned was called the Flight

Research Division. As described in reference 1.1, most of the research work

was conducted on full-scale airplanes.

Some simulation studies were made,

however, using special simulators

designed to study specific problems.

These simulators included a device

called the yaw chair, that enabled a

study of the ability of a human pilot to

control lateral oscillations over a wide

range of oscillation periods with both

stable and unstable damping. In addition, a device called the NAP (Normal

Oscillation and Pitch) chair was built

that simulated the vertical and pitching

motion of an airplane over a range of

vertical motion of about 6 feet. These

simulators allowed covering a range of

conditions systematically, rather than

obtaining different conditions by considering results on a number of different

airplanes. At the time the space program started, a three-axis rotational

simulator was under construction in

which a cockpit was mounted to provide

angular motion in pitch, roll, and yaw.

This simulator was intended to study

combined rolling and yawing oscillations

of an airplane, but it found use for other

purposes during the space program. In

contrast with modern simulators that

use electronic displays and general-purpose motion bases, these simulators

used mechanical systems to simulate

accurately the motion of the vehicle. The

output of the mechanical system was

amplified by a hydraulic servomechanism based on a variable displacement

hydraulic pump. Servomechanisms of

this type were available in Naval gun turrets. I have since learned that the development of these servomechanisms was

largely attributed to Charles Manley, the

same man who earlier perfected the

excellent radial motor used in Samuel

Langley’s aerodromes. 

Almost simultaneously with the start of

the space program, all testing of highspeed airplanes was transferred to the

High-Speed Flight Research Center at

Edwards Air Force Base, now called

the Dryden Flight Research Center.

I was left with the problem of deciding

on the best use for the engineers under

my supervision, who had been trained

in studying the stability and control of

airplanes.

Airplanes, of course, had been flying for

many years, and there was little need

for studying the basic principles of stability and control. Most simulation work

on airplanes was devoted to studying

optimal stability and control characteristics or to finding the characteristics that
36 Monographs in Aerospace History Number 40—Journey Into Space Research

Space Simulation Studies

would provide the most desirable handling qualities for the pilot. At the start of

the space program, before the first

manned orbital flight, there was much

less confidence in the ability of a human

pilot to perform the tasks required for

space operations. Many engineers

expressed the view that it would be

better to design spacecraft with completely automatic control. Test pilots, on

the other hand, who had at least

approached orbital flight conditions in

tests of very high-altitude airplanes,

usually felt confident that they could

control the entire flight of a spacecraft

just as they had controlled high-altitude

airplanes. 

To resolve some of these questions, I

felt that the conditions encountered in

the various phases of a space vehicle

flight should be simulated as accurately

as possible to give the astronauts

experience with the new problems of

space flight. The following discussion

describes some of the work done in this

period.

After the successful completion of John

Glenn’s first orbital flight, most doubts

concerning the effects of weightlessness were dispelled. Soon after this

time, however, definite space programs,

such as the Gemini and Apollo missions, were planned. The simulation

work then focused on specific problems

encountered in the launching, flight,

entry, and landing of the spacecraft

designed for these missions. These simulations are described in reference 5.1.

Lunar Landing Research 

Facility

Landing on the surface of the Moon was

known to be one of the most critical

phases of the Apollo program. Control

by an astronaut, at least during the final

phases of the descent, was considered

mandatory because the nature of the

lunar surface was not known in sufficient detail to plan the exact spot for

touchdown. Several conditions present

a control problem considerably different

from that of landing an airplane on

Earth. The lunar gravity is one-sixth that

on the Earth. All control of lift and attitude is provided by rockets, which often

provide a discontinuous, on-off control

rather than a linear variation of control

force familiar on airplane controls. The

complete lack of an atmosphere on the

Moon makes it impossible to use any

type of aerodynamic control.

When President Kennedy made his

announcement of a major program to

send men to the Moon on May 25, 1961,

I immediately started thinking about

how this operation could be simulated.

I wrote a memorandum on this subject in May 1961 and discussed the

subject with the Associate Director,

Lawrence K. Loftin, Jr. on June 26,

1961. 

The trajectory of the lunar vehicle would

be different from that on Earth because,

as stated previously, the gravitational

attraction of the Moon is only one-sixth

that of the Earth. To simulate the

reduced gravity, I visualized a suspension system for the simulated vehicle

that would exert a constant force in the

vertical direction equal to five-sixth the

weight of the vehicle. The force on the

cable on which the vehicle was suspended could be measured by a straingauge balance at the vehicle and used

to control the output of a servomechanism that reels the cable in and out as

required to apply the desired constant

force to the top of the cable. To provide

for horizontal motions of the vehicle in

the fore-and-aft and lateral directions,

sensors would measure the tilt of the

cable from the vertical and would be

used to control servomechanisms that

moved the suspension point to keep it

directly over the vehicle. 
Lunar Landing Research Facility

Monographs in Aerospace History Number 40—Journey Into Space Research 37

The motions of the vehicle in response

to pilot commands would be provided by

rockets. As in an actual lunar vehicle, a

rocket sufficiently powerful to support

the weight of the vehicle in the lunar

environment, plus some extra power to

maneuver, is required. Smaller rockets

are used to provide pitching, rolling, and

yawing moments. Previous studies had

found that a system using a platinum

catalyst to decompose hydrogen peroxide into steam and oxygen provided a

convenient and relatively safe means to

make a controllable rocket.

My first concern in designing the lunar

landing facility was to analyze the servomechanism used to maintain a constant

force in the suspension cable while the

vehicle was going through the maneuvers of landing. While the technical

details of this analysis are too involved

to present in this discussion, a brief

review of the problems involved in servomechanism design may be of interest.

An example of a simple type of servomechanism is an autopilot to hold an

airplane on a desired constant heading.

If the heading deviates from the desired

value, a compass or other heading

detector measures the error in heading.

The error may be converted to an electric voltage that is fed to an electronic

amplifier. The output of the amplifier

drives an electric motor that moves the

rudder of the airplane in the direction to

reduce the error. As the heading error is

reduced to zero, the rudder is returned

to its neutral position. The ratio between

the rudder angle and the error in heading is called the gain of the servomechanism. Increasing the gain increases

the speed with which the heading error

is reduced, but it may cause the rudder

to overshoot its neutral position and

oscillate about zero. Beyond a certain

value of the gain, the oscillations

increase with time, a condition called

dynamic instability. The gain must be

kept to a value safely below that which

produces instability. 

In the case of the lunar landing research

facility, a servomechanism maintains a

constant force in the suspension equal

to five-sixth of the vehicle weight while

the pilot controls the rocket that provides an additional one-sixth of the

weight plus whatever additional force is

required to control the rate of descent or

to slow the vehicle down for landing.

These force variations supplied by the

rocket act as disturbances to the force in

the cable. The error in the cable force is

corrected by the servomechanism by

varying the speed at which the cable is

reeled in or out.

If a steady disturbance is applied to a

system controlled by a servomechanism, a steady error may result. This

condition may be corrected by placing

an integrator in the feedback loop. The

integrator builds up a signal that

increases with time to offset the steady

error. An integrator also has a gain to

determine its speed of operation. If the

gain is too large, dynamic instability will

again result. In general, the tendency to

instability is greater with an integrator in

the circuit. 

In the case of the lunar landing facility, a

typical mode of operation is to let the

vehicle fall freely under a steady acceleration of one-sixth g until the descent

rate reaches the desired value to start

the landing run. In this case, the cable

tension should remain at its desired

value during this period of constant

acceleration. To maintain this steady

value during conditions of constant

acceleration, servomechanism theory

shows that a double integration of the

error is required. Such an arrangement

is called a type 2 servomechanism. I

therefore realized that a double integration should be included in the computer

of the lunar landing facility. With such

an arrangement, careful design of the
38 Monographs in Aerospace History Number 40—Journey Into Space Research

Space Simulation Studies

gains is required because an even

greater tendency to instability exists.

Another effect that influences the stability of the response of the system is the

time lag between the output of the servomechanism and the resulting force

applied to the vehicle. This lag results

from the time required for tension and

compression waves to travel down the

suspension cable. This speed is equivalent to the speed of sound in the cable.

If a braided steel cable is used, the

speed of sound in the cable is about

1000 feet per second. For a cable

200 feet long, the lag is two-tenths of a

second. 

Despite the effort to make an accurate

simulation of the trajectory and control

characteristics of the lunar module in

the lunar environment, one factor that

cannot truly simulate conditions on the

Moon is the gravitational force of the

Earth acting on the pilot’s body. The

effect of this force can be minimized by

strapping the pilot in and otherwise supporting his body so that this force does

not interfere with his control activities.

Other factors that complicate the analysis of the servomechanism are the

springiness of the cable, which changes

with the altitude of the vehicle, the

damping of the drive mechanism, and

the change in weight with fuel usage. I

considered as many of these factors as

possible in an analytical study of the

system. All these factors made the analysis difficult either with available theory

or with the computers available at that

date. I therefore considered an experimental study of the system necessary.

To test the feasibility of the contemplated system, a simplified system,

called the pilot model, was built in which

a pilot’s chair was suspended by a

vertical cable. A photograph of the pilot

model in operation is shown in figure 5.1-1 with the engineering test pilot

Jack Reeder at the controls. A servomechanism that reeled the cable in or

out was mounted in the girders in the

roof of the NACA Full Scale Tunnel,

60 feet above the vehicle. This facility

was chosen because the wind tunnel

had a compressed air supply that could

be used to provide thrust for the rocket

that was used to overcome the simulated lunar gravity of one-sixth of the

vehicle weight. An available analog

computer of fairly early design was used

to calculate the signals driving the servomechanism. With this apparatus, the

gains of the system were varied experimentally until a reasonably constant

cable tension could be maintained as

the pilot performed a simulated landing.

An important reason for using the overhead suspension is that if any loss of

control occurs, either due to pilot error

or some malfunction in the system,

the vehicle can be locked in place or

lowered slowly to the ground like an

elevator. 

The successful operation of the pilot

model, despite some claims that it

would not be feasible, gave me confidence to propose the design and construction of a full-scale system. I wrote a

memorandum on the proposed system

and made a trip with Lawrence K. Loftin

to NASA Headquarters in Washington,

DC. There we discussed the project with

Ira H. Abbot, who at that time was an

assistant director for space programs.

He quickly agreed to support the project

and to provide the necessary funds. 

At the same time that my project was

proposed, engineers at the Ames

Research Center proposed a flight vehicle that worked on the same principle.

This device, called the Lunar Landing

Training Vehicle (LLTV), used a turbojet

engine to support five-sixth of the vehicle weight. The engine was mounted on

gimbals and controlled by servos connected to an inertial measurement unit

so that it would always point vertically.
Lunar Landing Research Facility

Monographs in Aerospace History Number 40—Journey Into Space Research 39

The pilot’s cockpit was mounted in a

large frame that surrounded the jet

engine and contained the necessary

rocket engines to exert force to offset

the simulated lunar gravity and to provide pitch, yaw, and roll control. I

thought that this device would be very

dangerous to fly because it had no

means to recover in case of loss of control. Eventually, three of these vehicles

were built. The cost of this project was

undoubtedly many times that of the

Lunar Landing Research Facility

(LLRF), but the funding for the Apollo

FIGURE 5.1-1. Pilot 

model for LLRF being 

flown by NASA test 

pilot Jack Reeder.

L-63-9783
40 Monographs in Aerospace History Number 40—Journey Into Space Research

Space Simulation Studies

program was so generous that both

projects were supported.

The firm of Jackson and Moreland was

selected to build the gantry and operating system for the LLRF. The estimated

cost was $4,997,700, which was close

to the actual cost. The contract for a

piloted vehicle to be lifted on the LLRF

was let to Jered Industries, a small company with shops located under an old

football stadium in New England. This

company built the piloted vehicle for the

remarkably low cost of $250,000. This

vehicle differed from the LM used in the

FIGURE 5.1-2. Lunar 

Landing Research 

Vehicle showing original cab for pilot.
Lunar Landing Research Facility

Monographs in Aerospace History Number 40—Journey Into Space Research 41

Apollo mission because the LM had not

been designed at the time the LLRF

was constructed. The test vehicle differed from the LM in being smaller and

initially having a bulbous helicopter type

cockpit (fig. 5.1-2). Later the LLRF test

vehicle was equipped with a cockpit that

placed the astronaut in a standing position like that in the LM, with wide

windows to see the lunar landscape

(fig. 5.1-3). Both vehicles had outstretched legs with pads on the ends to

give a stable support on the lunar

surface.

A photograph of the completed LLRF is

shown in figure 5.1-4. The gantry, or

large crane structure used to suspend

the vehicle, is 300 feet long, 250 feet

high, and 100 feet wide. The overall

height of 250 feet was set by the limits

on the height of buildings on Langley Air

Force Base to avoid interference with air

traffic. The tracks on which the suspension system rode allowed a lateral travel

of ±15 feet and a movement down the

track of 250 feet. With allowance for the

space taken up by the structure and

suspension system and the overall

height of the suspended vehicle, the

change in altitude during a test run was

about 185 feet. Part of this amount was

taken up by the distance required to fall

at 1/6 g to the initial descent velocity.

The system was finished in 1966 and

completed initial testing in 1967.

After the initial planning of the LLRF and

the construction had been completed, I

took little part in actual operations.

Donald E. Hewes was placed in charge

of running the facility, with Thomas

O’Bryan as assistant. Among the other

NASA engineers assigned to the facility

were Eric Stewart, Maxwell Goode,

Randall Harris, Max Kurbjun, Amos

Spady, Marna Mayo, and Frank Read.

As the name implies, research work was

done on the facility to study the control

laws relating the pilot’s control inputs to

the vehicle response, the ability of the

pilot to make a sufficiently soft landing,

and so forth. NASA test pilot Lee

Person did much of this work. In later

stages of the work, Don Hewes

arranged to have piles of cinders placed

on the ground under the facility that

were shaped to simulate lunar craters

and terrain. In addition, tests were made

at night with lighting simulating the low

position of the Sun that would be

present in the actual lunar landing. The

shadow of the vehicle on the terrain,

shown in figure 5.1-5, gave the astronauts a good impression of the height of

the lander as it approached the surface.

All the astronauts who were scheduled

to make lunar landings in the Apollo program took part in test runs made under

these conditions. The astronauts later

stated that the landings were very good

simulations of the actual landings on the

Moon, and that they were very helpful in

training for these operations (ref. 5.1).

While the tests at Langley were in

progress, the Ames flying vehicle, the

LLTV, was placed in operation at the

Manned Space Center at Houston and

was flown by the astronauts. In one of

the early tests, the vehicle went out of

control. The astronaut, Neil Armstrong,

ejected barely in time to save his life,

and the vehicle was destroyed. I was

called to Houston to serve on the review

board that studied the causes of the

crash. The cause was found to be that

aerodynamic forces on the framework of

the vehicle in forward flight were large

enough to overpower the jets used for

control. One of the remaining vehicles

was then mounted in the Langley FullScale Tunnel to study means for reducing the aerodynamic forces on the

framework.

Later, another of the LLTVs went out of

control and crashed while being flown

by Joe Algranti, a former Langley test

pilot who was then in charge of flight

operations at Houston. The crash was
42 Monographs in Aerospace History Number 40—Journey Into Space Research

Space Simulation Studies

L-67-9108

FIGURE 5.1-3. Lunar 

Landing Research 

Vehicle hovering with 

stand-up cab for pilot.

L-69-6324

FIGURE 5.1-4. Lunar 

Landing Research 

Facility at NASA 

Langley Research 

Center, Hampton, 

Virginia.
Lunar Landing Research Facility

Monographs in Aerospace History Number 40—Journey Into Space Research 43

again found to be caused by a wind

gust, this time from the side, that overpowered the controls. Both Armstrong

and Algranti were saved by the MartinBaker ejection seat, a so-called zero

altitude ejection seat that shot the pilot

up from ground level with a rocket sufficiently powerful to put him at an altitude

where he could be saved by his parachute. This seat, an English invention,

had become available just in time to be

used in the program.

FIGURE 5.1-5. Simulated 

craters on terrain in 

landing area of LLRF. 

Shadow of vehicle 

with lighting simulates 

low Sun angle. 

L-69-4850
44 Monographs in Aerospace History Number 40—Journey Into Space Research

Space Simulation Studies

L-06088

L-06092

FIGURE 5.1-6. Lunar 

Landing Research 

Facility in use at crash 

test facility.

(a) Test aircraft about 

to impact ground in 

crash test facility.

(b) Results of crash 

test.
Lunar Orbit and Landing Approach (LOLA) Simulator 

Monographs in Aerospace History Number 40—Journey Into Space Research 45

The astronauts felt that both simulators

were of value in training for the lunar

landing. The LLTV had the advantage of

providing for a greater altitude at the

start of the maneuver, 300 or 400 feet

instead of about 185 feet in the LLRF.

On the other hand, the LLRF had the

advantage of more realistic simulation

of the terrain and lighting conditions.

The astronauts, like typical test pilots,

ignored the dangers inherent in the

flight vehicle and continued making simulated landings with the remaining vehicle, but great care was taken to restrict

testing to calm days. 

The Apollo program was stopped

abruptly after six successful lunar landings, even though two additional Saturn

launch vehicles had been constructed to

continue the program through two more

flights. Astronaut training flights were

therefore stopped. Don Hewes continued research with a small one-man

vehicle to study the feasibility of a flight

vehicle for lunar exploration in place of

the lunar rover that had been used on

the last three Apollo flights. The flight

vehicle showed promise for much

greater range than the rover because

the low gravity on the Moon allows a

rocket-supported vehicle to fly for long

distances. This project was also

dropped, however, when there was no

prospect for future lunar landings.

The LLRF stood idle for a number of

years and the servos and other equipment on top of the gantry were

removed. A new use was found for the

gantry as a crash test research facility.

In this application, used airplanes or airplane structures were hauled up to the

top of the gantry and allowed to fall in a

circular path, like a pendulum, to impact

the ground. For some tests, a rocket

boost was used to increase the speed of

the impact. These tests have been

found to be very useful in designing

the airplane and the cockpit structure

to protect the pilot in case of a crash.

Pictures of such a test are shown in figures 5.1-6 (a) and (b).

The most novel feature of the LLRF

from a technical standpoint was the servomechanism that maintained a constant tension in the suspension cable

during the landing maneuver. Other

uses for this feature are rather scarce,

but I did learn of one practical application. A group of engineers from Canada

came to Langley to discuss the use of

the constant-tension servo to haul a

helicopter down to the deck of a ship in

a rough sea. In this application, the

cable would be lowered from the helicopter and hooked onto the deck of the

ship by a crewman on the ship. Then the

cable would aid the pilots of the helicopter in descending to the deck without

experiencing large impact loads due to

the motions of the deck. 

The LLRF and the Research Vehicle

have been declared State Historic Landmarks. The gantry is still the most prominent feature on the NASA Langley

landscape, and the vehicle is on display

in the Virginia Air and Space Center in

Hampton.

Lunar Orbit and Landing 

Approach (LOLA) Simulator 

The Lunar Orbit and Landing Approach

(LOLA) simulator was, as the name

implies, intended to study the ability of a

pilot to control the LM following its separation from the Command and Service

Modules during the lunar orbiting phase

of the flight until it reached the desired

landing area. This simulator was placed

under the direction of my division,

although I was not involved in its concept or design. Most of the planning for

the Apollo mission had been based on

the idea of computer-controlled navigation based on either astronaut measurements of angles to the Sun, Moon, and
46 Monographs in Aerospace History Number 40—Journey Into Space Research

Space Simulation Studies

stars, or on Earth-based radar measurements. This idea was opposed by

Charles H. Zimmerman, an early

Langley employee who had made notable contributions to stability and control

research by originating the free-flight

tunnel and the spin tunnel and by publishing reports on airplane stability theory. He later left to join the Chance

Vought company where he supervised

the design of the Vought F5U-1 “Flying

Turtle” VTOL fighter airplane, but later

returned to Langley after this project

was cancelled. As a result of his long

experience, his opinions carried considerable weight among the center supervisors. For a time, he was assigned to

the Director’s office but later was

appointed as assistant head of my division, the Aerospace Mechanics Division. Zimmerman felt strongly that all

the complex computers and instrumentation planned for navigation of the

Apollo were unnecessary and that an

astronaut could direct a space vehicle to

its destination based solely on his visual

cues, just as a pilot (at that time) often

did in flying an airplane cross-country.

This opinion was supported by Clinton

E. Brown, an Assistant Director at

Langley. As a result, they placed much

emphasis on building a simulator that

could investigate the Apollo pilot’s navigational ability and could be used to

train astronauts to fly to the Moon in this

manner.

The simulator involved several original

features. A camera was moved in

response to the pilot’s inputs over

a large map covered with threedimensional images of the lunar terrain.

The lunar craters and other features

were based on photographs of the

Moon and machined into Styrofoam®

blocks with a computer-controlled milling machine. The terrain modeled covered a path around the Moon in the

vicinity of the orbit. The images photographed by the camera were projected

on the interior of a sphere about 10 feet

in diameter, where the pilot’s cockpit

was located. As the pilot flew the simulated vehicle, the view of the Moon

slowly moved under the pilot and

appeared as it would in an actual lunar

orbit. The altitude had to be limited to a

minimum value equivalent to a few hundred feet on the actual Moon to prevent

the camera from bumping into some of

the higher features on the map. 

The construction of the simulator was

very expensive and time-consuming

because a simulator based on these

ideas had not been constructed before.

The terrain map was constructed of

large blocks of Styrofoam®, which were

carved by digital milling machines or

molded to the correct shapes. A special

TV camera with multiple lenses

provided a wide field of view. The

pilot’s control inputs were fed into a

computer that calculated the attitudes

and orbital motions of the vehicle.

The camera moved along a track, with

its height and attitude controlled by

servomechanisms (ref. 5.2).

Because the project was supported by

high officials at Langley, funds and personnel were provided to keep the

project moving. The engineers said:

“what LOLA wants, LOLA gets,” the

words of a popular song of that period.

When the simulator was finally tested, it

worked as planned, but the results

proved rather disappointing. In typical

test runs, the pilot sat in his cockpit for

up to an hour with little to do but watch

the landscape go by. When the pilot

started his descent to land, the simulator cut off to protect the camera. The

main benefit gained from this project

was the later development of simulation

equipment suitable for aircraft landing

studies. The lunar terrain was replaced

by a picture of the airport. The same

camera and projection sphere were

employed to study the ability of a pilot to

land an airplane under various condi-
Docking Simulator

Monographs in Aerospace History Number 40—Journey Into Space Research 47

tions. Some years later, electronic displays were developed and the large

terrain map was no longer required.

I wrote a memorandum to Charles J.

Donlan, then the Director of Research

at Langley, pointing out the fallacy in the

use of piloted control for navigation of a

space vehicle. Because of the large

amount of fuel required to put each

pound of weight into orbit, missions

must be planned to use an optimal trajectory to minimize the amount of fuel

required. This system is possible on a

spacecraft because the trajectory, influenced mainly by the accurately known

gravitational attraction of the Earth,

Moon, Sun and other heavenly bodies,

can be calculated with extreme precision. Disturbance from other sources,

such as atmospheric drag, solar wind,

radiation pressure, and magnetic effects

are ordinarily very small, and can be

allowed for by small corrections to the

ideal trajectory. By contrast, an airplane

flying across the country is subject to

large unpredictable disturbances due to

winds and gusts, weather variations,

and so on. Sufficient excess fuel is

always carried to allow flight to an alternate airport, usually at least 500 miles

from the scheduled landing field. This

excess fuel allows the errors involved in

navigation by a human pilot to be

tolerated. In space, on the other hand,

automatic guidance equipment and

computer-controlled corrections for any

errors in the trajectory must be used. As

an example of the margin of error

that can be tolerated, Astronaut Neil

Armstrong, in making the first manned

lunar landing, had to make a slight

manual correction during his final

landing approach to avoid a crater. The

landing was made with just 3 seconds

of fuel remaining, yet no one seemed

concerned about this small tolerance

for error. I have heard estimates of

the fuel remaining ranging from 3 to

20 seconds.

Docking Simulator

Rendezvous and docking with a target

vehicle was one of the main objectives

of the Gemini program because it was

required in the Apollo program when the

upper part of the LM was propelled up

from the Moon and docked with the

command and service modules in lunar

orbit for the return trip to the Earth. The

final stage of the docking involved manual control by an astronaut because

precise control was required for the

close alignment and gentle impact

required for a successful docking. 

The docking simulator, suspended from

the roof of the large flight research hangar in the west area of the Langley

Research Center, was built to explore

the problems of this operation. Arthur W.

Vogeley proposed the concept for this

device and supervised the personnel

who made most of the tests with it. A

target vehicle was suspended at one

end of a track attached to girders in the

hangar roof. A movable vehicle was

driven along the track to approach the

target during a docking maneuver. A

gimbal system was suspended from the

movable vehicle by an ingenious system

of cables originated by Vogeley. The

cables were arranged in V-shaped pairs

that maintained the outer gimbal in a

horizontal position while keeping it

directly under the movable vehicle. The

gimbal system could be moved up and

down by reeling in each pair of cables

simultaneously on a large pulley in the

overhead vehicle. Inside the gimbal system was the approach vehicle, which for

most tests was a replica of the Gemini

capsule.

The gimbal system with the capsule

mounted inside was an existing piece

of equipment that had been built to

study the pitch, yaw, and roll oscillations of airplanes in lateral maneuvers.

The gimbal angles were controlled by
48 Monographs in Aerospace History Number 40—Journey Into Space Research

Space Simulation Studies

electrohydraulic servomechanisms that

were operated through an analog computer system with inputs from the pilot’s

control stick. The main application of the

docking simulator was to study sighting

and target devices that would allow

the astronaut to sense his rate of

approach and alignment with the target

vehicle. The most successful devices

incorporated a “two-layer” device in the

target vehicle, such as a cross mounted

ahead of a small circle that would allow

the astronaut to judge when he was

properly aligned. In recent years, the

docking simulator was honored as a

State Historical Landmark. A photograph of the docking simulator is shown

in figure 5.3-1.

Aids for Extravehicular 

Maneuvering

Two devices were proposed for extravehicular maneuvering, one by Harold I.

Johnson and one by John D. Bird. In

discussing the reasoning behind these

devices, the approaches proposed by

the Johnson Space Center and their

contractors should be kept in mind. In

general, the devices considered by the

space center consisted essentially of a

strap-on vehicle that could hold the

astronaut in his space suit. The vehicle

itself had a stabilization system with

gyroscopes and automatic control

equipment, a set of rockets to allow propulsion and attitude control, and two

hand controllers, one for attitude control

L-64-4307

FIGURE 5.3-1. Docking 

simulator.
Aids for Extravehicular Maneuvering

Monographs in Aerospace History Number 40—Journey Into Space Research 49

and one for translation. Essentially, the

proposed vehicles were complete

spacecraft that could fit around an

astronaut. No one doubted that such a

device could be made to work, but the

cost of manufacturing such a device

would run into millions of dollars. The

frugal NASA engineers at Langley

thought that much simpler and less

expensive devices could be made to

accomplish the same purpose, while at

the same time allowing the astronaut to

work with a less encumbering piece of

apparatus.

Harold I. Johnson called his device a

“Space Gun.” It consisted simply of a

tank of compressed gas and a handheld tube with a nozzle at the end. The

astronaut was intended to hold the tube

and control the flow of gas with a trigger-type controller. Harold Johnson

believed that the astronaut could readily

learn to control his attitude and motion

through space instinctively by directing

the thrust of the device properly with

respect to his center-of-gravity position.

John D. Bird’s device (called “jet shoes”)

was inspired by swimmers using swim

fins. He proposed putting a pair of nozzles on the astronaut’s shoes that would

allow control of the thrust by valves

operated by the astronaut’s toes and

directed as required by motions of his

legs and ankles. This method had the

advantage of allowing complete freedom of the astronaut’s arms and hands.

These devices seemed to me so

unusual that simulation of their operation would be required before they could

be considered for use in space. To illustrate the varied opinions of the value of

simulation studies, Hartley A. Soule, an

early expert on aircraft control and handling qualities, said that he had no doubt

whatever that such devices could be

operated by an astronaut, and did not

see the need for any simulation tests.

For a time this opinion put an end to

tests of these ideas at Langley.

Harold Johnson, perhaps because of

his desire to try out his concept, transferred to the Johnson Space Center. In

time, the “space gun” was assigned a

position as an experiment on one of the

space flights involving EVA, and a brief

test in space was made. The astronaut

involved thought that the device performed successfully. So far as I know,

no further use was made of the device.

The Johnson Space Center personnel

contracted for the construction of the

“space vehicle” type of device, and it

was tested in a large simulation facility

constructed by the Martin Company.

This facility, somewhat on the same

principle as the Langley Lunar Landing

Facility, suspended the astronaut in

his chair and simulated its motions in a

zero g environment. The simulation

facility allowed perfecting the characteristics of the device. This system has

since been used for all tests involving

EVA. The astronauts expressed preference for the vehicle-type device, probably because of a greater feeling of

security obtained in a vehicle that was

automatically stabilized.

Don Hewes undertook the tests of John

Bird’s idea of control through foot

motions. He made a very flat and

smooth floor by pouring slow-drying

epoxy cement on a flat floor area that

had boundaries at its edges. Don

thought Bird’s idea of thrust control by

toe switches was rather far-fetched.

Instead he used a hand controller, and

fitted the astronaut’s shoes with nozzles

that could fire fore or aft. The astronaut

lay on his side on a framework supported by three air bearings. These

bearings were flat disks that had small

holes on the bottom through which compressed air was admitted. These bearings supported the weight of the

astronaut and his equipment so that the

system was floating on a cushion of air.
50 Monographs in Aerospace History Number 40—Journey Into Space Research

Space Simulation Studies

Similar air bearings were used by

numerous people at Langley for space

simulations. They reduced the friction to

zero, so that the motion on the floor provided a two-dimensional representation

of the motion in space. Hewes found

that motion over the flat floor with the

foot-operated device could be controlled

very easily. 

To avoid the limitation to two-dimensional motion, several organizations

built large water tanks in which the

astronauts in their space suits, loaded

to a condition of neutral buoyancy, could

practice operations required in space.

This method eliminated any steady

forces on the astronaut in a motionless

condition, but of course it introduced

rather large drag forces opposing any

motion. Nevertheless, the method

proved effective because most motions

used in EVA were slow. Art Vogeley built

a water tank at Langley 30 feet deep

and 30 feet in diameter, in which the

Langley test pilots could don space

suits and experience the feeling of zero

gravity. These tests were soon stopped

because the space centers had larger

facilities, more trained personnel, and

because of safety considerations.

A fixed-base, 6 degree-of-freedom

visual simulator utilizing a projection

sphere, to be described later, was also

used to test Hewe’s foot-controlled

maneuvering device. These tests were

successful in demonstrating the ability

of a pilot to control tumbling motion in

space. Tests of the foot-controlled

maneuvering unit were later made in the

Skylab by astronauts Alan Bean and

Gerald Carr during space missions. The

hand-controlled unit proposed by the

Johnson Space Center was also tested

in these missions. As mentioned previously, the astronauts preferred the more

complex vehicle made under contract by

the Martin Company.
Monographs in Aerospace History Number 40—Journey Into Space Research 51

CHAPTER 6 My Work With Johnson 

Space Center

When the Space Task Group moved to

the Johnson Space Center, they soon

were in a period of rapid expansion and

were involved in contract work to produce ground facilities and space vehicles for the space program. Close

contact was maintained with Langley

research engineers to provide assistance with research and development

problems that arose. Axel Mattson, a

Langley engineer with long experience

in aerodynamics and in facility development, was appointed as the liaison

man stationed at Johnson Space Center to maintain contact with Langley

personnel.

Dr. Christopher C. Kraft, an engineer

who worked under me in the Stability

and Control Branch of the Flight

Research Division, joined the Space

Task Group and moved to the Johnson

Space Center. He first held a position as

Flight Controller and was instrumental in

designing the Flight Control Centers at

Cape Kennedy and later at Houston as

well as in directing many early flights.

Kraft was an excellent administrator and

held successively higher positions at the

Johnson Space Center until he became

the director of the Center shortly after

the start of the Shuttle program. Kraft

has written a book describing his work

as a flight controller (ref. 6.1). Kraft

always very generously gave me credit

for his early training in technical work.

When problems arose at Johnson, he

frequently called on me to assist with

their solution. I did not always have the

knowledge to provide the solutions to

these problems, but I was usually able,

through my contacts at Langley, to find

the necessary information or at least to

give a reasonable opinion as to the work

required. I cannot present in detail all

the problems on which I worked, but I

will summarize some of those that seem

most important.

Design of Shuttle Control 

System

My first important work connected with

the Johnson Space Center concerned

the Shuttle control system, although I

had made previous visits to that center

to discuss simulators for the Apollo. A

brief review of the background of the

Shuttle development is desirable to give

a basis for the various problems that

arose.

The Johnson Space Center was an

impressive place during the Apollo program. It had a beautiful campus with

large office buildings and laboratories.

No expense had been spared to make
52 Monographs in Aerospace History Number 40—Journey Into Space Research

My Work With Johnson Space Center

Apollo a success. As the Apollo program neared a close, however, the

Johnson engineers started to give serious thought to a follow-on program. Perhaps the most popular proposal was to

build a space station, which in turn

required a shuttle vehicle to supply it.

The Apollo program was a great success. It beat the Russians to the Moon,

completed its program on schedule, and

provided much important scientific data.

After the sixth Apollo flight, however, the

program had lost its political popularity,

and Congress failed to appropriate

funds for a seventh flight, even though a

Saturn launch vehicle had already been

built to carry the Apollo vehicle to the

Moon on its seventh mission.

With the abrupt halt of the Apollo program, funding for a space station was

not available. As a possible alternative,

the management proposed a shuttle

vehicle as a first step toward a space

station. Such an interim project would

keep the Space Center in operation. Little study had been made, however, on

the design of such a vehicle.

A young engineer in the Space Task

Group, Max Faget, had proposed the

design of the Mercury capsule, and later

extended the capsule concept to the

Apollo vehicle. His proposal for a space

shuttle also provided the basic concept

for the Space Shuttle that later was

actually built. Faget, a model airplane

enthusiast, brought in a balsa and tissue paper model of a shuttle that incorporated an unswept, low aspect ratio

wing, a rather fat fuselage, and a tail

with a wide-chord elevator that provided

sufficient control power to trim the vehicle to a very high angle of attack, probably 45°. The concept was to enter the

atmosphere at a very high angle of

attack to reduce the heating on the

leading edges and lower surface of the

vehicle, and later to pitch down for a

conventional landing at an airport.

Because of the capability of an unswept

wing to provide a relatively high maximum lift coefficient at subsonic speeds,

the vehicle would have had a landing

speed low enough to land at practically

any airport.

I am not sure of the sequence of events

that followed, but wind-tunnel tests of

Faget’s concept showed that at hypersonic speeds, very strong shock waves

formed at the intersection of the wing

and fuselage that would have caused a

heating problem on the side of the fuselage. Later, the proposal for a shuttle

design was sent to three contractors.

The winner, Rockwell, Inc., proposed a

delta-wing configuration with a large

fairing between the wing root and the

fuselage and included a large elevator

capable of pitching the vehicle to high

angles of attack at hypersonic speeds.

This configuration avoided the excessive heating on the sides of the fuselage, but it was capable of only relatively

low values of lift coefficient for landing.

As a result, long runways would be

required for landing. Later, the high

landing speeds resulted in problems

with brakes overheating and tires

exploding, but these problems were

overcome with new designs for brakes

and tires.

I have often thought that more study

should have been made of the problems

involved in Faget’s original design. Possibly wing fillets and root fairings could

have overcome some of the fuselage

heating problems. The capability to land

on shorter runways would certainly have

been a safety feature in later operations.

My first involvement in the design of the

Shuttle involved the control system. The

Shuttle was one of the first airplanes to

incorporate a complete digital fly-bywire control system. The term fly-bywire means a system in which all control

surfaces or other control components

are operated by electrical signals sent

through wires. A digital system means
Studies of Shuttle Control System

Monographs in Aerospace History Number 40—Journey Into Space Research 53

that control signals are generated by a

digital computer that contains all the

necessary control laws and signal transmission devices. Previous airplanes had

used fly-by-wire control systems using

analog components and usually with a

mechanical back-up system. An example is the highly successful control system on the Concorde. In the case of the

Shuttle, however, a digital system was

considered necessary because of the

wide changes in the control laws

throughout the flight required by the

wide range of Mach numbers and flight

conditions encountered. Mechanical

systems consisting of control cables

and pushrods would have had to handle

excessive forces and would have

encountered problems due to heating.

The development of digital computers

had reached a state that was considered to have adequate capability and

reliability to perform the control task,

though much development was required

to overcome the new problems encountered.

To verify the design of the control system, a large working mock-up of the

system was built at the Johnson Space

Center. One of the lead engineers in

this project was Robert G. Chilton, who

had worked under me in the Flight

Research Division at Langley. He gave

me a tour of the facility and a briefing

during one of my visits to the Center.

The system used three digital computers designed and programmed by the

Honeywell Corporation. Though each

computer was highly reliable, the reliability requirements are such that they

cannot be met by a single computer.

The consequences of a failure are so

severe that the system is required to

perform safely for millions of flight hours,

representing the lifetime of not just one

vehicle but of a whole fleet of vehicles.

This degree of reliability can be met by

using the principle of redundancy: that

is, three or more computers perform the

control task simultaneously. If any one

computer disagrees with the other two,

it is immediately shut down and repaired

after the vehicle lands. If a second

computer fails, a comparison of the output of the two computers is made and a

check based on expected output or

other means picks the best remaining

computer.

I was aware of an experimental triply

redundant digital control system that

had been installed in a helicopter at

MIT. Despite the redundancy, this

system had failed in flight. The problem

was that a programming error had

occurred in the software for the computers. The computer program was identical for the three computers. When this

error was encountered, all three computers shut down simultaneously, leaving the helicopter without a control

system. I discussed the problem with

Dr. Raymond C. Montgomery, an engineer in my division who knew more

about computers than anyone else in

the division. We concluded that the only

way to avoid such a problem on the

Shuttle was to install a fourth computer

programmed by an independent group.

The problem was discussed with personnel at the Johnson Space Center. As

a result, a fourth computer was programmed by personnel at the Draper

Lab. It was ruled that the fourth computer, like the other three, was a safety

of flight item. Thus, the Shuttle could not

be launched unless all four computers

were working properly. Once, while preparing for a Shuttle launch, the fourth

computer malfunctioned. The launch

was delayed until this computer had

been fixed.

Studies of Shuttle Control 

System

The Shuttle system was designed to be

fully automatic except for the final stage
54 Monographs in Aerospace History Number 40—Journey Into Space Research

My Work With Johnson Space Center

of the approach and landing, when the

astronauts took over. The initial design

of the system software, when tried on a

simulator, resulted in the Shuttle diverging to large angles when subject to certain disturbances. Such a divergence

would be catastrophic, and therefore

caused considerable concern among

the designers. At this point I was called

down to Houston by Dr. Kraft to study

the system and work with the designers

to obtain a satisfactory system.

I worked with Ken Alder, a contractor

from Lockheed who obviously had an

excellent knowledge of stability and

control. The work was mainly educational for me because considerable work

had already been done to provide a satisfactory system. Later, I observed test

runs on a simulator that traced the reentry trajectory of the Shuttle and

allowed the study of the effects of gusts,

cross winds varying with altitude, and so

on to provide a sufficient margin of

safety for all conceivable disturbances.

As mentioned previously, the vertical tail

of the Shuttle, mounted on top of the

fuselage, became ineffective at high

angles of attack. A method was worked

out to provide directional control using

only the elevons during the high angle

of attack part of the entry, which lasted

from the start or the descent at about

Mach 23 to Mach 2. By this method, the

elevons moved differentially in the

opposite direction from what would be

required for roll control at subsonic

speeds. To yaw to the right, for example,

the right elevon would move down (or to

a smaller upward deflection), increasing

the drag of the right wing. The left

elevon would have the opposite movement. This right yaw (or left sideslip),

because of the large dihedral effect

of the delta wing, would cause the

Shuttle to roll to the right despite the left

rolling moment caused by the elevon

deflection.

At low supersonic Mach numbers, when

the aerodynamic heating was reduced,

the Shuttle would be pitched to a lower

angle of attack, so that the rudder was

unshielded and became effective for

yaw control. In this regime, the elevons

were moved differentially in the normal

direction for roll control, opposite from

what had been done at higher Mach

numbers. The rudder then served to offset the yawing moments from the differentially deflected ailerons as well as to

provide yaw control. The controls were

then in a normal configuration so that

the astronauts could take control when

they made the flare and landing.

The variation of control laws with Mach

number is an example of a change that

can be made readily with a digital control system but would require some

complex device with a mechanical system. In fact, the digital system provided

a smooth ramp-like reversal in the

elevon control when the shift was made,

and in addition provided control gain

variations from various sensors such as

rate gyros and angle of attack and yaw

sensors throughout the descent. The

studies being made to improve the

safety and control effectiveness of the

system were mainly concerned with the

adjustments of these gain values for the

various phases of the descent.

After the changes in the software had

been worked out, I spent some time

watching the runs on a simulator, along

with one of the engineers. This simulator just plotted a trace of the trajectory

on a screen. On one run, I observed

that the trajectory near the end of

the run diverged. The engineer, who

had not been watching, was quite surprised. After analyzing the data, he concluded that this fault had been observed

before and had been corrected, but

the change had not been made in the

latest version of the program. This experience illustrates the vigilance required
Problem With Pilot-Induced Oscillations

Monographs in Aerospace History Number 40—Journey Into Space Research 55

in preparing software for computers in a

flight vehicle.

Problem With Pilot-Induced 

Oscillations

To give the astronauts practice landing

the Shuttle before going through the

dangers of a complete orbital flight, a

number of flights were made in which

the Shuttle was mounted on a trapeze

on top of a Boeing 747 airplane and

was released from an altitude of about

10,000 feet to glide to a landing on the

long runway at Edwards Air Force Base,

now the Dryden Flight Research Center.

In the fifth landing, the Shuttle made a

normal flare, but just before touchdown

it made two or three rather violent shortperiod oscillations. The Shuttle landed

safely after the co-pilot had told the pilot

to stop trying to control the oscillation

and let the Shuttle land itself.

Oscillations of the type experienced on

the Shuttle are called “Pilot Induced

Oscillations,” (PIO). for short. Such

oscillations have been experienced on

many airplanes, starting with the Wright

Brothers’ first flights, and became more

frequent with the introduction of hydraulically operated control systems. The

cause of these oscillations can often be

analyzed, and their reoccurrence can be

avoided after they have occurred, but

predicting the tendency for oscillations

beforehand can be much more difficult

because they can result from many different causes. In the case of the Shuttle,

a detailed analysis was made on the

response characteristics of the digital

control system, and the system was

found to have a response lag of 0.2 seconds or more following a pilot’s input.

Again I was called to the Johnson

Space Center to help with the analysis.

Dr. Robert Gilruth, who was the Director

of the Space Center, had run flying

qualities tests on 16 airplanes and, in

the early forties, had written a celebrated report called Requirements for

Satisfactory Flying Qualities of Airplanes. In this report he had stated that

a lag in the control system response of

greater than 0.1 second was unsatisfactory. Gilruth’s conclusion was based on

tests of spoiler ailerons on the wing of a

light plane. These spoilers were located

near the leading edge of the wing.

When they were abruptly deflected, the

flow over the spoiler would initially have

an effect similar to an increased wing

camber and would cause the lift to

increase. Then, as the boundary layer

air collected behind the spoiler, the wing

lift would indeed be “spoiled” and the

airplane would roll in the desired direction. The pilots considered the resulting

lag in response very undesirable.

Another problem with the Shuttle was

the time required for motion of the

elevons. These elevons were unusually

large and heavy and were operated by

hydraulic motors. The time to make a

large deflection was appreciable and to

return the elevon to neutral before making a movement in the opposite direction also had to be considered.

A third characteristic of the Shuttle that

was different from that of most airplanes

was the large, downward force applied

to the wing when the elevons were

deflected up. This force caused the center of gravity of the vehicle, as well as

the pilot’s cockpit, to move downward

following application of nose-up control,

and considerable lag occurred before

the pilot could feel that he was rising.

Apparently the designers of the Shuttle

had not considered the importance of

these effects. The 0.25-second lag in

the response was caused by the repetition rate of calculations in the digital

computer. An obvious correction that

was easy to apply was to approximately

double the repetition rate. This change
56 Monographs in Aerospace History Number 40—Journey Into Space Research

My Work With Johnson Space Center

was made before subsequent glide

tests, together with warnings to the

astronauts to apply the controls gently

and to allow sufficient time for flight path

changes required in landing. These

measures were apparently successful in

correcting the problem in subsequent

glide tests, although one of the later

landings showed some signs of an

oscillation.

Flight Control Review Group

Because of the complication of the

Shuttle Control System and the number

of organizations involved in its design,

the Flight Control Review Group was

organized to coordinate the work of the

various organizations. The Chairman of

the group was Donald C. Cheatham, a

former Navy pilot and a member of the

Naval Reserve, who had previously

worked for me at Langley in the Stability

and Control Branch of the Flight

Research Division and was now at the

Johnson Space Center working on the

Shuttle Control System. I was a regular

member. Other members were S. Bray

of the Ames Research Center, J. Weil of

the Dryden Flight Research Center,

R. G. Hoey of the Air Force Flight Test

Center at Wright-Patterson Air Force

Base, and about six members from various branches at the Johnson Space

Center. Meetings were held approximately quarterly in the 1978–79 period.

The number of organizations working on

the Shuttle Control System and the

number of independent simulators set

up to study its problems far exceeded

the numbers devoted to any other

aircraft. At least seven simulators

designed to study the complete entry of

the Shuttle from orbital flight to landing

were in existence. These included one

at Langley, one at the Dryden Flight

Research Center, one at the Air Force

Flight Test Center, and several at the

facilities of Johnson and its contractors.

In addition, the Johnson Space Center

had the Shuttle Training Aircraft (STA), a

Gulfstream with a modified control system to simulate as closely as possible

the control characteristics of the Shuttle.

The TIFS (Total In-Flight Simulator) airplane at Calspan was also used to study

specialized piloting problems. Just getting the various simulators to agree on

the same problem was a major task but

was solved with the aid of the large

number of engineers involved.

The large number of independent

groups working on the flight control

problem was an excellent method to

catch and eliminate errors in the programming as well as to take advantage

of the knowledge of the experts working

for the various contractors. The method

was also very expensive, but the support for the Shuttle at that time was sufficient to allow such expenditures. Later

airplanes, both military and commercial,

that made the first attempts at using digital fly-by-wire control systems without

the aid of such intensive design efforts

almost always encountered failures or

crashes.

The problem of pilot-induced oscillations was a major concern of the Flight

Control Group. The use of an increased

repetition rate in the computers

undoubtedly helped the situation. Still,

the slow response of the Shuttle to

longitudinal control inputs was a matter

of concern. This lag in response was

caused by the large inertia of the vehicle

in pitch and the short moment arm

between the elevons and the center of

gravity. I later made an analysis that

compared the longitudinal response of

the Shuttle with that of several other

large airplanes. The response time of

the Shuttle was over twice as long as

that of any other airplane (fig. 6.1). As

shown by this figure, the download on

the elevon at the start of a pull-up

caused the center of gravity of the
Flight Control Review Group

Monographs in Aerospace History Number 40—Journey Into Space Research 57

Shuttle to move down. Only after some

time did the pitch angle increase the lift

and cause the Shuttle to rise. A time lag

of 2.15 seconds passed before the center of gravity had returned to its original

altitude. This type of motion occurred on

other airplanes with delta wings but was

never as severe as on the Shuttle.

The sensation that the pilot experienced

of accelerating downward when the

control was applied for a nose-up

response had been analyzed previously by some researchers and had

been blamed as a cause of pilotinduced oscillations. I did not agree

with this conclusion. I pointed out that

several other airplanes, such as the

Gee Bee racers, had been flown with

the pilot sitting near the tail without

encountering any difficulty. I felt that the

pilot could become accustomed to his

location in the airplane and could visualize the response of the nose of the airplane or of its attitude in pitch.

As usual, accurate predictions of the

tendency to pilot-induced oscillations

was difficult. R. G. Hoey of the Air Force

Flight Test Center felt that despite

instructions and practice to teach the

astronauts to control the Shuttle with

slow and deliberate movements, they

would someday hit a disturbance that

would require a fast control movement

that would start a pilot-induced oscillation (PIO).

A device called the PIO Suppression Filter was devised by an engineer at the

Johnson Space Center to make the

Shuttle more resistant to PIO. This filter,

inserted in the control system after the

FIGURE 6.1. Comparison 

of height response of 

several airplanes: 

F-104 and B-52—

conventional aft tail, 

YF-12, B-58, and 

Shuttle—delta wing. 

Note that the Shuttle 

requires 2.15 s for the 

c.g. to return to its 

original altitude.

F-104, CL = 1.2

YF-12, CL = 0.6

B-52, CL = 1.0

Shuttle, CL = 0.6

B-58, CL = 0.6

160

120

80

40

0

0 12

Time, s

3 4

–40

200

Altitude of c.g., ft
58 Monographs in Aerospace History Number 40—Journey Into Space Research

My Work With Johnson Space Center

pilot’s controller, sensed the frequency

and amplitude of the motions of the control stick. If these motions became too

large or frequent, the amount of motion

of the elevons for a given controller

deflection would be reduced, eventually

reaching only one-third of its normal

value. This device was tested on simulators and on the Shuttle Training Airplane. The astronauts commented that

with the device in operation, it was very

difficult to produce a pilot-induced oscillation. There was some objection that in

a critical situation the pilot would be

unable to use full control, but in such a

situation the danger of a pilot-induced

oscillation would be greatest. After

extensive testing, the device was

installed in the Shuttle control system.

The subsequent series of successful

landings of the Shuttle can be attributed

to the astronaut training program as well

as to the suppression filter. Most of the

success can probably be attributed to

the training program. The suppression

filter has, to my knowledge, never been

forced to come into operation. Thus, the

fears expressed by R. G. Hoey and

other engineers were perhaps never

realized in practice.
Monographs in Aerospace History Number 40—Journey Into Space Research 59

CHAPTER 7 Continuation of Research 

Following Decline of Space 

Program

Following the completion of the design

and construction of the Space Shuttle,

administrators of the program had

expected a continuation of active space

activity involving manned space flight.

Changes in the policies of the presidents who later came into office and the

general lack of public interest in space

developments resulted in a rapid decline

in funding for this work. The Shuttle was

a technical success, but the expense of

its operation and the lack of a major program that required its use caused a

reduction in the frequency of flights to

less than four per year, instead of every

two weeks, as first envisioned by some

space enthusiasts. A temporary space

station, the Skylab, using one of the

Saturn tanks as its major component,

stayed in operation for a while, but even

this vehicle was allowed to fall back into

the atmosphere and burn up rather than

be sustained in orbit with a small expenditure of fuel.

I had continued to study some aeronautical problems during the space program

and following the decline in space activity, I resumed work to clean up some

problems that had not been completed

before the space program, and made

studies of a number of new aeronautical

problems. The remainder of this volume

gives brief accounts of a number of

these problems.

Variable Sweep Wing 

Supersonic Transport

A variable sweep wing appears desirable for a supersonic airplane because

for takeoff and landing an unswept wing

of high aspect ratio provides lower takeoff and landing speed, whereas at

supersonic speeds a highly swept wing

has much less drag. The X-5 experimental airplane was perhaps the first

that allowed us to study a variable

sweep wing in flight.

A problem with the variable sweep wing

is that as the wing is swept back, the

aerodynamic center of the wing moves

back with respect to the center of gravity

of the airplane. To balance the airplane,

a large download on the stabilizer is

required in the swept condition, resulting in high drag. Alternatively, if the

airplane is balanced in the swept condition, it becomes longitudinally unstable

in the unswept condition. This problem

is particularly critical on a supersonic

airplane because the aerodynamic

center of the wing also moves back

by about 25 percent of the chord at
60 Monographs in Aerospace History Number 40—Journey Into Space Research

Continuation of Research Following Decline of Space Program

supersonic speed because of the

effects of high Mach number.

To avoid this problem, the X-5 had the

wing mounted on a movable cradle so it

could be moved back or forward to suit

the flight condition. Such a system,

however, occupies an undesirably large

volume in the fuselage. 

In 1948, I made a model glider simulating a supersonic transport with a

variable sweep wing, a picture of which

is shown in figure 7.1. To keep the

model in trim with the wing swept back,

I added a retractable delta surface

near the nose. Suitable hills to test

model gliders are not common in the

area near Hampton, Virginia, where I

live, but I found a suitable small hill on

the Yorktown Battlefield and spent an

afternoon gliding the model. The model

glided well either with the wing swept

and the delta surface extended or with

the wing unswept and the delta surface

retracted. In this glider, the wing hinge

was at the centerline of the fuselage.

NACA LAL-57436

NACA LAL-57437

FIGURE 7.1. Figure 7.1. 

Glider model of supersonic transport with 

variable-sweep wing 

and retractable 

canards. Length, 30 

in., span (swept) 15 

in., span (unswept) 26 

in.

(a) Wing swept, 

canards extended.

(b) Wing unswept, 

canards retracted.
Differential Maneuvering Simulator (DMS)

Monographs in Aerospace History Number 40—Journey Into Space Research 61

Later, airplane companies discovered

the idea that if the wing panels were

hinged at a point some distance out on

the wing, the sweeping action would

move the inboard section of the wing

farther forward. This principle was used

on such airplanes as the Air Force

F-111 and F-14 Navy fighters and on

the B-1 Bomber. This system has been

successful, but it poses complicated

structural problems for the wing mounting and for fairings at the wing root.

Differential Maneuvering 

Simulator (DMS)

After graduating from MIT, I kept in

touch with another MIT student named

Herbert K. Weiss. He and I both came to

Hampton, Virginia, I with the NACA and

he with the Coast Artillery Board at Fort

Monroe. He was a brilliant engineer and

mathematician, and I often consulted

him on my problems. Later he went to

work at the Aberdeen Proving Ground in

Maryland. His work was primarily in

missile design, vulnerability of military

aircraft, and air combat problems. On

one occasion, probably in the forties

after WWII, he asked me to come with

some of my engineers to discuss mutual

problems. During the meeting, he suggested that it would be possible to build

an air combat simulator with two cockpits, two pilots, and displays showing

the image and motion of the opponent’s

airplane to each pilot. I thought about

this idea but concluded that the NACA

at Langley did not then have the facilities or funds to build such a simulator

and that the state of simulator design

had probably not advanced far enough

to undertake such a project.

In 1965, when the LOLA simulator was

well underway, an engineer named

Dr. John D. (Jay) Bird, who was a

branch head in my division, made a similar suggestion for an air combat simulator. At this point, there was much

interest in air combat as a result of the

wars in Korea and Vietnam. Jay Bird

was an ingenious research man. I concluded that with his enthusiasm it would

be possible to undertake an air combat

simulator. To gain experience, a simulator with just one projection sphere,

called the Tactical Effectiveness Simulator (TES), was built. It had a projection

sphere about 20 feet in diameter containing the pilot’s cockpit and a projector

to produce an image of the target airplane. The target airplane was controlled by a pilot in an external cockpit.

All the motions were controlled by a

large, digital simulation installation

recently installed at Langley.

A contract for building the TES was won

by the Rheem Corporation, a company

better noted for its work on heaters and

air conditioning systems, that had previously worked on simulators for the Air

Force. I was surprised that they did an

excellent job in designing the TES, and

especially the detailed solution of the

mathematics of the motions to be

solved by the digital computer. The

motions in three dimensions were

solved by the use of quarternions, a

system that avoided any gimbal lock in

the projectors. 

The TES was highly successful and was

used for several research studies. The

plans for the Differential Maneuvering

Simulator (DMS) went ahead rapidly. A

contract for its construction was let to

the Northrop Corporation. An artist’s

drawing of the simulator is shown in figure 7.2-1. A later drawing that is perhaps more accurate in certain details is

shown in figure 7.2-2.

The simulator had two large projection

spheres, each 40 feet in diameter, on

the inside of which was projected the

target airplane image, view of the Earth

and sky, and a Sun image. The pilot sat

in a cockpit which did not rotate but was
62 Monographs in Aerospace History Number 40—Journey Into Space Research

Continuation of Research Following Decline of Space Program

capable of oscillating to simulate buffeting. In addition, the pilot could wear a

“g suit” that could be inflated to simulate

g loads. The image of the target airplane was simulated by a detailed scale

model about 15 inches long that was

suspended in a box by a system of

wires moved by servos to rotate the target airplane in roll, pitch, and yaw and

was photographed by a camera to

present a correct image of the target airplane in the projection sphere. Motion of

FIGURE 7.2-1. Pictorial 

view of Differential 

Maneuvering Simulator (DMS). The large 

spheres are projection screens, and they 

contain the pilots’ 

cockpits, projectors, 

and servomechanisms to move the 

projected displays. 

Each pilot sees a 

view of the opposing 

airplane.

FIGURE 7.2-2. More 

detailed sketch 

of Differential 

Maneuvering 

Simulator.

Vehicle

“A”

simulator

Vehicle

“B”

simulator

Projection system

Cockpit

Buffet

system

Target image

generation system

(physically located

behind spheres)

Computer complex

(in adjacent building)

Computer console
Differential Maneuvering Simulator (DMS)

Monographs in Aerospace History Number 40—Journey Into Space Research 63

the entire scene through an angle of

270° was produced by a large hydraulic

servomechanism rotating the previously mentioned projectors to produce

the image as seen from a maneuvering

airplane. All these effects were duplicated in the other sphere so that either

pilot could be the attacker as the combat progressed.

The simulator was completed and

placed in operation in July 1969. By the

time the simulator was finished, Jay Bird

had lost interest in the project, and I was

faced with selecting a group of engineers to run the programs. Continual

help in operating the mechanics of the

simulator and modifying the digital computer programs was provided by the

Analysis and Computation Division

(ACD). The simulator cost $5.5 million.

The successful completion of the DMS

was valuable to both the Air Force and

Navy, who started construction of their

own combat simulators. These simulators were more complicated, with such

facilities as moving cockpits and the

capability of displaying four airplanes.

Both were finished after the DMS and

cost many times as much.

I once thought that a simulator such as

the DMS would be useful in developing

a theory of air combat. Consultation with

some noted mathematicians who had

considered this problem, however,

showed that it was an extremely difficult

problem. Certainly it was beyond the

capabilities of any of the engineers at

Langley. The simulator was very useful,

however, in developing empirical theories and in checking combat strategies

that had been developed by military

pilots. After some initial runs, pilots from

the Air Force and Navy were invited to

fly the simulator on a regular schedule.

These pilots all considered the simulator

runs extremely beneficial in improving

their flying techniques. A series of rules

for air combat developed by Al Meintel

was useful in training these pilots. 

Perhaps the most useful analytical

study to come out of the simulation

studies was a program developed by

George H. Burgin, Lawrence J. Fogel,

and J. Price Phelps of Decision Science, Inc., San Diego, California, working under contract to NASA (ref. 7.1).

This program acted as an artificial pilot

to serve as an opponent for a human

pilot in the simulator. Later, Walter W.

Hankins III, an engineer at the Langley

Research Center, gave an AGARD talk

on the program and wrote a Langley

Working Paper summarizing the results

of tests with the program (refs. 7.2

and 7.3). This program was so good that

experienced military pilots were often

beaten by it, and it was only after making a number of runs to uncover slight

weaknesses or peculiarities in the program that they were able to beat it

consistently. This type of program, of

course, suggested its use as an automatic pilot to replace the human pilot in

air combat. Such a program could save

many pilots’ lives in actual warfare. The

pilots, however, always opposed the use

of such a method. They had trained to

be combat pilots and did not wish to

leave the job to a machine, even if it

might have saved their lives. Only in

recent years when the use of unmanned

vehicles for military missions has

received increased attention has the

use of automatic combat pilots been

seriously studied.

The DMS is still in operation (2004) and

has served many useful purposes in

addition to studying air combat. For

example, the use of a single sphere to

study spinning characteristics of airplanes has allowed investigation of a

much wider range of characteristics

than could be done in flight tests. Since

my retirement in 1979, I have been out

of touch with simulation work, so I am

not familiar with much of the work that

has been done.
64 Monographs in Aerospace History Number 40—Journey Into Space Research

Continuation of Research Following Decline of Space Program

Circulation Control

In my own experiments on gust alleviation, as well as in most other studies

that have been made, flaps on the wings

are moved up and down to offset

upward and downward gusts, respectively. This method works well in an

experimental study. On a practical airplane, flaps must also be used for generating high lift for landing. On transport

airplanes, complex two-segment, double-slotted flaps are commonly used,

which would complicate the problem of

using flaps for gust alleviation. Possibly,

the rear segment of the existing double

segment flaps could be used for this

purpose, but no aircraft company, to my

knowledge, has attempted to study such

an arrangement.

Another method to produce high lift,

known mostly from wind-tunnel tests, is

circulation control produced by a jet of

air directed downward at the trailing

edge. With this method, very high values of maximum lift, around six or

seven, can be produced. Another technique, known as the Coanda effect, has

been used for this purpose. In this

method, a thin jet of air directed along a

sharply curved surface at the trailing

edge can deflect the jet downward and

produce high values of maximum lift. 

An engineer and assistant professor at

MIT named Joseph Bicknell was at MIT

when I was studying there. Later he

published a paper describing a method

for producing oscillating flow in a wind

tunnel. In this method, illustrated in figure 7.3-1, he used a cylinder, with its

FIGURE 7.3-1. Use of 

Coanda effect to 

deflect airstream at 

trailing edge of wing. 

Illustration shows 

effect of oscillating 

cylinder that closes 

one side of the opening or the other. A 

slightly smaller rotating cylinder could 

alternately close and 

open gaps at a high 

frequency, producing 

a rapidly oscillating 

airflow.

Compressed

air supply

In practice, gaps would be only a few thousandths of an inch wide.

Cylinder turned

clockwise

Cylinder turned

counterclockwise
Control Configured Vehicles (CCV)

Monographs in Aerospace History Number 40—Journey Into Space Research 65

axis slightly off center, rotating in an

opening at the rear of a symmetrical airfoil that was mounted to span the wind

tunnel ahead of the test section. Compressed air was blown through the rear

of the airfoil. The air jet, influenced by

the Coanda effect, followed first the

upper and then the lower surface of

the cylinder as a slot was opened at

the upper and lower surface of the airfoil. The cylinder could be rotated with

very little power and could produce an

oscillating flow in the tunnel at very high

frequencies. 

With slight modifications, this method

could be used as a control for gust alleviation. A source of compressed air,

such as bleed air from a turbojet engine

or a separate compressor, would be

required to produce the air jet. The cylinder would not rotate continuously, but

would oscillate about its axis just like the

flap on a gust-alleviation system. This

action would open a slot up or down to

deflect the flow as required to produce a

varying circulation about the airfoil.

A possible advantage of this system

would be that the deflected flow could

also be used as a landing flap, taking

advantage of the very high values of lift

coefficient that can be obtained with a

jet at the trailing edge.

Plans were underway at the Langley

Research Center to try this system on a

Cessna 402B airplane, but the funding

for the project was cancelled. A patent

was taken out on the system in the

names of Eric Stewart and myself. In

view of the continual disinterest of the

airplane companies in gust alleviation, I

do not believe that this system is widely

known.

Control Configured Vehicles 

(CCV)

The term CCV was introduced about

1969 by personnel of the Air Force

Flight Dynamics Lab to describe the

design of an airplane to obtain performance improvements by use of automatic control systems. The term was

much publicized about that period,

resulting in formation in a special committee at Langley and an intercenter

symposium on the subject. In general,

the term implied an airplane loaded with

electronic equipment with rather poorly

defined benefits in performance. At the

request of the associate director of

Langley, Lawrence K. Loftin, I wrote a

memorandum describing my ideas on

the benefits obtainable with this system.

The most apparent benefit was longitudinal stability augmentation, allowing

the use of a smaller horizontal tail or a

more rearward center-of-gravity location, thereby reducing drag. This benefit

was so obvious that some airplanes

were already being designed with this

feature. Many other suggested benefits,

however, required severe compromise

of other essential features of the airplane and were rarely used.

After considerable thought, my overall

conclusions were summarized in a

pair of charts shown as figures 7.4-1

and 7.4-2. The main point was that the

sizes of vertical and horizontal tails of

airplanes and their associated control

surfaces were based mainly on emergency flight conditions such as spin

recovery, stall avoidance and recovery,

and control with asymmetric power. The

reductions in tail sizes offered by CCV

were therefore not usable. As illustrated

on the second chart, the control power

required for increased stability was usually about one-third of that required for

emergency flight conditions, and the

control power for improved damping of
66 Monographs in Aerospace History Number 40—Journey Into Space Research

Continuation of Research Following Decline of Space Program

oscillations was only one-ninth of that

required for emergency conditions. The

benefits of CCV could be increased only

by designing the airplane to reduce the

control power required for emergency

conditions. Methods for doing this were

developed, but in the ensuing years,

such methods have not been generally

adopted.

Propulsive Effects Due to 

Flight Through Turbulence

In a wind-tunnel study made in 1922,

R. Katzmayr showed that an airfoil subject to periodic vertical motions of air in

a wind tunnel would experience a propulsive force. A more practical problem

FIGURE 7.4-1. Controlconfigured vehicle 

(CCV) chart.

FIGURE 7.4-2. Damping 

and stability control 

chart.

W H A T I S A C C V ?

A CONTROL– CONFIGURED VEHICLE IS AN

AIRPLANE FOR WHICH THE MOMENTS

REQUIRED FOR TRIM THROUGHOUT THE

NORMAL AND EMERGENCY FLIGHT

ENVELOPE ARE MINIMIZED

C O N T R O L R E Q U I R E D F O R D A M P I N G

A N D S T A B I L T Y

TOTAL CONTROL DEFLECTION

DAMPING

STABILITY
Decoupled Controls

Monographs in Aerospace History Number 40—Journey Into Space Research 67

is to determine the effect of flight

through random turbulence. The French

aerodynamicist Breguet made an early

study of this problem. His analysis was

correct in principle, but at that time the

mathematical tools for analyzing turbulence, such as power spectral density

and the spectra of atmospheric turbulence, were not available. As a result,

quantitative results were not obtained.

This problem, though it is considered to

be of some practical importance, had

apparently never been solved. I made

an analysis of this problem and presented the results in a note in the Journal of Aircraft (ref. 7.4). In this analysis,

the spectrum of atmospheric turbulence, which expresses the amplitude of

the gust intensity as a function of frequency, is represented by the familiar

Dryden spectrum, and the response

time of the airplane in responding to a

vertical gust is placed in frequencyresponse form. These two quantities are

then combined to give a formula for the

thrust coefficient.

The results show that a lightly loaded

aircraft, such as a soaring glider, flying

at a high lift coefficient, experiences an

increase in lift and a forward tilt of the lift

vector in upward gusts and a decrease

in lift and a rearward tilt of the lift vector

in downward gusts. A net increase in

thrust is produced, but such a lightly

loaded aircraft responds vertically to the

gust very quickly, reducing the effects of

change in angle of attack to a very short

duration. A heavily loaded aircraft, such

as a fighter or transport, is flying fast

and in the same turbulence experiences

much smaller changes in angle of

attack, but the heavy airplane moves

vertically much more slowly, so the

duration of the change in lift is longer.

The result is that both types of airplanes

experience about the same thrust effect,

which is very small even in severe turbulence. Calculated results for typical

examples show that a change in thrust

coefficient in severe turbulence would

be about 0.003 to 0.005.

Decoupled Controls

Though the early Wright Brothers’ airplanes used control systems that were

not consistent with the pilot’s normal

reactions, the early pioneers Paulhan

and Bleriot originated a system in which

fore and aft motion of the controller controlled the pitch control surface, side-toside motion of the controller controlled

the roll control surfaces, and rudder

pedal motion controlled the yaw control

surface. A throttle was used to control

engine power or thrust. This system has

been used almost universally since

then. With the development of automatic

electronic control systems, however,

designers realized that other types of

airplane response could be obtained.

One possibility was called decoupled

controls, in which a given controller

would control just one motion of the airplane. For example, one controller might

control only pitch angle, another might

control airspeed, and another lateral

velocity. Such controls were sometimes

thought to be easier for novice pilots to

learn, and in other cases, advantages

were claimed for gunnery or missile

accuracy. It should be realized that

more than one airplane control surface

would be used for each of the decoupled motions.

Numerous analyses of controls with various types of decoupling are available in

the literature, and flight tests of some

arrangements have been tried, in particular to study gunnery or missile accuracy. No great advantage has been

found for using a system different from

the standard control system. In fact,

some rather serious objections have

been raised by pilots to these systems.

For example, pilots use different control

techniques for upward or downward
68 Monographs in Aerospace History Number 40—Journey Into Space Research

Continuation of Research Following Decline of Space Program

control when flying near the ground.

They object to any control which applies

down elevator when flying near the

ground, even if the decoupled system

might not result in a dangerous flight

path. Decoupled systems are usually

unsuitable for emergency conditions

such as spin recovery, where pilots

have learned techniques appropriate

to a given airplane that might apply

controls opposite from those produced

by a decoupled system. Most work on

decoupled controls appears to have

disappeared, although automatic systems may be used for specific flight

regimes on individual airplanes, such as

stall-limiting devices or Mach number

control.

Soaring Gliders

The Wright Brothers experimented with

man-carrying gliders for three years

before they made their successful flight

in a powered airplane. Later, Orville

Wright, in 1911, returned to Kitty Hawk

to try a glider with a tail-aft location

which, by that time, had been adopted

by most other aviation pioneers. Orville,

slope soaring in the wind on the large

dune near the site of their first flight,

made a soaring flight of 9 minutes

45 seconds, which stood as a world

record for soaring endurance until after

WWI.

After the war, construction of airplanes

in Germany was forbidden. Many of the

German manufacturers went in for soaring glider activities, both for sport and

experimentation. The design and performance of soaring gliders improved rapidly. In this country, the center of glider

activity became concentrated in Elmira,

New York, where a level area at the top

of a steep hill provided a good site for

launching. This area became known as

Harris Hill, where a Lieutenant Harris

had been killed when his car overturned

while towing a glider.

The performance of soaring gliders

depended to a great extent on aerodynamic efficiency. As a result, many

aeronautical engineers did analytical

studies in this field. There had been

some glider activity at the Langley

Research Center before I arrived in

1940, but very little was done after that.

When the first radio-control systems for

models were developed in the early 40s,

I made some of the first radio-controlled

soaring glider models, which served to

keep up my interest in this field. Later,

about 1955, radio-controlled gliders

became a very popular branch of model

aviation. About 1968, Oran Nicks, who

was a soaring enthusiast, became Deputy Director of Langley. He organized an

annual technical conference on soaring,

held at MIT, and always requested that I

try to prepare a paper to be given at the

conference.

The first paper that I presented was

entitled Analysis of Effect of Asymmetric

Loading on Sailplane Performance in

Circling Flight (ref. 7.5).

The second paper that I presented was

entitled Gyroscopic Moments on a

Glider in Turning Flight (ref. 7.6). Soaring gliders, because of their high aspect

ratio, have a strong tendency to roll to a

larger bank angle when in a turn. Opposite aileron and rudder controls must be

applied to offset this tendency. This

effect was discovered by the Wright

Brothers and resulted in their development of the coupled rudder and wing

warping lateral control system that was

a major factor in their success in making

controllable flights. 

The gyroscopic moment acting on a

glider results from the tendency of all

rotating bodies to align themselves with

the plane of rotation. This moment tends

to reduce the tendency to roll to a larger

angle of bank. This effect is not very
Soaring Gliders

Monographs in Aerospace History Number 40—Journey Into Space Research 69

large, however. In a typical example, the

gyroscopic rolling moment was only

13 percent of the aerodynamic rolling

moment.

The third paper that I presented was

intended to study the effect of the trailing vortices shed from the wing tips of a

glider in circling flight on the forces acting on the glider in subsequent turns. To

study this effect, I made a flow visualization study. At that time, a large water

tank, 30 feet in diameter and 30 feet

deep, was being used at Langley to

study zero gravity effects on the performance of astronauts in space. I made a

model glider of 40-inch span out of solid

mahogany and weighted with about 4 lb

of lead in the fuselage. The glider was

FIGURE 7.5. Heavily 

weighted glider (40-in. 

wingspan) gliding 

slowly (about 3 ft/s) 

underwater in large 

tank. Fluorescent dye 

is emitted from wing 

tips. When glider made 

complete circles, trails 

from previous circle 

were always well 

above glider.

L-69-4307
70 Monographs in Aerospace History Number 40—Journey Into Space Research

Continuation of Research Following Decline of Space Program

launched underwater with a rubber catapult and would slowly glide in circles in

the tank at a speed of about 3 to 4 feet

per second (fig. 7.5). A fluorescent dye

carried in a tank in the model was

expelled through nozzles on the wing

tips. This dye left a clear trace of the

trailing vortices from the model as the

model slowly descended in the tank.

The conclusion was that the model

was always well below the vortex shed

in a previous circle. As a result, the

vortices would be expected to have a

negligible effect on the efficiency of the

model. These results were demonstrated to the attendees at the symposium with movies.

As a matter of interest, I took the lead

weights out of the model, equipped it

with radio control, and tried flying it in

air. The model weighed about a pound,

a rather heavy wing loading for a model.

Launched from a dune into a strong

wind of about 35 miles per hour, it would

glide with a speed exceeding 40 miles

per hour. I claimed that I had made the

first glider that flew both in air and

underwater, like a duck. The ratio of

densities of water and air is about 1000.

Another fact that I learned from these

experiments was that the buoyancy of

the parts of the model that are lighter

than water must be taken into account

in trimming the model for underwater

flight. For example, the tail surfaces

made of mahogany were buoyant

underwater, allowing the model to be in

trim with a center of gravity that would

be too far rearward to be stable in air. As

a result, I had to make a lighter set of

tail surfaces for flight in air. Buoyancy

effects also exist on the structure of a

conventional airplane, but the effects

are so small compared to the weight

of the airplane that they are rarely

mentioned.

Complementary Filters

When considering the subject of aircraft

control systems, a filter is considered to

be a device that modifies the pilot’s

input to improve the response of the airplane. In many cases, the filter is

designed so that its presence is not felt

at the pilot’s controller but is simply

recognized as part of the airplane

dynamics. For example, a longitudinally

unstable airplane may be made longitudinally stable from the pilot’s standpoint. 

The simplest types of filters may produce undesired side effects. For example, a filter that improves the longitudinal

stability may introduce an undesired

structural oscillation. To avoid such

undesired effects, a device known as a

Complementary Filter has been introduced. This system has relatively simple

design, and does not require complicated mathematics for its analysis, yet

has many applications in aeronautical

problems.

During the Apollo and Shuttle programs,

mathematicians introduced filters to

obtain an optimal flight path or other

objective based on some criterion such

as minimum time of flight, with provision

for continually correcting the path based

on periodic observations of measured

references such as line of sight to navigational stars and planets. The bestknown filter for this purpose is called the

Kalman-Bucy Filter. The design of such

a filter required advanced mathematics

that had never been covered in my college courses. Some of the bright

younger engineers had studied this subject in college and were able to follow

the development. Because of the importance of this subject, some prominent

mathematicians were hired to give

courses to the personnel of the Langley

Dynamics and Control groups, including

Kalman and Bucy themselves, as well

as other engineers prominent in this
Turbulence Problems

Monographs in Aerospace History Number 40—Journey Into Space Research 71

field. Because of my lack of background, I was never able to get anything

but a general understanding of such

subjects. In later years, companies

were formed that specialized in these

analyses and apparently made a good

living by assisting the aerospace companies in work that required this type of

knowledge.

Most airplane control system applications do not require the complication of

the Kalman-Bucy filter. In these cases,

the Complementary Filter provides a

readily understandable device that can

solve many of the practical problems

encountered. I was first introduced to

this filter by John F. Garren, Jr., an engineer in the Helicopter Branch. He found

that the conventional helicopter control

system that incorporated angle-ofattack sensors to improve the longitudinal stability and rate sensors to improve

the damping of oscillations caused an

undesirable amplification of the one-perrevolution vibration of the rotors. The

Complementary Filter provided an analog model of the helicopter response.

Then the output of a simplified response

model was passed through a high-pass

filter, the output of which was added to

that of a low-pass filter on the rate gyro.

In this way the high-frequency vibrations

sensed by the rate gyro were eliminated, whereas other high-frequency

motions as well as the low-frequency

response of the helicopter were allowed

to operate the controls. The device

proved quite effective in reducing the

one-per-revolution vibration of the

helicopter. This study is reported in

reference 7.7.

I later made a brief study of the use of a

Complementary Filter in reducing the

structural vibrations of a rocket during

launch, often called the pogo effect.

Turbulence Problems

In my previous book, Journey in Aeronautical Research, I devoted a large

amount of space to my studies of

response of airplanes to gusts and the

design of systems to produce a

smoother ride in turbulence. These systems have been called “gust alleviation

systems,” although it was the response

to gusts rather than the gusts themselves that was alleviated. In most of

this work, the gust disturbances were

assumed to be one-dimensional; that is,

the gust velocities varied along the flight

path but were assumed constant across

the wing span at any instant. This type

of analysis was useful because most of

the response of airplanes comes from

long wavelength gusts that do not usually have much variation across the

span. 

After finishing this work, which included

flight tests of a gust-alleviation system

on a Beech Model 18 (Navy C-45)

transport, I went to other subjects, but I

always kept in mind some related problems that had never been solved. One

of these problems was the effect of twodimensional turbulence, that is, gusts

with variations across the span as well

as along the flight path. To make such

studies mathematically tractable, the

assumption of isotropic turbulence is

usually made. This type of turbulence

shows the same statistical properties

along any flight path that penetrates the

turbulent region. Experimental studies

have shown that turbulence of this type

frequently occurs in the atmosphere.

A Langley engineer in the Structural

Dynamics Branch, Franklin W.

Diederich, made some valuable turbulence studies in which he calculated the

statistical properties of the wing

response of various planforms to flight

through isotropic turbulence. (The turbulence might be called axisymmetric
72 Monographs in Aerospace History Number 40—Journey Into Space Research

Continuation of Research Following Decline of Space Program

because the airplane was assumed to

be in straight horizontal flight.) Although

the mathematics involved was complex,

I considered Diederich’s approach easier to use than studies made previously

by other investigators.

I knew from previous studies that when

an airplane hit an abrupt gust, the

response was not instantaneous. There

was a lag in response called the

unsteady lift effect, which had been

investigated by several noted aerodynamicists. If a high-aspect ratio wing

hits a step-shaped gust, it travels five or

six chord lengths before the lift builds up

to a steady value. As the aspect ratio is

decreased, the lag is reduced until at an

aspect ratio of 3, the response is practically instantaneous. In the gust-alleviation systems that have been tried, the

gusts are usually measured by a vane

located ahead of the nose of the

airplane. If an airplane flies through a

turbulent region with high-frequency disturbances, the vane will respond accurately to the disturbance, but because of

the unsteady lift effect, the average

response of the wing lift over a period of

time will be reduced. A plot of the amplitude of the lift as a function of gust frequency will therefore show a decrease

as a function of frequency. 

Other investigators studying two-dimensional turbulence had concluded that

the response to high- frequency disturbances may be reduced because of

variations of gust velocity across the

wing span. In this case, the vane measures the disturbances along the centerline of the airplane, but the gust velocity

at other points along the wing will be different, and if the amplitude of response

is averaged across the span, the value

will be less than the amplitude at the

centerline. This problem was called the

“spanwise averaging effect.” These phenomena had been studied by different

groups of engineers and no effort had

been made to compare the relative values of the decrease in the amplitude of

response due to unsteady lift with the

decrease due to spanwise averaging. In

fact, in most studies, one or the other

of these two effects was investigated

and no account was taken of the other

one. I therefore undertook a study of

this problem.

Without my knowledge, an engineer in

the Structural Dynamics Branch named

Kermit G. (Cary) Pratt had been studying this same problem and published a

report before mine was completed

(ref. 7.8). It turned out that both analyses reached similar conclusions, but my

analysis was more complete from the

standpoint of logic and mathematics. I

therefore completed my report, which

was published as a NASA Technical

Memorandum (ref. 7.9). 

In this presentation, no attempt is made

to give the mathematical details. Several interesting points were encountered

in the analysis. The decrease in amplitude of response with increasing

gust frequency resulting from the spanwise averaging effect obtained from

Diederich’s report was given by a complex mathematical expression involving

Bessel functions. A complete plot of this

curve showed that a slight decrease in

amplitude of lift occurred as the frequency approached zero at very low

frequencies. This slight change in lift

was unexpected. I believe it may be

caused by the rare occurrence of an

occasional isolated gust of large amplitude, which when averaged over the

long period of time between such gusts,

shows up as a decrease in amplitude of

very low frequency. 

Another interesting discovery I made

was that Diederich’s complex expression could be approximated very accurately by a very simple expression

containing just two terms and no Bessel

functions, which applied at reduced frequencies greater than about 4. 
Turbulence Problems

Monographs in Aerospace History Number 40—Journey Into Space Research 73

The expressions for the reduction in

amplitude of the response caused by

the unsteady lift effect was calculated

for aspect ratios of 3 and 6 by methods

described in reference 7.10. A comparison of these results with those

due to the spanwise averaging effect

are given in figure 7.6. In this figure,

ω = frequency, rad/s, b = wing span, ft,

and U = airspeed, ft/s. These curves are

remarkably similar considering that they

came from completely different theories.

In practice, the values of the two effects

should be multiplied together to get the

total attenuation.

FIGURE 7.6. Comparison 

of attenuation of lift 

due to spanwise averaging on an elliptical 

wing with that due to 

unsteady lift effects 

for wings of aspect 

ratios 3 and 6.

Spanwise averaging

Unsteady lift, R = 6

Unsteady lift, R = 3

1.0

.8

.6

.4

.2

0 4 8 12

Reduced frequency, k = 

Attenuation of lift

16 20 24

ωb

U

Monographs in Aerospace History Number 40—Journey Into Space Research 75

CHAPTER 8 Some Nonaerodynamic 

Studies

Some Studies of Fireplaces

At one time, I was approached by

William J. Michael, then the Chief Scientist of the Langley Research Center, to

try to find some work for the Space

Radiation Effects Laboratory (SREL).

This laboratory was under the combined

direction of Langley and the College of

William and Mary and had been used

for studying radiation effects on materials for use in space. The laboratory was

also associated with the Virginia Associated Research Center (VARC), a headquarters building for SREL. The SREL

building contained a cyclotron to produce the radiation. These laboratories

were located in the northern end of

Newport News in an area separate from

the main NASA center and now called

Oyster Point. Unfortunately, funding for

the activities at SREL had been cut off

with the decline of the space program. A

proposal had been made to develop the

SREL into a nuclear research center.

This program was in the early development stages and required approval by a

consortium of Southern universities

(SURA), as well as approval by Congress and other groups. The problem

was to keep VARC alive with some

small contracts until the large nuclear

research program could be put into

operation.

I knew that VARC was a very useful

facility with a fine technical library and

several permanent employees, including mechanics. I found that the Department of Energy had a fund to provide

small grants to individuals or research

groups to improve the efficiency of fireplaces. The interest in fireplaces developed because a serious oil shortage

existed in this period, and many people

were trying to burn firewood to heat

their houses. Although I knew very little

about heat transfer or thermodynamics,

I submitted a proposal to the Department of Energy to study the efficiency of

fireplaces.

The funding was sufficient to give

employment to three summer students,

two men and one woman, who were

very capable and benefited from the

exposure to a technical problem. I went

to work at VARC two afternoons a week

to supervise the work.

I studied the works of Count Rumford

and Benjamin Franklin, both of whom

were noted for improving the fireplaces

of their day. Count Rumford’s main contribution was to change the shape of the

fireplace to a more narrow, tapered

shape to direct more heat radiation into
76 Monographs in Aerospace History Number 40—Journey Into Space Research

Some Nonaerodynamic Studies

the room. I concluded that Benjamin

Franklin knew more about the problems

of fireplaces than most people living

today. He developed a fireplace in which

the firebox was airtight. Air from the

room was heated in a closed container

in the firebox and returned to the room,

while air from the outside, coming under

the house, burned the logs and went up

the chimney. All of the circulation was

done by convection as there were no

electrically driven blowers in those days.

The fireplace greatly improved efficiency because cold air from the outside

was not sucked into the room. Franklin,

always a genius, ran the Post Office in

Philadelphia and installed one of his

fireplaces there, while selling piles of

iron castings to the customers to build

their own fireplaces. These fireplaces

were short-lived, however, because

sealing of the joints between the castings, done with a mixture of mud and

straw, soon developed leaks and

allowed smoke to escape into the room.

Franklin’s fireplaces using welded steel

joints would be excellent for use today

and would not make the distracting

noise of the blowers used on present

day fireplace inserts.

Franklin’s knowledge of fireplaces soon

became well-known, and many manufacturers called their fireplaces Franklin

stoves, though they did not incorporate

the advantages of Franklin’s invention.

When I started work on fireplaces, some

manufacturers of fireplace inserts had

already produced inserts with glass windows that allowed a view of the fire.

These glass windows quickly became

dirty with soot and pitch, which was very

difficult to clean off. I conceived the idea

of using a fine-mesh stainless steel

screen for the window, which would

allow some view of the fire, but which

would be kept clean by the small flow of

air through the screen. I found that finemesh stainless screen was produced in

large quantities for the paper industry,

and as a result was not as expensive as

I had imagined. One project that the

group undertook was to build a small

wind tunnel, with a test section about

4 by 8 inches, in which the pressure

drop through screens could be measured. Although screens were used in

some NASA wind tunnels to smooth the

airflow, no tests of the pressure drop

through screens as fine-meshed as

desired had ever been made.

Another project was to write a computer

program for predicting the efficiency of

fireplaces. This program accounted for

the heat transfer to the air in the chimney and to the room, but accounting for

the radiation between all the heated

parts was probably not done very accurately. The young lady who worked with

the group proved very skillful at computer programming.

Finally, two commercially available fireplace inserts were obtained to measure

their efficiency. Special instruments

were made to measure the airflow up

the chimney and the pressures and

temperatures in various parts of the system. One of the inserts, which used a

set of stainless steel tubes behind the

fire to take in air at floor level and blow it

into the room above the fire proved to

be about 60 percent efficient. The other

insert, which had a metal shell completely surrounding the fireplace to heat

air from the room, was found to be

about 80 percent efficient.

I soon found that numerous manufacturers wanted to improve fireplaces at the

same time that I did, and many of them

came out with efficient units. The air

above New Hampshire became so polluted by wood smoke that fireplace

inserts there were required to have a

catalytic converter, similar to those used

in automobile exhausts, to remove the

carbon monoxide and nitric oxide from

the combustion products.
Control System for a Small Hydrofoil Boat

Monographs in Aerospace History Number 40—Journey Into Space Research 77

I wrote a report on the studies that was

submitted to the Department of Energy.

Interest in the project soon declined

when the fuel shortage ended, and

the report was never published. The

VARC and SREL stayed alive, however,

and subsequently developed into the

Jefferson Laboratory, one of the main

centers in the country for nuclear

research.

Control System for a Small 

Hydrofoil Boat

My first boss, Dr. Robert R. Gilruth, who

was head of the Stability and Control

Branch of the Flight Research Division

when I came on duty, had shown an

interest in hydrofoil boats when he first

came to Langley. He had already built a

small hydrofoil sailboat and later built a

small outboard motor-propelled runabout and a larger sailboat, both lifted

from the water on hydrofoils. These

boats used surface-piercing foils, on

which the tips of the foils project above

the water when cruising. This feature

provides lateral stability, much like the

dihedral on an airplane wing. Longitudinal stability was provided by a submerged rear foil in conjunction with the

correct center of gravity. Later Gilruth

became a consultant to the Grumman

Company on the design of some large

hydrofoil boats for use by the Navy in

WWII. All this work was done as a

hobby, outside of working hours. Naturally, I also became interested in boats

of unusual design, although I did not

build any full-scale hydrofoil boats. I did

build a small rubber-motor propelled

hydrofoil boat with submerged foils,

which was stabilized laterally by a gyroscope linked to the front foil. The gyro

wheel was spun up by pulling a string

wound around the shaft. This boat conclusively proved to be stable in its short

runs.

In later years, hydrofoil passenger boats

were made in several European countries. The Boeing Company made one

in this country. These boats, which

used submerged foils for greater efficiency, required complex gyroscopic

systems and electronic autopilots to

provide stability.

I had a conventional 15-foot outboard

boat that I sailed in Hampton Roads. I

realized that a hydrofoil boat of the

same size and power would sail much

faster and more smoothly. I did not,

however, have the time or facilities to

build a full-scale boat. I did consider

how a simple mechanical autopilot

might be built to stabilize a hydrofoil

boat of this size. I made an analysis of

such a system at work with John D.

Shaughnessy. The analysis was done

by using a high-speed NASA digital

computer. I felt that this work was

appropriate in my position because I

was head of the Stability and Control

Division and because the AIAA at

that time published a Journal of

Hydronautics along with its other technical journals. A report on this work was

later published in the AIAA Journal of

Hydronautics (ref. 8.1).

The primary sensor for the control system was visualized as a long, streamlined stick pivoted at the hull to allow it

to swing fore and aft. The drag force of

the water on the stick would increase

with the depth of submersion. This stick

was linked to a trailing-edge flap on the

front foil to produce more downward flap

deflection when the drag on the stick

increased. Some damping of the slick

motion results from the variation of drag

on the stick with stick motion fore and

aft, and from the variation of flap hinge

moment with rate of change of flap

deflection. It was not known whether

these sources of drag would be sufficient to damp oscillations of the stick. To

further increase the damping, a bobweight was linked to the stick so that as
78 Monographs in Aerospace History Number 40—Journey Into Space Research

Some Nonaerodynamic Studies

the stick moved rearward, the bobweight would move up. The bobweight is

a weight mounted on a pivoted arm and

restrained by a spring. The bobweight

senses vertical acceleration at the location of its pivot. Locating the bobweight

near the front of the boat would presumably produce some lead in the acceleration of the weight, causing the flap to be

deflected up by an upward pitching or

by an upward vertical motion of the hull.

The equations of motion of the systems

are too complex to present in this report

but may be found in reference 8.1. The

stability of the system was studied by

root locus plots, by transient responses

to disturbances, and by frequencyresponse plots of the various variables

in the system. The root locus studies

show that adequate stability of all

modes of motion may be obtained by a

system of the type analyzed. The predominant low-frequency mode of the

boat, however, appears to have a frequency too low to interact with the bobweight system on the flap. The original

premise that the bobweight would contribute to the damping of the lowfrequency modes of the boat, therefore,

was found to be incorrect.

The system studied with a relatively low

value of the variation of restoring force

with vertical displacement provides

excellent attenuation of the vertical

motions of the boat due to head waves

through a large range of frequencies,

whereas in stern waves the motion is

attenuated to a value less than the wave

amplitude at frequencies above 0.8 Hz

but amplified at frequencies below this

value. Stabilization of the boat in stern

waves of low frequencies would probably require a more sophisticated control

system involving an attitude gyro. In

restricted bodies of water, long wavelengths are probably rare.
Monographs in Aerospace History Number 40—Journey Into Space Research 79

CHAPTER 9 Concluding Remarks

This volume has contained most of the

work that I conducted at Langley during

the space program. After this work

declined, I worked on many different

projects, mainly to provide interesting

subjects for my employees and to solve

some problems that arose in work

before the space program. I have presented four chapters that contain twelve

examples of projects or research conducted during this period. These examples represent only a small fraction of

the number of different studies that I

made. A bibliography of my reports that

were published during this period is presented at the end of this volume.

In 1979, after 39 years of service, I

found that much of my time as Chief of

the Stability and Control Division was

taken up by administrative matters. My

background and much of my earlier

work had been devoted to research.

Most of the other division chiefs at Langley had for some time been administrators, leaving the conduct of their

research to the personnel assigned to

their divisions. I found that I did not have

enough time to do personal research

and to adequately perform the administrative duties. I discussed this problem

with Oran Nicks, an assistant Director of

the Langley Research Center. He

advised me to resign and accept the

position of Distinguished Research

Associate (DRA). In this position, somewhat like that of a Professor Emeritus in

a college, I would be free to use the

facilities at Langley and to do research

as I desired. My retirement annuity

would be about two-thirds of my maximum salary as a federal employee. I

considered this offer as a good opportunity, and started what turned out to be a

long career as a DRA.

One objective of my career as a DRA

was to conduct a wind-tunnel test. Many

of the engineers at Langley were

engaged in operating the numerous

wind tunnels at this center. I had never

had this opportunity because when I

came on duty, I was assigned to the

Flight Research Division, in which the

duty of a flight engineer was to analyze

recorded data obtained by the test pilots

in flights of full-scale airplanes. The

closest I came to a wind-tunnel test was

shortly after I came on duty, when I was

assigned to bundle up in my overcoat

and climb into the cockpit of a Fairchild

F-22 airplane mounted in the Full-Scale

Tunnel. The airplane had been

equipped with a bob-weight in the control system. My duty was to apply

impulses to the control stick to measure

the damping of the elevator motion as

affected by the bob-weight.
80 Monographs in Aerospace History Number 40—Journey Into Space Research

Concluding Remarks

After I started work as a DRA, the Shuttle had started to fly, and it was soon

found that the very high landing speed

resulted in damage to tires and overheating of brakes. I believed that the

landing speed could be lowered by

installing a canard surface near the

nose of the Shuttle that would help to lift

the nose so that the elevons at the rear

of the delta wing could be trimmed down

and further increase the lift prior to

touchdown. I did not contemplate that

the test would be difficult, but I soon

found that all the major wind tunnels

had schedules that were booked up for

at least three years. I was able to get

some test time in the old 12-Foot Tunnel, a wind tunnel that was built in the

thirties and had originally been used to

create an airstream in which freely flying

small models would be tested. Later, the

tunnel was equipped with balances and

used in the conventional manner. The

model that I acquired from Rockwell

was an old balsa-wood Shuttle flutter

model, about 5 feet long that had been

partially crushed. I rebuilt the model and

ran tests on a number of canard

designs. I found that the flow in the tunnel was variable along its length so that

the results were not quantitative but

could be used for comparative purposes. The tests took over three years

to make and analyze. As a result, I

became more impressed by the work

required in wind-tunnel testing. On completion of the study, the results were

presented in a talk at the Johnson Flight

Research Center. The canard surfaces

were never used on the Shuttle because

of the difficulty in changing the design of

the Shuttle, and because some reduction in landing speed could be obtained

by rearward positioning of the center of

gravity combined with some downward

deflection of the elevons. This arrangement reduced the longitudinal stability,

but the stability could be restored by

adjusting the electronic control system.

A second interest that I had after

becoming a DRA was to learn more

about airfoils. I had studied airfoil theory

at MIT some 40 years earlier, but many

advances had been made in this field

with which I was not familiar. A notable

theory had been developed by Theodore Theodorsen at Langley to calculate the pressure distribution on an

airfoil given its contour. Later, Lighthill in

England, Trockenbrot in Germany, and

others had solved the inverse problem

of determining the contour required to

produce a given pressure distribution.

Robert T. Jones and Eastman Jacobs at

Langley also had developed an iterative

technique to solve this problem, but as

far as I know it was never published.

Other groups in this country and at

Langley developed boundary-layer theory that allowed the development of the

boundary layer and the resulting friction

drag to be calculated. These investigators at Langley were in a different group

from the airfoil theorists. I had suggested to Oran Nicks that the theories

be combined to allow the boundarylayer distribution on an airfoil to be calculated given the airfoil shape. Before

this analysis was done at Langley, however, Richard Eppler in Germany had

developed a computer program for a

theory that combined these parts of the

problem. Dan M. Somers, an engineer

at the Low-Turbulence Tunnel at Langley

arranged for Eppler to come to Langley

and explain his program to him and to

the people in his group. (refs. 9.1

and 9.2). I consulted with Somers to

learn the details of this program, and I

made many runs to study airfoils of different types. Later, I modified the program to allow the calculation of both

friction drag and pressure drag on an

airfoil as a function of angle of attack.

This work was presented in a Society of

Automotive Engineers (SAE) meeting at

Anaheim, California in October, 1988. 1

believe that experts at the large airplane
Monographs in Aerospace History Number 40—Journey Into Space Research 81

companies had developed similar programs, but the results had not been

published previously.

In most wind-tunnel tests to determine

drag of airfoils, the total drag (pressure

drag plus profile or skin-friction, drag) is

measured by means of a rake survey.

Until recent years, very few attempts

were made to separate the two sources

of drag or to determine the distribution

of these components of drag over the

surface of the airfoil. The only study of

this type with which I was familiar was a

remarkable analytical study by H. B.

Squire and A. D. Young made in 1937 in

England (ref. 9.3). Without modern computing facilities, calculations of this type

were extremely tedious. My paper

showed these characteristics for three

airfoils, each at three values of Reynolds number. The effects of uniform

suction through the surface of the airfoil

was also studied, and the possibility of

negative pressure drag, or thrust, on the

airfoil was demonstrated.

At that time, there was interest in very

high-altitude, unmanned aircraft to

make possible long endurance for surveillance or for communication purposes. I made recommendations for

airplane airfoils of this type. The personnel at the companies doing this work

contacted me because they had heard

of my experience with model airplanes.

They learned of my theoretical studies

later.

I was also interested in learning about

the theory of propellers. At this time,

most airplanes of interest were jet-propelled, and very little work on propellers

was being done at Langley. Earlier, in

the thirties and forties, there was much

interest in this work, and Theodorsen

had published a propeller theory that

was based on accurate aerodynamic

theory. Even as early as 1919, Betz and

Prandtl in Germany had developed a

theory based on some good approximations to the flow characteristics, and

Fred Weick at Langley in the thirties

built the Propeller Research Tunnel

and made empirical studies of full-scale

propellers. By this time, propellers

good enough for all practical purposes

could be designed. Incorporating the

fine points of aerodynamic theory did

not change the efficiency more than 2 or

3 percent.

A paper summarizing practically all that

was known about propeller design was

written by H. Glauert in England and

published in Volume IV of the Durand

Series in 1934. By the seventies, few

people paid any attention to this work,

but E. E. Larrabee at MIT studied the

article, made a few important corrections, and programmed the theory on a

pocket calculator. Later, I used this theory as an example of programming on

the HP 9820 and later on the HP 9830

computers. Designers of commercial

airplanes at that time could purchase

propellers from companies that specialized in this work, but homebuilders often

wished to design and build their own

propellers. I received over 50 requests

from all around the world for copies of

my programs.

The preceding paragraphs are examples of my work as a DRA. Many other

studies, probably of lesser importance,

were also conducted, some of which

are mentioned in the bibliography. In

addition I started writing a history of my

work at Langley. This book, entitled

Journey in Aeronautical Research was

published in November 1998, as the

NASA publication Monographs in Aerospace History, Number 12 (ref. 1.1).

This document covered the work to the

start of the space program in 1958. The

present volume contains my work during the space program and later work to

2004. This work is necessarily abbreviated because of the large number of

subjects that were encountered in the

work after the space program.
82 Monographs in Aerospace History Number 40—Journey Into Space Research

Concluding Remarks

The long duration of my work at the

Langley Research Center has involved

many changes. Perhaps the greatest

change, from the engineering standpoint, is the development and widespread use of computers. These

marvelous devices allow analyses to be

made in seconds that previously

required days or weeks. Most of the

older techniques are now obsolete

because they are incorporated in computer programs. Younger engineers who

grew up with these methods produce

results with computers with a facility that

is beyond my abilities. The changing

research emphasis, as well as the new

body of personnel involved, makes this

a good time to end this volume.
Monographs in Aerospace History Number 40—Journey Into Space Research 83

Appendix

Abbreviated Chronology of Space Flight Accomplishments

List of major accomplishments and total launch attempts in each

year through 1962, showing number of failures.

Major milestones in U.S. manned space program

through first lunar landing and return.

Year Date Name Notes

1957

10/04/57 Sputnik I First artificial satellite (Russian)

11/03/57 Sputnik II Second artificial satellite (Russian), carried dog, 

Laika

1958

2/01/58 Explorer I, 

Jupiter C

First successful U.S. artificial satellite, discovered 

Van Allen belts

3/26/58 Explorer III, 

Jupiter C

Radiation, micrometeoroid data

22 total launch attempts, Russian and U.S.; 7 achieved orbit

1959

U.S. made launch attempts of several artificial satellites, including Vanguard, 

Discoverer and Transit. Russia launched Luna II

25 total launch attempts, 13 achieved orbit

1960

U.S. launched Atlas Able (Pioneer 1960)

40 total launch attempts, 20 achieved orbit

1961

4/12/61 Vostok 1 Orbit, Yagi Gogarin (Russian, first man in space)

5/05/61 Mercury, 

Redstone 3

Suborbital Flight, Alan Shepard (first U.S. man in 

space)
84 Monographs in Aerospace History Number 40—Journey Into Space Research

Appendix

9/13/61 Mercury, 

Atlas D

One orbit, unmanned

10/29/61 Mercury, 

Atlas 5

Two orbits, Chimpanzee Enos

57 total launch attempts, 39 achieved orbit

1962

2/20/62 Mercury, 

Atlas 6

Three orbits, John Glenn

5/24/62 Mercury, 

Atlas 7

Three orbits, Scott Carpenter

10/03/62 Mercury, 

Atlas 8

Three orbits, Wally Schirra

81 total launch attempts, 74 achieved orbit

1963, 1964: at this point, total launch attempts are omitted, skip to major U.S. space programs in 1965

1965

7/28/65 Ranger 7 First successful close-up photos of Moon

12/04/65 Gemini 7 Borman and Lovell

12/15/65 Gemini 6 Schirra, Stafford; rendezvous with Gemini 7

1966

3/16/66 Gemini 8 target 

Atlas Agena D

3/16/66 Gemini 8 Armstrong, Scott docked with Gemini 8 target; 

stuck thruster caused emergency.

7/05/66 Apollo 2, 

Saturn 1B

AS-203, unmanned test

7/18/66 Gemini 10, 

Titan II

Young, Collins; first EVA, docked with Gemini 10 

target; raised its apogee to 755 km

8/10/66 Lunar Orbiter I 

Atlas Agena D

Returned lunar photos, crashed on Moon

11/08/66 Gemini 12, 

Titan II

Lovell, Aldrin docked with target, successful EVA 

tests

11/08/66 Atlas Agena D Target

1967

2/05/67 Lunar Orbiter 3 

Atlas Agena D

Returned lunar photos, crashed on Moon

1968

4/04/68 Apollo 6, 

Saturn V

Command module test

10/11/68 Apollo 7, 

Saturn 1B

Schirra, Cunningham, Eisele, Earth orbital test of 

Apollo

12/21/68 Apollo 8, 

Saturn V

Borman, Lovell, Anders; first circumlunar mission
Monographs in Aerospace History Number 40—Journey Into Space Research 85

1969

3/3/69 Apollo 8, LM 

Saturn V

McDivitt, Scott, Schweickert; Earth orbital test.

5/18/69 Apollo 10, LM, 

Saturn V

Stafford, Young, Cerman; LM undocking and 

docking in Lunar orbit

7/16/69 Apollo 11, LM, 

Saturn V

Armstrong, Aldrin, Collins; first lunar landing and 

return

Monographs in Aerospace History Number 40—Journey Into Space Research 87

 References

1.1. Phillips, William H.: Journey in Aeronautical Research, A Career at NASA Langley Research Center—

Monographs in Aerospace History Number 12, 1998.

1.2. Hansen, James R.: Spaceflight Revolution, NASA Langley Research Center From Sputnik to Apollo. NASA

SP 4308, 1995.

2.1. Anon: Space Log, Volume 32. Compiled by Editor, TRW Space Log, TRW Space and Electronics Group,

Redondo Beach, California 90278.

2.2. Swenson, Lloyd S., Jr.; Grimwood, James M.; and Alexander, Charles C.: This New Ocean, a History of

Project Mercury. NASA SP 4201, 1966.

2.3. Grimwood, James M.; Hacker, Barton C.; with Vorzimmer, Peter J.: Project Gemini, a Chronology. NASA

SP 4002, 1969.

2.4. Brooks, Courtney G.; Grimwood, James M.; and Swenson, Loyd S.: Chariots for Apollo. NASA SP 4205,

1979.

2.5. Anon: Notes on Space Technology. Compiled by the Flight Research Division, Langley Aeronautical Laboratory, Langley Field, Virginia, Feb.–May 1958.

2.6. Vyssotsky, Alexander N.: Exploration of Space From the Observatory of the University of Virginia. U. of

Virginia News Letter, Vol. XXXV, No.8, Jan. 15, 1959.

2.7. Allen, H. Julian; and Eggers, A. J., Jr.: A Study of the Motion and Aerodynamic Heating of Missiles Entering

the Earth’s Atmosphere at High Supersonic Speeds. NACA TN 4047, 1957.

2.8. Staff of the Langley Flight Research Division, Compiled by Donald C. Cheatham: A Concept of a Manned

Satellite Reentry Which Is Completed With a Glide Landing. NASA TM X-226, 1959.

2.9. Spencer, Bernard, Jr.: An Investigation at Subsonic Speeds of the Longitudinal Aerodynamic Characteristics at Angles of Attack From –4° to 100° of Delta-Wing Reentry Configurations Having Vertically Displaced

and Cambered Wing-Tip Panels. NASA TM X-440, 1961.

2.10. Olstad, Walter B.: Static Longitudinal Aerodynamic Characteristics at Transonic Speeds and Angles of

Attack up to 99° of a Reentry Glider Having Folding Wing-Tip Panels. NASA TM X-610, 1961.

2.11. Hondros, James G.; and Goldberg, Theodore J.: Aerodynamic Characteristics of a Group of Winged Reentry Vehicles at Mach Number 6.01 at Angles of Attack From 60° to 120° and –10° to 30° Roll at 90° Angle

of Attack. NASA TM X-511, 1961.
88 Monographs in Aerospace History Number 40—Journey Into Space Research

References

2.12. Popma, Dan C.: Spacecraft Life Support Systems. Presented at the Institute of Electrical and Electronic

Engineers. Region 3 meeting, Richmond, Virginia, April 24–26, 1963. Paper number CP 63-693.

2.13. Von Doenhoff, Albert E.; and Hallissy, Joseph M., Jr.: Systems Using Solar Energy for Auxiliary Space

Vehicle Power. I.A.S. Rept. 59-40, Jan. 1959.

3.1. Braün, Gerhard W.: An Analytic Treatment of the Unsteady Spinning of Airplanes of High Relative Densities. WADC TN WCLS 53-79, Nov. 1953.

3.2. Goldstein, Herbert: Classical Mechanics, Second Edition. Addison-Wesley Publ. Co., Reading, Massachusetts, 1980.

3.3. Chobotov, Vladimir A.: Spacecraft Attitude Dynamics and Control. Krieger Publ. Co., Malabar, Florida,

1991.

3.4. Hooper, John W.: The Damping of Metallic Cylindrical and Spherical Bodies Rotating in a Uniform Magnetic Field. ABMA Tech Report DG-R-15, Nov. 1, 1957.

4.1. Clohessy, W. H.; and Wiltshire, R. S.: Terminal Guidance System for Satellite Rendezvous. Preprint Mo.

59-93, S.M.F. Fund Paper, I.A.S., June 1959.

4.2. Battin, Richard H.: Astronomical Guidance. McGraw-Hill Book Co. Inc., New York, 1964.

5.1. O’Bryan, Thomas C.; and Hewes, Donald E.: Operational Features of the Langley Lunar Landing Research

Facility. NASA TM D-3828, 1957.

5.2. Phillips, William H.; Queijo, M. J.; and Adams, James J.: Langley Research Center Facilities for Manned

Space Missions. ASME paper No. 63-AHGT-91, Jan. 1, 1964.

6.1. Kraft, C. C.: Flight—My Life in Mission Control. DUTTON, Penguin Putnam, Inc., New York, Mar. 2001.

7.1. Burgin, George H.; Fogel, Lawrence J.; and Phelps, J. Price: An Adaptive Maneuvering Logic Computer

Program for the Simulation of One-on-One Air-to-Air Combat, Vol. 1, General Description.

7.2. Hankins, Walter W., III: First DMS Engagements Between Human Pilots and a Computer-Driven Opponent.

Langley Working Paper LWP 1127, Aug. 13, 1973.

7.3. Hankins, Walter W., III: Interactive Computerized Air Combat Opponent. Presented at the AGARD FMP/

GCP Joint Symposium on Flight Simulation/Guidance Systems Simulation. The Hague, Netherlands, Oct.

20–24, 1975.

7.4. Phillips, William H.: Propulsive Effects Due to Flight Through Turbulence. J. Aircr., vol. 12, no. 7, July 1975,

pp. 624–626.

7.5. Phillips, William H.: Analysis of Effect of Asymmetric Loading on Sailplane Performance in Circling Flight.

Presented at the Symposium on the Science and Technology of Motorless Flight, Cambridge, Massachusetts, Oct. 18–22, 1972.

7.6. Phillips, William H.: Gyroscopic Moments on a Glider in Turning Flight. “Technical Soaring,” Nov. 21, 1972.

7.7. Garren, John F., Jr.; Niessen, Frank R.; Abbott, Terence S.; and Yenni, Kenneth R.: Application of a Modified Complementary Filtering Technique for Increased Aircraft Control System Frequency Bandwidth in

High Vibration Environment. NASA TM X-74004, 1977.

7.8. Pratt, Kermit G.: Effect of Spanwise Variation of Turbulence on the Normal Acceleration of Airplanes With

Small Span Relative to Turbulence Scale. NASA TM X-72748, 1975.

7.9. Phillips, William H.; and Lichtenstein, J. H.: Comparison of Effects of Unsteady Lift and Spanwise Averaging in Flight Through Turbulence. NASA TM X-74028, 1977.
References

Monographs in Aerospace History Number 40—Journey Into Space Research 89

7.10. Jones, R. T.: The Unsteady Lift of a Wing of Finite Aspect Ratio. NACA Report No. 681, 1940.

8.1. Phillips, William H.: and Shaughnessy, John D.: Investigation of Longitudinal Control System for a Small

Hydrofoil Boat. J. of Hydronautics, vol. 10, no. 2, April 1976, pp. 39–42.

9.1. Eppler, R.; and Somers, D. M.: A Computer Program for the Design and Analysis of Low Speed Airfoils.

NASA TM-80210, 1980.

9.2. Eppler, R.; and Somers, N. M.: Supplement to a Computer Program for the Design and Analysis of Low

Speed Airfoils. NASA TM-81862, 1980.

9.3. Squire, H. B.; and Young, A.D.: The Calculation of the Profile Drag of Airfoils. RAE R.&M. No. 1838, 18 Nov.

1937.

Monographs in Aerospace History Number 40—Journey Into Space Research 91

Index

A

Adamson, David 6

Algranti, Joe 41, 43

Allen, H. Julian 7, 87

Armstrong, Neil 41, 43, 47, 84, 85

B

Battin, H. Richard 32, 88

beryllium 9

Bicknell, Joseph 64

Bird, John D. 48, 49, 61, 63

Braün, G. W. 18, 88

Burgin, George H. 63, 88

C

Calspan 56

Cheatham, Donald C. 6, 11, 56, 87

Chilton, Robert G. 53

Clohessy, W. H. 31, 88

closed-form solution 19, 31

Collins, Robert 33

D

Diederich, Franklin W. 71, 72

Donlan, Charles J. 14, 47

Draper Lab 32, 53

E

Eggers, A. J., Jr. 7, 87

Eggleston, John M. 33

ellipsoid of inertia 17, 19

Eppler, Richard 80, 89

Euler’s dynamical equations 18, 19

F

Faget, Maxime A. 7, 52

Fogel, Lawrence J. 63, 88

G

Garren, John F. 71, 88

Gilruth, Robert R. 6, 26, 55, 77

Goldstein, Herbert 18, 19, 22, 88

H

Halissy, Joseph M. 15

Hankins III, Walter W. 63, 88

Hewes, Donald E. 41, 45, 49, 50, 88

Hill, Paul 14

J

Jackson and Moreland 40

Jered Industries 40

Johnson, Harold J. 49
92 Monographs in Aerospace History Number 40—Journey Into Space Research

Index

K

Kalman-Bucy Filter 70, 71

Katzmayr, R. 66

Kennedy, John F. (President) 15, 29, 36

Kraft, Christopher C. (Dr.) 51, 54, 88

L

Loftin, Lawrence K. 36, 38, 65

Long Duration Exposure Facility (LDEF)

15

Lunar Landing Research Facility (LLRF)

39, 40, 41, 43, 45

Lunar Landing Training Vehicle (LLTV)

38, 41, 45

Lunar Module (LM) 32, 40, 41, 45, 47,

85

M

Mathews, Charles W. 6

Mattson, Axel 51

Mayer, J. P. 6, 33

Mercury Project 6, 7, 13, 87

MISS program (Man in Space Soonest)

6

Moment of inertia 25

moment of inertia 17, 20, 23

N

NACA (National Advisory Committee for

Aeronautics) 1, 2, 4, 6, 14, 15, 38, 60,

61, 87, 3

NASA (National Aeronautics and Space

Administration) 3, 4, 6, 7, 11, 13, 14, 20,

38, 39, 41, 42, 45, 49, 63, 72, 75, 76,

77, 81, 87, 88, 89

Newtonian flow 25

Nickel-cadmium (NiCad) batteries 15

Nicks, Oran 68, 79, 80

O

Ohlson, Roland 15

P

Pearson, Henry A. 4, 5, 22, 33

Person, Lee 41

Phelps, J. Price (Decision Science, Inc.)

63, 88

Pilotless Aircraft Research Division

(PARD) 6, 7, 14, 26

Poinsot, Louis 18, 19

Popma, Dan C. 14, 88

Pratt, Kermit G. (Cary) 72, 88

R

Reeder, John P. (Jack) 38, 39

regenerative space power systems 15

Rene 41 9

retro-rocket 9, 26

Russell, Walter J. 33

S

Shaughnessy, John D. 77, 89

Shuttle Training Aircraft (STA) 56

Somers, Dan M. 80, 89

Space Radiation Effects Lab (SREL) 14,

75, 77

Spaceflight Revolution 1, 87

Sputnik 1, 4, 83, 87

T

Tactical Effectiveness Simulator (TES)

61

Theodorsen, Theodore 80, 81

TIFS (Total In-Flight Simulator) airplane

56

TRW Space Log 3, 87

V

Verne, Jules 1

Vogeley, Arthur W. 47, 50

Von Doenhoff, Albert E. 15, 88
W

Monographs in Aerospace History Number 40—Journey Into Space Research 93

W

Wiltshire, R. S. 31, 88

Z

Zalovcik, John A. 8

Zimmerman, Charles H. 46
Phillips in 2002 at the age of 84. From 1979 to 2005, he was a

Distinguished Research Associate at the NASA Langley Research Center.
Monographs in Aerospace History Number 40—Journey Into Space Research 95

About the Author

William Hewitt Phillips was born in Port Sunlight, Merseyside, England, and came to

the United States with his parents at the age of 2. He was educated in the Belmont,

Massachusetts public schools and studied aeronautical engineering at MIT where he

obtained his S.B. degree in 1939 and his S.M. degree in 1940. His entire professional

career has been spent with the NACA, later NASA, at Langley Research Center in

Hampton, Virginia. Langley Research Center is the original government center for

aeronautical research in the United States. On entering duty in July 1940, he was

assigned to the Flight Research Division. He specialized in the study of flying qualities

and stability and control of airplanes. His duties included studies to improve the flying

qualities of many World War II military airplanes. After the war, he was involved in

research on the development of jet-powered fighter airplanes, supersonic airplanes,

stability augmentation and its effect on human pilot control, automatic control, gust

alleviation, and aeroelastic effects. His previous book, Journey in Aeronautical

Research, ends with the advent of the nation’s space program. After the start of the

space program, he became Chief of the Space Mechanics Division and supervised

80 to 90 people in the areas of space rendezvous, navigation, and lunar landing. As a

part of his responsibility to the space program, this division developed simulators for

the Gemini and Apollo programs. He developed the Lunar Landing Facility that was

used for training astronauts in landing on the Moon. His work also included consultation and analysis in the development of the Space Shuttle. Later work included supervising studies of effects of turbulence and of application of control theory and

contributing to the development of the Differential Maneuvering Simulator, a facility

used for air combat studies. He retired from government service in February 1979 but

continued until 2004 in the position of Distinguished Research Associate, during

which time he performed original research on solar-powered aircraft, propellers, airfoil

design, and wind-tunnel studies of canard surfaces use for the Space Shuttle. He

served as a consultant on studies of flight dynamics and control. He has received

numerous awards throughout his career, including the IAS Lawrence Sperry Award for

aeronautics in 1944 and the President’s Award for Distinguished Federal Civilian Service in 1979. In 2005, at the age of 86, he continues to design and fly model airplanes

and still has a keen interest in aeronautics.

Phillips married Viola Ohler in 1947 when she was head of the Editorial Office at

Langley. They had three children, Frederick H., Robert O., and Alice B. Phillips. All are
96 Monographs in Aerospace History Number 40—Journey Into Space Research

About the Author

now married. Frederick, whose wife is Joanne, is a financial consultant. Robert and

wife Cheryl have three children: Tyler, 25; Ross, 22; and Jocelyn, 20. Robert works at

The Volpe Center in Cambridge, Massachusetts. Alice and husband Thomas Check

have three children: Candace, 18; Nolan, 16; and Aubree, 14. Alice formerly worked

for robotics firms and is now a homemaker.
www.nasa.gov