NASA Technical Memorandum 101728

Integrated Flight-Propulsion

Control Concepts for Supersonic

Transport Airplanes

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Frank W. Burcham, Jr., Glenn B. Gilyard, and Paul A. Gelhausen

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NASA Technical Memorandum 101728

Integrated Flight-Propulsion

Control Concepts for Supersonic

Transport Airplanes

Frank W. Burcham, Jr. and Glenn B. Gilyard

NASA Ames Research Center, Dryden Flight Research Facility, Edwards, California

Paul A. Gelhausen

Ames Research Center, Moffett Field, California

1990

fU/L_A

National Aeronautics and

Space Administration

Ames Research Center

Dryden Flight Research Facility

Edwards, California 93523-0273
I1@

2

i

i
901928

Integrated Flight-Propulsion Control Concepts

for Supersonic Transport Airplanes

Frank W. Burcham, Jr. and Glenn B. Gilyard

NASA Ames-Dryden, Edwards, CA

Paul A. Gelhausen

NASA Ames Research Center, Moffett Field, CA

ABSTRACT

Integration of propulsion and flight-control

systems will provide significant performance improvements for supersonic transport airplanes. Increased engine thrust and reduced fuel consumption can be obtained by controlling engine stall HSCT

margin as a function of flight and engine oper- M

ating conditions. Improved inlet pressure recovery and decreased inlet drag can result from inlet PSC

control system integration. Using propulsion sys- SFC

tem forces and moments to augment the flight- TOGW

control system and airplane stability can reduce

the flight-control surface and tail size, weight, and WA

drag. Special control modes may also be de- oe

sirable for minimizing community noise and for /y

emergency procedures. The overall impact of integrated controls on the takeoff gross weight for z_

a generic high speed civil transport is presented.

NOMENCLATURE

ACSYNT

ADECS

A8

A9

CG

aircraft synthesis

adaptive engine control system

convergent nozzle area

divergent nozzle area

center of gravity

EPR

FCS

FNP

HIDEC

engine pressure ratio

flight-control system

net propulsive force, Ib

highly integrated digital

electronic control

high-speed civil transport

Mach number

performance-seeking control

specific fuel consumption

takeoff gross weight, Ib

airflow

angle of attack

angle of sideslip

change in parameter

INTRODUCTION

Interactions between the propulsion and flightcontrol systems (FCSs) of an airplane become

stronger as the cruise Mach number increases.

Minimizing unfavorable interactions and maximizing favorable interactions is a challenging task

for control integration. Supersonic transport airplanes, with extended periods of cruise flight at
Mach numbers in excess of 2.0, will have strong

propulsion system-airframe interactions. In addition, there will be requirements to minimize community noise during takeoff and landing, minimize

or eliminate sonic boom, and minimize emissions.

These characteristics make the use of integrated

propulsion-flight-control systems very beneficial.

NASA has conducted extensive flight studies

of propulsion-flight-control integration (1)* both

for the YF-12/SR-71 airplanes, which have a

cruise Mach number in excess of 3, (2,3) and for

the NASA F-15 highly integrated digital electronic

control (HIDEC) airplane (4). Design methods for

integrated control (5) have been developed and

integrated airframe-propulsion system architecture studies have been conducted (6,7). In addition, an adaptive optimization technique called

performance-seeking control (PSC) has been

studied (8,9).

NASA is currently involved in the High-Speed

Research Program. This program will determine

the feasibility of developing an economical and

environmentally acceptable high-speed civil transport (HSCT). Incorporation of integrated controls

is one of the technologies being investigated. It

is believed that control integration can improve

performance, reduce environmental impact, and

improve safety. When considered early in the

design phase, control integration can result in a

lighter, lower-drag, safer, and less expensive airplane. A design synthesis code (10,11) has been

used to assess the effects of the control

integration

This paper will present some preliminary

thoughts on the control requirements for a supersonic transport, identify the key control integration issues, and present some potentially beneficial integrated control modes, both for normal

operation and for emergencies. Results of pertinent integrated control modes currently being

tested are presented, and estimates of benefits

for a HSCT are made. The overall effect of these

benefits is assessed for a generic HSCT in terms

of reduction in takeoff gross weight (TOGW) for

a fixed range and payload.

•Numbers in parentheses designate references

at end of paper.

BACKGROUND

The United States supersonic transport design of the early 1970s had a limited experience

base in propulsion-flight-control integration.

Flight experience with the XB-70 and YF-12 airplanes had identified problems but few solutions.

The NASA flight-research program on the YF-12

airplane documented the propulsion-flightcontrol system interactions, showing that, at

Mach 3, forces and moments generated by the

mixed compression inlet were similar to those of

the flight-control system. Inlet unstarts, which occurred frequently, were violent and required significant control authority to maintain control. In

addition, atmospheric temperature gradients were

encountered which made it impossible to hold altitude and speed within the limits expected for

subsonic flight.

After years of control system analysis, simulation, and flight research, these problems were

solved. The cooperative control system, (1) implemented on the NASA YF-12C airplane, integrated the airdata, autopilot, autothrotUe, inlet,

and navigation functions. The system improved

flightpath control by a factor of 10, eliminated inlet unstarts, and provided inlet performance improvements that resulted in a 7-percent increase

in range. This concept was implemented on the

SR-71 fleet.

More recently, NASA, in conjunction with the

USAF, McDonnell Douglas, and Pratt & Whitney,

has conducted integrated flight-propulsion control research on an F-15 HIDEC airplane. Initially,

an active engine stall margin control mode was

developed and tested. Excess engine stall margin was traded for thrust at times when the full

stall margin was not needed. Specific fuel consumption (SFC) reductions were also obtained

at constant thrust. Later, another active control

mode was tested in which stall margin was traded

for lower engine turbine temperature, thus extending engine life.

Integrated trajectory guidance experiments

were also conducted, in which the flightpath and

throttle commands were generated in an onboard

computer. Minimum time, minimum fuel, or mini2
mum fuel to arrive at a specified time modes were

all investigated.

An inlet integration mode was also tested (12).

Flight-control and engine parameters were supplied to an algorithm that trimmed the positions of the inlet ramps, resulting in improved

performance.

A PSC system has recently been implemented

which performs an onboard engine parameter

identification, updates system models, and then

optimizes the engines, inlets, and nozzles in near

real time (1,9).

HIGH-SPEED CIVIL TRANSPORT

DESCRIPTION

nacelles. Typically, the propulsion system weight

will be approximately 18 percent of theempty weight.

INLET - Each engine will be fed by a variable

geometry inlet; an external compression inlet may

be practical for cruise Mach numbers up to 2.2.

At higher Mach numbers, a mixed compression

inlet will likely be required. Variable-geometry

compression surfaces will be required to achieve

high performance over the Mach range. Bypass

doors will be provided to match inlet capture to

engine demand. Boundary-layer bleed will be required to achieve high-inlet pressure recovery and

low distortion.

A conceptual design of an HSCT is shown in

Figure 1. The HSCT features a long slender fuselage, a large sharply-swept double delta wing,

and underwing nacelles. This HSCT is 293-ft long

and has a wingspan of 136 ft. The airplane will

carry approximately 250 passengers over a range

of approximately 5000 to 6000 nautical miles at

cruise Mach number between 2.2 and 3.2. The

takeoff gross weight (TOGW) will be approximately 650,000 Ib; approximately 55 percent willbe fuel.

Inlet Control - Control of the inlet will be a challenging and critical task for an HSCT. Inlet stability requires operating margins away from the

optimum position, but these margins will reduce

performance. Therefore, it is critical to operate

with the minimum acceptable margin. Integration

is a powerful method of minimizing these inlet operating margins. The inlet control system, either

for an external compression or mixed compression inlet, will be a multichannel digital system

with data bus communication to other systems.

9OO543

Figure 1. Generic high-speed civil transport.

PROPULSION SYSTEM

The propulsion system will likely consist of four

inlet--engine-nozzle units mounted in underwing

External Compression Inlet - External compression inlets are less sensitive than mixed compression inlets because there is no unstart potential. However, a complex system is still required to position the compression surfaces and

the bypass doors as a function of flight conditions and engine demand to achieve maximum

performance.

Mixed Compression Inlet - A mixed compression inlet can achieve higher performance, but

will have a much more complex control system

because the inlet must be started (the terminal

shock wave moved to an internal position downstream of the throat) and prevented from unstarting. Extensive studies of the mixed compression

inlet of the YF-12/SR-71 airplane have been conducted, and have shown that high performance

may be achieved without a significant incidence

of inlet unstart (1).

3
ENGINE- The HSCT engine design is still being studied, but will likely be a low pressure ratio

engine in the 60,000- to 70,000-1b thrust class.

Engine cycles being considered include turbojets,

turbofans, variable cycle engines, and turbine bypass engines. Afterburning may also be considered. There will be extensive variable geometry

to achieve high performance over the wide operating range of an HSCT.

Engine Control -The HSCT engines will be

complexand will require a carefully designed control system. A full-authortty digital control system

will be used to control the many engine variables.

It is likely that each engine will have its own engine mounted control, although some studies

have addressed the practicality of a remotely

mounted centralized engine control system. The

engine control will be interfaced through a data

bus to other systems on the HSCT.

EXHAUST NOZZLE -Each engine will be

equipped with a variable exhaust nozzle. The

nozzle will provide convergent section throat area

control for the engine, and divergent section control for supersonic cruise. Noise suppression will

be provided for takeoff, and will probably require

variable geometry.

Thrust vectoring capability could enhance performance for the HSCT. Low-speed control authority could be Increased, and flight-control surfaces could be trimmed to the minimum drag position. The same capability could be used for moment generation and surface trimming at other

flight conditions. This capability is not usually considered for an HSCT design, but a simple lightweight vectoring system might permit smaller and

lighter tails and control surfaces, and improved

performance.

Nozzle Control - The nozzle on the HSCT will

require accurate control to maximize performance

at cruise, and minimize noise at takeoff. The convergent nozzle area (AS) will be variable for engine control. The secondary nozzle area (Ag)

will be controlled to provide proper expansion as

Mach number increases. Takeoff noise control

will likely require additional nozzle variable geometry which will need to be positioned in concert

with engine variables. If thrust vectoring should

be available, it, too, will be controlled in an integrated manner with the rest of the nozzle control

and the other propulsion and flight controls.

FLIGHT CONTROLS

The flight-control system will be a key element

in the HSCT. There will most likely be a single

vertical tail with a rudder. Roll control will be provided by ailerons or elevons. For pitch control,

some configurations have separate horizontal

tails, while others use the elevons on the wing for

pitch control. There will possibly be highlift devices on wing leading edges in addition to

trailing-edge flaps. Some designs have employed

canards for additional pitch control. In some designs, multiple pitch control surfaces may be used,

with control surface blending used.

FLIGHT CONTROL SYSTEM -A multichannel digital flight-control system is planned for the

HSCT. The control and augmentation functions

will be conventional; however, the HSCT configuration place a major emphasis on minimization of

surface deflections to minimize total vehicle drag.

The static stability of the aircraft will be driven by

performance factors commensurate with the ability to control potential instabilities both longitudinally and lateral-directionally.

HIGH SPEED CIVIL TRANSPORT SYSTEMS

FOR INTEGRATION

There will be many systems on a typical HSCT

that will benefit from integration. !n_ad_ditionto the

previously discussed propulsion and flight-control

systems, there are other systems that need to be

included in the overall integration scheme.

AIRDATA -Airdata provides important information to the cockpit, flight-control system, navigation system, and propulsion system. A nose

mounted airdata system will be as much as 200

ft upstream of the inlets, and may be able to provide advance warning of atmospheric transients

that can be used by the inlet control system to

Ir

4
bias operation to higher stability. Use of a laser

alrdata system that looks ahead of the airplane

would provide longer warning times.

TRAJECTORY-NAVIGATION - An HSCT will

have new requirements for trajectory control and

navigation. Noise on takeoff will be controlled

by a combination of flightpath, throttle, and noise

suppressor. Climb will consume a significant percentage of fuel, and needs to be done at optimum conditions in terms of flightpath and throttle setting. Fuel consumption at cruise conditions

can be significantly affected by atmospheric conditions. Sonic boom considerations may also require careful flightpath control. Fuel consumption at subsonic loiter will be high; therefore flightpath, throttle control, and aerodynamic surface

positions should be managed to minimize drag.

The trajectory should also be optimized with respect to air traffic control requirements. Finally,

approach noise constraints may again require integrated control of throttle and flightpath. The

ability to compute an optimal flightpath and throttle setting in real time as requirements change

will provide significant benefits.

CENTER-OF-GRAVITY CONTROL - Centerof-gravity control will likely be provided by shifting fuel. The longitudinal CG will be controlled

to achieve the desired degree of static stability,

and lateral control may also be provided to minimize lateral control deflections. Fuel transfer systems are usually slow in response; therefore stability trades must consider potential unusual operations that may result from failures.

INTEGRATION ARCH ITECTURE - The architecture for implementing the control systems for

an HSCT will be studied for the next several years.

To facilitate the integration of the various systems, yet keep the hardware and software development and verification and validation manageable, great care will have to be taken early in

the design phase.

An overview of a potential integration hierarchy is shown in Figure 2. Individual control systems may be provided for the inlet, engine, and

nozzle. An integrated nacelle control system for

each propulsion system could be developed, followed by an overall propulsion system integrated

control. The next level might be the integrated

I •

Flight

path

Speed

Control

mode j

Pilot

C Rudder

C Aileron TM

Roll _ (Engine)

Yaw

Throttle

Integrated nacelle control system

Integrated propulsion control system

_. Integrated flight/propulsion control system

Elevator

Elevon

Canard

Integrated flight

control systemj

J

Flight path management system J

Figure 2. High-speed civil transport integrated control concept.

900545

5
flight-propulsion control system. The topmost

level could be the airplane flightpath management

system, which would include outer-loop

functions.

HIGH-SPEED CIVIL TRANSPORT CONTROL

MODES AND POTENTIAL BENEFITS

Some selected examples of control modes for

the various levels of integration shown in Figure 2

will be presented. Estimates of the potential benefits for an HSCT will be made, based on recent

experimental and analytical studies.

ENGINE-FLIGHT-CONTROL INTEGRATION -

Engine fan and compressor stall margins are normally made large enough to accommodate the

worst case combination of inlet and engine induced disturbances (for example, an afterburner

light during a high sideslip condition). At times

when this full level of stall margin is not required,

the operating point may be moved closer to the

stall line, and additional engine performance

(higher thrust, lower SFC, lower temperature) may

be achieved. Active real-time control of the stall

margins requires large numbers of flight-control

system and engine control system parameters.

The system shown in Figure 3 was developed

and flight tested on the NASA F-15 HIDEC airplane (4) in the adaptive engine control system

(ADECS) program. Engine pressure ratio (EPR)

was increased as a function of flight control and

engine variables. Thrust increases of 5 to 10 percent were measured. Fuel flow reductions to

maintain maximum afterburning thrust were found

to be 5 to 15 percent. Constant thrust could be

maintained at 20 ° to 80 ° F lower fan turbine inlet

] flight

I control

Airplane data

Mach, alt,

(:I, _,

stick, rudder

throttle

and surface

positions,

inertial data,

attitudes,

rates

EPR

Active stall margin mode

.._an stall line

Uptrlm as a

_S UPunction of

__._ flight control

_..._\ data

' _ Normal op line

Airflow

Fan stall margin Is modulated In

real time as a function of flight

control and engine parameters.

Digital

engine

control

Airflow, EPR

AEPR

835

Figure 3. Engine-flight-control integration mode tested on the NASA HIDEC airplane.

90OO92

6
temperatures. For an HSCT,the maneuverrequirements will be greatly reduced over the F-15

aircraft, and therefore, there will be smaller benefits for an ADECS mode. However, it is thought

that thrust increases of 3 percent may be achieved

in normal flight with constant throttle setting.

INLET-ENGINE-FLIGHT-CONTROL

INTEGRATION - There are significant benefits to

integrating the inlet control system with the flightcontrol and airdata system. As mentioned previously, a gust sensor on the nose could be used

to bias the inlet geometry to a more conservative position. Other flight-control system parameters, such as Mach, angle of attack, and angle

of sideslip, also can be used to advantage by the

inlet control.

Integration with the engine control is also beneficial. The inlet provides flow to the engine at a

given pressure and distortion level. In return, the

engine demands a certain airflow which changes

with throttle setting. Integrating these control systems allows both inlet and engine operating

margins to be reduced, and performance to be

Improved.

Figure 4 is a conceptual block diagram of an

integrated Inlet control mode for an HSCT,

equipped with a mixed compression inlet. The

bypass control mode uses bypass door position

to position the terminal shock wave to maximize

inlet pressure recovery. The unstart boundary,

caused by moving the terminal shock to the throat,

is a function of engine airflow. Without integration, an unstart margin of approximately 5 percent is necessary. This margin is needed either to

accommodate a sudden decrease in engine airflow, an external gust, or a combination of both

before the control system can react to open the

bypass. If airdata and engine data, including airflow information is provided, this margin may be

reduced and higher pressure recovery can be

obtained.

The compression surface or spike position

mode maintains the throat Mach number; efficiency is improved by maintaining throat Mach

number close to 1.0. If throat Mach number gets

Flight

control

parameters m

Airdata

Inlet

Inlet "__

parameters I I Spike I Bypass

Pressures and I I position I position

positions

Compression ramp control

Unstart, f(M,a,_)

drag

Bypass door control

Unstart, f(WA)

Pressure I _

recovery

|

I

Engine

--]WA

I Digital

I engine

I control

9OO548

Figure 4. Conceptual integrated inlet-engine-flight-contrel mode.

7
to 1.0, the inlet will unstart. Therefore, a margin

must be provided which results in the reduction

of the overall thrust minus drag of the inlet. The

throat Mach number is a function of Mach, angle of attack, and angle of sideslip. Integration

can provide these signals. This integration allows

the margin to be reduced and performance to be

increased.

An integrated inlet control mode similar to that

previously discussed, has been implemented on

the F-15 HIDEC airplane (12). The F-15 inlet incorporates a variable capture cowl to minimize

external drag, and also has a variable third ramp

to control compression and throat Mach number,

and a bypass door to modulate throat slot bleed.

In the normal F-15 aircraft, these variables are

positioned by an independent inlet control system. In the HIDEC inlet integration mode, biases

are computed for the variables based on knowledge of engine and airplane conditions. For example, the Inlet third ramp is repositioned to move

the terminal shock closer to the cowl lip, reducing

spillage and increasing pressure recovery. Accurate knowledge of engine airflow from the engine

control system is required to prevent supercritical

operation, and resulting distortion. The cowl has

some pitching moment authority on the F-15 aircraft, and cowl position can be adjusted to miniIncrease

in specific

excess

power,

percent

15 --

10 --

5--

0

1.6 1.7 1.8 1.9

Mach number

90O547

Figure 5. Flight measured results of the F-15

HIDEC integrated inlet control mode.

mize horizontal tail trim drag, inlet drag, and inlet recovery. The HIDEC inlet integration control

mode was flown and demonstrated increases in

excess thrust of as much as 10 percent at a Mach

number of 1.9 (Fig. 5). Such a mode could be

applied to an HSCT, and would be expected to

reduce drag by at least 1 percent.

Mixed Compression Inlet - Control integration

has been studied on the inlet of the YF-12 airplane (1). The inlet control was integrated with

the flight-control system in the cooperative control program. The SR-71 airplane was able to

achieve a range increase in excess of 5 percent

using digital integrated control. The HSCT inlet

will be more carefully optimized, but integration

should still provide 1-to 2-percent better

performance.

PERFORMANCE SEEKING CONTROL

With many variables involved in optimizing the

performance of an HSCT, it will be difficult to develop an a priori optimization scheme. Such

schemes must assume a nominal system model.

An alternate approach is to perform the optimization onboard the airplane, uslng the many

measured parameters that are already available

from the individual control systems (9). Measurements can be used to update models of components such as engines which may vary over time.

Figure 6 is a block diagram of a conceptual PSC

system on an HSCT. Development of such a system begins with nominal models.

NOMINAL MODELS - Models of the nominal

(predicted) propulsion system and trim aerodynamic characteristics are required. The differences between the actual aircraft and the nominal models form the basis for quantifying the differences using an estimator andsubsequently determining the model updates described in the following sections.

PARAMETER ESTIMATION - The adaptive capability of the PSC algorithm is provided by an

8
estimator. The flight measurements used by the

estimator consist of the measured inlet, engine,

and aircraft response parameters. These parameters are compared with the predicted nominal

operation of the propulsion system and aerodynamic trim control characteristics of the aircraft.

The estimator is driven by the difference of these

parameters and provides estimates which represent the difference between the predicted and actual propulsion system and aircraft performance.

MODEL UPDATE - The differences estimated

in the previous paragraph are used along with the

measured variables to update the model of each

engine. Inlets, nozzles, and the airframe probably do not change with time, and thus do not need

to be updated.

INTEGRATED MODEL -The individual models of the inlet, engine, nozzle, flight-control system, and airplane aerodynamics are then integrated so that the optimization process can solve

the overall integrated problem. Unmeasured parameters, such as stall margins and thrust are

calculated in the models. Although the basic models are linear, nonlinear effects can be included

as auxiliary equations.

OPTIMIZATION - Optimization is then carried

out on the combined system, including the engine, inlet, and aerodynamic trim characteristics

for the desired performance parameter, using an

optimization algorithm. Candidate performance

objectives could be maximum thrust, minimum

fuel, maximum engine life, and maximum thrust

at constant temperature. Outputs of the optimization are engine, inlet, nozzle, CG, and aerodynamic flight-control parameters. These parameters are computed as trims to the current control

inputs and as such are summed with the current

control positions.

A preliminary flight evaluation of the PSC concept is currently in the development and validation process on the NASA F-15 HIDEC aircraft.

Inlet, aircraft

end flight control

parameters

Inlet I l

Engines

Inlet Asro

model model

Nominal

models

Engine

parameters

Identification

Real-time

Nozzle Engine Model parameter

modal modal update Identification

logic (Kalman filter)

Figure 6. Conceptual HSCT performance-seeking control block diagram.
The algorithm, similar to that previously described,

Is an onboard real-time adaptive optimization of

engine, inlet, and nozzle parameters. An example of the optimization process at a Mach number of 1.9 at partial afterbuming is shown in Figure 7. The objective is to minimize fuel flow to

provide the required thrust for level flight. Predictions obtained from a full nonlinear PSC simulation show that engine, inlet-horizontal tail, and

nozzle parameters are all changed as a result of

the mode "seeking" the optimum. After approximately 80 passes through the optimization routine, the overall result is a 12-percent reduction in

fuel flow. In this case, as shown in the inset, the

engine net thrust is decreased, the nozzle drag is

increased and the inlet drag is decreased to hold

constant net propulsive force from the propulsion

system. These optimization benefits obviously

would not be available in a system where the optimization was being performed on the engine, inlet, nozzle, and horizontal tail independently.

400

200

AFNP, 0

Ib

-200

Inlet and

horizontal

tall drag,

Ib

700

5O0

300

100

-400

12,800 F

Englnethrust,netlb 112'6402,480 _

12,320

0 20 40 60 80 100

Iteration number

Figure 7.

m

rl

Engine Nozzle

_ kJ Inlet/ tall L__J

-320

Nozzle -400

drag,

Ib

-480

-560

28,000

I

! ! I I I

Total 26,400

fuel

flow,

Ib/hr 24,800

23,200

0 20 40 60 80 100

Iteration number

900549

Predicted performance-seeking control optimization for minimum fuel flow at constant thrust,

F-15 HIDEC airplane, Mach 1.9, 45,000 ft, power level angle = 120.

10
Figure 8 shows the fuel flow decrease at

Mach 1.6 and 2.0 over a range of partial afterburning power settings. Reductions range from

2 to 12 percent. For the HSCT, gains due to PSC

will be smaller, since the HSCT will not have the

maneuver requirements of an F-15, and can be

better optimized. However, it is estimated that a

3-percent reduction in SFC should be obtainable.

15-

Decrease 10

In total

fuel flow,

percent 5

0 I I I

)0 100 110 120

Throttle position, deg

Figure 8. Predicted PSC fuel flow reductions for

partial afterburning power settings, F- 15 airplane.

The PSC algorithm may also be optimized for

maximum thrust. For the F-15 airplane, thrust increases of 10 to 15 percent have been predicted

(1,9). For the HSCT, gains are expected to be

approximately 3 to 5 percent.

For the HSCT, PSC will employ stronger integration with the FCS and aerodynamics. For

example, the individual inlet bleed and bypass

forces and moments may be used to minimize

longitudinal control surface deflections. Individual thrust levels of the propulsion systems may

be adjusted to minimize lateral control deflections.

ENGINE FAILURE AT TAKEOFF ROTATION -

An application for integration is the loss of an engine at takeoff rotation. Current regulations require that the takeoff be completed without throttle motion. The asymmetric thrust caused by uncompensated loss of an outboard engine may size

the vertical tail. An integrated control mode could

reduce the thrust on the opposite outboard engine, increase thrust on the Inboard engines, retract the noise suppressors, and allow the tail size

to be reduced by approximately 25 percent. Of

course, there may then be other sizing constraints on the tail, but if not, this advantage may

be used to reduce the HSCT weight and drag.

RAPID DESCENT MODE -An HSCT may

have a requirement for a rapid descent mode,

due to a sudden loss of cabin pressurization.

Slowing down from the cruise speed and altitude

of 55,000 to 60,000 ft to subsonic speed at an

altitude of 20,000 ft in a short time will be difficult. At supersonic speeds, engine thrust is normally maintained at or above intermediate power

to avoid inlet buzz. (Inlet buzz is a potentially violent pressure oscillation that occurs when the airflow of an inlet operating at supersonic speeds

is reduced too far). An integrated control mode

Is needed for this case in which net propulsive

force needs to be minimized. The propulsion system thrust needs to be reduced to the lowest possible level, yet strong inlet buzz must either be

avoided, or the inlet strengthened to withstand

buzz. This means that the engine airflow will have

to be kept up well above idle values. If the HSCT

has mixed compression inlets, they can be opThe CG may be moved aft farther than normaily erated either unstarted or in a very low perforpractical by having propulsion system m'oments - - mance mode until the inlet starting Mach number

available to augment longitudinal stability quickly, is reached.

if required.

EMERGENCY CONTROL MODES

Integration between the propulsion and flight

control systems is also valuable in emergency

situations.

11
The control mode shown in Figure 9 integrates

the inlet, engine, and nozzle to produce minimum

thrust consistent with engine, inlet, and nozzle

operating limits. The inlet operation reconfigures

the ramps and bypass for minimum pressure recovery and airflow capability, in contrast to the

normal mode where the opposite is true.

The engine airflow is reduced to the inlet buzz

limit, and the nozzle throat area (,48) is opened

as far as possible to reduce thrust. Then, the

secondary nozzle (,49) is positioned to create as

much drag as possible. A high response sensor

at the engine face could be used to reduce airflow until very light buzz is sensed, then maintain

this condition. Integration with the flight-control

system is also required to permit the steepest descent consistent with the propulsion system limits. It is estimated that with this integrated control

mode to prevent buzz, the inlet weight could be

reduced by 2 percent.

HIGH SPEED CIVIL TRANSPORT DESIGN

SYNTHESIS PROGRAM

The aircraft synthesis program (ACSYNT)

(10,11 ) was used to determine the impact of integrated controls technology on the HSCT. This design code takes as inputs the required passenger

volume and range, and basic aerodynamics and

propulsion. It then iteratively computes a design

with the proper structure and fuel volume that will

meet minimum performance requirements for

takeoff and landing distance, transonic acceleration margin, and time to climb. The generic HSCT

design with the configuration from Figure 1 was

developed using 1995 technology turbine bypass

Idle throttle

Airflow

A8

Pressures Spike position

and position.,

Bypass position

Flight

control

parameters

Selected

control

mode

Airflow

Inlet control mode

Airdata

Pressure

recovery

Choke

Buzz

Airflow

A8

As_._t.___

Engine control mode

I __'_St all

Airflow

A9

Nozzle control mode

A,j 

Mach

9OO551

Figure 9. Conceptual integrated engine-inlet--nozzle control mode for minimum thrust.

12
Effect of integrated control technologies on takeoff gross weight.

Result of Technology Percent &TOGW Parameter

Technology Improvement Improvement percent sensitivity

Integrated engine/fit controls

Integrated engine/fit controls

Integr inlet/engine/fit control

Integr inlet/engine/fit control

Performance-seeking control

Engine loss at takeoff rotation

Emerg minimum thrust mode

Integrated control architecture

Reduction of engine weight 3.00

Nozzle weight reduction 1.00

Lower inlet drag, 1.00

% reduction of aircraft drag

Higher inlet recovery 1.00

and maximum thrust

Improvement in cruise SFC 3.00

Vertical tail size reduction 25.00

Inlet weight reduction 2.00

20% FCS weight reduction 20.00

(.5% of empty wt.)

Combined impact 5.07

0.42 0.141

0.09 0.087

0.22 0.216

0.36 0.364

2.44 0.812

1.16 0.046

0.09 0.047

0.55 0.028

engines. It carries 250 passengers 5000 nautical miles at Mach 2.4 with normal fuel reserves.

The ACSYNT computes sensitivities caused by

technology changes. For small changes, these

sensitivity factors are linear, so the effects of different technology impacts than those estimated

here could also be assessed.

IMPACT OF INTEGRATION ON THE HIGH

SPEED CIVIL TRANSPORT TAKEOFF

GROSS WEIGHT

The HSCT will experience significant benefits

from integration and onboard optimization. Based

on some of the reference results, including flight

results of the YF-12 and F-15 HIDEC programs,

estimates of performance improvements and

weight reductions have been made, and are

shown in the above table. For example, current

studies show that the HSCT engines may be sized

for time to climb. The use of an integrated engineflight-control mode should enable the engine to

be uptrimmed at these benign conditions, reducing the required engine weight by 3 percent. The

smaller engine will permit the nozzle to be smaller

also, with a 1-percent reduction in nozzle weight.

Inlet integration could also reduce inlet drag by

1 percent of total drag, and increase inlet recovery by 1 percent. Use of PSC concepts should reduce the cruise SFC by approximately 3 percent.

The inlet weight may be reduced by 2 percent

with the use of the minimum thrust mode. The

control integration architecture studies of reference 6 showed that integration could reduce the

weight of the control system by 20 percent; approximately one-half percent of overall airplane

empty weight.

The impact of each of the technology Improvements was determined by integrating them into

the generic HSCT design, using ACSYNT. Figure 10 shows the reduction in TOGW for each

of the items shown in the table. The table also

shows the sensitivity factor (the change in TOGW

divided by the change in the parameter) of each.

The largest effect is seen to be the result of SFC

improvements; drag reductions are less significant, and weight reductions have the least impact. The overall effect is an approximate

5-percent reduction in TOGW, a significant

reduction.

The sensitivity factors will be useful when more

detailed studies provide better estimates of the

benefits of integration. These factors also allow

prioritization of research, emphasizing fuel savings as the highest priority. In the HSCT actual

13
design, each of the integration concepts will need

to be studied, its benefits determined, and then a

decision made as to whether the concept can buy

its way into the design.

m

5

4

TOGW

reduction, 3

percent

2

1

0

O4

'P" g00552

Figure 10. Effect of integrated control technology

improvements on generic HSCT TOGW.

CONCLUDING REMARKS

A conceptual look at propulsion-flight-control

integration for a high speed civil transport has

been made. Potentially useful control modes

have been discussed, and related to integrated

control modes tested on the NASA YF-12 and

F-15 flight-research programs. The potential benefits have been estimated and used to assess

their impact on the takeoff gross weight for the

high:speed civil transport design mission. A 5-

percent reduction in takeoff gross weight is estimated, and shows the value of integrated controls. The largest benefits result from fuel savings, iess for drag reduction, and least for weight

reduction.

REFERENCES

. Burcham, Jr., Frank W., Glenn B. Gilyard,

and Lawrence P. Myers, "Propulsion SystemFlight Control Integration-Flight Evaluation

and Technology Transition," AIAA Paper 90-

2280, July 1990. See also NASA TM-4207,

1990.

.

,

.

=

.

Gilyard, Glenn B. and John J. Burken, Development and Flight Test Results of an Autothrottle Control System at Mach 3 Cruise, NASA

TP-1621, 1980.

Powers, Bruce G., Phugoid Characteristics of

YF-12 Airplane With Variable-Geometry Inlets

Obtained in Flight Tests at a Mach Number of

2.9, NASA TP-1107, 1977.

Myers, Lawrence P. and Kevin R. Walsh,

Performance Improvements ofan F-15 Airplane

With an Integrated Engine-Flight Control System, NASA TM-100431, 1988.

Smith, Kenneth L., W. Bernie Kerr, Gary L.

Hartman, and Charles Skira, "Aircraft Control Integration-Methodology and Performance Impact," AIAA Paper 85-1424,

July 1985.

Bangert, L.H., K.R. Henke, R.J. Grommes,

and W.B. Kerr, "Integrated Flight/Propulsion

Control System Architectures for a High

Speed Aircraft," AIAA Paper 83-2563,

Oct. 1983.

,

°

Blair, J.D., and C.M. Carlin, "Integrated Control System Concept for High-Speed Aircraft," AIAA Paper 83-2564, Oct. 1983.

Berg, D.F., J.A. Swan, S. Ahdibatlar, P.D. =

Shaw, and E.J. Tich, "Performance Seeking Control; Volume I: Final

AFWAL-TR-88-2067, Oct. 1989.

Report, ''_ _ _

14
9. Smith, R.H., J.D. Chisolm, and J.F. Stewart, "Optimizing Aircraft Performance with

Adaptive, Integrated Flight/Propulsion Control," ASME Paper 90-GT-252, June 1990.

10. Gregory, T.J., "Computerized Preliminary Design at the Early Stages of Vehicle

Definition," Presented at the AGARD 43rd

Flight Mechanics Panel Symposium on Aircraft Design Integration and Optimization,

TMX-62303, Sept. 1973.

11. Wampler, S.G., A. Myklebust, A. Jayaram,

and P. Gelhausen, "Improving Aircraft Conceptual Design - A PHIGS Interactive Interface for ACSYNT," AIAA Paper 88-4481,

Sept. 1988.

12. Chisholm, J. D., S.G. Nobbs, and J.F. Stewart, "Development of the HIDEC Inlet Integration Mode," paper presented at the

ASME Gas Turbine Conference, July 1989.

15
N/L A

6_ Adrm_trsl_

1. Report No.

NASA TM-101728

4. Title and Subtitle

Report Documentation Page

2. Government Accession No. 3. Recipient's Catalog No.

5. Report Date

Integrated Flight-Propulsion Control Concepts for Supersonic

Transport Airplanes

7. Author(s)

Frank W. Burcham, Jr., Glenn B. Gilyard, and Paul A. Gelhausen

9. Performing Organization Name and Address

NASA Ames Research Center

Dryden Flight Research Facility

P.O. Box 273, Edwards, CA 93523-0273

12. Sponsoring Agency Name and Address

National Aeronautics and Space Administration

Washington, DC 20546-0001

November 1990

6. Performing Organization Code

8. Performing Organization Report No,

H-1673

10. Work Unit No.

RTOP 533-02

11. Contract or Grant No.

i 13. Type of Report and Period Covered

Technical Memorandum

14. Sponsoring Agency Code

15. Supplementary Notes

Prepared as conference paper #901928 for presentation at the Society of Automotive Engineers (SAE)

Inc. Aerotech "90' Conference, Long Beach, CA, October 1--4, 1990.

16. Abstract

o.,'

Integration of propulsion and flight-control systems will provide significant performance improvements for supersonic transport airplanes. Increased engine thrust and reduced fuel consumption can be

obtained by controlling engine stall margin as a function of flight and engine operating conditions.

Improved inlet pressure recovery and decreased inlet drag can result from inlet control system integration.

Using propulsion system forces and moments to augment the flight-_ontrol system and airplane stability

can reduce the flight-_ontrol surface and tail size, weight, and drag. Special control modes may also be

desirable for minimizing community noise and for emergency procedures. The overallimpact of integrated

controls on the takeoff gross weight for a generic high speed civil transport is presented.

17. Key Words (Suggested by Author(s))

F-15, HSCT, Integrated control, Performance

seeking control, Integrated control

19. Security Classif. (of this report) 20. Security Classif. (of this page)

Unclassified Unclassified

18. Distribution Statement

Unclassified-Unlimited

Subject category - 08

21. No. of Pages 22. Price

15 A02

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