NASA 

National Aeronautics and 

Facts

Space Administration 

Dryden Flight Research Center 

P.O. Box 273

Edwards, California 93523 

Voice 661-258-3449 

FAX 661-258-3566 

pao@dfrc.nasa.gov FS-2000-02-022 DFRC 

F-15 Flight Research Facility

F-15 HIDEC landing with F/A-18 chase aircraft (NASA photo EC91-677-1) 

Flight research carried out by NASA with a highly modified F-15 aircraft demonstrated and evaluated advanced integrated 

flight and propulsion control system technologies that will help make next-generation aircraft more maneuverable, more fuel 

efficient, and safer to fly. 

The NASA F-15 was the first aircraft to demonstrate a fully integrated inlet-engine-flight control system, a self-repairing flight 

control system, and a propulsion-only flight control system. 

Background 

NASA F-15 835 was a unique one-of-a-kind aircraft called the F-15 Flight Research Facility. It was highly instrumented and 

equipped with an integrated digital electronic flight control system. It could be flown over a broad flight envelope to carry out 

complex and sophisticated research projects. 

It was used, among other things, to develop the Adaptive Engine Control System (ADECS), Self-Repairing Flight Control 

System (SRFCS), Performance Seeking Control (PSC), and Propulsion Controlled Aircraft (PCA) system. 

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NASA obtained the F-15, an “A” model, from the U.S. Air 

Force on Jan. 5, 1976, and used it for more than 25 advanced 

research projects involving aerodynamics, performance, 

propulsion control, control integration, instrumentation 

development, human factors, and flight test techniques. 

Among these projects was one in which it served as a testbed 

to evaluate aerodynamic pressures on Space Shuttle thermal 

protection tiles at specific altitudes and speeds. 

HIDEC 

The system that was developed on the F-15 to investigate and 

demonstrate methods of obtaining optimum aircraft performance was called HIDEC — Highly Integrated Digital 

Electronic Control. 

The major elements of HIDEC were a Digital Electronic 

Flight Control System (DEFCS), a Digital Electronic Engine 

Control (DEEC), an on-board, general purpose computer, and 

an integrated architecture to allow all components to “talk to 

each other.” 

Unlike standard F-15’s, which have a mechanical and an 

analog electronic flight control system, the F-15 HIDEC also 

had a dual-channel, fail-safe digital flight control system that 

could be programmed in such high-order computer languages 

as Pascal, Ada, and FORTRAN. It was linked to the H009 and 

Military Standard 1553B data buses, which tied all other 

electronic systems together. 

ADECS 

ADECS — Adaptive Engine Control System — traded excess 

engine stall margin for improved performance. This was 

achieved through the integrated and computerized flight and 

engine control systems. The engine stall margin — the 

amount that engine operating pressures must be reduced to 

provide a margin of safety against an engine stall from 

excessive pressure — was continually monitored and adjusted 

by the integrated system, based on the flight profile and realtime performance needs. 

Using this information, ADECS freed up engine performance 

that would otherwise be held in reserve to meet the stall 

margin requirement. Improved engine performance obtained 

through ADECS could take the form of increased thrust, 

reduced fuel usage, or lower engine operating temperatures 

because peak thrust was not always needed. 

NASA researchers in gold control room during an F-15 HIDEC Flight (NASA photo EC93-42219-FR2 

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Initial ADECS engineering work began in 1983. Research and 

demonstration flights with the ADECS system, which began 

in 1986, displayed increases in engine thrust of from 8 to 10.5 

percent (depending on altitude), and up to 16 percent lower 

fuel consumption at 30,000 feet and constant thrust. 

The increased engine thrust observed with ADECS improved 

the aircraft’s rate of climb 14 percent at 40,000 feet, and its 

time to climb from 10,000 feet to 40,000 feet was reduced 13 

percent at an airspeed of 350 knots (15 percent at 250 knots). 

Increases of 5 to 24 percent in acceleration were also experienced at intermediate and maximum power settings, depending upon altitude. Overall, engine performance improvements (rate of climb and specific excess power) were in the 

range of 10 to 25 percent at maximum afterburning power. 

No stalls were encountered during even aggressive maneuvering, although intentional stalls were induced to validate 

ADECS methodology. 

Self-Repairing and Self-Diagnostic Flight 

Control System 

During late 1989 and early 1990 the F-15 research aircraft 

investigated what could become a major breakthrough in 

airborne flight control capability. It was the first aircraft to 

demonstrate a Self-Repairing Flight Control System (SRFCS). 

The program, sponsored by the U.S. Air Force, demonstrated 

the ability of a flight control system to identify the failure of a 

control surface and reconfigure commands to other control 

devices such as ailerons, rudders, elevators, and flaps to 

continue the aircraft’s mission or allow it to be landed safely. 

As an example, if an aileron on an aircraft was damaged or 

failed in flight, the SRFCS immediately diagnosed the failure 

and determined how the remaining flight control surfaces 

could be repositioned to compensate for the damaged or 

inoperable control surface. 

A display in the cockpit also informed the pilot of the control 

surface reconfiguration, and information displayed by the 

SRFCS showed the pilot what operational limitations he or 

she had to observe as a result of the damaged or failed component. These limitations reduced “G” loading (acceleration 

expressed in relation to the force of gravity), reduced angleof-attack maneuvering, or reduced air speed and altitude 

margins. 

The SRFCS also had the capability of identifying failures in 

electrical, hydraulic, and mechanical systems. When a failure 

in a normal flight control system occurred, ground maintenance diagnostic tests had to be conducted to identify the 

origin of the failure so that appropriate corrective actions 

could be taken. Ground maintenance crews often spend up to 

60 percent of their time attempting to duplicate flight failures 

and correcting them. In many cases, the failure cannot be 

identified on the ground because actual flight conditions 

cannot be duplicated. This can be costly and time-consuming. 

System malfunctions on an aircraft with a SRFCS can be 

identified and isolated at the time they occur and then repaired 

as soon as the aircraft is on the ground. 

Among the participants in the SRFCS research program, 

along with NASA Dryden, were the Air Force Wright Research and Development Center, Wright-Patterson AFB, OH; 

McDonnell Aircraft Co., St. Louis, MO; and General Electric 

Aircraft Control Systems Division, Binghamton, NY. 

While the SRFCS was limited to failures of control surfaces, 

researchers at Dryden also wanted to identify failures involving the basic stability of the aircraft. They subsequently began 

looking into neural networks in conjunction with researchers 

from NASA’s Ames Research Center. In 1999 they began 

flight research with neural networks on another F-15, which 

had been specifically designed with computers that could 

handle such identification schemes. Known as the ACTIVE 

(Advanced Control Technology for Integrated Vehicles), this 

F-15 served as a testbed to identify failures in the basic 

stability of the aircraft and eventually correct for them. 

Performance Seeking Control 

Research flights with the F-15 HIDEC began in the summer 

of 1990 on a program to optimize total aircraft engine performance during steady-state engine operation. The project was 

called Performance Seeking Control (PSC). 

Previous modes used on the HIDEC aircraft employed stored 

schedules of optimum engine pressure ratios for an average 

engine on a normal day. Using digital flight control, inlet 

control, and engine control systems, PSC employed integrated 

control laws to assure that peak engine and maneuvering 

performance was available to the pilot at all times, regardless 

of the mission or immediate needs. 

PSC used highly advanced techniques to identify the condition of the engine components and optimize the overall system 

for best efficiency on the actual engine and flight conditions 

the pilot was encountering on a given day. 

Among the functions of PSC were reduction of fuel usage at 

cruise conditions; maximization of excess thrust during 

accelerations and climbs; and extending of engine life by 

reducing the fan turbine inlet temperature. 

PSC also included developing methods within the digital 

engine control system to detect degradation of components. 

This type of information, coupled with normal preventative 

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the small control forces and moments of engine thrust,

difficulty in controlling the airplane’s shallow dive and climb

motion, and difficulty in compensating for the lag in engine

response.

Three-view of the F-15 Flight Research Facility

maintenance, could help assure fail-safe propulsion systems in 

high performance aircraft of the future. 

The PSC system is applicable to a wide variety of aircraft. 

For example, the engine manufacturer has used the self-tuning 

onboard engine model in its advanced engine controllers, 

including those on the F119 engine used on the F-22 aircraft. 

Other aspects of HIDEC technology have found application in 

the F100-PW-229 and other advanced engines, with the flight 

demonstration and evaluation done at NASA Dryden contributing to the rapid transition of the technology into operational 

use. 

Propulsion Controlled Aircraft System 

Several accidents in which part or all of an aircraft’s flight 

control system was lost prompted Dryden to establish a 

research program to investigate the capability of a “propulsion 

controlled aircraft” (PCA), using only engine thrust for flight 

control. 

The NASA F-15 was modified to serve as the first-ever 

aircraft to intentionally demonstrate this PCA capability. 

Initial flight studies with the pilot manually controlling the 

throttles and all F-15 flight controls locked showed that it was 

possible to maintain gross control. Altitude could be maintained within a few hundred feet using both throttles together. 

To climb, thrust would be added; to descend, thrust would be 

reduced. Heading could be controlled to within a few degrees, 

using differential throttle to generate yaw, which resulted in 

roll. 

These initial flights also showed there was not enough precise 

flight control capability to land on a runway. This was due to 

Simulation studies at Dryden and at McDonnell Douglas 

duplicated the flight results. Control research and simulation 

studies also established the feasibility of using feedback of 

parameters such as flightpath angle, pitch rate, bank angle, roll 

rate, and yaw rate to augment the throttle control capability 

and to stabilize the aircraft. 

The NASA F-15 was an ideal testbed for this research. It 

incorporated digital engine controls and digital flight controls, 

and it had a general purpose computer and data bus architecture to permit these digital systems to communicate with each 

other. There was also a cockpit computer panel for the pilot to 

make control system inputs so as to select options and vary 

system gains. 

The only equipment added to the aircraft was a control panel 

containing two thumbwheels, one for the pilot’s flight path 

command, and the other for bank angle command. All of the 

needed sensors and actuators were available from previous 

integrated flight/propulsion control research. Control computations were performed in the research computer. All control 

parameters were recorded on the data system and telemetered 

to the ground. 

Tests of the PCA with the F-15 occurred at speeds of 150 

knots with the flaps down and at 170 to 190 knots with the 

flaps up. Initial flights tested the “up and away” control 

capability, with landing approaches down to less than 10 feet 

above the ground. 

Flight tests of PCA by Dryden with the F-15 concluded with a 

successful landing on April 21, 1993, using only engine power 

to turn, climb, and descend. A successful follow-on program 

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with an MD-11 transport aircraft conclusively demonstrated 

the success of the technology in 1995. Dryden worked 

together with NASA’s Ames Research Center on simulations 

for PCA and later versions of the technology called PCA Lite 

and PCA Ultralite that expanded the number of airplanes that 

could use the technology and also made it less expensive to 

install. 

Specifications 

McDonnell Aircraft Co., McDonnell Douglas Corporation, St. 

Louis, MO (now part of Boeing), designed the F-15 as a 

single-seat, twin-engine air superiority fighter. The first flight 

of the F-15 was in 1972. 

Two Pratt and Whitney F100-PW-100 or -220 engines 

normally power the F-15, depending on the aircraft model. 

The NASA F-15 was equipped with advanced versions of the 

F100, the F100 EMD (engine model derivative). The aircraft 

was capable of flying more than twice the speed of sound. 

The F-15 is 63.75 feet long and has a wingspan of 42.83 feet. 

The NASA F-15 was extensively modified for research 

activities and did not carry any armament. 

Sources: 

Frank W. Burcham, Jr., Ronald J. Ray, Timothy R. Conners, 

and Kevin R. Walsh, Propulsion Flight Research at NASA 

Dryden from 1967 to 1997 (Edwards, CA: NASA TP-1998-

206554, 1998). 

James F. Stewart, Integrated Flight Propulsion Control 

Research Results Using the NASA F-15 HIDEC Flight 

Research Facility (Edwards, CA: NASA TM 4394, 1992). 

Telephonic Interview with Dr. James F. Stewart, May 11, 

1999 

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