Article 14384 of rec.aviation.military:
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From: jfb@usgp1.ih.att.com (Joe Baugher)
Subject: New Fighter Series--McDonnell Douglas F-15 Eagle (18 of 26)
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Summary: NF-15B "Agile Eagle" 
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Date: Thu, 23 Feb 1995 02:42:52 GMT
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On October 3, 1984, the Flight Dynamics Laboratory of the Air Force's 
Aeronatical Systems Division awarded a contract to McDonnell Douglas 
for an advanced development Short Take-Off and Landing (STOL) 
Maneuvering Technology Demonstrator (MTD) experimental aircraft.  The 
basic idea behind the program was to develop an aircraft that could 
land and take off from sections of wet, bomb-damaged runway under 
bad-weather conditions and under severe crosswinds and without active 
ground-based navigational assistance.  The first two-seat F-15B 
(serial number 71-0290) was selected for modification as the STOL/MTD 
demonstrator.  The project was given the name *Agile Eagle*.  

For the first phase of the program, the F-15 STOL/MTD aircraft was 
fitted with movable canard aerodynamic surfaces attached to the upper 
edges of the forward air intakes.  It was provided with a four-channel 
fly-by-wire integrated flight/propulsion control (IFPC) system, and an 
improved set of cockpit controls and displays (similar to those 
intended for the F-15E).  In addition, the aircraft was fitted with a 
beefed-up undercarriage capable of handling rough field landings at 
high descent speeds.  The APG-70 radar of the F-15B was provided with 
a high-resolution ground-mapping mode to enable the pilot to locate 
the airfield from a great distance, and a LANTIRN set was fitted to 
the aircraft to project an image of the airfield onto the HUD during 
the final landing approach.  

The integrated flight/propulsion control (IFPC) system was developed 
by McDonnell Douglas and produced by General Electric.  The IFPC 
manages all control parameters for the aircraft.  It uses a new 
computer chip and employs high-level computer languages such as Ada.  
The system is intended to relieve the pilot of some of the more 
routine tasks of handling the aircraft.  There are five modes of 
operation--conventional, short takeoff/approach, short landing, cruise 
and combat.  Position sensors linked to the throttle, control stick 
and rudder pedals feed electrical signals to the IFPC system, and the 
computer converts them into a set of commands to the 
quadruply-redundant fly-by-wire activators to set the controls for the 
maneuvers required.  

The modified 71-0290 flew for the first time on September 7, 1988, 
company test pilot Larry Walker being at the controls The aircraft was 
assigned the designation NF-15B, the N meaning that the modifications 
were sufficiently drastic that the aircraft was not expected to be 
returned to its original configuration.  43 test flights were carried 
out in this configuration.  

In the second phase of the program, the standard circular dilating 
engine nozzles were replaced with rectangular two-dimensional 
thrust-vectoring, thrust-reversing nozzles.  These nozzles were built 
by Pratt & Whitney out of chemically-milled, welded titanium 
honeycomb.  They had flat upper and lower flaps that were 
independently driven and capable of adjusting the exhaust upwards or 
downwards by angles as much as 20 degrees.  There were a set of vanes 
above and below the nozzle that made it possible for the thrust to be 
reversed.  

The first flight with the thrust-vectoring nozzles took place on May 
16, 1989.  The plane was transferred to Edwards AFB for joint flight 
tests by the Air Force and McDonnell Douglas.  The two-dimensional 
nozzles were first tested in flight on March 23, 1990.  Test flights 
demonstrated that the thrust-vectoring features of the new nozzles 
worked as anticipated and validated the changes that had been made to 
the IFPC system software in order to accommodate the new 
thrust-vectoring nozzles.  It turned out that thrust-vectoring 
resulted in a 25 percent reduction in takeoff roll.  The 
thrust-reversing feature made it possible for the F-15 to land on just 
1650 feet of runway.  In addition, it was found possible to use thrust 
reversal during actual flight to produce rapid decelerations, a useful 
feature to have during close-in air-to-air combat.  During its flying 
life, the F-15 STOL/MTD made numerous vectored takeoffs with rotation 
demonstrated at speeds as low as 42 mph.  The shortest landing made by 
the plane took only 1366 feet, with a basic F-15 needing 7500 feet to 
land.  

The program ended on August 15, 1991, having accomplished all of its 
flight objectives.  The vectored thrust nozzles were returned to Pratt 
& Whitney.  

Sources:

   Agile Eagle, World Airpower Journal, Volume 1, Spring 1990.  

   McDonnell Douglas Aircraft Since 1920, Volume II, Rene J.
   Francillon, Naval Institute Press, 1990.

   Combat Aircraft F-15, Michael J. Gething and Paul Crickmore,
   Crescent Books, 1992.
   
   The American Fighter, Enzo Angelucci and Peter Bowers, 
   Orion, 1987.

   The World's Great Interceptor Aircraft, Gallery Books, 1989. 

   F-15 Eagle, Robert F. Dorr, World Airpower Journal, Volume 9,
   Summer 1992.


Joe Baugher			  **************************************
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jfb@uscbu.ih.att.com
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