The SR-71 Blackbird
The joint NASA-Air Force YF-12 research program lasted 10 years (1969-1979) and produced a wealth of data on materials, structures, loads, heating, aerodynamics, and performance for high-speed aircraft.
In something of a departure for Blackbird researchers, NASA and Lockheed engineers investigated space shuttle landing dynamics using the YF-12C. Several flights, conducted in April and June 1973, demonstrated shuttle-type flight characteristics during low lift-to-drag approaches. The descent profile maximized engine negative thrust-inlet drag, and also allowed for the lowest possible lift coefficient.
In 1974, NASA engineers used the YF-12 aircraft to study the landing dynamics of a low-aspect-ratio supersonic aircraft. The data validated the Flexible Aircraft Takeoff and Landing Analysis (FATOLA) computer program developed by NASA Langley, one that offered a six-degree-of-freedom rigid body simulation. Technicians from McDonnell Douglas Astronautics Corporation programmed FATOLA with the YF-12 structural mode data and computed the airplane response to taxi, landing, and takeoff using a measured runway profile. The program coordinated the research efforts of the NASA Langley Structures and Dynamics Division in developing an active landing gear control system for proposed SST aircraft. FRC researchers obtained experimental response data from flight tests to correlate with the response calculated using the FATOLA program. The validated FATOLA program defined the interactive characteristics of active-control landing gear systems with other aircraft characteristics and systems such as engine thrust, ground effect and crosswind aerodynamics, unsymmetrical touchdown conditions, airframe structural elasticity, and anti-skid braking.
A second landing project took place in 1977. This research demonstrated a dual-mode adaptive landing gear system to reduce the dynamic response of an airplane during ground taxi. An adaptive landing gear system can increase the lifespan of an airframe by reducing vibration stress incurred during taxi, takeoff, and landing. Lockheed engineers designed a dual-mode adaptive landing gear system for the YF-12A. The configuration included a strut with an optimized air load-stroke curve during landing, and an automatic switch-over system to allow for a flatter air load-stroke curve during taxi. The study demonstrated the effectiveness of a dual-mode adaptive landing gear system in reducing the dynamic response of an airplane during taxi. It also provided a database to aid in determining the degree of correlation between analytically predicted responses and actual test results with a full-scale YF-12A.
A final YF-12 landing study took place in March 1978. Dryden engineers scheduled three space shuttle orbiter landing approach simulation flights in the YF-12A. Researchers compared data collected from the YF-12 flights with that accumulated by simulated shuttle approaches flown in the F-8 Digital Fly-By-Wire aircraft and the NC-131H Total In-Flight Simulator. These simulations paved the way for the Approach and Landing Test (ALT) program using the space shuttle Enterprise.
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