Exploring the Extreme Educator Guide pdf - ER - NASA

maneuverable aircraft to lose control.Additionally, failures of the hydraulic system,such as ruptured fluid supply lines oroverheated pumps, plagued these designs.Fly-By-Wire Flight ControlsIn the 1960s, designers turned to electronicsand computer technologies to overcome manyof the problems associated with hydraulicallypowered flight controls. Hydraulic actuatorswere still necessary, but fly-by-wire meant thatthe pilot’s control stick movements were nowtransmitted electronically to the actuators.Also, a computer allowing much-improvedflight path control precision could control theairplane’s response. NASA research was thedriving force for the successful development offly-by-wire aircraft.The NASA Digital Fly-By-Wire (DFBW forshort) research aircraft, a modified U.S. NavyF-8 Crusader, was one of the most significantresearch programs in NASA history. On May25, 1972, NASA 802 became the first aircraftto fly completely dependent upon an electronicflight control system (no mechanical backup).It used a computer from the Apollo spacecraftto operate the flight controls. The DFBW F-8validated the concepts of the fly-by-wire flightcontrol systems now used on nearly all modernhigh-performance aircraft, military and civiliantransports, and the Space Shuttle flight controlsystem. 1 The F-15 ACTIVE research aircraft isequipped with a digital fly-by-wire flightcontrol system.Digital flight-control systems were able toincorporate “multi-mode” flight control lawswith different modes, each optimized toenhance maneuverability and controllabilityfor a particular phase of flight. Earliermechanical or electronic flight control systemscould be optimized for only one particular setof flight conditions, such as supersonic flight,weapons carriage, or perhaps takeoff andlanding. But the DFBW designs could “flip aswitch,” giving a separate set of softwarecontrol laws for each flight phase the aircraftwould encounter. Thus, a design might have atakeoff and landing mode with its set of controllaws, a cruise mode with a different set ofcontrol laws, a weapons delivery mode,supersonic mode, and so on. Development ofthrust vectoring control laws is part of the F-15ACTIVE research.Thrust Vectoring and Fly-By-WireCombinedThrust vectoring produces greater agility andmaneuverability, especially at slow airspeedsand at a high angle-of-attack (relationshipbetween the aircraft’s wings and actual flightpath). Whereas aerodynamic control surfaceslose their ability to produce pitch, roll, or yawat slow airspeeds, thrust vectoring still remainsquite effective. This is because the pressure ofengine thrust against the nozzles staysrelatively constant while the air pressure oncontrol surfaces goes down exponentially asairspeed decreases. In fact, aerodynamicsurfaces can lose effectiveness altogether if theangle-of-attack gets too high (called a stall).Fly-by-wire computers do the job of properlyblending the amount of control surfacedeflection and thrust vectoring needed. Thisallows the pilot to simply move the stick in thedesired direction, so that flying a thrustvectored airplane is no more difficult, ordifferent, than flying a conventional airplane.Other design benefits include less drag fromelevator/stabilator deflections for balance(trim drag); that is, the use of thrust vectoringinstead of control surface deflection forbalance requirements. This in turn results inbetter fuel efficiency (due to less trim drag)and reduced operating costs. Thrust vectoringmakes possible new, more aerodynamicallyefficient configurations, such as tailless aircraft6High Performance Learning Activities in Mathematics, Science and TechnologyEG-2003-01-001-DFRC