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Birds Change the Shape of Their Wings in Flight. Now, Aircraft Designers Have Come up with the Mission Adaptive Wing to Give Aircraft Some of the Same Advantages

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Birds Change the Shape of Their Wings in Flight. Now, Aircraft Designers Have Come up with the Mission Adaptive Wing to Give Aircraft Some of the Same Advantages Birds change the shape of their wings in flight. Now, aircraft designers have come up with the Mission Adaptive Wing to give aircraft some of the same advantages. Pilot Report: AFTI F-111 BY MAJ. SCOTT E. PARKS, USAF IRDS are beautiful and efficient Prior to the jet age, optimizing The Mission Adaptive flying machines. I have often wing shape was not a concern be- Wing, a radically new B concept, enables an observed hawks flying high above cause of limitations in aircraft al- aircraft to change the desert at Edwards AFB, Calif., titudes and airspeeds. Later expan- wing shape continu- effortlessly positioning their wings sion of the flight envelope, with the ously and smoothly to the optimum shape dictated by advent of jet-powered supersonic while in flight for greatly improved instinct and learned through experi- fighters and bombers, forced de- agility and perfor- ence. They soar smoothly in the signers to recognize the critical mance. Shown at summer afternoon thermals with need for a variable shape wing. right is the Advanced wings comfortably forward, only to High-performance aircraft need a Fighter Technology dive suddenly for an unsuspecting wing that is efficient at high sub- Integration (AFTI) test craft, a special F-111 target at high speed with wings sonic and supersonic speeds and fitted with the devel- swept back. Landings, on the other that at the same time can minimize opmental wing. hand, require the hawk's wing to be approach speeds for landing. Flaps forward and highly curved, or cam- are one answer to this dilemma. bered, as they turn into the wind to Flaps have been used for many achieve the slowest possible ap- years to allow aircraft to fly at lower proach speed. Precise control is approach speeds on landing. As air- achieved by small changes in the craft materials and control systems position of the feathers located on have been improved, flaps have the wingtips. been automated and their use ex- Aircraft designers, having less tended to flight at high speeds and experience with flight than the Al- elevated load factor. Flaps used for mighty does, have been constrained this purpose are often called maneu- to a fixed-wing shape that is op- vering flaps. A number of current timum for only one flight condition. aircraft, including the F-16 and F/ This means that in other flight con- A-18, employ maneuvering flaps. ditions, the wing is a compromise These give designers some ability that results in reduced range and/or to improve wing performance payload. throughout the flight envelope. 82 AIR FORCE Magazine / July 1988 The Advanced Fighter Technolo- gy Integration (AFTI) F-111 re- search program is designed to flight- test a totally new concept called the Mission Adaptive Wing (MAW). This wing, just like the hawk's, op- timizes its performance by continu- ously and smoothly changing shape in flight. The AFTI F-111 is spon- sored by the Air Force Flight Dy- namics Laboratory (AFFDL) and NASA. I had the opportunity to be one of the first two Air Force test pilots to fly the AFTI F-111 and was active in the program from March 1984 through my departure from Ed- wards AFB in July 1987. We began a two-phase flight-test program eval- uating the MAW concept in 1985. Phase I, completed in November 1986, met its objectives by deter- mining the feasibility of a MAW on high-performance aircraft. The sec- With the Mission Adaptive Wing in the fully cambered position, as in this photo, both the leading and trailing edges move approximately twenty degrees downward. The ond phase, currently in flight test at upper surfaces of both edges are made of high-strength, lightweight composite Edwards AFB, is demonstrating po- material that bends when actuated by internal hydraulic systems. tential uses for this unique wing de- sign. flight profile for every test flight is That first flight also established a The F-111 aircraft we used for flown first on the simulator, which new flying specialty. The project AFTI was flown from 1973 to 1979 allows the pilots to make maximum test pilots who flew in the right seat in a program called Transonic Air- use of available flight time. did not appreciate being referred to craft Technology (TACT). TACT We treated the first flight of the as copilot or navigator. Wishing to tested a unique wing shape called AFTI F-111 as if we were flying a alleviate the problem, Steve Smith the supercritical airfoil that im- new aircraft. Externally, the aircraft of the Air Force Flight Test Cen- proved cruise performance in high looks somewhat like an F-111, but ter—joint manager (with NASA's subsonic flight and verified the per- the unique wing and internal Louis Steers) of flight test—created formance advantage of this type of changes created many unknowns a new specialty, the Mission Adap- wing in cruise flight. An advanced that required a cautious approach. tive Wing Systems Operator, or version of this type airfoil became The flight profile consisted of little MAWSO. MAWSO became the one of the many shapes of the Mis- more than takeoff, systems checks, standard reference for the pilot fly- sion Adaptive Wing. controllability evaluation, and land- ing in the right seat. ing. It had been flown in the simula- The objective of the first flight- Testing a New Aircraft tor many times prior to flight. test phase was to determine the op- Simulation played an important The day before the first flight, a eration and basic aerodynamics of role in the engineering development dress rehearsal was conducted with the Mission Adaptive Wing. This in- of the MAW. Flying simulators is the control room operational and a cluded verification of structural in- definitely not the most popular part high-speed taxi down the runway. tegrity and controllability. We ac- of a program for the pilots, but for Control room operation is similar to complished this by cautiously ex- every hour in flight, we spent many Houston control for spacelaunches panding the flight envelope of the times that in the simulator. and depends on experts in every aircraft in altitude, airspeed, and Prior to first flight, our knowledge facet of the aircraft. One individual load factor, which is measured in G of how the aircraft would fly was is designated NASA 1 and is the forces. Within that envelope, actual very limited, thus requiring many only person allowed to communi- performance data could then be col- hours "in the box" evaluating con- cate with the aircraft. lected. trollability. In addition, the simula- Lt. Col. Frank Birk (USAF) and Results indicate that the potential tor was extremely useful in develop- Rogers Smith (NASA) manned the exists to meet or exceed the perfor- ing emergency procedures. For ex- aircraft on the first flight, while I mance goals established from wind- ample, we found that under certain flew chase in a T-38. Einar En- tunnel data. Comparing TACT and flight conditions, the aircraft would evoldson (NASA) was NASA 1. MAW, the goals include a thirty per- be uncontrollable if there were an The initial takeoff was made toward cent increase in range, a twenty per- uncommanded asymmetry between the dry lake bed at Edwards in case cent increase in sustained turn radi- the left and right wings. This knowl- of an abort. To the satisfaction of all us, and a thirty percent increase in edge changed our operating proce- involved, the flight went flawlessly usable buffet-free lift. dures to avoid this condition. The and inaugurated Phase I of testing. Systems evaluations are also con- 84 AIR FORCE Magazine / July 1988 ducted to verify proper operation of has two functions. First, during ification to the aircraft is the wing the MAW and its interface with the cruise flight, it will act to reduce the itself. It is designed with a com- aircraft. Operation with one hy- aircraft's susceptibility to gusts and pletely smooth upper surface and draulic system or one engine out provide a smoother ride. Secondly, actuation mechanism housed totally was of particular concern, and a sig- during maneuvering flight, this within the wing. The center portion nificant amount of ground testing mode will deflect the wing and hori- of the wing (wing box) is fixed in was required to determine if the zontal stabilizer to make the aircraft shape, with only the leading and wing could operate under these ad- more responsive in pitch. trailing edges capable of deflection. verse conditions. An unplanned test The wing box was also used in the of this was almost conducted on the How the Wing Works TACT program. The leading edge of aircraft's third flight and my first The F-111 used in the research the wing is a single-span surface, flight when the chase plane noted a program is a preproduction A model while the trailing edge consists of massive hydraulic leak from the that was used in the original F-111 three panels capable of independent bottom of the aircraft. Recovery flight-test program and has never motion. was made without any problem, and been brought up to the production Both the leading edge and trailing the leak was found to be unrelated standard. This poses some interest- edge move approximately twenty to the MAW. ing problems for the maintenance degrees in their fully deflected posi- Results of the first phase were team. Replacement parts have tions. The upper surface of the lead- very encouraging. The wing's per- sometimes been difficult to come ing and trailing edges is made of a formance had lived up to expecta- by, and unique "work-around" pro- composite material that actually tions.
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