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Thread: NASA/USAF Active Aerolastic Wing F/A-18A Hornet

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    NASA/USAF Active Aerolastic Wing F/A-18A Hornet

    Active Aeroelastic Wing (AAW)

    The Active Aeroelastic Wing project at NASA's Dryden Flight Research Center was a two-phase flight research program that investigated the potential of aerodynamically twisting flexible wings to improve roll maneuverability of high-performance aircraft at transonic and supersonic speeds. Traditional control surfaces such as ailerons and leading-edge flaps were used as active trim tabs to aerodynamically induce the twist. From flight test and simulation data, the program developed structural modeling techniques and tools to help design lighter, more flexible high aspect-ratio wings for future high-performance aircraft, which could translate to more economical operation or greater payload capability.

    The program used a modified F/A-18A Hornet as its testbed aircraft, with wings that were modified to the flexibility of the original pre-production F-18 wings. Other aircraft modifications included a new actuator to operate the outboard portion of a divided leading edge flap over a greater range and rate, and a research flight control computer system to host the aeroelastic wing control laws.

    AAW flight tests began in November 2002 with checkout and parameter-identification flights. Based on data obtained during 50 research flights over a five-month period, new AAW flight control software was then developed over the following year. A second series of research flights that began in late 2004 evaluated the AAW concept in a real-world flight environment, using the newly created control laws in the aircraft's research flight control computer. Another 36 research missions were flown over a four-month period in the second phase of flight testing that concluded in March 2005. Extensive analysis of data acquired during the project is continuing.

    The Active Aeroelastic Wing Program was jointly funded and managed by the Air Force Research Laboratory and NASA Dryden Flight Research Center, with Boeing's Phantom Works as prime contractor for wing modifications and flight control software development. The F/A-18A aircraft was provided by the Naval Aviation Systems Test Team and modified for its research role by NASA Dryden technicians. Begun in late 1996, the eight-year project was completed within schedule and under its budget of about $45 million, including about $29 million in direct monetary outlay and about $16 million in indirect support.
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    Sheer genius

    Possibly one of the best threads yet!!

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    Back to the Future:</I> Active Aeroelastic Wing Flight Research

    NASA's Dryden Flight Research Center, Edwards, Calif., in cooperation with the U.S. Air Force Research Laboratory (AFRL) and Boeing Phantom Works, researched a high-tech adaptation of the Wright Brothers rudimentary "wing-warping" approach to aircraft flight control in the Active Aeroelastic Wing (AAW) flight research program. The focus of AAW research was on developing and validating the concept of aircraft roll control by twisting a flexible wing on a full-size aircraft. The test aircraft chosen for the AAW research is a modified F/A-18A obtained from the U.S. Navy in 1999.

    Image Right: How differential deflection of the inboard and outboard leading-edge flaps affected the handling qualities of this modified F/A-18A was evaluated during the first check flight in the Active Aeroelastic Wing program at NASA's Dryden Flight Research Center. NASA Photo: EC02-0264-19.

    The aerodynamic forces acting on the F/A-18s traditional aircraft control surfaces, such as ailerons and leading-edge flaps, were used to twist a more-flexible wing to provide aircraft roll maneuvering control.

    Historical Background

    When Orville Wright first took to the air on Dec. 17, 1903, he didn't have ailerons or flaps to control his airplane. Instead, the Wright brothers had chosen to twist or "warp" the wingtips of their craft in order to control its rolling or banking motion. Rather than using one of the craft's two control sticks to make the wingtips twist, they had devised a "saddle" in which the pilot lay. Cables connected the saddle to the tips of both wings. By moving his hips from side-to-side, the pilot warped the wingtips either up or down, providing the necessary control for the Wright Flyer to make turns.

    Current Status

    Begun in 1996, the AAW flight research program was completed in the spring of 2005. After completion of detailed design and wing modifications required for the program in the late 1990s, the test aircraft was extensively instrumented and reassembly was completed by early 2001. Over the course of the year, the AAW test aircraft was subjected to extensive structural loads, wing stiffness and vibration tests, installation of the initial control software into the aircraft’s research flight control computer, systems checkout and flight simulation activity.

    Image Left: Comparison drawing of conventional and active aerolastic wings.

    The first-phase parameter identification flights in the two-phase flight test program began in late 2002 and concluded in April 2003 after 50 research flights. These flights were used to measure the forces available from each surface to twist the wing and control the aircraft. That was followed by a year-long period of data analysis and control software redesign to optimize the performance of the flexible wing. The final phase of flight tests to evaluate the AAW control laws and evaluate the handling and performance qualities available from the flexible wing concept began in late 2004 and concluded in March 2005. About 25 research missions were flown in the second phase, covering 18 test points ranging from speeds of Mach .85 to Mach 1.3 and altitudes ranging from 5,000 to 25,000 feet. Several additional flights were flown to re-evaluate several test points with different gains in the control laws and to evaluate the ability of the system to alleviate structural loads on the wing before AAW flights concluded. Analysis of flight data and preparation of technical reports is expected to continue for some time into the future as staff time is available.
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    Goals and Results

    The AAW program's goal was to demonstrate improved aircraft roll control through aerodynamically induced wing twist on a full-scale high performance aircraft at transonic and supersonic speeds. Data was obtained to develop design information for blending flexible wing structures with control law techniques to obtain the performance of current day aircraft with much lighter wing structures. The flight data included aerodynamic, structural and flight control characteristics that demonstrated and measured the AAW concept in a comparatively low cost, effective manner. The data also will provide benchmark design criteria as guidance for future aircraft designs.

    Image Right: With landing gear and flaps down, NASA Dryden's Active Aeroelastic Wing F/A-18A research aircraft rolls towards final approach to the Edwards Air Force Base Runway at the end of a test flight. NASA Photof: EC03-0039-7.

    Over the course of the second phase of flight tests, roll rates adequate for lateral control, or within 15 to 20 percent of that obtained by a production F/A-18, were obtained by use of active control of wing flexibility alone, without use of the differential rolling horizontal tail used by standard F/A-18s at transonic and supersonic speeds. Roll rates at 15,000 feet were highest at Mach .85 and Mach 1.2, and lowest at Mach .95, similar to a conventional F/A-18.

    Aircraft Modifications

    The wings from NASA's now-retired F-18 #840, formerly used in the High-Alpha Research Vehicle (HARV) program, were modified for the AAW flight research program and installed on the AAW test aircraft. Several of the existing wing skin panels along the wing box section of the wing just ahead of the trailing-edge flaps and ailerons were replaced with thinner, more flexible skin panels and structure, similar to the prototype F-18 wings.

    Image Left: With a long flight data probe extending from its nose, this F/A-18A has been modified to conduct flight research in the Active Aeroelastic Wing (AAW) project at NASA's Dryden Flight Research Cetner, Edwards, California. NASA Photo: EC01-0288-5.

    Original F-18 wing panels were comparatively light and flexible. During early F-18 flight tests, however, the wings were observed to be too flexible at high speeds for the ailerons to provide the specified roll rates. This was because the high aerodynamic forces against a deflected aileron would cause the wing to deflect in the opposite direction.

    In addition, the F/A-18’s leading-edge flap was divided into separate inboard and outboard segments, and additional actuators were added to operate the outboard leading-edge flaps separately from the inboard leading-edge surfaces. By using the outboard leading-edge flap and the aileron to twist the wing, the aerodynamic force on the twisted wing provided the roll forces desired. With AAW control technology, a flexible wing will now have a positive control benefit rather than a negative one.

    In addition to the wing modifications, a new research flight control computer was developed for the AAW test aircraft, and extensive research instrumentation, including more than 350 strain gauges, was installed on each wing.

    Funding

    Image Right: Three-view drawing of AAW.

    The AAW project received its funding from NASA's Aeronautics Research Mission Directorate, as well as from the U.S. Air Force Research Laboratory. The Boeing Company's Phantom Works division in St. Louis, Mo., performed the AAW wing modifications, installed portions of the wing instrumentation and assisted in software development under contract with the Air Force Research Laboratory and NASA. Lockheed-Martin and BAE Systems developed the AAW research flight control computer, while Moog developed the actuators for the outboard leading-edge flaps. The total budget for the entire AAW project was approximately $45 million, including about $29 million in direct monetary outlay and about $16 million for in-kind support, spread over eight years.

    Technology Commercialization

    With the successful demonstration of actively controlled "wing warping" techniques for aircraft roll control at transonic speeds in the Active Aeroelastic Wing project, engineers will now have more freedom in designing more efficient, thinner, higher aspect-ratio wings for future high-performance aircraft while reducing the structural weight of the wings by 10 to 20 per cent. This will allow increased fuel efficiency or payload capability, along with potentially reduced radar signature. The technology also has application to a variety of other future aircraft, such as high-altitude, long-endurance unmanned aircraft, transports, and airliners.
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    FINAL GROUND TESTS PREFACE FIRST ACTIVE AEROELASTIC WING FLIGHTS
    September 9, 2002


    Engineers and technicians at NASA's Dryden Flight Research Center are wrapping up the last major ground tests this month before beginning the first research flights in a project to demonstrate that twisting or warping flexible wings can enhance aircraft performance.

    The ground vibration and structural mode interaction tests on the Active Aeroelastic Wing (AAW) F/A-18A test aircraft began in late August, and should be completed in mid-September, according to Dryden's AAW project manager Denis Bessette. Following final pre-flight checks, control room training of project staff and updating of mission rules and flight plans, the modified jet fighter could fly in mid-October.

    A joint program of the U.S. Air Force Research Laboratory (AFRL), Boeing's Phantom Works and NASA Dryden, Active Aeroelastic Wing is researching the use of lighter-weight flexible wings for improved maneuverability of future high-performance military aircraft. The program intends to demonstrate improved aircraft roll control through aerodynamically induced wing twist on a full-scale manned supersonic aircraft.

    "The project reflects both a return to aviation's beginnings, when the Wright Brothers devised a primitive wing-warping method to control the Wright Flyer, and a gateway to the future--a future where aircraft will sense their environment, morph, and adapt their shape to the existing flight conditions," said Bessette. "These future aircraft will take advantage of years of evolutionary lessons exhibited in bird-like flight."


    AAW research could also enable thinner, higher aspect-ratio wings on future aircraft, which could result in reduced aerodynamic drag, allowing greater range or payload and improved fuel efficiency. Data obtained from flight tests at Dryden will provide benchmark design criteria as guidance for future aircraft designs.

    "Active Aeroelastic Wing technology is important to the Air Force because it represents a new approach to designing wings, and is applicable to a wide variety of future air vehicle concepts that are under study," said Pete Flick, AAW program manager for the AFRL Air Vehicles Directorate. "The AAW design approach removes some constraints that limit conventional wing design, opening up the envelope for future designers." During the current tests, the F-18 rests on three large airbags, while electro-mechanical shakers induce vibrations into the wings at varying amplitudes and frequencies. Test instrumentation measures how the structure reacts as these vibrations propagate through the aircraft to determine potentially adverse effects.

    In the ground vibration tests, the F-18's hydraulics were powered up, but the control surfaces were inactive. The structural mode interaction tests take the process one step further, with the flight controls operating and the interaction of the flight control surfaces with the aircraft structure observed. This test assures that vibrations caused by the actions of the flight controls are damped or suppressed, rather than reinforcing each other to cause large, uncontrolled vibrations or "flutter" that could lead to catastrophic failure of the aircraft structure.

    "The ground vibration and structural mode interaction tests are designed to input vibrations into the aircraft and determine if these vibrations are damped (suppressed) in the expected manner," said Bessette. "The data is used to confirm flutter models and the interaction of the flight control system with the structural elasticity of the aircraft."

    The testbed F/A-18A, provided by the U.S. Navy, has been modified with additional actuators, a split leading edge flap actuation system and thinner wing skins that will allow the outer wing panels to twist up to five degrees. The traditional wing control surfaces—trailing edge ailerons and the leading and trailing edge flaps—are used to provide the aerodynamic force needed to twist or "warp" the wing. Project engineers hope to obtain almost equivalent roll performance of production F/A-18s at transonic and supersonic speeds without using the horizontal stabilators and with smaller control surface deflections. A six-month long structural loads testing program on the F/A-18's modified wings—one of the most extensive tests ever performed in Dryden's Flight Loads Laboratory—was conducted in 2001. As part of those tests, the wings were subjected to loads up to 70 percent of the design limit load of the airplane, with load distribution over the wings a particularly critical item.

    The two-phase AAW flight tests will begin with a series of about 30 to 40 parameter identification flights. Boeing's Phantom Works will use data obtained from the first series of flights to refine wing effectiveness models and design the AAW flight control laws. The second phase of research flights to demonstrate the AAW concept with effective control laws should begin in mid- to late 2003, almost 100 years after the Wright Brothers' first powered flight on December 17, 1903.

    "We've been successful to date, but the real test of this technology is when we start flying, and we see how the flight data correlates to our predictions of aircraft response," Flick added.

    The AAW program receives its funding from the AFRL's Air Vehicles Directorate and NASA's Office of Aerospace Technology. The Boeing Company performed the AAW F/A-18 modifications under contract with the AFRL Air Vehicles Directorate. The eight-year program's total cost is about $41 million, of which about $25 million is in direct costs and about $16 million in in-kind services.
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    Active Aerolastic Wing F/A-18A Hornet #5
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    Active Aerolastic Wing F/A-18A Hornet #6
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    these people should concentrate on some hybrid afterburning scram jets give a super manouvarable plane some super speed.




    so mix that technoligywith one of these bad boys and you got one bitchin plane.

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    This is a really interesting article. This wing warping thing could be very useful in the fututure. The only question I have is how and in what manner do they twist the wing?

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    Russians were flying test aircraft in the 1960s with flexing leading edge and wing profiles for differnet handling characteristics. The B2 had special software controlling the movable surfaces to control the bend on the wing surface. IIRC that was more for stability than for additional agility Northrop are also developing a different wing-warp technique for a new high-soaring aircraft.

    This is definately the way forward. The ultimate "flex" wing for the materials specialists to develop is one that as well as flex for maneouvrability will also be able to expand and give low speed performance for take-off/landing and will thin out for ultra high speed - what the F-14 achieves with the bulky swept wing.
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    Quote Originally Posted by The BIG BAD
    these people should concentrate on some hybrid afterburning scram jets give a super manouvarable plane some super speed.




    so mix that technoligywith one of these bad boys and you got one bitchin plane.
    yeah thats obvious and easy to say but speed, maneuverability, and stealth are all conflicting characteristics
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    Quote Originally Posted by The BIG BAD
    these people should concentrate on some hybrid afterburning scram jets give a super manouvarable plane some super speed.




    so mix that technoligywith one of these bad boys and you got one bitchin plane.
    A clocking ( i have no idea how that is spelled) devicce like Klingon Warships would be even be better.

    Quote Originally Posted by d-quik
    yeah thats obvious and easy to say but speed, maneuverability, and stealth are all conflicting characteristics
    Not to menton that scramjet technology is still far, far away from a realistic airplane.
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    interestingly enough, wing warping was essential to the wright flyer getting off the ground. the warping was controlled by the pilot sliding from side to side, pushing levers in the process, and causing the wings to twist.
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    Psh...I'd still take a nice Bimmer over this...


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    Amazing post Matt!
    Has this just set the precedent for aircraft in the Hide-out? I've got 300+ high-res fighter pics...

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