X-29 forward-swept wings

(Text, photo, and sketches: NASA courtesy)

Two X-29 aircraft, featuring one of the most unusual designs in aviation history, were flown at the NASA Ames-Dryden Flight Research Facility (now the Dryden Flight Research Center), Edwards, Calif., as technology demonstrators to investigate advanced concepts and technologies. The multi-phased program was conducted from 1984 to 1992 and provided an engineering data base that is available in the design and development of future aircraft. X-29 in flight view from above

The X-29 almost looked like it was flying backward. Its forward swept wings were mounted well back on the fuselage, while its canards – horizontal stabilizers to control pitch – were in front of the wings instead of on the tail. The complex geometries of the wings and canards combined to provide exceptional maneuverability, supersonic performance, and a light structure. Air moving over the forward-swept wings tended to flow inward toward the root of the wing instead of outward toward the wing tip as occurs on an aft swept wing. This reverse air flow did not allow the wing tips and their ailerons to stall (lose lift) at high angles of attack (direction of the fuselage relative to the air flow).

The concepts and technologies the fighter-size X-29 explored were the use of advanced composites in aircraft construction; variable camber wing surfaces; the unique forward-swept wing and its thin supercritical airfoil; strake flaps; close-coupled canards; and a computerized fly-by-wire flight control system to maintain control of the otherwise unstable aircraft.

X-29 fighter aircraft reverse airflow sketch

Research results showed that the configuration of forward swept wings, coupled with movable canards, gave pilots excellent control response at up to 45 degrees angle of attack. During its flight history, the X-29s were flown on 422 research missions – 242 by aircraft No. 1 in the Phase 1 portion of the program; 120 flights by aircraft No. 2 in Phase 2; and 60 flights in a follow-on « vortex control » phase. An additional 12 non-research flights with X-29 No. 1 and 2 non-research flights with X-29 No. 2 raised the total number of flights with the two aircraft to 436.

Program History

Before World War II, there were some gliders with forward-swept wings, and the NACA Langley Memorial Aeronautical Laboratory, Hampton, Va., did some wind-tunnel work on the concept in 1931. Germany developed a motor-driven aircraft with forward-swept wings during the war known as the Ju-287. The concept, however, was not successful because the technology and materials did not exist then to construct the wing rigid enough to overcome bending and twisting forces without making the aircraft too heavy.

The introduction of composite materials in the 1970s opened a new field of aircraft construction, making it possible to design rugged airframes and structures stronger than those made of conventional materials, yet lightweight and able to withstand tremendous aerodynamic forces.

graphic showing X-29 Demonstrator Technologies

Construction of the X-29’s thin supercritical wing was made possible because of its composite construction. State-of-the-art composites permit aeroelastic tailoring, which allows the wing some bending but limits twisting and eliminates structural divergence within the flight envelope (i.e., deformation of the wing or breaking off in flight).

In 1977, the Defense Advanced Research Projects Agency (DARPA) and the Air Force Flight Dynamics Laboratory (now the Wright Laboratory), Wright-Patterson Air Force Base, Ohio, issued proposals for a research aircraft designed to explore the forward swept wing concept. The aircraft was also intended to validate studies that said it should provide better control and lift qualities in extreme maneuvers, and possibly reduce aerodynamic drag as well as fly more efficiently at cruise speeds.

From several proposals, Grumman Aircraft Corporation was chosen in December 1981 to receive an $87 million contract to build two X-29 aircraft. They were to become the first new X-series aircraft in more than a decade. First flight of the No. 1 X-29 was Dec. 14, 1984, while the No. 2 aircraft first flew on May 23, 1989. Both first flights were from the NASA Ames-Dryden Flight Research Facility, later renamed the Dryden Flight Research Center.

Flight-Control System

graphic comparing conventional aircraft to X-29

The flight control surfaces on the X-29 were the forward-mounted canards, which shared the lifting load with the wings and provided primary pitch control; the wing flaperons (combination flaps and ailerons), used to change wing camber and function as ailerons for roll control when used asymmetrically; and the strake flaps on each side of the rudder that augmented the canards with pitch control. The control surfaces were linked electronically to a triple-redundant digital fly-by-wire flight control system (with analog back up) that provided an artificial stability.

The particular forward swept wing, close-coupled canard design used on the X-29 was unstable. The X-29’s flight control system compensated for this instability by sensing flight conditions such as attitude and speed, and through computer processing, continually adjusted the control surfaces with up to 40 commands each second. This arrangement was made to reduce drag. Conventionally configured aircraft achieved stability by balancing lift loads on the wing with opposing downward loads on the tail at the cost of drag. The X-29 avoided this drag penalty through its relaxed static stability.

Each of the three digital flight control computers had an analog backup. If one of the digital computers failed, the remaining two took over. If two of the digital computers failed, the flight control system switched to the analog mode. If one of the analog computers failed, the two remaining analog computers took over. The risk of total systems failure was equivalent in the X-29 to the risk of mechanical failure in a conventional system.

Phase 1 Flights

The No. 1 aircraft demonstrated in 242 research flights that, because the air moving over the forward-swept wing flowed inward, rather than outward as it does on a rearward-swept wing, the wing tips remained unstalled at the moderate angles of attack flown by X-29 No. 1. Phase 1 flights also demonstrated that the aeroelastic tailored wing did, in fact, prevent structural divergence of the wing within the flight envelope, and that the control laws and control surface effectiveness were adequate to provide artificial stability for this otherwise extremely unstable aircraft and provided good handling qualities for the pilots.

The aircraft’s supercritical airfoil also enhanced maneuvering and cruise capabilities in the transonic regime. Developed by NASA and originally tested on an F-8 at Dryden in the 1970s, supercritical airfoils – flatter on the upper wing surface than conventional airfoils – delayed and softened the onset of shock waves on the upper wing surface, reducing drag. The phase 1 flights also demonstrated that the aircraft could fly safely and reliably, even in tight turns.

Phase 2 Flights

The No. 2 X-29 investigated the aircraft’s high angle of attack characteristics and the military utility of its forward-swept wing/canard configuration during 120 research flights. In Phase 2, flying at up to 67 degrees angle of attack (also called high alpha), the aircraft demonstrated much better control and maneuvering qualities than computational methods and simulation models had predicted. The No. 1 X-29 was limited to 21 degrees angle of attack maneuvering.

During Phase 2 flights, NASA, Air Force, and Grumman project pilots reported the X-29 aircraft had excellent control response to 45 degrees angle of attack and still had limited controllability at 67 degrees angle of attack. This controllability at high angles of attack can be attributed to the aircraft’s unique forward-swept wing- canard design. The NASA/Air Force-designed high-gain flight control laws also contributed to the good flying qualities.

Flight control law concepts used in the program were developed from radio-controlled flight tests of a 22-percent X-29 drop model at NASA’s Langley Research Center, Hampton, Va. The detail design was performed by engineers at Dryden and the Air Force Flight Test Center at Edwards Air Force Base. The X-29 achieved its high alpha controllability without leading edge flaps on the wings for additional lift, and without moveable vanes on the engine’s exhaust nozzle to change or « vector » the direction of thrust, such as those used on the X-31 and the F-18 High Angle-of-Attack Research Vehicle. Researchers documented the aerodynamic characteristics of the aircraft at high angles of attack during this phase using a combination of pressure measurements and flow visualization. Flight test data from the high-angle-of-attack/military-utility phase of the X-29 program satisfied the primary objective of the X-29 program – to evaluate the ability of X-29 technologies to improve future fighter aircraft mission performance.

Graphic showing X-29 vortex

Vortex Flow Control

In 1992 the U.S. Air Force initiated a program to study the use of vortex flow control as a means of providing increased aircraft control at high angles of attack when the normal flight control systems are ineffective.

The No. 2 X-29 was modified with the installation of two high-pressure nitrogen tanks and control valves with two small nozzle jets located on the forward upper portion of the nose. The purpose of the modifications was to inject air into the vortices that flow off the nose of the aircraft at high angles of attack.

Wind tunnel tests at the Air Force’s Wright Laboratory and at the Grumman Corporation showed that injection of air into the vortices would change the direction of vortex flow and create corresponding forces on the nose of the aircraft to change or control the nose heading.

From May to August 1992, 60 flights successfully demonstrated vortex flow control (VFC). VFC was more effective than expected in generating yaw (left-to-right) forces, especially at higher angles of attack where the rudder loses effectiveness. VFC was less successful in providing control when sideslip (relative wind pushing on the side of the aircraft) was present, and it did little to decrease rocking oscillation of the aircraft.

Summary

Overall, VFC, like the forward-swept wings, showed promise for the future of aircraft design. The X-29 did not demonstrate the overall reduction in aerodynamic drag that earlier studies had suggested, but this discovery should not be interpreted to mean that a more optimized

Three-view graphic of X-29

design with forward-swept wings could not yield a reduction in drag. Overall, the X-29 program demonstrated several new technologies as well as new uses of proven technologies. These included: aeroelastic tailoring to control structural divergence; use of a relatively large, close-coupled canard for longitudinal control; control of an aircraft with extreme instability while still providing good handling qualities; use of three-surface longitudinal control; use of a double-hinged trailing-edge flaperon at supersonic speeds; control effectiveness at high angle of attack; vortex control; and military utility of the overall design.

The Aircraft

The X-29 is a single-engine aircraft 48.1 feet long. Its forward-swept wing has a span of 27.2 feet. Each X-29 was powered by a General Electric F404-GE-400 engine producing 16,000 pounds of thrust. Empty weight was 13,600 pounds, while takeoff weight was 17,600 pounds.

The aircraft had a maximum operating altitude of 50,000 feet, a maximum speed of Mach 1.6, and a flight endurance time of approximately one hour. The only significant difference between the two aircraft was an emergency spin chute deployment system mounted at the base of the rudder on aircraft No. 2. External wing structure is primarily composite materials incorporated into precise patterns to develop strength and avoid structural divergence. The wing substructure and the basic airframe itself is aluminum and titanium. Wing trailing edge actuators controlling camber are mounted externally in streamlined fairings because of the thinness of the supercritical airfoil.

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Charles « Chuck » YEAGER – 65 years ago !

THE RIGHT STUFF  / L’ETOFFE des HEROS

Supersonic aircraft X-1 in flight
Photo: NASA

Captain Charles « Chuck » YEAGER broke the sound barrier with the help of his friend Jack RIDLEY on a 14th of October 1947 – He did it 61 years ago!

Brigadier General Charles Chuck Yeager next to his X-1 aircraft

(U. S. Air Force illustration/Mike Carabajal)

Supersonic aircraft X-1
Photo: NASA

Supersonic aircraft X-1 pre-flight inspection

Photo: U.S.Air Force Link

XLR-11 ROCKET POWERED AIRCRAFT

Birth of Manned Rocket Research Airplanes: 1946 to 1975

The first reliable, effective rocket engine that would provide boost for experimental research aircraft was produced by four members of the American Rocket Society (ARS) who combined forces to form Reaction Motors Incorporated (RMI) (Rockaway, New Jersey) for developing the Experimental Liquid Rocket (XLR-11) rocket motor. The XLR-11 engine had four separate rocket chambers. Each chamber provided 1500 lb of rated thrust and could be operated independently as a means of throttling thrust in quarters, up to 6000 pounds. The XLR-11 possessed remarkable longevity, powering an impressive fleet of rocket aircraft for more than a quarter of a century (1946 to 1975). This fleet of vehicles were the first rocket aircraft devoted solely to high performance experimental flight research. They were not constrained by military or commercial demands and ranged from being the first to break the sound barrier (XS-1), to the first to reach Mach 2.0 (D-558-II [fig. 5]), to the first to exceed the X-2 Mach 3.2 record (X-15 with two XLR-11 engines).

D-558-II airplane on Rogers lakebed

Figure 5. The D-558-II airplane on Rogers lakebed.

The X-1E – Early Development of Energy Management

Design efforts to extend aircraft performance produced increased wing loadings, W/S, and decreased lift-to-drag ratios, L/D. These design changes were beneficial in reducing drag to achieve supersonic and hypersonic speeds, but were also detrimental in that they reduced the area of the maneuvering footprint and presented difficulties in the approach and landing.

As L/D values decreased, the glide slope angle and the rate of descent increased, making it more difficult for pilots to estimate distances and times required for acceptable landings. The X-1E (fig. 6) was modified with a low-aspect-ratio wing having a thickness-to-chord ratio of four percent – the only aircraft of the X-1/D-558 series to have sufficiently low L/D values to require unique energy management techniques. This X-1E was the first to experiment with approach patterns designed to give
the pilot more time in the traffic pattern to manage energy.

The landing pattern was approached in a conventional manner except that altitudes and speeds were somewhat higher than for
powered aircraft. The initial reference point was established at 12,000 ft (mean sea level) on a downwind heading (180 deg remaining to turn). The downwind leg was offset some four miles from the centerline of the landing runway. On downwind, abeam the touchdown point, landing gear and partial flaps were deployed at a speed of 240 knots. Full flaps were usually deployed on the final approach. At the initial reference point the pilot had almost three minutes until touchdown – additional time for handling increased speeds and sink rates.7,8

X-1 supersonic aircraft on Lakebed

Figure 6. The X-1E airplane on Rogers lakebed.

X-1E supersonic aircraft under B-29 Mothership

Secret declassified USAF pilot Charles Chuck Yeager after breaking the sound barrier on X-1

Report from www.archives.gov

X-1 supersonic aircraft instrument panel

(Text from the NASA at: http://www.nasa.gov/centers/dryden/home/index.html)

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YVES Fusionman ROSSY, the FIRST Aviation History PIONEER of the 21st CENTURY

Yves Fusion Man Rossy smiling portrait

A few days after he succeeded in crossing the Channel, I thought it was time to show who and what gave Yves Rossy the incentive to perform such breathtaking feats. Let’s have a look at this hero’s career.

When he was a child, he said « When I am older, I will be pilots » – with an S ! This became his motto from the day he got unable to go down from a tree by himself. The child has now become « Fusionman ». In order to understand what motivated this pilot, watch and listen to Yves Rossy’s comments (in French) on the video below:

As he explained, Yves Rossy has always admired the first pioneers. Every attempt used to end by death or breakthrough. Yves Rossy has now become « Fusionman », the first man flushed in a jet-engine-propelled wing, flying as if he were Icarus.

Yves Rossy was born on the 27th of August 1959 in Neufchatel – Switzerland. Both gazing skywards, and having his feet firmly planted on the ground, he was taught technical education and passed a mechanics baccalauréat. Natural-born sportsman, he has practised everything that glides, slides, or flies – surfing, waterskiing, wakeboarding, skysurfing, parachuting, aerobatics, motorcycling, rafting, hang-gliding, etc. Flying with a jet-powered wing is the crowning of a 30-year career and numerous stunts, feats, and premieres.

FIGHTER PILOT

Certainly one of the most intense periods in his career. Yves Rossy flew the supersonic Mirage III for 15 years. During this period, he flew some historical aircraft such as the Hunter or the Venom, one of the first English jet-engine fighters. He got the idea of going round Switzerland throughout several activities within a day. He carried out this feat on the 3rd of July 1991. During his trip, he flew a DC-9, went motorcycling, skiing, snowboarding, mountaineering, paragliding, mountain-biking, bungee-jumping, he flew a helicopter, went skydiving, rafting, hydrospeeding, canoeing, drove a sportscar, went hang-gliding, horse-riding, barefooting, waterskiing, wakeboarding, and finally speedboating – that’s enough… 25 vehicles were used this day along 1,000 km for 15 hours and a half! Yves Rossy is a Swiss Air Force retiree, and keeps flying the two-seater Hunter belonging to the association Amici del Hunter. He works as a captain at Swiss Airlines, and his spare-time is dedicated to his passion. He has been supported since February 2007 by Jean-Claude BIVER, HUBLOT watches’ CEO.

HE FANCIES DOING WHAT NEVER HAPPENED BEFORE

Yves Rossy is used to venturing off the beaten tracks. He devotes all his hobbies to flight in all its forms. He multiplies the tests on contrivances that change with the passing experiments. An inflatable wing made him get over the 12-kilometer distance between the two shores of Lake Geneva. Many stunts were reported such as hang-gliding over the huge Geneva spray to surf on top of it, then land on the lake to grab a waterskiing handle, and get to the shore without getting wet! Another feat – he skydived on a disk over the Matterhorn. As Yves Rossy whished to get beyond his feats and dreams, he wanted to fly with as little instrumentation as possible – like a bird with the ability to move and steer into space, he got the idea of adding scale model jet engines under a wing.

JET-POWERED WING

The first attempt occurred in March, 2003. The German Jet-Cat company supplied the engines which were added under an inflatable wing, but this trial was a failure for lacking of rigidity. He developed a rigid spreadable carbon wing built-up at ACT Composites’ in 2004. It made an indifferent start. He spun and had to drop his wing at Al-Ain airshow. The wing parachute tore, and the device was damaged. From that time, the pilot worked hard to improve the spreading of the wing and aerodynamics at the wing tips in order to provide more stability. He achieved two flights with a two-jet-engine-propelled wing in 2005. He had a narrow shave a month later: an uncontrollable sway led him to drop his wing which crashed. After a long year and two extra jet engines added, the wing became more secure. As a matter of fact, the 5’40 » over Bex – Switzerland – came up as an awaken dream for this pioneer. Since then, Yves Rossy has relentlessly been training to optimize his wing. Yves was compelled again to drop his prototype wing while in a new test flight in April 2007. The wing was seriously damaged and took a few months to be repaired. In the aftermath of this failure, Yves Rossy decided to build up a new, more reliable, higher-performance wing. Since early 2008, his wings have become more and more sophisticated.

Finally, Yves « Fusionman » « Rocketman » « Jetman » Rossy found his place in Aviation History on the 26th of September 2008, having joined Calais – France – to Dover – England. Congratulations to Yves Rossy and thanks to MEDIA IMPACT and its staff which supplied me with materials and information to write a post about Yves Rossy.

Please visit their website at: http://www.jetman.com/

Pilot Yves Rossy flying his wing


WING SPECIFICATION SHEET

  • Wingspan: 2.50 m.
  • Central part span: 1.80 m.
  • Length of a spreadable part: 35 cm.
  • Spreading device: by gas-spring completed in half a second.
  • Weight with fuel and smoke-emission device: 55 kg.
  • Dry weight: 30 kg.
  • 4 self-started Jet-Cat P200 jet-engines (thrust: 22 kg each) – stabilized in slow-running in 25 seconds.
  • Fuel: mixed with kerosene and 5% turbine oil for lubrication
  • Rating speed: 200 km/h
  • Climb-out speed: 180 km/h (330 m/min)
  • Sink rate: 300 km/h
  • Flight endurance: 10 minutes
  • Parachute: « Parachutes de France – Legend R »
  • Canopy: PD Spectra 230
  • Harness: dropped with an automatic engine-shut-off system and, an automatic parachute opening system for proper recovery.
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NASA OBLIQUE WING CONCEPT

NASA Dryden flight

A program conducted between 1979 and 1982 at the NASA Dryden Flight Research Center, Edwards, Calif., successfully demonstrated an aircraft wing that could be pivoted obliquely from zero to 60 degrees during flight. The unique wing was demonstrated on a small, subsonic jet-powered research aircraft called the AD-1 (Ames Dryden -1). The aircraft was flown 79 times during the research program, which evaluated the basic pivot-wing concept and gathered information on handling qualities and aerodynamics at various speeds and degrees of pivot.

The oblique wing concept originated with Robert T. Jones, an aeronautical

engineer at NASA’s Ames Research Center, Moffett Field, Calif.

Analytical and wind tunnel studies Jones initiated at Ames indicated that a transport-size oblique-wing aircraft, flying at speeds up to Mach 1.4 (1.4 times the speed of sound), would have substantially better aerodynamic performance than aircraft with more conventional wings. At high speeds, both subsonic and supersonic, the wing would be pivoted at up to 60 degrees to the aircraft’s fuselage for better high-speed performance. The studies showed these angles would decrease aerodynamic drag, permitting increased speed and longer range with the same fuel expenditure. At lower speeds, during takeoffs and landings, the wing would be perpendicular to the fuselage like a conventional wing to provide maximum lift and control qualities. As the aircraft gained speed, the wing would be pivoted to increase the oblique angle, thereby reducing the drag and decreasing fuel consumption. The wing could only be swept in one direction, with the right wingtip moving forward.

The AD-1 aircraft was delivered to Dryden in February 1979. The Ames Industrial Co., Bohemia, N.Y., constructed it, under a $240,000 fixed-price contract. NASA specified the overall vehicle design using a geometric configuration studied by the Boeing Commercial Airplane Company, Seattle, Wash. The Rutan Aircraft Factory, Mojave, Calif., provided the detailed design and load analysis for the intentionally low-speed, low-cost airplane. The low speed and cost of course limited the complexity of the vehicle and the scope of its technical objectives.

NASA AD-1 X-plane

Piloting the aircraft on its first flight Dec. 21, 1979, was NASA research pilot Thomas C. McMurtry, who was also the pilot on the final flight Aug. 7, 1982. Powered by two small turbojet engines, each producing 220 pounds of static thrust at sea level, the aircraft was limited for reasons of safety to a speed of about 170 mph. The AD-1 was 38.8 feet in length and had a wingspan of 32.3 feet unswept. It was constructed of plastic reinforced with fiberglass, in a sandwich with the skin separated by a rigid foam core. It had a gross weight of 2,145 pounds, and an empty weight of 1,450 pounds. A fixed tricycle landing gear, mounted close to the fuselage to lessen aerodynamic drag, gave the aircraft a very « squatty » appearance on the ground. It was only 6.75 feet high. The wing was pivoted by an electrically driven gear mechanism located inside the fuselage, just forward of the engines.

Read full article on the NASA (www.nasa.gov) website: NASA Dryden Past Projects: AD-1 Oblique Wing – updated August 12, 2009

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