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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RAFALE evaluation in SWITZERLAND

French Air Force RAFALE fighter aircraft takeoff

The next aircraft (the last one was the Gripen) being evaluated in the framework of the replacement of the Swiss F-5, is the Dassault-Aviation-manufactured RAFALE until November 7. Two two-seaters stationed at Emmen airfield – Switzerland – are being tested the same way the two Swedish Gripens were tested previously.

Latest Dassault Aviation creation, the RAFALE performed its maiden flight on July 4, 1986! Its program highlighted all the major French suppliers such as: SNECMA for the M88 engine; Thales (former Thomson – CSF) for the RBE-2 phased array radar; Dassault systems; SAGEM (electronics and optronics); and the English Messier – Dowty for the landing gear.

Unlike the Mirage 2000 which versus its American competitors, the RAFALE does not fear its opponents as far as technical performance is concerned:

  • RBE-2 phased array radar
  • Latest generation SPECTRA (electronic warfare system)
  • OSF (Front-sector optronic system)
  • a GPS (Global Positioning System)
  • last but not least: a lower cost of development and maintenance compared to the majority of its opponents…

The RAFALE has a wide range of weapons at its disposal: the infrared and radar MICA missile, the SCALP (air-to-surface cruise missile) as well as the future long-range European METEOR missile. The multirole Dassault fighter aircraft is able to be equipped with various American-made bombs: Laser-guided Paveway III, for instance, but it is a shame that foreign weapons have not been licensed for the RAFALE yet.

The RAFALE fighter aircraft are parted into three standards:

  • F1 standard: air-to-air-mission dedicated only. This standard fields the French Fleet Air Arm.
  • F2 standard: encompasses the F1 standard, and has the air-to-surface capability to its disposal. The French Air Force is fielded with these aircraft.
  • F3 standard encompasses the previous skills plus the strategic capability which enables this fighter to carry out nuclear-deterrence/strike missions, reconnaissance missions, and anti-ship-strike missions. This latter standard might field the Swiss Air Force (without the nuclear and anti-ship capabilities)

SOURCE :

AVIANEWS Article

Photos 1 & 2 French Air Force, Rafale 5/330 Squadron Côte-D’argent at Dijon.

Photo 3 Pascal Kümmerling, Rafale of the 5/330 at Geneva during BEX meeting in 2007.

Bern, 09th of October 2008 – Photo: Pascal Kümmerling – The second applicant to the replacement of the Tigers ( TTE ) landing at Emmen. The French RAFALE has already started the second TTE in-flight and ground-test series in Switzerland. The European EADS Eurofighter third and last applicant will follow in November.

About thirty flights are scheduled among which some night flights for the tests at Emmen. Around 50 sorties will be needed. They will be carried out by F/A-18s, and F-5s in order to make up the targets (means playing the role of targets) and the formation flying tests. The assessment flights occur within the frame of the flights share, which means that there should not be any increase in the number of sorties on the airfields that are concerned.

The sequel: The arrival of the European EADS Eurofighter is expected on November 6, 2008. The testing syllabus is the same for the three fighter aircraft.

The flight and ground tests will be examined as well as the tenders that were handed in on July 2nd, 2008. The collected data will be used as a basis for a second call for tenders in January 2009.

The choice of the type of aircraft should come after the evaluation of the second tender, assessing equipment and price, and when everything has been put down on a balance-sheet report expected in May 2009. Then the choice should be stated in July 2009.

These aircraft belong to the 1/7 « Provence » Fighter Squadron stationed at Saint Dizier – Robinson. The « Provence » was the first squadron that had been operational with the RAFALE. The first 1/7 RAFALE flight happened in 2006. Photos: Pascal Kümmerling.

VERY SPECIAL THANKS to Pascal Kümmerling since this post is adapted from his articles on his blog called AVIA NEWS: http://psk.blog.24heures.ch/

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FRENCH AIR FORCE BASES TO CLOSE DOWN:

The French Prime minister François Fillon has addressed an official statement this morning:

After the reform, “The French Army will have shed 20 Regiments/Batallions”, The Air Force will have shed 11 Air Bases,and the Navy will have shed “a Fleet Air Arm Base”.

The units or sites concerned are small, medium, and large ones – from tens of people up to 2,502 people as far as Metz AF Base is concerned.

  • As early as 2009, the French government plans the closing down of the AF Base 101 stationed at Toulouse.
  • In2010 Colmar-Meyenheim (Haut-Rhin) AF Base 132 should close down (1,276 people).
  • From 2011 -2012, Nîmes Garons Fleet Air Arm Base (1,332 people) will close down, as will the AF Base 112 stationed at Reims (1,545 people), and Taverny Air Base (Val-d’Oise, 986 people) as well. The AF Base 128 (Metz-Frescaty, Moselle, 2.502 people), AF Base 103 of Cambrai-Haynecourt (Nord, 1,364 people), AF Base 217 at Bretigny-sur-Orge (Essonne, 1,955 people). Overseas AF Bases: 365 Lamentin (650 people) in Martinique in the French West Indies, and overseas AF Bases 190 Papeete – Faa’a (Tahiti), in Polynesia (920 people), and AFB 181 Sainte-Clothilde, La Réunion. The radar Air Force Base 943 Nice Mont-Agel is to be shed too.

While 83 military sites will close down, it is deemed that around 60 sites will be operationally-meant reinforced. Evreux (Eure) Air Force Base 105 is expected to get a reinforcement up to 800 people.

The French government plans 54,000 jobs to be axed in the Armed Forces and Defense within a seven-year period. The current France strength is 320,000 (without the Gendarmerie). The French Air Force should reach down to 50,000 strength.

 

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First RAF pilot to fly F-22 Raptor

(source: http://www.af.mil)

A former RAF Leeming F3 pilot has spoken for the first time since arriving in the United Kingdom at the controls of one of the United State’s 5th generation fighters – the F-22 Raptor.

Speaking after a 7 ½ flight which involved eleven refuelling transfers, Flt. Lt. Dan Robinson spoke of his fortune at being the first RAF pilot to fly the aircraft. CLICK HERE TO WATCH THE VIDEO

© UK Crown copyright 2008

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Why not fly NUCLEAR AIRCRAFT ?

I was reading a gripping blog in French called “Objets du ciel » (broken link) when I bumped into an amazing article written by Carl Conrad. I first thought that this post was unbelievable. I daresay that all the articles he writes are amazing. I am going to report hereafter what I have read about this topic – nuclear-powered aircraft – from different sources, but Carl Conrad’s article is the one that inspired me most.

Convair NB-36H X-6

© Photo: National museum of the USAF

As a major oil crisis is looming, airlines are cancelling some less financially viable air links of theirs. The future of aviation as we currently know it, seems to be in jeopardy. Nothing seems to be used as a substitute for any current kind of energy, not even electricity. What about nuclear-powered engines?

Nowadays, nobody would bear any nuclear-powered test flights. However those tests did occur within a USAF-carried-out weapons system (WS 125-A) nuclear-powered bomber aircraft programme. Those tests were performed with a 1,000-kilowatt-nuclear jet engine airborne on a Convair NB-36H. This aircraft named « The Crusader », took-off 47 times during the 50s. The engine was not used for propelling. It only worked at an altitude which was deemed sensible. Those tests allowed to assess the nuclear engine drive performance. Every flight would involve troops deployment in the area to prevent as soon as possible from any accident fallout spreading. The aircraft was modified in order to enhance the five crew member’s safety. The USAF considered the concept not realistic and gave the programme up in late 1956.

However, this technology might be coming back to fly some drones for long-lasting flights. People might be relunctant to see nuclear-powered drones taking-off and flying past over their heads. Who knows? Maybe some day.

Another project to mention: Project Orion should have become a 4,000-ton, long-range spacecraft powered by controlled nuclear pulses, or explosions. For this purpose, a small test vehicle was built. It was dubbed « Hot Rod », and was conventional-explosive-powered craft. Finally, Orion was cancelled in 1965 because it would not have been politically correct and because of technical challenges.

I have not found a piece of information about nuclear-powered craft after the year 2004. By the way, if someone knows further information about nuclear-powered aircraft, they will be welcome if they want to add some comments.

SPECIFICATIONS:
Span: 230 ft. 0 in.
Length: 162 ft. 1 in. (as B-36H, the NB-36H was slightly shorter)
Height: 46 ft. 8 in.
Weight: 357,500 lbs. (max. gross weight)
Armament: None
Engines: Six Pratt & Whitney R-4360-53 radials of 3,800 hp each (takeoff power) and four General Electric J47-GE-19 turbojets of 5,200 lbs. thrust each
Crew: Five ( pilot, copilot, flight engineer and two nuclear engineers)

PERFORMANCE:
Maximum speed: Approx. 420 mph at 47,000 ft.
Cruising speed: 235 mph
Service ceiling: Approx. 47,000 ft.

Sources:
http://www.nationalmuseum.af.mil/

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