Military Review

Experimental plane with the wing reverse sweep Grumman X-29

With increasing flight speeds in aviation the transition from the use of the direct wing to the swept one became quite natural. This fact is well known. However, from both the layout and the aerodynamic points of view, the use of CBS, the reverse sweep wing, was seen as a much more attractive solution. Work on aircraft with such a wing was carried out in many countries. For example, in Russia such a project was the Su-47 (S-37) Berkut fighter. In the United States, a similar machine was created by Grumman Aviation Corporation (since 1994 Northrop Grumman). The experimental fighter was designated Grumman X-29.

Wing backward sweep (CBS)

It is known that on airplanes with a straight sweep wing, the oncoming flow of air flows from the root to the tip and forms two powerful whirlwinds that descend from there. In this case, the resistance that is created by the wake (the air flow in the form of vortices, which breaks off the wing tips of the aircraft in flight) is called inductive. In the case of KOS, the overflow occurs in the opposite direction - from the tip to the fuselage, while the co-current jet has a lower intensity, which leads to a significant decrease in inductive resistance. In this case, the location in the zone of action of the wake-up jet behind the wing of the reverse sweep of the small surfaces of the aerodynamic control leads to an increase in the maneuverability of the aircraft.

The fact that the aircraft with KOS has a significantly smaller margin of static stability also contributes to an increase in the maneuverability of the aircraft. This is achieved due to the fact that the aerodynamic focus of an aircraft with KOS is much easier to combine with its center of mass, rather than in the case of using a straight sweep wing. Another advantage of this scheme is that it is possible to more evenly distribute the lifting force over the span, which in turn leads to a simplified calculation of the wing and contributes to the improvement of controllability and aerodynamic qualities.

The layout advantage of the WWTP in the development of passenger, military or transport aircraft is that the massive wing spar is located far behind the center of mass of the aircraft, where the passenger compartment or bomb bay is located. All these facts were known to designers and scientists in the years of the Second World War. Back in 1944, an experimental aircraft was designed in Nazi Germany - a heavy bomber Ju-287 with a backward-swept wing. This prototype, due to the low priority of the program and the large number of problems that arose during the work on them, did not go beyond the framework of ordinary, albeit flying, prototypes.

What prevented the realization of knowledge? The backward swept wing was actually implemented on a few samples of aviation equipment. The fact is that the backward-swept wing had one, but very overwhelming drawback: this wing is a very unstable design in terms of reinforcement. Under the action of air flow, the reverse sweep wing tends to bend. This process has received the designation of aerodynamic divergence. You can fight this process by making the design of the reverse-swept wing absolutely rigid. But this decision in turn led to a sharp increase in the mass of the aircraft. Therefore, for many years the idea of ​​an aircraft with KOS could not get a logical development and embodiment in the metal.

Grumman X-29

Beginning with the 1977 year, the United States began to conduct research that was aimed at studying promising schemes for highly maneuverable combat aircraft. This program was carried out under the guidance of DARPA. In 1980, Grumman, General Dynamic, and Rockwell created projects with backward-swept wing aircraft. To substantiate the configurations presented by them, tests of models of aircraft in wind tunnels were conducted. After reviewing the submitted projects, DARPA chose Grumman. In December, 1981, the company received a contract for 80 million dollars, which provided for the construction of two experimental aircraft, which received the designation Grumman X-29A.

Experimental aircraft Grumman X-29A was built using aerodynamic "duck" and with a wing sweep back. In addition, the aircraft received a full-circle front horizontal tail (GIP), which could aerodynamically interact with the wing of the aircraft. The front wing spar was made of titanium alloy using electric welding. The rear spar, as well as the transverse and longitudinal force sets were made of aluminum alloy. Three wing ailerons were located throughout the wing span.

It was CBS that was the highlight of the X-29A. In the root part, it occupied the length of the 2 / 3 aircraft fuselage. The strength of the wing was achieved through the use of welded caisson from titanium and other light alloys. The upper and lower wing linings were made one-piece from a special material CFRP (carbon-reinforced plastic). At the ends of the wing, the skin was glued together directly from 156 layers of this material. This skin had a very high level of strength with a fairly small mass. The sweep of the wing on the fourth chord was equal to 34 degrees, while the wing was able to withstand even very high loads.

The X-29 semi-monocoque fuselage was made of aluminum alloys. The cockpit canopy opened up and back with the help of special hydraulic cylinders. The cockpit was sealed, it installed the Martin-Baker ejector seat GRQ7A. On the sides of the fuselage of the car, starting from the root of the wing, there were nodules, which ended in deflectable guards to control the eddies, which descended from the wing of the aircraft. In addition to this, the flaps could be used to facilitate the detachment of the aircraft's nose-wheel at take-off, increasing the lifting force when the aircraft approaches the landing, as well as with the PGO and the hanging ailerons to balance the car. The keel and plane of the aircraft were also made of aluminum alloys.

The chassis of the experimental aircraft was made three-point, with one-wheel racks. The chassis was equipped with oil-pneumatic shock absorbers of the Menasco company, as well as pneumatics and wheels of the Goodrich company. All racks of the aircraft landing gear were removed by turning forward. The plane used side flat air intakes. As a power plant, the engine used was General Electric »F404-GE-400, possessing a two-shaft scheme and a degree of bypass 0,34. The stock of fuel was located in two soft tanks in the aircraft fuselage, as well as in compartments-tanks in the root of the wing. Above all, the plane had an auxiliary power unit, which provided the drive for emergency generators and hydraulic pumps.

On board the Grumman X-29, a special digital EDSU was installed - the Honeywell electrical control system of the company, which has threefold redundancy. Initially, the X-29 had a statically unstable layout that allowed it to maneuver very intensively. At the same time, the EDSU provided the aircraft with artificial stability, carrying out a coordinated deflection of the CG, fuselage covers and ailerons. Also on the plane was installed full-fledged radio-electronic equipment, which included the Lytton LR-80 spatial course system and other navigation equipment. In addition, the plane had the Teledyne RT-1063B / APX-101V identification system and the Magnevox AN / ARC-164 communications equipment operating in the decimeter wavelength range. The inertial navigation system appeared on the second experimental sample.

An important task in the development of X-29 was to reduce the cost of the aircraft. For this reason, the company Grumman widely used in the construction of units and components of existing machines: the nose landing gear and cab from the F-5A Freedom Fighter, the main landing gear and fuel tanks from the F-16 Fighting Falcon, the power plant was a "half" version such on the F / A-18 Hornet, hydraulic filters from the Grumman E-2C aircraft.

Experimental aircraft Grumman X-29 was designed to fly at a relatively small supersonic speed, the static stability of the machine in flight was provided by artificial means. The first flight of the aircraft made 14 December 1984 of the year. The X-29А aircraft was used to carry out the initial assessment of the piloting and flight characteristics of an aircraft with a forward swept wing. The correspondents who covered his flight were delighted with the new aircraft and its appearance. Journalists who are accustomed to the traditional type of jet aircraft with a straight swept wing, even believed that the aircraft was flying backwards. In this case, the plane flew quite intensively. Sometimes he made up to 4 flights per day, on average, he performed 8 flights each month. During the test flights, the aircraft was able to reach the maximum height of 15 500 meters, speed M = 1,47 and angle of attack 22,5 degrees. It was also possible to achieve an overload in 6,4g (80% of the calculated maximum value) during the execution of forced turns.

Flight tests of the experimental aircraft confirmed the results that were already obtained while performing purges in wind tunnels. The machine did not fall down in flight, even with very large angles of attack, and retained the ability to commit a controlled roll, even at sufficiently low flight speeds. In the autumn of 1988, the first aircraft took part in a series of tests, the main purpose of which was to evaluate the combat maneuverability of the aircraft as part of the United States Air Force's database development program, which would quantitatively compare and determine the maneuverability parameters of aircraft.

The second plane, Grumman X-29, performed the first flight of the 18 in May, 1989. It was used to conduct research on the borderline of maneuverability during flights at high angles of attack. On this plane managed to reach a very high angle of attack - 67 degrees. Also, the potential customer of the American Air Force estimated the suitability of the “duck” scheme with a backward-swept wing and with three surfaces controlled by pitch - wing steering surfaces, PGO and fuselage shields. Also evaluated were the capabilities of the CBS aircraft to achieve a high angular velocity of rotation and roll control when flying at high angles of attack. Experimental machine could maintain good handling at angles of attack to 45 degrees.

However, in the future, it was decided to abandon the use and continuation of tests of the Grumman X-29 aircraft. The ideas of building a combat aircraft with a forward swept wing were not implemented either. The reasons were that the aerodynamic advantages of the use of KOS, from the point of view of the American military, were not as high as expected. In addition, during the implementation of the program, serious difficulties were identified with the creation of an EDSU for such an aircraft due to the presence of serious difficulties in eliminating cross-connections when operating the machine. On top of that, during the development and testing of Grumman X-29, emphasis was placed on the requirements for new combat aircraft: supersonic cruising flight speed came to the forefront while maintaining a sufficiently large maximum speed and reduced visibility. At the same time, when using CBS, the maximum speed characteristics deteriorate due to an increase in wave drag at supersonic flight speed.

The total cost of the program for the creation and testing of two experimental aircraft was about 250 million dollars. At the same time, the test program of the first X-29 ended December 2 1988 of the year after making 254 flights, the second - September 30 of 1991 years after making 120 flights. The total number of flights thus reached 374. This is more than for all other American aircraft with the letter X in the index. Currently, the aircraft are used as exhibition samples.

Grumman X-29 flight performance:

Dimensions: wingspan - 8,29 m, length - 16,44 m, height - 4,36 m, wing area - 17,54 m2.
Empty aircraft weight - 6260 kg, maximum take-off - 8074 kg.
The power plant 1 TRDDF General Electric F404-GE-400, the maximum thrust at the afterburner - 7260 kgf.
The maximum achieved flight speed is 1770 km / h (M = 1,48).
Practical ceiling - 16 670 m.
Crew - 1 man.

Information sources: (фото)
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  1. Hairy Siberian
    Hairy Siberian 24 November 2014 08: 10
    Following the Grumman X-29 and the Su-47 "Berkut", the Chinese are also creating their own fighter with KOS. There are images and drawings of the aircraft, which may be a naval version of the fifth generation stealth fighter J-20. Perhaps he will receive forward-swept wings.
    1. The comment was deleted.
    2. PV KGB of the USSR
      PV KGB of the USSR 24 November 2014 10: 35
      Quote: Hairy Siberian
      Following the Grumman X-29 and Su-47 "Berkut" the Chinese create their fighter with CBS

      From the project Su-47 "Berkut", our country refused in favor of the PAK FA. Today, the Su-47 "Berkut" exists in a single copy and is a flying laboratory.
    3. bigELDAK
      bigELDAK 24 November 2014 12: 00
      +1 PSAKING
      There are images and drawings of the aircraft, which may be a naval version of the fifth-generation stealth fighter J-20

      Even if they buy engines, the main fleet is "stupid" modernization of the MiG-21 (J-7 ... 10), copy-paste of Israeli, Soviet-Russian, American projects. To create something at least a similar wing (Su-47) they try very hard.
      1. bigELDAK
        bigELDAK 25 November 2014 10: 14
        Ok ok i give up there are * images * laughing yes, BUT provide development drawings, information otherwise why is it not PSAKING? am am No.
  2. saag
    saag 24 November 2014 10: 35
    The drone can be blinded from it, with folding wings ...
  3. samoletil18
    samoletil18 24 November 2014 11: 00
    In the 90s, when the Su-47 was shown and told everywhere that this is a miracle of Russian engineering, which created the prototype of the future main aircraft, it has no analogues, foreign experts froze, etc. (I, too, was overwhelmed with optimism), the appearance of invisibility was noted for radars as well. Who really understands this, can write something, is it really so? The feeling is that the topic is dead. And then I was sure that this is our answer to American invisible planes.
    1. Argon
      Argon 24 November 2014 12: 37
      The greatest pride is that the USSR passed the stage of construction of experimental machines, Simonov (the father of the Soviet KOS) solved all the questions in theory. "Berkut" in a number of 5eats was laid as a pre-production deck. during the manufacture, panels of the bearing cladding (made of composites of a certain type) of a large area and curvature of the 3rd, 4th order were used. One of the functions of this material is that it absorbs microwave radiation. On the Raptor, such panels were 3 times smaller and had a curvature of the 2nd order , respectively, the area of ​​joints (radar is a noticeable element) is larger. However, in general, from the point of view of "Stealth" technologies, the F-22 is a much more progressive machine in comparison with the Su-47.
      1. samoletil18
        samoletil18 24 November 2014 18: 06
        Thank you very much and + for the interesting information.
      2. Kassandra
        Kassandra 26 November 2014 00: 45
        what exactly?
    2. luiswoo
      luiswoo 24 November 2014 18: 59
      Well, the Su-47 has no analogues so far: it flies faster, higher and farther than the X-29 (why the J-20 with its triangular wing was dragged higher here is not clear).
      The topic died out, as I understand it, due to the heavy load on the twisting of the wing during overheating, which over time should lead to its destruction. Obviously, they did not solve the problem. Once both programs are closed.
  4. saag
    saag 24 November 2014 11: 15
    Quote: samoletil18
    The feeling is that the topic is dead

    Well, like, the carbon fiber on the wings has degraded, so this thing has been curtailed
    1. samoletil18
      samoletil18 24 November 2014 18: 20
      Quote: saag
      carbon fiber on the wings degraded,
      And this is in the homeland of Mendeev and Zelensky!
      1. samoletil18
        samoletil18 25 November 2014 10: 15
        I was here from the tablet. Correctly Mendeleev and Zelinsky. Damn, the inventor of the gas mask and Ho.H.
      2. The comment was deleted.
    2. Kassandra
      Kassandra 26 November 2014 00: 27
      but on the wings of direct sweep, does he really degrade somehow differently?
  5. Bongo
    Bongo 24 November 2014 14: 15
    Currently, aircraft are used as exhibition samples

    One of the 2's built by the X-29 is currently on display at the Edwards Air Base Memorial Complex.
  6. Petrucho
    Petrucho 24 November 2014 16: 59
    Wow, how many hours were spent at the computer, first at computer science lessons, then at home, when an iron beast wound up there with index 286 behind the F29 Retaliator toy. Thing!
  7. kirpich
    kirpich 24 November 2014 17: 27
    I agree that here we were not the first. BUT WHY is this promising topic not being developed? what Maybe I missed something?
  8. Boa kaa
    Boa kaa 24 November 2014 20: 32
    Quote: kirpich
    BUT WHY is this promising topic not being developed?

    Once infa flashed that on the new AVU there will be such decks along with the adapted T-50 under the sea. The advantage of such an aircraft was its compactness with folded wings, and so on.
    The photo is clickable, showing the product with its wings folded.
  9. askold
    askold 24 November 2014 21: 58
    An interesting experiment, the main purpose of which was to increase the aircraft’s maneuverability by giving it a statically unstable design. That is, the glider of this aircraft, without a specially designed EMDS, will not be able to fly, or rather it will be uncontrollably tumbling. A good example of this is an arrow firing forward. in order to be able to control such an aircraft, the on-board computer (3 digital computers, and 3 emergency analog ones) needed to process data from 18 gyroscopes (6 for each yaw, pitch and roll angle), 9 accelerometers (3 for each of the three directions ) and a whole network of sensors showing the pressure of the incoming air flow and the angle of attack, it is worth noting the intensity of these commands, -40 corrections per second. The pilot controlled the aircraft not directly (arm, pen, booster, hydraulics, aileron), but through the intermediary, on-board A computer, when its actions were only input signals for the computer. After processing all the corrections and human actions, the computer issued control signals to the devices actuating steering surfaces.
    PS During the public display of this aircraft in the summer of 1984, US Vice President George W. Bush, himself a former naval aviation pilot, was present. After examining the new aircraft, he jokingly remarked "A wonderful model, but its wings are set backwards."
    Thanks to the author, an interesting article about an unusual aircraft.
    1. Argon
      Argon 24 November 2014 22: 12
      In the same way as in the Su-30; 35, only in our case rotary nozzles of the engines also take part in all this "mess".
    2. Kassandra
      Kassandra 26 November 2014 00: 25
      X-29 was statically stable - they did not solve this problem
  10. uzer 13
    uzer 13 24 November 2014 22: 23
    [quote] [/ made of titanium alloy using electric welding.]

    Rather, argon-arc welding was used. Somehow I tried to weld at least something on a titanium plate, nothing came of it.