What are the flaws of the forward swept wing layout? What are the advantages and disadvantages of a

The most serious flaw of the forward-swept wing is in the structural aspect:

The bending deformation along the curve direction of the structure will increase the angle of attack of the outer wing along the direction of the airflow, increase the lift of the outer wing, and further increase the bending deformation of the wing. At high enough speeds, this phenomenon creates a vicious cycle until the wing bends and breaks. This phenomenon is called twisting divergence.

The velocity at which the flexional divergence begins is called the flexural divergence (critical) velocity. In order to increase the flexional divergence speed of the forwardswept wing, the bending stiffness of the wing needs to be increased, which will lead to an increase in the weight of the wing structure, which will completely negate the benefits of using the forwardswept wing. This is the main reason why forward-swept wing aircraft are rarely adopted.

With the development and application of composite materials, this defect has been compensated to a certain extent.

The defects are that the supersonic drag is high, and the wing stress is too strong, which is prone to aeroelastic divergence.

The main advantage of a swept wing is that compared to a swept wing, a swept wing will cause a local stall of the wingtip due to the airflow of air flow from the wing surface, and even if it does not stall, it will lose lift, resulting in a lower overall lift-to-drag ratio.

On the other hand, the swept wing does not have this problem of reduced wingtip lift, on the contrary, its wingtip lift efficiency is very high. The air flowing to the wing roots is blocked by the fuselage and flows to the tail, which can be adjusted with a flat tail or movable end plate to provide strong trim ability and improve maneuverability.

However, the supersonic drag of the aircraft mainly comes from the shock drag, for the normal layout of the aircraft, the shock wave of the front of the aircraft only occurs in the nose and cockpit, and for the forward swept wing, the two wingtips also have a strong shock wave, and the drag is greatly increased.

In addition, the wingtip lift effect of the forward-swept wing is strong, which is an advantage, but too strong wingtip lift will lead to wing deformation, mega wing tip upturning, and the wing itself is elastic, when the lift changes, the wing will produce elastic deformation, which will cause the wing to repeat, and the wing itself will lead to greater changes in lift, which will lead to a sharp change in the force of the wing, and the amplitude will increase, and eventually lead to the loss of control or even disintegration of the aircraft.

The forward-swept wing has a unique advantage in aerodynamics, with a high lift-to-drag ratio; It can ensure a better connection between the wing and the fuselage; Conducive to take-off and landing; Moreover, its greatest benefit is maneuverability, and this advantage is most pronounced in the subsonic range. If the forward-swept wing layout is combined with the thrust vectoring control system, the aircraft is even more powerful in air combat. Of course, the forward-swept wing isn't perfect.

For example, its technology is complex, the related technical requirements for it are relatively high, the strength of pneumatic components is large, and the problem of wingtip tremor cannot be completely solved so far. So at the moment there are still very few fighters with this layout. However, it represents a kind of aircraft development direction.

Russian Su-47 "Golden Eagle" forward-swept wing fighter.

The aircraft uses a forward-swept wing to improve controllability at low speeds and improve aerodynamics in all flight conditions. Adopting the aerodynamic layout and thrust vector control technology of three-wing surface, double vertical tail, front and rear full-motion control surfaces, the fuselage is widely made of composite materials, which has good supersonic cruise, super-maneuverability and stealth capabilities. Two AL-41F thrust vectoring turbofan engines are installed, each with a maximum afterburner thrust of 175 kN and a thrust-to-weight ratio of about 10.

The length of the aircraft, the height of the aircraft, the wingspan meters, the maximum take-off weight of 34 tons, the maximum speed of Mach, the ceiling of 18,000 meters, the maximum range of 3,300 kilometers. The on-board equipment includes the most advanced digital multi-channel equipment made in Russia, an automated integrated command system, an integrated navigation system, and a new generation of crew life support and ejection integrated systems. Equipped with advanced radar, LiDAR and rearview radar with TV, thermal infrared, and laser equipment are used.

The cabin can carry ultra-long-range air-to-air missiles and long-range air-to-air missiles, including the KS-172 missile, a two-stage missile that can reach hypersonic speeds and is equipped with a composite guidance system capable of striking air targets up to 400 kilometers away. It can also carry an air-to-ground assault**, while retaining the 30mm cannon.

Golden Eagle "Su--47 (Su-47).

Basic data: Length: meters.

Wingspan: m. Take-off weight: 24 tons.

Max speed: Mach.

Maximum overload: more than 27G for the Su-9

Construction materials: 13% of the weight is made of composite materials, aluminum alloy and titanium alloy.

The aerodynamic characteristics of the forward-swept wing aircraft are superior, and there are many advantages including high critical Mach number, low wave resistance and overcoming wingtip stall, but the problem of torsion is also an obstacle to the widespread practical application of the forward-swept wing aircraft, so composite materials must be used

The advantage is maneuverability and speed, the disadvantage is the inability to stealth and the production process is complex.

Due to the complex structure, the variable swept wing has many problems. To support the variable sweep angle of the wing, the wing must consist of a variable mechanism. Increased fuselage weight, reduced wing suspension points, reduced load, reduced agility.

The complexity of the mechanism and the number of firmware are increased, the reliability is reduced exponentially, and the production complexity and maintenance costs are increased exponentially, resulting in excess returns. And even the sacrifice of so many aspects does not compensate for the reduction in its structural strength.

Such as the classic F-14. First, the ailerons were removed, and then the key parts had to be made of titanium alloy, which could not be welded conventionally, and for its aerodynamic principle, even airbag-like parts were used to supplement the missing parts of the trailing edge of the wing, and even then its weight was much higher than that of similar fighters. This greatly increases manufacturing and maintenance costs.

This is very disadvantageous for a kind of routine mass production.

However, even if it has these problems, it cannot hide its strong advantages in maneuverability.

When the aircraft is flying, the requirements for the wings of low-speed and high-speed flight are different. Flying at low speeds, a small sweep angle is required, preferably a straight wing, the faster the flight speed, the greater the sweep angle of the aircraft.

Variable swept wings have movable wings that stretch out their wings for a while, like an eagle spreading its wings; For a while, he retracted his wings backwards, like a petrel skimming water.

The disadvantages of the variable swept wing are: complex structure, increased weight. So the designers introduced a new variable-wing aircraft - the tilt-wing aircraft.

The wings of this type of oblique aircraft are straight and move slowly along the axis of the fuselage. During take-off and landing, the wings are horizontal, and when flying at high speeds, the wings gradually turn and tilt, like a large pair of open scissors, so they are also called "flying scissors".

The structure of the tilt-wing aircraft is simpler than that of the variable-swept wing aircraft, and at the same time takes into account the requirements of low-speed flight.

A swept wing aircraft is an aircraft in which the front and trailing edges of the wing are extended backwards (swept back). Early swept wing aircraft were mostly military aircraft. Later, in order to meet the different requirements of different altitudes, speeds and take-off and landing for wing sweep angles, variable-swept wing aircraft were produced.

Swept-wing aircraft appeared in the 40-50s of the 20th century. For example, the American F-100 supersonic fighter and B-52 strategic bomber; The former Soviet Union's "MiG"-19 fighters, Tu-16 long-range bombers and other military aircraft are all swept wing aircraft.

A wing whose grazing angle can be changed in flight is called a variable swept wing.

In the design work of the aircraft, there is a contradiction that is not easy to overcome: in order to increase the number of m in flight, it is necessary to choose a wing with a large sweep angle and a small aspect ratio to reduce the shock drag of the aircraft, but such wings have less lift in the subsonic state, the induced drag is larger, and the efficiency is not high. From an aerodynamic point of view, in order to meet the requirements of the aircraft for supersonic flight, subsonic cruise and short-moment take-off and landing at the same time, it is best to make the wing sweep and use different sweep angles to adapt to different flight conditions.

The study of variable swept wings began with:

40s, but until.

It was only in the 60s that practical variable-swept wing aircraft were designed.

The inner wing segment of the general variable sweep wing is fixed, and the outer wing is connected with the inner wing with a hinge shaft, and the outer wing is controlled to rotate back and forth through a hydraulic booster to change the rear friction angle of the outer wing segment and the aspect ratio of the whole wing.

The disadvantage of the variable swept wing is that the structure and control system are complex, and the weight is large, which is not suitable for light aircraft.