The mechanism of aeroelastic divergence is simple and direct. The forward-swept wing tip is located in front of the wing root, that is, the wing tip is in front and the wing root is behind. Under the action of aerodynamic force, the wing tip flutters and twists and deforms, which in turn causes the wing tip angle of attack. The increase in the angle of attack causes an increase in aerodynamic force, which reacts on the wing tip, ultimately forming a positive feedback vicious cycle in which the wing tip angle of attack increases - the aerodynamic force increases - and the torsional deformation of the wing tip continues to increase the angle of attack.
Eventually, the wing suffered structural damage, broke and was damaged, and a flight accident occurred.
This is a fatal problem in the field of forward-swept wings that cannot be solved at all. Like a cancer, the aerodynamic design of forward-swept wings has been pronounced dead by aviation experts around the world.
The Su-47 'Golden Eagle' forward-swept wing fighter developed by the serious Sukhoi Design Bureau adopts a forward sweep angle of 37°. Its maneuverability and comprehensive performance are second to none. It is almost unmatched by fighters of the same generation, but it still remains the same. He was unable to formally serve and declared a miscarriage.
In addition to factors other than the inability to meet stealth requirements, the aeroelastic divergence problem that cannot be overcome by the forward-swept wing aerodynamic design is also the core reason for the suspension of the Su-47 Golden Eagle.
The body of the Su-47 Golden Eagle is made of titanium alloy, and the wings are made of 80% composite materials. This only initially meets the requirements for flight and maneuvering at subsonic speeds, preventing the wingtips from being torsionally damaged and going one step further. Transonic flight maneuvers and supersonic flight are still unavoidable.
Yang Wei, who has been rooted in the field of aviation design for decades, is experienced and rich, and he clearly knows whether the fifth-generation aircraft design idea proposed by Zuo Xue is feasible.
The design idea is generally feasible and meets the current domestic and foreign performance preset requirements for fifth-generation aircraft.
However, if the most fatal design difficulty of aeroelastic divergence cannot be solved, no matter how good the design performance is, it can only stay on the drawings, and it will never be possible to develop and install the unit.
"Teacher, I'm going to use graphene composite materials." Zuo Xue was not surprised by Yang Wei's expected question, and immediately gave the answer she had prepared.
Graphene composites.
The hardness and strength of high-purity graphene are the highest among known materials in the world, 200 times that of steel, and it has extremely high stretchability and ultra-thinness, and its mechanical properties are completely perfect.
In addition to its high strength and light weight, graphene also has extremely high thermal conductivity and chemical stability, making it a perfect aviation material.
If graphene is used as the main body to develop new composite materials, its performance will be much higher than the carbon fiber composite materials currently used in the aviation field.
"Graphene composite materials..."
Hearing this answer, Yang Wei was thoughtful, and Yang Wei's thoughtful self-talk echoed on the phone. After a few seconds, his voice was slightly serious: "Xiaoxue, do you think graphene composite materials can solve the problem of aeroelastic divergence? "
"Yes, teacher, I think graphene composite materials can withstand the torque force generated by the lift of forward-swept wings, thereby solving this problem. In the 1980s, Sukhoi and Grumman used carbon fiber composite materials to achieve sub-zero forward-swept wings. In transonic flight, 40 years later, graphene composite materials can fully meet the lift torque of forward-swept wings in subsonic maneuvers and supersonic maneuvering lift torque."
Zuo Xue looked serious and affirmed: "As you know, aeroelastic divergence cannot be fundamentally solved through aerodynamic design."
The problem of aeroelastic divergence has been a headache for every aircraft designer since the birth of aircraft, and it is particularly prominent in the field of forward-swept wing design.
If a forward-swept wing is used, aeroelastic divergence will inevitably occur unless the aerodynamic layout of the forward-swept wing is changed, a series of advantages of the forward-swept wing are abandoned, and a conventional swept wing is converted.
Graphene composite materials are the solution Zuo Xue came up with after thinking for a long time - using materials to solve the problem.
"Xiaoxue, do you know the price of high-purity graphene?" Yang Wei thought for a moment, agreed with Zuo Xue without refuting, and then asked from a different angle.
Zuo Xue immediately responded: "Well, I know that the current market price of 99.9% pure graphene is 1,200 RMB per gram. The purity of aviation-grade graphene needs to reach 99.99% level, and the price is 3,200 RMB per gram. But I think this is It is worth it. The use of graphene will make the performance of the machine reach the target. In addition, the large-scale application of graphene materials will also further reduce the market price."
Entering 2020, the price of high-purity graphene has dropped a lot, from 5,000 yuan per gram a few years ago to 1,200 yuan per gram now.
The market price of two-nine aerospace-grade graphene materials has dropped from RMB 8,000 to RMB 3,200 per gram.
Still, the price of high-purity graphene is astronomical.
What is the concept of 3200 yuan per gram?
In April this year, the price of gold was about 400 yuan per gram, and the price of two nine-purity graphene was eight times that of gold.
8 times!
In other words, if graphene composite materials are used on a large scale, the cost of fighter aircraft development will increase geometrically.
Assuming that the empty weight of the fifth-generation fighter is about 25 tons, and based on the calculation that the composite material usage rate of the aircraft body is about 20%, at least five tons of graphene composite materials will be used.
A full 5 tons!
3,200 yuan per gram, converted to a price of 3.2 billion yuan per ton, 5 tons is 16 billion yuan, equivalent to 2.47 billion U.S. dollars.
This price is simply sky-high, ridiculously high.
The purchase cost of composite materials alone for the fifth-generation fighter aircraft exceeds that of the world's most expensive B-2 strategic stealth bomber. If a series of subsystems such as avionics, integrated electronic warfare, and fly-by-wire control are added, the price of a single aircraft is close to thirty years. One hundred million U.S. dollars.
However, in Zuo Xue's view, these investments are completely worth it. As long as the performance indicators required by the fifth-generation fighter aircraft are achieved, it can greatly increase national defense strength and protect the country's territory and people's security.
Moreover, the high initial investment is mainly due to the scarcity of high-purity graphene production. With the extensive use of graphene composite materials in the aviation field, material costs will plummet.
Perhaps, the price of two nine-purity graphene will be reduced to 1,000 yuan per gram, 500 yuan, or even lower.
"Regarding the problem of aeroelastic divergence, besides applying new materials, are there any other solutions?" Since Zuo Xue knew the price, Yang Wei did not delve into the price issue and continued to ask.
Yang Wei also agreed with Zuo Xue's opinion. Regardless of whether the price is expensive or not, as long as a fifth-generation fighter can be produced, it will be half successful.
The cost mainly depends on large-scale production to dilute the cost. Once the scale increases, the price will naturally drop.
If graphene composite materials can indeed meet the needs of fifth-generation fighters, the national level will inevitably accelerate the in-depth development of the graphene industry.
