The mechanism of aerodynamic elastic divergence is simple and direct. The forward-swept wing tip is located in front of the root of the wing, that is, the wing tip is in front and the wing root is behind. Under the action of aerodynamic power, the wing tip flutters and twists and deforms, which in turn leads to an increase in the angle of attack of the wingtip. The increase in the angle of attack of the wingtip causes an increase in the aerodynamic power, which ultimately forms a positive feedback cycle in which the wingtip angle increases - the aerodynamic increase - the torsional deformation of the wingtip continues to increase the angle of attack.

In the end, the wings are structurally damaged, broken and damaged, and a flight accident occurs.

This is a fatal problem in the field of front-swept wings and cannot be solved at all. Like cancer, the front-swept wing aerodynamic design was sentenced to death by world aviation experts.

The serious Sukhoi Design Bureau developed the Su-47 "Golden Eagle" front-sweeping wing fighter, which uses a forward-sweeping angle of 37°, with its maneuverability and comprehensive performance, and its contemporary fighter jets are almost unparalleled, but they still failed to officially enter service and are declared abortion.

In addition to factors that cannot meet the invisibility needs, the aerodynamic elastic divergence problem that the forward swept wing aerodynamic design cannot overcome is also the core reason why Su-47's "Golden Eagle" dismounted.

The Su-47'Golden Eagle' fuselage is made of titanium alloy and the wings are made of 80% composite material. This is only a preliminary meeting of the requirements of subsonic stage flight and maneuvering, which prevents the wingtip torsion and damage. Further transsonic flight maneuvering and supersonic flight are still unavoidable.

Yang Wei, who has been rooted in the field of aviation design for decades, is experienced and rich in experience and knows clearly whether the fifth-generation aircraft design idea proposed by Zuo Xue is feasible.

The design idea is generally feasible and meets the current performance preset requirements for fifth-generation machines at home and abroad.

However, if the most fatal design difficulty of aeroelastic elasticity divergence cannot be solved, even if the design performance is good, it can only stay on the drawings and it is impossible to develop and install troops.

"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 that had been prepared.

Graphene composite material.

The hardness and strength of high-purity graphene is the highest among the known materials in the world, 200 times that of steel, and has extremely high tensile and ultra-thin properties, and has completely full mechanical properties.

It has high strength and light weight. In addition, graphene also has extremely high thermal conductivity and chemical stability, which can be called a perfect aviation material.

If new composite materials are developed with graphene as the main body, their performance will be much higher than that of carbon fiber composite materials currently used in the aviation field.

"Graphene composite material..."

Hearing this answer, Yang Wei felt thoughtful, and Yang Wei's melodious voice 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 composites can withstand the torque force generated by the lift of the forward swept wing, thus solving this problem. In the 1980s, Sukhoi and Grumman used carbon fiber composites to enable the forward swept wing to achieve sub-transonic flight. 40 years have passed, and graphene composites can fully meet the lift torque and supersonic lift torque that the forward swept wing bears in the sub-transonic maneuver.

Zuo Xue had a serious face and said affirmatively: "You know that the aerodynamic elastic divergence cannot be fundamentally solved from the aerodynamic design."

The problem of aeroelastic divergence has been a headache and trouble that has bothered every aircraft designer since the birth of the aircraft, and is particularly prominent in the field of forward swept wing design.

If the forward swept wing is to be used, aeroelastic elastic divergence will inevitably occur, unless the aerodynamic layout of the forward swept wing is changed, the series of advantages possessed by the forward swept wing are abandoned and converted into conventional swept wings.

Graphene composite material is the solution that Zuo Xue came up with after thinking for a long time - using materials to solve it.

"Xiaoxue, do you know the price of high-purity graphene?" Yang Weiss said for a moment, without refuting, agreed with Zuo Xue's statement, and then changed the cutting corner and asked.

Zuo Xue immediately responded: "Well, I know, the current market price of graphene with a 99.9% purity is 1,200 yuan per gram, and the purity of aviation-grade graphene needs to reach 99.99%, and the price is 3,200 yuan per gram. However, I think this is worth it. Using graphene will make the body's performance reach the indicators. In addition, large-scale application of graphene materials will also further reduce the market price."

Entering 2020, the price of high-purity graphene of 9 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-grade aviation-grade graphene materials has been reduced from RMB 8,000 per gram to RMB 3,200.

Despite this, the price of high-purity graphene is still astronomical.

What is the concept of 3200 RMB per gram?

The price of gold in April this year was about 400 yuan per gram, and the price of two nine-purity graphenes is 8 times that of gold.

8 times!

In other words, if graphene composite materials are used on a large scale, the cost of fighter jet research and development will increase in geometric form.

Assuming that the air weight of the fifth-generation fighter is about 25 tons, and according to the use rate of the body composite material of about 20%, at least five tons of mass graphene composite material will be used.

A full 5 tons!

3,200 yuan per gram, the price per ton is 3.2 billion yuan, and 5 tons is 16 billion yuan, equivalent to US$2.47 billion.

This price is simply breaking through the sky, and it is ridiculously high.

The fifth-generation fighter jet alone surpasses the world's most expensive B-2 strategic stealth bomber in terms of composite materials. If a series of subsystems such as avionics, comprehensive electronic warfare, and telecommunications control are added, the single-machine price is close to 3 billion US 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 jet are realized, they can greatly increase national defense strength and protect national territory and people's security.

Moreover, the initial investment is mainly due to the scarce production of high-purity graphene. With the large use of graphene composite materials in the aviation field, the material cost will plummet.

Perhaps, two nine-purity graphenes will be reduced to 1,000 yuan, 500 yuan per gram, or even lower.

"Are there any other solutions to the problem of aeroelastic divergence besides the application of new materials?" Since Zuo Xue knew the price, Yang Wei did not investigate the price issue and continued to ask.

Yang Wei also agreed with Zuo Xue's opinion, not to worry about whether the price is expensive or not. As long as you can create a fifth-generation fighter, it will be half the success.

The cost of construction mainly depends on large-scale production to dilute costs. Once the scale is increased, the price will naturally drop.
Chapter completed!