Chapter 881: Trouble with Signal Transmission
Although the Y-9 at this time has no blood relationship with any other models, there is actually not much room for innovation in the overall design of military transport aircraft.
In particular, the superior units and users have now given very clear technical indicator requirements.
Not to mention anything else, the two requirements of "the cross-sectional area of the cargo hold is not less than 76% of that of the Il-85" and "turbofan power" do not leave much room for operation at the design level.
Turboprop-powered transport aircraft can accommodate some strange designs due to their slower flying speeds.
However, for jet transport aircraft whose cruising speed is generally above 600km/h, their overall aerodynamic characteristics have become highly homogenized.
All-metal semi-monocoque structure, swept-back cantilevered upper wing and T-tail, suspended engine...
Basically, it is an Il-76 with a lower height and shorter length, but the width remains roughly the same.
Or it can be said to be a C17 that is scaled down in all aspects.
There is little room for cutting corners through ingenuity.
It's basically a matter of hard work.
The key to the success of a model lies in the design at the structural level and the supplementation and improvement of some details.
For example, the radical air-blown lift-increasing technology is too risky for a tactical twin-engine aircraft and is a design that is not worth the cost.
As for winglets, China already has rich experience in past models, so it is worth a try.
In addition, tactical transport aircraft need to take off and land on unpaved runways, so special attention needs to be paid to the design of engine foreign body protection and landing gear structure. Fortunately, even the larger Il-76 has this capability, so it is not completely in the dark...
In short, almost on the way back to Nanzheng from the capital, Liang Shaoxiu had already roughly conceived the overall outline of this plan.
What Ding Gaoheng said before was very clear.
"Led by Qinfei Group."
That means we can also get support from other brother units within the aviation industry system.
In fact, this is normal.
An aircraft with a mass of 80-90 tons may not sound large, but it is still a blank for China Aviation Industry.
We must definitely concentrate our efforts on tackling these problems.
However, that is all after the project is officially launched.
The most urgent task is to turn the Y-9 from a requirement into a formal project.
Therefore, after getting off the plane, the first thing Liang Shaoxiu did was to concentrate the main research and development forces of Qinfei Group and start deploying preliminary research work...
……
On the other hand, Chang Haonan didn't know at this time that Ding Gaoheng had already arranged the research and development work of Y-9.
He is having a headache trying to perfect the ultra-short laser processing technology as quickly as possible...
Still in the conference room of the Aviation Power Group.
Another lively project seminar is underway.
The reason why I say "again" is because since the project was officially launched last month, a similar scene has been played out here almost every few days.
First, Chang Haonan gave his routine presentation of theoretical progress, and then several leaders in charge of hardware research and development began to debate.
Today’s situation…
It's almost the same.
As usual, Chang Haonan was the first to speak:
"Last week, Academician Hou's team used femtosecond pulse lasers to verify the ablation threshold model I proposed earlier."
"Moreover, thanks to the fact that femtosecond lasers can be used to perform experiments with smaller pulse widths, we also noticed some conclusions that were not obtained by calculation alone before."
The Xi'an Institute of Optics and Precision Mechanics developed a femtosecond (one thousandth of a picosecond) laser in the mid-90s, but its peak power could not meet the requirements of industrial production, so it was not selected as the light source by Chang Haonan.
However, it is enough for materials research.
"According to the ablation threshold model, when the laser irradiates the surface of a metal material, due to the small specific heat capacity of the electrons in the metal and the violent inverse bremsstrahlung radiation, the electrons absorb a large amount of laser energy in a very short period of time, the electron activity increases instantly, and through collisions between the electrons, the Fermi-Dirac distribution appears."
"At this time, because the temperature of the free electrons is much higher than that of the lattice, the temperature of the lattice gradually rises by colliding with the hot electrons to obtain heat, and finally reaches a thermal equilibrium state. The specific collision time required to reach the thermal equilibrium state is mainly determined by the electron-phonon collision relaxation time, but for most metal materials, it is around 10 picoseconds."
"But now we have found that below 10 picoseconds, the action process can be further divided into three more detailed processes."
Theory and experiment always complement each other.
Before Chang Haonan proposed the ablation threshold model, this femtosecond laser did not show particularly significant scientific research value in the first few years of its birth.
Without this laser for experimentation, the pace of improving the ablation threshold model would be greatly slowed down.
After a brief pause, Chang Haonan switched to a new page of PPT and continued:
"Ten femtoseconds after the high-energy laser is irradiated on the surface of the metal material, stimulated ionization of electrons will be induced. If the irradiation time is extended to 10 femtoseconds, electron-phonon coupling will begin to occur, but at this time there will be no visible thermal effect."
"If we extend it further to 1 picosecond, the electron lattice thermal equilibrium process will begin. At this time, the thermal effect has gradually begun to appear, but the number of molecules affected is far less than the number of molecules directly converted to the plasma state, and can basically be ignored..."
"Thanks to this discovery, I revised the ablation threshold model again, adding two variable parameters related to the non-thermal melting process. The differential expression after solving it by the implicit method is..."
When Chang Haonan introduced the new progress, the atmosphere in the conference room was generally calm.
Apart from Academician Hou who frequently took the initiative to communicate, only one or two people would occasionally raise their hands to ask questions.
Firstly, these sub-picosecond studies are more concerned with future war needs and do not have much impact on the current picosecond project.
Secondly, and more importantly...
There are indeed not many people who can fully understand it.
However, the following part is not so harmonious...
After a short tea break, the two technical teams responsible for controlling signal transmission and light source control started arguing.
The main problem is that this device is so awkward.
Han Zhigao, the head of the light source control team, first expressed his opinion:
"Mr. Chang, after the last meeting, we built a simple prototype for testing. So far, we have found at least eight major factors that affect laser processing."
"In addition to the beam quality and pulse width that we have already thought of, there are also flux density, polarization state and defocus. Here it refers to the defocus itself. That is to say, even if the energy acting on the material surface is the same, different defocus will produce different processing effects..."
The general meaning of this statement is:
The control requirements for this processing method are extremely sophisticated. The signal transmission process must meet the requirements of low latency, low noise, high bandwidth and high stability. In addition, due to the high complexity of the equipment itself, the outward radiated electromagnetic signals must also be controlled at an extremely low level.
Huo Penghua, who is in charge of the signal transmission team, said that you must be dreaming. The two low-loss conversions between optical and electrical signals alone are enough to give you a headache. How can there be such a good thing that can meet so many of your requirements, especially the requirement of low electromagnetic radiation, which itself conflicts with high bandwidth. Unless a shielding layer with extremely ridiculous thickness and weight is added, it is impossible to achieve.
What’s more troublesome is that in order to compensate for the signal delay at the acquisition end and the control end, a technology called “real time delay line” needs to be introduced. However, the compensation ability of this thing is related to the physical length, which can be tens or hundreds of meters, which will have an adverse effect on transmission delay and loss…
Chang Haonan looked at Academician Hou, who said that the problems mentioned by both of them exist objectively and it is indeed difficult to satisfy them all at the same time.
So the situation remained at a stalemate.
