Chapter 881 Trouble at the Signal Transmission Level
Although the Yun-9 at this time has no blood relationship with any other model, the overall design of a military transport aircraft does not actually have many tricks. .
In particular, superior units and user levels have now given very clear technical indicator requirements.
Not to mention anything else, just the "cargo compartment cross-sectional area is not less than 85% of the IL-76" plus "turbofan power" do not leave much room for manipulation at the design level.
Turboprop-powered transport aircraft can also tolerate some weird designs due to their slow flight speed.
But for jet transport aircraft whose cruising speeds are generally above 600km/h, their overall aerodynamic characteristics are highly homogeneous.
All-metal semi-monocoque structure, cantilevered upper monoplane with swept back angle and T-shaped tail, hanging engine...
In general, it is a plane with reduced height and length. Shortened, but the width remains roughly the same as the IL-76.
In other words, it is a C17 that has been reduced in all aspects.
There is little room for opportunism through ingenuity.
It's basically just hard work.
The key to the success or failure of a model lies in the design at the structural level and the addition and improvement of some details.
Radical air-blowing lift technology, for example, is too risky for a tactical twin-engine aircraft and is a design that outweighs the gain and loss.
As for the winglets, Huaxia already has a lot of experience with past models, so it’s worth a try.
In addition, tactical transport aircraft have the need to take off and land on non-paved runways, so special attention needs to be paid to the design of the engine's anti-foreign object and landing gear structure. Fortunately, even the larger IL-76 With the ability in this area, it’s not like you’re blind...
In short, almost on the way back to Nanzheng from the capital, Liang Shaoxiu had already roughly conceived the overall appearance of this plan.
What Ding Gaoheng said before was very clear.
"Take the lead with Qinfei Group".
That is to say, we can also get support from other brother units in the aviation industry system.
Actually, this is normal.
An 80-90 ton aircraft may not sound big, but for China Aviation Industry, it is still a blank slate.
We must concentrate our efforts on tackling key problems.
However, that is all after the official establishment of the project.
The top priority is to turn Yun 9 from a demand 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 pre-research work...
...
On the other side, Chang Haonan did not know at this time that Ding Gaoheng had already arranged the research and development work of Yun-9.
He is working hard to perfect the ultra-short laser processing technology as soon as possible...
Still in the conference room of the Aerospace Power Group.
Another lively project seminar is underway.
The reason why I say "again" is because since the project was officially approved last month, similar plots have been staged here almost every few days.
First, Chang Haonan routinely demonstrated the progress at the theoretical level, and then several leaders in charge of hardware research and development began to argue.
The situation today... is similar.
As usual, Chang Haonan was the first to speak:
"Last week, Academician Hou's team has used femtosecond-level pulse lasers to verify the ablation threshold model I proposed before."
"Moreover, thanks to the femtosecond laser, pulses with smaller step sizes can be used. Through extensive experiments, we also noticed some conclusions that had not been reached by calculation alone.”
The Xi’an Institute of Optics and Mechanics developed a femtosecond (one-thousandth of a picosecond) laser in the mid-1990s. However, the peak power could not meet the needs of industrial production, so it was not selected as a light source by Chang Haonan.
But it is enough to just conduct material science research.
“According to the ablation threshold model, when 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 the collision between electrons, a Fermi-Dirac distribution appears. ”
"At this time, since the temperature of the free electrons is much higher than the temperature of the crystal lattice, the temperature of the crystal lattice gradually rises by obtaining heat through collision with hot electrons, and finally reaches a thermal equilibrium state. The specific collisions required to achieve a thermal equilibrium state The time is mainly determined by the electron-phonon collision relaxation time, but for most metallic materials, it is on the order of 10 picoseconds. "
"But now we find that below 10 picoseconds, It can be further divided into three more detailed processes. "
Theory and experiment are always complementary to each other.
Before Chang Haonan proposed the ablation threshold model, this femtosecond laser did not show particularly considerable scientific research value in the first few years of its birth.
Without this laser for testing, the improvement of the ablation threshold model will be greatly slowed down.
After a slight pause, Chang Haonan switched to a page of PPT, and then continued:
“10 femtoseconds after the high-energy laser irradiates the surface of the metal material, it will cause stimulated ionization of electrons, and it will continue to prolong. When the irradiation time reaches 100 femtoseconds, electron-phonon coupling will begin, but no visible thermal effect will be shown at this time."
"If it continues to be extended to 1 picosecond, electrons will begin to couple. During the lattice thermal equilibrium process, the thermal effect at this time has gradually begun to appear, but the number of affected molecules is far lower than the number of molecules directly converted to the plasma state, which is basically negligible..."
"Thanks to this Xiang found that I revised the ablation threshold model again and added two variable parameters related to the non-thermal melting process. The differential expression after solving through the implicit method is..."
In Chang Hao When Nan introduced new developments, the atmosphere in the conference room was generally calm.
In addition to Academician Hou's frequent active exchanges, one or two people would occasionally raise their hands to ask questions.
First of all, these sub-picosecond level studies are more considering the needs of the future and will not have a great impact on the current picosecond level project.
Secondly, and more importantly...
There are indeed not many people who can fully understand it.
However, the next part is not so harmonious...
After a short tea break, the two technical teams responsible for controlling signal transmission and light source control started fighting.
Mainly because this device is so awkward.
Han Zhigao, the head of the light source control team, first stated:
“Mr. Chang, after the last meeting, we built a simple prototype for testing. So far, we have discovered There are at least 8 main factors that affect laser processing. "
"In addition to beam quality and pulse width, which we have thought of before, there are also luminous flux density, polarization state and defocus, here refers to the defocus. The amount of focus itself, that is to say, even if the energy ultimately acting on the material surface is the same, different amounts of defocus will produce different processing effects..."
The general meaning of these words is one:
The control requirements of this processing method are extremely precise. The signal transmission process must meet low delay, low noise, high bandwidth and high stability. In addition, due to the high complexity of the equipment itself, Therefore, it is necessary to control the electromagnetic signals radiated outward to an extremely low level.
Huo Penghua, the head of the signal transmission team, said that you may not be dreaming. Just two low-loss conversions between optical signals and electrical signals are enough to cause a headache. How can it be so good? Things that can meet so many of your requirements, especially the requirement of low electromagnetic radiation, itself conflicts with high bandwidth. Unless a layer of shielding layer with an outrageous thickness and weight is added, it is simply impossible to achieve.
What’s more troublesome is that in order to compensate for signal delay between the acquisition end and the control end, a technology called “real time delay line” needs to be introduced, and the compensation ability of this thing is related to the physical length. It can easily be tens or hundreds of meters, which will have adverse effects on transmission delay and loss...
Chang Haonan looked at Academician Hou, who said that the problems they mentioned exist objectively and are indeed very difficult. Satisfied at the same time.
So, the situation became deadlocked.
(End of this chapter)