Chapter 881 Troubles in Signal Transmission

Although the Y-9 has no blood relationship with any other models at this time, military transport aircraft cannot be designed with many tricks in terms of overall design.

In particular, the superior units and users have given very clear technical indicators.

Apart from other things, the two requirements of "the cross-sectional area of ​​the cargo compartment is not less than 85% of that of the Il-76" and "turbofan power" do not leave much room for operation at the design level.

Turboprop-powered transport aircraft can still allow some strange designs due to their slow flight speed.

But for jet transport aircraft with a cruising speed of more than 600km/h, their overall aerodynamic characteristics are highly homogenized.

All-metal semi-monocoque structure, cantilevered upper wing with swept angle and T-tail, hanging 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 that the C17 is reduced in all directions.

There is little room for tricks by ingenuity.

It's basically a competition of hard work.

The key to the success of a model lies in the design of the structural level and the supplementation and improvement of some details.

For example, the radical air-blown lift technology is too risky for a tactical twin-engine aircraft and is a design that does not make up for the gains.

As for winglets, China has had relatively rich experience in past models, so it is worth a try.

In addition, tactical transport aircraft have the 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, Liang Shaoxiu had roughly conceived the overall appearance of this plan almost on the way back to Nanzheng from Beijing.

What Ding Gaoheng said before was very clear.

"Led by Qinfei Group".

That is to say, it can also get support from other brother units in the aviation industry system.

In fact, this is normal.

An aircraft with a volume of 80-90 tons may not be big, but it is still a blank for China's aviation industry.

We must concentrate our efforts on tackling the problem.

However, that is something that will happen after the project is officially launched.

The most urgent task is to turn 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 R&D forces of Qinfei Group and start deploying pre-research work...

On the other hand, Chang Haonan didn't know that Ding Gaoheng had already arranged the R&D work of Y-9.

He was having a headache trying to improve the ultra-short laser processing technology as soon 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 that since the project was officially launched 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 R&D began to argue.

And today's situation...

is similar.

As usual, Chang Haonan was the first speaker:

"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 use smaller pulse widths for experiments, we have also noticed some conclusions that were not obtained by calculation alone before."

The Xi'an Institute of Optics and Precision Mechanics developed femtosecond (one thousandth of a picosecond) lasers in the mid-1990s, but the peak power could not meet the needs of industrial production, so it was not selected as a light source by Chang Haonan.

But if it is just for materials research, it is still enough.

"According to the ablation threshold model, when the laser is irradiated on 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 time, the electron activity increases instantly, and the Fermi-Dirac distribution appears through collisions between electrons."

"At this time, since the temperature of the free electrons is much higher than the temperature 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, it can be further divided into three more detailed action processes."

Theory and experiment are always complementary.

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.

And if there is no experiment with this laser, the improvement speed of the ablation threshold model will be greatly slowed down.

After a brief pause, Chang Haonan switched to a new page of PPT and continued:

"10 femtoseconds after the high-energy laser irradiates the surface of the metal material, it will cause stimulated ionization of electrons. If the irradiation time is extended to 100 femtoseconds, electron-phonon coupling will begin to occur, but at this time there will be no visible thermal effect."

"Continue to extend it to 1 picosecond, and the electronic lattice thermal equilibrium process will begin. At this time, the thermal effect 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, and can basically be ignored. …”

"Thanks to this discovery, 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..."

When Chang Haonan 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 based on the needs of the future and will not have a great impact on the current picosecond-level project.

Secondly, and more importantly...

There are really 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, head of the light source control team, first expressed his position:

"Mr. Chang, after the last meeting, we built a simple prototype for testing. So far, we have discovered at least 8 major 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 amount. This refers to the defocus amount itself. That is to say, even if the energy ultimately acting on the material surface is the same, different The amount of defocus will also produce different processing effects..."

The general meaning of the words is this:

The control requirements for this processing method are extremely precise. The signal transmission process must meet low latency, low noise, high bandwidth and high stability. In addition, because the equipment itself is highly complex, the electromagnetic signals radiated outwards must be controlled at extremely low levels. level.

Huo Penghua, the head of the signal transmission team, said that you are probably not dreaming. Just two low-loss conversions between optical signals and electrical signals are enough to cause a headache. How can something so good can satisfy you so much? The requirements, especially the requirement of low electromagnetic radiation, are in conflict 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 even 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. The compensation ability of this thing is related to the physical length, which can easily be dozens or hundreds. meters, which will have an adverse impact on transmission delay and loss...

Chang Haonan looked at Academician Hou, who said that the problems they mentioned existed objectively, and it was indeed difficult to satisfy them at the same time.

So, the situation became deadlocked.