The military-industrial scientific research system of the academic master

at the same time.

USA, New York State.

Carlspan University at Buffalo Research Center.

Although it was almost late at night, a large semi-open building located in the northwest corner of the research center was still brightly lit.

More than a dozen technicians from Boeing and the Air Force Research Laboratory are gathering around a large wind tunnel with a total length of nearly 40 meters. Slowly transfer out of the edge-shaped working cavity.

This place, which is completely different from most similar equipment, is the most typical feature of the LENS-1 wind tunnel.

Professor Yuval Diamond, director of the research center, held a document board in his hand and quickly came to Shapur Collinger, the director of the X51A project.

"Doctor, the first round of test results have been analyzed. You sign here first, and then I will take you to the control room next door to extract the data..."

After hearing this, Collinger turned around, briefly glanced at the top line, and then signed his name with a few strokes at the end——

This document only confirmed the successful completion of the test work and did not involve the confirmation of any specific data. He had been working with the Buffalo Research Center for many years and was very familiar with this process.

"Let's go..."

After signing, Collinger motioned to his deputy Charlie Brinker, who was not far away, to temporarily take charge of the on-site command. Then he followed Diamond toward the outside of the testing workshop and carefully put the pen back into his jacket pocket.

As we all know, in a research group, only the person in charge has the right to have his or her own pen.

Others' will be converted into public assets within a short period of time.

When the two were approaching the door, Collinger's eyes suddenly looked to the other side of the workshop.

There is another wind tunnel that is significantly larger in scale, but the back of the nozzle is surrounded by tooling racks and railings. It is obviously in a state that cannot be used normally:

"Yuval, when will your LENS-2 wind tunnel be upgraded?"

Diamond, who was walking slightly ahead, paused, with a hint of embarrassment in his tone:

"Uh... The test results of the expansion tube sample provided by Dublin are somewhat inconsistent with the design parameters, so it is expected to be postponed to the second or third quarter of 2008... In addition, this wind tunnel is in After the upgrade, it should be called LENS-X..."

Although construction delays are not uncommon these days, it is not a shameful thing to mention it so bluntly.

After that, perhaps in order to change the subject, he did not wait for Collinger to continue asking, but came to preemptively strike on the spot:

"But Shapur... why are you asking this suddenly?"

"What I mean is...both LENS-2 and the modified LENS-X are mainly oriented towards research at medium Mach numbers, and are not in line with your project requirements."

The construction of LENS-1 at that time was not for aerodynamic research, but to meet the aerothermal and aero-optical evaluation of the kinetic energy interceptor of the anti-missile system. Since it mainly simulated the environment of outer space above 100km, and the KKV used as the test object was small in size , so the test interval is relatively narrow and can only accommodate scaled models.

For this reason, the Buffalo Research Center later built LENS-2, which has lower parameters on paper, but larger volume and longer effective simulation time. The two were built in the same test workshop and even shared the main compressor. Machines, ballast gas tanks, data acquisition systems and other auxiliary equipment, focusing on full-scale simulations in the range of Mach number Ma=2.5~6.

The target flight speed of the X51A project is above Mach 5.5. Although LENS-2 can also reach a test range of about 1000K total temperature at Mach 6, it has deviated far from the optimal working range.

"Is this..."

Collinger said as he took off his helmet and goggles, revealing a head of gray but thick hair that did not match his age, attracting a burst of envy from the other party:

"I want to further test the compression ability of the two-stage variable shock angle kissing cone waverider configuration on high-enthalpy incoming flow in the Mach number range of 4.5 to 5.5..."

He gave an answer that sounded very clear at first glance, but was actually somewhat ambiguous.

Because there are many kinds of needs that fit this description.

However, since Diamond can be the top responsible person in the Buffalo Center where elites gather, he is naturally not an ordinary person. After thinking about it for a while, he guessed:

"Mach 4.5 to 5.5...incoming flow compression...are you worried about the stability of Pratt \u0026 Whitney's engine?"

This issue involves the selection of core suppliers, which is actually somewhat sensitive.

For a project like X51A that covers a wide range of fields, technology is only one aspect, and the issue of dividing the cake must also be considered.

Therefore, even as the R\u0026D director, Collinger must be cautious enough about his statements involving suppliers.

But considering that the two had known each other for more than twenty years, Diamond still asked.

As expected, Collinger shook his head:

"That's not true."

Perhaps he felt that simple denial was not convincing enough, so he emphasized it again:

"It's really not true... I have seen the test process and results of SJX61-1, and they are completely consistent with the design parameters. What's more, we have had some experience with X43A before, so there is nothing to worry about..."

In fact, Collinger did not tell lies.

What he is really worried about is not the scramjet engine itself, but how much inflow compression potential the combination of the rocket booster, the waverider kissing cone precursor, and the binary inlet can provide -

Due to temporary changes in the design plan midway, the volume and weight of the current X51A have increased compared to the original plan. Although by using new solid propellants, theoretically the weight-increased flying body can fully meet the expectations of SJX61-1 However, as the project leader, Collingie still hopes to have a clearer understanding of the performance boundaries of the entire system and be aware of it.

However, the whole matter involved some non-compliant operations such as temporary replacement of Party B, so Collinge could not explain it clearly.

The result actually triggered the principle of "only what is officially denied can be trusted", which led Diamond to become even more convinced of his judgment just now...

He showed an expression that said, "You don't have to say anything, I understand." He patted Collinger on the shoulder:

"Before this test, I saw your design documents. Didn't you already leave a 13.5% margin...could there still be problems?"

According to Boeing's habits, 13.5% is already considered a considerable design margin.

To some extent, it also reflects their lack of sufficient confidence at the theoretical level.

Check out the 16-9 book bar and see the correct version!

"I hope so..."

Collinger showed a noncommittal expression and sighed slightly.

In fact, the reason why he was so worried was largely because of the margin that was too generous compared to usual.

There are already too many variables in the X51A project. Although sufficient design margin itself can reduce risks, if human factors are also taken into consideration, lack of clear understanding of performance boundaries will inevitably lead to slack in a certain link. heart.

If it's just small increments, the 13.5% margin may be manageable.

But as time goes by, the situation becomes difficult to say...

…

The two finally ended this difficult topic and quickly arrived at the wind tunnel control room upstairs.

LENS is a shock wave wind tunnel that uses heated light gas as power and reflection operation. The safety risk is far less than the explosion shock wind tunnel that requires mixing hydrogen and oxygen before igniting. Therefore, there is no need to separate personnel with high walls or even armor plates. open.

The staff had already exported the test results to PDF files and presented them on a laptop.

"I have to say that your two-stage series waverider configuration has quite good adaptability. It can maintain a lift-to-drag ratio of at least 2.93 within the range of angle of attack 0-3° and Mach number 6-8. The optimal design point is even more It can reach 3.47, and the aerodynamic performance is one level better than the previous X43A..."

"..."

As an outstanding engineer of the old Boeing Zhenglan Banner, Kelingjie was an old comrade who had participated in various technical verification projects including X43A. Naturally, he had no say in terms of ability, and he did not have any emotional fluctuations because of Diamond's praise. It was just Silently scrolling the mouse wheel backwards.

After a while, he finally looked away from the computer screen.

"I remember that the maximum total temperature of LENS-1 when driven by helium was 2700K. Why does this result when considering aerodynamic heating reach the level of 6300K?"

he asked with a serious look on his face.

"Strictly speaking, 6300K is the equivalent total air flow temperature..."

Diamond shrugged:

"We previously discovered that if the test gas is heated twice by shock waves and reaches a stagnation state, it may cause part of the gas to dissociate, or cause the free flow to reach non-equilibrium. This state cannot directly measure the total temperature of the air flow, but it can By indirectly deriving an equivalent temperature through parameters such as Mach number and Reynolds number, and then checking it with the data obtained during the past few test flights, we can basically ensure that the reduction degree reaches more than 90%. "

If Chang Haonan or Jiang Zonglin could hear these words across the Pacific Ocean, they would immediately realize that the Buffalo Research Center has fallen into the "flow state simulation trap", that is, using traditional wind tunnel ideas to design superb In sonic wind tunnels, the faster the test speed is, the greater the deviation between the obtained aircraft stagnation heat flow transfer law and the actual situation.

This is a problem that Mr. Guo Yonghuai pointed out as early as the 1960s, but engineering technology is sometimes like this. A seemingly inconspicuous point, if no one points it out, may even affect the next ten or even decades. development direction.

Therefore, although Collinger also felt that this method was not perfect, he could not come up with any better plan for a while.

In any case, having a measured parameter is more reliable than simply relying on numerical calculations and simulations...