Chapter 1311 Falling into the Trap
New York, USA.
Carl Span 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.
A dozen technicians from Boeing and the Air Force Research Laboratory are gathered around a large wind tunnel with a total length of nearly 40 meters, slowly transferring a wind tunnel model made of chromium-nickel-inconel alloy out of the octagonal working chamber behind the Laval nozzle.
This is the most typical feature of the LENS-1 wind tunnel, which is completely different from most similar equipment.
Professor Yuval Diamond, director of the research center, walked quickly to Shapur Collinger, director of the X51A project, with a file board in his hand.
"Doctor, the results of the first round of tests have been analyzed. Please sign here first, and then I will take you to the control room next door to extract the data..."
After hearing this, Ke Lingjie turned around, glanced at the top line, and signed his name at the end.
This document only confirms that the test work was successfully completed and does not involve the confirmation of any specific data. He has been working with the Buffalo Research Center for many years and is very familiar with this process.
"Let's go..."
After signing, Collinger signaled to his deputy Charlie Brink, who was not far away, to temporarily take charge of the on-site command. Then he followed Diamond out of the test 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 own pen.
Others will be transformed into public assets in a very short time.
When the two were about to reach the door, Ke Lingjie's eyes suddenly looked to the other side of the workshop.
There was another wind tunnel that was significantly larger, but the nozzle was surrounded by tooling racks and railings, and it was obviously not in a normal state:
"Yuval, when will your LENS-2 wind tunnel be upgraded?"
Diamond, who was walking a little ahead, paused and spoke with a hint of embarrassment:
"Uh... the test results of the expansion tube sample provided by Dublin don't match the design parameters, so it is expected to be postponed to the second or third quarter of 08... In addition, this wind tunnel should be called LENS-X after the upgrade..."
Although construction delays are not uncommon these days, it is not a proud thing to be mentioned so bluntly.
After that, perhaps to change the subject, he didn't wait for Ke Lingjie to continue asking, but took the initiative on the spot:
"But Shapur...why do you suddenly ask this?"
"What I mean is... both LENS-2 and the modified LENS-X are mainly aimed at medium Mach number research, which is not in line with your project requirements."
LENS-1 was not built for aerodynamic research, but to meet the aero-thermal and aero-optical evaluation of the kinetic interceptor of the anti-missile system. Since it mainly simulates the environment of outer space above 100km and the KKV used as the test object is very small, the test range is relatively narrow and can only accommodate scaled models.
To this end, the Buffalo Research Center later built LENS-2, which has lower paper parameters but a larger size and longer effective simulation time. The two were built in the same test workshop and even shared auxiliary equipment such as the main compressor, ballast gas tank and data acquisition system, focusing on full-scale simulation in the Mach number range of Ma=2.5~6.
而X51A项目的目标飞行速度在5.5马赫以上，尽管LENS-2也能在6马赫下达到约1000K总温的测试范围，但已经远远偏离了最优化的工作区间。
"Is this..."
As he spoke, Ke Lingjie took off his helmet and goggles, revealing a head of gray but thick hair that did not match his age, which attracted envious glances from the other party:
"I want to further test the compression capability of the two-stage variable shock wave angle tangent cone waverider configuration on high enthalpy incoming flow within the Mach number range of 4.5 to 5.5..."
He gave an answer that seemed very clear at first glance, but was actually somewhat ambiguous.
Because there are many kinds of needs that fit this description.
However, since Diamond could become the top person in the elite Buffalo Center, he must be no ordinary person. After a little thought, he guessed:
"4.5 to 5.5 Mach...flow compression...Are you worried about the stability of Pratt & Whitney's engines?"
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 how to divide the cake must also be considered.
Therefore, even as the head of R&D, Collinger must be cautious in his statements regarding suppliers.
But considering that the two have known each other for more than twenty years, Diamond still asked.
As expected, Ke Lingjie shook his head:
"That's not it."
Perhaps he felt that a simple denial was not convincing enough, so he emphasized it again:
"Really not... I've seen the test process and results of SJX61-1, and they completely match the design parameters. Moreover, we have had some experience with X43A before, so there's nothing to worry about..."
In fact, Collinger did not lie.
What he was really worried about was not the scramjet engine itself, but how much flow compression potential the combination of the rocket booster, the waverider tangent cone forebody, and the dual inlet could provide.
Due to the temporary change of the design plan in the middle, the current X51A's volume and weight have increased compared to the original plan. Although by using new solid propellants, in theory the increased weight of the flying body can meet the expected launch conditions of SJX61-1, but as the project leader, Ke Lingjie still hopes to more clearly understand the performance boundaries of the entire system and have a clear idea of it.
But the whole thing involved some less-than-compliant operations such as the temporary replacement of Party B, so Colin couldn't explain it very clearly.
The result was that the principle of "only official denials are credible" was triggered, which made Diamond more convinced of his previous judgment...
He showed an expression that said, "You don't need to tell me, I understand everything," and patted Ke Lingjie on the shoulder:
"Before this test, I looked at your design documents. Didn't you leave a 13.5% margin? Could there still be a problem?"
According to Boeing's practice, 13.5% is already a considerable design margin.
To some extent, it also reflects their lack of sufficient confidence at the theoretical level.
There is no wrong version in the 6 book forum!
"I hope so..."
Ke Lingjie showed a noncommittal expression and sighed slightly.
In fact, the reason why he had such concerns was largely because the margin was too generous compared to usual times.
There are already too many variables in the X51A project. Although sufficient design margins can reduce risks, if human factors are taken into account at the same time, then in the absence of a clear understanding of performance boundaries, it is inevitable that slackness will occur in some links.
If it's just a small amount of traffic, then the 13.5% margin may be enough to cope with it.
But as time goes by, the situation becomes uncertain...
……
The two finally ended this difficult topic and soon came to the wind tunnel control room upstairs.
LENS is a shock wave wind tunnel that uses heated light gas as its power and operates by reflection. The safety risk is far less than that of a detonation-powered wind tunnel that requires hydrogen and oxygen to be mixed before ignition, so there is no need to use high walls or even armor plates to separate personnel.
The staff had already exported the test results as a PDF file and presented it on a laptop.
"I have to say that your two-stage tandem waverider configuration has excellent adaptability. Within the range of attack angle 0-3° and Mach number 6-8, it can maintain a lift-to-drag ratio of at least 2.93. The optimal design point can even reach 3.47. The aerodynamic performance is a notch higher than the previous X43A..."
"..."
As an outstanding engineer of Boeing Zhenglanqi, Collinger had participated in various technical verification projects including X43A. His abilities were naturally beyond reproach, and he did not show any emotional fluctuations because of Diamond's praise. He just silently rolled the mouse wheel backwards.
After a long while, he finally turned his eyes away from the computer screen.
"I remember that the highest total temperature of LENS-1 when driven by helium was 2700K. Why did the result reach 6300K when aerodynamic heating was considered?"
He asked seriously.
"Strictly speaking, 6300K is the equivalent total airflow temperature..."
Diamond shrugged.
"We have previously discovered that if the test gas is heated twice by shock waves and reaches a stagnant state, it may cause partial gas dissociation or make the free flow non-equilibrium. In this state, the total airflow temperature cannot be directly measured, but an equivalent temperature can be indirectly derived through parameters such as the Mach number and Reynolds number. By verifying it with the data obtained from the past few test flights, it can basically ensure that the restoration degree reaches more than 90%."
If Chang Haonan or Jiang Zongli could hear this sentence across the Pacific Ocean, they would definitely realize at the first moment that the Buffalo Research Center has fallen into the "flow state simulation trap", that is, using the idea of traditional wind tunnel to design a hypersonic wind tunnel, resulting in the faster the test speed, 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 60s, but engineering technology is sometimes like this. A seemingly insignificant point, if no one points it out, may even affect the development direction for the next ten or even dozens of years.
Therefore, although Collinger also felt that this method was not perfect, he could not come up with a better solution at the moment.
In any case, having a measured parameter is always more reliable than simply relying on numerical calculation simulation...
