Máy bay phản lực quân sự

Động tác corbra của cậu Tuat Huyphuc81_nb mô tả ở phần trước hoá ra là tạo phụ tải +3G (theo phi công thử nghiệm) chứ không có tạo ra G âm
Không biết động tác Corbra âm siêu tốc nào nữa ? Chú Tuat Huyphuc81_nb có thể cho link không?
The Cobra
We discussed the Cobra in our flight brief. It went something like this:
Me: "I would like you to show me the Cobra maneuver."
Kvochur: "Yes, sure."
Me: "What entry airspeed and altitude should we use?"
Kvochur extended the fingers of both hands in a calming gesture and said: "I show you."
That was it. I looked toward our interpreter for a read on this physical punctuation, but she returned the internationally universal shoulder shrug. So I took his brevity as an admonition against prying too much into this top-secret aerobatic phenomenon and made a mental note to be prepared to absorb as much technical data as I could during his demo.
When I was ready for the demo, he had me turn off the angle of attack limiter and another fly-by-wire switch that was never explained completely to me. Then he said, "I do one. We do one. You do one." The setup was 350 kilometers per hour (approximately 190 knots) in straight and level flight. He pulled the stick all the way back, and the airplane pitched nose up past vertical. In a little more than one second, we were more than 90 degrees nose up after the stick pull. He recovered the plane back to straight and level, and the maneuver was complete. The speed was about 90 knots as the nose approached the horizon. During the "We do one," I was again surprised at the non-aggressive control inputs. He used large pedal displacements during the first half of the pitch-up then transitioned to differential throttle control to keep the roll and yaw minimized. For the nose-down recovery, the stick was moved well forward but not all the way. Differential throttle that gave way to rudder-pedal activity essentially kept us wings-level throughout. My turn: I replicated what I had just ridden through, and the results were the same. I didn?Tt get past 90 degrees nose up like Kvochur, but I was awed anyway. Despite the radical attitude change, the entire maneuver was completed under 3G. Throughout this seemingly suicidal contortion, the engines never complained, and there was no implication of an impending loss of control.

http://www.flightjournal.com/fj/articles/su27/su27_5.asp

Học thuyết của Không quân Liên xô ảnh hưởng đến việc thiết kế máy bay của họ.
http://www.fas.org/nuke/guide/russia/industry/docs/strode.htm
Theo nội dung này thì (có lẽ) không phải Liên xô kém không làm được đồ hiện đại mà họ thấy không cần phải làm đến mức ấy.
Liên xô không làm máy bay đa năng như Mỹ (vdụ F-4 làm cả tiêm kích và ném bom) mà thiết kế máy bay theo nhiệm vụ cụ thể (mission-specific: ví dụ Mig-21 cho air superiority).

Các ưu thế của Mig-25 theo phía Nga.
MiG-25 Engines -
Engine control at high Mach is extremely difficult in a design like the MiG-25, let alone a system like the A-12/YF-12/SR-71. The problem is that the engine begins to act like a ramjet at speeds in excess of Mach 2.5 or so, and the turbine''s speed is increasingly dictated by the flow through the propulsion duct rather than by fuel control. In the case of the Blackbird (or Cygnus), the J58 engine bypasses air past the rear stages of the compressor straight into the afterburner duct. This bypass, along with the complex inlet and nacelle bypass door contol system, works to stabilize the flow through the engine. The R-15 lacks the J58''s compressor bypass, and the MiG-25 has only a single inlet duct bypass system. So--without going into gory engineering details--the results are engine speed control problems at high Mach. Engineering analysis aside, you might want to consider the following facts:
The MiG-25 that was clocked at Mach 3.2 by the Israelis achieved this speed while running from an intercepting F-4 (which can barely manage Mach 2 on a good day--before running out of fuel). Upon landing, both engines in the MiG had to be replaced.
Victor Belenko, the Foxbat pilot who defected in 1976, stated that the top speed of the MiG-25 was Mach 2.8, but flight above Mach 2.6 was difficult because of a tendency of the engines to overspeed. Victor related that MiG-25 pilots were in fact restricted to flying below Mach 2.5 except with special permission.
Foxbat g-Limits -
Thomas'' analysis of the Foxbat''s load limits is intersting, but hardly accurate. The Foxbat is only cleared for 4.5g supersonic maneuvers when its fuel is almost depleted. When the internal tanks are more than half full, the load limit is 3g. You might note, Thomas, that the Foxbat did not have to conform to the "tough safety regulations" (implying high design safety factors) because of the performance levels that needed to be attained. You''ll note that Foxbats can''t operate off dirt strips like other MiGs, either.
This said, your assessment that the MiG-25 has no real requirement to pull high g''s at supersonic speeds is probably correct. In a high Mach intercept mission, the MiG-25 should be using its excess thrust for climb, not for turning. The GCI should ensure that the Foxbat is positioned so that it can complete the intercept without violent maneuvers.
You might note that the A-12/YF-12/SR-71 is limited to 45 degrees bank at design speed and altitude. It is also limited to 1.5g under these con***ions. Furthermore, the Blackbird is only cleared up to 400 KEAS at high Mach, a far cry from the (often ignored and exceeded) Foxbat''s 650 KEAS limit. Compared with the SR-71, the MiG-25 is quite agile at speed.
MiG-25 Speed Limit -
Thomas said that the Foxbat can carry its full weapons load to Mach 2.8, while a clean recon version can do Mach 3+. Actually, the recon versions have the same limit as the interceptors: Mach 2.83. This is not a thrust limit. You might note that the RB versions of the Foxbat can carry four bombs(!) to Mach 2.83. The Mach 2.83 is a theoretical stability limit on the airframe (which has been safely exceeded on numerous occasions by test pilots). At speeds greater than Mach 2.6 however, throttle control must be precise to keep the engines from overspeeding.
Western Fighter Comparisons -
Lest you think that I am implying that the Foxbat is not a capable aircraft, especially in performance, you might consider the abilities of Western fighters. The F-16 can just barely squeak past Mach 2.0 with a pair of tip ''winders. The F-14 can only manage Mach 1.81. And the mighty Eagle is only good for Mach 1.78. The Foxbat can outclimb all of these fighters by a healthy margin, and has a mauch better supersonic endurance than the best Western fighter. Furthermore, the Foxbat has demonstrated the ability to outrun all U.S. frontline fighters at _low_ altitude. The Foxbat is hardly a dud.
Gulf War Experience -
Did you know that a MiG-25PD recorded the only Iraqi air-to-air kill of the Gulf War? It dropped an F-18C on the first night of the war--then went on to fire another missile at an A-6 and buzz an A-7, all while avoiding escorting F-14s and F-15s.
An isolated incident? How about the single Iraqi Foxbat-E that eluded eight sweeping F-15s then tangled with two EF-111As, firing three missiles at the Ravens and chasing them off station. Unfortunately, the Ravens were supporting an F-15E strike, and the EF-111''s retreat led to the loss of one of the Strike Eagles to a SAM. Oh BTW, the Foxbat easily avoided interception and returned safely to base.
There''s more. When F-15 pilots were fighting for the chance to fly sweeps east of Baghdad late in the war, itching for a chance to get a shot at an Iraqi running for Iran, they weren''t expecting the fight that a pair of Foxbats put up. Two Foxbats approached a pair of F-15s, fired missiles before the Eagles could get off shots (the missiles were evaded by the Eagles), then outran those two Eagles, four Sparrows and two Sidewinders fired back at them. Two more Eagles maneuvered to cut the Foxbat''s off from their base (four more Eagles tried, but were unable to effect an intercept), and four more Sparrows were expended in vain trying to drop the Foxbats.
The Iraqis had a total of twelve MiG-25PDs at the beginning of the war, of which maybe half were operational at any given time. Imagine what trouble they would have caused if there had been more. The Foxbats, when well flown, proved capable of engaging allied fighters and avoiding them at will. Only the limitations of their weapons proved a problem.

Foxbat''s Effect on Eagle Design-
Dispite the attempts of Riccioni, Spey and Boyd, the F-15 Eagle turned out to be quite a disappointment. Designed as a replacement for the F-4 with a multi-role capability (I bet you thought it was designed strictly for air superiority; wrong!), the design modifications brought on by misconceptions about the Foxbat made the Eagle an expensive, less-than-capable aircraft. (A mistake, IMHO) The Eagle ended up with a range significantly inferior to the F-16. It is slower at high and low altitudes than the Falcon. Its huge radar, thermal and visual signatures negate many of the advantages of its (somewhat unreliable) radar. It has proven expensive to procure, maintain, and support.
We had a counter for the Foxbat: the F-12B. The Eagle should have remained a multi-role aircraft. The Strike Eagle has proven the airframe''s abilities in this role.

http://aeroweb.lucia.it/~agretch/RAFAQ/23vs15.html
I checked with a friend of mine who is a bit of an authority about the Arab-Israeli aerial conflicts. He said that to his knowledge no F-15s were lost, but two were hit during the 1982 conflict. One F-15 was hit by an IR SAM while egressing at low altitude. The SAM took out one engine and destroyed most of one vertical stab, and the other engine was coming apart when the Eagle landed at a forward base. The other Eagle was hit by an R-3S fired by a MiG-21MF. A section of Eagles were flying a high-altitude CAP when one of them noticed the flash of the missile launch and saw the MiG. A warning was given, but the target F-15 could not maneuver sufficiently to avoid being hit by one of the two missiles fired. The missile destroyed one engine and damaged the other. The Eagle made an emergency landing at a nearby base.

Mig-29 so sánh với F-16
http://aeroweb.lucia.it/~agretch/RAFAQ/Fulcrum&Falcon.html
Su-25 so với A-10
http://aeroweb.lucia.it/~agretch/RAFAQ/Su-25.html
Tu-160 so với B-1
http://aeroweb.lucia.it/~agretch/RAFAQ/Tu-160.html

hôm nay tớ mới quay lại, thường chỉ vào cuối tuần! ví dụ đổ chì vào nước của chú sao mà đắt được[r33)(nhớ xem lại Thermodynamics)]!!! khi đổ 1 nồi chì nóng vào nước:
- chì nguội đi
- thể tích (volume) giảm đi (co lại)
-mật độ tăng lên
phụt 1 khối khí nóng vào khí loãng:
-nhiệt độ của khí nóng giảm đi
-thể tích tăng lên rất nhanh (trước đó bị nén)
-áp suất giảm rất nhanh (như pháo hay bóng bay nổ)
-mật độ theo đó cũng giảm đi.
Đây là kết quả Simulation cho 1 Jet-engine dùng cho tầu lượn, tuy không to như của máy bay khách hay quân sự, nhưng tốc độ phụt ra và nhiệt độ tương đương với máy bay khách:


qua đó thấy temperature giảm nhanh như thế nào, từ gần 1000kelvin xuống còn 315K (khoảng 40°C). Sẽ tiếp về vấn đề "phụt khói"
Được falke_c sửa chữa / chuyển vào 15:26 ngày 17/12/2005

Tiếp tục về chuyện "phụt khói", có vẻ phức tạp hơn anh em ta bàn tán trên này! trước hết 1 chút lý thuyết cơ sở:

quan sát Diagram(tương tự như link của kqndvn) thấy khi máy bay đi qua 1 vùng trời phụt khói nóng ra thì do áp suất cân bằng rất nhanh nên cân bằng nhiệt độ xẩy ra trên đường "isobar"(tự google xem isobar là gì) và như vậy có 3 trường hợp:
- đường này nằm dưới saturation curve(xanh lá cây)--> không có đuôi.
- đường này tangential (đen)hoặc cắt saturation curve 1 ít--> có đuôi, nhưng đuôi tan nhanh.
- đường này cắt hẳn saturation curve (đỏ)-->có đuôi và đuôi không tan.
đó là diễn nôm cho dễ hiểu, các qui trình xẩy ra trên thực tế như sau:
- đươ

chú ý trục thời gian mà tớ đánh dấu: chỉ sau khoảng 1s (giây) là đã đầy băng, mầm đá (condensation nuclei), thêm 1 hình minh hoạ Simulation, bên trái sau 0,56s, và bên phải sau 0,7s:

Simulation sau đuôi 1 chiếc 747:
Tạm thế đã
17/12/2005
Được falke_c sửa chữa / chuyển vào 15:51 ngày 17/12/2005

Mới tìm được cái này trên Encatar
[A vital military gain for combat capabilities of Air Force and Navy equipment came directly from the research laboratory. One of the major problems faced by the Air Force''''s high-flying bombers were the vapor trails (contrails) emitted by its jets, which visually marked the aircraft for many miles. A new process developed by the Cornell Aeronautical Laboratory reduced the production of contrails so markedly that they were invisible to the naked eye on the ground when the airplanes flew at 40,000 to 50,000 ft.
© 1993-2003 Microsoft Corporation. All rights reserved.]
Có bạn nào biết về nghiên cứu này của Cornell không vì bài này của Encatar đến đây là ngưng luôn rùi.
Được vhs79 sửa chữa / chuyển vào 09:58 ngày 19/12/2005

Cảm ơn bác falk_c, em hiểu rồi.
Em quên mất khí gas trong máy điều hòa nhiệt độ Khí áp suất cao bung ra mạnh nên giảm nhiệt nhanh, không phải là trao đổi khí với ngòai trời.
Tuy nhiên việc khẳng định máy bay phải bay qua vùng cận bão hòa mới sinh đuôi thì quá đúng (được 1/2 sự thật)
Bác kqndvn làm khổ cái siêu máy tính quá PC Pen3 chạy tốt cái mô phỏng này bác ạ
Được kien098 sửa chữa / chuyển vào 02:26 ngày 20/12/2005

Bac falk_c đúng là chuyên gia xịn đấy nhỉ !
Xem công thức thấy không có siêu máy tính thì không thể tính toán mô phỏng được.