SDF Aerospace and Aerodynamics Corner

MiG-29 · Dec 31, 2011

Engineer said:
Yet, MiG-21 cannot fly as fast even with a similar intake system. This shows it is not the inlet that determines the performance of the aircraft. What determine the performance are the airframe and engine, both are modified on the Ye-1666.

This does not dispute the fact that with only two shocks, J-10B's DSI in 2005 has better performance than the inlets of F-4D, the latter being variable-geometry generating three shocks.

DSI does not have to change its geometry. It is an advantage, not a disadvantage. In fact, by not having to change geometry, it reduces weight significantly as well as drag. The result is increase in performance over variable-geometry inlets like that on F-4D.

Cowl capture area is the physical size of the mouth of the inlet, and is fixed also in the case of variable-geometry inlets. What variable-geometry inlets do is adjust the position of the oblique shockwaves to position them as close to the intake lip as possible. It does not make the mouth of the inlet wider or narrower.

And variable-geometry inlet like that of F-4D is inferior to DSI, even though the variable-geometry inlet on F-4D is supposed to adapt the intake cowl to different mach number.

Also, in your list of aircraft, F-111 have poor maneuverability compared to F-14 and F-15. SR-71 and XB-70 have worst maneuverability of all. Complex inlet system leads to increase in weight and cancels out advantages gained in any increase of pressure recovery ratio.

Su-35S cannot supercruise at the same speed as F-22, despite employing what you claimed to be more efficient inlet system. This shows performance of an aircraft is based on other factors, and not solely on inlet design.

intake capture are is not fixed Inlet geometry is altered when the spike retracts toward the engine, approximately 1.6 inches per 0.1 Mach. At Mach 3.2, with the spike fully aft, the air-stream-capture area has increased by 112 percent and the throat area has shrunk by 54 percent.

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and J-10B at Mach 3.2 won`t turn better than SR-71 or MiG-31 simply because it never will reach that speed hahahaha and Su-35S can dogfight with tyhe J-10B

J-10B never will go faster than MiG-25, Sr-71 never ever never will be more agile at that speed hahahahahaa

DSI is not for Mach 2.8 or Mach 3.2 the WS-10 will turn off and fail before that speed hahaha

Engineer · Dec 31, 2011

MiG-29 said:
hahaha

Ye-166, Sr-71 and MiG-21 have the same type of variable geometry intake just optimised to different cowl intake mach number

hahaha you can not admit your knowledge is wrong haha

So why can't MiG-21 fly at Mach 3? By your argument, if all these aircraft employ the same inlet design, they should have the same performance. The fact that MiG-21 flies slower shows despite using the same intake design shows that airframe design and engine choice affect the performance of the aircraft.

This is the reality: your claims are wrong, and your incoherent argument betrays your desperate attempt at denial.

MiG-29 · Dec 31, 2011

Engineer said:
So why can't MiG-21 fly at Mach 3? By your argument, if all these aircraft employ the same inlet design, they should have the same performance. The fact that MiG-21 flies slower shows despite using the same intake design shows that airframe design and engine choice affect the performance of the aircraft.

This is the reality: your claims are wrong, and your incoherent argument betrays your desperate attempt at denial.

they are the same type of intake read the link and they are just optimized for different speeds and different type of engines one is a turbojet MiG-21 while the Sr-71 has tuboram

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Engineer · Dec 31, 2011

MiG-29 said:
intake capture are is not fixed Inlet geometry is altered when the spike retracts toward the engine, approximately 1.6 inches per 0.1 Mach. At Mach 3.2, with the spike fully aft, the air-stream-capture area has increased by 112 percent and the throat area has shrunk by 54 percent.

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Wrong! Just like your equating of optimal speed with top-speed, this is where your unfamiliarity with terminology result in your wrong claims. Air-stream-capture-area is an imaginary area bounding the streamtube far away in front of the inlet, and it does not corresponds to the physical capture area of the inlet. Note the incorporation of "air-stream" as oppose to merely "capture-area".

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Preliminary calculation of aerodynamic said:
Ac: streamtube cross section at the inlet, also called inlet area or cowl capture area. (With accompany figures.)

Once again, the mechanical movement within a variable-geometry inlet has to do with positioning of the oblique shockwaves as close to the intake lip as possible. It is not a valve that changes the amount of flow into the inlet.

Engineer · Dec 31, 2011

MiG-29 said:
and J-10B at Mach 3.2 won`t turn better than SR-71 or MiG-31 simply because it never will reach that speed

Neither can MiG-21, F-4D, F-14, F-15, Su-27 family, etc. reach that speed.

These aircraft use variable-geometry inlets, right? If by your argument, that an aircraft cannot reach Mach 3 means the aircraft's inlets are inferior, then variable-geometry inlets are inferior. In other words, you contradict yourself.

MiG-31 has horrible maneuverability, and SR-71 completely lacks maneuverability. These two aircraft doesn't jump from 0 to Mach 3, they can also fly at low subsonic speed. Yet, even at this speed, they turn like airliners. This illustrates my point quite clearly: the more complex the intake, the heavier the aircraft, and the increase in weight cancels out advantages gained by increasing pressure recovery ratio.

MiG-29 said:
hahahaha and Su-35S can dogfight with tyhe J-10B

J-10B can dogfight with Su-35S despite the latter use of variable-geometry inlets. What does this say? It says J-10B is just as good. In fact, J-10B's DSI has better pressure recovery ratio than F-4D's inlets at dogfight speed. What does this say? It says your claim that DSI being inferior is wrong.

MiG-29 said:
J-10B never will go faster than MiG-25, Sr-71 never ever never will be more agile at that speed hahahahahaa

DSI is not for Mach 2.8 or Mach 3.2 the WS-10 will turn off and fail before that speed hahaha

Neither can MiG-21, F-4D, F-14, F-15, Su-27 family, etc. fly at that speed. This shows your claim that variable-geometry inlet automatically makes an aircraft to have better performance as false.

Whether J-10B can fly at Mach 3 is irrelevant. Aircraft that flies at Mach 3 are not fighter aircraft. The important point is that with DSI, J-10B performs just as well as aircraft that utilizes variable-geometry inlets, and in some cases even better.

MiG-29 · Dec 31, 2011

Engineer said:
Wrong! Just like your equating of optimal speed with top-speed, this is where your unfamiliarity with terminology result in your wrong claims. Air-stream-capture-area is an imaginary area bounding the streamtube far away in front of the inlet, and it does not corresponds to the physical capture area of the inlet. Note the incorporation of "air-stream" as oppose to merely "capture-area".

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Once again, the mechanical movement within a variable-geometry inlet has to do with positioning of the oblique shockwaves as close to the intake lip as possible. It is not a valve that changes the amount of flow into the inlet.

hahaha the intake has moved aft, the increase in area has happened, in fact look at the F-14 intake at max supersonic it is

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at subsonic speed

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on Sr-71 happens the same

Engineer · Dec 31, 2011

MiG-29 said:
they are the same type of intake read the link and they are just optimized for different speeds and different type of engines one is a turbojet MiG-21 while the Sr-71 has tuboram

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Exactly! They use the same type of inlet, but have different top-speed. This means it is not inlet design, but factors such as airframe design and capability of engine determine the performance of the aircraft.

Engineer · Dec 31, 2011

MiG-29 said:
hahaha the intake has moved aft, the increase in area has happened, in fact look at the F-14 intake at max supersonic it is

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at subsonic speed

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on Sr-71 happens the same

Throat area is not capture area. Your use of "area" instead of "capture area" shows you are now trying to mislead.

The diagram clearly shows cowl-capture-area as unchanged. What is cowl-capture-area? It is the physical area of the mouth of the inlet. The diagram also shows the purpose of the ramps is to position the shockwaves as close to the inlet lip as possible, just like what I have said.

In any case, F-14 is unable to reach Mach 3, unlike SR-71. This says inlet design alone does not determine the speed of the aircraft. The diagram also does not dispute the fact that DSI can operate at Mach 2.0.

Engineer · Dec 31, 2011

MiG-29 said:
mass flow moves the shock position, so a shock plane has to be optimised for a cruise speed other wise if you want to cruise at Mach 3 but you have a bump optimized for a shock plane for Mach 1 and different mass flow, you won`t achieve the same pressure recovery.

These are physical facts, that is the reason the DSI at Mach 2 drops to 0.87 while a F-14 or SR-71 can achieve higher pressure recovery

Actually, the physical fact is that F-14's pressure recovery ratio also drops greatly from 0.99 at Mach 0.6 to 0.92 at Mach 2.0. The drop which you pointed out for DSI is a phenomenon also found on variable-geometry intakes (F-4D, F-111, F-14, F-15, F-104, F-105) and fixed inlet (F-16). The reason being is that all intakes, variable-geometry or not, are optimized for a certain airspeed.

It is obvious from the graph that variable-geometry intakes do not have constant pressure recovery ratio throughout their entire operation regime. Thus, variable-geometry intakes designed to operate best at transonic speed will have their pressure recovery drops so low as to not function at higher Mach number.

MiG-29 · Dec 31, 2011

Engineer said:
Throat area is not capture area. Your use of "area" instead of "capture area" shows you are now trying to mislead.

The diagram clearly shows cowl-capture-area as unchanged. What is cowl-capture-area? It is the physical area of the mouth of the inlet. The diagram also shows the purpose of the ramps is to position the shockwaves as close to the inlet lip as possible, just like what I have said.

In any case, F-14 is unable to reach Mach 3, unlike SR-71. This says inlet design alone does not determine the speed of the aircraft. The diagram also does not dispute the fact that DSI can operate at Mach 2.0.

no i am not trying to mislead anyone because the throat area is reduced thus the capture area is reduced too

The intakes are of multi-ramp wedge configuration and offer a straight path for the air entering the engines. Each intake has a pair of adjustable ramps attached to the upper part of the inner intake. Hydraulic actuators in the upper part of the intake adjust the positions of the first and second ramps in the upper surface of the inlet and of the diffuser ramp located further aft, reducing the inlet air to subsonic velocity before admitting it to the engine. A gap between the back edge of the second ramp and the leading edge of the diffuser ramp allows bleed air to escape from the inlet, passing overboard via a bleed-air door in the outer surface of the inlet. The inlet ramps are under the automatic control of a computer, which calculates the optimal position for the ramps based on engine speed, air temperature, air pressure, and angle of attack. At supersonic speeds, the hinged panels narrow down the throat area while diverting the excess airflow out of the ducts through aft-facing spill doors at the top of the intakes. At low speeds (especially during takeoff) when more engine air is needed, this airflow is reversed and extra air is sucked in via the spill doors

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Why open at low speed the throat area? why reduce the throat area at high speed and bypass the extra mass flow?

11. At higher supersonic speeds, the pitot type of air intake is unsuitable due to the severity of theshockwave that forms and progressively reduces theintake efficiency as speed increases. Amore suitabletype of intake for these higher speeds is known asthe external/internal compression intake (fig. 23-8). This type of intake produces a series of mild shockwaves without excessively reducing the intake efficiency.12. As aircraft speed increases still further, so also does the intake compression ratio and, at high Mach numbers, it is necessary to have an air intake that has a variable throat area and spill valves to accommodate and control the changing volumes of air (fig. 23-9).The airflow velocities encountered in the higher speedrange of the aircraft are much higher than the enginecan efficiently use; therefore, the air velocity must be decreased between the intake and the engine air inlet.The angle of the variable throat area intake automatically varies with aircraft speed and positions the shockwave to decrease the air velocity at the engine inlet and maintain maximum pressure recovery within the inlet duct. However, continued development enablesthis to be achieved by careful design of the intake andducting. This, coupled with auxiliary air doors to permitextra air to be taken in under certain engine operatingconditions, allows the airflow to be controlled withoutthe use of variable geometry intakes. The fuselageintakes shown in fig. 23-10 are of the variable throat area

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