SDF Aerospace and Aerodynamics Corner

Engineer said:

You are shown that your claims are wrong and now you go into denial. The diagram is a generic representation of an intake system, where both fixed and variable-geometry inlet are included. The terminologies used on one type of inlets do not vary when used on another type of inlets.

Note that capture area refers to the physical area within the intake mouth, not the area beneath the ramps. The ability to vary the inlet area can be found on F-15, but not F-14 and Su-35S as you wrongly claimed.



You are wrong in confusing movable cowl on F-15 with ramps. The movable cowl of F-15 is situated on the outside of the inlet and it is what varies the capture area of the inlet. Ramps are positioned inside the inlet, and their purpose is to control the angle of the shock waves.

F-14, aircraft in the Su-27 family, Tu-22 do not have adjustable cowling like F-15.

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see picture F-14 intake is open, and F-14 intake ramp deployed on one you see less of the engine face and in one the whole engine face and the reduced throat

at subsonic speed


your intake drawings are of fixed geometry

F-15 moves the intake cowl at take off and landings to have better AoA at the intake not to reduce throat area in fact does not make sense in that position for landing



cruise flight

MiG-29 said:

i will tell you why your whole argument is wrong first the intake ramp is like a door, at low subsonic the door is open at high supersonic speeds the door is semi closed.

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There is nothing wrong with my argument. What is wrong is your insistence on portraying your opinions as facts, despite being shown you are wrong.

The ramps are there to position the oblique shock waves for maximum efficiency. Your are wrong in equating the ramps as valves. By , flow rate increases when the fluid encounters a decrease in cross sectional area, so as to preserve mass flow.

MiG-29 said:

same is the spike, it is like a plug, on SR-71, the moving of the cone closes or opens the tube like a valve, simple like that they regulate the amount of air by decreasing or increasing the throat area

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Wrong. The role of the intake cone is to position the shock waves.

Engineer said:

The figure is cropped due to the limited vertical resolution of my screen. The full figure has been posted many times already, but if you like, here it is:

The paragraph says the following:


So there you have it: variable-geometry inlet is also designed to operate within an optimal range of speed. From the graphs, we can see this is true, as the pressure recovery curve of variable-geometry inlets has an apex. As Mach number moves away from the optimal speed, pressure recovery ratio decreases.

You claimed that the above phenomenon only occurs on DSI, but this is not the case. Therefore, your argument that DSI is inferior based on drop in pressure recovery ratio doesn't work.

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at what speed Mach 0.3? the low subsonic speed is not used for BVR and max speed, an not for supercruising for sure and dogfight is at mach 0.7-0.9

MiG-29 said:

no my friend it is a fixed intake, the ramp collapses on F-14, the ramps becomes lower angled

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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Click to expand...

The drawing is a generic representation of an intake, including fixed and variable-geometry. The terminologies used in the diagram are applicable on all types of inlets.


The ramps in F-14 are not the same as the adjustable cowl on F-15's inlets. The adjustable cowl is what enabled the control of the capture area. The ramps are there to adjust the position of the shock waves. Likewise, the cone within axis-symmetric intakes has the purpose of positioning the shock wave.

You are again trying to mislead by portraying intake ramps as inlet cowling.

MiG-29 said:

at what speed Mach 0.3? the low subsonic speed is not used for BVR and max speed, an not for supercruising for sure and dogfight is at mach 0.7-0.9

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Irrelevant. This retort has nothing to do with my points. Furthermore, your purposely replaced "low supersonic speed" with "subsonic speed" shows that you are once again trying to mislead.

Variable-geometry inlet has a range of speed in which the inlet works at optimal performance. You claimed that DSI cannot work in all Mach number, and argued it being the reason that DSI is inferior. I have shown you that this argument doesn't work, as variable-geometry inlet also doesn't work in all Mach number.



The paragraph says the following:

Aircraft engine design said:

The improved performance of variable geometry mixed compression inlets and external compression inlets at high Mach numbers comes with some reduced performance at low supersonic Mach numbers due to the increased frictional losses.

Click to expand...

So there you have it: variable-geometry inlet is also designed to operate within an optimal range of speed. From the graphs, we can see this is true, as the pressure recovery curve of variable-geometry inlets has an apex. As Mach number moves away from the optimal speed, pressure recovery ratio decreases.

From


Capture area and throat area are two distinct concepts. Movement of ramps within a variable-geometry inlet results in variation of throat area, not capture area.

From , A1 is the capture area.


To vary capture area, mechanisms like that on F-15 are needed as shown in this . F-14 and Su-35S cannot vary the capture area.

also has the following to say regarding the speed range in which variable-geometry inlets work most optimally.

Aircraft engine design said:

The improved performance of variable geometry mixed compression inlets and external compression inlets at high Mach numbers comes with some reduced performance at low supersonic Mach numbers due to the increased frictional losses.

Click to expand...

So unlike what you are trying to portray, variable-geometry inlet is not absolutely superior, nor can this type of inlet operates at all Mach number. Your argument "DSI cannot function at all Mach number therefore is inferior" does not work.

MiG-29 said:

your intake drawings are of fixed geometry

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That is wrong. The drawings are generic representation of inlet, both fixed and variable-geometry. Furthermore, the terminologies used in the diagram apply on all type of inlets. The diagrams clearly showed capture area and throat area are two distinct concepts. Your equating of the two is nothing more than you inventing definition to mislead people.

MiG-29 said:

F-15 moves the intake cowl at take off and landings to have better AoA at the intake not to reduce throat area in fact does not make sense in that position for landing

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cruise flight

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Click to expand...

This is where you are wrong: capture area is not throat area. The movement of cowling does not affect throat area. It is the ramps movement that affect throat area.

Engineer said:

The drawing is a generic representation of an intake, including fixed and variable-geometry. The terminologies used in the diagram are applicable on all types of inlets.

The ramps in F-14 are not the same as the adjustable cowl on F-15's inlets. The adjustable cowl is what enabled the control of the capture area. The ramps are there to adjust the position of the shock waves. Likewise, the cone within axis-symmetric intakes has the purpose of positioning the shock wave.

You are again trying to mislead by portraying intake ramps as inlet cowling.

Click to expand...

the dawing has a fixed intake, in fact on the F-14 pictures i gave you can see the intake is semiclosed, thoat area is reduced, the F-15 rotates the intake at landings and take off, it can also help to reduce auxiliary intake doors but it is mostly use as AoA handling in the same way Eurofighter lowers the intake lip at landing
F-15 cruise



F-15 take off





Eurofighter at take off



eurofighter cruise

"Repeat a lie a thousand times and it becomes the truth" is apparently your motto. But it doesn't work on somebody who is more logical than you are.

You have been shown that your claims are wrong. You are now repeating your original arguments, showing you are arguing for the sake of arguing. No matter how many times you repeat yourself, your wrong claims are not going to become right.

MiG-29 said:

the dawing has a fixed intake

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This is wrong. Nothing in the drawing specifically said it is a fixed intake. The drawing is a general representation of all types of intake, and the terminologies used in the drawing also applicable on all types of intake. As indicated by the drawings, capture area and throat area are two distinctive concepts.

MiG-29 said:

in fact on the F-14 pictures i gave you can see the intake is semiclosed, thoat area is reduced, the F-15 rotates the intake at landings and take off, it can also help to reduce auxiliary intake doors but it is mostly use as AoA handling in the same way Eurofighter lowers the intake lip at landing[/B]
F-15 cruise

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F-15 take off

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Eurofighter at take off

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eurofighter cruise

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Click to expand...

Wrong. Throat area being reduced does not mean capture area is being reduced. The F-15 has adjustable cowling to affect the capture area, but the F-14, aircraft in Su-27 family, and many other fighter aircraft doesn't have such mechanisms.

The ramps are for adjustment of position of oblique shock waves. They are not valves that limit airflow into the engine. By , air at the throat will simply move faster to compensate for the reduced cross section of that portion of the intake. The amount of air going into the engine is not affected.

In fact, if ramps can regulate the volume of air going into the engine, there would be no need for bypass doors. The presence of bypass doors pretty much tells you that the ramps do not regulate the amount of air going into the engine.

Engineer said:

That is wrong. The drawings are generic representation of inlet, both fixed and variable-geometry. Furthermore, the terminologies used in the diagram apply on all type of inlets. The diagrams clearly showed capture area and throat area are two distinct concepts. Your equating of the two is nothing more than you inventing definition to mislead people.



This is where you are wrong: capture area is not throat area. The movement of cowling does not affect throat area. It is the ramps movement that affect throat area.

Click to expand...

here is a fig of a variable geometry intake