SDF Aerospace and Aerodynamics Corner

Engineer said:

"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.



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.



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

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, 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.

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hahaha let us see a real variable geometry intake

MiG-29 said:

here is a fig of a variable geometry intake

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Terminologies are invariant with respects to the type of inlet under discussion. "Capture area" still refers to capture area whether you are talking about fixed or variable-geometry inlets. Let alone there is nothing in my drawing which indicates it is only applicable to fixed inlets.

You got proven wrong. Quit complaining.



The image shows capture area is different from throat area, which says your claim as wrong.

MiG-29 said:

hahaha let us see a real variable geometry intake

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It says the exact same thing as the diagram below - that A1 is capture area:


Once again, capture area and throat area are two different concepts. The ramps inside variable-geometry inlets control the angle of oblique shock waves. As a consequent, throat area changes, but this does not mean capture area changes.

You do not fully understand what you are talking about, and you create your own definition for well define terminologies. This is your problem.

Engineer said:

It says the exact same thing as the diagram below - that A1 is capture area:

Once again, capture area and throat area are two different concepts. The ramps inside variable-geometry inlets control the angle of oblique shock waves. As a consequent, throat area changes, but this does not mean capture area changes.

You do not fully understand what you are talking about, and you create your own definition for well define terminologies. This is your problem.

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ah but what about mass flow, see it changes




As the SR-71 increases its speed, the inlet varies its exterior and interior geometry to keep the cone-shaped shock wave and the normal shock wave optimally positioned. 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

MiG-29 said:

ah but what about mass flow, see it changes

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First, this plot doesn't make your argument equating throat area to capture area any less incorrect. The plot shows mass flow performance changes with respects to speed, not change of capture area. Second, control of airflow, specifically the dumping of excess air is achieved using bypass doors. Read what the book has to say about the excess air:

Aircraft engine design said:

The difference between these mass flow rates is air flow that either accepted by the inlet and then bypassed about the engineback to the atmosphere, or spilled about the inlet, or a combination of bypassed and spilled.

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At a given airspeed, the air will travel faster at the throat to compensate for the decrease in throat area. Put it in simpler terms, he ramps don't restrict mass flow because air is compressible and can squeeze through restricted area. This is , and apparently you do not know about this most fundament aerodynamic principle.

MiG-29 said:

As the SR-71 increases its speed, the inlet varies its exterior and interior geometry to keep the cone-shaped shock wave and the normal shock wave optimally positioned. 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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You are still wrong in claiming F-14 and aircraft in Su-27 family vary their capture area with intake ramps. Using bold letters and large font size do not add any strength to your argument, just as yelling in the real world does not add any strength to your argument.

Capture area refers to the area within the inlet mouth, which is represented as A1 in the following diagram from :


Note that A1 is invariant in your very own diagram of two different inlet geometries:


Intake cones and ramps do not do what you imagine they do. Their role is to position the shock waves for optimal inlet performance, not for controlling mass flow. What control mass flow are auxiliary inlets and bypass doors.

The reality is this: F-15 can vary capture area of its inlets. F-14 and aircraft in the Su-27 families have variable-geometry inlets, but the physical capture area is fixed.

Aside from having more ramps to create more shocks, variable-geometry inlets do not achieve anything that DSI cannot achieve. Pressure recovery ratio between DSI of J-10 and inlets on F-4D shows DSI as superior, contrary to your claim that variable-geometry inlet is always superior.

Yes, you can use more ramps to raise pressure recovery ratio further, but that brings in complexity and weight that reduce performance gain. The fact that no Mach 3 aircraft is a fighter and no fighter aircraft flies at Mach 3 speaks volume.

You can spin all you want and repeat your lies a thousand times, but lies won't turn into facts.

Engineer said:

First, this plot doesn't make your argument equating throat area to capture area any less incorrect. The plot shows mass flow performance changes with respects to speed, not change of capture area. Second, control of airflow, specifically the dumping of excess air is achieved using bypass doors. Read what the book has to say about the excess air:


At a given airspeed, the air will travel faster at the throat to compensate for the decrease in throat area. Put it in simpler terms, he ramps don't restrict mass flow because air is compressible and can squeeze through restricted area. This is

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, and apparently you do not know about this most fundament aerodynamic principle.

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all what you say is totally wrong the graph shows two ramp positions, and the respective mass flow at different speed.

Engineer said:

You are still wrong in claiming F-14 and aircraft in Su-27 family vary their capture area with intake ramps. Using bold letters and large font size do not add any strength to your argument, just as yelling in the real world does not add any strength to your argument.

Capture area refers to the area within the inlet mouth, which is represented as A1 in the following diagram from

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:

Note that A1 is invariant in your very own diagram of two different inlet geometries:

Intake cones and ramps do not do what you imagine they do. Their role is to position the shock waves for optimal inlet performance, not for controlling mass flow. What control mass flow are auxiliary inlets and bypass doors.

The reality is this: F-15 can vary capture area of its inlets. F-14 and aircraft in the Su-27 families have variable-geometry inlets, but the physical capture area is fixed.

Aside from having more ramps to create more shocks, variable-geometry inlets do not achieve anything that DSI cannot achieve. Pressure recovery ratio between DSI of J-10 and inlets on F-4D shows DSI as superior, contrary to your claim that variable-geometry inlet is always superior.

Yes, you can use more ramps to raise pressure recovery ratio further, but that brings in complexity and weight that reduce performance gain. The fact that no Mach 3 aircraft is a fighter and no fighter aircraft flies at Mach 3 speaks volume.

You can spin all you want and repeat your lies a thousand times, but lies won't turn into facts.

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haha here the only one saying unaccurate things is you, the illusatrations show two ramp positions and the graph shows their respective mass flow which are different.

MiG-29 said:

haha here the only one saying unaccurate things is you, the illusatrations show two ramp positions and the graph shows their respective mass flow which are different.

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Um...if I'm not mistaken that ramp is actively changing the capture area...

latenlazy said:

Um...if I'm not mistaken that ramp is actively changing the capture area...

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that is correct latenlazy, it adjusts the ramp depending on mach number and mass flow needs