SDF Aerospace and Aerodynamics Corner

MiG-29 said:

All what you write is not true, but you know i just answered to you not because i know you will admit what the article says which stablishes clearly variable throat S1 and S1" have different mass flows, that is clear why


throat area at cruise conditions<transonic throat area

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Of course throat area at cruise is smaller than transonic speed, but this doesn't mean S1 and S1' have different mass flow. Change in mass flow ratio is independent of throat area, since the ratio is defined as A0i/A1. A0i is the free-stream flow area, whereas A1 is the physical capture area of the inlet. It has nothing to do with throat area.

MiG-29 said:

why?

this article proves how wrong you are
cause is simple variable geometry intake and the article mentions it
cruise airflow < transonic air flow


cruise air flow is 70% of transonic flow

Transonic flow is 100%.


throat area at cruise conditions<transonic throat area

Click to expand...

Repeating the ad infinitum is not going to get you anywhere. We know the mass flow ratio is independent of throat area because throat area As does not appear in the ratio:


So why don't you talk about the equation? Because you like to spin, and you can't put spin on an equation as you can with people's words.

The reduction in mass flow at cruise condition that your article speak of is taken care by bypass, as explained in another citation of your's:


The collapsing and expansion of intake ramp is called creating a throat when needed, and putting it away when it is not need. This isn't the same as controlling the mass flow.

So your latest article changes nothing.

MiG-29 said:

You are wrong and i know you won`t admit it, pride is what really makes you tick, but definitively i know i won`t have a conversation with you. it is senseless, however i left to others the articles, they will decide, but at the end this is not a popularity contest, real jets have variable geometry intakes to control air mass and shock position, you think that just by denying anything i post you win or you outsmart me by saying your fallacies, but you won`t change reality.

Click to expand...

Wrong. Fact and logical argument is what makes me tick. Don't pretend you know me, because you don't. Also, if you ask around on this board, you would find other members think you are the one who is unreasonable, and that talking with you is senseless.

Covering your ears and accusing me of being wrong isn't going to make your claim any less incorrect. You are now hindered by your own fallacies, and you would go into great length to perpetuate your bias even when it means lying to yourself, or going into denial when you are presented with ample facts. You operate on pride, as evident by your disagreement with anything I say regardless of what I say. Shouting A happens together with B so A controls B is all you have ever done in this thread. You are unable to explain a thing.

Assuming the engine is operating at a constant RPM, the remaining limiting factor on mass flow is the normal shock, known as . Mass flow rate (m_dot) is define as:
m_dot = ρ A V

At the normal shock V is Mach 1, since the flow is sonic. The equation then depends only on ρ and A.

Thus the limiting factor on flow is the area of the normal shock. When you vary the throat area the normal shock simply shifts, a fact admitted by yourself. But since different section of the inlet has different cross sectional area, variable A in the above equation also varies. When throat size is too small, the normal shock simply moves further into the inlet to find a bigger area, resulting in supercritical condition. In other words, the normal shock shifts to accommodate flow regardless of throat size.

The ability to control the position of normal shock is one great advantage of variable-geometry inlet. However, when you control the position of the normal shock by varying the throat area, absolutely nothing is done in altering the size of the normal shock, hence absolutely nothing is done in altering the mass flow.

The above phenomenon can be seen in the following diagram. As long as normal shock is inside the inlet, mass flow is conserved:


The only person who is employing fallacies is you. is one of them, where you attribute one thing is the cause another without showing any link. An argument employing fallacy isn't a proper argument, and when you use fallacy you are essentially saying nothing. Time and again I warned you of your fallacies, and time and again you ignore my warnings and repeat the same fallacies ad infinitum, so it is your own damn fault that you are angry. isn't going to alter facts to suit your opinion.

MiG-29 said:

this article summariezes everything

With a top speed of Mach 1.6, the Lockheed Martin F-35 Joint Strike Fighter has an inlet design that is far simpler than that of the Mach 3-plus SR-71; the single-engine JSF inlet cannot vary its geometry. The F-35’s engineers could get away with a less complicated design because at vehicle speeds up to about Mach 2, the shape of the inlet itself can slow down much of the supersonic air before it enters the inlet. The JSF inlet is, however, a breakthrough design: It has no diverters. Traditional fighter inlets, such as those found on the F/A-18 and F-22, have slots, slats, and moving parts to divert or channel airflow. The F-15 inlet has ramps and doors that alter its external and internal shape to adjust airflow as needed

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The rest is just you pretending to know, i do not need you agree with me, real aircraft use variable geometry for a reason

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Of course variable-geometry inlet is used for a reason, but the above article does nothing to support your claim that variable-geometry inlet is always better. F-35's top-speed being Mach 1.6 doesn't mean all aircraft employing DSI have top-speed of Mach 1.6, and claiming otherwise is . As for variable-geometry, it is used to optimally position the oblique shock waves. It can also be used to increase the strength of the oblique shock waves, improving performance. As simple as that.

We have already seen that pressure recovery ratio of J-10B's DSI is higher than three-shock variable-geometry inlet, meaning DSI actually performs better in comparison. Time after time I have brought this up, and time after time you go into denial mode. But denying facts isn't going to make them go away.

Finally, I am not you; I don't need to pretend I know -- I know. I can connect different concepts together and explain why things happen the way they are, you cannot. All you can do is repeat your initial claim, make some fallacies, and hope that you can get away with it. Unfortunately for you, fallacies don't work for you this time. That's one of the differences between you and me.

MiG-29 said:

The chinese use DSI for the same reasons the americans do, more economical fixed intakes with good stealth and price

Click to expand...

DSI is simpler and lighter, that's one advantage. DSI also has higher pressure recovery compared to a three-shock variable-geometry inlet, that's another advantage. Stealth and price are just bonus.

Engineer said:

Of course throat area at cruise is smaller than transonic speed, but this doesn't mean S1 and S1' have different mass flow. Change in mass flow ratio is independent of throat area, since the ratio is defined as A0i/A1. A0i is the free-stream flow area, whereas A1 is the physical capture area of the inlet. It has nothing to do with throat area.



Repeating the

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ad infinitum is not going to get you anywhere. We know the mass flow ratio is independent of throat area because throat area As does not appear in the ratio:

So why don't you talk about the equation? Because you like to spin, and you can't put spin on an equation as you can with people's words.

The reduction in mass flow at cruise condition that your article speak of is taken care by bypass, as explained in another citation of your's:

The collapsing and expansion of intake ramp is called creating a throat when needed, and putting it away when it is not need. This isn't the same as controlling the mass flow.

So your latest article changes nothing.



Wrong. Fact and logical argument is what makes me tick. Don't pretend you know me, because you don't. Also, if you ask around on this board, you would find other members think you are the one who is unreasonable, and that talking with you is senseless.

Covering your ears and accusing me of being wrong isn't going to make your claim any less incorrect. You are now hindered by your own fallacies, and you would go into great length to perpetuate your bias even when it means lying to yourself, or going into denial when you are presented with ample facts. You operate on pride, as evident by your disagreement with anything I say regardless of what I say. Shouting A happens together with B so A controls B is all you have ever done in this thread. You are unable to explain a thing.

Assuming the engine is operating at a constant RPM, the remaining limiting factor on mass flow is the normal shock, known as

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. Mass flow rate (m_dot) is define as:
m_dot = ρ A V

At the normal shock V is Mach 1, since the flow is sonic. The equation then depends only on ρ and A.

Thus the limiting factor on flow is the area of the normal shock. When you vary the throat area the normal shock simply shifts, a fact admitted by yourself. But since different section of the inlet has different cross sectional area, variable A in the above equation also varies. When throat size is too small, the normal shock simply moves further into the inlet to find a bigger area, resulting in supercritical condition. In other words, the normal shock shifts to accommodate flow regardless of throat size.

The ability to control the position of normal shock is one great advantage of variable-geometry inlet. However, when you control the position of the normal shock by varying the throat area, absolutely nothing is done in altering the size of the normal shock, hence absolutely nothing is done in altering the mass flow.

The above phenomenon can be seen in the following diagram. As long as normal shock is inside the inlet, mass flow is conserved:

The only person who is employing fallacies is you.

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is one of them, where you attribute one thing is the cause another without showing any link. An argument employing fallacy isn't a proper argument, and when you use fallacy you are essentially saying nothing. Time and again I warned you of your fallacies, and time and again you ignore my warnings and repeat the same fallacies ad infinitum, so it is your own damn fault that you are angry.

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isn't going to alter facts to suit your opinion.



Of course variable-geometry inlet is used for a reason, but the above article does nothing to support your claim that variable-geometry inlet is always better. F-35's top-speed being Mach 1.6 doesn't mean all aircraft employing DSI have top-speed of Mach 1.6, and claiming otherwise is

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. As for variable-geometry, it is used to optimally position the oblique shock waves. It can also be used to increase the strength of the oblique shock waves, improving performance. As simple as that.

We have already seen that pressure recovery ratio of J-10B's DSI is higher than three-shock variable-geometry inlet, meaning DSI actually performs better in comparison. Time after time I have brought this up, and time after time you go into denial mode. But denying facts isn't going to make them go away.

Finally, I am not you; I don't need to pretend I know -- I know. I can connect different concepts together and explain why things happen the way they are, you cannot. All you can do is repeat your initial claim, make some fallacies, and hope that you can get away with it. Unfortunately for you, fallacies don't work for you this time. That's one of the differences between you and me.




DSI is simpler and lighter, that's one advantage. DSI also has higher pressure recovery compared to a three-shock variable-geometry inlet, that's another advantage. Stealth and price are just bonus.

Click to expand...

You are saying a bunch of fallacies simply like that, variable geometry throat change tha mass flow ratio, at subsonic speeds F-14 needs more air so it opens wider the throat at higher speeds needs less air, so it narrows the throat.

So your fallacy can not explain why you need to open wider the throat, since you claim conservation of mass, a wider or narrower throat will always have the same mass according to you, however because air is spilled you can not explain why the difference between capture area and throat area mass flow, flow ratio is a rate of both flows.
In the first place you claim air can not be spilled, since conservation of mass will compress the air and always the same amount of air will pass regardless if you narrow the throat or you open it wider always the same amount of air passes, you claimed bernoulli`s principle, however the shock wave is positioned according to the mass flow.
The throat will ingest less air thus some air is spilled, the same as a sink, this should not be happening accroding to you, since bernoulli`s principle means air can be compressed and air mass will remain the same, but it spills hahahaha, so you now try to skip it and claim a bunch of fallacies, trying to say always it is supercritical.

However intakes have a throat mach number, at lower speeds the ratio is lower than 1, in order to be 1 you always need to increase or decrease the throat mach number accordingly that is what variable geometry does, in fact at take off the bypass doors in concorde become auxiliary intake doors increasing mass flow, since even the variable throat is uncapable to get all the air it needs.

MiG-29 said:

You are saying a bunch of fallacies simply like that, variable geometry throat change tha mass flow ratio, at subsonic speeds F-14 needs more air so it opens wider the throat at higher speeds needs less air, so it narrows the throat.

Click to expand...

Just because you are unable to grasp what I said that doesn't make my statements fallacies. Fallacy refers to improper reasoning, such as which you are repeatedly using.

Variation in throat area doesn't change mass flow, that's a fact. The reduction in mass flow on the F-14 is achieved by bypass:


At supersonic speed, the intake ramps are expanded to create oblique shock wave, consequently narrowing the throat area. But , and just because the two events occur together that doesn't automatically mean one is in control of another.

MiG-29 said:

So your fallacy can not explain why you need to open wider the throat, since you claim conservation of mass, a wider or narrower throat will always have the same mass according to you, however because air is spilled you can not explain why the difference between capture area and throat area mass flow, flow ratio is a rate of both flows.

Click to expand...

Nope, there is no fallacy in what I have said. You have no idea what a fallacy is and you should refrain from using a term that you do not understand.

I have already explained that the wider throat is a result of putting the throat away when it isn't needed. I have also pointed out that variation in mass flow ratio is a result of shock geometry by using your own source. Just because you refuse to accept facts, that doesn't mean I haven't or unable to explain things.


I have also explained the concept of , where area of normal shock determines the mass flow, and supercritical condition can occur where the normal shock shifts to a location with larger area to match the mass flow. Just because you are unable to comprehend it, that doesn't mean I didn't offer explanation.

As for you, all you have done is shout A happens and B happens so A controls B. That's , and repeating it ad infinitum isn't going to do a thing to strengthen your argument. Other than fallacies and denial, you have not provide explanations.

MiG-29 said:

In the first place you claim air can not be spilled, since conservation of mass will compress the air and always the same amount of air will pass regardless if you narrow the throat or you open it wider always the same amount of air passes, you claimed bernoulli`s principle, however the shock wave is positioned according to the mass flow.

Click to expand...

You are now resorting to , which is a fallacy. It is a fallacy because I never claimed air cannot be spilled, and you are trying to misrepresent my position to mask your own mistakes.

Observe what I have said about spillage:

Engineer said:

Spillage can occur with inlets with no variable-geometry, such as DSI. You can read about spillage of DSI

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. Thus, spill air is not caused by variation in throat area.

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The fact that I said spillage can occur means I didn't claim air cannot be spilled. The two are mutually exclusive. I have also pointed out why spillage occurs, such as this statement I quote below:

Engineer said:

Spillage occurs because normal shock wave is outside of inlet's mouth, this is called sub-critical condition. This phenomenon occurs on all inlets, such as DSI.

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So you see, at no time did I claim spillage cannot occur. You are unable to back up your own claim or show that my statements are wrong, so now you are attempting to put words into my mouth. Weak.

As for normal shock wave, the fact it can shift to change its own area to accommodate the flow condition means throat area does not effect mass flow.

Engineer said:

The throat will ingest less air thus some air is spilled, the same as a sink, this should not be happening accroding to you, since bernoulli`s principle means air can be compressed and air mass will remain the same, but it spills hahahaha, so you now try to skip it and claim a bunch of fallacies, trying to say always it is supercritical.

Click to expand...

Your water-in-a-sink example is flawed, because air is compressible where as water isn't. And since water isn't compressible, it cannot result in shock wave. Without shock wave, your example is not applicable. Your insistence on this wrong example is one reason why you are unable to grasp simple concepts.

Spillage is a result of normal shock wave being pushed outside of the inlet mouth due to high pressure within the inlet duct. This is your so call sub-critical condition. DSI has spillage yet there is no variable geometry. Thus spillage is not a result of variation in throat area, consequently change in throat size does not affect mass flow.

When the throat area is too narrow, and the normal shock does not have sufficient area for the flow condition, the normal shock moves inward the inlet to seek a larger area. This is your so called super-critical condition. Any act of resizing the throat to bring the shock backs to the desired location has no affect on the area of the normal shock, thus no effect is made to mass flow.

The above conditions are illustrated in the following examples.

Engineer said:

However intakes have a throat mach number, at lower speeds the ratio is lower than 1, in order to be 1 you always need to increase or decrease the throat mach number accordingly that is what variable geometry does, in fact at take off the bypass doors in concorde become auxiliary intake doors increasing mass flow, since even the variable throat is uncapable to get all the air it needs.

Click to expand...

That's called creating a choked condition, not controlling mass flow. Once choked condition is achieved, the normal shock can shift, changing its area to accommodate the flow condition. Changing the throat size to keep the normal shock in one position does nothing in changing the area of the normal shock, thus no effect is made to the mass flow.

Observe how in the following video, the mass flow is set with the valve to the vacuum pump. We know that for much of the video, mass flow is constant because no adjustment is made to the valve. Narrowing of the throat area only pushes the normal shock further down stream where the shock seeks a larger area to accommodate the mass flow. Mass is conserved, thus variation in throat area does not affect mass flow.
[video=youtube;JhlEkEk7igs]http://www.youtube.com/watch?v=JhlEkEk7igs[/video]

Engineer said:

Just because you are unable to grasp what I said that doesn't make my statements fallacies. Fallacy refers to improper reasoning, such as

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which you are repeatedly using.

Variation in throat area doesn't change mass flow, that's a fact. The reduction in mass flow on the F-14 is achieved by bypass:
At supersonic speed, the intake ramps are expanded to create oblique shock wave, consequently narrowing the throat area. But

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, and just because the two events occur together that doesn't automatically mean one is in control of another.



Nope, there is no fallacy in what I have said. You have no idea what a fallacy is and you should refrain from using a term that you do not understand.

I have already explained that the wider throat is a result of putting the throat away when it isn't needed. I have also pointed out that variation in mass flow ratio is a result of shock geometry by using your own source. Just because you refuse to accept facts, that doesn't mean I haven't or unable to explain things.

I have also explained the concept of

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, where area of normal shock determines the mass flow, and supercritical condition can occur where the normal shock shifts to a location with larger area to match the mass flow. Just because you are unable to comprehend it, that doesn't mean I didn't offer explanation.

As for you, all you have done is shout A happens and B happens so A controls B. That's

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, and repeating it ad infinitum isn't going to do a thing to strengthen your argument. Other than fallacies and denial, you have not provide explanations.



You are now resorting to

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, which is a fallacy. It is a fallacy because I never claimed air cannot be spilled, and you are trying to misrepresent my position to mask your own mistakes.

Observe what I have said about spillage:


The fact that I said spillage can occur means I didn't claim air cannot be spilled. The two are mutually exclusive. I have also pointed out why spillage occurs, such as this statement I quote below:


So you see, at no time did I claim spillage cannot occur. You are unable to back up your own claim or show that my statements are wrong, so now you are attempting to put words into my mouth. Weak.

As for normal shock wave, the fact it can shift to change its own area to accommodate the flow condition means throat area does not effect mass flow.



Your water-in-a-sink example is flawed, because air is compressible where as water isn't. And since water isn't compressible, it cannot result in shock wave. Without shock wave, your example is not applicable. Your insistence on this wrong example is one reason why you are unable to grasp simple concepts.

Spillage is a result of normal shock wave being pushed outside of the inlet mouth due to high pressure within the inlet duct. This is your so call sub-critical condition. DSI has spillage yet there is no variable geometry. Thus spillage is not a result of variation in throat area, consequently change in throat size does not affect mass flow.

When the throat area is too narrow, and the normal shock does not have sufficient area for the flow condition, the normal shock moves inward the inlet to seek a larger area. This is your so called super-critical condition. Any act of resizing the throat to bring the shock backs to the desired location has no affect on the area of the normal shock, thus no effect is made to mass flow.




That's called creating a choked condition, not controlling mass flow. Once choked condition is achieved, the normal shock can shift, changing its area to accommodate the flow condition. Changing the throat size to keep the normal shock in one position does nothing in changing the area of the normal shock, thus no effect is made to the mass flow.

Observe how in the following video, the mass flow is set with the valve to the vacuum pump. We know that for much of the video, mass flow is constant because no adjustment is made to the valve. Narrowing of the throat area only pushes the normal shock further down stream where the shock seeks a larger area to accommodate the mass flow. Mass is conserved, thus variation in throat area does not affect mass flow.

Click to expand...

all what you write is utterly false,


here this article proves you are utterly wrong, if variation of the throat does not increase mass flow why do it? air is compressible according to you, so spillages should not occur, if variation of throat always will give same mass no need to get more air mass using variable geometry throat simple like that since mass flow will remain the same

MiG-29 said:

all what you write is utterly false,

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You keep on claiming that, but the fact that you are unable to point out anything specifically that is false speaks volume. In any case, just because the facts I have presented don't conform to your opinion, it doesn't make the facts wrong. It means you have to re-evaluate your opinion.

MiG-29 said:

here this article proves you are utterly wrong, if variation of the throat does not increase mass flow why do it? air is compressible according to you, so spillages should not occur, if variation of throat always will give same mass no need to get more air mass using variable geometry throat simple like that since mass flow will remain the same

Click to expand...

First, variation of throat size is a result of other intentions, such as controlling the oblique shocks or optimally positioning of the normal shock. Just because it occurs, that doesn't mean it occurs for the reasons that you assumed. As we have seen from the mass flow ratio, A0i/A1 is independent on throat size As, showing that variation in throat size does not alter mass flow.

Secondly, air being compressible is a fact. We know this compressibility is at work in a inlet because there are shock waves. Your act of placing doubt on this compressibility issue is essentially placing doubt on the present of shock waves in an inlet, as simple as that. In any case, air being compressible is not mutually exclusive with spillage. Spillage happens because the normal shock gets pushed out of the inlet's mouth. The normal shock acts somewhat like a seal and when there is a gap, air that is supposed to enter the inlet escape instead. Spillage occurs with no involvement of variable-geometry, with DSI being one example.

Thirdly, variation in throat area does nothing to change the mass flow, that's why variable-geometry inlets require bypass. Variable-geometry inlet has its advantages, but that is not proof that variable throat size controls the mass flow.

MiG-29 said:

Click to expand...

The reason that mass flow at supersonic speed is smaller than subsonic speed has to do with the bypass. In the case of the Concorde, F-14, F-15, and other aircraft that employ similar inlet design, a gap is left between the intake and diffuser ramp where air can be bleed out.


Another way to reduce mass flow is with bypass doors:


Mathematically, the mass flow ratio is dependent on two variables: the cross-sectional area of free-stream air A0i, and the physical capture area of the inlet A1. There is no involvement of throat area As, hence varying throat area does not alter mass flow.

Engineer said:

You keep on claiming that, but the fact that you are unable to point out anything specifically that is false speaks volume. In any case, just because the facts I have presented don't conform to your opinion, it doesn't make the facts wrong. It means you have to re-evaluate your opinion.



First, variation of throat size is a result of other intentions, such as controlling the oblique shocks or optimally positioning of the normal shock. Just because it occurs, that doesn't mean it occurs for the reasons that you assumed. As we have seen from the mass flow ratio, A0i/A1 is independent on throat size As, showing that variation in throat size does not alter mass flow.

Secondly, air being compressible is a fact. We know this compressibility is at work in a inlet because there are shock waves. Your act of placing doubt on this compressibility issue is essentially placing doubt on the present of shock waves in an inlet, as simple as that. In any case, air being compressible is not mutually exclusive with spillage. Spillage happens because the normal shock gets pushed out of the inlet's mouth. The normal shock acts somewhat like a seal and when there is a gap, air that is supposed to enter the inlet escape instead. Spillage occurs with no involvement of variable-geometry, with DSI being one example.

Thirdly, variation in throat area does nothing to change the mass flow, that's why variable-geometry inlets require bypass. Variable-geometry inlet has its advantages, but that is not proof that variable throat size controls the mass flow.




The reason that mass flow at supersonic speed is smaller than subsonic speed has to do with the bypass. In the case of the Concorde, F-14, F-15, and other aircraft that employ similar inlet design, a gap is left between the intake and diffuser ramp where air can be bleed out.

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You are wrong

simply like that you have two different throat areas and you have two different air mass, the article says you are wong and in fact the F-14 reduces or enlarges the throat, is not by pass, otherwise they would use a fixed intake, and air is spilled


cause is simple variable geometry intake and the article mentions it
cruise airflow < transonic air flow=transonic air flow has more air with larger throat area


cruise air flow is 70% of transonic flow=two different air mass flows

Transonic flow is 100%.


throat area at cruise conditions<transonic throat area =two different throat areas



.

For typical HSCT-type engines the requiered cruise air flow can be as low as 70% of the required air flow at transonic conditions, To provide for the large airflow rates at transonic condition the inlet throat area must be larger than at the cruise condition, this increased area is provided by the variable inlet geometry




hahaha but i know for you pride is what is more important
but you are wrong and the article proves it hahaha

MiG-29 said:

You are wrong

simply like that

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Nope. Just because the facts I presented don't conform to your opinion, that doesn't mean I am wrong. What is wrong is your claim of control of mass flow through throat size, because you still assume air works like water, and because we already have equations saying mass flow ratio is not dependent on throat area.

Denying facts isn't going to magically change how things work to your favor. Deal with it.

In addition, your fallacies are not going to work on me, which is why you are angry. But deal with that also.

MiG-29 said:

you have two different throat areas and you have two different air mass, the article says you are wong and in fact the F-14 reduces or enlarges the throat, is not by pass, otherwise they would use a fixed intake, and air is spilled



cause is simple variable geometry intake and the article mentions it
cruise airflow < transonic air flow=transonic air flow has more air with larger throat area


cruise air flow is 70% of transonic flow=two different air mass flows

Transonic flow is 100%.


throat area at cruise conditions<transonic throat area =two different throat areas



.

For typical HSCT-type engines the requiered cruise air flow can be as low as 70% of the required air flow at transonic conditions, To provide for the large airflow rates at transonic condition the inlet throat area must be larger than at the cruise condition, this increased area is provided by the variable inlet geometry




hahaha but i know for you pride is what is more important
but you are wrong and the article proves it hahaha

Click to expand...

You are repeating the same old fallacy, called , because you assume that two events occurring together means one is in control of another. All you have been able to do is repeat this fallacy ad infinitum, but you are not able to explain a thing. Using large font size isn't going to magically enhance your argument either.

The different throat sizes are consequents of collapsing and expansion of the intake ramps. These ramps are used to control position of shock waves. When the ramps are needed at supersonic speed, they are expanded. At subsonic speed, shock waves cannot be generated, so the ramps are collapsed. No where in your article does it say that throat size is in control of mass flow.

The reduction in mass flow at cruise condition that your article speak of is taken care by bypass, as explained in another citation of your's. Two things are mentioned. The first is that bypass door is open to handle excess flow at high subsonic speed. The second is that bypass door remains open at supersonic speed.


Thus, the reduction in mass flow already has an explanation, and it is not the throat size. This is a fact. A fact which is also confirmed by the equation below, which shows mass flow ratio is dependent on two variables. They are the physical capture area A1 and free-stream area A0i. It has no involvement of throat area As:


Why don't you talk about this equation? Because you like to spin, and you cannot put a spin on equation like you can do with people's words. But your denial of the existence of this equation doesn't mean the equation is not there. Throat size does not affect the mass flow rate, that's one of the things says by the above equation. As simple as that.

Finally, we talk about spillage. Spillage starts with the normal shock being pushed out the inlet by high pressure air inside the inlet. This causes a gap between the normal shock and the inlet's mouth, and air that should have entered the inlet escape from the gap instead. Spillage occurs on pitot inlet, as shown in the following diagram:


The faction spilled is defined as (Ac - A0)/Ac, which again has no involvement of throat area.

Spillage also occurs on DSI as explained , without any variable-geometry. In fact, spillage is dependent upon shock geometries, not internal geometries of the inlet. Signal of a restriction at the throat propagates at the speed-of-sound, which is slower than the supersonic flow that travels into the inlet's mouth. In kiddies' terms, the air inside the inlet cannot tell the air outside that there is a restriction.

The compressibility of air Bernoulli's principle and also dictate that air will simply occupy less volume and moves faster to compensate for a narrower throat. Mass is still conserved.

Thus variable throat-size is not in control of spillage.

Engineer said:

Nope. Just because the facts I presented don't conform to your opinion, that doesn't mean I am wrong. What is wrong is your claim of control of mass flow through throat size, because you still assume air works like water, and because we already have equations saying mass flow ratio is not dependent on throat area.

Denying facts isn't going to magically change how things work to your favor. Deal with it.

In addition, your fallacies are not going to work on me, which is why you are angry. But deal with that also.



You are repeating the same old fallacy, called

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, because you assume that two events occurring together means one is in control of another. All you have been able to do is repeat this fallacy ad infinitum, but you are not able to explain a thing. Using large font size isn't going to magically enhance your argument either.

The different throat sizes are consequents of collapsing and expansion of the intake ramps. These ramps are used to control position of shock waves. When the ramps are needed at supersonic speed, they are expanded. At subsonic speed, shock waves cannot be generated, so the ramps are collapsed. No where in your article does it say that throat size is in control of mass flow.

The reduction in mass flow at cruise condition that your article speak of is taken care by bypass, as explained in another citation of your's. Two things are mentioned. The first is that bypass door is open to handle excess flow at high subsonic speed. The second is that bypass door remains open at supersonic speed.

Thus, the reduction in mass flow already has an explanation, and it is not the throat size. This is a fact. A fact which is also confirmed by the equation below, which shows mass flow ratio is dependent on two variables. They are the physical capture area A1 and free-stream area A0i. It has no involvement of throat area As:


SpillThus variable throat-size is not in control of spillage.

Click to expand...

the article is for an axisymmetric intake, however it holds true for F-14 and this articles further proves the XB-70 uses air mass control by choking its engines depriving them of the right amount of air mass and feeding them lower air mass as in engine buzz, the engine thus reduce thrust.

But i know you will stick to your own self deception, i know pride is more important for you.

MiG-29 said:

the article is for an axisymmetric intake, however it holds true for F-14 and this articles further proves the XB-70 uses air mass control by choking its engines depriving them of the right amount of air mass and feeding them lower air mass as in engine buzz, the engine thus reduce thrust.

Click to expand...

Nope. You let your imagination run wild once again. Also, you clearly do not understand what is a choked condition, but I will explain that later. Inlet buzz is due to the oscillation of normal shock. Observe:


We know the purpose of shock waves is to slow air down to subsonic speed. When a normal shock suddenly forms inside the inlet, then speed of air in there suddenly decreases, so of course this will result in mass flow change. But this doesn't prove in anyway that variation of throat size controls mass flow, because all that does is shift the normal shock up and downstream.

Although boundary layer plays a role, this role is separation which causes a normal shock to develop deep within the inlet, which is even said so in your own citation. Ingestion of boundary layer causes a normal shock to form within the inlet, and back pressure increases which pushes out the shock wave. The process then repeats:



Once the normal shock gets pushed out of the inlet, pressure within the inlet escapes and spillage occurs, resulting in more loss of mass flow. The process depends on pressure, not throat geometry, which only serves to confirm what I have already said.

MiG-29 said:

Click to expand...

Now on to choked flow.

First, you are putting words into the authors' mouth again. That paper never mentions choked condition deprives the engine of air and reducing thrust. Rather, the engines were throttled down intentionally to allow the inlets to be un-choked. They did this repeatedly because they wanted to find the minimum engine setting and throat size which would result in a choked condition, so that the noise from the compressor can be blocked. Depriving the engines of air is solely your own invention.

Secondly, as I have said in the beginning of this post, you do not understand what is a choked condition. A choked condition refers to the condition where the flow at the throat is Mach 1, simple as that. You are probably thinking about depriving air to a person, and if that's the case it shows your lack of understanding in the subject.

Thirdly, as I have explained earlier, the area of normal shock imposes a limit on the mass flow. Theoretically, a choked condition would impose a maximum limit on the mass flow, since the normal shock is at the narrowest point and is constrained in area. Practically, the normal shock simply shifts downstream to accommodate the mass flow. I have mentioned this process earlier multiple times. You keep on accusing me of being wrong, but your lack of ability to back up that accusation speaks volume.

MiG-29 said:

But i know you will stick to your own self deception, i know pride is more important for you.

Click to expand...

The only person who is sticking to his own self-deception is you. What you are displaying here is a classic case of . This is what Wikipedia has to say about it:

...a psychological defense mechanism where a person subconsciously denies his or her own attributes, thoughts, and emotions, which are then ascribed to the outside world, usually to other people.

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So, first you are proven wrong. Then you go into denial. Finally, you ascribe your denial characteristics and your own perception of pride on to me. Like I have said, this is a classic case of projection.

No matter how you deny, it isn't going to change facts; and one fact is that mass flow is altered by variation of shock geometries, not throat geometry. When the throat is too narrow and the normal shock there has an area which is insufficient for the flow condition, the shock shifts downstream until its area is big enough for the flow. Hence, mass flow ratio is independent of throat area as shown by this equation:


And what I have said is confirmed by your very own source. Read below:


A bypass must be needed to remove excess air to prevent spillage from occurring. For internal and mixed compression inlets, this spillage is known as unstart:



But hey, what would a few extra pieces of facts do anyway? Knowing you and how you view your pride as more important, you are just going to use more fallacies to cover your mistakes, and stick to your own self delusion.

Engineer said:

Nope. You let your imagination run wild once again. Also, you clearly do not understand what is a choked condition, but I will explain that later. Inlet buzz is due to the oscillation of normal shock. Observe:


We know the purpose of shock waves is to slow air down to subsonic speed. When a normal shock suddenly forms inside the inlet, then speed of air in there suddenly decreases, so of course this will result in mass flow change. But this doesn't prove in anyway that variation of throat size controls mass flow, because all that does is shift the normal shock up and downstream.

Although boundary layer plays a role, this role is separation which causes a normal shock to develop deep within the inlet, which is even said so in your own citation. Ingestion of boundary layer causes a normal shock to form within the inlet, and back pressure increases which pushes out the shock wave. The process then repeats:


Once the normal shock gets pushed out of the inlet, pressure within the inlet escapes and spillage occurs, resulting in more loss of mass flow. The process depends on pressure, not throat geometry, which only serves to confirm what I have already said.



Now on to choked flow.

First, you are putting words into the authors' mouth again. That paper never mentions choked condition deprives the engine of air and reducing thrust. Rather, the engines were throttled down intentionally to allow the inlets to be un-choked. They did this repeatedly because they wanted to find the minimum engine setting and throat size which would result in a choked condition, so that the noise from the compressor can be blocked. Depriving the engines of air is solely your own invention.

Secondly, as I have said in the beginning of this post, you do not understand what is a choked condition. A choked condition refers to the condition where the flow at the throat is Mach 1, simple as that. You are probably thinking about depriving air to a person, and if that's the case it shows your lack of understanding in the subject.

Thirdly, as I have explained earlier, the area of normal shock imposes a limit on the mass flow. Theoretically, a choked condition would impose a maximum limit on the mass flow, since the normal shock is at the narrowest point and is constrained in area. Practically, the normal shock simply shifts downstream to accommodate the mass flow. I have mentioned this process earlier multiple times. You keep on accusing me of being wrong, but your lack of ability to back up that accusation speaks volume.






And what I have said is confirmed by your very own source. Read below:

A bypass must be needed to remove excess air to prevent spillage from occurring. For internal and mixed compression inlets, this spillage is known as unstart:

But hey, what would a few extra pieces of facts do anyway? Knowing you and how you view your pride as more important, you are just going to use more fallacies to cover your mistakes, and stick to your own self delusion.

Click to expand...

Yeah engineer more fallacies from you, Like i said to you you change your fallacies now you can not say bypass doors, since your first fallacy bypass doors now does not work, not you go round and round without explaining anything just saying things i already know and trying to make it fit, of course it is expected you love decieve your self and you want others to do it with you



to start there is a detail you do not count, the XB-70 reduces engine speed and engine mass flow, what did cause the that? simple, the intake is choking thus less air mass is passing the intake is not delievering enough air to the engine, what is the result? simple the engine reduces its demand for air flow, simple like that so the engine is working at lower RPM and lower thrust.
what caused the intake lower air mass? simple the intake throat area reduces, simple like that, that reduction in area reduces the air mass forcing the engine to lower its demads of air flow and unchoking the intake



and this fits perfectly because

For typical HSCT-type engines the requiered cruise air flow can be as low as 70% of the required air flow at transonic conditions, To provide for the large airflow rates at transonic condition the inlet throat area must be larger than at the cruise condition, this increased area is provided by the variable inlet geometry


logic engineer i am right you just love decieve your self

See the throat what does it say



Throat width for cruise 22 inch, and throat width for take off 48 inch so we have cruise thoat area is smaller than take off area why? same as F-14 and same as all the papers i have mentioned hahahaha but live in your own fallacies i won`t do the same




But of course you want to play the game i am the expert look, when in reality you just decieve your self