SDF Aerospace and Aerodynamics Corner

Engineer · Jan 15, 2012

MiG-29 said:
haha the text shows perfectly how wrong you are.

Nope. Your very own sources say the exact same thing as I have been saying, which is the opposite definition of wrong.

You keep on claiming that I am wrong and disagree with everything that I have said, yet your inability to specifically quote me on the wrong part is telling. Misrepresenting my position isn't going to help you, since for every single of your attempt, I simply need to reference what I have actually said.

MiG-29 said:
first air can be spilled, you initially claimed no air was spilled but it was bernuolli`s principle, second you claimed the Throat does not control the sock`s position, it does, reducing mass flow ratio, in few words reducing the amount of air mass the intake takes.

Nope. I never claimed that air cannot be spilled. In fact, I have said that spillage happens, and is not an unique phenomenon to variable-geometry inlet. See below:

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.

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.

As for mass flow ratio, I have never once claimed it doesn't change. Observe what I have actually said:

Engineer said:
As far as mass flow ratio is concerned, the change is attributed to the change in oblique shock waves. This is not a unique phenomenon that occurs on variable-geometry inlet. Fixed inlets and DSI have oblique and normal shock waves as well, so these two inlets will also see change of mass flow ratio.

What we have here is that you are unable to show that I am wrong, so you are now conjuring up positions that I didn't actually have. This is called

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.

MiG-29 said:
the text show an inlet without bypass doors can just by varing the inlet throat do air mass control just like by pass doors.

The text shows movement of shock waves, which is exactly what I have said before. Bypass door regulates the amount of air actually going into the engine. Recall what you have said:

MiG-29 said:
If you were right you only would need the by pass doors, not variable geometry throats.

And in fact, we do see inlet only needs bypass door to function. An example is F-22's inlet.

Engineer · Jan 15, 2012

MiG-29 said:
your argument was the F-14 does not use the throat size to positon the shock. you claimed air mass control was done uniquely by bypass doors, now that you know the throats do the same thing bypass doors you deny it

Wrong.

For one, I never once claimed variable-geometry does not cause shock wave position to change. In fact, I claimed the opposite, such as here:

Engineer said:
The purpose of variable-geometry is to optimally position the shock waves...

And this statement of mine is verified by your very own source here:

For two, you claimed air mass control is controlled by the ramp, to which I responded that the functions for the ramp is to control shock waves and that role of mass flow control falls to the bypass system. You disagreed, then made the statement quoted below. You are now refusing to acknowledge it, showing you are the one who is in denial.

MiG-29 said:
If you were right you only would need the by pass doors, not variable geometry throats.

You keep on claiming I am wrong, but you are unable to specifically quote me on my wrong statements. Now, you are resorting to accuse me of claiming things that I have never said, which is a

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. So, the only person who is in denial is you, because you are unable to accept the fact that what I have been saying are correct and confirmed by your very own sources.

Engineer · Jan 15, 2012

MiG-29 said:
in fact i wil leave you a present

The results show that under design point condition,the average total pressure recovery coefficient at exit of bump inlet is nearly 0.87 at design Mach number of 2.0,and no less than 0.91 at mach number of 1.8

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What F-16 has the same performance than DSI almost 20 years ago!

ah i see DSI is used simply because it is stealthier and cheaper to build and maintain

Why, thank you for your present. I will respond by giving you a present of my own. Observe what the paper says:

The results show that under design point condition,the average total pressure recovery coefficient at exit of bump inlet is nearly 0.87 at design Mach number of 2.0,and no less than 0.91 at mach number of 1.8.

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Now compare the pressure recovery ratios above with the pressure recovery ratio of various aircraft in the graph below:

What we see is that DSI has better performance than variable-geometry inlets on the F-4D. The variable-geometry inlets on F-4D has three shocks, so DSI is better than variable-geometry inlets with three shocks system. Adding to this is what you have said: DSI is stealthier, cheaper and easier to maintain. Less complexity also means less weight, which means the enhance in performance has no penalties, unlike variable-geometry inlets.

MiG-29 · Jan 15, 2012

Engineer said:
Why, thank you for your present. I will respond by giving you a present of my own. Observe what the paper says:

Now compare the pressure recovery ratios above with the pressure recovery ratio of various aircraft in the graph below:

What we see is that DSI has better performance than variable-geometry inlets on the F-4D. The variable-geometry inlets on F-4D has three shocks, so DSI is better than variable-geometry inlets with three shocks system. Adding to this is what you have said: DSI is stealthier, cheaper and easier to maintain. Less complexity also means less weight, which means the enhance in performance has no penalties, unlike variable-geometry inlets.

when was the F-4first flew? 1957 that is 55 years ago, DSI are from 1997

Now is DSI better than the F-14 2D ramp? well that will depend for what pressure recovery? no it is not. Stealth? yes it is.

Do you need a DSI for those number .91 at mach 1.8? no you do not a variable geometry is better SR-71, F-111, F-15, F-14, XB-70, Su-27, MiG-29, F-16-79 and F-104 prove it

MiG-29 · Jan 15, 2012

Engineer said:
Wrong.

For one, I never once claimed variable-geometry does not cause shock wave position to change. In fact, I claimed the opposite, such as here:

And this statement of mine is verified by your very own source here:

For two, you claimed air mass control is controlled by the ramp, to which I responded that the functions for the ramp is to control shock waves and that role of mass flow control falls to the bypass system. You disagreed, then made the statement quoted below. You are now refusing to acknowledge it, showing you are the one who is in denial.

You keep on claiming I am wrong, but you are unable to specifically quote me on my wrong statements. Now, you are resorting to accuse me of claiming things that I have never said, which is a So, the only person who is in denial is you, because you are unable to accept the fact that what I have been saying are correct and confirmed by your very own sources.

do you understand what means conjuction? means togather, as such bypass doors and variable geometry throat are used to position the shock and air mass control

Now you are just denying what you really said you claim F-14 did not use the throat to control mass flow but now i prove it it does, with the F-111 and the book.

The throat size on F-14, is controlled by the ramps, therefore you were denying what i said by lack of knowledge, not because you did know throats control the shock position

Engineer · Jan 16, 2012

MiG-29 said:
when was the F-4first flew? 1957 that is 55 years ago, DSI are from 1997

Now is DSI better than the F-14 2D ramp? well that will depend for what pressure recovery? no it is not. Stealth? yes it is.

It doesn't matter when inlet on F-4 was first employed. The fact is that this type of inlet has variable-geometry, and that its pressure recovery ratio is exceeded by DSI. Therefore, DSI has better performance. This shows your claim that DSI is inferior and variable-geometry inlet is always better as wrong.

MiG-29 said:
Do you need a DSI for those number .91 at mach 1.8? no you do not a variable geometry is better SR-71, F-111, F-15, F-14, XB-70, Su-27, MiG-29, F-16-79 and F-104 prove it

Variable-geometry inlet is only better if it can offer better performance without suffering penalties. The inlets on SR-71 and XB-70 are so complex and heavy that they cannot be used on fighter aircraft, that's penalty. At the same time, internal compression inlets require very good flow conditions or unstart will occur, that's penalty.

For the rest of your aircraft that have variable-geometry inlets, increase in performance by variable-geometry always comes with the cost of extra complexity and weight, as well as lower performance at low supersonic speed; these are penalties. Do you think General Dynamics didn't know about variable-geometry inlet when they designed the F-16? Of course not, but they went with a pitot inlet instead because the penalties cannot be justified by the performance increase.

Sometime, the increase in performance brought by variable-geometry inlet is still not good enough as compared to designs such as DSI, as we have seen in the case of F-4 and F-104. For example, does any of these aircraft in your list supercruise? No! The F-22 with fixed inlets can. J-20 with DSI intends to. This means your claim that variable-geometry is always better is unsubstantiated.

If anything your list of aircraft proves, it is that these are old aircraft with inlet designs that are being phased out. May be in the future there will be a resurrection of variable-geometry inlets, but right now variable-geometry is not used anymore on new aircraft such as F-18, F-35, F-22, J-10B and J-20. Why? Because there are designs available such as DSI that can increase performance without incurring as sever penalties.

If the Russians were to use DSI, you would be claiming how better DSI is. Unfortunately for you, the Russians do not have enough money to research into new inlet designs, so they have to stick with variable-geometry inlets. This is why you keep on yapping about variable-geometry inlets.

Engineer · Jan 16, 2012

MiG-29 said:
do you understand what means conjuction? means togather, as such bypass doors and variable geometry throat are used to position the shock and air mass control

Now you are just denying what you really said you claim F-14 did not use the throat to control mass flow but now i prove it it does, with the F-111 and the book.

The texts you used to prove me wrong say that variable-geometry is used to position the shock waves and actually verify what I have said. I also said that mass flow ratio change with respect to shock waves position, and your texts also verify this. In fact, I have quoted myself on my claims and statements in every instance where you tried to misrepresent my position. So nope, I am not denying anything since referencing myself is mutually exclusive with denying my own statements.

Variable-geometry inlet needs bypass doors to work, while inlets with only bypass doors have no need of variable-geometry. Recall what you have said:

MiG-29 said:
If you were right you only would need the by pass doors, not variable geometry throats.

And we see that F-22 does not need variable-geometry.

MiG-29 said:
The throat size on F-14, is controlled by the ramps, therefore you were denying what i said by lack of knowledge, not because you did know throats control the shock position

Wrong again. I have specifically mentioned the throat size changes as a consequence of having to vary the ramps to optimally position shock waves. Here is exactly what I have said.

Engineer said:
...the ramps cause throat area to change...

Then I said the same thing here:

Engineer said:
Throat area is reduced as a consequent of having to position the ramps to optimally place the shocks. It is explained
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:

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.

Click to expand...

It sounds like you are the one who is in bitter denial.

MiG-29 · Jan 16, 2012

Engineer said:
It doesn't matter when inlet on F-4 was first employed. The fact is that this type of inlet has variable-geometry, and that its pressure recovery ratio is exceeded by DSI. Therefore, DSI has better performance. This shows your claim that DSI is inferior and variable-geometry inlet is always better as wrong.

Variable-geometry inlet is only better if it can offer better performance without suffering penalties. The inlets on SR-71 and XB-70 are so complex and heavy that they cannot be used on fighter aircraft, that's penalty. At the same time, internal compression inlets require very good flow conditions or unstart will occur, that's penalty.

For the rest of your aircraft that have variable-geometry inlets, increase in performance by variable-geometry always comes with the cost of extra complexity and weight, as well as lower performance at low supersonic speed; these are penalties. Do you think General Dynamics didn't know about variable-geometry inlet when they designed the F-16? Of course not, but they went with a pitot inlet instead because the penalties cannot be justified by the performance increase.

Sometime, the increase in performance brought by variable-geometry inlet is still not good enough as compared to designs such as DSI, as we have seen in the case of F-4 and F-104. For example, does any of these aircraft in your list supercruise? No! The F-22 with fixed inlets can. J-20 with DSI intends to. This means your claim that variable-geometry is always better is unsubstantiated.

If anything your list of aircraft proves, it is that these are old aircraft with inlet designs that are being phased out. May be in the future there will be a resurrection of variable-geometry inlets, but right now variable-geometry is not used anymore on new aircraft such as F-18, F-35, F-22, J-10B and J-20. Why? Because there are designs available such as DSI that can increase performance without incurring as sever penalties.

If the Russians were to use DSI, you would be claiming how better DSI is. Unfortunately for you, the Russians do not have enough money to research into new inlet designs, so they have to stick with variable-geometry inlets. This is why you keep on yapping about variable-geometry inlets.

To start F-104 has better performance than DSI, it is F-105 which has worse performance.

Variable geometry is not used in modern fighters because none flies faster than Mach 2.

F-22 does not go beyond Mach 2, F-35 is a Mach 1.6, JF-17 is a Mach 1.7.

Here the reason why we are dicussing is because originally i said i doubt the J-20 and J-10B are Mach 2.5 or Mach 2.3 fighters.

Originally i stated that i think J-20 is a Mach 2 at the most with decent supercruise at Mach 1.6-1.7.

I said J-10B must be at the most a Mach 2 fighter.

And the reason i said that is because F-111`s external compressionintake at mach 2 becomes supercritical unless they do the proper variable geometry steps.

In fact at Mach 2.5 the F-111 could not maneuvre, it could only maneuvre at Mach 2.2

Second as i originally said loses in pressure recovery will low reduce thrust and reduce reliability.

XB-70 if you read the paper says onces the jet becomes unstarted at high speeds might damage the engines.

SR-71 becomes a ramjet to avoid damage on the engines.

So my point has been F-35 is kept to a low speed to remain in the best performance of its inlet.

Your position has been DSI can go Mach 2.3 or Mach 2.5, i said originally J-10B most likely it has a reduction in max speed.

True i think at transonic speeds the J-10B must have better performance or at least as good as J-10A.

Today`s fifth generation fighters used fixed intake for stealth, not because variable geometry intakes can not get better performance as you claim.

MiG-29 · Jan 16, 2012

Engineer said:
The texts you used to prove me wrong say that variable-geometry is used to position the shock waves and actually verify what I have said. I also said that mass flow ratio change with respect to shock waves position, and your texts also verify this. In fact, I have quoted myself on my claims and statements in every instance where you tried to misrepresent my position. So nope, I am not denying anything since referencing myself is mutually exclusive with denying my own statements.

Variable-geometry inlet needs bypass doors to work, while inlets with only bypass doors have no need of variable-geometry. Recall what you have said:

And we see that F-22 does not need variable-geometry.

Wrong again. I have specifically mentioned the throat size changes as a consequence of having to vary the ramps to optimally position shock waves. Here is exactly what I have said.

Then I said the same thing here:

It sounds like you are the one who is in bitter denial.

To start you did not know shock waves are controlled by the throat and the throat is variable due to the ramps position that is moveable because you claimed air is not spilled and throat size can not control the amount of air it is spilled.
In few words i claimed the throat size changes the amount of air the intake takes, when the mass flow ratio is 1, it means there is no spillage. when it is 0.5 it means half of the air of the potential capture area only enters and some air is spilled, if the mass flow ratio goes below it means less air enters the intake.
So if you change the throat size less air will be ingested, so it is not the same amount all the time.

Second F-22 is not a Mach 3.2 aircraft like SR-71 or Mach 2.5 like F-15 niether a Mach 2.4 like F-14.

If you want to go beyond supercritical states you need variable geometry and mixed compression, physics won`t change.

RAMJETS and SCRAMJETS scrap the engines thus pressure recovery is not as important as in turbojets and usually they use rockets or a second inlet with turbojets to go to Mach 2.9 and start the ramjet

Engineer · Jan 16, 2012

MiG-29 said:
To start F-104 has better performance than DSI, it is F-105 which has worse performance.

Looking at the graph again, F-104's inlet does not have better performance than DSI. At best, the performance of the two are the same.

MiG-29 said:
Variable geometry is not used in modern fighters because none flies faster than Mach 2.

F-22 does not go beyond Mach 2, F-35 is a Mach 1.6, JF-17 is a Mach 1.7.

For sure F-35 and JF-17 do not fly faster than Mach 2, but there is no proof that F-22 top speed is below Mach 2.

MiG-29 said:
Here the reason why we are dicussing is becuase originally i said i doubt the J-20 and J-10B are Mach 2.5 or Mach 2.3 fighters.

Originally i stated that i think J-20 is a Mach 2 at the most with decent supercruise at Mach 1.6-1.7.

I said J-10B must be at the most a Mach 2 fighter.

I agree with you here that J-10B and J-20 cannot reach anywhere close to Mach 2.5. However, if they reach Mach 2.1, they are still faster than Mach 2.0.

MiG-29 said:
And the reason i said that is because F-111`s intake at mach 2 becomes supercritical unless they do the proper variable geometry steps.

In fact at Mach 2.5 the F-111 could not maneuvre, it could only maneuvre at Mach 2.2

F-111's intake is incredibly complex, and while such intake can be justified on a bomber, it cannot be justified on a fighter.

MiG-29 said:
Second as i originally said loses in pressure recovery will low reduce thrust and reduce reliability.

I do not disagree with this, but this phenomenon isn't unique to fixed inlet and DSI.

MiG-29 said:
XB-70 if you read the paper says onces the jet becomes unstarted at high speeds might damage the engines.

SR-71 becomes a ramjet to avoid damage on the engines.

Actually, the paper says that the inlet was unstarted as a result of engine damage, not the other way around. SR-71's engines become ramjets as a result of having to bypass almost all the air around the engines into the afterburners.

MiG-29 said:
So my point has been F-35 is kept to a low speed to remain in the best performance of its inlet.

F-35 as an aircraft is not required to fly at high supersonic speed. This has to do with the requirements of the aircraft, not a limitation as a result of using DSI.

MiG-29 said:
Your position has been DSI can go Mach 2.3 or Mach 2.5, i said originally J-10B most likely it has a reduction in max speed.

That's not my position as I have made no such claim.

MiG-29 said:
True i think at transonic speeds the J-10B must have better performance or at least as good as J-10A.

PLAAF is unlikely to accept J-10B if the aircraft has less performance than J-10A. So J-10B must either have the same or better performance than J-10A.

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