J-20 5th Gen Fighter Thread IV (Closed to posting)

[latenlazy]

Look this is not about me or you as you are trying to portrait, in order to justify your lack of supporting evidence, but this is about the feasability the J-20 with a DSI can reach Mach 2.5 or more, the original patent by the DSI inventors say it is fixed, there have been test of DSI at Mach 3 or more, i do not deny it

A diverterless hypersonic inlet (DHI) ..... The DHI is optimized for a particular design flight Mach number

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however you have to see what means optimized for a mach design number.


it means it only works for a specific speed and ramjets use a rocket booster to achieve hypersonic speeds.

the X-51A safely separated from the B-52 and the rocket booster fired as planned.

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Since J-20 does not use ramjet or scramjet technology and needs to fly from 0 to mach 2 whith a fixed intake the throat of the DSI on J-20 also is optimized from Mach 1 to Mach 2.

And that is the reality, J-20 is a Mach 2 aircraft at the most and very likely is a Mach 1.8 as an ideal intake

in fact the DSI is not for mixed compression but for external compression


the DSI is an external compression inlet concept in which the external compression surface is developed by streamline tracing from a simple conical flow field generator

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Any way let us cut it here, i will give you a last reply and let us move on.

It's nice that you finally acknowledge how DSIs can be designed for different mach numbers. Now, if only you had evidence the J-20's DSI was designed to be limited at mach 1.8-2.0.

 

[Engineer]

Look this is not about me or you as you are trying to portrait, in order to justify your lack of supporting evidence, but this is about the feasability the J-20 with a DSI can reach Mach 2.5 or more, the original patent by the DSI inventors say it is fixed, there have been test of DSI at Mach 3 or more, i do not deny it

A diverterless hypersonic inlet (DHI) ..... The DHI is optimized for a particular design flight Mach number

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however you have to see what means optimized for a mach design number.


it means it only works for a specific speed and ramjets use a rocket booster to achieve hypersonic speeds.

the X-51A safely separated from the B-52 and the rocket booster fired as planned.

Please, Log in or Register to view URLs content!

Since J-20 does not use ramjet or scramjet technology and needs to fly from 0 to mach 2 whith a fixed intake the throat of the DSI on J-20 also is optimized from Mach 1 to Mach 2.

And that is the reality, J-20 is a Mach 2 aircraft at the most and very likely is a Mach 1.8 as an ideal intake

in fact the DSI is not for mixed compression but for external compression


the DSI is an external compression inlet concept in which the external compression surface is developed by streamline tracing from a simple conical flow field generator

Please, Log in or Register to view URLs content!

Any way let us cut it here, i will give you a last reply and let us move on.

Your claim that J-20 can only fly at maximum of Mach 1.8 or Mach 2.0 is every bit as ridiculous as the claim saying J-20 can fly at Mach 3.0. Those patents that you have quoted said nothing about a speed limit and does not help your case. Neither does claiming optimization help your case, since an inlet is designed around the maximum speed which could be higher than Mach 2.0 if the engineers deemed reasonable.

 

[MiG-29]

It's nice that you finally acknowledge how DSIs can be designed for different mach numbers. Now, if only you had evidence the J-20's DSI was designed to be limited at mach 1.8-2.0.

I can tell you you can design a DSI for Mach 5 or Mach 6 but since it is fixed they can not be used for other speed ranges beyond their design numbers


A variable Geometry intake has 2 important aspects first changes the throat area as such will change the geometry of the intake allowing for a wider speed range simply like that, and second is adjusts the geometry in accordance of the shocks.

So yes you can have Mach 3 DSIs but the problem is by being fixed is limited to a narrower speed range.


J-20 flies from 0 to 2000km/h and this means at different moments the inlet requires different mass flows.


If you can not understand that i can not help it, i won`t argue 10 pages to repeat the same or answer posts of others that do not want to see reality.


The DSI of J-20 or J-31 are designed for Mach 1.6 or Mach 1.8 operations since they are external compression intakes.

read first the limits of external compression fixed intakes all are limited to Mach 1.8 + or - if you designed a optimized DSI for Mach 5, it only works for speeds in that range not for higher or lower Machs for such reason X-51 with a fixed intake needs a rocket booster.


I give you the last reply and let us move on

 

[latenlazy]

I can tell you you can design a DSI for Mach 5 or Mach 6 but since it is fixed they can not be used for other speed ranges beyond their design numbers


A variable Geometry intake has 2 important aspects first changes the throat area as such will change the geometry of the intake allowing for a wider speed range simply like that, and second is adjusts the geometry in accordance of the shocks.

So yes you can have Mach 3 DSIs but the problem is by being fixed is limited to a narrower speed range.


J-20 flies from 0 to 2000km/h and this means at different moments the inlet requires different mass flows.


If you can not understand that i can not help it, i won`t argue 10 pages to repeat the same or answer posts of others that do not want to see reality.


The DSI of J-20 or J-31 are designed for Mach 1.6 or Mach 1.8 operations since they are external compression intakes.

read first the limits of external compression fixed intakes all are limited to Mach 1.8 + or - if you designed a optimized DSI for Mach 5, it only works for speeds in that range not for higher or lower Machs for such reason X-51 with a fixed intake needs a rocket booster.


I give you the last reply and let us move on

Here's the problem with your logic. We can now agree that DSIs can be designed for different speed envelopes, but how do you know the J-20s DSI was designed to be limited at Mach 1.6-1.8?

I presume you're getting this number from the F-16's tested DSI (since that's been the most well documented case), but the problem with assuming that because the F-16's test DSI started to see drop off at Mach 2.0 the J-20's must be likewise is that the F-16's DSI was designed to be most efficient at transonic speeds, because that's where the F-16 operates in. It only goes above the transonic speeds for short dashes. We can presume that this is also true of the F-35.

However, we can't presume that this is true of the J-20. If we believe the J-20 is meant to supercruise, then ideally the DSI should be optimized for good pressure recovery above the transonic speed envelope. If the optimization and designed parameters are different, we can't simply transplant the pressure recovery drop off for a DSI inlet designed for one plane onto another. Therefore, unless you have strong evidence that the J-20's DSI is indeed limited at the Mach numbers you claim, your assertion is purely based on unfounded conjecture.

The other possibility is that you're assuming all external compression inlets are limited to mach 1.8-mach 2.0. However, that is a meaningless assertion, because external compression inlets can also be designed for higher mach numbers. External compression inlets are a broad category that have nothing to do with effective mach numbers.

 

[MiG-29]

Here's the problem with your logic. We can now agree that DSIs can be designed for different speed envelopes, but how do you know the J-20s DSI was designed to be limited at Mach 1.6-1.8?

I presume you're getting this number from the F-16's tested DSI (since that's been the most well documented case), but the problem with assuming that because the F-16's test DSI started to see drop off at Mach 2.0 the J-20's must be likewise is that the F-16's DSI was designed to be most efficient at transonic speeds, because that's where the F-16 operates in. It only goes above the transonic speeds for short dashes. We can presume that this is also true of the F-35.

However, we can't presume that this is true of the J-20. If we believe the J-20 is meant to supercruise, then ideally the DSI should be optimized for good pressure recovery above the transonic speed envelope. If the optimization and designed parameters are different, we can't simply transplant the pressure recovery drop off for a DSI inlet designed for one plane onto another. Therefore, unless you have strong evidence that the J-20's DSI is indeed limited at the Mach numbers you claim, your assertion is purely based on unfounded conjecture.

The other possibility is that you're assuming all external compression inlets are limited to mach 1.8-mach 2.0. However, that is a meaningless assertion, because external compression inlets can also be designed for higher mach numbers. External compression limits are a broad category that have nothing to do with effective mach numbers.

This is my last reply on this thred to you about this topic, the J-20`s DSI simply can not be used for several mach numbers as long is fixed, simply like that if you can not understand it read a few papers explaining why F-15 uses a variable geometry intake of external compression and XB-70 uses mixed compression on a variable geometry intake the reason is the air mass flow that changes with speed and that will require a different size intake.

Variable geometry changes for that the throat

 

[latenlazy]

This is my last reply on this thred to you about this topic, the J-20`s DSI simply can not be used for several mach numbers as long is fixed, simply like that if you can not understand it read a few papers explaining why F-15 uses a variable geometry intake of external compression and XB-70 uses mixed compression on a variable geometry intake the reason is the air mass flow that changes with speed and that will require a different size intake.

Variable geometry changes for that the throat

I wouldn't call optimization from transonic cruise to supercruise mach numbers "several mach numbers".

What's lost in this discussion is the assumption that inlets designed for one range of mach numbers simply cannot operate in others. This assumption is not absolute. Total pressure recovery tells us whether the engine is getting enough air to operate efficiently, but what is enough air depends on the engine, and falling pressure recovery by itself doesn't dictate that an engine will stop working with certainty. Efficiency drops off first before the engine stalls. What this also means is that theoretically an intake can be designed for better pressure recovery at higher speeds in exchange for worse efficiency at lower ones. For all we know, the J-20's inlets could be optimized for efficiency at supercruise, which could raise the mach number at which pressure recovery begins to drop off in exchange for reduced pressure recovery and efficiency at lower speeds, relative to a fixed inlet optimized for the transonic speed envelope.

To sum it all up, no one's disputing that fixed inlets have limitations. What we're disputing is the assertion that all fixed inlets share the same performance parameters.

 

[Engineer]

I can tell you you can design a DSI for Mach 5 or Mach 6 but since it is fixed they can not be used for other speed ranges beyond their design numbers


A variable Geometry intake has 2 important aspects first changes the throat area as such will change the geometry of the intake allowing for a wider speed range simply like that, and second is adjusts the geometry in accordance of the shocks.

So yes you can have Mach 3 DSIs but the problem is by being fixed is limited to a narrower speed range.

J-20 flies from 0 to 2000km/h and this means at different moments the inlet requires different mass flows.

If you can not understand that i can not help it, i won`t argue 10 pages to repeat the same or answer posts of others that do not want to see reality.


The DSI of J-20 or J-31 are designed for Mach 1.6 or Mach 1.8 operations since they are external compression intakes.

read first the limits of external compression fixed intakes all are limited to Mach 1.8 + or - if you designed a optimized DSI for Mach 5, it only works for speeds in that range not for higher or lower Machs for such reason X-51 with a fixed intake needs a rocket booster.


I give you the last reply and let us move on

Wrong, as there are many aircraft that can exceed Mach 2.0 and utilize external compression inlets. The use of external compression does not limit an aircraft speed to Mach 1.6 or Mach 1.8. Your notion that an inlet being fixed must perform worse than a variable-geometry one has also been debunked. F-22 can fly faster than Mach 2.0 with fixed inlet. The F-22 can also supercruise with fixed inlet whereas many aircraft with variable-geometry inlet cannot. The only thing that matters for an inlet is the pressure recovery ratio. "At Mach 2.0 the pressure recovery ratio is 0.87" for DSI, the same as that of a 3-shock variable geometry inlet at Mach 2.0. DSI actually has better pressure recovery overall, implying a better speed range than a 3-shock variable-geometry inlet.

DSI does not have any limitation at Mach 1.6, Mach 1.8 or even Mach 2.0. That's the reality and isn't going to change no matter how often you repeat your myths.

 

[Skywatcher]

the translation was provided since the webpage quoted important fact says

Максимальная скорость , км/ч М=2.00 which means max speed Mach 2, the webpage says J-20 max speed is Mach 2

What's the source for that? Are we just to take them at their word.

Paul Metz, the test pilot for the F-22, states that the F-22 has fixed inlet (it obviously has speeds far in excess of Mach 2.0).

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Aviation Week Jan 8 2007, "Turn and Burn", D.A. Fulghrum and M.J. Fabey

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(Third page)

So should I believe Mr. Metz or some random Russian site?

I look forward to your concession.

 

[ahadicow]

MiG-29, you defy logic here. If DSI can only be optimized for a specific point of speed then how is it different than a simple fixed geometry inlet design? Why bother? why not just optimize the inlet geometry to suit the flight at specfic mach number?

The fact that inlet design went from fix geometry to varable geometry to DSI shows DSI is the result of sophsitication in aero dynamic modeling and design. Not backward, like you have suggested, to sacrifice aero-dynamic perfomance for the sake of simplicity or stealth.(there is no evidence that DSI would improve stealth whatsoever) The core idea of DSI is to use a single fixed geometry "bump" to modify the air flow at a wide range of airspeed. Percisely becuase of the need to optimize for different airspeed, This "bump" need to have very complex shape that requires precise computer modeling of the airflow over its surface at various speed. It is because of this, only a few country had mastered this technology.

But in your brilliant mind, US and Chinese engineers just went lazy. "Let's go simple and leave hard stuff for Russians" and so decided to gimp high mach performance on their latest and most advanced fighter jet. But the fact is, both have successfully designed varible-geometry engine inlet before and chose DSI for its superior aerodynamic performance. Russia had never designed a single DSI hence lack the experiance and would rather nor risk experimenting that on their most important project so they went old-school, plain and simple.

 

[latenlazy]

MiG-29, you defy logic here. If DSI can only be optimized for a specific point of speed then how is it different than a simple fixed geometry inlet design? Why bother? why not just optimize the inlet geometry to suit the flight at specfic mach number?

The fact that inlet design went from fix geometry to varable geometry to DSI shows DSI is the result of sophsitication in aero dynamic modeling and design. Not backward, like you have suggested, to sacrifice aero-dynamic perfomance for the sake of simplicity or stealth.(there is no evidence that DSI would improve stealth whatsoever) The core idea of DSI is to use a single fixed geometry "bump" to modify the air flow at a wide range of airspeed. Percisely becuase of the need to optimize for different airspeed, This "bump" need to have very complex shape that requires precise computer modeling of the airflow over its surface at various speed. It is because of this, only a few country had mastered this technology.

But in your brilliant mind, US and Chinese engineers just went lazy. "Let's go simple and leave hard stuff for Russians" and so decided to gimp high mach performance on their latest and most advanced fighter jet. But the fact is, both have successfully designed varible-geometry engine inlet before and chose DSI for its superior aerodynamic performance. Russia had never designed a single DSI hence lack the experiance and would rather nor risk experimenting that on their most important project so they went old-school, plain and simple.

Well, since a DSI does reduce drag and weight, an argument could be made that sacrifices in top speed could be made for simplicity's sake. However, this still would not address the other bad assumptions being made, such as the notion that fixed geometry inlets all share the same operation parameters.