SDF Aerospace and Aerodynamics Corner

Engineer said:

The reality here is that you have no evidence to make your theory come anywhere close to being reality. It is very simple really: you claim that variable-geometry inlet allows an aircraft to reach Mach 2.0, and both F-104 and F-4D employ this type of inlet to reach/exceed Mach 2.0. DSI having higher pressure recovery ratio means the inlet functions more efficiently than variable-geometry inlets. It is quite logical: DSI have better performance than the variable-geometry inlets on F-104 and F-4D.

Let's face it. You have no support whatsoever that DSI cannot reach Mach 2.0. When this claim of yours is wrong already, claiming DSI has an absolute speed limit of Mach 1.7 is just as wrong.

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hahaha thepaper says:

The oblique shock and
normal shock wave impinge near the cowl lip
and continues on ........
while the supersonic characteristics are evaluated at M∞
= 1.7, which is near the design Mach number for the intake





hahaha


DSI are used simply because the reduce weight, are stealthy and cheapen production and maintainance



successful design, such as that on the Lockheed Martins F-35 Lightning II, shows that a
Diverterless Supersonic Inlet (DSI) compared to a conventional intake can reduce the weigh,t
and weight is the primary driver to reduce cost and increase performance of a fighter aircraft

MiG-29 said:

hahaha thepaper says:

The oblique shock and
normal shock wave impinge near the cowl lip
and continues on ........
while the supersonic characteristics are evaluated at M∞
= 1.7, which is near the design Mach number for the intake

Click to expand...

LMAO!

The paper didn't say Mach 1.7 is the speed limit of DSI. The words "design Mach number" does not mean "speed limit", and if you are serious in equating these two phrases, it means you have absolutely no idea what you are talking about.

Also, the fact that the papers mentioned about the shockwaves being generated show the main principle behind DSI is much like that of variable-geometry, which is generation of shockwaves to slow supersonic flow to subsonic speed.

MiG-29 said:

hahaha


DSI are used simply because the reduce weight, are stealthy and cheapen production and maintainance


successful design, such as that on the Lockheed Martins F-35 Lightning II, shows that a
Diverterless Supersonic Inlet (DSI) compared to a conventional intake can reduce the weigh,t
and weight is the primary driver to reduce cost and increase performance of a fighter aircraft

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Click to expand...

DSI is used also because of its ability to fly at supersonic speed, and we have seen the quoted figures of DSI being 0.87 at Mach 2.0 - similar to the Mach 2 variable-geometry inlets of F-4D. The value of this ratio is 0.91 at Mach 1.8, higher than the inlets on the F-4D. This pretty much blows your theory that DSI cannot reach/exceed Mach 2.0 right out of the water.


Observe what the paper says:

For DSI, pressure recovery coefficient is higher than 0.91 at M0.8. At M2.0, the coefficient decreases to 0.87. This suggests that the DSI being tested can reach Mach 2.0.

Engineer said:

LMAO!

The paper didn't say Mach 1.7 is the speed limit of DSI. The words "design Mach number" does not mean "speed limit", and if you are serious in equating these two phrases, it means you have absolutely no idea what you are talking about.

Also, the fact that the papers mentioned about the shockwaves being generated show the main principle behind DSI is much like that of variable-geometry, which is generation of shockwaves to slow supersonic flow to subsonic speed.



DSI is used also because of its ability to fly at supersonic speed, and we have seen the quoted figures of DSI being 0.87 at Mach 2.0 - similar to the Mach 2 variable-geometry inlets of F-4D. The value of this ratio is 0.91 at Mach 1.8, higher than the inlets on the F-4D. This pretty much blows your theory that DSI cannot reach/exceed Mach 2.0 right out of the water.

Observe what the paper says:

For DSI, pressure recovery coefficient is higher than 0.91 at M0.8. At M2.0, the coefficient decreases to 0.87. This suggests that the DSI being tested can reach Mach 2.0.

Click to expand...

no mach is not speed of sound and aircraft are not say to fly at mach 2, hahaha poor of you, by the max design Mach number means the jet has its max speed efficiency at such speed, who do you think you are lying to?

You lie to your self, the paper means is near the max speed where the DSI is operationally efficient, the number might be Mach 1.85.


And since that number is lower than what a F-15 or F-14 intakes can achieve, it is obvious the intake is not for Mach 2.35.

But for the benefit of others since you have chosen to lie to your self


DSI are used to cheapen the price as the swedish document stablishes, true they are good at speeds below Mach 2, they are operationally efficient at speeds of around 1.7, allow stealth and cheap prices at manufacture and maintainance.

For aircraft ike JF-17, F-16 and F-35 are good.

What you do not understand is 2D intakes are more expensive to build and maintain and mask with stealth features, but in performance a Su-35S can achieve better pressure recovery at Mach 2.2 than a J-10B or JF-17 but it has the disadvantage of higher maintainance, price, weight and less intrinsic stealth traits

Re: J-20... The New Generation Fighter III

MiG-29 said:

i will ask you do you have an official source saying at this moment China has 200 J-10s?
Second China has bought 500 Al-31s, but not all the Al-31 have been delivered yet in fact it is probable they have not gotten 200-150 engines yet,
they have not recieved 122 Al-31 for sure since they just signed the contract for them in October 2011.
While there is a small chance a few J-10 might be re-engined, it is not logic if you have WS-10 do not re-engine them with WS-10s, most J-10s have less than 7 years.

Second if WS-10 wiill replace Al-31s soon re-engine J-10s in 2014-2017 might be logic.

Now most likely it was designed with the ability to be fitted into J-10s using Al-31, that is the most logic design criteria.

I will ask you why then China has bought 500 Al-31s if the entire fleet of J-10s is 200 jets? it means production is slow, i doubt J-10s can not be produced in numbers of 30 jets a year or even 40, if production is so low and the fleet so young even having WS-10s, it leaves you three possible reasons:

A) production of J-10 will speed up and numbers increase that is the reason they bought 500 Al-31s and WS-10 is still not ready


B)production J-10 is very high that WS-10 production is not enough, but you say production is slow

C)Early J-10s can not be fitted with WS-10, production is slow and they will switch to WS-10 soon, see here the contradiction, Chengdu did not design J-10s with the ability to accept easily WS-10s so they have to buy 2 engines per plane, two Al-31s equal 6 million dollars, it means fitting Ws-10 to an early J-10 is more expensive than 3 million dollars.


So Chengdu obviously favours not WS-10, their own engine, who wins Saturn


So my conclusion is WS-10 is not ready, why? simple Chengdu favours WS-10, so by logic they designed it with the ability to be retrofitted to J-10s currently using Al-31 at a low price per modification, lower than buying newer Al-31s.

Third in order to protect the national jet engine industry they will try to make last Al-31s the longest so each Al-31 goes to a new J-10 airframe and its replacement will be a WS-10 even in J-10s currently using Al-31s

Click to expand...

I will reply in this is their such thing as official figures for anything regarding PLA inventory numbers. I wasn't evening referencing or talking about WS-10, so don't bring that into play. Saying they are building this amount of number of J-10's based on orders for AL-31. Even if they have that many engines that, you don't look at the amount of engines bought but the capacity of the assembly line. I don't question they can build more J-10's per year, but it does seem to be slowing down a bit.

You even said that not all 500 have been delivered. You argue that ~200 is not right based on the fact that 500 will be acquired eventually once contract has been delivered. ~200 is around current numbers, i didn't say 200 will be built with 500 engines that will be eventually provided. Your assumptions is based of just one variable 500 engines, and you predicted 30-40 J-10 a year. If 30-40 J-10's a year you have just assumed that J-10 will be in production for 12-17 years.

Don't twist my post into an argument that suits yours.

MiG-29 said:

no mach is not speed of sound and aircraft are not say to fly at mach 2, hahaha poor of you, by the max design Mach number means the jet has its max speed efficiency at such speed, who do you think you are lying to?

Click to expand...

LOL! You are so desperate right now in making your wrong theory seems right that you can't even come up with coherent argument! Mach speed is the airspeed of an aircraft in multiples of speed of sound. Go read up on as you don't seem to have a good understanding as to what it means.

The phrase "design Mach number" does not refer to "max speed". It means the speed at which peak efficiency is achieved and in no way represents the maximum air speed at which an inlet can operate. Graphically, the peak efficiency is the apex of the curve in the following graph. We can see that the apex of the curve for F-15 is at the transonic regime, but this doesn't mean F-15 is limited to airspeed of Mach 1.0 as your claim would imply.


Like I have said, you do not know what you are talking about. Knowing a couple of terminologies and throwing out a bunch of technical terms incoherently do not make turn fiction into fact.

MiG-29 said:

You lie to your self, the paper means is near the max speed where the DSI is operationally efficient, the number might be Mach 1.85.


And since that number is lower than what a F-15 or F-14 intakes can achieve, it is obvious the intake is not for Mach 2.35.

But for the benefit of others since you have chosen to lie to your self

Click to expand...

Nope, there are no lies on my part. Lying means one is saying some fictional as if it is a fact. Example of lying is claiming DSI cannot work at Mach 2.0. Another example of lying is portraying optimal speed at which an inlet is most efficient as the absolute speed limit.

DSI has higher pressure recovery ratio than the variable geometry inlets of F-104 and F-4D, which is a fact. The latter two aircraft can reach/exceed Mach 2.0 is also a fact. Presenting facts is not an act of lying. The act of pointing out DSI has better pressure recovery ratio thus is more efficient and conclude DSI is functional at Mach 2.0 is called making proper argument, because the conclusion is based on facts and logic is employed.

Re: J-20... The New Generation Fighter III

MiG-29 said:

DSI are used to cheapen the price as the swedish document stablishes, true they are good at speeds below Mach 2, they are operationally efficient at speeds of around 1.7, allow stealth and cheap prices at manufacture and maintainance.

For aircraft ike JF-17, F-16 and F-35 are good.

What you do not understand is 2D intakes are more expensive to build and maintain and mask with stealth features, but in performance a Su-35S can achieve better pressure recovery at Mach 2.2 than a J-10B or JF-17 but it has the disadvantage of higher maintainance, price, weight and less intrinsic stealth traits

Click to expand...

As you've said, variable-geometry intake (which you referred to as 2D intake) is more expensive to build and maintain. Why? Because such intake is mechanically complex. The more shockwaves to be generated, the more ramps are needed, and the complexity increases. Increase of complexity causes increase in weight, which cancels out any efficiency gained.

Claiming inlet X has better pressure recovery ratio than Y does not prove Y cannot operate in Mach 2.0 speed. In other words, you still have yet to be able to provide proof that DSI cannot operate at Mach 2.0. On the other hand, we see the quoted figure of pressure recovery ratio is higher for DSI than some Mach 2 variable-geometry inlets, meaning there is no reason that DSI cannot operate at Mach 2.0.

Re: J-20... The New Generation Fighter III

Engineer said:

As you've said, variable-geometry intake (which you referred to as 2D intake) is more expensive to build and maintain. Why? Because such intake is mechanically complex. The more shockwaves to be generated, the more ramps are needed, and the complexity increases. Increase of complexity causes increase in weight, which cancels out any efficiency gained.

Claiming inlet X has better pressure recovery ratio than Y does not prove Y cannot operate in Mach 2.0 speed. In other words, you still have yet to be able to provide proof that DSI cannot operate at Mach 2.0. On the other hand, we see the quoted figure of pressure recovery ratio is higher for DSI than some Mach 2 variable-geometry inlets, meaning there is no reason that DSI cannot operate at Mach 2.0.

Click to expand...

i have never said DSI can not operate at Mach 2, i simply said, the ideal operational speed is near 1.8, but true DSI has advantages, for a J-20 i guess still gives it good supercruise ability of Mach 1.6-1.7 and perhaps very short dashes at Mach 2 . that could be possible.

But what you are unwilling to see its the the limits of DSI intakes, in performance a F-14 or F-111 has better pressure recovery, but for the F-111 or F-14 stealth is harder to achieve.

So there is a trade off, lower pressure recovery but better stealth, on the Su-35S, it can supercruise, it is very agile but is more visible on radar, so of course J-10B frontally has better stealth potential than Su-35S.


Su-35 by having better pressure recovey allows its lower thrust engines achieve supercruise thanks to more efficient pressure recovery than F-35 or J-10B.


On F-22 the fixed intakes limit the speed, the 2D nozzles add weight so it needs very powerful engines to overcome its fixed intake design and 2D nozzles.

F-22 wastes thrust, but it has good engines, Su-35S can not do that 117 has lower thrust, so round nozzles and variable geometry intakes give it higher speed Mach 2.2 and at 14.4 tonnes each reach supercruise.

However Su-35 has not the stealth of F-22 niether its supercruise top stealth.

Re: J-20... The New Generation Fighter III

MiG-29 said:

i have never said DSI can not operate at Mach 2, i simply said, the ideal operational speed is near 1.8, but true DSI has advantages, for a J-20 i guess still gives it good supercruise ability of Mach 1.6-1.7 and perhaps very short dashes at Mach 2 . that could be possible.

Click to expand...

Ideal operational speed for any type of inlet is lower than the top-speed of the aircraft. This is true also for variable-geometry inlets. Ideal operational speed however, is not the same as maximum operation speed.

MiG-29 said:

But what you are unwilling to see its the the limits of DSI intakes, in performance a F-14 or F-111 has better pressure recovery, but for the F-111 or F-14 stealth is harder to achieve.

Click to expand...

All intakes have their limitation, and never have I once said that DSI has no limitation whatsoever. As for pressure recovery ratio, a higher value means the inlet is more efficient, but it does not mean the aircraft flies more efficiently. You must also consider the weight of the inlet, as well as the airframe design. Higher pressure recovery is only useful as long as there is nothing else the incurred penalties are less than the gain.

Re: J-20... The New Generation Fighter III

MiG-29 said:

So there is a trade off, lower pressure recovery but better stealth,

Click to expand...

That lower pressure recovery ratio that you point at is still higher than the value of some variable-geometry inlets. The use of a variable-geometry inlet does not automatically make an aircraft better.

MiG-29 said:

on the Su-35S, it can supercruise, it is very agile but is more visible on radar, so of course J-10B frontally has better stealth potential than Su-35S.

Su-35 by having better pressure recovey allows its lower thrust engines achieve supercruise thanks to more efficient pressure recovery than F-35 or J-10B.

On F-22 the fixed intakes limit the speed, the 2D nozzles add weight so it needs very powerful engines to overcome its fixed intake design and 2D nozzles.

F-22 wastes thrust, but it has good engines, Su-35S can not do that 117 has lower thrust, so round nozzles and variable geometry intakes give it higher speed Mach 2.2 and at 14.4 tonnes each reach supercruise.

However Su-35 has not the stealth of F-22 niether its supercruise top stealth.

Click to expand...

Not so. Su-35 employs same style of inlets as Su-27, but Su-27 cannot supercruise. If the type of inlets is all that matters, then Su-27 should be able to supercruise as well.

What enable Su-35 to supercruise are increase in thrust by the use of 117S engines over Al-31F, and a redesigned body to improve the aircraft's aerodynamics. It has little to do with the inlets.

Re: J-20... The New Generation Fighter III

Engineer said:

That lower pressure recovery ratio that you point at is still higher than the value of some variable-geometry inlets. The use of a variable-geometry inlet does not automatically make an aircraft better.



Not so. Su-35 employs same style of inlets as Su-27, but Su-27 cannot supercruise. If the type of inlets is all that matters, then Su-27 should be able to supercruise as well.

What enable Su-35 to supercruise are increase in thrust by the use of 117S engines over Al-31F, and a redesigned body to improve the aircraft's aerodynamics. It has little to do with the inlets.

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ii is not that simple, to put you and example 117 is a 14.5 tonnes thrust engine while f119 is a 15+ tonnes engine.

Pressure recovery means which engine will lose more thrust and spend more fuel.

If F-22`s pressure recovery is at Mach 1.7; 0.92, it will reduce its F119 thrust of 15.8 tonnes to something like 13 tonnes, first because the flat nozles reduce thrust around 10% or more and the pressure recovery thrust lose will be another 11%.

So pressure recovery is very important.

If Su-35 has 14.5 tonnes of thrust in each 117 and has pressure recovery of 0.96 at Mach 1.8, it will lose around 6% of thrust and by having no flat nozzles, so the loses of the 117 will be lower at mach 1.8 than F119 at Mach 1.7.

Speed: The F-22's speed class is Mach 2.



Maximal airspeed :
H=200 m, km/h 1,400
H=11,000 m , M 2.25


so while it is true F-22 has more thrust, the intake of Su-35S is good to reduce thrust loses and fuel comsuption

by the way merry christmas engineer and all of you