SDF Aerospace and Aerodynamics Corner

MiG-29 said:

MiG-31 has a more effective intake for speeds beyond Mach 2,

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This does not mean DSI cannot reach or exceed Mach 2.0. Claiming that it is "more effective" does not prove your claim in anyway, especially in light of the fact that the quoted figure of pressure recovery ratio for DSI is higher than the intakes on F-104 and F-4D, both capable of reaching/exceeding Mach 2.0.

MiG-29 said:

in fact if you read what the page says

Боевой радиус действия, км
operational radius km
при полете к на сверхзвуковой скорости 720
at flight at supersonic speed 720km

So its range is around 1420km at a speed of 2500km/hr, that is around 35 minutes flight, however considering landing it might 30 minutes.

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If you read carefully, it reads "operational radius km at flight at supersonic speed". What is supersonic speed? Supersonic speed means that the airspeed is above Mach 1.0, it doesn't have to mean top speed. In other words, 35-minute is another number which you pulled out from thin air as it has nothing to do with flight duration at top speed.

MiG-29 said:

This is the closest aircraft to a F-22, however MiG-31 uses afterburner and carries at least 20000kg in fuel.
Масса, кг:
пустого самолета 21820 empty weight 21820
нормальная взлетная 41000 normal take off 41000
максимальная взлетная 46200 max yake off weight 46200
боевая нагрузка - 3000 кг weapons load 3000kg

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Try to catch a MiG-31, is a pretty hard thing specially now that it is armed with AA-12 and (R-37) AA-13.

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This is complete rubbish. MiG-31 needs afterburner for supersonic cruise, where as F-22 doesn't. A more complex inlets cannot allow the MiG-31 to achieve something that fixed inlets on the F-22 can do, and this blows your "MiG-31 inlets are more effective" retort out of the water.

Variable-geometry intake isn't superior to all other types of intakes as you claimed.

MiG-29 said:

Now DSI is well designed to reduce manufacturing and maintainance costs.

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DSI is also designed to achieve what variable-geometry intakes can do without the weight penalty. We can tell this is the case by noting DSI's better pressure recovery ratio than variable-geometry intakes of F-104 and F-4D.

MiG-29 said:

And you are pretty wrong, by achieving lower pressure recovery, it will have increased risks of engine failure and limit the flight time at top speed.

The F-104 and F-4D won`t fly as long as a MiG-31 at Mach 2.35 simply because their lower pressure recovery implies higher fuel comsuption and higher risk of engine damage, surge or flame outs.

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Actually, this is merely your opinion. The fact is, flight time at top speed is not determined by pressure recovery ratio alone, but has more to do airframe design which affects lift-to-drag ratio. Being able to go faster does not automatically implies the aircraft can also fly longer. The MiG-31, which requires afterburner to sustain supersonic cruise, will not fly longer than F-22 which is capable of supersonic flight without afterburner.

Pressure recovery ratio is a measurement of the efficiency of the inlets, and is not a measurement of probability of an engine failure. Risks of engine failure have a lot to do with the engine design itself, such as compressors design. At level flight, an aircraft having an inlet with lower pressure recovery ratio will not be able to accelerate pass the point where the engine cannot produce effective thrust. Your assumption of a situation where the aircraft accelerates faster than the engine can bared isn't realistic.

MiG-29 said:

On the F-104 by being a single engine aircraft, will meant fatal crashes if the only engine fails, on the F-4D it will mean less risk, but it will mean more maintainance, in fact you are so illogical as to claim for the US navy the F-4 was as good as the F-14! the F-14 was better simply because it meant higher reliability, in fact the F-14D was years ahead of Any F-4D or E but of course you want to prove at any cost.

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You sound desperate here. The figures we have seen prove your claims are wrong, and now you are up to your usual tricks by making up statements that I did not say. Of course, we both know that you are unable to quote where I've ever said "F-4D is as good as the F-14".

You claimed that variable-geometry intake must be employed for an aircraft to reach or exceed Mach 2.0. I have shown you figures that DSI can achieve higher pressure recovery ratio than the inlets of F-4D, and since that ratio is a measurement of inlet efficiency, it means DSI is fully capable of reaching and exceeding Mach 2.0.

Your claims are wrong. But of course, you are now dragging in irrelevant points such as number of engines on an aircraft to hide that fact at any cost.

MiG-29 said:

DSI intakes are designed for speeds bellow Mach 2, Mach 2 is the upper limit of that intake type, for single engine fighters with DSI Mach 1.7 is the ideal top speed

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This is your opinion, and one that is already proven as wrong. So far, you have provided no evidence to indicate DSI has an absolute upper limit of Mach 2.0.

Engineer said:

This does not mean DSI cannot reach or exceed Mach 2.0. Claiming that it is "more effective" does not prove your claim in anyway, especially in light of the fact that the quoted figure of pressure recovery ratio for DSI is higher than the intakes on F-104 and F-4D, both capable of reaching/exceeding Mach 2.0.


If you read carefully, it reads "operational radius km at flight at supersonic speed". What is supersonic speed? Supersonic speed means that the airspeed is above Mach 1.0, it doesn't have to mean top speed. In other words, 35-minute is another number which you pulled out from thin air as it has nothing to do with flight duration at top speed.


This is complete rubbish. MiG-31 needs afterburner for supersonic cruise, where as F-22 doesn't. A more complex inlets cannot allow the MiG-31 to achieve something that fixed inlets on the F-22 can do, and this blows your "MiG-31 inlets are more effective" retort out of the water.

Variable-geometry intake isn't superior to all other types of intakes as you claimed.

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hahaha poor of you what about this more specific page

Боевой радиус действия при полёте к рубежу перехвата, км
на сверхзвуковой скорости (М=2.35) без ПТБ

720




it says clearly operational radius at the speed of Mach 2.35 720km without external fuel tanks

Engineer said:

DSI is also designed to achieve what variable-geometry intakes can do without the weight penalty. We can tell this is the case by noting DSI's better pressure recovery ratio than variable-geometry intakes of F-104 and F-4D.


Actually, this is merely your opinion. The fact is, flight time at top speed is not determined by pressure recovery ratio alone, but has more to do airframe design which affects lift-to-drag ratio. Being able to go faster does not automatically implies the aircraft can also fly longer. The MiG-31, which requires afterburner to sustain supersonic cruise, will not fly longer than F-22 which is capable of supersonic flight without afterburner.

Pressure recovery ratio is a measurement of the efficiency of the inlets, and is not a measurement of probability of an engine failure. Risks of engine failure have a lot to do with the engine design itself, such as compressors design. At level flight, an aircraft having an inlet with lower pressure recovery ratio will not be able to accelerate pass the point where the engine cannot produce effective thrust. Your assumption of a situation where the aircraft accelerates faster than the engine can bared isn't realistic.


You sound desperate here. The figures we have seen prove your claims are wrong, and now you are up to your usual tricks by making up statements that I did not say. Of course, we both know that you are unable to quote where I've ever said "F-4D is as good as the F-14".

You claimed that variable-geometry intake must be employed for an aircraft to reach or exceed Mach 2.0. I have shown you figures that DSI can achieve higher pressure recovery ratio than the inlets of F-4D, and since that ratio is a measurement of inlet efficiency, it means DSI is fully capable of reaching and exceeding Mach 2.0.

Your claims are wrong. But of course, you are now dragging in irrelevant points such as number of engines on an aircraft to hide that fact at any cost.


This is your opinion, and one that is already proven as wrong. So far, you have provided no evidence to indicate DSI has an absolute upper limit of Mach 2.0.

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i put it simply as mach increases pressure recovery lowers in the DSI, efficiency drops, on a F-14, F-111 and F-15 the pressure recovery coefficient is higher at Mach 1.8 than the DSI and again is higher at Mach 2, a loss of .13 will mean around 20% loss of thrust and 10% increase on fuel.

As a result the DSI is less suited for supercruise and Mach 2.35 than the inlet of a F-14, MiG-31 or F-111 and much less efficient than the SR-71 at Mach 2.35.


In order to keep an ideal pressure recovery of 0.91 the DSI needs speeds of Mach 1.8 and achieve near .95
speeds of Mach 1.5, F-35 and JF-17 show that.

lower pressure recovery means higher risk of:
the flow conditions around the blade change very quickly. The changing flow conditions can cause flow separation in the compressor, a compressor stall, and can cause structural problems for the compressor blades. A good inlet must produce high pressure recovery, low spillage drag, and low distortion

MiG-29 said:

i put it simply as mach increases pressure recovery lowers in the DSI, efficiency drops

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The same phenomeon occurs on all type of inlets, not just DSI.

MiG-29 said:

on a F-14, F-111 and F-15 the pressure recovery coefficient is higher at Mach 1.8 than the DSI and again is higher at Mach 2, a loss of .13 will mean around 20% loss of thrust and 10% increase on fuel.

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And the pressure recovery ratio of DSI is higher than the inlets on F-104 and F-4D. The latter two aircraft can achieve and exceed Mach 2.0, so there is no reason a more efficient of DSI cannot do the same or better. You are unable to form a valid retort for this, not to mention that you have yet to have any support for your claim that DSI has an absolutely speed limit of Mach 2.0.

MiG-29 said:

As a result the DSI is less suited for supercruise and Mach 2.35 than the inlet of a F-14, MiG-31 or F-111 and much less efficient than the SR-71 at Mach 2.35.

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This is complete rubbish. First, you need to understand what supercruise is. Supercruise refers to the ability to fly at supersonic speed without the need of afterburner. It does not mean an flying at Mach 2.35. Making up definition will not help you in turning your false claims into facts.

Secondly, none of the aircraft that you claimed to have highly efficient inlets, be it F-14, F-15, F-111, or MiG-31, has such ability. The only aircraft proven to have supercruise capability so far is the F-22, which employs a fixed inlet. The ability of F-22 to supercruise while those other aircraft cannot means F-22 is more efficient.

Third, J-20 is intended to be a 4th generation fighter (5th generation fighter by Western standards), which has to achieve 4-S criteria. One of the criterias is the ability of supercruise. The employment of DSI on such an aircraft means DSI is perfectly capable of being used in supercruise. Your claim that DSI is less suitable in supercruise is completely fictional and is merely your own opinion. Obviously, the designers of the actual aircraft have more knowledge and tools than you who can't manage to grasp simple aerodynamic terms, so the designers would be right and you would be wrong.

Forth, the fact that F-22's fixed inlets allow the aircraft to have a capability to supercruise while the other aircraft cannot shows that inlets efficiency is not a representation of flight duration. Your argument that fixed inlet performs poorly compared to variable-geometry inlets and that DSI being fixed therefore also performs poorly is a complete fail.

MiG-29 said:

In order to keep an ideal pressure recovery of 0.91 the DSI needs speeds of Mach 1.8 and achieve near .95 speeds of Mach 1.5, F-35 and JF-17 show that.

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You are wrong again. 0.91 is not the ideal pressure recovery, nor is it a cutoff point for aircraft that can reach/exceed Mach 2 and those that cannot. It is simply a value of inlet's efficiency at Mach 1.8, nothing more. It does not represent absolute speed limit of the inlet.

You claimed that variable-geometry intakes are needed to reach/exceed Mach 2.0. Well, F-104 and F-4D employ this type of inlets, yet their pressure recovery ratio is lower than that of DSI. We both know you keep on evading this point because it proves you wrong.

MiG-29 said:

lower pressure recovery means higher risk of:
the flow conditions around the blade change very quickly. The changing flow conditions can cause flow separation in the compressor, a compressor stall, and can cause structural problems for the compressor blades.

Click to expand...

No it doesn't. Pressure recovery ratio is a measurement of inlet efficiency, not a probability value for engine surge. Once again, you are making up definition.

MiG-29 said:

A good inlet must produce high pressure recovery, low spillage drag, and low distortion

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Click to expand...

Good inlet design is reflected in the value of pressure recovery ratio, and we see value of this ratio for DSI is higher than that of F-4D at Mach 1.8. We also see this ratio for DSI is higher than that of F-104 at Mach 2.0. Thus, DSI is the better design in both of these cases, contrary to your claim that variable geometry intakes must be used.

MiG-29 said:

hahaha poor of you what about this more specific page

Боевой радиус действия при полёте к рубежу перехвата, км
на сверхзвуковой скорости (М=2.35) без ПТБ

720




it says clearly operational radius at the speed of Mach 2.35 720km without external fuel tanks

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Click to expand...

Is that the point of contention? No. But to entertain you, we can compare this value to the , which is quoted at 759km. This is done with 8200kg of fuel, compared to . Who is more efficient?

Granted, the loaded weight of MiG-31 is about 1/3 more heavy than F-22, but MiG-31 requires twice the amount of fuel than F-22. Who is more efficient?

F-22 can achieve said range without the use of afterburner, while MiG-31 needs afterburner to reach supersonic speed. Who's more efficient.

F-22 also has enough lift left over to pull 9g maneuvers, where as MiG-31 can't. This means more engine thrust is devoted into keeping the aircraft in the sky in the case of MiG-31. Who is more efficient?

Giving a random specification is meaningless. Like I have pointed out, flight duration has a lot more to do with just pressure recovery ratio. Giving a random value is not a proof that inlets with more complexity are better than inlets with less complexity.

Engineer said:

Is that the point of contention? No. But to entertain you, we can compare this value to the

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, which is quoted at 759km. This is done with 8200kg of fuel, compared to

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. Who is more efficient?

Granted, the loaded weight of MiG-31 is about 1/3 more heavy than F-22, but MiG-31 requires twice the amount of fuel than F-22. Who is more efficient?

F-22 can achieve said range without the use of afterburner, while MiG-31 needs afterburner to reach supersonic speed. Who's more efficient.

F-22 also has enough lift left over to pull 9g maneuvers, where as MiG-31 can't. This means more engine thrust is devoted into keeping the aircraft in the sky in the case of MiG-31. Who is more efficient?

Giving a random specification is meaningless. Like I have pointed out, flight duration has a lot more to do with just pressure recovery ratio. Giving a random value is not a proof that inlets with more complexity are better than inlets with less complexity.

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But you forget a detail, MiG-31, flies at Mach 2.35 while F-22 flies at Mach 1.7, and small detail we are comparing DSI intakes to 2D ramp with diverters and variable geometry, for the F-22 to fly at Mach 2 needs afterburner , so for F-22 to fly at 2.35 needs afterburner like MiG-31 and a variable geometry intake.

MiG-29 said:

But you forget a detail, MiG-31, flies at Mach 2.35 while F-22 flies at Mach 1.7, and small detail we are comparing DSI intakes to 2D ramp with diverters and variable geometry, for the F-22 to fly at Mach 2 needs afterburner , so for F-22 to fly at 2.35 needs afterburner like MiG-31 and a variable geometry intake.

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In other words, if MiG-31 were to fly at Mach 1.8, it needs afterburner where as F-22 doesn't. If according to you, more complex inlet makes engine more efficient to produce more thrust, then MiG-31 should be able to supercruise. Sadly for you, that isn't the case. Instead we see F-22 with fixed inlets being the one that can supercruise.

And you are right that we are comparing DSI to 2D ramp with diverters and variable geometry. Comparing the pressure recovery ratio shows DSI is better than the inlets on F-4D. We see from this that DSI is perfectly efficient enough to work at Mach 2.0, thus debunking your theory.

Engineer said:

In other words, if MiG-31 were to fly at Mach 1.8, it needs afterburner where as F-22 doesn't. If according to you, more complex inlet makes engine more efficient to produce more thrust, then MiG-31 should be able to supercruise. Sadly for you, that isn't the case. Instead we see F-22 with fixed inlets being the one that can supercruise.

And you are right that we are comparing DSI to 2D ramp with diverters and variable geometry. Comparing the pressure recovery ratio shows DSI is better than the inlets on F-4D. We see from this that DSI is perfectly efficient enough to work at Mach 2.0, thus debunking your theory.

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ha haha, first by flying at Mach 2.35 a MiG-31 flies around 500km/hr faster than the F-22, for the F-22 to catch it up in speed needs afterburner, so hahaha is not the other way around, MiG-31 won`t slow down but speed up.

Now MiG-31 is a 1976 aircraft while the F-22 is a 1997 jet.

DSI has the pressure recovery of an F-4D of 1962, wow, you do not understand what is DSI, DSI never was meant to be a Mach 2.3 intake、its design limit is Mach 1.7, however you think is so great, buut the reality is it can not achieve the pressure recovery of 2D intakes with 4 shocks and mixed or external compression, true DSI is better than the intake of the F-16, well suited to cheapen and lighten the F-35

The subsonic characteristics are evaluated
at M∞ = 0.8 while the supersonic characteristics are evaluated at M∞
= 1.7, which is near the design Mach number for the intake

But at 0.87 at 0 alpha AoA and 0 Beta AoA flying at Mach 2, is not great, in fact the F-111 achieves the same numbers at AoA higher than 0 degrees both at Alpha and Beta or in other words higher than 0 yaw and 0 pitch angles.

The DSI exhibits 0.87 pressure recovery coefficient at 0 yaw and 0 pitch but add higher AoA both at yaw or Alpha it will go below 0.87 and 0.87 is still lower than what and F-15 or F-14`s 2D intakes, proof well the F-14 and F-15 replaced and surpassed the F-4 both in turning ability where yaw and pitch AoA reduces pressure recovery and at high speed where their pressure recovery is higher.


F-4 was not superior to F-15 niether to F-14.


Yes DSI is good for stealth, cheapens the price but is not for extended supersonic flight or higher speeds of Mach 2.