SDF Aerospace and Aerodynamics Corner

MiG-29 said:

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.

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LOL! You have no clue as to how aerodynamic works. Afterburner gives an aircraft more thrust by dumping and igniting fuel in the hot exhaust, as result an aircraft using afterburner consumes more fuel than an aircraft that leaves afterburner off. This means MiG-31 requires more fuel thus is less efficient than F-22, not the other way around.

If higher pressure recovery ratio automatically makes an aircraft more efficient, then MiG-31 should be able to supercruise. Clearly, this isn't the case. Pressure recovery ratio only reflects the efficient of an inlet, nothing more.

MiG-29 said:

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

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EXACTLY! This is the only thing you have got right since this discussion began. MiG-31 is a 1976 aircraft, over 20 years older than F-22. In these 20 years, aerodynamics advanced enough to enable fixed intakes to let F-22 sustains supersonic flight without afterburner and exceeds Mach 2.

You argue that fixed intakes are inferior to variable-geometry inlets, and so DSI must be inferior. But this argument doesn't even work since F-22's inlets achieved what variable-geometry inlets have yet able to achieve.

MiG-29 said:

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

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This is only your opinion. You desperately try to place an absolute speed limit on DSI because you cannot accept Chinese jets are capable of flying at Mach 2. Yet, the reality is the Mach 1.7 speed limit you imposed does not exist. You have no evidence that it exists.

For DSI, pressure recovery coefficient is higher than 0.91 at M1.8. At M2.0, the coefficient decreases to 0.87. The value at Mach 1.8 is better than that of F-4D, and the value at Mach 2.0 is same as that of F-4D. F-4D's inlets have intake ramp, enabling the aircraft to achieve/exceed Mach 2.0. The fact that its pressure recovery ratio is worse compared to DSI means DSI is fully capable of reaching/exceeding Mach 2.0.

MiG-29 said:

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

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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.

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And F-22 surpasses MiG-31 in turning capability, even though the latter employs a variable-geometry intake. This shows pressure recovery ratio is not a measurement of turning capability. Employing more ramps may increase efficiency of an inlet, but the resulting complexity and weight cancels out gains in that efficiency, and this is clearly illustrated in the F-22 vs. MiG-31 comparison.

From the 2005 figure, we see DSI having a pressure recovery ratio of 0.87 at Mach 2.0. Mach 2.0! This means DSI has no issue flying at that speed. On other hand, you have no evidence that DSI cannot fly faster than Mach 1.7.

MiG-29 said:

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.

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DSI reduces complexity thus weight, while increases the pressure recovery ratio when compared to the variable-geometry intakes on F-4D. Given that F-4D's inlets function at Mach 2.0, a more efficient DSI would perform equally well if not better.

Engineer said:

LOL! You have no clue as to how aerodynamic works. Afterburner gives an aircraft more thrust by dumping and igniting fuel in the hot exhaust, as result an aircraft using afterburner consumes more fuel than an aircraft that leaves afterburner off. This means MiG-31 requires more fuel thus is less efficient than F-22, not the other way around.

If higher pressure recovery ratio automatically makes an aircraft more efficient, then MiG-31 should be able to supercruise. Clearly, this isn't the case. Pressure recovery ratio only reflects the efficient of an inlet, nothing more.


EXACTLY! This is the only thing you have got right since this discussion began. MiG-31 is a 1976 aircraft, over 20 years older than F-22. In these 20 years, aerodynamics advanced enough to enable fixed intakes to let F-22 sustains supersonic flight without afterburner and exceeds Mach 2.

You argue that fixed intakes are inferior to variable-geometry inlets, and so DSI must be inferior. But this argument doesn't even work since F-22's inlets achieved what variable-geometry inlets have yet able to achieve.

Click to expand...

hahaha let us see if you are right

The detailed shock wave structure in the vicinity of the bump
compression surface and the inlet cowl is shown in Fig. 7. Mach
number distribution on seven equally spaced horizontal planes is
shown for this purpose. Oblique shock waves originate from the
leading edges of the bump compression surface as seen from this
figure (Fig. 7). Normal shock wave is apparent just short of the inlet.
The imprint of this normal shock wave on the bump surface forms
the ‘W’ shape (Fig. 6), as discussed earlier. The oblique shock and
normal shock wave impinge near the cowl lip, which shows a
relatively high intake mass flow ratio near intake design point.


Here we have the proof at Mach 1.7 the DSI generates only two shock waves, a normal and an oblique shock wave; so you have a two shock wave system, F-14 has a four shock wave system, now 4 shock waves system achieves at Mach 1.7 higher values of pressure recovery than a 2 shock waves system.


Now the bump is fixed, F-35 and J-10B have fixed bumps, the cowl lips on F-35 and J-20 are identical, designed to have better AoA and have changed the bump to avoid boundarily layer ingestion, thus F-35 has kept at Mach 1.6 but here we have claims of Mach 2.5.

The reality is unless China has a new technology not see on F-35, it will achieve Mach 2.5, but under regular DSI technology, it won`t.

Bump and cowl are fixed to divert boundary layer, thus mass flow can not be regulated by variable geometry.

Then your theory does not correspond to reality, real DSI have lower pressure recovery than 2D 4 multishock variable horizontal ramps on F-14, F-15, MiG-31 or 1/4 semiconical intakes like on F-111.

Engineer said:

This is only your opinion. You desperately try to place an absolute speed limit on DSI because you cannot accept Chinese jets are capable of flying at Mach 2. Yet, the reality is the Mach 1.7 speed limit you imposed does not exist. You have no evidence that it exists.

For DSI, pressure recovery coefficient is higher than 0.91 at M1.8. At M2.0, the coefficient decreases to 0.87. The value at Mach 1.8 is better than that of F-4D, and the value at Mach 2.0 is same as that of F-4D. F-4D's inlets have intake ramp, enabling the aircraft to achieve/exceed Mach 2.0. The fact that its pressure recovery ratio is worse compared to DSI means DSI is fully capable of reaching/exceeding Mach 2.0.

And F-22 surpasses MiG-31 in turning capability, even though the latter employs a variable-geometry intake. This shows pressure recovery ratio is not a measurement of turning capability. Employing more ramps may increase efficiency of an inlet, but the resulting complexity and weight cancels out gains in that efficiency, and this is clearly illustrated in the F-22 vs. MiG-31 comparison.

From the 2005 figure, we see DSI having a pressure recovery ratio of 0.87 at Mach 2.0. Mach 2.0! This means DSI has no issue flying at that speed. On other hand, you have no evidence that DSI cannot fly faster than Mach 1.7.



DSI reduces complexity thus weight, while increases the pressure recovery ratio when compared to the variable-geometry intakes on F-4D. Given that F-4D's inlets function at Mach 2.0, a more efficient DSI would perform equally well if not better.

Click to expand...

hahah yeah what you can not see is the bump of a DSI only generates two shock waves and generates less pressure recovery than F-14, F-15, F-111`s variable geometry intakes, that is based upon studies not gossips or theories.

Ah and by the way Su-35S has variable geometry intakes is faster than F-22, has supercruise showing your fantasy of 2d intakes being a hindrance is false in fact MiG-31 is less agile than F-22 just because it is an interceptor an its engines are older than F-22`s F119

MiG-29 said:

hahah yeah what you can not see is the bump of a DSI only generates two shock waves and generates less pressure recovery than F-14, F-15, F-111`s variable geometry intakes, that is based upon studies not gossips or theories.

Ah and by the way Su-35S has variable geometry intakes is faster than F-22, has supercruise showing your fantasy of 2d intakes being a hindrance is false in fact MiG-31 is less agile than F-22 just because it is an interceptor an its engines are older than F-22`s F119

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It's not just the number of shocks, but how the shock interacts with the inlet and tunnel geometry. Furthermore, shocks are also generated by the nose and interior of the plane. You're oversimplification and lack of regard for quantitative variation is startling.

MiG-29 said:

hahaha let us see if you are right

The detailed shock wave structure in the vicinity of the bump
compression surface and the inlet cowl is shown in Fig. 7. Mach
number distribution on seven equally spaced horizontal planes is
shown for this purpose. Oblique shock waves originate from the
leading edges of the bump compression surface as seen from this
figure (Fig. 7). Normal shock wave is apparent just short of the inlet.
The imprint of this normal shock wave on the bump surface forms
the ‘W’ shape (Fig. 6), as discussed earlier. The oblique shock and
normal shock wave impinge near the cowl lip, which shows a
relatively high intake mass flow ratio near intake design point.

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Here we have the proof at Mach 1.7 the DSI generates only two shock waves, a normal and an oblique shock wave; so you have a two shock wave system, F-14 has a four shock wave system, now 4 shock waves system achieves at Mach 1.7 higher values of pressure recovery than a 2 shock waves system.

Click to expand...

And shock system is very important in slowing down supersonic flow into subsonic flow for the engine. The paper shows that such shock waves exist, just as there are shock waves from variable-geometry intakes. On the other hand, there is no mentioning anywhere in the paper that DSI is limited to below Mach 1.7. The paper did not prove you are right.

MiG-29 said:

Now the bump is fixed, F-35 and J-10B have fixed bumps, the cowl lips on F-35 and J-20 are identical, designed to have better AoA and have changed the bump to avoid boundarily layer ingestion, thus F-35 has kept at Mach 1.6 but here we have claims of Mach 2.5.

Click to expand...

LOL! You must be very desperate right now to come up with such ridiculous claim that F-35 and J-20 cowl lips are identical. Being the same type of inlet does not make them identical. Identical would imply the inlets on both aircraft share the exact same dimension in all components, but this is impossible since J-20 is not designed by Lockheed Martin, nor can Chengdu and Lockheed Martin have any join research program to allow such occurrence. Basic engineering principles would also say this is impossible, since two aircraft are of complete different design and have complete different requirements for their inlets.

MiG-29 said:

The reality is unless China has a new technology not see on F-35, it will achieve Mach 2.5, but under regular DSI technology, it won`t.

Bump and cowl are fixed to divert boundary layer, thus mass flow can not be regulated by variable geometry.

Then your theory does not correspond to reality, real DSI have lower pressure recovery than 2D 4 multishock variable horizontal ramps on F-14, F-15, MiG-31 or 1/4 semiconical intakes like on F-111.

Click to expand...

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.

Engineer said:

On the other hand, there is no mentioning anywhere in the paper that DSI is limited to below Mach 1.7. The paper did not prove you are right.


.

Click to expand...

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

hahaha the paper it does say hahaha

MiG-29 said:

hahah yeah what you can not see is the bump of a DSI only generates two shock waves and generates less pressure recovery than F-14, F-15, F-111`s variable geometry intakes, that is based upon studies not gossips or theories.

Click to expand...

What you cannot see is that DSI is perfectly capable of reaching/exceeding Mach 2.0. Do you have any proof that DSI cannot do so? The simple answer is, you do not, and this situation pretty much speaks for itself.

It doesn't matter how many more shock waves variable-geometry inlet can make, as it doesn't alter the figures where DSI has a higher pressure recovery ratio than Mach 2 capable variable-geometry inlets.

MiG-29 said:

Ah and by the way Su-35S has variable geometry intakes is faster than F-22, has supercruise showing your fantasy of 2d intakes being a hindrance is false

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Here you are again, projecting your own attitude on to people and expect others to do what you are doing. Just because you base your arguments on your fantasy, that doesn't mean everybody do the same thing. Just to name a few:

• You claim DSI cannot reach/exceed Mach 2 - a fantasy
• You claim DSI has an absolute speed limit of Mach 1.7 - a fantasy
• You claim variable-geometry inlets must be used to for Mach 2.0 speed - a fantasy
• You claim pressure recovery ratio as if it is a measurement of flight duration of an aircraft - a fantasy
• You claim higher pressure recovery ratio automatically makes an aircraft more efficient than another - a fantasy

The trend is pretty clear - you argue with dreams, not with facts. Anyway, I digress.

The reality is simple: weight of an inlet system is correlated with the complexity. More weight means less efficiency, which cancels out advantages brought on by more shockwaves.

MiG-29 said:

in fact MiG-31 is less agile than F-22 just because it is an interceptor an its engines are older than F-22`s F119

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False. This shows you do not have any understanding of basic aerodynamic theories.

MiG-31 is less agile because of its lower wing loading. The aircraft is more heavy, thus more area of the wing is devoted to keep the aircraft from falling out of the sky. To generate lift, the engine must produce thrust which counteracts drag. An aircraft that uses more thrust to keep flying is an aircraft that is less efficient. MiG-31 variable-geometry inlets got beaten by F-22 fixed inlets by so many ways, and the capability of the aircraft to supercruise is the most obvious one.

MiG-29 said:

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

hahaha the paper it does say hahaha

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Click to expand...

It says "design Mach number". I do not see "speed limit" in any of these three words.

Get a grip on yourself and stop grasping at straws.