SDF Aerospace and Aerodynamics Corner

MiG-29 said:

Look, all what you are saying is a way to divert attention from technical issues. isentropic compresion is achieved by bumps or cones, they use the same principle, however F-104 and DSI by being fixed and generate isentropic compression are limited in fixed throat and capture area, therefore both are external compression systems.

Click to expand...

Nope. First of all, you need to stop projecting. Inlets on F-104 employ diverter, while DSI is a classification specifically refers to inlets that do not employ diverter. Just because you ignore this to dodge a technical issue, that doesn't mean others do the same, and your assumption otherwise is called projection. In any case, because the way boundary layer is manipulated is different on the two types of inlets, they are not the same thing.

Secondly, the only person who is trying to divert attention is you, as evident by in your arguments. Your focus on how isentropic compression is generated does nothing to prove your position that inlets on F-104 and DSI are of the same type, thus it is nothing more than an attempt at distraction, making it one of your fallacies.

Thirdly, never have I claimed the inlets do not employ external compression, and your attempt to misrepresent that my position is called . You try to misrepresent my position to make it seems you have provided successful retorts, but you haven't actually responded to my point at all. This is another one of your fallacies.

MiG-29 said:

MiG-21. YE-150, F-111 or SR-71 use variable geometry to change capture area and throat area.

SR-71 by being variable geometry and work with supercitical shockwaves is a mixed compression system, DSI is not a Mixed compression system

Click to expand...

Again, this is a strawman argument and is a fallacy. No where did I claim DSI is a mixed compression system.

DSI is an external compression system, but doesn't employ boundary layer diverter. Inlets on F-104 have diverter. Because of the existence of this difference, the two inlets are not the same type.

MiG-29 said:

To see what happens when jets go to speeds their inlets are not designed for check this video
watch from minute 4, Victor Belenko says after MiG-25 flying at Mach 3.2 on a short flight you must change its engines, why? simple the inlet was working at an unstarted state for so long that it damaged the intakes beyond repair

[video=youtube;LZgFd4h15rs]http://www.youtube.com/watch?v=LZgFd4h15rs&feature=mfu_in_order&list=UL[/video]

Click to expand...

Nope. All Belenko said was "you must change its engine", the rest is your opinion. What get damaged are the engines, not intakes. And what causes the damage is overheating, not working at an unstart state. Inlet unstart causes severe drag, and it is something to be avoided, not something to be operated in to reach Mach 3 contrary to your claim.

MiG-29 said:

The US used turboramjets where the turbojet is skipped and only ram thrust is used preventing the engine from damage, and since i know you can not mention a single jet with fixed intake that uses turbojets or turbofans from take off to Mach 3 you give me speech about fallacy but the reality there is no real aircraft that uses turbojets and goes to mach 3 with fixed intake, all are variable geometry, SR-71, MiG-25, T-4, XB-70, engineer

Click to expand...

You claimed fixed inlet cannot operate above Mach 3, and I proved your wrong by showing fixed inlet is employed on hypersonic test vehicles that fly beyond the speed of Mach 5. That's the reality.

You couldn't prove fixed inlet is not used above Mach 3, but you don't want to admit you are wrong, so you use fallacies to make it appear that you provided retorts when you didn't. That's also the reality.

Engineer said:

Nope. First of all, you need to stop projecting. Inlets on F-104 employ diverter, while DSI is a classification specifically refers to inlets that do not employ diverter. Just because you ignore this to dodge a technical issue, that doesn't mean others do the same, and your assumption otherwise is called projection. In any case, because the way boundary layer is manipulated is different on the two types of inlets, they are not the same thing.

Secondly, the only person who is trying to divert attention is you, as evident by

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in your arguments. Your focus on how isentropic compression is generated does nothing to prove your position that inlets on F-104 and DSI are of the same type, thus it is nothing more than an attempt at distraction, making it one of your fallacies.

Thirdly, never have I claimed the inlets do not employ external compression, and your attempt to misrepresent that my position is called

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. You try to misrepresent my position to make it seems you have provided successful retorts, but you haven't actually responded to my point at all. This is another one of your fallacies.




Again, this is a strawman argument and is a fallacy. No where did I claim DSI is a mixed compression system.

DSI is an external compression system, but doesn't employ boundary layer diverter. Inlets on F-104 have diverter. Because of the existence of this difference, the two inlets are not the same type.




Nope. All Belenko said was "you must change its engine", the rest is your opinion. What get damaged are the engines, not intakes. And what causes the damage is overheating, not working at an unstart state. Inlet unstart causes severe drag, and it is something to be avoided, not something to be operated in to reach Mach 3 contrary to your claim.



You claimed fixed inlet cannot operate above Mach 3, and I proved your wrong by showing fixed inlet is employed on hypersonic test vehicles that fly beyond the speed of Mach 5. That's the reality.

You couldn't prove fixed inlet is not used above Mach 3, but you don't want to admit you are wrong, so you use fallacies to make it appear that you provided retorts when you didn't. That's also the reality.

Click to expand...

to start you claim F-104 intakes are 2D, that shows you have no idea of what type of intake F-104 has.
Second you do not understand why variable geometry intakes exist originally you claimed bernuolli`s principle forbids spilling, later you changed, you claimed the throat can not control the shock position but it does.

Good efficiency of the fixed-geometry diffuser is achievable only within a narrow speed-band. A more flexible solution for adjusting intake geometry to a varying flight speed is provided by the variable geometry diffuser
And thrid you have not given me a single example of a jet that goes from 0km/h to mach 3 and has fixed intake without the aid of a rocket

Okay Gentlemen, enough about inlets on the 104, This is the Brat speaking, your number 1 aerodynamic fan boy. Lets fix the F-35. First question, an easy one, Afterburner lighting our tailfeathers on fire? Titanium overlay? I'm just joking about the 104 inlets, but the J-20 and F35 thread stink without aero discussion, even when you repaint, you have to rebalance to eliminate flutter? Sorry to interupt, but I'd rather talk about airplanes.

---------- Post added at 04:59 PM ---------- Previous post was at 04:53 PM ----------

Then we can get to the good stuff, like transonic roll off and buffetting, but we'll save the good stuff for later. Thanks to both of you, I feel like I understand the function of the leading edge strakes, and I'm starting to get my mind wrapped around those stinkin canards. I wonder if theres not a miscreant breakaway or burble coming from around the fuselage inlet juncture, thats causing a rumble?

Air Force Brat said:

Okay Gentlemen, enough about inlets on the 104, This is the Brat speaking, your number 1 aerodynamic fan boy. Lets fix the F-35. First question, an easy one, Afterburner lighting our tailfeathers on fire? Titanium overlay? I'm just joking about the 104 inlets, but the J-20 and F35 thread stink without aero discussion, even when you repaint, you have to rebalance to eliminate flutter? Sorry to interupt, but I'd rather talk about airplanes.

---------- Post added at 04:59 PM ---------- Previous post was at 04:53 PM ----------

Then we can get to the good stuff, like transonic roll off and buffetting, but we'll save the good stuff for later. Thanks to both of you, I feel like I understand the function of the leading edge strakes, and I'm starting to get my mind wrapped around those stinkin canards. I wonder if theres not a miscreant breakaway or burble coming from around the fuselage inlet juncture, thats causing a rumble?

Click to expand...

The most important parameter for a jet is max lift coefficient, because it determines its max instantaneous turn rate, as the aircraft turns drag kill lift thus thrust balances drag.
So it is not if it has canards or it is tailess or has LERX or delta wing but lift, of course some configurations do increase lift, so basicly it is a balancing act.

To put you an example. Mirage 2000 is as good to tangle with an F-16 despite F-16 has LERX (strakes) and Mirage 2000 is a tailess with small strakes on the intake cowl; or AJ-37 can be beaten by F-15 despite F-15 has no leading edge flaps and F-15 has tailplanes while AJ-37 has canards.

LCA has a very low wing loading, so it is very competive despite it is a simple aircraft


Hence for this aircraft, the maximum sustainable turn rate occurs at the maximum CL, where
thrust available equals drag. This result is generally true if the corner turn rate is not sustainable.
In that case the highest turn rate occurs by using



The F-22's combat configuration is "clean", that is, with all armament carried internally and with no external stores. This is an important factor in the F-22's stealth characteristics, and it improves the fighter's aerodynamics by dramatically reducing drag, which, in turn, improves the F-22's range


Internal carriage. Alternative approaches for missile carriage include conventional external carriage,
conformal carriage, and internal carriage. Conventional external carriage has disadvantages of high radar
cross section (RCS), high carriage drag, and potentially adverse aeroelastic, stability, and control interactions
with the aircraft platform. Conformal carriage has an advantage of reduced RCS and drag compared to
conventional carriage. However, the preferred approach for the lowest carriage RCS and the lowest drag is
internal carriage. Figure 15 shows examples of internal carriage and loadouts for low observable fighters,
bombers, and helicopters. In the upper left is shown the F-22 internal center bay. The F-22 center bay
typically has an outboard partition for air-to-air weapons (e.g., AMRAAMs) an





So the great advantage of F-35 over the F-16 is carrying its weapons internally increases sustained turn rate by reducing drag.
Same is F-22 over F-15 or J-20 over Rafale

So back to the question of the F-35s burning tailfeathers, it obvious that the 135 in full AB makes lots of heat. R the horizontal stabs of the F-35 all carbon fiber, not only was the trailing edge sinjed, but there was some missing material. While I have little doubt aluminum would have some damage as well, it seems like we have flame cutting of the trailing edge is a very obnoxious problem.

---------- Post added at 10:22 PM ---------- Previous post was at 10:11 PM ----------

So the great advantage of F-35 over the F-16 is carrying its weapons internally increases sustained turn rate by reducing drag.
Same is F-22 over F-15 or J-20 over Rafale[/QUOTE]
It would seem that the F-35 has a heavier wing loading when compared to the F-16 especially the A model, wouldn't the buffet contribute to aerodynamic drag as you approach the 20 degree AOA where the buffeting begins and create a condition where parasite drag causes a loss of energy degrading terminal performance?

Air Force Brat said:

It would seem that the F-35 has a heavier wing loading when compared to the F-16 especially the A model, wouldn't the buffet contribute to aerodynamic drag as you approach the 20 degree AOA where the buffeting begins and create a condition where parasite drag causes a loss of energy degrading terminal performance?

Click to expand...

I guess so, buffeting affects, but when it carries only its weapons internally it suffers less drag than when the F-16 carries weapons externally.

But like the article says lift is the most important factor.

I have read that F-35 has the F-16`s agility but with higher stealth.

The F-35A conventional takeoff and landing
(CTOL) variant is a multirole, supersonic, stealth
fighter that has extraordinary acceleration and
9-g maneuverability with F-16-like agility.

MiG-29 said:

to start you claim F-104 intakes are 2D, that shows you have no idea of what type of intake F-104 has.
Second you do not understand why variable geometry intakes exist originally you claimed bernuolli`s principle forbids spilling, later you changed, you claimed the throat can not control the shock position but it does.

Click to expand...

Nope, nope and nope.

To start with, you claimed that F-104's inlets and DSI are of the same type, which is like claiming a cube without corners is the same shape as a sphere. I have pointed out why the two inlets aren't of the same type with two reasons. The first reason is that F-104 inlets are designed in 2D while DSI is designed in 3D. The second reason is that F-104's inlets have diverter while DSI doesn't. All you have done now is just throw out more fallacies and avoid having to confront that two technical issues.

Secondly, no where did I claim there is no spilling, and the fact that you haven't been able to quote me on claiming "no spillage occurs" for over ten pages is quite telling. For the record, I have made clear that spillage occurs on all inlets:

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.

Click to expand...

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.

Click to expand...

Spillage occurs because mass flow ratio changes, and mass flow ratio depends on capture area A1 and free stream cross sectional area A0i. The fact is that free stream cross sectional area is due to shock wave geometries, not variation in throat area.


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

Engineer said:

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

Click to expand...

So, the problem does not lie with me but with you. Your claim shows you either have no idea about intakes, or that you blatantly ignore facts so long as it suits your opinion. Furthermore, you now have to resort to put words in my mouth, and if you are in the right you wouldn't need to resort to such tactics.

MiG-29 said:

Good efficiency of the fixed-geometry diffuser is achievable only within a narrow speed-band. A more flexible solution for adjusting intake geometry to a varying flight speed is provided by the variable geometry diffuser

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Click to expand...

You claimed only variable-geometry inlet is capable of Mach 3, and I proved you wrong with examples of hypersonic test vehicles. Whether or not fixed inlets have a narrow operation range does not eliminate the fact that hypersonic test vehicles use fixed inlets.

You keep on claiming variable-geometry inlet is more efficient. Yet, F-22 with fixed inlet can supercruise while aircraft employing variable-geometry still have to use afterburners at supersonic speed. You tried to use speed as your premise, but this also fails because of two reasons. The first being that fixed inlet and DHI both operate at even higher speed. The second being that all of the aircraft capable of Mach 3 are useless as fighters.

Also, I should mention that using large font size is not going to magically make your argument any stronger. Likewise, increasing your already large font size from 5 to 6 isn't going to help much more either.

MiG-29 said:

And thrid you have not given me a single example of a jet that goes from 0km/h to mach 3 and has fixed intake without the aid of a rocket

Click to expand...

I have no need to, because this is a . You claimed fixed inlets cannot operate at or above Mach 3, I proved you wrong, and that's that.

---------- Post added at 05:22 AM ---------- Previous post was at 05:02 AM ----------

Air Force Brat said:

Okay Gentlemen, enough about inlets on the 104, This is the Brat speaking, your number 1 aerodynamic fan boy. Lets fix the F-35. First question, an easy one, Afterburner lighting our tailfeathers on fire? Titanium overlay? I'm just joking about the 104 inlets, but the J-20 and F35 thread stink without aero discussion, even when you repaint, you have to rebalance to eliminate flutter? Sorry to interupt, but I'd rather talk about airplanes.

---------- Post added at 04:59 PM ---------- Previous post was at 04:53 PM ----------

Then we can get to the good stuff, like transonic roll off and buffetting, but we'll save the good stuff for later. Thanks to both of you, I feel like I understand the function of the leading edge strakes, and I'm starting to get my mind wrapped around those stinkin canards. I wonder if theres not a miscreant breakaway or burble coming from around the fuselage inlet juncture, thats causing a rumble?

Click to expand...

This thread was started because certain member has the habit of polluting the J-20 thread. If you want to know more about the J-20, you can start here and here.

The aerodynamics of J-20 is based upon the paper of its designer Research on Low Wingspan High-Lift Aircraft Layout. Unfortunately, that paper has yet been translated into English.

Engineer said:

Nope, nope and nope.

To start with, you claimed that F-104's inlets and DSI are of the same type, which is like claiming a cube without corners is the same shape as a sphere. I have pointed out why the two inlets aren't of the same type with two reasons. The first reason is that F-104 inlets are designed in 2D while DSI is designed in 3D. The second reason is that F-104's inlets have diverter while DSI doesn't. All you have done now is just throw out more fallacies and avoid having to confront that two technical issues.

Secondly, no where did I claim there is no spilling, and the fact that you haven't been able to quote me on claiming "no spillage occurs" for over ten pages is quite telling. For the record, I have made clear that spillage occurs on all inlets:


Spillage occurs because mass flow ratio changes, and mass flow ratio depends on capture area A1 and free stream cross sectional area A0i. The fact is that free stream cross sectional area is due to shock wave geometries, not variation in throat area.

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


So, the problem does not lie with me but with you. Your claim shows you either have no idea about intakes, or that you blatantly ignore facts so long as it suits your opinion. Furthermore, you now have to resort to put words in my mouth, and if you are in the right you wouldn't need to resort to such tactics.




You claimed only variable-geometry inlet is capable of Mach 3, and I proved you wrong with examples of hypersonic test vehicles. Whether or not fixed inlets have a narrow operation range does not eliminate the fact that hypersonic test vehicles use fixed inlets.

You keep on claiming variable-geometry inlet is more efficient. Yet, F-22 with fixed inlet can supercruise while aircraft employing variable-geometry still have to use afterburners at supersonic speed. You tried to use speed as your premise, but this also fails because of two reasons. The first being that fixed inlet and DHI both operate at even higher speed. The second being that all of the aircraft capable of Mach 3 are useless as fighters.

Also, I should mention that using large font size is not going to magically make your argument any stronger. Likewise, increasing your already large font size from 5 to 6 isn't going to help much more either.



I have no need to, because this is a

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. You claimed fixed inlets cannot operate at or above Mach 3, I proved you wrong, and that's that.

---------- Post added at 05:22 AM ---------- Previous post was at 05:02 AM ----------



This thread was started because certain member has the habit of polluting the J-20 thread. If you want to know more about the J-20, you can start here and here.

The aerodynamics of J-20 is based upon the paper of its designer Research on Low Wingspan High-Lift Aircraft Layout. Unfortunately, that paper has yet been translated into English.

Click to expand...

Look axisimmetric half cones and bumps generate both the same type of shocks, and no axisymmetric cone or semicone is called 2D, 2D intakes have wedges as ramps.
F-104 fixed cone
X-35 fixed cone
Movable cone of Su-20
On the SR-71 the cone is in a plug and moves backwards at higher Mach number
The Mirage III also has



Second you have no proven a thing you are just looking at your self into the mirrow and claiming you are right to your self.

third you can not even grasp what the article says and why you need a rocket to boost an aircraft with fixed geometry to Mach 4.


The reason is simple, as the article says :

Good efficiency of the fixed-geometry diffuser is achievable only within a narrow speed-band. A more flexible solution for adjusting intake geometry to a varying flight speed is provided by the variable geometry diffuser


The ability to leap from a narrow band of speeds to a wider range of flight speeds is achieved with variable geometry intakes, fixed intakes are limited to a narrower speed range.

What does it mean?
Simple it measn if you design a fixed intake is just for some speeds, a fixed Mach 2 intake, near its max flow ratio near 1 will be working supercritical, why? Well engine flow demands decrease as speed goes faster while intake flow ratio grows, thus more air mass is bipassed.

A variable geometry increases the speed range wider because pressure recovery increases because the less air mass flow is bypassed why? simple the variable intake is smaller and has a variable throat that control mass flow and shock position .

Then a Fixed intake has from take off to max speed a Mach 2 range, while a variable intake can go to Mach 2.5 in external compression and 3 in mixed compression

No aircraft with fixed intake can reach mach 3 on fixed intake from take off, the only way for a fixed intake to go to mach 4 is by boosting the aircraft to mach 4 with a rocket and designing the intake for Mach 4 operation without a engine.

Turbofans and turbojets are operational in speeds up to Mach 2.5, around speeds of mach 3 their operation is limited.


What does it mean? simple a Mach 5 fixed intake is uncapable to operate form 0km/h to Mach 4 becasue is limited to a narrow range of speeds.

The external compression is performed with low-intensity
inclined shocks, limited to about Mach 1.4, so it ends with a
normal shock at the level of the cowl. The profile is mobile,
to adapt to the Mach number. The Concorde has intakes
like this.
Purely internal compression is abandoned in favour of
mixed external and then internal compression. As the
internal compression is more limited and is for lower Mach
numbers (about 2), self-starting is possible. The American
SST project had an air intake of this type. We may mention
the possibility of translating the central body to adapt the
intake to the Mach number.
6. Supersonic Air Intakes [/B]




From the axisymmetrical concept, we get semi-circular air
intakes (Mirage, GELA) or quarter-circle designs
(F 111).
Of course, t

Yeah thanks guys, engineer I am reading the J-20 thread where you pointed out to me, very interesting reading, the math is way over my head but I can try to wrap my mind around the fluid aspect of air and try to picture what is happening. I knew a little about turbulent flow off the close coupled canards, but this is making that more clear. Thanks to you both. The J-20 thread is real boring without the aero part of the discussion although there are some neat pictures and vids that also help.

MiG-29 said:

Look axisimmetric half cones and bumps generate both the same type of shocks, and no axisymmetric cone or semicone is called 2D, 2D intakes have wedges as ramps.
F-104 fixed cone
X-35 fixed cone
Movable cone of Su-20
On the SR-71 the cone is in a plug and moves backwards at higher Mach number
The Mirage III also has

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Click to expand...

Just because two inlets generate the same type of shocks, that does not make them the same type of inlets. Variable-geometry and fixed inlet both generate oblique shocks, but the two inlets are clearly of different types. Likewise:

• F-104's inlets were designed in 2D whereas DSI is designed in 3D;
• F-104's inlets have diverter while DSI has none;
• F-104's inlets feature axis-symmetric cone whereas DSI does not

mean the two inlets are not of the same type. They cannot be the same when they have difference.

MiG-29 said:

Second you have no proven a thing you are just looking at your self into the mirrow and claiming you are right to your self.

Click to expand...

Go on and keep on comforting yourself with that. The fact is that fixed inlet has application on hypersonic test vehicles, meaning fixed inlet can function above Mach 3, nice and simple. This means your argument that fast flying aircraft use variable-geometry inlets because only variable-geometry inlets can fly at high speed is a flawed one.

MiG-29 said:

third you can not even grasp what the article says and why you need a rocket to boost an aircraft with fixed geometry to Mach 4.


The reason is simple, as the article says :

Good efficiency of the fixed-geometry diffuser is achievable only within a narrow speed-band. A more flexible solution for adjusting intake geometry to a varying flight speed is provided by the variable geometry diffuser


The ability to leap from a narrow band of speeds to a wider range of flight speeds is achieved with variable geometry intakes, fixed intakes are limited to a narrower speed range.

What does it mean?

Click to expand...

It means you are still trying to divert attention away from the fact that fixed inlet is employed in flight condition where speed is above Mach 3.

Operation limits exist on variable-geometry inlets too, as evident by the following graph. This is why F-14 and F-15 cannot fly at Mach 3. Also, the fact that many aircraft that employ variable-geometry inlets cannot reach Mach 3 is quite telling, because it shows factors other than variable-geometry determine the top-speed these aircraft can travel. Factors such as the number of shocks generated, whether the airframe has low enough drag, or whether the engines are powerful enough.

MiG-29 said:

Simple it measn if you design a fixed intake is just for some speeds, a fixed Mach 2 intake, near its max flow ratio near 1 will be working supercritical, why? Well engine flow demands decrease as speed goes faster while intake flow ratio grows, thus more air mass is bipassed.

A variable geometry increases the speed range wider because pressure recovery increases because the less air mass flow is bypassed why? simple the variable intake is smaller and has a variable throat that control mass flow and shock position .

Click to expand...

Variable throat is a consequent of having to vary the ramps' angle to position the oblique shock waves. This means if you want the oblique shocks at certain position, then throat area would become certain size regardless of whether you want more or less air. Bypass doors are what control mass flow, and this is why an inlet that has variable-geometry requires bypass doors, yet an inlet that has bypass doors does not require variable-geometry.

MiG-29 said:

Then a Fixed intake has from take off to max speed a Mach 2 range, while a variable intake can go to Mach 2.5 in external compression and 3 in mixed compression

No aircraft with fixed intake can reach mach 3 on fixed intake from take off, the only way for a fixed intake to go to mach 4 is by boosting the aircraft to mach 4 with a rocket and designing the intake for Mach 4 operation without a engine.

Turbofans and turbojets are operational in speeds up to Mach 2.5, around speeds of mach 3 their operation is limited.

Click to expand...

Fixed inlet can be found on hypersonic test vehicles that travel at higher speed than Mach 3. This is a fact. Whether or not the test vehicles can propel themselves to their operating speed without the aid of rocket does not eliminate the above fact.

Furthermore, being able to employ mixed compression is not an ability exclusive to variable-geometry inlet. Fixed inlet can operate in hypersonic regime precisely because mixed compression is employed. Mixed compression allows an inlet to operate at high speed because the compression method generates higher number of oblique shocks than external compression, which means it is the number of oblique shocks that correlates inlet performance. Adopting a variable-geometry inlet would not magically make an aircraft travels at Mach 3, and indeed F-14 and F-15 cannot fly at Mach 3.

MiG-29 said:

What does it mean? simple a Mach 5 fixed intake is uncapable to operate form 0km/h to Mach 4 becasue is limited to a narrow range of speeds.

The external compression is performed with low-intensity
inclined shocks, limited to about Mach 1.4, so it ends with a
normal shock at the level of the cowl. The profile is mobile,
to adapt to the Mach number. The Concorde has intakes
like this.
Purely internal compression is abandoned in favour of
mixed external and then internal compression. As the
internal compression is more limited and is for lower Mach
numbers (about 2), self-starting is possible. The American
SST project had an air intake of this type. We may mention
the possibility of translating the central body to adapt the
intake to the Mach number.
6. Supersonic Air Intakes [/B]




From the axisymmetrical concept, we get semi-circular air
intakes (Mirage, GELA) or quarter-circle designs
(F 111).
Of course, t

Please, Log in or Register to view URLs content!

Click to expand...

Once again, whether or not the test vehicles can propel themselves to their operating speed without the aid of rocket does not eliminate the fact that fixed inlet can operate at above Mach 3. An operational range does not mean the maximum speed of an inlet is capped at certain Mach number. The lower bound and the upper bound of that operational range can shift, meaning maximum speed at which an inlet can operate can shift, too.

Variable-geometry inlet also has operational range, as evident by the following graph. This is why aircraft like F-14 and F-15 cannot reach Mach 3 despite employing variable-geometry inlets.


It is also why as speed decreases, variable-geometry inlet loses performance. From :


So, it's not like with variable-geometry inlets, a flight vehicle can go from 0 to Mach 5 either. Theoretically, it could be done, but the inlet would be so heavy as to be practically worthless. Then there's the issue of engine: at hypersonic speed, a ramjet or scramjet is needed.