SDF Aerospace and Aerodynamics Corner

Engineer said:

It doesn't. F-14 and F-15 both use variable-geometry inlets, and they both cannot reach Mach 3. This says speed of the aircraft depends on other factors, not whether the inlet geometry can change or not. What are those other factors? One being the engines, another being the airframe. However, speed is irrelevant, because what measures the performance of an inlet is not speed but pressure recovery.

Pressure recovery ratio correlates with the number of oblique shocks. The more numerous the shocks the better, because each shock can be made weaker resulting in less performance loss per shock. In fact, a fixed-inlet can be used above Mach 3 as long as it can create numerous oblique shocks, and this is exactly the approach taken on hypersonic test vehicles. If an infinite number of shocks can be created then it's even better, because the condition is close to isentropic. This is one reason why DSI has better performance than a variable-geometry intake with three shocks, because the former is close to isentropic while the latter isn't.

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you just are saying more fallacies, to start hypersonic vehicles are ramjets and scramjets and use rockets to get the the speed the intake is designed, in few words the intake`s mach number and only Sr-71 uses ramjet but uses variable geometry intakes plus ramjets and scramjets do not use turbofans and turbojets[video=youtube;UDvyDb6ICwo]http://www.youtube.com/watch?v=UDvyDb6ICwo&feature=mfu_in_order&list=UL[/video]
[video=youtube;XV8AfgbGh5M]http://www.youtube.com/watch?v=XV8AfgbGh5M&feature=relmfu[/video]


fixed intakes have lower mach numbers because as mass flow ratio gets closer to 1 it becomes more and more supercritical, to put it in plain english as you increase speed the mass flow is so great that the intake has problems delivering the right amount of air to the engine, therefore variable geometry intakes are used, why? well because variable geometry intakes have smaller size and bypass less air however even up to Mach 2.5 external compression becomes supercritical so the intake becomes mixed but still they use variable geometry

MiG-29 said:

you just are saying more fallacies, to start hypersonic vehicles are ramjets and scramjets and use rockets to get the the speed the intake is designed, in few words the intake`s mach number and only Sr-71 uses ramjet but uses variable geometry intakes plus ramjets and scramjets do not use turbofans and turbojets[video=youtube;UDvyDb6ICwo]http://www.youtube.com/watch?v=UDvyDb6ICwo&feature=mfu_in_order&list=UL[/video]
[video=youtube;XV8AfgbGh5M]http://www.youtube.com/watch?v=XV8AfgbGh5M&feature=relmfu[/video]

fixed intakes have lower mach numbers because as mass flow ratio gets closer to 1 it becomes more and more supercritical, to put it in plain english as you increase speed the mass flow is so great that the intake has problems delivering the right amount of air to the engine, therefore variable geometry intakes are used, why? well because variable geometry intakes have smaller size and bypass less air however even up to Mach 2.5 external compression becomes supercritical so the intake becomes mixed but still they use variable geometry

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Nope, there is no fallacy on my part. Fallacies refer to improper reasoning, and you are using fallacies because you are using to misreprsent my position. Never have I said hypersonic vehicles don't use ramjet and scramjet. What I have said are:

• F-14 and F-15 cannot reach Mach 3 despite using variable-geometry inlet.
• Fixed inlet is used on hypersonic vehicle which travels at Mach 5 and above, contrary to your claim that fixed inlet is limited at below Mach 3.
• What measures inlet performance is pressure recovery, not speed.

The fact is this: hypersonic vehicle employs fixed inlet. showing the intake ramps are built into the fuselage and are fixed. Hypersonic means speed above Mach 5, hence we have examples disproving your claim that fixed inlet cannot be used at or above Mach 3. Going off tangent on SR-71 inlet doesn't make this fact go away.

Another fact is that pressure recovery is what measures the performance of an inlet, not speed. What is positive correlate with pressure recovery is the number of shocks generated. The more numerous the oblique shocks the better, because each shock can be made weaker therefore resulting in less performance loss per shock. This is how fixed inlet functions at hypersonic speed.

MiG-29 said:

2D ramps are wedges not cones, the rest what you say is pure fallacy no text says F-104 has 2D intakes.

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Nope. refers to improper reasoning used in an argument, and there is no fallacy in what I have said because unlike you, I refrain from using tactics such as . Your avoidance of my points and going off tangent to present an illusion of providing proper retort is a fallacy. When you don't know what a term means, you should not use it.

Half-cone axis-symmetric inlet is designed and analyzed in 2D, not 3D like DSI, and this already tells you they are not the same type of inlet.

MiG-29 said:

Both F-104 and F-35 use isentropic shock, but DSI has no diverter while F-104`s has it

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Then DSI is not the same type of inlet as F-104's inlets, because they cannot be the same when they are different. DSI is a type of inlet which specifically refers to inlets that do not have diverter. This is just like fixed inlet is one type of inlets and variable-geometry inlet is another type of inlet. The application of isentropic shock does not make this distinction on diverter disappear.

Engineer said:

Nope, there is no fallacy on my part. Fallacies refer to improper reasoning, and you are using fallacies because you are using

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to misreprsent my position. Never have I said hypersonic vehicles don't use ramjet and scramjet. What I have said are:

• F-14 and F-15 cannot reach Mach 3 despite using variable-geometry inlet.
• Fixed inlet is used on hypersonic vehicle which travels at Mach 5 and above, contrary to your claim that fixed inlet is limited at below Mach 3.
• What measures inlet performance is pressure recovery, not speed.

The fact is this: hypersonic vehicle employs fixed inlet.

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showing the intake ramps are built into the fuselage and are fixed. Hypersonic means speed above Mach 5, hence we have examples disproving your claim that fixed inlet cannot be used at or above Mach 3. Going off tangent on SR-71 inlet doesn't make this fact go away.

Another fact is that pressure recovery is what measures the performance of an inlet, not speed. What is positive correlate with pressure recovery is the number of shocks generated. The more numerous the oblique shocks the better, because each shock can be made weaker therefore resulting in less performance loss per shock. This is how fixed inlet functions at hypersonic speed.

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fixed intake that uses a rocket to get to mach 4, it can not get from 0 to mach 4 by its own, it needs a rocket

Engineer said:

Nope.

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refers to improper reasoning used in an argument, and there is no fallacy in what I have said because unlike you, I refrain from using tactics such as

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. Your avoidance of my points and going off tangent to present an illusion of providing proper retort is a fallacy. When you don't know what a term means, you should not use it.

Half-cone axis-symmetric inlet is designed and analyzed in 2D, not 3D like DSI, and this already tells you they are not the same type of inlet.



Then DSI is not the same type of inlet as F-104's inlets, because they cannot be the same when they are different. DSI is a type of inlet which specifically refers to inlets that do not have diverter. This is just like fixed inlet is one type of inlets and variable-geometry inlet is another type of inlet. The application of isentropic shock does not make this distinction on diverter disappear.

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cones or bumps generate isentropic shocks, the reason the DSI gets similar performance is because both use the bump or cone in the same way, the only difference is the bump is also used to divert the boundary layer, thus it becomes fixed, on the MiG-21 or Mirage 2000, the cone can move because it does not divert bounday layer, on F-104 they left it fixed, on Mirage 2000 they made it moveable

MiG-29 said:

fixed intake that uses a rocket to get to mach 4, it can not get from 0 to mach 4 by its own, it needs a rocket

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This doesn't mean your claim that fixed-inlet has a speed limit of Mach 3 is true.

MiG-29 said:

cones or bumps generate isentropic shocks, the reason the DSI gets similar performance is because both use the bump or cone in the same way, the only difference is the bump is also used to divert the boundary layer, thus it becomes fixed, on the MiG-21 or Mirage 2000, the cone can move because it does not divert bounday layer, on F-104 they left it fixed, on Mirage 2000 they made it moveable

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Using isentropic compression does not make DSI the same as inlets on F-104. Your claim that their use of isentropic compression makes them the same is no different than claiming fixed and variable-geometry inlets are the same because they both use oblique shocks. You are saying "they are same but different", and I am telling you that they cannot be the same because they are different. DSI is diverterless, the type of inlets on F-104 is not, hence they are not of the same type.

Engineer said:

This doesn't mean your claim that fixed-inlet has a speed limit of Mach 3 is true.

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it has a limit, because it can not get by its own and it is a ramjet, it does not have a turbojet.
tell me what aircraft with turbojet or turbofan gets to mach 3 from take off to cruise flight by its own with a fixed intake?


none, no aircraft with turbojets and fixed intakes gets to mach 3 from take off to cruise flight, only your imaginary aircraft
[video=youtube;XV8AfgbGh5M]http://www.youtube.com/watch?v=XV8AfgbGh5M&feature=player_embedded[/video]

Engineer said:

Using isentropic compression does not make DSI the same as inlets on F-104. Your claim that their use of isentropic compression makes them the same is no different than claiming fixed and variable-geometry inlets are the same because they both use oblique shocks. You are saying "they are same but different", and I am telling you that they cannot be the same because they are different. DSI is diverterless, the type of inlets on F-104 is not, hence they are not of the same type.

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they are the same simply by shock generation and fixed nature, they are only different in boundary layer treatment, both are fixed and have similar performance, DSI has no advantage in pressure recovery only in stealth and maintainance

MiG-29 said:

it has a limit, because it can not get by its own and it is a ramjet, it does not have a turbojet.
tell me what aircraft with turbojet or turbofan gets to mach 3 from take off to cruise flight by its own with a fixed intake?

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That's a fallacy, specifically a , because you are trying to mislead by portraying that limit as upper speed limit. You claimed fixed inlet cannot operate at or above Mach 3. I proved you wrong, it's that simple.

MiG-29 said:

none, no aircraft with turbojets and fixed intakes gets to mach 3 from take off to cruise flight, only your imaginary aircraft
[video=youtube;XV8AfgbGh5M]http://www.youtube.com/watch?v=XV8AfgbGh5M&feature=player_embedded[/video]

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This is another one of your fallacy called . You are trying to misrepresent my position; you want to believe that variable-geometry inlet is the only type that can go beyond Mach 3. I pointed out fixed inlet can operate above Mach 3, and proved your claim as incorrect.

MiG-29 said:

they are the same simply by shock generation and fixed nature, they are only different in boundary layer treatment, both are fixed and have similar performance, DSI has no advantage in pressure recovery only in stealth and maintainance

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What you are saying here is "they are the same but different", which is contradictory. Since they have difference, specifically one have diverter and the other is diverterless, they cannot be the same.

is a proper definition of the word same.

Merriam Webster said:

1. • resembling in every relevant respect
   • conforming in every respect —used with as
2. • being one without addition, change, or discontinuance : identical
   • being the one under discussion or already referred to
3. 
   corresponding so closely as to be indistinguishable
4. 
   equal in size, shape, value, or importance —usually used with the or a demonstrative (as that, those) in all senses

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Gentlemen.. stop double posting. Use the edit button if no one has responded to your post or you brainacs have an after thought..

C) Do not make another(multiple) post without someone responding to your previous post. If no one has not responded to a post you have made and you want to make another post simply edit your last post to include your latest thought. That's what the edit button is for.

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Thank you.

bd popeye super moderators

Don't know who Braniac is..

Brainiac is a fictional character that appears in comic books published by DC Comics. The character first appeared in Action Comics #242 (July 1958), and was created by Otto Binder and Al Plastino.

An extraterrestrial android (in most incarnations), Brainiac is a principal foe of Superman, and is responsible for shrinking and stealing Kandor, the capital city of Superman's home planet Krypton. Due to complex storylines involving time travel, cloning, and revisions of DC's continuity, several variations of Brainiac have appeared. Most incarnations of Brainiac depict him as a green-skinned being in humanoid form. He is bald, except for a set of diodes protruding from his skull.

The character is the origin of the informal eponymous word which means "genius". The name itself is a portmanteau of the words brain and maniac, with influence from ENIAC, the name of an early computer. In 2009, Brainiac was ranked as IGN's 17th Greatest Comic Book Villain of All Time.

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That's a compliment by the way..'Cause I have no clue what you are discussing..

Engineer said:

That's a fallacy, specifically a

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, because you are trying to mislead by portraying that limit as upper speed limit. You claimed fixed inlet cannot operate at or above Mach 3. I proved you wrong, it's that simple.



This is another one of your fallacy called

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. You are trying to misrepresent my position; you want to believe that variable-geometry inlet is the only type that can go beyond Mach 3. I pointed out fixed inlet can operate above Mach 3, and proved your claim as incorrect.

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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.

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



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]


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