SDF Aerospace and Aerodynamics Corner

MiG-29 said:

Sorry but you do not understand how DSI works niether how intakes work, and the reason is you do not understand and know why do you need to control the air mass flow at different speeds.

And i will explain it to you


F-111 and F-14 for example do control the air mass flow, on F-111, the intake semi cone expands or collapses depending on the speed and air mass flow, why? simple engines do not only need to slow dow the flow from supersonic speeds or transonic, but also regulate the volume of air that gets into the intake.

Capture area refers to the volume of air the intake takes, on F-111, and basicly SR-71 or Mirage III/2000 by moving the intake longitudinaly or collapsing or expanding the cone/semicone control the air volume, thus the air mass flow is control, they do this to prevent subcritical or supercritical states, subcritical and supercritical states mean the oblique and normal shocks change their location lowering pressure recovery, the critical state is the highest pressure recovery at an ideal mass flow.

Click to expand...

First of all, no one is debating the working principles of supersonic intakes. Your bringing up of these principles do not prove variable-geometry inlets as superior, nor do they challenge any point I have made prior.

Secondly, you got many points wrong:

• Capture area refers to the cross sectional area of the intake, not the volume of air that intake takes. See, one is "area" which is in m^2 and the other one is "volume" which is m^3.
• The movement of the cone has the same purpose as adjustment of ramps, and that purpose is to position the oblique shockwaves close to the intake lip to improve pressure recovery.
• Mass flow to the engine is determined by size of the inlet and the intake ducts. These are fixed.

MiG-29 said:

On F-14 the air mass flow is controlled and bled by a bypass slot and bypass doors, the air mass flow is bled so only the amount of air the jet needs enters.

Click to expand...

Bypass door is not the same as cone or ramp. Bypass system can be found on F-22 as well, an aircraft that uses fixed inlets.

MiG-29 said:

As speed goes higher so air mass flow increases, variable geomety and bypass doors are a most as you go faster and faster on a Sr-71.

Click to expand...

None of the aforementioned aircraft (F-14, F-15, F-111, Mirage III/2000) with variable-geometry inlets can reach Mach 3. Employing variable-geometry inlets does not automatically make an aircraft better and fly faster. Your logic fails as usual.

Furthermore, which flies at speed two times faster than SR-71 strictly uses fixed inlet system. Your claim that variable-geometry inlet being a must is nothing more than your own opinion.

MiG-29 said:

On the DSI you have several limitations in shockwave generation and fixed geometry

Click to expand...

And yet you cannot point out the limitations. In fact, all you have done is going around with circles avoiding having to point out the limitations, because you don't know of any. Your argument involving fixed geometry doesn't work, as we have seen F-22 has better performance than all aircraft with variable-geometry inlets.

Engineer said:

First of all, no one is debating the working principles of supersonic intakes. Your bringing up of these principles do not prove variable-geometry inlets as superior, nor do they challenge any point I have made prior.

Secondly, you got many points wrong:

• Capture area refers to the cross sectional area of the intake, not the volume of air that intake takes. See, one is "area" which is in m^2 and the other one is "volume" which is m^3.
• The movement of the cone has the same purpose as adjustment of ramps, and that purpose is to position the oblique shockwaves close to the intake lip to improve pressure recovery.
• Mass flow to the engine is determined by size of the inlet and the intake ducts. These are fixed.

Bypass door is not the same as cone or ramp. Bypass system can be found on F-22 as well, an aircraft that uses fixed inlets.



None of the aforementioned aircraft (F-14, F-15, F-111, Mirage III/2000) with variable-geometry inlets can reach Mach 3. Employing variable-geometry inlets does not automatically make an aircraft better and fly faster. Your logic fails as usual.

Furthermore,

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which flies at speed two times faster than SR-71 strictly uses fixed inlet system. Your claim that variable-geometry inlet being a must is nothing more than your own opinion.



And yet you cannot point out the limitations. In fact, all you have done is going around with circles avoiding having to point out the limitations, because you don't know of any. Your argument involving fixed geometry doesn't work, as we have seen F-22 has better performance than all aircraft with variable-geometry inlets.

Click to expand...

you are arguing first without knowing and second just for the sake of arguing.

SR-71 has a variable geometry intake and flies up to Mach 3.4:

As the SR-71 increases its speed, the inlet varies its exterior and interior geometry to keep the cone-shaped shock wave and the normal shock wave optimally positioned. Inlet geometry is altered when the spike retracts toward the engine, approximately 1.6 inches per 0.1 Mach. At Mach 3.2, with the spike fully aft, the air-stream-capture area has increased by 112 percent and the throat area has shrunk by 54 percent.




this shows you only say things for the sake of arguing


now RAMJETS can not generate static thrust


Therefore, ramjets are lighter and simpler than a turbojet. Ramjets produce thrust only when the vehicle is already moving; ramjets cannot produce thrust when the engine is stationary or static. Since a ramjet cannot produce static thrust, some other propulsion system must be used to accelerate the vehicle to a speed where the ramjet begins to produce thrust. The higher the speed of the vehicle, the better a ramjet works until aerodynamic losses become a dominant factor.


SR-71 has a variable geometry intake to go from 0 to Mach 3.4 in order to adapt to the different mass flows and generate the most of shocks via internal external compression.


THE SR-71 ENGINE AIR INLET IS A MIXED EXTERNAL AND INTERNAL
COMPRESSION, AXI-SYMMETRIC INLET, WITH GRADUAL ISENTROPIC
COMPRESSION APPROACHING THE THROAT

A Ramjet or scramjet can be optimised to a mach number and taken to that speed by a rocket or a variable geometry intake of a turbojet like SR-71

The combustion that produces thrust in the ramjet occurs at a subsonic speed in the combustor. For a vehicle traveling supersonically, the air entering the engine must be slowed to subsonic speeds by the aircraft inlet. Shock waves present in the inlet cause performance losses for the propulsion system. Above Mach 5, ramjet propulsion becomes very inefficient. The new supersonic combustion ramjet, or scramjet, solves this problem by performing the combustion supersonically in the burner.




XB-70 had variable geometry intake with 2D ramps and flew at Mach 3


Six General Electric J93-GE 3 turbojet engines that each delivered around 30 000 lb (13 608 kg) of thrust in afterburner, powered the Valkyrie. Because of installation design, an engine could be removed and replaced in only a couple of hours. The engines were mounted side by side at the rear of the underwing pod. Two large rectangular inlet ducts provided two-dimensional airflow. A series of variable ramps inside the intakes, called the Air Induction Control System (AICS), would expand and contract to manipulate airflow to the engines and protect them from powerful shock of supersonic air. The system detected small changes in pressure during flight and reduced supersonic air to subsonic speeds at the engine faces.

[video=youtube;_wsPLthWrr8]http://www.youtube.com/watch?v=_wsPLthWrr8[/video]
this shows the advantages of variable geometry over fixed geometry
With a top speed of Mach 1.6, the Lockheed Martin F-35 Joint Strike Fighter has an inlet design that is far simpler than that of the Mach 3-plus SR-71; the single-engine JSF inlet cannot vary its geometry. The F-35’s engineers could get away with a less complicated design because at vehicle speeds up to about Mach 2, the shape of the inlet itself can slow down much of the supersonic air before it enters the inlet. The JSF inlet is, however, a breakthrough design: It has no diverters. Traditional fighter inlets, such as those found on the F/A-18 and F-22, have slots, slats, and moving parts to divert or channel airflow. The F-15 inlet has ramps and doors that alter its external and internal shape to adjust airflow as needed

MiG-29 said:

you are arguing first without knowing and second just for the sake of arguing.

SR-71 has a variable geometry intake and flies up to Mach 3.4:

As the SR-71 increases its speed, the inlet varies its exterior and interior geometry to keep the cone-shaped shock wave and the normal shock wave optimally positioned. Inlet geometry is altered when the spike retracts toward the engine, approximately 1.6 inches per 0.1 Mach. At Mach 3.2, with the spike fully aft, the air-stream-capture area has increased by 112 percent and the throat area has shrunk by 54 percent.

Click to expand...

So why can't other aircraft with variable-geometry inlets do it? I will tell you why, because these aircraft aren't designed to fly at Mach 3. Merely using variable-geometry inlets does not make an aircraft better; pressure recovery ratio isn't everything. SR-71 flies fast, but it cannot even maneuver.

MiG-29 said:

this shows you only say things for the sake of arguing

Click to expand...

You are projecting your own attitude onto others. You have already admitted that DSI has no limitation at Mach 2. The "debate" pretty much finished from that point on. Whether SR-71 can fly at Mach 3 has nothing to do with DSI. Your continue arguing is arguing for the sake of arguing.

Engineer said:

So why can't other aircraft with variable-geometry inlets do it? I will tell you why, because these aircraft aren't designed to fly at Mach 3. Merely using variable-geometry inlets does not make an aircraft better; pressure recovery ratio isn't everything. SR-71 flies fast, but it cannot even maneuver.



You are projecting your own attitude onto others. You have already admitted that DSI has no limitation at Mach 2. The "debate" pretty much finished from that point on. Whether SR-71 can fly at Mach 3 has nothing to do with DSI. Your continue arguing is arguing for the sake of arguing.

Click to expand...

let me explain you



With a top speed of Mach 1.6, the Lockheed Martin F-35 Joint Strike Fighter has an inlet design that is far simpler than that of the Mach 3-plus SR-71; the single-engine JSF inlet cannot vary its geometry. The F-35’s engineers could get away with a less complicated design because at vehicle speeds up to about Mach 2, the shape of the inlet itself can slow down much of the supersonic air before it enters the inlet. The JSF inlet is, however, a breakthrough design: It has no diverters. Traditional fighter inlets, such as those found on the F/A-18 and F-22, have slots, slats, and moving parts to divert or channel airflow. The F-15 inlet has ramps and doors that alter its external and internal shape to adjust airflow as needed


DSI or any fixed intake is limited not because of the design it self but simply because variable geometry means the ability to jump from a flight envelop to another


DSI on F-35 is fixed no moveable parts and designed from 0 to Mach 2 speeds.

F-14 has 3 settings from 0 to transonic speeds, for transonic speeds and low supersonic and for high supersonic.

SR-71 is even more complicated it has internal compression, same is XB-70.

on SR-71 the cone sike moves 16 inches for every Mach 0.1 increase oin speed
Inlet geometry is altered when the spike retracts toward the engine, approximately 1.6 inches per 0.1 Mach. At Mach 3.2, with the spike fully aft,
By having variable geometry, these jets change the geometry of the intake for several different flight envelops.


F-35 is designed for 1.6, F-14 for Mach 2.34, SR-71 for 3.4.

now there is something you do not understand and is


SR-71 and F-35 have ISENTROPIC intakes, on F-35 like F-104 these are fixed, on Mirage 2000 and SR-71 these are variable geometry intakes.

F-104 and F-35 are not as different as you think in fact are the same type of ISENTROPIC intakes, but on F-35 it is divertless and on F-104 it has a diverter.

Multi-shock and isentropic plus terminal shock systems have been manifested in practice by using spikes in circular inlet geometries, (i.e. aircraft B-58, SR-71), or segments of a circle (i.e. F-104), as well as 2-D rectangular inlets (F-15, B-1, F-22). Recently rounded 3 dimensional variations of the basic 2D rectangular inlets with the same basic external shock system characteristics using stream tracing techniques have been proposed, such as described in a patent issued to Davis

Read more:

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MiG-29 said:

now RAMJETS can not generate static thrust


Therefore, ramjets are lighter and simpler than a turbojet. Ramjets produce thrust only when the vehicle is already moving; ramjets cannot produce thrust when the engine is stationary or static. Since a ramjet cannot produce static thrust, some other propulsion system must be used to accelerate the vehicle to a speed where the ramjet begins to produce thrust. The higher the speed of the vehicle, the better a ramjet works until aerodynamic losses become a dominant factor.

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SR-71 has a variable geometry intake to go from 0 to Mach 3.4 in order to adapt to the different mass flows and generate the most of shocks via internal external compression.


THE SR-71 ENGINE AIR INLET IS A MIXED EXTERNAL AND INTERNAL
COMPRESSION, AXI-SYMMETRIC INLET, WITH GRADUAL ISENTROPIC
COMPRESSION APPROACHING THE THROAT

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A Ramjet or scramjet can be optimised to a mach number and taken to that speed by a rocket or a variable geometry intake of a turbojet like SR-71

The combustion that produces thrust in the ramjet occurs at a subsonic speed in the combustor. For a vehicle traveling supersonically, the air entering the engine must be slowed to subsonic speeds by the aircraft inlet. Shock waves present in the inlet cause performance losses for the propulsion system. Above Mach 5, ramjet propulsion becomes very inefficient. The new supersonic combustion ramjet, or scramjet, solves this problem by performing the combustion supersonically in the burner.




XB-70 had variable geometry intake with 2D ramps and flew at Mach 3


Six General Electric J93-GE 3 turbojet engines that each delivered around 30 000 lb (13 608 kg) of thrust in afterburner, powered the Valkyrie. Because of installation design, an engine could be removed and replaced in only a couple of hours. The engines were mounted side by side at the rear of the underwing pod. Two large rectangular inlet ducts provided two-dimensional airflow. A series of variable ramps inside the intakes, called the Air Induction Control System (AICS), would expand and contract to manipulate airflow to the engines and protect them from powerful shock of supersonic air. The system detected small changes in pressure during flight and reduced supersonic air to subsonic speeds at the engine faces.

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[video=youtube;_wsPLthWrr8]http://www.youtube.com/watch?v=_wsPLthWrr8[/video]
this shows the advantages of variable geometry over fixed geometry

Click to expand...

This does not mean DSI cannot reach/exceed Mach 2.

goes even faster at a speed of Mach 7, but they do not employ variable-geometry inlets. F-14, F-15, F-111, Mirage III/2000, etc. cannot go at Mach 3 even though they use variable-geometry inlets. What does this say? It says inlet design is not everything. Indeed, variable-geometry inlet is not good enough, SR-71 has to convert its engines into ramjet while in flight in order to achieve that kind of speed.

SR-71 and XB-70 can go at Mach 3, yes, but the inlets they employed are far more complicated than even that of F-14. I have said this before and I will say this again: you can make an inlet ultra complex to get the best pressure recovery ratio, but that comes at the price of increase weight. Increase weight reduces advantages gained by increase in pressure recovery ratio. What else can SR-71 and XB-70 do aside from flying fast? Absolutely nothing. They turn like airliners. This illustrates my point perfectly.

Launch vehicles (rockets) can go even faster and they do not even require an inlet. By your argument rockets would be more efficient than any type of inlet. Your comparison based solely on speed and purposely ignoring all other factors illustrate your typical grasp at straws behavior.

MiG-29 said:

With a top speed of Mach 1.6, the Lockheed Martin F-35 Joint Strike Fighter has an inlet design that is far simpler than that of the Mach 3-plus SR-71; the single-engine JSF inlet cannot vary its geometry. The F-35’s engineers could get away with a less complicated design because at vehicle speeds up to about Mach 2, the shape of the inlet itself can slow down much of the supersonic air before it enters the inlet. The JSF inlet is, however, a breakthrough design: It has no diverters. Traditional fighter inlets, such as those found on the F/A-18 and F-22, have slots, slats, and moving parts to divert or channel airflow. The F-15 inlet has ramps and doors that alter its external and internal shape to adjust airflow as needed

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Click to expand...

That's the beauty of DSI - get rid of moving parts while enjoying increase pressure recovery ratio. We have seen this increase from comparison of pressure recovery ratio between DSI and F-4D's variable-geometry inlets. No moving parts is an advantage, not a disadvantage.

Now, F/A-18 and F-22 employ fixed inlets, specifically Caret inlets. These are designed and analyzed in 3-dimension space so they are not your traditional fighter inlets. Your attempt to lump them together with your variable-geometry inlets as "traditional fighter inlets" show that modern fixed inlet design functions just as well as variable-geometry inlets.

Your argument that fixed inlets perform poorly compared to variable-geometry inlets therefore DSI being fixed also performs poorly doesn't work for two reasons:

1. Using only fixed inlets, F-22 have better performance than many aircraft that employ variable-geometry inlets. Your first premises failed.
2. DSI and fixed-inlet are two different types of inlets. Although both have no moving parts, the former is diverterless while the latter must have a diverter. Your second premises failed.

MiG-29 said:

let me explain you



With a top speed of Mach 1.6, the Lockheed Martin F-35 Joint Strike Fighter has an inlet design that is far simpler than that of the Mach 3-plus SR-71; the single-engine JSF inlet cannot vary its geometry. The F-35’s engineers could get away with a less complicated design because at vehicle speeds up to about Mach 2, the shape of the inlet itself can slow down much of the supersonic air before it enters the inlet. The JSF inlet is, however, a breakthrough design: It has no diverters. Traditional fighter inlets, such as those found on the F/A-18 and F-22, have slots, slats, and moving parts to divert or channel airflow. The F-15 inlet has ramps and doors that alter its external and internal shape to adjust airflow as needed


DSI or any fixed intake is limited not because of the design it self but simply because variable geometry means the ability to jump from a flight envelop to another


DSI on F-35 is fixed no moveable parts and designed from 0 to Mach 2 speeds.

F-14 has 3 settings from 0 to transonic speeds, for transonic speeds and low supersonic and for high supersonic.

SR-71 is even more complicated it has internal compression, same is XB-70.

Click to expand...

This illustrates my points perfectly:

1. Increase complexity to increase pressure recovery ratio leads to increase in weight, and this weight penalizes advantages of increase inlet efficiency. SR-71 and XB-70 can fly fast but has to turn like airliners. Flying fast is their only advantage.
2. F-14, F-15 and aircraft that employ similar variable-geometry inlets cannot fly at Mach 3. This says other factors are at play, and variable-geometry inlet alone does not determine efficiency of aircraft, flight duration, or top-speed.

The beauty with DSI is there is no moving parts while enjoying increase pressure recovery ratio. We have seen this increase from comparison of pressure recovery ratio between DSI and F-4D's variable-geometry inlets. No moving parts is an advantage, not a disadvantage.

Now, F/A-18 and F-22 employ fixed inlets, specifically Caret inlets. These are designed and analyzed in 3-dimension space so they are not your traditional fighter inlets. Your attempt to lump them together with your variable-geometry inlets as "traditional fighter inlets" show that modern fixed inlet design functions just as well as variable-geometry inlets.

MiG-29 said:

on SR-71 the cone sike moves 16 inches for every Mach 0.1 increase oin speed
Inlet geometry is altered when the spike retracts toward the engine, approximately 1.6 inches per 0.1 Mach. At Mach 3.2, with the spike fully aft,
By having variable geometry, these jets change the geometry of the intake for several different flight envelops.

Click to expand...

The intake cone of a MiG-21 also moves inward, but MiG-21 cannot fly at Mach 3 despite having a variable-geometry inlet. Neither can F-14, F-15, etc. fly at such speed.

MiG-29 said:

F-35 is designed for 1.6, F-14 for Mach 2.34, SR-71 for 3.4.

Click to expand...

So in other words, overall design of an aircraft plays a role at how fast an aircraft can fly (and for how long). Not everything is based on the type of inlet alone.

MiG-29 said:

now there is something you do not understand and is


SR-71 and F-35 have ISENTROPIC intakes, on F-35 like F-104 these are fixed, on Mirage 2000 and SR-71 these are variable geometry intakes.

F-104 and F-35 are not as different as you think in fact are the same type of ISENTROPIC intakes, but on F-35 it is divertless and on F-104 it has a diverter.

Multi-shock and isentropic plus terminal shock systems have been manifested in practice by using spikes in circular inlet geometries, (i.e. aircraft B-58, SR-71), or segments of a circle (i.e. F-104), as well as 2-D rectangular inlets (F-15, B-1, F-22). Recently rounded 3 dimensional variations of the basic 2D rectangular inlets with the same basic external shock system characteristics using stream tracing techniques have been proposed, such as described in a patent issued to Davis

Read more:

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Click to expand...

Then the intakes on F-35 and F-104 are not the same type of intake. You cannot call them the same type of inlets when one doesn't employ a diverter while another one does, especially in light of the importance of the diverter for an inlet.

Engineer said:

This illustrates my points perfectly:

1. Increase complexity to increase pressure recovery ratio leads to increase in weight, and this weight penalizes advantages of increase inlet efficiency. SR-71 and XB-70 can fly fast but has to turn like airliners. Flying fast is their only advantage.
2. F-14, F-15 and aircraft that employ similar variable-geometry inlets cannot fly at Mach 3. This says other factors are at play, and variable-geometry inlet alone does not determine efficiency of aircraft, flight duration, or top-speed.

The beauty with DSI is there is no moving parts while enjoying increase pressure recovery ratio. We have seen this increase from comparison of pressure recovery ratio between DSI and F-4D's variable-geometry inlets. No moving parts is an advantage, not a disadvantage.

Now, F/A-18 and F-22 employ fixed inlets, specifically Caret inlets. These are designed and analyzed in 3-dimension space so they are not your traditional fighter inlets. Your attempt to lump them together with your variable-geometry inlets as "traditional fighter inlets" show that modern fixed inlet design functions just as well as variable-geometry inlets.



The intake cone of a MiG-21 also moves inward, but MiG-21 cannot fly at Mach 3 despite having a variable-geometry inlet. Neither can F-14, F-15, etc. fly at such speed.



So in other words, overall design of an aircraft plays a role at how fast an aircraft can fly (and for how long). Not everything is based on the type of inlet alone.




Then the intakes on F-35 and F-104 are not the same type of intake. You cannot call them the same type of inlets when one doesn't employ a diverter while another one does, especially in light of the importance of the diverter for an inlet.

Click to expand...

look, you do not understand at all how intakes do work, and it is obvious for the things you say,to start, intakes use oblique shocks to weaken the strength of the normal shock.

On a pitot tube intake like those on MiG-19 or F-100 the intakes work efficiently up to mach 1.3, they only create a single normal shock



On F-104 or F-35, the isentropic intake generates a oblique and normal shock allowing the intake to raise the speed around Mach two these are fixed intakes.

F-15 use two oblique shock and a normal shock allowing speeds up to Mach 2.5. the F-14 has more sensitive engines thus it generates 3 oblique and a normal shock but they are external compression intakes.


On SR-71 and XB-70 they have mixed compression which generate less drag and are also multishock intakes that allow some of the compression being done inside the intake
why do you need more shocks on the F-15 or F-14 to get more pressure recovery?
The pressure recovery increases with an increase in the number of oblique
shocks employed.
Why F-14 and F-15 have intakes of lower mach capability than XB-70? well the answer is they are external compression while XB-70 and SR-71 are mixed compression why?


The total flow
turning angle, however, increases rapidly with the number of oblique shocks
employed. This results in high cowl drag1. Due to this reason, external compression
intakes are undesirable at high Mach numbers wherein efficient flow deceleration
requires multiple shocks.
as speed increases the intake needs to regulate mass flow through out intake capture area why?

Problems related to Supersonic Intake Design
The important performance parameters that dictate the design of an intake are
the drag and total pressure recovery. These are subject to constraints related to the
compressor (or combustor in case of scramjets and ramjets) entry, namely static
pressure, Mach number and flow uniformity. Another important parameter is the mass
flow rate. The problem is, as the static pressure and mass flow rate are increased, the
pressure recovery reduces while the drag increases. Hence an optimum design needs
to be arrived at.


F-35 is fixed thus it can not generate more oblique shocks and regulate the mass flow as MiG-21 or SR-71 do.

MiG-21 does not translate the intake spike as much as SR-71 thus it is limited to lower speed on SR-71 its Inlet geometry is altered when the spike retracts toward the engine, approximately 1.6 inches per 0.1 Mach. At Mach 3.2, with the spike fully aft

On XB-70 it also generate more oblique shocks than F-15 but it does it internally, thus it is faster.


So DSI by being fixed: With a top speed of Mach 1.6, the Lockheed Martin F-35 Joint Strike Fighter has an inlet design that is far simpler than that of the Mach 3-plus SR-71; the single-engine JSF inlet cannot vary its geometry


DHI allows for increased lower speeds so a turbojet can be used to reach RAMJET speeds, DHI for RAMJET ands SCRAMJET do not generate static thrust.

this intake pictures show how do intakes work

MiG-29 said:

look, you do not understand at all how intakes do work, and it is obvious for the things you say,to start, intakes use oblique shocks to weaken the strength of the normal shock.

Click to expand...

Actually, I understand how intakes work better than you do, and in fact I have corrected you on many instances. Throwing out random terminologies does not indicate you know what you are talking about, especially when you need to be corrected on concepts as simple as area vs. volume.

MiG-29 said:

On a pitot tube intake like those on MiG-19 or F-100 the intakes work efficiently up to mach 1.3, they only create a single normal shock

Click to expand...

DSI isn't being fixed isn't comparable to pitot intake. In fact, DSI creates both oblique and normal shocks.

MiG-29 said:

On F-104 or F-35, the isentropic intake generates a oblique and normal shock allowing the intake to raise the speed around Mach two these are fixed intakes.

Click to expand...

Wrong! F-35's DSI is one type of intake whereas fixed-inlet is another type, therefore DSI being fixed does not make it an isentropic intake.

MiG-29 said:

F-15 use two oblique shock and a normal shock allowing speeds up to Mach 2.5. the F-14 has more sensitive engines thus it generates 3 oblique and a normal shock but they are external compression intakes.

Click to expand...

Yet they cannot reach Mach 3. You claimed by employing variable-geometry inlets alone, aircraft fly efficiently and go fast. Yet, the fact these aircraft cannot fly at Mach 3 while other aircraft can indicates while inlet efficiency is important, it does not determine the speed of an aircraft.

MiG-29 said:

On SR-71 and XB-70 they have mixed compression which generate less drag and are also multishock intakes that allow some of the compression being done inside the intake
why do you need more shocks on the F-15 or F-14 to get more pressure recovery?
The pressure recovery increases with an increase in the number of oblique
shocks employed.
Why F-14 and F-15 have intakes of lower mach capability than XB-70? well the answer is they are external compression while XB-70 and SR-71 are mixed compression why?

Click to expand...

The more shocks you create, the more complex the inlet becomes. More complexity leads to increase weight, which cancels out advantages in increased pressure recovery ratio. SR-71 and XB-70 can only fly fast and do nothing else, and both of these aircraft turn like airliners. This illustrates my point quite clearly.

Fighter aircraft do not fly at Mach 3 because the excess weight of being able to fly at Mach 3 means no maneuverability. Within the operating speed of a fighter aircraft (from 0 up to and slightly exceeding Mach 2), DSI offers better pressure recovery ratio than fixed inlets like those found on F-4D. That's all the matters. Bringing in Mach 3 aircraft doesn't challenge this point in anyway.

MiG-29 said:

The total flow
turning angle, however, increases rapidly with the number of oblique shocks
employed. This results in high cowl drag1. Due to this reason, external compression
intakes are undesirable at high Mach numbers wherein efficient flow deceleration
requires multiple shocks.
as speed increases the intake needs to regulate mass flow through out intake capture area why?

Problems related to Supersonic Intake Design
The important performance parameters that dictate the design of an intake are
the drag and total pressure recovery. These are subject to constraints related to the
compressor (or combustor in case of scramjets and ramjets) entry, namely static
pressure, Mach number and flow uniformity. Another important parameter is the mass
flow rate. The problem is, as the static pressure and mass flow rate are increased, the
pressure recovery reduces while the drag increases. Hence an optimum design needs
to be arrived at.

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F-35 is fixed thus it can not generate more oblique shocks and regulate the mass flow as MiG-21 or SR-71 do.

Click to expand...

Neither can variable-geometry inlets on F-14, F-15 or MiG-31 generate as many shocks as SR-71 inlets can. Using variable-geometry inlets does not make an aircraft fly more efficiently and faster. What SR-71 does where fighter aircraft does not is the transformation of turbojets into ramjets at high Mach number.

MiG-29 said:

MiG-21 does not translate the intake spike as much as SR-71 thus it is limited to lower speed on SR-71 its Inlet geometry is altered when the spike retracts toward the engine, approximately 1.6 inches per 0.1 Mach. At Mach 3.2, with the spike fully aft

Click to expand...

Translating the intake cone more is not going to make a MiG-21 reach Mach 3. If it is that simple, the designers would have done it and they would have a Mach 3 MiG-21. Yet, they didn't, because they couldn't. Inlet does not power the aircraft and so does not make an aircraft fly fast. What makes an aircraft fly fast are airframe geometry, thrust and exhaust velocity of the engine.

MiG-29 said:

On XB-70 it also generate more oblique shocks than F-15 but it does it internally, thus it is faster.

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XB-70 also has six engines whereas F-15 only has two. XB-70 can only turn like airliners whereas F-15 is one of the most maneuverable aircraft ever created. What does this say? It says to achieve Mach 3, a lot of sacrifice in maneuverability was made. This illustrates my point quite clearly: the more complex the inlet leads to more weight, and this weight cancels out the advantages gained.

It also illustrates my other point quite clearly: inlet alone does not determine the efficiency and speed of an aircraft. What determine these are airframe geometry, thrust and exhaust velocity of an engine.

MiG-29 said:

So DSI by being fixed: With a top speed of Mach 1.6, the Lockheed Martin F-35 Joint Strike Fighter has an inlet design that is far simpler than that of the Mach 3-plus SR-71; the single-engine JSF inlet cannot vary its geometry

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F-35 having a top-speed of Mach 1.6 does not mean DSI has a top-speed of Mach 1.6. F-35 top-speed is limited because of the use of an engine with larger bypass ratio. DSI, as we have seen in the paper below has no problem operating at Mach 2.0.


The quoted pressure recovery ratio in that paper clearly shows DSI being better than variable-geometry inlets on F-4D and F-104.

MiG-29 said:

DHI allows for increased lower speeds so a turbojet can be used to reach RAMJET speeds, DHI for RAMJET ands SCRAMJET do not generate static thrust.

this intake pictures show how do intakes work

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Cannot generate static thrust is not the same as cannot operate at hypersonic speed. The fact that such a patent exists means DSI does not have absolute speed-limit as you claimed. Of course, the inlet must be optimized to be able to operate at those speed, and this rule applies to variable-geometry inlets as well.

SR-71 can fly fast because it is able to :

Wikipedia said:

This configuration is essentially a ramjet and provides up to 70% of the aircraft's thrust at higher mach numbers.

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There is a that illustrates how this work.