SDF Aerospace and Aerodynamics Corner

paintgun said:

okay, let's agree on a few things :

1. it is possible that a diverterless intake design can remove boundary layer for any given mach number range it is designed for
2. it is possible that a diverterless intake design can maintain an effective pressure recovery ratio for any given mach number range it is designed for

now if the next argument is airflow mass control, please read this, it's a paper for SAAB stealth fighter project with many details, which also describes how DSI controls mass flow in different mach numbers by bump interaction with inlet cowl

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will you agree to the next point that :
3. it is possible that a diverterless intake design can produce an effective mass flow control in any given mach number range it is designed for

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In addition, step 97 may comprise reassessing shock positions, cowl plane Mach number, and capture area, and assessing boundary layer thickness and surface pressure gradients; and step 99 may comprise evaluating off-design conditions and augmenting with DHI forebody flow control

here basicly says they have to optimise the intake capture area for a given Mach number, even in Ramjets pressure recovery plays a role, however in the turbofan`s case, they need subsonic speeds so the engine does the further compression of a well determined volumne of air.

Capture area controls the position of the shocks.

To do all this you need variable geometry intakes.

To be honest, i did not find anything on the swedish document that suggest that you can have a DSI for several mach numbers, niether i found in the document you presented you have a single intake for all mach numbers.

To suggest there is a fixed DHI intake that can be used from take off to Mach 5, is something which does not make sense and the documents clearly says they optimise the intake to a given speed.

In my opinion the DHI design is used only from Mach 2.5 to Mach 10, with an optimised mach number where pressure recovey reaches a peak allowing the use of a turbojet up to mach 2.5-2.8 on an independent nacelle and with its own intake
and i see this as a proof The DHI has been computationally proven for at least Mach 3 to Mach 10 applications, The turbojet, ramjet, and scramjet engine applications forthe DHI of the present invention include flight speeds of approximately Mach 2.5 to 10.


the reason i think that is because turbofans have different needs in flow speed, that is around mach 0.5 while ramjet can work with higher speed flows and probably different mass flows, which makes highly contradictory to have an intake that works at Mach 1.5 and also works perfect at mach 6.

By allowing a lower limit of Mach 2.5, the DHI dispenses of a rocket engine and overlaps the performance envelop of a turbojet, leaving room for an aircraft that uses both turbojets and ram engines

i said for any given mach number range the intake is designed for

i guess i have to jump the plane now, you are too embedded in your opinion to see other possibilities

paintgun said:

i said for any given mach number range the intake is designed for

i guess i have to jump the plane now, you are too embedded in your opinion to see other possibilities

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Paintgun


I am just saying why i do not think they can make a DSI that jumps from Mach 1 to Mach 3 with the same performance.


Variable geometry intakes are designed because the mass flow is controlled, the SR-71 at Mach 2.3 if it suffers an unstart, changes the capture area through out the use of variable geometry intake technology.

The DHI at Mach 2.5-Mach 3 supossedly can start using the RAMJET, so it is not dealing any more with a turbojet.
But a DSI from take off to Mach 2.5 is dealing with a turbojet or turbofan, so it has very extrict conditions.

A F-14/Su-35S intake has the ability to change the capture area in flight, the ability to increase the number of shocks as it flies faster, and the ability to control the mass flow at a given speed.

The paper talks about the need to optimise the cowl plane mach number, the capture area, the shock positions to a very specific mach number.

So if you optimize the cowl intake to Mach 4, it is unlikely it will operate well at other mach numbers simply because the mass flow at different mach will change.


So here is the question, do you think a DHI will have the same performance at Mach 1.5 when it is using a turbofan, Mach 3 and Mach 5?

Unless there is a way to control the capture area, control the shock plane and mass flow at all mach speeds it flies, it is unlikely the DHI will perform at any speed the same.

mass flow moves the shock position, so a shock plane has to be optimised for a cruise speed other wise if you want to cruise at Mach 3 but you have a bump optimized for a shock plane for Mach 1 and different mass flow, you won`t achieve the same pressure recovery.


These are physical facts, that is the reason the DSI at Mach 2 drops to 0.87 while a F-14 or SR-71 can achieve higher pressure recovery


Is not that i am closed, but simply the physics of intakes do not add up for a HDI that is good for all mach speeds from take off to Mach 10

The paper is a methodology of how design a DHI for an specific mach number, not a DHI for all mach numbers

be reasonable Mig-29, read what i say carefully, this is the habit of yours misunderstanding people or misquote what people actually say

i'm out of my mind if i say a DSI can maintain pressure and flow all the way from Mach 1 to 3, there will be loss, as with variable intake

and for the love of god, don't compare a mach 1.6 class DSI with SR-71
i bring a new material, and you simply able to use in every wrong way

let's have a new twist, F-16 can go mach 2 in DSI, do you think it can go Mach 2.2 if the airframe permits? if not why?

F-22 is fixed style intake, how does it control mass flow and pressure shocks without ramps?

paintgun said:

be reasonable Mig-29, read what i say carefully, this is the habit of yours misunderstanding people or misquote what people actually say

i'm out of my mind if i say a DSI can maintain pressure and flow all the way from Mach 1 to 3, there will be loss, as with variable intake

and for the love of god, don't compare a mach 1.6 class DSI with SR-71
i bring a new material, and you simply able to use in every wrong way

let's have a new twist, F-16 can go mach 2 in DSI, do you think it can go Mach 2.2 if the airframe permits? if not why?

F-22 is fixed style intake, how does it control mass flow and pressure shocks without ramps?

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i am not using the material wrong, i will give you some facts about the F-16 intake, it works quiet fine before Mach 1.6, after that it drops abruptly down to around 0.78 of pressure recovery coefficient at Mach 2.


In Fact is very likely the J-10B and J-10A have better supersonic performance than the F-16, the inlet supposed to have a longer duct diffuser, but in order to save weight the duct was made shorter.
The only benefit from the variable-geometry intake was in specific excess power at Mach 1.6. General Dynamics concluded that for the F-16 mission requirements the fixed normal-shock inlet was the best

F-104 also had simple intakes
The air intakes were modified in shape and were fitted with half-cone center bodies which had been omitted from the two XF-104s. The fixed-geometry central intake shock cone had an internal bleed slot which exhausted some intake air through the fuselage for afterburner cooling and helped to reduce the aircraft's base drag. An

the F-14 had also more advanced intakes than F-104

So here is not that the F-16 can not reach Mach 2 it can but its performance is not on peak condition, the J-10 very likely has better performance near Mach 2 with or without DSI

see the original LWF proogram conteners




the original Boeing 980 LWF contender had a J-10 styled intake


This graphics shows the air intake design of the F-14 Tomcat. The idea behind this layout is, that the airflow into the engine has to be undisturbed and at subsonic speed even if the aircraft is flying at supersonic speeds! Early demonstrations with the TF30 showed that this engine was extremely sensitive to inlet imperfections. Therefore a number of ramps are placed inside the air intake and are moved by actuators to divert the airflow as desired. Also, shockwaves (snake lines) do not occur inside the airinlet due to the design




in these pictures you see clearly how the ramps deploy and the capture area is controlled


here you see the bypass slot of the F-14 intake



Tu-22M intake with ramps deployed

actually on our previous chart it's already on 0.78 at mach 1.6
so how did they test the F-16 DSI to mach 2?

before we go to another aircraft let's finish what we have first

F-22 is fixed style intake, how does it control mass flow and pressure shocks without ramps?

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paintgun said:

actually on our previous chart it's already on 0.78 at mach 1.6
so how did they test the F-16 DSI to mach 2?

before we go to another aircraft let's finish what we have first

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F-22 has bypass doors above the intake like an F-14 watch the video, however a fixed intake generate less oblique shocks thus it has higher　pressure losses than a variable geometry intake, more oblique shocks means weaker normal shock wave thus higher pressure recovery
[video=youtube;glv4O4JrZEE]http://www.youtube.com/watch?v=glv4O4JrZEE[/video]


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.

The cone shape of the spike also incrementally reduces the speed of the incoming supersonic air without producing a drastic loss of pressure. The farther back over the cone the air moves, the more speed it bleeds off. As the slowed, but still supersonic, air continues to move farther into the inlet, the normal shock wave springs up between the inlet throat and the engine compressor—exactly where it is supposed to be. Once there, the normal shock wave slows the air passing through it to subsonic speeds, preparing it to enter the compressor.

It is a constant balancing act to keep the normal shock wave in the right position. The inlet has an internal pressure sensor, and when it detects that the pressure has grown too great, it triggers the forward bypass doors to open, expelling excess air. The inlet also has a set of aft bypass doors, controlled by the pilot. The forward and aft bypass doors work in opposition to each other: Opening the aft doors causes the forward doors to close, and when the pilot closes the aft doors, the forward doors open in turn.






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.

Re: J-20... The New Generation Fighter III

MiG-29 said:

The Su-35 supercruise thanks to several factors, but the more important is the engine, however pressure recovery will reflect the mass flow the engine in using, the thrust to weight ratio the engine it self achieves.

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So can aircraft such as F-14, F-15, Su-27, etc. that has variable-geometry inlets supercruise? No they cannot. This already shows your theory as being wrong, and using variable-geometry inlets does not automatically make an aircraft better.

Su-35S achieved supercruise capability with 117S engines and a redesigned airframe, and still couldn't supercruise as fast as F-22 can. If variable-geometry inlets on the Su-35S allow the aircraft to supercruise faster than F-22, then you could say Su-35S inlets are better. Otherwise, they are worse.

MiG-29 said:

With a fixed intake the F-22 supercruises, true, but the speed the jet gets is still lower than what a MiG-31 or Su-35S can achieve, the su-35S will supercruise and higher pressure recovery will always help it to achieve higher yield at higher speeds thus higher top speed.

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This is merely your opinion. There is no evidence showing that F-22 top speed is slower than Su-35S. There is no evidence showing variable-geometry inlets on Su-35S have a higher pressure recovery ratio than F-22's fixed inlets. Everything you have said so far is based on your assumption that variable-geometry inlets on those aircraft are better, but that's only an assumption. Figures that are publicly available indicate the opposite of what you've said.

Futhermore, supercruise speed is not the top speed. F-22 can fly without afterburner at Mach 1.8, whereas the estimated supercruise speed for Su-35S with a clean configuration (no weapons) is only Mach 1.5. This isn't a sign of higher yield, but quite the opposite.

Re: J-20... The New Generation Fighter III

MiG-29 said:

this show you do not even know intake geometry, cones are 3D bodies, and they can have 2 slopes, F-111 when it expands has two angle slopes on the semicone
by expanding or collapsing it keeps the critical state and the oblique and normal shocks impinged on the intake lips cowls, without it they won`t impinge on the cowl lips and will create subcritical or supercritical states reducing pressure recovery

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Quit grasping at straws. Inlets with cones are very much 2D inlets. It seems you are the one who do not know intake geometry here.

2D inlets are so called because they are designed and analyzed in 2-dimension space. This is why these inlets are all either circular, semi-circular, and rectangular in shape.