F-35 with supercruise

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gf0012-aust RE:F-22 supercruise without variable inlet - typo 2/17/2005 4:23:58 AM

glodfish = goldfish ;)

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Adamantine F104 2/17/2005 9:37:58 AM

It flies at about Mach 2.2 ;)

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gf0012-aust RE:F104 2/17/2005 11:38:26 AM

adamantine, IIRC the world speed record holder F-104 went to Mach 2.5. I think it was an unmodified airframe.

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Adamantine RE:F104 2/17/2005 11:49:24 AM

"adamantine, IIRC the world speed record holder F-104 went to Mach 2.5. I think it was an unmodified airframe" Must be the highest for a plane with non variable inlet. the speed bump probably helps. F-35 intake is similar but more stealthy. :) Looks like if you add a variable bypass engine to F-35, the air intake may actually enable it to fly higher supercruise speed than F-22 because the bump slow down supersonic air , compressed it and prevent engine surge.

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Adamantine Question on engine surge 2/17/2005 11:59:36 AM

Hi guys, Hope you can enlightened me on some question regarding air intake. My understanding of variable air intake is spotty. wish to understand more. The utility of a variable air intake lies in its ability to compress and slow down supersonic air to subsonic speed before the compressed air enters the engine. The intake ramp will narrow down the air stream, cause a shockwave to form which has the effect of slowing down incoming air while compressing it. You create the shock wave using the variable ramp and you do when the aircraft is in SUPERSONIC speed, probably the ramp is used at Mach 1.2 and above, or it may varies continuously according to speed regime. The reason why you want to slow down the air stream , according to some source , is that you want to prevent supersonic air entry to cause the engine to surge and stalls. Question: Why the engine will stalls if the air enter the inlet at supersonic speed? Logically once the air hit the fan, it should slow down from supersonic speed to subsonic speed, why do you need to slow it down by using the ramp and creation of shockwave prior to entry into the engine fan?? It cannot be due to the need to reduce temperature of entry air BECAUSE a subsonic but highly compressed air has roughly same temperature as lighly compressed supersonic air. Is the real reason due to the need to reduce overall air flow? Is it because in supersonic speed, the air intake takes in more air mass and you have to reduce the mass of air ingested by producing a shockwave to reduce mass flow of air ?? Thanks for enlighteneing. ciao

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Shaken Those bumps... RE:F-35 with supercruise 2/17/2005 10:08:07 PM

> (Wagner) > You're correct, but Shooter is also correct. I think without a variable inlet supercruise would be > difficult at best. If the capability was not part of the initial requirements, not baked into the drag > profile, etc., it wouldn't be possible. They had very specific things in mind for the F-35 and > supercruise was not one of them. After all, what else are all those F-22s good for? (Shaken) Not weighing in on the supercruise speculation fest... The inlet bumps on the F-35 are wizard cool bits of aero. You should take some time and search online for articles. My understanding is they shape the air equivilantly to a variable ramp through most of the sub-mach two regime, except with no moving parts AND providing an obstruction for radar waves looking into the air intakes. The folks I've talked to with aero backgrounds are VERY impressed by this work. (I've heard it described as an unprecedented achievement). The design software used to develop this is reputed to be astonishing as well. Essentially, designers created the shape they wanted the _air_ to make at various points in the envelope and the computer created a shape that would make this happen. -- Shaken - out --

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Shaken F-104 inlets... to GF 2/17/2005 10:58:53 PM

>> (Adamantine?) >> "Note that no aircraft with fixed inlet ever manage to go beyond Mach 2.1 or 2.2 without >> variable inlet." > > (GF) > hmmmm.... whats the F-104 - a bowl of glodfish? ;) He is right and he is wrong. There is no aircraft that has flown faster than mach xxx without some form of method of controlling the airflow to the engine face. This is traditionally done with variable ramps (F-4, F-15) or translating shock cones (MiG-21, SR-71). On the F-104 this is accomplished by bleeding air off through a variable slot (just behind the inlet cone) and ducting it around the engine. This was very innovative and quite secret when the Starfighter was introduced. -- Shaken - out --

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Adamantine To shaken 2/18/2005 2:15:38 AM

So is there any variable air bleeding device/slot within F-22A fixed inlet ? I think have read in some forum that there is some kind of internal variable ram or diffuser kinds of stuff within F-22a to negate the disadvantage of a fixed inlet but I cannot remember the detail, nor do I think the info that I have read is reliable.

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perfectgeneral RE:Those bumps... F-35 with supercruise 2/18/2005 10:15:19 AM

Thanks Shaken. This site outlines the test process. I found sites hard to find so if you have anything on the flow qualities of the final duct, then please post on here. link

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Shaken RE:To shaken 2/21/2005 3:10:26 AM

> (Adamantine) > So is there any variable air bleeding device/slot within F-22A fixed inlet ? There have been mentions in reliable sources (AvWeek, IAPR or JDW) of internal ramping to bypass air around the engines in some regimes. The mentions are vague (as are MANY details about the Raptor). It is not clear how these operate and what performance impacts are garnered. -- Shaken - out --

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Adamantine To shaken again 2/21/2005 3:18:23 AM

"There have been mentions in reliable sources (AvWeek, IAPR or JDW) of internal ramping to bypass air around the engines in some regimes. The mentions are vague (as are MANY details about the Raptor). It is not clear how these operate and what performance impacts are garnered." If the reports are true, the maximum dash speed of F-22 would have been limited more by the melting temperature of its skin than the design of the inlet since the F-22 inlet is not as "fix" as it seems. I will give it a Mach 2.2 to 2.3 dash.

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elcid Any one know why they dont give the F-35 supercruise? 2/21/2005 6:34:50 AM

Because it is a bad idea. Supercruise is not fuel efficient. If you want an efficient platform, you don't design for speed that rarely matters, and that ALWAYS forces you to operate less efficiently (fuel wise) with less range. It is worse than that - actually - but that is the foundation of why.

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Adamantine RE:Any one know why they dont give the F-35 supercruise? 2/21/2005 2:42:24 PM

"Because it is a bad idea. Supercruise is not fuel efficient. If you want an efficient platform, you don't design for speed that rarely matters, and that ALWAYS forces you to operate less efficiently (fuel wise) with less range. It is worse than that - actually - but that is the foundation of why" For air to air engagement, supercruise DO confer you advantage in certain phase of engagment. In desperate situation when you are lock on and you are trying to escape without running out of fuel by punching the afterburner, a supercruise flight regime might enable you to outrun enemy missiles without running out of fuel in fuel guzzling afterburning mode.. Supercruise greatly reduce your exposure time when you overfly heavily defended area and it also permit you to reduce the lethal radius of enemy's missile. And dun forget one point, you can still fly at fuel efficient subsonic regime most of the time. You only supercruise when the situation demands you to do so. Do not assume that a supercruising plane has to supercruise all the way from point A to point B and then back to point A.

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blacksmith RE:Any one know why they dont give the F-35 supercruise? 2/21/2005 8:19:37 PM

Another factor that can affect supersonic performance is fineness ratio. That is the ratio of the length to cross secional area. High fineness ratio improves supersonic performance (flying needls like Concorde, F-104, SR-71). Without exact dimensions, the F-35 looks relatively stubby. It's a short fat fuselage, the better to hold internal weapons bays. But not a contributor to supercruise.

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Aircraftfan RE:F-35 with supercruise - inlet design 2/22/2005 3:12:44 PM

According to the book "Ultimate Fighter" by Sweetman, the F-35 does not and was not designed to support supercruise, hence a much simpler inlet design was used as compared to the F-22. The new inlet is just as stealthy, but much less expensive. The book implies that the target temperatures for the F-35 engines would not sustain prolonged supercruise either. The specs for the F-35 deemed supercruise to be of limited value for a strike fighter geared toward ground attack role.

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