F-35 with supercruise

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Shooter RE:F-35 with supercruise 2/16/2005 10:16:36 PM

Super cruise is a function of inlet geomitry, drag profile and engine thrust. I dought that a plane as small as that is will not be able to SC at some throttle setting less that AB-1. But like Gfxxxaust? I think that not getting the "Official" monicer is part PR and part politics. (Sincerely sorry I can't remember your exact handle!) The F-35 has fixed inlets with a "speed bump" on the side of the fuselage just before the actual inlet. Those fixed inlets will, like all other planes with fixed inlets be doomed to poor performance in "OFF DESIGN" paramiters. They are hopping that the bumps will mitigate this some what! Super cruise is not new! Check the later models of F-104's flight manuals! It still holds the worlds speed record at low altitude! A speed that could have translated into SR-71 beatting record at high altitude had Darrel Greenmier not lost the plane! Do a search of the REDBARRON-104.

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wagneraj RE:F-35 with supercruise 2/16/2005 11:46:28 PM

I stand corrected on variable bypass. This afternoon I googled with no luck, but when I added the words "gas turbine" I found it. 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?

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AussieEngineer RE:F-35 with supercruise 2/17/2005 12:47:27 AM

I wouldn't be suprised if it did turn out to have supercruise capabilty. I guess we will have to wait and see.

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Adamantine F-22 supercruise without variable inlet 2/17/2005 3:28:04 AM

"I think without a variable inlet supercruise would be difficult at best." You can supercruise with fixed inlet, not much problem at all. Problem arise ONLY when you try to do more than Mach 2.2. Note that no aircraft with fixed inlet ever manage to go beyond Mach 2.1 or 2.2 without variable inlet. F-22 max supercruise speed is officially touted to be Mach 1.7. Actual figure could be slightly more say between Mach 1.8 to Mach 1.85. Maximum dash speed of F-22 with afterburner has been quoted to be as low as Mach 1.8 (due to fixed inlet and temperature sensitive plastic skin) to as high as Mach 2.4. I wager that the max dash speed of F-22 is probably between Mach 2.05 to Mach 2.25. No proof though. F-35 can defintely supercruise albeit at lower speed. The supercruise speed of F-35 is about the same as Rafale and Eurofighter. Thats anywhere between Mach 1.21 to Mach 1.45. If F-136 engine is used, F-35 can potentally supercruise near the speed of F-22. Thrust to weight ratio of F-35 is lower than F-22. BUT NOTE that maximum supercruise speed is a function of bypass ratio and maximum turbine inlet temperature rather than maximum thrust. The maximum thrust of an engine are normally its maximum value at STATIC sea level condition. When a plane fly high and fast, the maximum thrust drop precipitiously, especially if a high bypass and high overall ratio turbonfan like GE F110 are used. The lower the BYPASS ratio, the smaller will be the reduction in maximum thrust of the engine when the plane fly fast and high. A low bypass ratio engine normally reduces the overall pressure ratio and also the compression level in the compressor. With less compression, overheating at high speed is less severe. A low bypass engine tends to have SMALLER FAN too, the smaller FAN reduce supersonic drag. A very high bypass ratio engine will have huge first stage fan just like commercial jet engine.

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gf0012-aust RE:F-22 supercruise without variable inlet 2/17/2005 4:07:01 AM

"Note that no aircraft with fixed inlet ever manage to go beyond Mach 2.1 or 2.2 without variable inlet." hmmmm.... whats the F-104 - a bowl of glodfish? ;)

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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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