F-35 with supercruise

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Adamantine RE:F-35 with supercruise 2/16/2005 1:23:13 AM

F-35 CAN supercruise. If they say it cannot, it is because USAF want to protect the funding for F-22A. By admitting tha F-35 can supercruise, F-22a would be in even deeper where funding is concern. In fact the air intake of F-35 uses some of the same principle behind the air intakes of Mirage 2000 and F-104 Starfighter. That semi-conical protrusion slow down air (abit like a ramjet spike air intake). At this point of time, the bypass ratio of F-135 engine is not published (correct me if i am wrong). One source did indicate that F-135 has the same bypass ration as F-119. This is not likely as quite a few source did says that F-135 engine will have HIGHER bypass ratio to increase subsonic SFC at the expense of supercruise performance. Think carefully, supercruise is a relative concept. Rafale and Typhoon and probably MIG-31 could all supercruise BUT they can ONLY do so at lower speed (between Mach 1.21 to Mach 1.4). F-22A is officially capable of supercruising at Mach 1.7. You can bet that the actuall figure may be as high as Mach 1.8. So when you say that F-35 CANNOT supercruise (as in some source), it probably means that F-35 cannot supercruise AS FAST AS F-22A. I reckon that F-35 could eaily supercruise at Mach 1.35 even if the byspass ratio of F-135 is as high as 0.4:1 However if F-135 has a 0.7:1 or 0.8:1 bypass ratio and a 32 to 35:1 overall ratio, there is a small possibility that F-35 cannot supercruise because the high bypass ratio will imply a very high preesure and temperature core, supersonic speed will MELT the engine. On the other hand, the special SPIKE in F-35 may be what that is needed to reduce air intake speed to prevent high speed engine surge.

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USN-MID RE:F-35 with supercruise 2/16/2005 4:47:22 AM

Nobody has outright SAID one way or the other. Considering it could legitimately be viewed as a kind of F-22 offspring, supercruise is definitely in the realm of possibility here.

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AussieEngineer RE:F-35 with supercruise 2/16/2005 4:51:36 AM

The F136 engine may be variable bypass like the F120 that was used on the YF-23 prototype.

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Adamantine F136 2/16/2005 5:22:19 AM

"The F136 engine may be variable bypass like the F120 that was used on the YF-23 prototype" I certainly hope so. If F136 is variable bypass, it would be able to make F119 and F135 look semi-obsolete. If F136 is variable bypass, you can expect goof SFC in both the subsonic and supercruise flight regime.

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perfectgeneral RE:F136 2/16/2005 10:55:56 AM

Given the F136 is trying to overtake F135 for orders in the same aircraft I would expect them to be bringing something new to the table (not just more thrust). Otherwise the F135 team could argue that their engine testing is further along and that they will be bringing out a higher thrust model shortly. As a Brit I hope the F136 team get the lions share of the orders, but they will need something special (like variable bypass) if they are going to close the gap on the F135 development.

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Adamantine RE:F136 2/16/2005 12:24:03 PM

"F136 team get the lions share of the orders, but they will need something special (like variable bypass) if they are going to close the gap on the F135 development. " They better do. Without variable bypass, you cannot wring the LAST drop of performance out of F-35 excellent air intake.

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wagneraj RE:F-35 with supercruise 2/16/2005 2:02:32 PM

I'm an engineer in the gas turbine industry. I've never heard of "variable bypass." Neither GE or Pratt refer to it in their websites about the F119, F135, or F136. Could it be that you're refering to variable inlet geometry or variable bleed? Both of those are airframe dependent and not part of the engine. As for the F-35, there will be no supercruise with one obvious reason why: F-22 60,000-lb Max Takeoff Weight, 2X 35,000-lb thrust F-35 50,000-lb Max Takeoff Weight, 1X 40,000-lb thrust Do the math. There are many factors involved in SFC, but I think it's fair to say that such and obvious difference in thrust to weight ratios is one of the big ones.

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AussieEngineer RE:F-35 with supercruise 2/16/2005 9:31:45 PM

no definately variable bypass. The YF120 prototype used in the YF-23 and YF-22 was a variable bypass engine but the F119 was chosen because it was seen as more "safe", less new technology. At least thats the reason I've heard for its selection, you never know unless you are actually part of the tender process (I've learnt this from gf).

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AussieEngineer RE:F-35 with supercruise 2/16/2005 9:54:50 PM

When you look at the thrust to weight ratios of Rafale and Eurofighter, which can apparently supercruise it does not appear to be out of the realm of possibility for the F-35 to be able to supercruise especially considering the internal weapons carriage. I think the limiting factor will not be T2W but the aerodynamics of the aircraft.

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Adamantine RE:F-35 with supercruise 2/16/2005 10:03:16 PM

"I'm an engineer in the gas turbine industry. I've never heard of "variable bypass." Neither GE or Pratt refer to it in their websites about the F119, F135, or F136. Could it be that you're refering to variable inlet geometry or variable bleed? Both of those are airframe dependent and not part of the engine." NO NO. Variable bypass is the ability to change bypass ratio during flight. Go check in internet the meaning of bypass ratio. Up to now, only F120 is officially a variable bypass engine. F-136 may or may NOT be one, no one knows. It has nothing to do with variable geometry inlet etc. Note only GE F120 is variable bypass in the whole world. That is one of the engine use in YF-23.

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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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