I think the number people are looking for is L/D, a measure of drag compared to lift. Its analogous to T/W. The F-22 has ~70,000 lbs of thrust, the Boeing 747 has 300,000, which is the hotter performer?

Give me four of those engines and I'll give you a fighter that can hull a$$......just don't asked it to turn.



Purple

dwight, good analysis! While engines are the key to supercruise, one should point out however that aerodynamics tailored to wave-drag (oblique area ruling etc.) is just as important as pure thrust. I believe even the F-22 is optimized for the low-supersonic regime to be able to break the sound barrier as efficiently as possible. So they have experience with that, and while the F-35 wasn't optimized for this as the F-22 was (see wing planform and bipass ratio), I would be very surprised if the F-35 didn't have some sort of super cruise ability, by merits of clean airframe and excess thrust. This would only make sense, however, if it could clear the drag rise just around (and after) mach 1 (even up until mach 1.2 is considered trans sonic and drag will diverge until noticeably "beyond" the sound barrier. Barely scratching the supersonic realm will do little for fuel efficiency and just make a lot of noise. But my feeling is that this will be well within the F-35's ability, given initial reports.

Bypass ratios have something to do with the suitability of an engine for propelling an aircraft at supersonic speeds on dry thrust. But, the difference between say 0.2:1 (F119), 0.4:1 (EJ200) and 0.57:1 (F135) is probably quite insignificant. It'll be like saying the F404 (0.34:1) bypass is much better for supercruising than an EJ200 (0.4:1) or an F100 (0.6:1). In essence, these are all turbojets with a little bit of bypass flow more for cooling, reducing smoke and feeding the afterburner than anything else. Supercuise at around Mach 1.5 can be achieved even with 2.0:1 bypass, which is the ratio of the JT8D series of turbofans that is frequently proposed with Mach 1.5 class "quiet" supersonic business jet concepts floating around.

It is often said that exhaust velocity is what makes thrust in supersonic flight. This is not correct; mass x velocity of the exhaust makes thrust. 2 units of mass flow x 1 unit or velocity makes no more or no less thrust than 1 unit of mass flow and 2 unit of velocity. The problem with using high bypass designs in supersonic flight is that intake drag tends to be higher. Flowing lots of air through the engine means you need to ingest a lot of air. This means that the intakes need to be bigger. The bigger intakes add to drag because all the air going into the intake must be slowed to subsonic speeds before hitting the compressor face or it is highly unhealthy for the engine. Ingesting and braking more air incurs more drag than ingesting and braking less air. Well, yes. But so does pylons, fuel tanks, missiles the fuselage and everything else punching through the air stream, so we need to look at the entire aircraft not the bypass ratio or the slightly larger or smaller intakes for the given engine thrust rating.

The best way for minimizing drag in supersonic flight (from a propulsion stand point) is to ingest no air at all; a rocket engine incurs no ram drag whatsoever. The next best thing is to produce as much gross thrust as you can while sucking in as little air as possible so the intakes can be as small as possible. A Turbojet does that. When it comes to low bypass turbofans (generally bypass less than 1:1), the exhaust velocity is more a function of the nozzle area than the bypass ratio. A bigger fan allows you to tap on the excess power of the core to move air this gives you more thrust for a given core size and fuel consumption. A smaller fan reduces the diameter of the engine making the powerplant more compact and lighter. Those are the trade offs really -- the exhaust velocity you can pretty much control with variable nozzles. You can "squeeze" the exhaust jet to a higher speed by reducing the size of the nozzle at higher speeds which is what the variable nozzles do. Unless you are talking about the difference between say a 0.2:1 engine (F119; F-22), a 2.0:1 engine (JT8D; DC-9/MD-80/737-200) and a 11.0:1 engine (Rolls-Royce Trent 1000; Boeing 787), the issue of bypass ratio and exhaust velocity should not the be center of the discussion

am I reading to much into your comments

I'd say so.