CLEARANCE: Top Secret
- Mar 17, 2009
- Reaction score
The range would increase by the 30%+ as mentioned; the adaptive cycle AETP engines (GE's XA100 and P&W's XA101) are both specifically designed / sized to fit the F-35 (they're by no means plug and play, but the F135 and F-35's engine bay was the reference size to match).As for the F-35, it would maybe give it a substantially higher speed in military power, but how much longer would its range in subsonic regime be would greatly depend on the maximum BPR the new engines provide, and even then, the higher the BPR, the more SFC worsens with speed.
I got numbers mentally mixed up; 0.57 is the F135's bypass ratio, not TSFC - for the F135's TSFC there's competing numbers - there's 0.7lb/lbf/hr from one website published in 2004 that's incorrect about some F135 figures (so I don't trust it that much), and another of 0.886lb/lbf/hr that's supposedly from Janes, but with no specific reference, plus that number is rather high for an engine that should be relatively fuel efficient (exceptionally high combustion temperatures, a reasonable bypass ratio, etc). In any case you can look at TSFC numbers of other military turbofans here, and they're generally in the 0.7-0.8 range: http://www.jet-engine.net/miltfspec.htmlOk, I think my confusion comes from having seen TSFC data in different conditions. For the F135 I had read something like 0.7 or maybe a bit better, which makes sense for the bypass ratio of the engine, but this is probably static and at sea level (where did you see 0.57?). For the high-bypass turbofans you mention, the value I had seen was ca. 0.55, but that is in cruise mode, actually the flight regime that is relevant in this case. With TSFC at subsonic cruising speed for current fighter jets we could know if the claim of 30% reduction with newer engines makes sense or not, but I didn't find anything reliable yet...
Regardless of what the F135's TSFC is however, the 30%+ range increase is coming directly from GE and (kinda) P&W.
GE's website claims that their "ACE" (XA100) will offer a 50% improvement in loiter time, 35% increase in range, 25% reduction in fuel consumption and 60% increased heat transfer rate for the engine's heat exchangers: https://www.geaviation.com/military/engines/ge-adaptive-cycle-engine
P&W haven't given numbers for their XA101 / "F135 Growth Option 2" engine, but their "Growth Option 1" option, which just swaps out one of the F135 modules (without adding a 3rd airstream / adaptive cycle capabilities) offers 5-6% lower fuel burn and 6-10% greater thrust across the entire flight envelope of the engine; so evidently there's been improvements made in things like compressor and turbine design that offer increased fuel burn at the same bypass ratio: https://www.ainonline.com/aviation-...-outlines-three-step-f135-development-pathway