Engine upgrades

All about the Pratt & Whitney F135 and the (cancelled) General Electric/Rolls-Royce F136
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quicksilver

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Unread post07 Aug 2019, 11:05

“Sure, just using that speed as a lower threshold to get some feel for endurance time, speed and range before it's throttled-up. I suspect loiter, max-endurance (not necessarily the same V) and max-range cruise speed are all going to be quite close to each other at mid to upper jetstream altitude range.”

How do you define loiter? What is it’s purpose? In other words, if I looked ‘loiter’ up in your flight manual, how would it be different from max endurance?

http://www.eaa1000.av.org/technicl/perf ... tm#Figure_

We’ve talked about this before, but apart from max end and max range everything else is circumstantial. For example, if I was IMC with a wingman (necessarily in parade formation), max end or max range would make formation keeping difficult for that wingy because the jet is so far back on the power that its response to throttle movements lags; not good. So, you’d pick something a little faster that met mission requirements (make your land time...not run out of gas...give yourself some reserves, etc) and put the jet in an rpm range that provided better throttle response.
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element1loop

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Unread post07 Aug 2019, 14:45

quicksilver wrote:How do you define loiter? What is it’s purpose? In other words, if I looked ‘loiter’ up in your flight manual, how would it be different from max endurance?


Best-endurance speed is usually a bit slower than a specified loiter speed, I've always seen that as a result of loiter involving banking in orbits so having more speed margin and performed for a shorter period so a slightly higher flow doesn't matter, it's temporary. While best-endurance is sustained in a straight line so a stability margin is not needed thus lower flow rate and slightly more time up your sleeve.
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weasel1962

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Unread post07 Aug 2019, 23:31

quicksilver wrote:
eloise wrote:1620 nm combat radius is insane, holy sh...t :o


Range...not radius, to wit — “That range improvement applied to the F-35C would add 420nm – taking range for the USN's variant to 1,620nm.”


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sprstdlyscottsmn

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Unread post07 Aug 2019, 23:47

the 600nm radius was also with sub-optimal cruise.
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marauder2048

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Unread post08 Aug 2019, 21:07

quicksilver wrote:How do you define loiter? What is it’s purpose? In other words, if I looked ‘loiter’ up in your flight manual, how would it be different from max endurance?



I've only ever seen it defined as the portion of on-station time flown at the max-endurance fuel flow rate.

And since the on-station average fuel consumption is going to be distorted upwards by the
attack fuel flow requirements, the interplay between those those two fuel flow rates is what typically
guides planners.
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playloud

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Unread post09 Aug 2019, 19:22

quicksilver wrote:
eloise wrote:1620 nm combat radius is insane, holy sh...t :o


Range...not radius, to wit — “That range improvement applied to the F-35C would add 420nm – taking range for the USN's variant to 1,620nm.”

And we know the 1,200 nmi number is already below the spec. It demonstrated a 670 nmi combat radius (A2G), per the SAR. That would make its range at least 1,340 nmi before the upgrade. Internal A2A would be even higher. F-35A is listed at 760 nmi for A2A, giving it a range of 1,520 nmi (before upgrade). The C model should give similar numbers.
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