John R Weiss wrote:

"Guy Alcala" wrote...

When you come to a F-18 / F-35 STOVL loadout, there could be a LOT of F-18
tankers supporting 1+30 cycles for the F-35, or the cycle times will be
reduced
to 1+15 or less.

Don't see why. The F-35B will have considerably more internal fuel than an
F-18A-D
with similar weight, a single engine and no need for 3-5,000 lb. of recovery
fuel
reserve. Marine profile mission radius (KPP) is 450nm from a 550' STO (590nm
for
the USAF F-35A mission profile; 600nm for the USN F-35C mission profile), with
a VL
bringback of .2 x 1k JDAMs and a pair of AIM-120s, plus reserve fuel.

What are the comparative thrust and specific fuel consumptions of the 2
airplanes' powerplants?

Actual thrust numbers, SFC, BPR, pressure ratio etc. are all still unavailable for
the F135 and 136; basic layout (turbine and compressor stages) is about all that you
can find. P&W & GE both just say "40,000 lb. thrust class." I've seen somewhere
(but can't find it) that Rolls-Royce mentioned ca. 34,000 lb. dry, 56,000 lb. wet
for the F136, but that may include the lift fan. The F136 is based on the F120
design, and IIRR that engine was variable-cycle. The use of the lift fan eliminates
the Harrier problem of needing a very high bpr to generate sufficient lift for VTOL,
screwing the SFC in throttled back cruise or at high CAS.

As to the F-18A-D, off the top of my head F404-400s were rated at about 10,800 lb.
mil (or maybe that was the internal fuel), 16,000 lb. A/B, with the -402 boosted to
17,600 lb. max. A/B.

What will the fuel burn be for a typical approach and
vertical landing for the F-35?

Considering how low it was for the Harrier, with the F-35B being easier to control,
it should be minimal. Harrier transition and landing takes a minute (or two at the
outside), with max. fuel burn (wet) of 220 lb./minute for the -406, and presumably a
bit more for the -408. The F-35B probably has between 50 and 100% more power in the
hover, with a newer engine design and using an optimized lift fan plus a
less-optimized core engine, so you can make your own estimates.

Why will there be a significantly lesser fuel reserve requirement?

Because there's no little need for multiple looks at the deck -- no bolters, no
fouled decks. Enough fuel for one go-around seems to be about the max required, at
least in wartime. Peacetime requirements will undoubtedly be greater, but still
considerably less.

Will the
bingo fuel requirement be less for a STOVL airplane than a CTOL airplane?

Are you referring to bingo fuel to the beach, or mission bingo? You have little
need for the former. In Sherman Baldwin's book "Ironclaw," he describes the Midway
trying to get a single F-18 back on board at night just prior to DS, while they were
running at 30 knots or so, directly towards Iranian territorial waters. IIRR they
tanked the guy a couple of times, and spent an hour getting him aboard. Just about
the time they were going to have to bingo him because they had to change course to
stay out of Iranian waters, they got him aboard. None of that would have been
necessary if he'd been flying a STOVL a/c. The Midway could have been cruising
along at any speed above steerage way, and he would have recovered on the first
pass.

For mission bingo, it has been less for Harriers. As John Shinal alluded to, during
the Falklands war, the CO of 801 Squadron told his pilots that if they landed back
on board with more than 800 lb. of fuel from a CAP mission, he'd "put his boot up
their arse." Average fuel at land on seems to have been under that, in the 600 lb.
range, with several landings with 400 lb., and in at least one case, when the
visibility was perhaps 50 feet in fog and the pilot in question made one missed
approach and then had the carrier shine a spotlight straight up, descending
vertically next to it and landing on without ever seeing the deck or the island (or
they him), 200 lb. Flight ops had already been shut down prior to his recovery.

Over Bosnia, USN F-18s were originally operating with 5,000 lb. landing reserves,
subsequently cut to 3,500 lb. to increase weapons bringback. Even being really
generous, it's hard to see why an F-35B would need more than 2,000 lb. landing
reserve. Night landings, even Case III, just aren't the same white-knuckle affair
that they are when you have to trap.

The F/A-18 hasn't met fuel specs yet, to my knowledge. The A/B/C/D never met
the original requirements, and the C/D specs were "adjusted" so much from the
original requirements that it is almost impossible to make an apple-apple
comparison.

The F-18E/F supposedly meets the original F-18A spec. The threshold radius for the
F-35B is greater than that.

So far, I believe the combination of cost and performance requirements for the
F-35 are hopelessly optimistic...

Aren't they all? But they are paying a lot more attention to cost ceilings on the
program than they've done in the past; that is indeed one of the prime drivers.
We'll just have to see how the performance falls out.

Guy