F-35 internal fuel, range

Discuss the F-35 Lightning II
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Gums

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Unread post07 Jan 2020, 03:52

Salute!

Getting some good poop here last few days.

One thing for all the armchair folks to consider is the initial climb/cruise phase. You don't takeoff and keep the burner going, comb hair forward and pull out your Zippo. In Linebacker II we didn't accelerate until about 100 miles out, and descended a few thousand feet to help. You try to save as much gas as you can before you need to push it up.

OTOH, at Red Flag one time I had two of the big tanks and 6 or 8 Mk-82 on MER's. Down on the deck at 540 kts I was burning 4500 to 5000 lb/hr and still had about 9,000 lbs of gas. No refueling in or out. I was "comfortable".

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Corsair1963

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Unread post07 Jan 2020, 04:02

The F-35's large internal fuel volume and excellent aerodynamic performance can't be underestimated.... 8)
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steve2267

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Unread post07 Jan 2020, 04:20

Gums wrote:OTOH, at Red Flag one time I had two of the big tanks and 6 or 8 Mk-82 on MER's. Down on the deck at 540 kts I was burning 4500 to 5000 lb/hr and still had about 9,000 lbs of gas. No refueling in or out. I was "comfortable".

Gums sends...


Gums, were you at full MIL down on the deck? Or were you still a handful of RPM's back from full MIL? (0.94 Mach? Am guessing you were all the way forward, but not in burner just yet...)
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.
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Unread post07 Jan 2020, 04:53

Salute!

No, Steve, I was maybe 90% rpm and not full mil power. That rascal was fast! 'vaarks and Thuds faster, but we had the A2A capability that they didn't have. Recall the Bomb Comp at Lossiemouth.

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Unread post07 Jan 2020, 05:23

At those speeds, the MERs were probably galloping a little. :shock:
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steve2267

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Unread post07 Jan 2020, 05:40

Gums wrote:Salute!

No, Steve, I was maybe 90% rpm and not full mil power. That rascal was fast! 'vaarks and Thuds faster, but we had the A2A capability that they didn't have. Recall the Bomb Comp at Lossiemouth.


I'm not a motor guy... but am inferring that fuel consumption is NOT a linear function of rpm?

And now after looking at some numbers I'm confused...

Wiki says the F-100-PW-220 gets about 0.73lb/hr/lbf for gas mileage. If full MIL is 14,600lb thrust, then full MILL should be drinking about 10.6K/hr. Dividing your fuel flow rate of 5000lb/hr by .73 gives only 6850lb of thrust. That seems too low? If you were on the deck @ Nellis, that puts you at what 4-5000 MSL? So the air is thicker than here in Denver. What am I missing? Installed thrust vs static, sea-level thrust? Damn, I'm going to have to go dig out some old text books...
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.
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Unread post07 Jan 2020, 08:05

presumably the Lt Col was referring to 388TFW's 81 bomb comp? +1.

I note the F-16 outcome was all ground targets destroyed, 88 A2A kills, and no losses with a near-perfect score.
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Unread post07 Jan 2020, 08:42

weasel1962 wrote:Weasel's note: 1 engine vs 2 engine is less relevant since low power use at optimal cruising speed is probably imho roughly equivalent in terms of fuel usage (if similar TW, ceteris paribus and using simple logic. However carrying one extra engine does increase weight...). imho, F-35A should be able to achieve 1600+nm ferry range on the 15% less internal fuel. Drag from 4 AAMs is not that significant and suks are generally quite slick. Don't forget the Russians designed the Su-27 as an air superiority (not multi-role) fighter first.


It's more the increased frontal area and associated drag of two engines versus one, and the Flanker definitely has a fair amount of drag, considering the relatively modest subsonic acceleration performance of the plane.

Due to less drag and less weight, the F-35 is very likely to consume considerably less fuel per distance than the Flanker, likely enough to give it greater combat range than the Su-27/30.
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Unread post07 Jan 2020, 09:41

knowan wrote:It's more the increased frontal area and associated drag of two engines versus one, and the Flanker definitely has a fair amount of drag, considering the relatively modest subsonic acceleration performance of the plane.

Due to less drag and less weight, the F-35 is very likely to consume considerably less fuel per distance than the Flanker, likely enough to give it greater combat range than the Su-27/30.


which again is not totally relevant. Consider the F-15 vs F-16. The extra thrust more than compensates for the drag. Of course in the case of the F-35, there is a lot more thrust vis the F-16 for a lower amount of drag. But from a purely aircraft performance angle, I'd rather be in an F-22 than an F-35.

I don't think the range difference is that significant between the Suk and an F-35. The Russians have always liked long ranged planes due to their geography and have designed their planes as such. The difference is more how the pilot uses the plane. Good pilots will be able to squeeze more out of the same plane.
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Unread post07 Jan 2020, 11:19

weasel1962 wrote: The extra thrust more than compensates for the drag.


Not with Flanker vs F-35.
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Unread post07 Jan 2020, 11:32

Factually at least 28% more thrust than the F-35. Do kindly share your drag coefficient "sauces" to demonstrate...
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ricnunes

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Unread post07 Jan 2020, 11:33

weasel1962 wrote:The Russians have always liked long ranged planes due to their geography and have designed their planes as such. The difference is more how the pilot uses the plane. Good pilots will be able to squeeze more out of the same plane.


IMO, not necessarily true.
Most of the Migs, namely the Mig-21, Mig-29 and also the Mig-23 do not follow such long ranged plane 'philosophy'.

Resuming the Russians also seem to have favored "point-defense" (short range) interceptors, at least until a relatively recent past.
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Unread post07 Jan 2020, 11:48

knowan wrote:Su-35 has about 22% more fuel than the Su-27 and Su-30, so it would have a fair bit more range.

The 1500 km combat radius claims for the Su-27 and Su-30 though? Basically propaganda; a realistic figure would be more like 1000 km.


It's really interesting that Sukhoi does not claim much better range for Su-35 than for Su-27, but 20% longer range than Su-30. Here are their figures with 2xR-27R1 and 2xR-73E with halfway launch. I don't think it's really even supposed to be realistic combat flight profile though. Real world figures would naturally be a lot lower depending on mission and carriage.

Su-27 1,340 km low / 3,530 km high
Su-30 1,270 km low / 3,000 km high
Su-35 1,580 km low / 3,600 km high

IMO, it would make much more sense to overestimate Su-35 range than old aircraft like Su-27. They are marketing and trying to sell their new equipment after all. I find it interesting that Su-35 range is almost 18% better in low altitudes but only less than 2% better at high altitudes. Su-30 is 5.5% inferior at low altitudes but almost 18% inferior at high altitude.

I bet this is because both Su-30 and Su-35 are a lot heavier than Su-27 and burn more fuel reaching the optimal high cruise altitude. Su-35 has huge amount of fuel and probably pretty similar amount of drag to Su-27. So at low altitudes it has significantly better range. Su-30 is both heavier and draggier, so it's slightly inferior at low altitudes and has quite significantly inferior range at high altitudes.
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Unread post07 Jan 2020, 11:58

ricnunes wrote:
weasel1962 wrote:The Russians have always liked long ranged planes due to their geography and have designed their planes as such. The difference is more how the pilot uses the plane. Good pilots will be able to squeeze more out of the same plane.


IMO, not necessarily true.
Most of the Migs, namely the Mig-21, Mig-29 and also the Mig-23 do not follow such long ranged plane 'philosophy'.

Resuming the Russians also seem to have favored "point-defense" (short range) interceptors, at least until a relatively recent past.


Accepted. However, doesn't change the fact that the su-27 was designed as a long-ranged fighter, not a point defence fighter like the Migs.
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Unread post07 Jan 2020, 12:04

ricnunes wrote:
weasel1962 wrote:The Russians have always liked long ranged planes due to their geography and have designed their planes as such. The difference is more how the pilot uses the plane. Good pilots will be able to squeeze more out of the same plane.


IMO, not necessarily true.
Most of the Migs, namely the Mig-21, Mig-29 and also the Mig-23 do not follow such long ranged plane 'philosophy'.

Resuming the Russians also seem to have favored "point-defense" (short range) interceptors, at least until a relatively recent past.


Quite true. Even the Mig-25 was a reflection of this, a situation not rectified until the advent of the Mig-31. Sukhoi started with the goal of creating an "anti-F-15", something that could outperform it. Thus, the SU-27 had to be a big machine in order to carry the radar, fuel etc.necessary to achieve its goal. In fact, it needed to be even bigger than its western counterpart, given Soviet electronics/avionics were inferior and quite a bit heavier than the AN/APG-63.

They wound up with something that could carry vast amounts of fuel internally, and when requirements were changed early on for more range, had the available space. I don't know that we'll see a return to point defense interceptors anytime soon, as even the Mig-35 has much longer legs than the Mig-29. Russian design philosophy has apparently shifted, as there are no aircraft on Mig's or Sukhoi's drawing board that appear to sacrifice range vs. the Flanker. If anything, the SU-57 should have even greater range than its predecessor...
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