Lockheed Proposes 40% F-35A fuel increase with EFTs

Dragon029 · by **Dragon029** » 13 Jun 2019, 11:52

https://www.aviationweek.com/defense/lo ... rade-f-35a

Lockheed Martin has started engineering studies focused on substantially extending the range of the F-35A by increasing the total onboard fuel capacity by 40% and improving the aircraft’s fuel efficiency, Aviation Week has learned. The studies would resurrect a long-abandoned plan to install external fuel tanks under the wings of the conventional takeoff-and-landing variant. The range-extension study also could benefit from proposed propulsion improvements, such as Pratt & ...

A 40% increase in fuel would translate to roughly 2x 540 gallon tanks.

By comparison, the tanks that some will recall having previously been designed and wind-tunnel tested were 426 gallon tanks, optimised down from a 480 gallon baseline tank design.

Israel was interested in integrating 600 gallon tanks; it's possible that with drag and separation optimisation this is the range-equivalent to the 600 gal tanks that they wanted.

taog · by **taog** » 13 Jun 2019, 13:43

Lockheed confirms that it is now engaged in a study about the option for a 600-gal. fuel tank and a wing pylon that can be jettisoned. The tank is designed to be integrated on the inboard stations—3 and 9—on each wing, the company says. Although the pilot can restore the F-35A’s stealth signature to radar by jettisoning the tank and pylon, it is not clear how the radar cross-section is affected with the equipment attached to the wing.

marsavian · by **marsavian** » 13 Jun 2019, 14:41

Basically what F-22 has.

sprstdlyscottsmn · by **sprstdlyscottsmn** » 13 Jun 2019, 15:30

Well, there goes any discussion at all of a Strike Eagle going farther. It was already close. With a 70k MGTOW the F-35A with two internal AIM-120s and two internal GBU-31s and two external 600gal tanks still has nearly 9,000lb payload remaining. You could slap on two more external GBU-31s and a pair of Winders and not even be close to MGTOW. Meanwhile, the Mudhen cannot carry more than two GBU-31s if it triple bags without going over MGTOW. If it double bags it can carry 4.

madrat · by **madrat** » 13 Jun 2019, 19:18

sprstdlyscottsmn wrote:Well, there goes any discussion at all of a Strike Eagle going farther.

Badda boom, badda bing!

marsavian · by **marsavian** » 13 Jun 2019, 20:14

Strike Eagle still carries more fuel with CFT and EFT, 31,500 lb with two 600gal and 35,500 lb with three 600gal whereas the F-35A with two 600gal is 26,000 lb.

marauder2048 · by **marauder2048** » 13 Jun 2019, 20:33

sprstdlyscottsmn wrote:Well, there goes any discussion at all of a Strike Eagle going farther. It was already close. With a 70k MGTOW the F-35A with two internal AIM-120s and two internal GBU-31s and two external 600gal tanks still has nearly 9,000lb payload remaining. You could slap on two more external GBU-31s and a pair of Winders and not even be close to MGTOW. Meanwhile, the Mudhen cannot carry more than two GBU-31s if it triple bags without going over MGTOW. If it double bags it can carry 4.

I'm assuming that the increase in volume is only possible by virtue of not having to accommodate adjacent
external store separation/jettison.

sprstdlyscottsmn · by **sprstdlyscottsmn** » 13 Jun 2019, 21:00

marsavian wrote:Strike Eagle still carries more fuel with CFT and EFT, 31,500 lb with two 600gal and 35,500 lb with three 600gal whereas the F-35A with two 600gal is 26,000 lb.

As has been mentioned many times before, it also guzzles fuel at prodigious rates due to it's sheer weight and drag.

sprstdlyscottsmn · by **sprstdlyscottsmn** » 13 Jun 2019, 21:02

marauder2048 wrote:
sprstdlyscottsmn wrote:Well, there goes any discussion at all of a Strike Eagle going farther. It was already close. With a 70k MGTOW the F-35A with two internal AIM-120s and two internal GBU-31s and two external 600gal tanks still has nearly 9,000lb payload remaining. You could slap on two more external GBU-31s and a pair of Winders and not even be close to MGTOW. Meanwhile, the Mudhen cannot carry more than two GBU-31s if it triple bags without going over MGTOW. If it double bags it can carry 4.

I'm assuming that the increase in volume is only possible by virtue of not having to accommodate adjacent
external store separation/jettison.

I assume you are referring to a three-bag eagle carrying two GBU-31s to a two-bag eagles four? Is that is the case then the issue is purely weight.

wrightwing · by **wrightwing** » 13 Jun 2019, 21:08

marsavian wrote:Strike Eagle still carries more fuel with CFT and EFT, 31,500 lb with two 600gal and 35,500 lb with three 600gal whereas the F-35A with two 600gal is 26,000 lb.

Along with a higher drag index, and 2 engines.

marauder2048 · by **marauder2048** » 13 Jun 2019, 21:08

sprstdlyscottsmn wrote:
marauder2048 wrote:
sprstdlyscottsmn wrote:Well, there goes any discussion at all of a Strike Eagle going farther. It was already close. With a 70k MGTOW the F-35A with two internal AIM-120s and two internal GBU-31s and two external 600gal tanks still has nearly 9,000lb payload remaining. You could slap on two more external GBU-31s and a pair of Winders and not even be close to MGTOW. Meanwhile, the Mudhen cannot carry more than two GBU-31s if it triple bags without going over MGTOW. If it double bags it can carry 4.

I'm assuming that the increase in volume is only possible by virtue of not having to accommodate adjacent
external store separation/jettison.

I assume you are referring to a three-bag eagle carrying two GBU-31s to a two-bag eagles four? Is that is the case then the issue is purely weight.

No the F-35. The reason why you had the early comparatively low fraction external fuel tanks was the need
to accommodate adjacent store separation typically JSOW or GBU-31. If that restriction is relaxed you
can design tanks that are both drag efficient and volume efficient.

sprstdlyscottsmn · by **sprstdlyscottsmn** » 13 Jun 2019, 21:55

Oh okay, I'm tracking. It may have borne out in testing that the separation issues were overcome by other means. We may never know.

magitsu · by **magitsu** » 13 Jun 2019, 22:38

Very interesting tweets about the previous rejection of 426 gal efts.

Scott Williams (UK F-35 pilot):
"Interesting Steve. I chaired the government meetings that effectively removed the 426 Gal EFT requirement back in 2010. Fuel fraction wasn’t worth it back then. A 600 Gal option changes the ball game in that regard."

https://twitter.com/scottmox/status/1139175881707012097

"Difficult to justify if they are niche. The Fuel Fraction of 426 Gal obviously favored the B best and C worst. It was still only a 12% range increase for the B though! Deemed unanimously by all partner requirements officers to not be worth the effort."

https://twitter.com/scottmox/status/1139179249028534272

sprstdlyscottsmn · by **sprstdlyscottsmn** » 13 Jun 2019, 22:51

My first iteration of performance modeling for the F-35A said the same thing. The 426 wasn't worth it.

sferrin · by **sferrin** » 13 Jun 2019, 23:21

sprstdlyscottsmn wrote:My first iteration of performance modeling for the F-35A said the same thing. The 426 wasn't worth it.

Sounds like the fuel tanks they thought about putting on top of the SR-71's wing. Would have gave them, "about 80 more miles" so they passed.