Range of F35B in VTO mode

[old_rn]

If one assumes that F35B is dispersed to oilers or destroyer flight decks, what is the range it would have carrying 2 x AMRAAM and 2 x AIM9 when taking off vertically?

[spazsinbad]

This aspect has been discussed before as one would expect. First how does the F-35B get to that VTO only option deck space? That deck likely has to survive the VL otherwise the F-35B must be craned onboard somehow. Then what the F-35B can carry in fuel plus any weapon load is a relatively simple math add/subtract equation given what we know of the empty weight of the F-35B and the STOVL power of the engine (from which source also) with fuel allowed AFAIK not many weapons if any to get any range at all but I would have to check eh. IIRC the range with just fuel is very low indeed - it is said to be only useful to reposition the F-35B for a STO elsewhere nearby with a proper fuel/weapon load. D'accord?

CLUES (without the math because otherwise we have to haggle over the figures and I'm tired of it) - Buehler can do it:

First F-35B Vertical Takeoff Test
20 May 2013 LM

"An F-35B test aircraft completes the first-ever vertical takeoff (VTO) at NAS Patuxent River, Md., on May 10, 2013. While not a capability used in combat, VTOs are required for repositioning of the STOVL in environments where a jet could not perform a short takeoff. In these cases, the jet, with a limited amount of fuel, would execute a VTO to travel a short distance."

Source: http://www.lockheedmartin.com/us/news/f ... -vtol.html

Quelle Horreur an FORA URL: viewtopic.php?f=22&t=28199&p=305885&hilit=vertical+take+off+takeoff+VTO%2A#p305885
&
The latest available LM Fast Facts published near the end of last year would be my common reference even though there are other references scattered all over for different bits of the same information - it is all near enough for this purpose:

LM Fast Facts
13 Sep 2016 LM PR

F-35B empty weight: --------32,300 lb
Uninstalled Thrust Ratings: 40,500 lbs Vertical

Source: https://a855196877272cb14560-2a4fa819a6 ... final_.pdf (90Kb)

IF you take these figures as a guide for the sake of illustration then there is an allowance of 8,200 lbs for a VTO minus some margin for things such as temperature (we remain at sea level). What are the weights of these missiles mentioned? I have no idea but you get the idea and do the math and I'm going to get some rest. And of course as I was going up the stairs I remembered that this VTO aircraft has to land. How does it do that and with what? Good question to factor in eh.

[spazsinbad]

To give an idea of minimum fuel required for an F-35B perhaps we can deduce from this fuel requirement for the F-35A:

F-35A OPERATIONS PROCEDURES
7 JUNE 2012 Flying Operations AIR FORCE INSTRUCTION 11-2F-35A, VOLUME 3

"...3.20.3. Normal Recovery Fuel. The fuel on initial or at the final approach fix at the base of intended landing or alternate, if required. Fuel quantity will be as established locally or 2,500 pounds, whichever is higher.

3.20.4. Declare the following when it becomes apparent that an aircraft may land at the intended destination or alternate, if required, with:

----- 3.20.4.1. Minimum Fuel. 1,800 pounds or less. This is based on 20 minutes reserve at 10,000 feet MSL flying max endurance airspeed (fulfilling AFI 11-202V3 fuel reserve requirements); and,

----- 3.20.4.2. Emergency Fuel. 1,200 pounds or less...."

Source: http://www.bits.de/NRANEU/others/END-Ar ... f-35av3(12).pdf (0.6Mb)

[steve2267]

To summarize:

Two AIM-120
Two AIM-9X (with 100lb pylons)
175lb pilot

~65 nm range with one minute at full MIL and one minute at full MAX. NOTE, however, that I did not use the MIL and MAX fuel for going anywhere. I assumed you are swirling in a circle, defending or attacking.

Out and back @ max conserve ~ 105nm, but possibly somewhat greater, since I guesstimated the range at a max endurance cruise speed of 250kts (a total swag). One way reposition would be around 210nm.


Here's my back-of-the-napkin estimates:

Running with Spaz' numbers,

40,650 (thrust STOVL mode, see attachment) - 32,300 (F-35B empty weight) = 8350lbs payload

AIM-120 @ 335lbs
AIM-9X @ 190lbs
Pilot @ 175lbs

With pilot + 2 x AIM-120 + 2 x AIM-9X ... 8350 lbs - (2x335 + 2x190 + 175) = 7125 lbs for fuel. BUT how much do the AIM-9X pylons weigh??? I'm going to guess 100lbs each. So we are left with 6925 lbs for fuel.

From other threads, the SFC for the F135 has been estimated at 0.7 lb/lbf-hr (TEG), and as high as 0.886 lb/lbf-hr. MAX (i.e. reheat) is estimated at 1.95 lb/lbf-hr. TEG felt that the F135 is closer to 0.7 lb/lbf-hr, but he also mentioned that in STOVL mode, it will have a higher SFC since the engine has to be run at a higher temperature to extract the power for the lift fan. So I'm going to use 0.7 lb/lbf-hr for conventional flight, but 0.886 lb/lbf-hr for STOVL mode. Having said all that... according to the information Spaz dug up, listed above, emergency reserves of 1800lb fuel for 20 minutes of flight equates to 90lb / min. I estimate, from watching videos, that it takes the F-35B about one minute to perform a VL and about the same to perform a VTO. At 40650 lbf thrust * 0.886 lb/lbf-hr SFC / 60 min ~= 600lbs / min.

So VTO / VL I estimate to consume 1200lbs. If you leave an emergency reserve of 1200lbs at the very end, you will have approximately 6925 lbs fuel - 1200 lbs fuel (VTO/VL) - 1200 lbs fuel (emerg reserve) = 4525 lbs to "play with".

I am guessing max endurance airspeed is 250 kts. A total swag. One way: 4525 lbs fuel / 90 lb/min * 4.17 nm/min ~= 210 nm. Out and back would be 105nm. Since these are numbers based on max endurance, max range should be somewhat greater.

But this leaves no gas for combat. One minute of combat at MIL ~ 0.7 lb/lbf-hr * 27000 lbf / 60min = 315lbs. One minute of combat @ MAX ~ 1.95 lb/lbf-hr * 41000 = 1335 lbs.

Allowing for one minute @ MIL = 315lbs and one minute @ MAX = 1335 lbs --> 1650lbs.

4525 lbs fuel - 1650 lbs fuel (combat) = 2875 lbs / 2 = 1437.5 lbs fuel (out and back) @ 90lb / min = ~16 min flying time @ 4.17nm/min = 66.5 nm, so round down to 65nm.

me_f135_stovl_pCard.pdf

From the P&W F135 website

(702.13 KiB) Downloaded 433 times

[quicksilver]

F-35B will never operate from a 'small boy' (i.e. LCS, DDG, or CG). Ain't gonna happen. I'm not gonna count the reasons why, I'll let you figure them out (hint: they are obvious if you think about 'em a bit; imagine a cork bobbing around in one's bathtub).

Additionally, all nominal VTO/VL ops (F-35B or Harrier or Yak) require assumed decrements for control margins and 'jet effects' (suckdown). I don't know what those margins are for F-35B.

In Harrier, there was (is) a significant difference between VTO performance and VL performance because (in part) the beneficial effects of the LIDS are not wholly effective during a VTO. Not sure how much delta that creates in F-35 (I think less perhaps).

Bottom line: VTO is not useful for anything other than a re-position -- as spaz cites above.

[kostas29]

F-35B will never operate from a 'small boy' (i.e. LCS, DDG, or CG). Ain't gonna happen.

don't be so certain

The LCS can move with 40knot, add 10knot of average wind speed and you get up to 50knot of wind velocity around the wings of a F35B taking off vertically. This wind speed produces significant aerodynamic lift.
Some have estimated the take off speed during the short take off of F35B as being 80knot. No big difference between 50 and 80knot.

If you take into consideration that the LCS will be operating much, much closer to the area of operations compared with the LHA/LHD or even more CVN, then a range of even "just" 150-200nm becomes very interesting...

PS: the upgraded engine will offer 10% more thrust, this will make things even more interesting for the aforementioned scenario

[steve2267]

F-35B will never operate from a 'small boy' (i.e. LCS, DDG, or CG). Ain't gonna happen.

don't be so certain

With respect,

The LCS can move with 40knot, add 10knot of average wind speed and you get up to 50knot of wind velocity around the wings of a F35B taking off vertically. This wind speed produces significant aerodynamic lift.

The F-35B's would be launching from the rear of the LCS -- within the unsteady wake created by the ship's superstructure. Recent articles posted around here somewhere (I think it was a DT-III thread aboard USS America), referenced technical papers that were dealing with trying to predict the wake effects of the ship superstructure so that computer models could be verified and used in analyzing landing and takeoff off operations aboard the ship. It was NOT an insignificant effect. So at initial liftoff of a VTO from the back of an LCS, the aircraft will basically be seeing 0 kts or a very low, unsteady (potentially dangerous) wind across its wings. It may be safer to slow the LCS down to 10-20 knots to conduct VTO ops.

Also, to be able to conduct VTO / VL on an LCS, the ship's pitching / rolling / heaving must be within operational limits. From the DT-III USS America tests recently completed, that seems to be on the order of +/- 5° roll and a few degrees pitch. Considering the sea state required to cause a 45,000 ton LHA to roll +/- 5° and pitch a few degrees... what would the same sea state cause an LCS to do? In addition, the ship's deck has to be able to withstand the combined thermal and physical loading of the F-35B liftfan + turbofan exhaust. Now I am not saying it is impossible, but I AM SAYING it is no slam dunk.

When I raised the possibility of basing F-35Bs on a 10,000 ton class destroyer, maybe even such a ship modified with a hollow superstructure and an EMALS catapult, and hosting, say, four F-35Bs... the most pertinent replies were of videos showing helo recovery in bad weather aboard an Arleigh Burke class destroyer. The ROLL and PITCHING motions (dunno about heave) were HUGE. They were talking about 5 degree roll and several degrees pitching as being the limits aboard an LHA class amphibious assault ship (aka helo carrier). So I do not see basing F-35Bs on anything like a destroyer or smaller as feasible at all. Even something like a San Antonio class LPD (or is that an LSD?) would pitch and roll more than an LHA.

Some have estimated the take off speed during the short take off of F35B as being 80knot. No big difference between 50 and 80knot.

Again, with respect, yes, it is. It is a 30kt difference. And 30kt is a sizeable fraction of 80kt. Also, if it was no big difference, then the F-35B would takeoff @ 50kts on a STO.

If you take into consideration that the LCS will be operating much, much closer to the area of operations compared with the LHA/LHD or even more CVN, then a range of even "just" 150-200nm becomes very interesting...

I will give you this: if there is a future shooting war, and someone really screws the pooch, and the CVNs are sunk or damaged (combat ineffective) or nowhere to be found (in port / out of position, etc) and the LHAs are sunk / damaged... and you need somewhere to land / base / operate F-35Bs... then perhaps repositioning them as a last resort on any sort of flat deck space may make sense. However, it may be more like recover (land) them, and then get them to land somewhere. Many ships are unable to handle an MV-22. Rule of thumb (as far as I can tell) is: if you can't handle an MV-22, you sure aren't going to handle an F-35B. Think of it this way... with an F-35B you are basically applying two dynamic loads of about 19.5 tons each on a spot of deck that is several feet across. Many decks, without significant re-enforcement (lots of engineering, lots of modification, lots of $$), may not be able to handle an F-35B.

That being said, it may behoove NAVSEA (or whatever their moniker is) and NAVAIR to do some basic engineering analyses to see if anything like this is even possible... should they ever have to open the last-ditch Operation Doolittle portion of their F-35B CONOPS.

PS: the upgraded engine will offer 10% more thrust, this will make things even more interesting for the aforementioned scenario

At first glance, one would think this. But whereas it may be a fairly easy swap to slide a new +10% thrust engine into an -A or -C variant, with the -B, the increased thrust has to be balance with the shaft horsepower transfer to the lift fan. Also, the liftfan and transmission / gearbox / clutch has to be able to handle the increased shaft horsepower. I have seen no one here, and no one anywhere on the interwebs, posit what, if any, growth potential exists in the liftfan portion of the F-35B. So, again, it is not a simple engine swap, and lots of $$ will need to be spent on design / analysis / test and possibly new hardware. Not cheap.

[popcorn]

The wings generate zero lift in VTO. The moment the jet's wheels leave the deck, forward momentum is lost well before the jet transitions from hover to forward flight.

[steve2267]

The wings generate zero lift in VTO. The moment the jet's wheels leave the deck, forward momentum is lost well before the jet transitions from hover to forward flight.

I think the previous poster was trying to say that an LCS moving at 40 kts, with a 10kt headwind, would result in 50kts over an F-35B during a VTO, so it would be more like a STO. I think the unsteady superstructure wake would greatly affect that, possibly meaning a near 0kt headwind during the intial phase of the VTO.

If an F-35B did VTO from the back of a ship moving at 40kts, if the F-35B keeps pace as it lifts off (angles thrust forward) / clears the superstructure wake, will it not be moving into a 40kt slipstream?

The problem as I see it, is that you are not going to have anything like the benefits of a STO roll due to superstructure wake effects.

[spazsinbad]

'kostas29' any upgraded F135 engine will be ONLY for the F-35A & F-35C both will NOT require any modification. The F-35B WOULD REQUIRE modification - this seems to be a non-starter according to a recent article - engine sub forum search.

FARNBOROUGH: ​Pratt & Whitney proposes Block 1 engine upgrade for F-35
10 Jul 2016 Leigh Giangreco

"...The proposed Block 1 upgrade would improve the baseline F135 engine, with 5-7% better fuel burn and up to 10% more thrust, Croswell says. That could increase the engine’s capability up to a thrust rating of 47,300lb (210kN).

But that increase could affect the lift system for the short take-off and vertical landing variant, Croswell notes. With an increased thrust on the back of the engine, P&W must keep the balance by increasing the thrust on the front, he says.

While the company is in talks with Rolls-Royce and the US Navy, there is no technology programme for lift system components yet.

“The technology work to do it is about four or five years behind where we are on the engine,” Croswell says."

Source: https://www.flightglobal.com/news/artic ... in-427150/

[sprstdlyscottsmn]

It might not help a VL but a STO should still be improved. The nozzle would need to be programmed to a lesser amount of deflection so the vertical component stays the same and the longitudinal component would increase meaning the "Bee" could get to the same speed in less time/space. Maybe.

[spazsinbad]

'quicksilver' has STOVL experience whilst I have only anecdotes told to me via e-mail from ex-A4G pilots gone STOVL in the Hairier world back in the mid 1980s (some were on exchange in that world before that date). As indicated by 'steve2267' the VTOL deck in this case has to be capable of dealing with the weight and heat of the F-35B either landing or taking off or both - in vertical mode. Somewhere on forum there is a story about a VX squadron testing this capacity (that is already designed in by the way). SHOL diagrams are important and one exists on this forum for the first F-35B WASP test (search on SHOL).

F-35B SHOL Diagram USS Wasp 2011: viewtopic.php?f=57&t=24438&p=283226&hilit=SHOL#p283226

Although the control laws and designers have made STOVL easier for the F-35B compared to the Hairier there is still the ship movement to consider. Flat water is usually found in a harbour. At sea anything can happen to a small ship in a seaway. The F-35B is not indestructible when hitting a heaving rolling pitching (6 degrees of freedom remember 'Translation Pitch Roll Heave Sway Yaw') swaying deck on the back of a small sized ship would be no joke. The F-35B airframe is designed to VL on suitable large decks to withstand AFAIK a 12 feet per second sink rate when it is limited to 7 feet/sec by control laws.

Great 6 page PDF article on the STOVL engine here: download/file.php?id=19133 (1.5Mb)

[old_rn]

Thanks for all the replies. My only comment would be "never say never". The UK used Fearless and Intrepid in the Falklands war as "lilypads" on occasion, and that was never planned before the war!

[spazsinbad]

YEAH but did they operate from those decks OR did they land there because of an emergency situation - then take off again as the F-35B may do to get loaded in a more appropriate place. The photos I have seen appear to show these ships near land in calm seas most likely. For example: http://www.iwm.org.uk/collections/item/object/205190417

ATLANTIC CONVEYOR had an appropriate VL deck installed and tested: http://en.wikipedia.org/wiki/SS_Atlantic_Conveyor

"...A Royal Navy Sea Harrier piloted by Lieutenant Commander Tim Gedge of No. 809 Naval Air Squadron to test its recently installed flight deck at Devonport, 25 April ’82..."

http://www.combatreform.org/harrierover ... ership.jpg

[weasel1962]

It shouldnt take very long nor costly to place flat-tops with ski jumps onto old container ships or tankers, if required. Even AM2 mats work.