Lockheed Martin F-35A, B, C and other ideas

[pyro-manic]

Can Dave do the dead stop like the Harrier could? Or is the transition to hover too automated to allow it?

[Taiidantomcat]

The UKs first:

http://www.flightglobal.com/blogs/the-dewline/assets_c/2012/04/F12-16157-155123.html

[pyro-manic]

Not keen on the roundel being reduced to a polo mint.

[McColm]

Great work guys.

[PR19_Kit]

Can Dave do the dead stop like the Harrier could? Or is the transition to hover too automated to allow it?

If the aircraft is already in the hover mode it could, but takes a while to clutch in the lift fan to the main shaft of the engine, longer than it takes to translate the main nozzle to the vertical.

[rickshaw]

Can Dave do the dead stop like the Harrier could? Or is the transition to hover too automated to allow it?

If the aircraft is already in the hover mode it could, but takes a while to clutch in the lift fan to the main shaft of the engine, longer than it takes to translate the main nozzle to the vertical.

Do they lose thrust when they clutch it in?  I assume it would be a case of forward flight, clutch fan, open doors, increase fan RPM, drop nozzle and come to the hover, go down?   

[Hobbes]

The lift fan absorbs something like 10 MW, so yes, you'd lose a large amount of horizontal thrust.

[PR19_Kit]

As Hobbes says, it's the MOTHER of a fan, around 5 ft in dia and the blades are around 18" deep and I think there's 32 of them! The drive shaft for the fan is around  6" in dia too, so it's all a hefty piece of kit.

AFAIK they can't run the fan with the doors shut or it would suck the top one in and blow the bottom ones clean off the airframe, so they must clutch the fan in with some considerable forward thrust on so that the fan power doesn't slow the aircraft down too much, and then cycle the aft nozzle to the vertical while adjusting the throttle to give the required amount of vertical thrust.

From John Farley's book it seems the plan was to do all this automatically, with almost zero pilot input. He flew the development Harrier T2 using the F-35 type of control system, and did a 'single-button-push return to base', and that included the vertical landing!

AFAIK the F-35 doesn't have the ability to use less than 90 deg thrust deflection, but they may have changed that since the X-35 was flown.

While the darn thing may be quicker and stealthier than any Harrier, it seems as if they've lost something in the low speed range by usuing the 'fan and single nozzle' configuration to my mind.

[Caveman]

AFAIK the F-35 doesn't have the ability to use less than 90 deg thrust deflection, but they may have changed that since the X-35 was flown.

Whilst I think I understand what you are getting at, the F35 definitely can use less than 90 degree thrust, how else would you build up speed for STO? There are some videos on youtube which show the rear nozzle varying very dynamically along the take off runs in the trials off the USS Wasp.

However VIFFing is definitely not a capability of the F35

[PR19_Kit]

What I meant was the nozzle can't stop at the internediate positions, unlike a Harrier which can fly at 30 deg all day until the fuel runs out if need be. At least, as I said in the original post, the X-35 couldn't, or it couldn't in its original form.

It woiuld take a VERY tricky control system to get the rear nozzle to produce an amount of thrust that balanced that of the front fan EXACTLY at all angles of nozzle. It has to do that or the aircraft will go out of control in pitch rather quickly. As the thrust of the lift fan depends only on the throttle setting, it doesn't have variable pitch and there isn't a variable speed drive incorprated withing the clutch AFAIK, the direct jet thrust of the rear nozzle would have to be modulated in some other fashion, and I can't imagine what that might be.

Answers would be very welcome if anyone else has an idea how they'd do it.

[Caveman]

The rear nozzle can definitely be moved to intermediate positions.
http://www.youtube.com/watch?v=WxQTvqVvVoE
However I dont think the pilot has direct control of this.

For thrust control, perhaps they use a slipping/overspeeding clutch? I hadnt considered it before but you must be right. They must balance the vertical component of thrust from the rear nozzle, and I doubt that the puffers will provide sufficient moment to do so.

hmm.

[PR19_Kit]

After searching all ove the Net like  bloodhound I've found the answer to this conundrum.  

This Wiki page tells all but you have read, mark, learn and inwardly digest what it's saying. If you're a Brit you need to clench your teeth against the somewhat pro-American bias in there as they bad-mouth the Harrier, just slightly but it's there. Remember guys, we did it FIRST, OK!

It seems the lift fan, while operating at constant speed, that of the engine mainshaft of course, not only has a thrust vectoring nozzle underneath it but the lift fan intake can be throttled too! When in VSTOL mode the main engine apparently switches from being a turbofan to a conventional turbo-jet although it doesn't say how it does that, thus limiting the thrust of the exhaust nozzle. The nozzle is also varied in area to balance the thrust of the lift fan, in the way I suggested earlier.

Not anywhere in the plethora of official Lockheed-Martin, Pratt & Whitney, US Navy, US Marines, USAF or Rolls-Royce outpourings about the F-35 does it mention this anywhere!

The Wiki page I mention is here :-

http://en.wikipedia.org/wiki/Rolls-Royce_LiftSystem

and the paragraph you need to understand is the one entitled 'Operation' about 1/3 of the way down the page.

Enjoy....  

Various things are notable about the F-35 that I learned from viewing AGES worth of video this evening.

The nosehweel retracts forwards VERY quickly, followed rather more slowly by the main wheels. Where have I seen that before? Ah yes, another aircraft called a Lightning, but with two engines, one above the other. 

The F-35B, when launching off a flat  deck carrier, uses almost full down elevator as it shoots off the edge. Quite why I can't figure out but it must be because there's a nose-up pitching moment imparted by the engine-fan combination that only becomes apparent in free air. The Harrier didn't need this flying of a ski-jump, in fact John Farley did it many times flying hands-off under similar circumtances. One hopes that the RAF/FAA F-35 crews have stonger arms or their aircraft have larger tailplanes!

The USAF F-35A has its boom-type refuelling socket waaaaay aft, astern of the where the twin main engine auxiliary intakes would be if the -A version had them. The -B and -C types have a retractable probe on the starboard side of the cockpit .

The -B type has two massive doors that open underneath the main engine exhaust to allow it to swivel downward and these doors open in conjunction with the lift fan intake, exhaust doors and the auxiliary intakes. All this with the mian nozzle still pointing aft.

What I have yet to see is some vid from above showing just WHEN the lift fan speeds up during this transition process. 

[Caveman]

not forgetting

[Hobbes]

You're right Kit, that page has me going  

I also noticed the engine drawing they show is of a turbojet...

this is a better description of the lift fan system.

Also, http://www.designnews.com/document.asp?doc_id=214108&dfpPParams=industry_aero,aid_214108&dfpLayout=article

[Taiidantomcat]