Forum: F-35 Spotting & Photography

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Question about the B model Roll Nozzle Doors.
It almost appears as if those doors are in different locations on the two pictures.
I wasn't aware that the doors themselves were part of the roll control thrust vector mechanism unless I am just seeing the doors in mid close.

Not sure what you mean. IMHO the photo series above shows the F-35B in a 'test only' mode - being in STOVL mode with wheels up. This phenomena has been highlighted elsewhere. Here is some text:

“F-35B STOVL Mode Gear Up – 11 May 2011 USMC Lt. Col. Fred Schenk took the F-35B into STOVL mode with gears up for the first time on 6 May 2011. The test, which occur-red on Flight 118 for the aircraft, was part of the envelope expansion for the F-35B. Photo by Andy Wolfe”: http://www.codeonemagazine.com/news_ite ... tem_id=319

http://www.codeonemagazine.com/images/n ... 4_8250.jpg

archeman wrote:

Question about the B model Roll Nozzle Doors.
It almost appears as if those doors are in different locations on the two pictures.
I wasn't aware that the doors themselves were part of the roll control thrust vector mechanism unless I am just seeing the doors in mid close.

I don't think the doors are in the path of the jets. The roll post nozzles look to be thin and rectangular and point straight down in that image.

Not sure if the roll posts would have moveable nozzles or not. I'm guessing not because banking and side slipping could just be countered by increasing thrust to one nozzle or the other.

If the nozzle doors are in full open position in that pic then it means the nozzles can't turn outwards.

Designer words: "...The lift fan provides one lift post. Vectoring the cruise nozzle down would create another lift post. Shifting power between the lift fan and cruise nozzle would provide control in pitch. Similarly, engine bypass air could be ducted off to nozzles in the wings and thrust could be shifted from one wing to the other to provide roll control...."

Genesis of the F-35 Joint Strike Fighter Paul M. Bevilaqua | Nov-Dec 2009
http://pdf.aiaa.org/getfile.cfm?urlX=-% ... 0%20%20%0A

Some photos of the STOVLie Bits from Code One I think - dunno.

Another pic: http://www.defense-aerospace.com/base/util/121682_1.jpg

Hey thanks Spaz for the great follow-up info and pics. Reading my question, I now realize I didn't make it very clear. It appeared to me that the ANGLE of the roll nozzle cover door (not position on the wing) was different in the two pictures. If that were the case then the possibly there was some intent to use the door surface itself to deflect the air blast out of the nozzle providing some additional control mechanism, although my math isn't good enough to estimate what effect that might be. Looking at the door hinges, they appear to be stout, but not more than you would need to hold the panel steady in a subsonic airstream. I would also expect to see more heat deflection surface on the inside. I now doubt that they were intended for directional control as that appears to be the purpose of the vanes in the nozzles themselves. Those vanes appear much more complex than what I would expect to see for a static hot air exit nozzle.

Arch, the roll post nozzles do not have vanes and (as you have deduced) the RPN doors are not used to steer the exhaust vector The picture labeled 'vane nozzle box' above is the lift fan VAVBN (variable area vane box nozzle) mechanism by which lift fan exhaust is vectored during Mode 4 flight - both jet-borne and semi-jetborne. The STOVL integrated flight propulsion control system modulates roll thrust by controlling the size of the exhaust orifices at the roll posts (through the roll post nozzle actuators).

Conceptually, the RPNs are not unlike the reaction control ducts on Harrier. Simple differences are that F-35B RPN has a much larger exhaust area and uses bypass air, while Harrier uses 8th stage HPC bleed and has a fraction of the exhaust area. Orifice shutters are different also.

Last edited by spazsinbad on Feb 10, 2012 - 02:50 AM; edited 4 times in total

Fair enough. My understanding vaguely is that the direction gained by those vanes inside the nozzle is constant. Thrust is varied either side to gain control stability with fore and aft as described above - all computer controlled - to accord with pilot control input. I'll investigate further to see what can be found.

OK I see 'quicksilver' has answered more or less at same time (whilst I was typing and looking at photos). I'll see what else can be found.

One place to go that may answer some parts of the question would be here:

F-35B - Roll Posts by Graham Warwick at 12/9/2011

"...The roll posts duct engine bleed-air at high pressure and temperature from the compressor to mid-wing, where thrust is modulated for roll control using fast-acting nozzles...."
&
"...There are doors that close over the roll posts for stealth in up-and-away flight, and they are perforated to allow heat to escape. These doors are cracking in high-speed flight, so stiffeners have been added, beginning with test aircraft BF-3."

http://www.aviationweek.com/aw/blogs/av ... 925abcbdfa

This is a zoom of the top of the duct only from: http://sitelife.aviationweek.com/ver1.0 ... d.Full.jpg

Here ya go Spaz -- see "Stablising Ducts" (spelling in the original) at the link below.

http://www.ingenia.org.uk/ingenia/artic ... ?index=576

Thanks QS, that article has been very useful in the past with the first graphic especially. I hope the website give more details of various aspects of the STOVL engine and controls at some point. Here is the text that does not really explain an answer but anyway:

"Stabilising ducts
While the 3BSM and the LiftFan provide the prime sources of vertical thrust, two smaller but equally critical components we call ‘roll posts’ represent the third main element of the Rolls-Royce LiftSystem. These are ducts, one in each wing, that direct 1,950 lb of thrust each from the main engine during short take-off and vertical landing, providing aircraft roll control and lateral stability. Each requires a flexible sealed joint to decouple the duct from the engine during wing deflections as the F-35B manoeuvres in flight – once again, a novel approach unique to the LiftSystem. The ability to regulate the amount of thrust produced by these roll posts is via a compact flap mechanism on the roll post nozzle, which can be closed entirely during normal flight.

The duct needs to contain up to 125 psi (8.6 bar) pressure at high temperatures within the wing and utilises titanium tubes formed under high pressure with highly controlled welding techniques to give the required strength, weight and integrity in the confined space within the wing."

Graham was mistaken about the source of RPN air -- it is bypass, not bleed.

Another bit of info:

X to F: F-35 Lightning II And Its X-35 Predecessors

http://www.codeonemagazine.com/article.html?item_id=28

Butterfly Valves
"...The roll nozzles themselves now serve as the cutoff valves for the roll control air from the engine. The performance requirements for the F-35B roll nozzles are also greater because they have to deal with asymmetric external store loads."

I guess a lot of details must be classified? But whatever here is another titbit:

http://www.rolls-royce.com/Images/LiftS ... 2-6697.pdf (0.4Mb)

"...Roll Posts
Direct 1,950lbf (8.7kN) bypass thrust from main engine
Hydraulically actuated nozzles during STOVL operations
Provide aircraft roll control and lateral stability

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