F-35 vs Su-30/35

The F-35 compared with other modern jets.
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f119doctor

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Unread post05 Dec 2019, 19:57

To clarify my answer regarding F119 engine nozzle vectoring

There is no physical connection between the two engine nozzles - they are free to move independently, under the command of the F-22 Integrated Flight & Propulsion Control (F-22 nomenclature for FLCS). The engine is an integral part of the IFPC - when the pilot moves the throttle, IFPC send a thrust request to the engine and the engine provides real time feedback on the thrust achieved. The pilot moves the stick and rudder pedals, IFPC sends a nozzle vector request to the engine and receives real time feedback on the nozzle vector angle achieved within the physical limits of the nozzle for a specific thrust and flight condition .

If the IFPC sent a differential nozzle vector rolling request to the engines, the nozzles would vector differentially. One reason that they don't use this flight control strategy could be that the nozzle are too close together to have significant rolling authority. With widely spaced engines, like the F-14, Su-27/30/35, and Su-57, that answer can be different.

In the Terry Scott interview, he did say that nozzle vectoring provided an advantage at low speeds (<250 knot) and a supersonic speeds. I don't know the IFPC nozzle vector control strategy at supersonic speeds, but I can speculate that there might be a few degrees of static nozzle up vector dialed in to push the tail down to offset the deflection of the horizontal stabs as the center of lift moves aft supersonic. This would move the horizontal stabs into a more streamline position for less trim drag and to improve both pitch and roll authority available in these conditions.
Last edited by f119doctor on 05 Dec 2019, 20:17, edited 1 time in total.
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sprstdlyscottsmn

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Unread post05 Dec 2019, 20:06

f119doctor, thank you for the explanation. Looking at the moment arms, the large H-Stabs on the F-22 are much better suited to roll than the close coupled motors. The difference in lateral moment arms looks nearly an order of magnitude more than the difference in longitudinal moment arms.
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Unread post06 Dec 2019, 16:46

That F-119 is something else. There are no words to describe the power being put out while it takes off, particularly if at an airshow where you're closer to the runway. Only the B-1B seemed to come close, with twice as many engines LOL.

Question: If the Russians or Chinese make a breakthrough in engine tech that allows the SU-57/J-20 to gain an advantage over the F-22, will the F-119 be upgraded? Better question: Can it be upgraded? Meaning more thrust, or less SFC??

Whenever the F-135 is discussed, those upgrades are always mentioned. I've heard nothing about the F-119 though (curiously enough), in the same context.
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f119doctor

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Unread post06 Dec 2019, 19:31

mixelflick wrote:That F-119 is something else. There are no words to describe the power being put out while it takes off, particularly if at an airshow where you're closer to the runway. Only the B-1B seemed to come close, with twice as many engines LOL.

Question: If the Russians or Chinese make a breakthrough in engine tech that allows the SU-57/J-20 to gain an advantage over the F-22, will the F-119 be upgraded? Better question: Can it be upgraded? Meaning more thrust, or less SFC??

Whenever the F-135 is discussed, those upgrades are always mentioned. I've heard nothing about the F-119 though (curiously enough), in the same context.


I agree that the F119 is a spectacular engine, both from a performance and a maintenance standpoint. There has been much speculation in this forum about the thrust and weight of the engine (mostly false), but it has outstanding performance and durability.

Has it been upgraded? The engine meets it's performance specification, and continues to do so. Most of the Component Improvement Program funding that the USAF has spent has been focused on correcting some individual component durability / reliability shortfalls, and to reduce the cost of ownership.

Can it be upgraded? There has been some studies on incorporating the F135 core module (Core = Intermediate Case, High Compressor, Combustor, and High Pressure Turbine) into the F119. Since the F135 core module was a derivative of the F119, this reverse technology insertion could be relatively simple, but the cost/benefit trade has bought itself into the program. The cost might be offset during the engine's 2nd depot overhaul, where many of the fatigue life limited parts of the engine will have to be replaced. Besides parts commonality with the F135, the biggest improvement would be higher hot section temperature capability, but this might not result in higher thrust capability if the Fan / Low Pressure Turbine remains the same.

A bigger upgrade could be the Growth Option 1 F135 Core, which has been said to improve SFC for the F135 by 5-6%. Once again, thrust increase is likely to be limited with the original Low spool. Would 5% SFC improvement be worth it?

To go to a variable bypass engines like the X101 is a whole new engine.
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gta4

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Unread post07 Dec 2019, 11:10

The "F119 differential deflection helps roll rate" source is AIAA 92-5399 and AIAA 2105-832, flight test on F-22 prototype.
No rudder pedal input and air to air configuration.
roll rate tvc.png
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f119doctor

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Unread post07 Dec 2019, 16:21

gta4 wrote:The "F119 differential deflection helps roll rate" source is AIAA 92-5399 and AIAA 2105-832, flight test on F-22 prototype.


You will note that the AIAA papers say "TV On" and "TV Off". They do not say differential TV nozzle deflection is the source of the increased roll rate at high AOA.

The thrust vectoring on the F-22 is symmetric, relieving the horizontal stabs of some of their pitch responsibilities and increasing their available roll authority, thus increasing the roll rate capability at high AOA.
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marsavian

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Unread post07 Dec 2019, 17:56

What that paper also tells me is that without its TVC the F-22 would not roll as well as the F-35 at very high AoA which says a lot positively about the aerodynamic design of the F-35.
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Unread post07 Dec 2019, 18:50

If TV can not deflect differentially , how could it increase roll rate?
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f119doctor

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Unread post07 Dec 2019, 18:56

marsavian wrote:What that paper also tells me is that without its TVC the F-22 would not roll as well as the F-35 at very high AoA which says a lot positively about the aerodynamic design of the F-35.


Thanks for bringing this discussion back to the F-35!
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steve2267

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Unread post07 Dec 2019, 18:59

gta4 wrote:If TV can not deflect differentially , how could it increase roll rate?


What part of f119doctor's statement do you not understand?

f119doctor wrote:The thrust vectoring on the F-22 is symmetric, relieving the horizontal stabs of some of their pitch responsibilities and increasing their available roll authority, thus increasing the roll rate capability at high AOA.
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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blindpilot

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Unread post07 Dec 2019, 19:01

gta4 wrote:If TV can not deflect differentially , how could it increase roll rate?

read the response. -
f119doctor wrote:... relieving the horizontal stabs of some of their pitch responsibilities and increasing their available roll authority, thus increasing the roll rate capability at high AOA.

Back to the F-35

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PS Ooops Steve beat me to it. What he said.
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madrat

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Unread post07 Dec 2019, 20:57

So fighters like Su-57 and J-20, which use all-moving stabs, may be overloading the stabs where they won't have as much roll authority?
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steve2267

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Unread post07 Dec 2019, 21:18

madrat wrote:So fighters like Su-57 and J-20, which use all-moving stabs, may be overloading the stabs where they won't have as much roll authority?


I think the answer is "it depends." One would need to look at wind tunnel test data, flight test data, and possibly CFD analysis results to make such a judgement. But based on the AIAA paper gta4 has quoted, and the statement by f119doc, that is a possibility.

I am going to say that the flow around the stabs would be determining factor. What I mean by that is... it could be that for whatever reason -- flow coming off the wing / flaperons / vertical tail etc -- the stabilator is not as efficient as it could be, and in those cases augmenting roll by differential engine nozzle gimbaling was the solution.

It does appear, though, that LM either designed it that way, or considered the wind tunnel data / CFD analysis results and determined that it made a lot more sense from an aerodynamic / control dynamics / control system software (simpler?) point-of-view to utilize the engine thrust vectoring in pitch-only, thus maximizing stabilator effectiveness for other things (e.g. roll control).

If my short term memory serves, f119doc stated above that the F119 engine nozzles _can_ gimbal differentially, its just that they are not commanded that way. But, given statements elsewhere about how, for example, the F-35 flight control system commands flight control surfaces in ways sometimes not anticipated, and can adjust for battle damage... that, in my mind, begs the question: could/would the F-22 flight control system possibly command differential engine gimbal to affect desired roll rates if Plan A did not work (e.g. in the case of battle damage, say, to the left horizontal stab?) But that is a question probably better suited for the F-22 forum.
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 Dec 2019, 21:36

Me Likee this Repeatee Quotee:
31 May 2013 “...For example, the F-35 can fly with one horizontal tail and one rudder missing....” http://www.aviationpros.com/article/109 ... ke-fighter
A4G Skyhawk: www.faaaa.asn.au/spazsinbad-a4g/ & www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/videos?view_as=subscriber
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Unread post08 Dec 2019, 01:17

marsavian wrote:What that paper also tells me is that without its TVC the F-22 would not roll as well as the F-35 at very high AoA which says a lot positively about the aerodynamic design of the F-35.


That's not surprising. Single engine aircraft has lower moment of inertia in roll axis. F-16, F-35, etc will outroll F-15, F-22, etc especially since moment of inertia increase with r^2 while roll moment increase with r.
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