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Last edited by zeroyon04 on Jul 11, 2007 - 06:28 PM; edited 3 times in total

I keep reading posts by the Sukhoi fanboys everywhere that "The F-22 only has thrust vectoring in the pitch axis (2D-TVC), some Sukhois have them in the pitch/yaw axis (3D-TVC), so therefore the sukhoi is superior blah blah blah etc".... but I am wondering, does it really even matter? Does a 3D nozzle offer that much of a maneuvering ability over a 2D nozzle? or any at all?

Also, to add, why exactly does the F-22 have a 2D nozzle and not a 3D one? So, far, I have come up with:
1) It was not a requirement for the ATF project
2) The technology was too new at the time in the late 1980's for the YF-22
and
3) The 2D nozzle design is stealthier. The F-22's 2D-TVC system works in such a way that it creates a much lower IR signature by cycling exhaust gases back over the tail of the jet and down into slots above the engines. This would not be possible with a 3D TV design.

About #3, thats all I really know about it, but could someone who knows about this system explain it to me please? I can't find much information on it...
Also, is #2 really true at all?

Thank you Very Happy

EDIT: nevermind about what I said above... i guess no Su-3X aircraft actually have true 3D TVC, and the Su-37 only has 2D TVC, see page 2

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Elite 1K Joined: Jan 31, 2004 Posts: 1561 Status: Offline

You make some good observations.
1. Dunno, but I'll take that as a valid assumption.

2. The tech was there but many just weren't convinced of its usefulness. Highly reliable BVR missles were maturing so people didn't think ACM would get so close that you'd need a TV advantage. There used to be an "axisymmetric thrust vectoring nozzle" Viper testbed that did some seriously wicked tricks but I think only the IDF/AF actually fielded it.

3. I'd look at it from the aspect of available space. If you look at the Su, the nozzles are placed under each vertical fin and have plenty of room for full 3D movement. But I'd suspect the nozzle's IR sig is pretty high also. On the Raptor, the nozzles are tucked in between the tails to help reduce the IR sig (thru active and passive means). So a 3D nozzle just wouldn't have the physical room to move throughout its envelope in such a confined space. The Flight Control gurus at Lockheed may have compensated by editing the FLCS algorithms to add more yaw authority via the rudder (the rudder area is quite large) coupled with other surface deflection to give a pseudo-vectored yaw axis.

Of course....if you're a Raptor driver and you let the engagement degrade to a close-in knife fight instead of splashing the guy with a Slammer up the snot locker, I'd tell ya to cranium back to Tyndall for some more schoolin'! Wink

Enthusiast Joined: Jul 19, 2006 Posts: 74 Status: Offline

LinkF16SimDude wrote:

The Flight Control gurus at Lockheed may have compensated by editing the FLCS algorithms to add more yaw authority via the rudder (the rudder area is quite large) coupled with other surface deflection to give a pseudo-vectored yaw axis.

A couple of articles have mentioned yaw rates in excess of 30 deg/s at some speeds. That's more than enough. Cool

There's video on YouTube of the Raptor pitching up into a Cobra, going full left rudder and just swapping ends to fly in the other direction. Those rudders are big for a reason.

Last edited by zeroyon04 on Dec 12, 2006 - 06:18 AM; edited 2 times in total

I agree that the Raptor driver should take out the enemy at BVR before entering WVR, but it's good to know that your aircraft is maneuverable and can fight with a knife in a phonebooth if it somehow becomes that situation.

Do you have a link to that video JCSVT? I've seen a video before of the raptor going straight vertical, coming to a stop while vertical, then rotate 180 degrees to face straight down and fly out (called a hook by some people). I've always wondered how the raptor did this since it doesn't have yaw TVC. Unfortunately I don't have a video clip, it was on the military channel a few years ago.... I'll try to find it online.

LinkF16SimDude, I think you are referring to the F-16 MATV, and yes it did have an axis symmetric thrust vector nozzle on it. The program was a success, but the resulting analysis showed that TVC doesn't offer much of anything to WVR combat with the current proliferation of HOBS heaters. I don't think the IDF/AF field any TVC on any of their aircraft. Dryden/NASA also tested a pitch/yaw nozzle on the F-15 in a project called the F-15 ACTIVE in the early 1990's. The F/A-18 also had a pitch/yaw vector nozzle, but was of the paddle type as used on the X-31. A good image is here with them all (except the F-15) together:http://www.dfrc.nasa.gov/Gallery/Photo/Fleet/HTML/EC94-42513-3.html Very Happy

I believe the F-22 has better flight control computers then the sukhois, and doesn't need 3d TVS to accomplish the same feets.

LinkF16SimDude wrote:

You make some good observations.
3. I'd look at it from the aspect of available space. .... On the Raptor, the nozzles are tucked in between the tails to help reduce the IR sig (thru active and passive means). So a 3D nozzle just wouldn't have the physical room to move throughout its envelope in such a confined space. The Flight Control gurus at Lockheed may have compensated by editing the FLCS algorithms to add more yaw authority via the rudder (the rudder area is quite large) coupled with other surface deflection to give a pseudo-vectored yaw axis.

You pretty much covered it with the geometry discussion. There are always tradeoffs in any design, and in this case 3D nozzles just didn't 'fit'. Another issue is simply the significant additional weight and complexity that 3D brings vs 2D.

As for the rudders, big or not they are effectively completely blanked at the kinds of AOA's you see during a Cobra or helicopter maneuver and are basically useless. The horizontal tails are used differentially for yaw control at those AOA's.

zeroyon04 wrote:

I agree that the Raptor driver should take out the enemy at BVR before entering WVR, but it's good to know that your aircraft is maneuverable and can fight with a knife in a phonebooth if it somehow becomes that situation.

Nobody in the Raptor community is "worried" that some SU or Mig (or anyone else for that matter) will "outmaneuver" them because of the differences in TV approaches.

Every Raptor pilot I've talked to were rather bored during BFM because it's SO EASY for them to take out their opponents in knife fighting/dogfighting/close-in or whatever you want to call it range. NOBODY can outmaneuver it. In reality, the Raptor's maneuverability is very much UNDERSTATED, whereas the MIGs and SUs are doing everything they can to sell their aircraft based on what it can do in a airshow configured, heavily modified airframe with a specially trained company pilot flying them.

And yeah, it's nice to know despite the Raptor's superior maneuverability, that is more than likely not how it's going to kill you.

Enthusiast Joined: May 31, 2007 Posts: 29 Status: Offline

Hi Guys Im new to F-16.net and I really appreciate the level of knowledge found in this forum that is very uncommon in others.... makes for actual intellegent discussion rather than f-22 vs su-XX reruns. As JCSVT mentioned before, the youtube videos of the raptor demonstrating excellent yaw control with nearly zero airspeed-- the helicopter manuver i guess its called?-- are pretty sweet. I would like to know how the raptor can execute what looks like a controlled nearly flat spin with 2-d VC... something to do with the huge control surfaces or perhaps sending more thrust through one pipe than the other???

Elite 1K Joined: Jul 20, 2005 Posts: 1035 Status: Offline

Afterburned wrote:

Hi Guys Im new to F-16.net and I really appreciate the level of knowledge found in this forum that is very uncommon in others.... makes for actual intellegent discussion rather than f-22 vs su-XX reruns. As JCSVT mentioned before, the youtube videos of the raptor demonstrating excellent yaw control with nearly zero airspeed-- the helicopter manuver i guess its called?-- are pretty sweet. I would like to know how the raptor can execute what looks like a controlled nearly flat spin with 2-d VC... something to do with the huge control surfaces or perhaps sending more thrust through one pipe than the other???

Well thrust vectoring has nothing to do with the 'helicopter spin' maneuver. It is accomplished simply by the pilot inputing directional commands and the computer uses the control surfaces to point the jet where the pilot is telling it to. No asymetric thrust is used...and thats directly from the pilot.

-Check

Enthusiast Joined: May 31, 2007 Posts: 29 Status: Offline

wow even with very low/ stall airspeed? cool $hit...

Elite 1K Joined: Aug 01, 2006 Posts: 1003 Status: Offline

zeroyon04 wrote:

Also, to add, why exactly does the F-22 have a 2D nozzle and not a 3D one? So, far, I have come up with:
1) It was not a requirement for the ATF project
2) The technology was too new at the time in the late 1980's for the YF-22
and
3) The 2D nozzle design is stealthier. The F-22's 2D-TVC system works in such a way that it creates a much lower IR signature by cycling exhaust gases back over the tail of the jet and down into slots above the engines. This would not be possible with a 3D TV design.
D

(1) Thrust Vectoring was not a requirement of the ATF project period. The YF-23 does not feature it and BOTH aircraft exceeded the agility requirements.

(2) The slide bearing feathering nozzle used on Russian the 3D vectoring designs were not new in 1991.

(3) Yes, it is more difficult to make a "round" nozzle stealthy although some degree of RF stealth is certainly possible and the F-35 as well as the LOAN nozzle tested on the F-16 mules featured it. Remember, the F-22 nozzle is not simply 2D vectoring, it is 2D convergent-divergent as well.

The ONLY advantage that a 3D nozzle has is yaw control when the aircraft is moving extremely slowly or at extremely high AoA or both. When there is very little airspeed the rudders are useless. At very high AoAs, the wing and the fuselage "blanks" the rudders and make them useless. Very slow and very high AoA handling is not useful at all in combat when you never want to be very slow and if you are not very slow you cannot pull very high AoAs without exceeding 9~12Gs (which isn't much really). In any case, modern flight control software gets around the rudder blanking problem by using the wing and horizontal tails for improvised yaw control automatically beyond certain AoAs. Basically, what they do is move the left and right controls asymmetrically such that net roll moments are near zero but one side has more drag than the other inducing a yaw moment.

do the intakes and high sweep angle provide any vortex effect to allow the canted fins to grab air?

Elite 1K Joined: Aug 01, 2006 Posts: 1003 Status: Offline

sprstdlyscottsmn wrote:

do the intakes and high sweep angle provide any vortex effect to allow the canted fins to grab air?

Vortice in the F-22 come from primary three places... the nose, the intake lips and the wing itself. The design is such that they intertwine and form one large vortex that snakes its way across a large swath of surface area above the fuselage and wing proving significant lift enhancement. The F-35, sharing a similar layout should also be similar in its vortex characteristics.

This is how it looks like...

so that would allow for true RUDDER controll at high alpha when they should be "blocked out"

Elite 1K Joined: Aug 01, 2006 Posts: 1003 Status: Offline

sprstdlyscottsmn wrote:

so that would allow for true RUDDER controll at high alpha when they should be "blocked out"

Actually no. Not really. When the rudders are blanked they are blanked. The vortice simply improve high AoA lift performance of the fuselage and wings. In fact, the vortice can be a problem for the rudders and vertical tails. The is because they can decompose explosively and buffet the tail fins causing a lot of stress. This is especially an issue for V tailed aircrafts because the vertical tails are likely to be very close to the vortice. The F-18 for instance had cracking problems associated with the vertical tails because of vortice buffeting. This affected early F-18A models and was later cured by adding a pair of fences on the LEX to reduce the vortex slightly and also delay its decomposition to some point aft of the tails under most circumstances. The tails were also reinforced with external gussets.

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