Forum: F-22A Raptor

Elite 1K Joined: Aug 19, 2004 - 09:19 AM Posts: 1092

Some of you may know about the Advanced Figther Technology Integration (AFTI)/F-111 Mission Adaptive Wing program conducted in the early 1990s by NASA. The idea was to use both leading and trailing edge flaps to optimize flight performance. Now if anyone has been paying close attention to some of the F-22 videos in the public domain, s/he will have noticed that both the leading and trailing edge flaps are active and moving throughout a variety of different types of maneuvers. Even when the F-22 is performing a roll I see them moving. Is this the first fighter to employ a truly mission adaptive wing?

-Raptor One

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MAW was a lot more than just LEF + TEF ...

Elite 1K Joined: Aug 19, 2004 - 09:19 AM Posts: 1092

habu2 wrote:

MAW was a lot more than just LEF + TEF ...

Yes... I understand that. I have numerous technical reports on it (some that aren't even available online from old AIAA Journal of Aircraft issues), but thought I'd make my first post as simple as possible. One major difference between the AFTI/F-111's MAW and the F-22's LEF + TEF combination is the fact that the F-111's LEFs and TEFs merged smoothly with the main wing section no matter what their deflections. So you really did get a different wing depending on how much the LEF and/or TEF was deflected. The F-22's LEF and TEF are the most basic type of flap. They simply deflect. There is no smooth transition from leading edge flap surface to wing surface to trailing edge flap surface.

That being said, I don't know of any fighter that uses both its LEF and TEF together throughout a variety of combat maneuvers. It also looks as though they're both used for cruise, although this may only be for subsonic speeds. The F-16 and F/A-18 make use of their LEFs for cruise and combat maneuvering, but the TEFs are only regularly deployed when the gear comes down.

In the videos I've seen of the Raptor in flight and maneuvering, the LEF and ailerons were moving, not the inner portion of the TEF. Since the F-16 doesn't have separate ailerons it's not really an apples to apples comparison. I have seen the F-18 in flight using LEF and ailerons like the Raptor.

Either way, since the control surfaces are not smoothly integrated like the original MAW demonstrator, I'd say the Raptor just uses conventional control surfaces.

Raptor_One wrote:

The F-16 and F/A-18 make use of their LEFs for cruise and combat maneuvering, but the TEFs are only regularly deployed when the gear comes down.

Hi Raptor

I'm not 100% sure about the Hornet models A-D, but I know the Super Hornet uses its TEFs for roll control at low AOA as well as its LEFs and traditional rolling surfaces. Also, if I remember correctly symmetric TEF deployment is a function of AOA and perhaps airspeed when in Up-auto cruise mode. Ailerons are also scheduled to deflect to half flap position at low AOA and to zero degrees at high AOA, I think for load alleviation.

Its also interesting to see how the JSF Naval C model, uses its ailerons symmetrically on approach, touchdown, rotation and flyaway.

Obi

Active Member Joined: Aug 28, 2006 - 05:58 AM Posts: 191

There is a USAF recruiting commercial out right now that has the T-birds female camera person as it's focus. In that commercial she's on board as the group does a loop. During that manevver you can see both the leading edge and trailing edge device deflected on the plane besides hers (I believe).

Elite 1K Joined: Aug 19, 2004 - 09:19 AM Posts: 1092

Well... the F-16 uses "flaperons" for roll control in addition to differential elevator deflections. So the F-16 is a bad example because its flaps also provide roll control. There is a flight control mode where the F-16 uses its TEFs while the gear is up, but this does not provide optimal performance (much more induced drag) and increases departure succeptability. It would be used for intercepts on very flow flying aircraft and that's about it. If memory serves, when the pilot engages the "ALT FLAPS" switch, the aircraft switches to standby gains in which the TEFs are scheduled as a function of calibrated airspeed and the LEFs are locked at 15 degrees deflection. When in cruise gains, the F-16 only uses its LEFs to improve its aerodynamics.

Active Member Joined: Aug 28, 2006 - 05:58 AM Posts: 191

Don't know, but it was in a loop, not rolling. Keep your eye out for that commercial. Thanks

Elite 1K Joined: Aug 19, 2004 - 09:19 AM Posts: 1092

bf-fly wrote:

Don't know, but it was in a loop, not rolling. Keep your eye out for that commercial. Thanks

You can find a F-16 -1 manual or ask one of the F-16 pilots around here if you don't believe me. Like I said, the trailing edge flaps are used only for roll control in cruise gains. If the pilot engages the "alt flaps" switch, then the trailing edge flaps will deflect a certain percentage based on calibrated airspeed. The trailinge edge flaps are not used for additional lift, pitch control, etc. in cruise gains. So what you saw was an F-16 in standby gains because the pilot engaged the alt flaps switch or because the pilot or flight control system commanded a flaperon deflection. You'd probably have to see what both flaperons were doing to tell which one it was. I suspect it was the latter since an F-16 performs a loop just fine without the use of the alt flaps function. In fact, it might be dangerous to try a slow speed loop with the trailing edge flaps deployed.

Active Member Joined: Aug 28, 2006 - 05:58 AM Posts: 191

It wasn't a question of not believing you, I said thanks,

Raptor_One wrote:

If the pilot engages the "alt flaps" switch, then the trailing edge flaps will deflect a certain percentage based on calibrated airspeed.

The 'alt flaps' switch basically engages the gear down flap schedule when the gear is not actually down. And yes, the gear down (power approach) flap schedule is a function of Vcas, so at higher speeds there would be no deflection.

Raptor_One wrote:

So what you saw was an F-16 in standby gains because the pilot engaged the alt flaps switch ...

This is not quite an accurate statement. As background (for anyone who might not know) several of the gains in the F-16 flight control system (FLCS) are scheduled as a function of flight condition (qc, Mach, etc). In certain failure modes (most commonly, multiple airdata probe failures of some sort) the FLCS flags the airdata parameters it needs as invalid, and thus has nothing to use to compute gains. In this case it switches to predefined constant gains, called standby gains, which were computed to provide adequate and safe flying qualities over the widest possible range of flight. There are two sets of gains, one for up-and-away and one for gear down. The pilot can force the system to use the gear down gains without putting the gear down by selected the alt/flaps switch, so that's where that connection is. I believe the pilots are trained to hit the alt/flaps switch if they are in standby and feel the airplane getting 'loose' as they are slowing (if they aren't ready to put the gear down).
So yea, nobody's gonna be doing any loops in standby. At that point they would be strictly straight and level and hoping to get on the ground asap.

As to the question of flaps during a loop, I haven't seen the commercial so I'm not sure what it looks like. If the flap is moving somewhat quickly in and out, it's probably being used differentially for roll correction.

As to the original question regarding the F-22 I won't go into specifics other than to say that control surface usage is highly optimized, such that every surface pair is used both symetrically and asymetrically, depending on flight condition (with the exception of one pair, which is only deflected symetrically).

Elite 1K Joined: Aug 19, 2004 - 09:19 AM Posts: 1092

Hey R_C (hehehe... I think you coined R_1 for me),

I wasn't looking at a -1 manual for the F-16 when I wrote those posts, so I was going by what I remembered about the gains schedules and whatnot. I was just trying to get across the point that the F-16 only uses the TEFs as high-lift devices with the gear up via the alt flaps switch, and it's highly doubtful any F-16 pilot would want to try a low speed loop with alt flaps engaged. I think there's some sort of operational directive to F-16 pilots not to use alt flaps in an attempt to increase maneuverability in a dogfight (or something along those lines). I think it's obvious that bf-fly was seeing differential flaperon movement. Would the flaperons ever be commanded by the flcs (and not the pilot via the flcs) in a basic loop for any reason?

As for your comments regarding the F-22, you confirm what I suspected from the videos I've seen. I think it's obvious that the LEFs are only deflected symmetrically. I've never heard of LEFs being deflected asymmetrically and I know they're not on the F-16. The F-22 is certainly a marvel in the area of dynamics and control.

Active Member Joined: Aug 28, 2006 - 05:58 AM Posts: 191

I saw that USAF commercial again. It seems there is a short and long version, the longer shows far more shots from the plane in formation, the short doesn't have what I was referring to.

Raptor_One wrote:

Hey R_C (hehehe... I think you coined R_1 for me),

I wasn't looking at a -1 manual for the F-16 when I wrote those posts, so I was going by what I remembered about the gains schedules and whatnot. I was just trying to get across the point that the F-16 only uses the TEFs as high-lift devices with the gear up via the alt flaps switch, and it's highly doubtful any F-16 pilot would want to try a low speed loop with alt flaps engaged. I think there's some sort of operational directive to F-16 pilots not to use alt flaps in an attempt to increase maneuverability in a dogfight (or something along those lines). I think it's obvious that bf-fly was seeing differential flaperon movement. Would the flaperons ever be commanded by the flcs (and not the pilot via the flcs) in a basic loop for any reason?

As for your comments regarding the F-22, you confirm what I suspected from the videos I've seen. I think it's obvious that the LEFs are only deflected symmetrically. I've never heard of LEFs being deflected asymmetrically and I know they're not on the F-16. The F-22 is certainly a marvel in the area of dynamics and control.

Don't know if you've seen this but check this out:

http://semperapollo.com/Media/Video/Avi ... A_AC06.mpg

The good stuff starts around the 30 second mark. There are actually spots where the "flaps" are UP. Heh, heh, there's so much going on you almost have to watch it several times and stare at the different control surfaces. I just noticed the rudders going back and forth at the same time.

Elite 1K Joined: Aug 19, 2004 - 09:19 AM Posts: 1092

Yeah... you can tell that the F-22 relies heavily on its fly-by-wire flight control system based on all the control surface activity. You know the pilot isn't commanding all those seemingly random control surface movements.

Forum: F-22A Raptor

F-22 using mission adaptive wing (MAW) concept?