Forum: General F-22A Raptor forum

The Raptor almost looks alive when going into that vertical climb. Laughing

I've got a video of the Raptor in CTF testing and when it rolls the ailerons and TEFs both deflect along with the tailplanes.

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Raptor_One wrote:

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.

Well you could have told that without ever seeing the jet.

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

hansundfranz wrote:

Raptor_One wrote:

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.

Well you could have told that without ever seeing the jet.

Yes... most modern fighters use fly by wire flight control systems. Even the F-15 is partially a fly-by-wire jet. That wasn't my point though. I was just noting how active the control surfaces are. Smile

Anyone here ever heard of Gurney flaps?

Together with divergent trailing edges they change the Kutta condition on the airfoil. To minimize noise and drag, advanced CFD allows three-dimensional design of the trailing edge which can eliminate the Karman vortex.

For an in service example look at the MD-11.

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

I have direct experience with 2D airfoil simulation and implementation of the Kutta condition to close the system of equations when using the vortex panel method. I also know that the Kutta condition is an idealized one that assumes two particles separate at the leading edge of an airfoil and meet back up at the trailing edge at precisely the same time. While this assumption may be acceptable for ideal flight conditions, it certainly doesn't hold for an F-22 pulling airshow-like maneuvers. I guess the MAW concept on the F-111 wasn't really applied to non-ideal flight conditions (like high AoA) though. I'm ashamed to admit, but I forget what the Karman vortex is. Very Happy

Raptor_One wrote:

I have direct experience with 2D airfoil simulation and implementation of the Kutta condition to close the system of equations when using the vortex panel method. I also know that the Kutta condition is an idealized one that assumes two particles separate at the leading edge of an airfoil and meet back up at the trailing edge at precisely the same time. While this assumption may be acceptable for ideal flight conditions, it certainly doesn't hold for an F-22 pulling airshow-like maneuvers. I guess the MAW concept on the F-111 wasn't really applied to non-ideal flight conditions (like high AoA) though. I'm ashamed to admit, but I forget what the Karman vortex is. Very Happy

The MAW on the F-111 was friggin' HEAVY too IIRC.

Raptor One here's a movie of the Karman Vortex, turbulent flow behind a body. Usually causes flutter in control systems.

http://www.itsc.com/movies/vtran2.mpg

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

asiatrails wrote:

Raptor One here's a movie of the Karman Vortex, turbulent flow behind a body. Usually causes flutter in control systems.

http://www.itsc.com/movies/vtran2.mpg

Ahhh rgr. Would that be referred to as vortex shedding as well, or am I thinking of something else (hopefully similar... hehehe)?

Asia, the Karman vortices are usually only behind a bluff body at lower Reynolds numbers. That means that when you start getting separated flow after you stall the airfoil you'll get them. You can get it on a cylinder too, but only at low Reynolds (like 100-2000, much less than comparatively useful Reynolds). Are you guys talking about a fully morphing wing like the stuff that NASA was studying? Or was it dealing with chaning the shape of the wing with LEF and TEF or multi piece or blown flaps. There's all sorts of crazy stuff out there. Asiatrails, could you give a reference for those flaps you were talking about?

I think every Aero deals with panel method whether they want to or not. Kutta condition is fun, means we don't have an over-defined system. I'm not sure its exactly as you described Raptor_One, but it's far too late and I'm too lazy to break out one of my aerodynamics books.

Raptor_One wrote:

asiatrails wrote:

Raptor One here's a movie of the Karman Vortex, turbulent flow behind a body. Usually causes flutter in control systems.

http://www.itsc.com/movies/vtran2.mpg

Ahhh rgr. Would that be referred to as vortex shedding as well, or am I thinking of something else (hopefully similar... hehehe)?

Raptor_One, yes it is, hence the large separation between heavies in commercial aviation.

Von Karman's way of describing it is by throwing a lot of greek symbols all over the place, in real life flutter modes occur when the frequencies of the torsional and lateral frequencies are very close.

You can see these vortices's in many places e.g. a bridge pillar or a trout swimming upstream. Here is a link to the institute

http://www.vki.ac.be/

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

Don't worry... I know vortices. Smile

I'm actually working on some CFD code and use the classic lid-driven cavity as a test case. All you get there are vortices.

Forum: General F-22A Raptor forum

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