I'm working on a scratch build that has an inverted exaggerated gull wing and was thinking about adding vertical stabilizers that are canted (tilted) inward. The stabilizer will have rudders attached to the last 1/4th or 1/8th. My question is, how much does this affect the flight performance in regard to pitch while using rudder control? If I stay within a certain limit (say 30 degrees) am I safe and won't really need to add mixing with the elevator? I know the F-22 and F-18 are canted outward to get into "cleaner" air during higher alpha values as well as stealth characteristics. Since those planes need computer assistance I'm assuming they also mix elevator control when using the rudders. Is this true? If so I'll most likely need to mix it for more accurate flight on my scratch build??

Thanks!
Azeiku

30 degrees is kinda steep, there will be a pitch effect with rudder deflection.
5 or 10 degrees would look OK, and be kinder in pitch.

Full scale F/A-18s use very little, if any, elevator mix w/ rudder application. However, in landing/takeoff configuration both rudders are at near full deflection inward to assist w/ positive aoa. Nearly all other surfaces are mixed together, with values dependent upon airspeed. Stabilators, flaps, LE flaps, and ailerons all work together in both pitch and roll.

Tim

Sounds like a plan. I'll most likely use 10 degrees and see how that performs. If it does make too much of a difference I'll change it. I'm not too worried though. I guess I'm just hoping this thing flies when I'm done with it! :-) I think the dihedral at the tips will cause it to be tough to roll but I was hoping I had enough wing area on my anhedral area of the wings. But glide tests showed otherwise. *shrugs* such is life!

Thanks guys!
Azeiku

WIth rudder application the geometric up that is mixed in is cancelled by a similar down mix on the other side. V tails work this way and your canted fins would do the same thing. So set them to any angle you like that goes with the looks and you won't have any problem or need any mixing at all as long as both sides move the same.

Just be sure that you have enough effective vertical area to provide the stability you need. Perhaps make up a little flat sectioned profile all sheet test model of around 12 to 16 inch span. You can tell a lot from how such a model flies even if it's unstable from a lack of dihedral. But pitch and yaw stability is easy to see.

If you plan on using only "differential" rudder deflection (both rudders deflect in the same direction) instead of "collective" rudder deflection (one rudder deflects left and the other right), I would expect that you wouldn't see too much pitch coupling even at 30 degrees of cant. Collective rudder deflection is not a terribly efficient way to generate pitching moment.

I've never heard of using this "collective" rudder in a V or angled tail. But I agree that IF someone used it that way then there's big problems a'brewin' from it. But it's not the usual way to run twin rudders or V tails so it's not really an issue.

Thanks you everyone for all your replies. Here's a picture of my project and you can see the canted vertical stabilizers. Haven't flown her yet but hopefully today I will and hopefully she comes back in one piece.

Thanks again!
Azeiku

Front View (still under construction)


Top View (ready to fly)

You shouldn't need any mix with the design in the pictures