Define 'level', if the wings are level, REALLY level, the rudder will produce a torgue to turn the nose until the counter-acting moment produced by beta is equal and there she'll stay, in a skid, but no turning. In fact, as Dave noted, you have to cross control with the ailerons to keep the aircraft from banking and turning if you step on a rudder. The Wright Brothers got it right from teh get-go; else why bother with wing-warping if rudders would do the job?
Try turning a plane that can fly knife edge level flight about 90 degrees and
see if you don't get an approximately 1 G flat turn from rudder with the wings
level. That you don't get much from most planes is just designed in control
setups towards coordinated turns and low adverse yaw instead of good flat turns that
are much less useful for GA. No physics rule there though other than how
they're designed. Even then you can probably do it at least a little, the turn
rate would just be low.
For the Wrights it might have a little to do with having designed the wing-warping long before the rudder control was put in. They only thought of controlling the rudder after they slipped to the side from no control. A bird doesn't have rudders so hard to think of a rudder only turn when designing the plane, it was the last thing done.
John Wojnaroski wrote:
Very true, something like a Harrier will turn by virtue of thrust vectoring in hover and helicopters are a whole different breed. (In fact, watch a helicopter when it is in forward motion. It banks to make a turn) If a fixed wing aircraft can turn with rudder while maintaining wings level (i.e; phi = 0.0) then it should be possible to derive and demonstrate that from the kinematics and general EOMs.
Try it and watch what happens to all the sin(phi) terms when the bank angle is zero and the forces and accelerations produced. True you can yaw the nose with rudder, but that is not the same as turning or generating a psi-dot in the inertial frame. To turn the aircraft in the inertial frame you need to produce a psi-dot.
Uh guys, can you do a forward slip? As in bank one way, for turning rate one way, and rudder the other way for turning rate the other way, to go straight? Level the wings, and see if you don't get a noticable turn to the rudder side now that you've stopped the countering bank turn part the other way. Or just start a coordinated right turn. Now give a bit of left aileron to level the wings. Hmm more lift and drag needed on the right wing to raise it that's also helping it go even slower and need more lift and drag. You don't get one drop of left bank to counter the turn since you're just level, and you end up with a butt load of right adverse yaw to get an even better right turn. That is assuming you're in a real airplane and not some GA junk that has almost all the adverse yaw tuned out of it. Even then you can get an ok turn rate out of full right rudder and balancing left aileron on the 172 in FG. Actually as slow as a banked turn seems in the 172 I was a bit surprised the flat one turned around as quick as it did knowing it has most adverse yaw tuned out. Still would take a while to do a 360. It is just enough you can even do a slight left bank while still clearly turning right. I'll have to try a better plane but you don't really need the Harrier.
And BTW a heli hangs from a rotor disc that forms a suspension plane (geometry plane that is). It has little if any fuse being yawed into the relative wind or nose thrust vector as you get in a normal plane. The rotor disc is a frisbee, and that is what does the flying. The tail rotor only points the nose and body, and the body alignment is really only a reference for orientation to fly the frisbee. I can put in tail rotor so the body rotates constantly, and still fly the frisbee around and do loops and rolls. You just rotate your right stick at the same rate as the spinning. More away from the center is forward, back through the center is back, advance a bit faster than the spin rate is one way left or right and retard a bit over the spin rate is the other way. Easy as pie. Does help to keep moving, if you bring it to hover and have the cyclic centered it can be hard to start back out in a controlled direction while still spinning.
Might want to try some other things than just FG! :) And GA aircraft are simply not the thing to look to for what's possible or not for a plane. Pretty hard to think a plane can't do flat turns when you can hold an RC plane's wings level and zip it around at a significant rate in one. Even if it takes me a bit to recall the exact details for how and why it works and why normal aircraft stink at it, it was never in doubt in my head. At least download FMS and try some sim flying from outside the box, some good backgrounds from FMS for RC. Actually heck now that I think of it FMS stinks on rudder, they do not have the fuse area or thrust vector modeled well so even the quick planes have terrible yaw rates in it.
Alan
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