having had similar happen (broke off control horn on rudder in flight):
1. Would the pressure from the spiralling prop wash pushing on the left side of the fin now have more authority and cause the plane to yaw to the left and induce a left spiral dive because the rudder is not holding the aircraft straight.
2. Would the left side pressure also push the rudder to the right, holding up the nose in the turn.
3. Or would the rudder just flap frantically in the breeze fishtailing the aircraft and making it hard to control.
4. Or have you got your own theory.
1) This is speed dependant and fuselage design dependant. (also thrust angle.. too many variables) If You get the rudder flutter... this point will never come up.
2) See #1, as this is really the other side of the same question.
3) the flutter issue is airspeed and rudder design dependant. At high speed 9when it broke) the rudder was buzzing like crazy. Slowed down and it quit. While the rudder fluttered the plane wanted to dance all over the place.
4) (sort of...) Depending on the model, you may be able to have good enough control to land it.
Rule #1 on a failure that leads ot a control surface flapping: SLOW DOWN. You want the model to be below the speed where the surface flutters.
You need to verify good control before attempting landing. If the plane doesn't have good control... plant it in a tree or in the dirt as far from people as possible.
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I have had the rudder come loose as described in the original scenario, and was able to save it. I have seen the rudder come off of a model and it be saved. (with the rudder hanging by the clevice!)
I have had an aileron clevce break in flight... the model was controllable only AT stall speed. I landed that one out in the weeds about 50 ft further than the runway. (lost both wingtips in a mid-air playing R/C combat... and was missing 1/4 of one wing.)
I have had a plane seem to explode in flght... lost one FULL wing due to overstress, and I put the plane into knife edge to get it pointed away from the pits. That one I planted in the trees and totaled the rest of the airframe.
Whatever the failure... DON'T PANIC. Do your best to regain control and put the plane down safely. (as in not hitting anyone.. to heck with the model.)