Rudder in the turn

[usernothername]

Why do some aircraft (gliders) use lots of rudder in the turn but others use little or none. I know I should know this, but just can't remember.:(

[Volume]

There´s no easy answer to that, but lets point out some reasons :

Anytime you use the aileron, a yawing moment in opposite direction results. This is primarily based on the induced drag, so even differential deflections don´t help too much.
Beeing an effect of induced drag, it increases strongly with increased Cl, and the gliders are typicaly slow when using their Aileron which means at high Cl, much higher as typically used on other planes.
With the typically large wingspan of gliders, a much more powerfull (i.e. larger) aileron is needed to achive adequate roll rates with the large roll damping of such wings. This large ailerons produce large drag differences at long momentum arms, a much larger negative yawing moment results.

For drag reduction purpose, the vertical tail of gliders is small in comparison to other aircrafts, this is possible because you don´t have to fight moments from engine torque, slipsteam effects, asymmetrical thrust or single engine failure.

Also for drag reduction purpose and for better handling quality in maneuvers, yaw- and picth stability of gliders is low. This results in large yaw angles even with moderate yaw moments inducing this. Sweptback wings as for large transports that increase yaw stability strongly, are not used on gliders. Even negative wingsweep is used to bring the pilot (mostly the second pilot) closer to CG.

And glider pilots care for yaw angles, because it costs a lot of performance. So they fight them with the rudder instead of accepting a sideslip angle which also produces a compensating yawing moment. Pilots on other planes don´t care much about sideslip angles, they have enough power to compensate the additional drag.

I think this is even more answer than you intended to get

[Evo7]

I recently got to try this out in an Aeronca Champ - the ailerons produce so much adverse yaw that without rudder you do not turn! Useful demonstration for a Spamcanner like me :)

[bookworm]

The out-of-turn yawing moment (which is what you're countering with the rudder) results partly from the difference in speed of, and therefore drag from, the inner and outer wings. So it scales with wingspan/radius-of-turn. That means it's likely to be a lot bigger for a glider than for a fast jet!

[usernothername]

Thanks for the info.