dmanson's and majortomski's explanations about engine torque having VERY LITTLE to do with the need for down/sidethrust are correct. The reason for side thrust is mainly due to the effect of the spiralling slipstream against the fin. During high-alpha flight (take off and slow speed flight) the "P-effect" may be noticable depending on the propeller pitch and rpm. On full scale aircraft this is usually compensated for by using rudder trim.
Gyroscopic effects are only noticable during yaw and pitch movements. The effect of gyroscopic precession is to "shift" the force 90 degrees in the direction of rotation, e.g. assuming a propeller rotating in the normal clock-wise direction when viewed from behind, a yaw to the left will produce a nose up pitching moment and vice versa.

2slow2matter wrote:
In a way you are right but the effect is the opposite of what you think. The engine torque (which for our model aircraft engine is very small) has to be compensated for by a a very small rolling moment to the right which has to be provided by the wing. Assuming a normal 5 lbs, .40 size aircraft with a 1 bhp engine rotating a prop at 10000 rpm the rolling force needed to counteract the torque is approximately 0.7 N (approx. 0.16 lbf) which is approximately 3% of the total lift generated by the wing in order to keep the aircraft flying straight and level. The differential lift will cause the induced drag on the right part of the wing to be slightly higher than the induced drag on the left part of the wing. This will give the aircraft a slight tendency to yaw to the right which should be compensated for by introducing LEFT thrust or LEFT rudder.

As you are aware, what is usually needed is not left thrust but rather RIGHT thrust and that is because the effect of the spiralling slipstream on the rear part of the fuselage and part of the wing is a much stronger effect than the effect of the induced drag described above.

/Red B.