There has been some good information in the previous posts and some not quite accurate. I will try to summarize.

Gyroscopic precession affects all airplanes with a turning propeller. The effect may be significant or not depending on the relative size of the rotating mass. Obviously the old WW I aircraft with their light fabric construction and heavy rotary engines, and the WW II fighters with their large propellers powered by thousand plus horsepower are significantly effected. On the other hand for modern light aircraft with a six-foot propeller twisted by a small engine the effect is rarely noticeable. Significant or not, the effect is always there. For models, whether the effect is significant likewise depends on the relative size of the rotating mass. It is usually not significant except in 3D flight where the aerodynamic forces are overshadowed by thrust and power.

Of course any maneuver that changes the direction of thrust will involve gyroscopic forces. However there are mainly two conditions where gyroscope forces may be noticed. First, if the tail of a tail wheel configured aircraft is raised rapidly, the nose will tend to swing left. This has not been noticeable in the full-scale aircraft I’ve flown, mostly because rapidly raising the tail is really poor technique. Normally the tail is allowed to rise on its own accord as the speed builds and any gyroscopic forces are not apparent.

The other gyroscopic force arises from the so-called P-factor. The asymmetric thrust due to the propeller disc not being perpendicular to the direction of motion (like in climbing flight), exerts a left turning moment on the propeller disc (as previously described). Gyroscopic precession converts this to a nose up pitching moment on the airplane. It is not necessary for the axis of rotation to be displaced for the gyroscopic precession to occur. A force on the rim produces a force ninety degrees out of phase at the axis, even when the axis is not moved.

None of this explains the tendency of an airplane of conventional configuration to turn left when climbing at high power and slow speed. There are two other forces that must be considered. First there is torque. The torque driving the propeller produces a rolling moment in a direction opposite the propeller rotation. For high-powered aircraft with relatively short spans (such as WW2 fighters) it can loom pretty large. The pilot resists this rolling force with the aileron control, which produces a yawing moment (due to adverse yaw) requiring rudder input to compensate. For small low powered aircraft it isn’t much of a factor.

This leaves us with the twist of the propeller slipstream, which is the primary source of the left turning tendency. The air effected by the propeller is accelerated aft producing thrust and at the same time is given a slight twist in the direction of rotation. The twist is not a tight spiral like the threads on a screw, but rather a gentle twist more like the grooves in a rifle barrel. A typical light aircraft has the fin/rudder area well above the thrust line and this twist changes the angle at which the slipstream passes the tail causing it to move to the right, swinging the nose to the left. Many old free flight models (Zipper, Playboy, etc.) took advantage of this twist to control the climb profile. A large sub rudder and a few degrees of down thrust and there was about as much area below as above the thrust line which effectively eliminated the left turn tendency. The high pylon on which the wing was mounted was effected by the slipstream twist by tending to roll right when climbing under power. With this setup, the airplane was easily adjusted to climb in a tight right hand spiral under power and glide in a wide circle to the left in the glide. Some pattern ships have a low profile fin/rudder with a sub rudder, which not only minimizes the left turn tendency in a climb, but also reduces roll coupling in knife-edge flight.

In the final analysis, with the exception of some high powered aircraft with large propellers where torque may be a factor, the tendency to turn left when in high power, low speed climb, is due to slipstream twist, period.