THE PYLON RACER IN TURNS

Racing models need to turn efficiently at very high speeds. This is done by banking with ailerons and bringing the banked wing to a high angle of attack by applying up elevator. It is the wing lift, directed sideways, that turns the model. Too much up elevator can bring the wing to its stalling angle and precipitate a crash.

In a turn, since the wing is necessarily at a higher Cl than in level flight, wing vortex drag increases and the model loses speed. This loss is unavoidable. To attempt to turn with insufficient bank produces very high drag and even greater slowing down in a wide, skidding and yawing turn.

13.4 THE RUDDER-STEERED MODEL

Many model sailplanes, and some elementary powered models, are turned by the rudder alone with no ailerons. This, as mentioned in the previous chapter, requires the wings to be set at a dihedral angle. The yaw induced by the rudder increases the angle of attack of the wing on the side pointing into the resulting side-slip, and this wing rises. The resulting bank produces the turning force. Compared with the well executed aileron-plus-rudder turn, this control system is less efficient in that the initial yaw and slip creates some drag, but with a well trimmed model, once the turn is established little if any control deflection is needed to maintain it When the span is large, the rudder action may be somewhat slow, but providing no rapid turns are required, as may usually be the case with thermal soarers, the ‘rudder only’ control may be quite acceptable. The dihedral angle must be rather large for adequate control.