UNDERCARRIAGES

Wheels if not retractable should be as thin as possible and enclosed in a well-fitted ‘spat’, with a streamlined strut On some racing models the wheels are arranged in tandem, one behind the other, which is aerodynamically good since two wheels in this position cause less drag than two separately, one lying in die wake of the other. If close together, the rear wheel acts as a rough fairing for the front one and drag may then be less than for a single wheel. If too far apart there may be a net loss.

11.2 COOLING DRAG

On racing models, attention should be given to airflow through the engine cowling. Drag inside the cowling is just as effective in slowing the model as drag outside it, and the smooth flow inside a good cowl will help engine cooling. The air intake should be designed to admit enough air and direct it where it is needed for cooling (usually through the fins on the cylinder head) rather than allowing it to disperse generally inside a chamber. Provision for exit of the heated air must also be made, not through a ragged hole somewhere at the rear, but through a smooth passage. Though unlikely to be noticeable in practice, the expansion of the air caused by the engine cooling function can be used to give a small increase of thrust if the air channels are arranged like those of a jet engine. The exit for the hot air should be larger than the intake.