Typically when we talk about R/C powered flight we are talking about IC Engine power and that will usually be a Glo Plug type engine but in the case of the larger models it can be spark Ingnition petrol engines.

Glo Plug Engines come in two stroke or four stroke format. The two stroke is typically a high revving engine and will develop its power at the high end of the rev range, where the four stroke engine will provide much more torque at lower revs enabling it to drive a large propeller.

This example on the right is powered by a .91 Cu.In Four Stroke Engine which is turning a 15 x 6 propeller. The large prop allows a greater degree of control along with a greater ability to provide easy vertical flight. The typical four stroke engine will be in general quieter in operation.