In terms of automotive gas, these helicopters run on high octane, with lead if possible.[citation needed] Because gasoline engines require a spark plug to ignite the mixture, some early gasoline radio control helicopters used spark ignition similar to that of automotive engines, but were heavy and complex.
A typical fuel for use in model helicopters is a mixture of 20–30% nitromethane, 10–15% synthetic oil (such as castor oil or a synthetic oil) and the remainder methanol. Some fuels will also contain small percentage of nitro-propane to act as a cooling agent.
Fuels containing a higher nitromethane content are used for racing, or 3D aerobatics, where high peak power is more important. These fuels often require special handling precautions due to nitromethane's toxicity and flammability. Fuels with a higher oil content are used for hovering, where maximum power at reduced RPMs is more important, and the risk of the engine becoming too hot due to the reduced airflow is greater.
