WATCH: Aircraft Engine Starter
Many variations of aircraft engine starting have been used since the Wright brothers made their first powered flight in 1903. The methods used have been designed for weight saving, simplicity of operation and reliability. Early piston engines were started by hand, with geared hand starting, electrical and cartridge-operated systems for larger engines being developed between the wars.
Gas turbine aircraft engines such as turbojets, turboshafts and turbofans often use air/pneumatic starting, with the use of bleed air from built in auxiliary power units (APUs) or external air compressors now seen as a common starting method. Often only one engine needs be started using the APU (or remote compressor). After the first engine is started using APU bleed air, cross-bleed air from the running engine can be used to start the remaining engine(s).
Aircraft began to be installed with electrical systems around 1930, powered by a battery and small wind-driven generator the systems were initially not powerful enough to drive starter motors. Introduction of engine-driven generators solved the problem.
Introduction of electric starter motors for aero engines increased convenience at the expense of extra weight and complexity. They were a necessity for flying boats with high mounted inaccessible engines. Powered by an onboard battery, ground electrical supply or both, the starter is operated by a key or switch in the cockpit, the key system often combining switching of the magnetos.
In cold ambient conditions the friction caused by thick engine oil causes a high load on the starting system, another problem is the reluctance of the fuel to vaporise and combust at low temperatures. Oil dilution systems were developed (mixing fuel with the engine oil), engine pre-heaters were used (including lighting fires under the aircraft) and a Ki-Gass priming pump system was used to assist starting of British engines.
Aircraft fitted with variable-pitch propellers or constant speed propellers are started in fine pitch to reduce air loads and current in the starter motor circuit.
Many light aircraft are fitted with a ‘starter engaged’ warning light in the cockpit, a mandatory airworthiness requirement to guard against the risks of starter motor failure.