Coffman engine starter

The Coffman engine starter (also known as a "shotgun starter") was a starting system used on many piston engines in aircraft and armored vehicles of the 1930s and 1940s. The Coffman system was one of the most common brands; another was the Breeze cartridge system, which was produced under Coffman patents. Most American military aircraft and tanks which used radial engines were equipped with this system. Some versions of the Rolls-Royce Merlin engine used in the British Supermarine Spitfire used the Coffman system as a starter. The Hawker Typhoon also used the Coffman system to start its Napier Sabre engine.

A derivation of the Coffman starter was used on a number of jet engines, including such engines as the Rolls-Royce Avon, which were used in the English Electric Canberra and Hawker Hunter.

The Coffman device used a large blank cartridge containing Cordite that, when fired, pushed a piston forward. A screw thread driven by the piston engaged with the engine, turning it over. This was in contrast with other type of cartridge starter which acted directly to drive the engine piston down and so turn the rest of the engine over, such as those used on the Field-Marshall agricultural diesel tractor.

The other systems used during the period were electric motors (such as those used in automobiles today), inertia starters (cranked either by hand or an electric motor) and compressed-air starters, which operated much like Coffman starters but were powered by pressurized air tanks.

Shotgun starters are composed of a breech, into which the cartridge is inserted, which is connected to the motor by a short steel pipe, which acts like a gun barrel. The blank cartridge fits into the breech, and is triggered either electrically or mechanically. When the aircraft's ignition is turned on and the cartridge is fired, high-velocity, high-pressure gas (~1,000 psi (6.9 MPa) at ~600 ft/s (180 m/s)) shoots down the pipe, forcing the motor to spin and engage the starter ring gear on the engine, which is attached to the crankshaft.

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