Coffman engine starter

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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. Most American military aircraft and tanks which used radial engines were equipped with this system. A derivation of the Coffman starter was also used on a number of jet engines, including notable engines such as the Rolls-Royce Avon.

The device used a blank gunpowder cartridge that, when fired, would cause the propeller to turn over and hopefully start the engine. 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 operate much like Coffman starters but are powered by pressurized tanks.

Shotgun starters are composed of a breech and a motor, which are connected by a metal line. The cartridge fits into the breech, and is triggered either electrically or mechanically. The expanding gases from the cartridge pressurize the line and cause the motor to spin and engage the starter ring on the engine, which is attached to the crankshaft.

The advantage of the cartridge system over electric starters is that the batteries of the time were weak and trouble-prone. Aircraft with electric motors often required the use of a battery cart and jumper cables, or large, heavy batteries carried in the plane. Inertia starters use a heavy wheel, usually made of brass, which is spun by a hand crank or electric motor, then the spinning wheel is made to engage the starter ring. The Coffman system weighs less.

The primary disadvantages of the shotgun starter are the need to keep a stock of cartridges, one of which is used for each attempt to start, and the short time that the motor is spun by each cartridge. Compressed-air starters, which use the same type of motor, are usually recharged by an engine-driven compressor, negating the need to carry cartridges. Hybrid systems can be made simply by adding a cartridge breech or an air tank to an existing system.

The Coffman starter was the most common brand of cartridge starters during the mid-1930s, and the name was used as a generic description. The starter became famous as a plot device in the movie The Flight of the Phoenix, when pilot James Stewart had a limited number of cartridges with which to start the makeshift aircraft's engine. (This was also featured in the 2004 remake of the film.)

Some modern military diesel engines still use this device, but advances in battery technology have made shotgun starters obsolete for most uses.