Today modern military aircraft are typically started with the aid of a starter hose or cart. In the old days, props had to be hand-chucked which was dangerous as, if the engine caught before the mechanic got his hands off, odds are he could wrench an arm out of the socket.
Well back in the 1930s increasingly larger and more powerful military grade radial engines were impractical to hand start and most of the electric start systems of today weren’t around. This led to the Coffman and later Breeze engine starters which were developed in 1935 and used in the P-36 and later military aircraft. Basically it used a blank shotgun shell to kick start the engine.
4ga shell compared (left) to 12 gauge 3-inch high brass shell of today
Here is a 1945 FM-2 Wildcat (USN BU 86774) being started for the first time in decades with a vintage 4-gauge Coffman shell.
The science behind it: “ The Coffman starter uses a specially made 4 gauge paper shell with an electric primer. It is filled with .25″ and .187″ diameter cordite pellets for slow burning powder. The shell fires into a starter assembly on the accessory case of the engine, same position as an electric starter. It DOES NOT fire directly into a cylinder of the engine. The gasses force a piston inside the starter assembly forward towards the engine collapsing spiral gears on top of each other converting it into a circular motion. This engages the starter dog and rotates the starter gear. After the piston reaches the end of its travel a valve released the residual pressure and a die spring resets the whole process.”
