When you board a plane today, your aircraft’s engines will likely start using an electric starter motor, a generator, or air. Starting an aircraft, especially a large airliner, is complex enough that it could be an art form. Nearly a century ago, there was a far more crude way to get your engines running. In the 1930s, you could start a plane using a shotgun shell-like blank to fire compressed air into an engine, turning it over. It’s called the Coffman engine starter and here’s what happened to this piece of history.
Over the weekend, I flew out to San Diego to send some side-by-sides in the incredible dunes of Glamis, California. I enjoy watching plane movies while I’m flying, and one of the movies for this round was the 2004 remake of Flight Of The Phoenix. In the movie, a sandstorm causes a Fairchild C-119 to crash in a desert.
The aircraft’s occupants use the surviving parts of the crashed Fairchild to build a new plane. Dramatic scenes in the movie show the pilot attempting engine starts with what looks like shotgun shells.
Take a look:
I knew this was a technology for aircraft and I have watched this movie a number of times before, but this time, I wanted to know more.
The Coffman Engine Starter
This technology takes us back nearly a century to the 1930s. Back then, aircraft starting technology was similar to how it is today. Aviators often cranked their engines into life using starter motors. They also had the option to start their aircraft using an inertia starter. In that design, a heavy flywheel would be spun by hand or by a motor. Once the flywheel reached an appropriate speed it would be connected to the engine, using inertia to spin the engine over. Other engines used pneumatic systems that emptied compressed air from tanks to spin an engine over.
As Hemmings notes, these starting methods became a problem in remote areas where there wasn’t electricity or where battery power wasn’t available. In 1935, Roscoe Alexander Coffman filed for a patent for a solution to this. The “Oscillatory starter and rotary breech mechanism therefor,” commonly called the Coffman engine starter, didn’t need batteries or shore power to get an aircraft engine running. Instead, it used a rotary breech and shotgun shell-like propulsive charges to fire an engine into life.
There isn’t much published out there about Coffman or why he decided to solve this issue. What I can tell you is that based on patents filed with the United States Patent and Trademark Office, Coffman was a bit of an inventor and had a knack for aviation. In 1928, Coffman filed a patent for a high-speed aircraft engine starter. In 1930, Coffman filed a French patent for an improvement to an engine. Two years later, he would file a patent in Canada for some other engine-related improvement. Sadly, the patent records I was able to find did not explain what those two ideas detailed.
By 1934, Coffman realized his engine starters had created a fueling problem in aircraft. His starters could spin engines over at 250 RPM in temperatures as low as -30 degrees Fahrenheit, but then-current fueling systems allowed cold fuel to pool, potentially creating an explosive situation. Thus, he filed a new patent for a “Priming system for internal combustion engines.” Coffman’s solution was a priming system that broke fuel down into particles without the aid of a carburetor before injecting it into an engine. Apparently, all of this happened in sync with Coffman’s engine starters.
The very next year, Coffman returned to engine starters and filed a patent for the “Rotary breech mechanism for power generating propulsive charges” as well as a patent for an “Oscillatory starter and rotary breech mechanism therefor.” This time, Coffman doesn’t explain why his invention is necessary. Instead, he dedicates 8 out of the 12 pages of the one patent to talk about how his then-new starter worked. Together, both patents appear to make up Coffman’s whole system. The explanation goes into, frankly, confusing detail and you can read it by clicking here. Otherwise, I’ll summarize for you.
The Coffman engine starter utilized shells that looked like they belonged in a shotgun, but were cartridges filled with Cordite propellant. Often, these 4-gauge cartridges would be placed in a revolver-like rotary breech assembly. Cartridge assemblies carried anywhere between just a single shot to six shots. Here’s a video from YouTuber Conrad showing the shells and system in action with a Grumman FM-2 Wildcat:
To put the size of the cartridges into perspective, common shotgun shell gauges include 12-gauge and 10-gauge, both are smaller than the Cordite cartridges. When fired, either through a button pressed in the cockpit or a mechanical method such as a hammer, the Cordite would blow, sending high-pressure gas through a steel pipe into a special piston that drove a screw thread. This acted on the engine’s starter ring gear. The Coffman “shotgun starter” acted as an engine starter and spun the engine over fast enough for it to start. Reportedly, the first aircraft engine to get the new Coffman starter was the Junkers Jumo 205 in 1936.
Engine start cartridges themselves also got pretty large. Here’s one that was allegedly for a B-57 bomber. To give you a sense of scale, the cartridge is a little over three inches in diameter:
Some variations of Coffman’s engine starter design were applied to ground vehicles like Field-Marshall tractors, Snowcat vehicles, and tanks. In Marshall and Field-Marshall diesel tractors, made between 1930 and 1957, the Cordite charges didn’t act on a crude starter, but directly on one of the engine’s pistons, forcing the engine to turn over. During this process, a smoldering piece of paper worked like what we’d call a glow plug today.
Ever watch a tractor start like this?
While Coffman invented the starter in the early 1930s, he wouldn’t be granted patents for it until 1940 and 1942. At first, the Coffman engine starter offered advantages over other starting equipment of the day. Electric starter motors required heavy batteries or some external form of power. As vehicle historian YouTuber Johnny Johnson points out, some aircraft utilized portable power trolleys to start their engines when their batteries couldn’t handle it. All of this required some sort of external infrastructure, some of which didn’t exist if the aircraft was parked somewhere remote. The Coffman engine starter didn’t require any external infrastructure and was far lighter than carrying around batteries. A pilot carrying Cordite charges had a way to get back into the sky.
As I mentioned before, inertia propping was also a thing, but the flywheel needed for the process was heavy, and cranking an engine in this manner wasn’t very quick. Likewise, while hand-propping–starting an engine by turning the propeller with your hands–was a thing, pilots didn’t start large aircraft in that manner. Period videos do show aviators moving large props by hand, but this is to clear the radial engine’s cylinders of oil that leaked past the rings.
Rise And Fall
So, for a period, if you wanted to get an aircraft engine going as quickly as possible with as little complexity as possible, starting it by firing a “shotgun shell” was a good bet. As such, Coffman starters became equipment used in many World War II aircraft. Famed engines such as the Supermarine Spitfire’s Rolls-Royce Merlin and the Grumman FM-2 Wildcat’s Pratt and Whitney R-1820 could be started with a Coffman system, same deal with the Napier Sabre engines found in the Hawker Tempest and the Hawker Typhoon.
Hemmings notes that even after the war, the Coffman engine starter found use in civilian aircraft such as the de Havilland Canada DHC-1 Chipmunk and the de Havilland Canada DHC-2 Beaver aircraft equipped with Pratt & Whitney Wasp Jr. R-985 engines. You might be able to find some avgeek pilots still using Coffman systems today, but most have been phased out.
While Coffman starters allowed pilots in unimproved areas to get their aircraft back into action, they were a wasteful way to start an aircraft. The Coffman engine starter caused carbon build-up in the starting cylinder. In the Field-Marshall tractors, it meant possibly jamming the decompression valve. In aircraft, the carbon build-up required pilots to waste some charges to clear the carbon out.
If that wasn’t bad enough, the Coffman system required the aircraft’s crew to carry cartridges and each cartridge represented one shot to start the engine. The cartridges spun the engine over but only for so long. So, if one cartridge couldn’t start your plane, you had to blow another cartridge in hopes that you’d bring the engine back to life.
Eventually, starting technology improved enough to render the “shotgun starter” obsolete. Now, unless you’re watching either version of Flight Of The Phoenix, which used actual Coffman starters during filming, you’re unlikely to run across such a system. For some weird trivia, the Fairchild C-119 used in the second movie (a C-82 Packet was in the first movie) didn’t come with a Coffman starter from the factory, so the film took some artistic license.
Even I didn’t see a Coffman engine starter in use during this year’s EAA AirVenture Oshkosh, though I’m certain someone out there had at least one. Today, the Coffman engine starter exists as a sort of weird blip of aviation history that isn’t talked about much anymore. Pilots may not have started their planes by shooting their engines with shotgun shells, but it sure looked like that was the case!
(Topshot: 20th Century Studios)
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