Coffman engine starter
Encyclopedia
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. Similarly, the British Supermarine Spitfire
used the Coffman system to start its Rolls-Royce Merlin
engine. 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 engine
s, including such engines as the Rolls-Royce Avon
, which were used in the English Electric Canberra
and Hawker Hunter
.
that, when fired, pushed a piston forward. A screw thread driven by the piston engaged with the engine turning it over.http://www.flightglobal.com/pdfarchive/view/1938/1938%20-%201051.html 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 (~1000 psi
at ~600 ft/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.
Shotgun starters had several advantages over other starting systems in use at the time. Electric starters required large, heavy, and often troublesome batteries to be carried on board, or external charging equipment had to be located at every place where the vehicle was anticipated to operate. Inertia starters used a heavy wheel, usually made of brass, which was spun by a hand crank or electric motor, causing the spinning wheel to engage the starter ring gear. The Coffman system was more lightweight and compact than inertial starters or internal batteries, and it did not require any special auxiliary equipment, an important feature when operating in remote areas.
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, but adding requirements for the compressor and air tank. Hybrid systems can be made simply by adding a cartridge breech or an air tank to an existing system. Air tanks can also be recharged from an external source in an emergency, such as a hand pump or a portable air compressor.
The Coffman starter was the most common brand of cartridge starters during the mid-1930s, and the name was used as a generic description. Some modern military diesel engine
s still use this device, but advances in battery technology have made shotgun starters obsolete for most uses.
, in which pilot Frank Towns (James Stewart
) has 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.)
Piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...
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. Similarly, the British Supermarine Spitfire
Supermarine Spitfire
The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and many other Allied countries throughout the Second World War. The Spitfire continued to be used as a front line fighter and in secondary roles into the 1950s...
used the Coffman system to start its Rolls-Royce Merlin
Rolls-Royce Merlin
The Rolls-Royce Merlin is a British liquid-cooled, V-12, piston aero engine, of 27-litre capacity. Rolls-Royce Limited designed and built the engine which was initially known as the PV-12: the PV-12 became known as the Merlin following the company convention of naming its piston aero engines after...
engine. The Hawker Typhoon
Hawker Typhoon
The Hawker Typhoon was a British single-seat fighter-bomber, produced by Hawker Aircraft. While the Typhoon was designed to be a medium-high altitude interceptor, and a direct replacement for the Hawker Hurricane, several design problems were encountered, and the Typhoon never completely satisfied...
also used the Coffman system to start its Napier Sabre
Napier Sabre
The Napier Sabre was a British H-24-cylinder, liquid cooled, sleeve valve, piston aero engine, designed by Major Frank Halford and built by Napier & Son during WWII...
engine.
A derivation of the Coffman starter was used on a number of jet engine
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
s, including such engines as the Rolls-Royce Avon
Rolls-Royce Avon
|-See also:-Bibliography:* Gunston, Bill. World Encyclopaedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:**** a 1955 Flight article on the development of the Avon...
, which were used in the English Electric Canberra
English Electric Canberra
The English Electric Canberra is a first-generation jet-powered light bomber manufactured in large numbers through the 1950s. The Canberra could fly at a higher altitude than any other bomber through the 1950s and set a world altitude record of 70,310 ft in 1957...
and Hawker Hunter
Hawker Hunter
The Hawker Hunter is a subsonic British jet aircraft developed in the 1950s. The single-seat Hunter entered service as a manoeuvrable fighter aircraft, and later operated in fighter-bomber and reconnaissance roles in numerous conflicts. Two-seat variants remained in use for training and secondary...
.
Design
The Coffman device used a large blank cartridge containing CorditeCordite
Cordite is a family of smokeless propellants developed and produced in the United Kingdom from 1889 to replace gunpowder as a military propellant. Like gunpowder, cordite is classified as a low explosive because of its slow burning rates and consequently low brisance...
that, when fired, pushed a piston forward. A screw thread driven by the piston engaged with the engine turning it over.http://www.flightglobal.com/pdfarchive/view/1938/1938%20-%201051.html 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
Air start system
An air-start system is a power source used to provide the initial rotation to start large diesel and gas turbine engines.Compared to a gasoline engine, diesel engines have very high compression ratios to provide for reliable and complete ignition of the fuel without spark plugs...
, 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
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
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 (~1000 psi
Pounds per square inch
The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...
at ~600 ft/s
Feet per second
The foot per second is a unit of both speed and velocity . It expresses the distance in feet traveled or displaced, divided by the time in seconds...
) shoots down the pipe, forcing the motor to spin and engage the starter ring gear on the engine, which is attached to the crankshaft.
Shotgun starters had several advantages over other starting systems in use at the time. Electric starters required large, heavy, and often troublesome batteries to be carried on board, or external charging equipment had to be located at every place where the vehicle was anticipated to operate. Inertia starters used a heavy wheel, usually made of brass, which was spun by a hand crank or electric motor, causing the spinning wheel to engage the starter ring gear. The Coffman system was more lightweight and compact than inertial starters or internal batteries, and it did not require any special auxiliary equipment, an important feature when operating in remote areas.
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, but adding requirements for the compressor and air tank. Hybrid systems can be made simply by adding a cartridge breech or an air tank to an existing system. Air tanks can also be recharged from an external source in an emergency, such as a hand pump or a portable air compressor.
The Coffman starter was the most common brand of cartridge starters during the mid-1930s, and the name was used as a generic description. Some modern military diesel engine
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
s still use this device, but advances in battery technology have made shotgun starters obsolete for most uses.
Notable use
The starter became famous as a plot device in the 1965 movie The Flight of the PhoenixThe Flight of the Phoenix (1965 film)
The Flight of the Phoenix is a 1965 American film produced and directed by Robert Aldrich and based on the 1964 novel The Flight of the Phoenix by Elleston Trevor...
, in which pilot Frank Towns (James Stewart
James Stewart (actor)
James Maitland Stewart was an American film and stage actor, known for his distinctive voice and his everyman persona. Over the course of his career, he starred in many films widely considered classics and was nominated for five Academy Awards, winning one in competition and receiving one Lifetime...
) has a limited number of cartridges with which to start the makeshift aircraft's engine. (This was also featured in the 2004 remake
Flight of the Phoenix (2004 film)
Flight of the Phoenix is a 2004 remake of a 1965 film, both based on the 1964 novel The Flight of the Phoenix, by Elleston Trevor, about a group of people who survive a plane crash in the Gobi Desert and must build a new plane out of the old one to escape. The film stars Dennis Quaid, Tyrese...
of the film.)