Koffman starter

Koffman starter. The Koffman starter is a type of pneumatic starter motor developed for aircraft engines, particularly during the mid-20th century. It utilizes stored compressed air to drive a turbine or vane motor, which in turn rotates the engine's crankshaft to initiate combustion. This system offered a reliable and powerful alternative to electric starters and cartridge starters, especially for larger piston engines and early jet engines.

History and development

The starter was invented by Eugene Koffman, an engineer who founded Koffman Engineering in the United Kingdom. Its development was driven by the needs of the Royal Air Force and the expanding civil aviation sector post-World War II, which required more dependable starting systems for increasingly powerful engines. The design evolved from earlier pneumatic motor concepts and was influenced by technology from companies like Bendix Corporation and Lucas Industries. Key testing and refinement occurred at facilities such as the Royal Aircraft Establishment at Farnborough Airfield, with adoption by major aircraft manufacturers like de Havilland and Avro. The system saw significant use during the Cold War era on various military and transport aircraft.

Design and operation

The core component is a vane motor or air turbine connected directly to the engine's accessory drive or gearbox. High-pressure air, typically stored in air tanks charged by an engine-driven compressor or ground power unit, is admitted into the motor. This air expands against the vanes, creating rotational torque that is transmitted through a sprag clutch or similar mechanism to the engine's ring gear. The clutch disengages automatically once the engine exceeds starter speed, preventing damage. Control is managed via a pneumatic valve operated from the cockpit, often integrated with the aircraft's fuel system and ignition system for a coordinated start sequence. The design prioritized robustness for operation in diverse climates, from the deserts of the Middle East to the cold of Alaska.

Applications and usage

The Koffman starter was widely installed on British and Commonwealth aircraft. Notable applications include the Avro Shackleton maritime patrol aircraft, the de Havilland Comet jet airliner, and the English Electric Canberra bomber. It was also used on certain versions of the Vickers Viscount and found service on engines like the Rolls-Royce Avon and Armstrong Siddeley Sapphire. Its reliability made it suitable for Royal Australian Air Force and Royal Canadian Air Force aircraft operating in remote areas. Furthermore, the system was employed in ground support equipment and as an auxiliary power unit starter on some larger aircraft. Its use declined with the advent of more compact and powerful electric starters and integrated gas turbine starters.

Variants and derivatives

Several models were produced, differing in size, output torque, and mounting configurations. The Koffman Type 100 series was common for piston engines, while the more powerful Type 200 series was developed for early turbojet and turboprop engines. Licensed production or similar designs emerged from companies like Dowty Group and Smiths Industries. A derivative system, known as the APU starter, was adapted for starting auxiliary power units on aircraft like the BAC One-Eleven. The fundamental pneumatic principle also influenced later air starter designs used in industrial and marine propulsion contexts, such as those for diesel engines on Royal Navy vessels.

Technical specifications

Typical units operated on air pressures ranging from 100 to 300 pounds per square inch (PSI). Starter motors could generate substantial torque, often exceeding 200 pound-foot (lb-ft), with free-run speeds over 10,000 revolutions per minute (RPM). The vane motors were constructed from hardened steel and aluminum alloy housings for light weight. Air consumption during a start sequence varied but could require several cubic feet of stored air, necessitating robust air compressor systems. The starters were designed to meet rigorous UK Ministry of Defence specifications and standards from the Air Registration Board, ensuring interoperability with aircraft hydraulic systems and electrical systems for control and indication.

Category:Aircraft components Category:Engine starting systems