DAP BRISTOL BEAUFIGHTER CARB/AIR TEMP SELECTOR SWITCH

Following the highly successful development and manufacture of Australia’s home grown CAC Buffalo single seater fighter and the two seater CAC Wirraway light bomber/trainer, the Australian Commonwealth Aircraft Corporation (CAC) secured a licence to manufacture their own version of the Bristol Beaufort twin engine bomber and later, an Australian version of the British heavily armed Bristol Beaufighter fighter/bomber.

Known as the DAP Beaufighter, it was used extensively by the RAAF in the maritime anti-shipping role, such as during the Battle of the Bismarck Sea during which Beaufighters were used in a fire-suppression role in a mixed force with USAAF Douglas A-20 Boston and North American B-25 Mitchell bombers.

It soon became feared by the Japanese who named it the ‘Whispering death’ and RAAF DAP Beaufighters were instrumental in harassing enemy shipping and supply lines across the Papua New Guinea region and outer islands.

Over 370 DAP Beaufighters rolled out of the CAC's Fishermans Bend, production facilities in Victoria during the course of the war. All were heavily modified to endure the region's damp and humid tropical conditions - especially in regard to its electrical and fuel systems.

Like the CAC Boomerang and Wirraway, the DAP Beaufighter featured a modified Carburettor Air Heat & Cooling system designed to prevent or remove ice formation in the Beaufighter’s carburettor which could occur when its engines were run at mid throttle under conditions of high humidity or at high altitude and in adverse weather conditions. Uncorrected, the ice formation could quickly result in engine failure or significant reduction in engine efficiency. 

It did this by enabling the pilot to direct hot air from the engine exhaust manifold shrouds directly into the air mixture chamber below the aircraft’s carburettors.

Unfortunately, the Beaufighter’s powerful two 1,735hp Bristol Hercules VII or XVIII engines required high manifold pressure for take-off and landing which in turn, meant high cylinder head temperatures and increased the risk of engine overheating. 

Engine overheating could also occur during prolonged climbing and full throttle operations and pilots were given detailed instructions to ensure they maintained cylinder head temperatures within acceptable limits.

As the cylinder head temperature rose, Cold air - not Hot was required to be directed into the carburettor's air mixture chamber.

To enable this ability to ‘alternate' the flow of Cold or Hot air into the mixing chamber, the pilot toggled the Beaufighter's Carburettor / Outside Air Temp Switch as conditions required.

Mounted to the bottom right of the Beaufighters main flying panel immediately in front of the pilot’s rudder elevator adjustment wheel, the Carburettor / Outside Air Temp Switch was a critical component of the Beaufighter's Carburettor Air Heat Control system.

The 2 Position Carb/Air Temp Switch linked an air temperature thermometer to two thermocouple units - one fitted in the air mixing chamber below the carburettor and the other, enclosed in a chamber of the wing section’s leading edge which provided fresh air ventilation to the pilot’s cockpit.

A small Exhaust Gas Analyser was also installed which monitored the proportions of the air/fuel mixture entering the engine by electrically analysing the exhaust gasses. 

When at high altitude or in cold adverse weather conditions, the pilot toggled the Carb/Air Temp Switch to 'Position 1’ , which directed Hot air from the exhaust manifold shroud directly into the mixing chamber.

For takeoff and landing, the Carb/Air Temp Switch was toggled to ‘Position 2’ so that Cold Air from the wing’s leading edge could be directed into the chamber. This was also true for prolonged climbs, diving and full throttle operations.

As the Carburettor Air Heat Control System was operated by the aircraft's 12v battery, it was always important for the Switch to be toggled to the ‘OFF’ position after engine shutdown.

Still bearing its ‘service inspection’ stamp on the side of its bakelite casing, and with its large rotary knob still operating and its rear electrical connectors still connected, this is a rare example of early Australian aviation innovation.

Now, mounted in its 100yr old Mango Wood Display Stand with engraved Plaque, printed and laminated Fact Sheet plus a highly detailed, custom-built Scale Model of this iconic Australian designed and built fighter/bomber perched atop its magnetic display arm, you've really got the ideal gift that's perfect for any aviation enthusiast.

All DAP Beaufighter Instruments come complete with detailed 1/72, larger 1/48 or super detailed 1/32 Scale Model, Mango Wood Stand & Plaque plus Printed Fact Sheet featuring photo of instrument in aircraft cockpit.

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