BRISTOL BEAUFORT RADIO ALTITUDE LIMIT SWITCH

While the Bristol Beaufort's service with the RAF in Europe had delivered mixed and often disappointing results, its service in the Pacific with the RAAF was totally different.

By 1938 the Australian Government had partnered with three companies to establish the Commonwealth Aircraft Corporation with the aim of developing and producing a locally designed and built fighter and fighter bombers. Production was already underway with the CAC Wirraway trainer and the Buffalo single-seat fighter when the 8th production Bristol Beaufort MK I was shipped to Australia to be used as the pattern for the wartime production of an Australian Beaufort. 

The first CAC Beaufort flew in August 1941 and the first 50 examples built were designated as Beaufort MK V aircraft which used the US designed and Australian built Pratt & Whitney engines.

Over the course of the war, 700 Australian Beauforts rolled out of the CAC factory, going onto serve with newly formed RAAF squadrons in operations against Japanese forces in Papua New Guinea.

They attacked shipping in all areas of the South-West Pacific and sank cruisers, destroyers and submarines, as well as bombing and strafing inland supply dumps and troops. They were also used for routine convoy protection and coastal reconnaissance.

One of the key Bristol Beaufort targeting systems used by its pilot and bomberdier to ensure accurate depth charge and torpedo release height was the US designed and manufactured General Electric AN/APN-1 radio unit.

The unit comprised two components: the ID-14/APN-1 Radio Altitude Controller and the Radio Altitude Limit Switch (shown here).

The AN/APN-1 was the US Navy's primary airborne frequency modulated, radar altimeter which was designed to emit a downward signal from the aircraft's transmitter antenna. It was installed in both the USN's carrier-launched TBF Avenger and Helldiver dive bombers. 

As the terrain changed in hight and composition with the rise and fall of the aircraft's flight, a 'bounced' return signal would be received by a separate receiver antenna. The difference in signal frequency and time interval from send and receive gave a highly accurate height reading.

The timing and correct height of torpedo or dive bomb release was crucial to ensure the weapons had enough time to self arm and hit their targets.

The pilot first set the Radio Altitude Controller switch to the desired bombing run height. He then set the minimum height required on the Radio Altitude Limit switch to ensure the aircraft did not drop below that height.

The combined system provided a dual range indicator of 0-400 feet and 400-4000 feet; having an accuracy within plus or minus 6 feet on the 400-foot range and within plus or minus 60 feet on the 4000-foot range.

If the aircraft descended below this limit a red light would illuminate on the panel while a green light indicated the aircraft was too high. A yellow light indicated the correct selected height.

What a special gift for the aviation enthusiast in your life!  - An original, WWII DAP Bristol Beaufort, General Electric Radio Altitude Limit Switch mounted in its 100yr old Mango Wood Display Stand with engraved Plaque, printed and laminated Fact Sheet plus a highly detailed, custom-built 1/72 or more detailed 1/48 scale Model of this iconic Australian built bomber perched atop its magnetic display arm.

* Note that this Bristol Beaufort Instrument is pictured with a 1/48 scale model rather than the standard detailed, but smaller 1/72 scale. Click on the 'Model Upgrade' option at the top of this page for the larger 1/48 scale.

This DAP Bristol Beaufort Instrument comes complete with detailed Scale Model, Mango Wood Stand & Plaque plus Printed Fact Sheet featuring photo of instrument in aircraft cockpit

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