Long before the introduction of the highly accurate world-wide GPS system we know of today, the military and commercial aviation industries had been dependant on a Radio Navigation System based on WWII radio direction finding technology (RDF).
The RAF used a Radio Directional Finder (DF) Loop, rotatable antenna which could be rotated to a home airfield’s transmitting frequency. Mounted on the outside of the fuselage (as seen on the Lockheed Hudson) or inside, under the cockpit canopy (as seen in the De Havilland Mosquito), the airfield’s signal transmission was effectively a homing beacon, enabling the aircraft to follow the radio beam back to its origin.
The RDF delivered a constant signal to the aircraft’s visual L/R Beam Approach Indicator mounted on the pilot’s main instrument panel. Featuring two floating, cross-hair needles, it provided the pilot with a visual indicator of the aircraft’s position in relation to the radio transmission - directing him to turn either left or right to stay on course.
Whilst the RDF system proved to be highly effective, it gave no actual aircraft positioning data other than a heading to steer by, as it relied on just a single radio signal.
Many British night-time bombers, already low on fuel, were returning from raids to blacked-out or fog-shrouded airfields and lining up on an almost invisible runway whilst attempting to obtain the correct angle of approach (Glide), was not a job for the faint hearted.
After having survived anti-aircraft flak and predatory Luftwaffe night fighters, bomber pilots were often faced with the unenviable choice of either diverting to another airfield or to continue circling, hoping for a glimpse of the runway.
Many aircraft simply dropped out of the sky after running out of fuel. Others collided with each other in the darkness or hit powerlines or trees after missing the runway in the dense fog. In fact, more aircraft were lost during WWII to bad weather conditions than to any enemy action.
As well as experimenting with 'burning off' runway fog, the British Air Ministry also introduced a crude Runway & Glide Angle positioning system relying on series of airfield-installed radio transmitters, which broadcasted multiple signals on different frequencies to the pilot’s Beam Approach Indicator.
Differing from the aircraft’s L/R Beam Approach Indicator (which had guided them back to the airfield via a single homing transmission) the Beam Approach Indicator used two intermittent flashing lights and buzzers to indicated the aircraft’s horizontal and vertical alignment position to the runway.
When the instrument’s lights and buzzers gave a constant illumination and audible tone, the pilot knew he was approximately aligned and at the correct glide angle. Even so, struggling to manoeuvre a damaged 17 tonne Lancaster bomber approaching the airfield at over 275 mph gave the pilot no reaction time whatsoever and once they started their descent, they were committed.
By the 1950s and at the height of the Cold War, both these rudimentary radio-based navigations systems had been substantially improved. Multiple radio signals from large networks of strategically placed ground transmitters now gave the pilot a constant and accurate aircraft position via radio triangulation. This also enabled the pilot to navigate cross country or over oceans by jumping to the next transmitter on the intended route.
Known as VHF omni-directional range (VOR), the short-range radio navigation system was used by both the military and commercial airline industry and remained in operation across the world up until 2005 but has since been slowly phased out by the new satellite Global Positioning systems GPS.
By the 1950s, the old Beam Approach system had also undergone a significant transformation, with computerised radio and radar arrays installed around airports providing pilots with extremely accurate runaway alignment positioning as well as real time glide angle data.
Known as the Instrument Landing System Localiser (LOC), today it’s an integral and critical component of aviation navigation and airport flight traffic control. Computerised and fully automated, many commercial and military flights can actually land on autopilot via these systems with the aircraft's controls responding to ground instructions.
This Cold War / Vietnam War era Bendix MN-97 Omni-Mag Course Indicator was used by both the US military and the world’s commercial carriers.
In military applications of the 1950/60’s it was known as either the ID-249A/ARN or ID-249/ARN and used in the AN/ARN-14 Radio Navigational System. Installed in Vietnam War era helicopters such as the Bell Huey UH-1, the Omni-Mag was also installed in the USAF strategic bomber, the B-52 and the super sonic jet fighter, the F-100 Super Sabre.
Using a combination of navigation instrument functionality, the Bendix Omni-Mag featured a flight path deviation indicator, an ambiguity indicator, and a relative magnetic heading stabiliser which could be dialled in via the bottom left ’Set’ knurled knob to set the course heading.
The central ‘aircraft’ shaped pointer maintained its position as long as the aircraft was on its VOR or LOC course via a floating vertical line marker providing directional alignment and a horizontal line - the glide-scope angle.
A small ‘Marker Beacon Indicator light’ usually located at the top right (Missing on this instrument) illuminated when passing over radio beacons with an ‘orange flag’ indicating if the unit was off line due to weak signal strength.
In the 50s/60’s, the Omni-Mag Course Indicator was installed just below the aircraft's large Artificial Horizon Indicator on the pilot's main flight panel but in modern aircraft today, it is now integrated into the Artificial Horizon Indicator and visible by two small pointers just below and either side of the ‘Horizon Line’
This Cold War/Vietnam War veteran represents an important step in aviation technology and mounted in its 100 yr old Mango Wood Display with engraved Plaque, Fact Sheet and custom built highly detailed 1/72 or larger 1/48 scale model of the iconic Bell Huey would be a fantastic gift for any aviation enthusiast.
This Bell UH-1 Huey Instrument comes complete with detailed Scale Model, Mango Wood Stand & Plaque plus Printed Fact Sheet featuring photo of instrument in aircraft cockpit.
* Note that this Bell UH-1 Huey 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.
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