Provision of Add On GPS for RAF Transport Aircraft Without Airframe Modification

Anthony Haddrell, Simon Butcher, Joe Bliss

Abstract:	The Royal Air Force of the UK has a large number of transport and general duties aircraft currently not fitted with GPS. One of the reasons for this concerns the cost and aircraft down time associated with fitting to the airframe of new antennas,power supplies, interface wiring etc., and the integration of the GPS information with existing systems. Once every year the RAF operates a trial campaign known as the ARIES flight, in which studentsat the Deportment of Air Warfare at RAF Cranwell learn to operate and evaluate a range of navigation equipment. The trial is divided into a number of sorties, typically lasting 3 or 4 days. On the 1991 flight aboard a Comet 4 aircraft, a Navstar XR4 receiver was flown along with two P-code equipments, to evaluate the relative performance of the c/A code for genefal route navigation. As a resut of this trial and the subsequent evaluation, the DAW team determined that the unit could provide the basis of a low cost navigation system. In particular, the GPS output could be used to improve the Datum position used during navigation training on the unit's Dominie aircraft commonly utilised in this role. Because various aircraft are assigned to this task, a transferable GPS fit was required. A unique solution was developed jointly by the RAF and Navstar personnel. The majority of the RAF's transport fleet are fitted with a sextant tube in the upper fuselage, for use with a sextant utilised for en route navigation. The transferable GPS fit was realised by engineering a GPS antenna subsystem able to fit in the tube, thereby needing no changes to the airframe or pressure hull. Further, the power supply provided for lighting withii the sextant was utilised for powering the complete GPS equipment, again avoiding changes to the aircraft wiring. The XR4 GPS Receiver/Display is mounted at the navigator’s station, and wired directly to teh antenna subsystem within the fuselage interior. The paper gives details of the engineering, installation and flight trials carried out as part of the project. Some later features have also been added and are reported. Navigation results from both the original ARIES trial and the subsequent DAW proving flights are presented.
Published in:	Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992) September 16 - 18, 1992 Albuquerque, NM
Pages:	1159 - 1163
Cite this article:	Haddrell, Anthony, Butcher, Simon, Bliss, Joe, "Provision of Add On GPS for RAF Transport Aircraft Without Airframe Modification," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 1159-1163.
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