From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Letter from The British Aeroplane Co., Ltd. to W.A. Robotham at Rolls-Royce concerning gun and cannon installations on aircraft.
| Identifier | ExFiles\Box 175\3\ img249 | |
| Date | 31th October 1940 | |
| C O P Y. 3 The British Aeroplane Co., Ltd., Filton House, B R I S T O L. Your ref. Rm.{William Robotham - Chief Engineer}9/ML. Our ref. Tech/D/F/40/177. 31st October, 1940. W.A. Robotham, Esq., Messrs. Rolls-Royce Ltd., D E R B Y. Dear Robotham, Sorry I have been so long sending you some points on guns and their installation, but we have been very busy. Firstly, with regard to alignment and harmonisation, I am sending you a copy of D.T.D. Technical Circular No.8 referring to fixed guns and turret guns. We always design the harmonising gear itself, so that, having adjusted the gun up and down or sideways, one clamping motion only is necessary to hold it in that position, and this clamping action must be arranged not to pull the gun alignment in either direction. Firing Gears. Pneumatic firing is undoubtedly the most satisfactory, and the addition of electric operation of the air valve is required for two reasons: firstly, to bring the firing button up to the moving control wheel or joy-stick more easily than one could with air pipes; and secondly when interrupter gears are fitted to cut-out the firing of the gun when passing across any part of the aircraft structure, such as the tail unit, it is very convenient to have a reduced image of these parts operated via an electric contact. Cannons. With regard to the cannon, anything that you can do to enable cannons to fire at very low temperatures will be a definite step forward. We are having many strange troubles on the Hispano at the moment, all due to the uncertain action at low temperatures, and the question of supplying enough cabin heating to the cannons is very difficult. I do not know if, before firing, your cannon permits air to blow down the barrel and out through the ejection orifice, but this certainly happens on the Hispano and causes considerable cooling of the gun which often makes it too cold to fire the first shot. This is prevented in some installations, by a cap over the end of the barrel which is blown off by the first shot. This does not prevent the gun from freezing up again if the flight is prolonged for another attack. We have, therefore, concocted a hinged cap over the end of the gun which is lifted clear each time a shot | ||