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).
Investigation into engine cutting out, focusing on petrol heating and ignition system performance at high altitude.
| Identifier | ExFiles\Box 178\4\ img024 | |
| Date | 12th March 1932 | |
| By applying heat to the petrol, a slight improvement was noted. This was done in several ways; by jacketing the petrol filter, by having heated air intakes, and by having the diffuser, and throttle bodies connected in parallel, these all helped slightly. There was no improvement marked enough to enable us to put the trouble down to any definite cause. With regard to the Ignition Theory, a test was carried out at the works in order to see if the spark was jumping across outside the cylinder. The sparking plug was put in a chamber, and subjected to a pressure corresponding to the compression pressure of the engine at an altitude of 27,000 ft. where most of the cutting out was taking place. The magneto was placed in another chamber, the pressure of which was reduced gradually. When the corresponding pressure to atmospheric at 27,000 ft. was reached, the spark jumped across at the terminals in the distributor lead, instead of at the plug points. This suggests that the terminals might be improved. Actually the density in the cylinder at 27,000 ft is less in the engine due to heating of the charge than in the chamber used in the ground test, and as the voltage required for a spark to jump a gap depends on density, and not pressure, the jumping across outside the cylinders would not occur for several thousands of feet more than represented in the test. The Magneto is considered by the experts to be quite safe up to an altitude well above the ceiling of the machine. The voltage required to jump the spark gap at 32,000ft is 6000 volts, and to jump the plug gap, only 3000 volts, so there is a large factor of safety in the magneto. These figures are for the Watford Magneto which is considered not to be quite as good as the B.T.H. However the terminals appear to be rather near the limit and could be improved. Some climbs were to have been carried out with lubricated cables, and improved terminals, but before this could be done the machine crashed on landing, so putting an end to the investigations at Martlesham. It was decided to allot a new Fury K.2048 to the R.A.A. and to continue the investigations. Two climbs were done with the machine in a standard condition, and the engine cut out at 28,000 ft temperature being - 36°C, this was typical. | ||