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).
The performance of the Wraith petrol system during high altitude testing, focusing on pump starvation and vapour lock issues.
| Identifier | ExFiles\Box 108\1\ scan0117 | |
| Date | 27th August 1937 | |
| CHATEAUROUX. Rm{William Robotham - Chief Engineer}/JBD{John B. Dixon - Fuel Systems}/4/JAB.27.8.37 To. Rm.{William Robotham - Chief Engineer} The Wraith Petrol System on 26.G.VI. The following results were obtained on a visit to Toulouse District including an ascent of the Pic du Midi 8,500' as reported by Rm{William Robotham - Chief Engineer}/IMW{Ivan M. Waller - Head of Chateauroux}/3/JAB.26.8.37. With the A.C. T type pump alone, no starvation of any kind was experienced after prolonged hard driving on the level with temperatures as follows:- Air 26° R.Water 81° Pump temp. 52° Oil 108°, nor could any starvation be detected during a 9 miles ascent of the Col du Tourmalet with air temperature falling from 21° to 18° and Water 96° Pump at 62° Oil 91°. At the summit of the Col, a halt of 10 minutes was made when the temperature at the pump rose to 68°c. No difficulty was experienced starting the engine but after 20 yards the engine cut right out and brought the car to a standstill. Attempts to start the car on the starter failed nor was it possible to fill the carburetter with the hand priming trigger on the pump. Admittedly this is a small capacity pump but it has emphasised an inherent fault in a mechanically operated pump, namely that if there is not sufficient petrol in the float chamber to keep the engine going until the mechanical pump has cleared the system of vapour, the car is brought to a standstill. The pump is then dependent on the slow engine speed given by the starter motor to clear a system in which vapour is still forming and the time to do so is unreasonably long. The Oldsmobile which is fitted with the large type pump (intended to be tried on the Wraith) was also brought to a complete standstill under similar conditions, but here owing to the large capacity of the pump and lower engine demand, it was possible to start the engine after a reasonable time using the starter motor. The failure of the car was witnessed by owners of a Ford V 8 who spotted that the pump was identical with that on their car and admitted having had considerable trouble. We changed over without delay to the S.U. pump on the dash which promptly started delivering petrol and vapour at a temperature of 46°c with the pump working at full speed and a successful get-away was accomplished. The climb was continued on this pump to the summit, petrol shortage limiting the speed to 20 MPH. in 2nd gear but with no fear of being | ||