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).
Comparison of American and British aircraft engine oil systems, focusing on oil returns and scavenging.
| Identifier | ExFiles\Box 27\3\ Scan219 | |
| Date | 15th May 1939 guessed | |
| 13. Oil Systems Oil returns of American engines are very much higher than those of British engines; the Cyclone "C" engine, for example, has a return of 380 gallons/hour with 104 gallons/hour through the centre section. The Wright 14-cylinder engine has a return of about 600 gallons/hour, and the Pratt & Whitney 14-cylinder Twin Wasp about 700 gallons/hour. Pratt & Whitney are now using 100 second oil, but Wrights still favour 120 second oil. In cool climates oil dilution by fuel is very widely applied, and has been found quite satisfactory. American engines are extremely clean, with positively no oil leaks and no emission of oily mist from the breathers. Wrights are still using breathing through the airscrew shaft, and Pratt & Whitney are still breathing satisfactorily from two pipes of ½" and 5/8" bore, from the rear half crankcase and rear cover respectively. Pratt & Whitney especially are employing scavenge pumps which exceed the capacity of the pressure pump considerably - by at least 300%. They said quite definitely that this is essential for good scavenging as the pumps have froth rather than solid oil to pick up, and they assured me that the use of big pumps does not encourage frothing. At least 3 separate scavenge pumps are used - 1 for the front section, and one for the crankcase (i.e. oil sump), and one for the rear section. One disadvantage of these big scavenge pumps has found to be that at low speeds air is drawn into the crankcase, and as this air may be moist some corrosion trouble has been experienced. Frothing has been experienced by both Wrights and Pratt & Whitney. Wrights say that they overcame it by attention to the drainage of the crankcase, and Pratt & Whitney by suitably baffling the oil tanks. Pratt & Whitney oil inlet temperature is 85°C with an outlet temperature of 115°C. On a particular test observed at Wrights the oil inlet temperature was 60°C and outlet 120°C. Pratt & Whitney stated quite definitely, however, that on their later engines the temperature rise through the engine was much smaller. | ||