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 Vacuum Oil Company discussing Mobiloil Aero 'H' performance in Prestone-cooled Wright 'Conqueror' engines.
| Identifier | ExFiles\Box 145\1\ scan0017 | |
| Date | 4th May 1933 | |
| Y56-1311. No. 2. V.O.Co.,Ltd., to Messrs. Rolls-Royce Limited. 4th May, 1933. It will be seen therefore that Mobiloil Aero "H" has a margin of some 20°F to 25°F over Mobiloil Aero "W" when the two oils are of the same viscosity and in the region of the boiling point of water. From information received from our friends in New York we understand that the Prestone-cooled "Conqueror" engine (Wright) the normal operating temperatures are inlet Prestone 230°F, outlet 250°F while the corresponding oil temperatures are 150°F and 180°F max. It seems from information supplied that when Prestone-cooling was first adopted in U.S.A. difficulty was experienced with excessive oil consumptions and piston seizures and in the first instance these were eliminated by increasing the working clearances but at a later date piston ring drainage was improved when it was found possible to empty normal ring clearances in the grooves for both water and Prestone-cooled engines. In the case of the Wright "Conqueror" engine they use two compression rings and two oil rings. The compression ring having a desired clearance of 0.005" in the groove and the oil rings .001". The corresponding ring gaps are .018" and .014". It is stated that the ring tensions are the same both as regards oil and compression rings viz: six to seven pounds, with a fall of 15% to 20% after the first run. The rings are stated to have a hardness of 95/105 on the Rockwell "B" scale, which corresponds to a Brinnel hardness of 200-250. For this class of service Mobiloil Aero "H" is reported to give excellent results. The above information is supplied as a matter of interest and we have pleasure in enclosing Aviation Bulletin No.28, which was recently forwarded to us by the Vacuum Oil Company of New York. While this may have no direct connection with your engines the bulletin contains information of general interest with regard to aircraft engines which we hope will prove useful. It appears to us that for steam-cooled engines where oil sump temperatures are somewhat elevated, use of a heavier oil than D.T.D.109. is desirable and we shall be glad to supply quantities of Mobiloil Aero "H" for experimental purposes if desired. | ||