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).
Aero engine connecting rod failures and comparing blade versus articulated rod designs.
| Identifier | ExFiles\Box 179b\1\ img310 | |
| Date | 3rd February 1933 | |
| HS.{Lord Ernest Hives - Chair} ) FROM R.{Sir Henry Royce} ORIGINAL R1/M3.2.33. C. to SC. WGR. F.{Mr Friese} EV.{Ivan Evernden - coachwork} AERO WORK. CONNECTING RODS. I have read the memos. concerning these very carefully, especially the one written personally by HS.{Lord Ernest Hives - Chair} If I have the right impression HS{Lord Ernest Hives - Chair} says that it is not due to any abnormal use of the engine, such as by rolling the aeroplane, for the reason that two out of the eight failures were certainly not due to aerobatics. I think therefore we have to take a broader view than the temporary oil failure suggested, and the following are points which come to my mind: (1) I have never liked the blade rod construction because of the narrow blade rod pressing on the joint or weak part of the big end block, so distorting the surface, and the weakness of the forked rod. I therefore tried my best to get the articulated rods tested to see if we could prove whether there were the better rods, as I firmly believed. (2) My impressions are that the maximum HP. we have ever attained from the 'R' engine was successfully run with this (articulated) type of rod, and that over 90% of engines outside our own make, and over 400HP., use articulated rods. (3) The distribution of the load on the crankpin bearing is much less disturbed by the influence of the articulated rod than by the blade rod. (4) To my mind it appears that the conditions that brought about these failures may have come on slowly because the conditions now are the same as they were when we first put in a supercharged engine. I am not quite sure in saying that the supercharged engine has a greater load on the con. rods than those unsupercharged. This extra load if persisted in for a length of time may bring about the conditions under which the bearing or lubrication fails. This seems a probable aspect of the case. (5) The modifications being made to the con. rods and crankshaft can I think be considered important because one would suppose that both the hard shaft and the Kelmit surfaced bearing would not so quickly become in a bad condition that might lead to failure. This is independent of whether the con. rods are blade or articulated type. I think it good to point out that the articulated type may retain the oil better than the blade type owing to the bearing of the articulated rod having a much longer axial length for oil retaining. (1) | ||