Crankshaft torsional period and brake thumps on the 25 HP car.
| Identifier | ExFiles\Box 11\4\ 04-page030 | |
| Date | 5th May 1932 | |
| K7941. To Hs {Lord Ernest Hives - Chair} /Rm. {William Robotham - Chief Engineer} From G.W.R. Hotel de France, Chateauroux(French test region), FRANCE. 5th May 1932. We have received your memo. Hs {Lord Ernest Hives - Chair} /Rm. {William Robotham - Chief Engineer} 1/AD3.5.32. CRANKSHAFT TORSIONAL PERIOD. I quite agree with you that we should stick to the loads of the low inertia damper, as we find them satisfactory during 10,000 miles tests. The load of 14 lbs was obtained as a result of work by Mx. {John H Maddocks - Chief Proving Officer} and myself some, approx. 2 years ago, which gave the best all round results. Since then, I believe I am right in saying, that we have been trying out crankshafts with bigger journals and crankshafts in different materials, and the load of 17 lbs is the outcome to suit these crankshafts. As far as I know we have had no trouble with the Phantoms for some considerable time, and I admit that our last two or three 10,000 miles tests with Phantoms, the friction load has been of an average of 17 lbs. We have been up to 22 lbs, but find that it did not remain at this load. The present crankshaft we are running, is a balanced crankshaft, R's 8 weight scheme, with 2.800" diameter journals and 2.375" crankpins. Therefore the loads of the slipper wheel for this crankshaft naturally will vary with the present standard crankshaft. I am in no way standing out for any particular load, and my sole object is to obtain satisfactory conditions for production, and I believe you will agree with this. BRAKE THUMPS ON THE 25 HP CAR. The 25 HP car has been very prone to front brake thumping since the fitting of front brakes. An enquiry from the Test Dept will enlighten you to the effect that they have great difficulty in turning out cars free from thumps. I am quite aware that the fitting of the pilot shoe tends to make it worse, with having to have the increased clearance. I still maintain that the servo of the 25 HP. car is not large enough for the work it has to do. I tried to get Mr.Elliott interested in this job, but was not successful, because he upheld that the servo's area was ample for the work. I maintain that it is not a question of the servo's area, but the radius of the levers are too small on this servo, and that a very small amount of falling off of the servo efficiency, causes it to grab, and the friction of the arm of the servo has to be in the neighbourhood of 30 lbs to overcome it. We have tried your suggestion; which is very logical, of utilising the dashpot, but find that it is too sensitive to get satisfactory results for production work. We will, | ||
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).