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 permanent twisting of propeller shafts due to foot brake application and an analysis of their torsional elastic limits.
| Identifier | ExFiles\Box 77\1\ scan0098 | |
| Date | 3rd July 1911 | |
| B1/ GB4711. N Barrington "G" Dept. Drawing Office X484 3rd July 1911. Mr. Royce, Re 1100 to 1600 Propeller Shafts. The Propeller Shafts in above series still continue to show a permanent twist in a direction due to foot brake application. We have carefully tested a propeller shaft to find its torsional elastic limit, as they gave one the impression of having a much greater difference between the tensile and torsional (or shear) elastic limit than is generally accepted. The propeller shaft took a permanent set in two experiments at a gross torsional moment of 400 lbs at 40" radius, or 16,000" lbs. This shows a torsional elastic limit of only 9 tons. The greatest twisting moment exerted by the engine with the first speed engaged is 9,000" lbs - this is assuming the engine to develop 55 b.h.p at 1,000 revs. - showing a factor of safety of 1.8 to 1 on driving side. The corresponding frictional grip of road at tyre diameter is 1650 lbs., which - assuming 28 cwt load on rear wheels for an open car with luggage - gives a frictional co-efficient of .5. Of course the greatest stress is from using the foot brake, when, if the twisting is due, directly and only, to the frictional grip of tyre on road, a grip of 3,000 lbs is necessary to cause the damage. In other words, the co-efficient of friction between tyre and road is unity. This, however, does not seem credible in every case, but it would appear to indicate that the foot brake is strong enough | ||