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).
Calculations for propeller shaft and footbrake torque requirements.
| Identifier | ExFiles\Box 77\1\ scan0105 | |
| Date | 8th March 1911 | |
| R.R. 235A (100M) (W 314 8.3.11) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 1525 -3- forward and upward; this change of direction is brought about by the pressure between the tyre and the rise in the road causing the deflection. This pressure may be additional to the ordinary bump load above mentioned because the movement of the body does not, of course, synchronise with that of the axle. Although this load is only imposed momentarily, I think the wheels would be dragged round a greater distance than the spring of the propellor shaft would allow. For these reasons I do not believe it is safe to assume that the tyres will slip at a certain point, and to make the propeller shaft strong enough to withstand the torque so calculated, but that we should design the footbrake so that it cannot restrain a torque greater than the maximum torque for which the propeller shaft is designed. I think, however, that we should increase the propeller shaft sufficiently for it to withstand a torque of 10500 in. lbs. with a factor of safety of 2. This figure is the braking torque required to pull up a car weighing 50 cwts. in 24 yds. when travelling at 25 m.p.h., or a car weighing 33 cwts. in 16 yds. at 25 m.p.h. The footbrake should be designed to be capable of restraining a torque of 20,000 in. lbs. [Handwritten] Torque due to letting clutch in | ||