Rolls-Royce Archives
         « Prev  Box Series  Next »        

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).
Analyzing braking test methodologies and their inherent inaccuracies.

Identifier  ExFiles\Box 32\2\  Scan064
Date  23th March 1925
  
R.R. 493A (50m) (D.B. 175 25-9-24) J.H.D.

EXPERIMENTAL REPORT.

Expl. No.

REF: Hs{Lord Ernest Hives - Chair}/Eml/LG23.3.25.

ANALYSIS OF BRAKING CURVES.

As we have previously pointed out, the results of braking tests are of little value unless they are carried out with great care, and the human element largely eliminated as a measuring device. We have purposely always avoided giving distances to pull up because they mean nothing and are of no value.

'The Motor' tests appear to have been carried out by means of the 'Pass a post and shout' method. In this case the passenger shouts to the driver to stop when opposite a post, whereupon the driver applies the brakes, the distance from the subsequent position of rest of the car to the post being measured and taken as the distance required for a stop to be made.

We find this method to be quite useless at speeds of 10 and 20 m.p.h. as the driver either anticipates the observers command, or applies the brakes late, the results being easily affected by 25% either way.

This is exactly what appears to occur in 'The Motor' tests. On the Bentley car, the decelerations from the figures given are :-

10 m.p.h. 30.8 ft/sec2
20 m.p.h. 23.2 ft/sec2
30 m.p.h. 23.0 ft/sec2

so that for some obscure reason the brakes are 30% more efficient at 10 m.p.h. than at 20 and 30 m.p.h.

contd :-
  
  


Copyright Sustain 2025, All Rights Reserved.    whatever is rightly done, however humble, is noble
An unhandled error has occurred. Reload 🗙