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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).
Analysis of vehicle acceleration and braking performance calculations based on a speed diagram.

Identifier  ExFiles\Box 113\2\  scan0170
Date  11th November 1930 guessed
  
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distance A-G.{Mr Griffiths - Chief Accountant / Mr Gnapp} However, as we are only counting the 17th M.P. as half a second, the halfof the distance traversed by this last M.P. must likewise be deducted from the distance A-G.{Mr Griffiths - Chief Accountant / Mr Gnapp} In order to facilitate this calculation, the value to be deducted in proportion to the speed of travel has been fixed in the table at the end of this booklet. To summarise, the following indications are given by the acceleration diagram -

1.- Acceleration has taken place from the start.
2.- A maximum speed of 79 km. per hour has been attained.
3.- The course traversed (A-G) to attain this speed is 241 metres less 11 metres (distance indicated in the table for 79 kilometres per hour) = 230 metres.
4.- The time required to attain the speed of 79 kilometres per hour and to travel the distance of 230 m was 16 seconds, representing 17 measurement periods (M.P) the first and the last of which are only counted as half a second each.
5.- The acceleration in m/sec. 2 can be determined for each second by dividing by 3,600 (seconds per hour) the difference between the average speed in metres per hour for one second and for the following second, for example -

Average speed of 2nd period of measurement (point D) 15750 m/hr.
Average speed of 3rd period of measurement (point S) 24200 " "
difference - 8450 met./hr.

Acceleration = 8450 / 3600 = 2.35 metres per second 2

The acceleration graph is very simply constructed by means of the speed diagram, and by using a free space on the chart. The construction is effected by drawing as many equidistant verticals as there are measurement periods. In order to simplify construction, the punctures recorded at the bottom and at the top of the diagram paper should be made use of. The speed at any second is shown horizontally. Joining the points thus fixed, we obtain the acceleration graph reproduced on the left of the speed diagram in Fig. 5.

b) Braking - The 19th M.P. presents, in relation to the 17th and 18th, a reduction of speed, represented on the diagram by
  
  


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