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).
Performance analysis memo comparing the aerodynamic drag coefficient of the 'Burma' car with other vehicles.
Identifier | ExFiles\Box 26\1\ Scan088 | |
Date | 23th June 1960 | |
To: Hy.{Tom Haldenby - Plant Engineer} from Ev.{Ivan Evernden - coachwork} Re: Burma Performance I have been studying the recent tests of Burma car 53.B which were made to establish the value of its aerodynamic drag co-efficient. The measurements showed the maximum propeller shaft power to be 115.5 h.p. This figure seems to me to be very low, in view of the fact that on the test-bed the engine has given 159 h.p. One has to assume that the losses due to the fan, the exhaust system, the air intake silencer and the installation amount to 43.5 h.p. which is a loss of 27.4%. As a matter of interest I have made an analysis of the performance of the Vauxhall Cresta, as given in the Autocar Road Test, to arrive at a value for "K". Our long range photograph of the car shows that the frontal projected area to be 21.6 sq.ft. whilst our tests on similar "off the shelf" tyres show the road drag power to be 25.6 h.p. for the tested car weight of 1.375 tons at the recorded maximum average speed of 87.6 m.p.h. At this speed the engine is well past the peak power (see graph) and of the 70 h.p. available at the road wheels, only 44.4 h.p. would represent air drag. These figures give the Cresta a "K" of .00054 which is the same as the "K" for the Bentley S.1. The general shape of Cresta is much more like that of "Burma" than it is like that of the Bentley S.1, yet the "K" of Burma is .00078; and greater by 44.5%. This would seem to indicate that not the general shape of "Burma" need be greatly changed to reduce the aerodynamic drag, but the secondary shapes and the details of the form. Ev.{Ivan Evernden - coachwork} | ||