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).
Page discussing the aerodynamic design of a car, its practical disadvantages, and general principles for reducing air resistance.
| Identifier | ExFiles\Box 24\1\ Scan037 | |
| Date | 12th December 1931 guessed | |
| 3. consumption from 13.8 m.p.g. to 22. 5 at an average speed of 32 m.p.h., and in addition, obtained the expected results of better ventilation, less draught for the passengers, less noise and better visibility owing to the raindrops being deflected from the windscreen. Figs. 1 and 2 give a good idea of the general arrangement of this car. From an aerodynamic point of view, I think it is probably as good as can be achieved, but I would draw your attention to three practical disadvantages. They are Firstly, a considerable portion of the overall length of the car is due solely to aerodynamic considerations, and otherwise is of no practical value; Secondly, the rear passengers are seated behind the rear axle; and thirdly, only one access door is provided for the passengers, as the projection of the streamlining of the front wings prevents the front door being fitted. Clearly, this design whilst achieving its object, of reducing wind resistance, was not intended to meet any other conditions, and our next step must be to ascertain the requirements of a low resistance co-efficient and see how these other points can be met. Wind tunnel tests show that a streamline body must possess the following general characteristics:- Firstly, a tapering tail, and it is immaterial whether the body tapers in both planes or in only one plane. Secondly, the highest and broadest part of the car should be well in front, certainly not more than one third of the total length of the car from the front. Thirdly, there should be a minimum of excrescences, and any excrescences there are should be smooth and rounded. Provided these general conditions are fulfilled the air resistance of the car will be drastically reduced, perhaps not to the absolute minimum, but near enough to the minimum for all practical purposes, and the real problem | ||