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).
Article from 'The Motor' magazine discussing car performance, wind resistance, and the benefits of streamlined bodywork.
| Identifier | ExFiles\Box 160\4\ scan0011 | |
| Date | 7th March 1939 | |
| The Motor 172 March 7, 1939. Topical Technics Theme and Variations in Design and Development Performance As most owners have their cars overhauled and tuned up in readiness for another year's motoring it is a matter of some importance to them to know to what extent their monetary expenditure is being repaid, also for how long the improvement in running continues. There are few better methods of checking this than by using the Tapley performance meter. The little “Q” type which I have had on my own car now for nearly a year works extremely well and, as I have frequently written about this device before, I will now only repeat its bare essentials. The Tapley meter shows on a scale the rate at which the car is accelerating and the gradient which it will climb on top gear. It also shows the chassis friction, which has a very important bearing on fuel consumption and maximum speed. If one desires one can also carry out interesting experiments in measuring windage. These negative factors are recorded on what one might term a negative scale on the dial. This division into plus and minus enables one further to discover the maximum speed of the motorcar even if one cannot find a piece of level ground. In the ordinary course of events when one is accelerating from 50 to, say, a maximum of 70, the dial will steadily read on the plus side. If, however, one were going down a gradient, this figure would be diminished. At the moment when the dial swings over to zero one has the true maximum speed of the car irrespective of the gradient. Windage THE tremendous wind resistance of the conventional saloon type of body was clearly brought home to the occupants of the 12-cylinder Lagonda which recently did a fast run from Berlin, as recorded on another page in this issue. Releasing the accelerator at 100 m.p.h. caused the car to slow up to quite an amazing extent without any application of the brakes. The difference between 80 m.p.h. and 100 m.p.h. is most noticeable, as, indeed, one would expect from the fact that theoretically nearly double as much power is required at the latter speed as at the former. The favourable influences of the streamlined form of bodywork in reducing this excessive power are, perhaps, more clearly realized by the saving in fuel that follows than from the increase in maximum speed. Horch, for instance, on their latest streamlined model claim 90 m.p.h. with a 90 b.h.p. engine on a car that is comfortably a six-seater and has ample headroom. In other words, they save about 15 h.p. at this speed as compared with a slim sports saloon type as known in this country. Against this one must put the fact that the car is heavier and that to achieve the best consumption at high speeds with low power one needs an overdrive. From a more personal point of view it may be observed that the majority of streamlined saloon cars have restricted headroom, particularly in the back seats, and this to some extent offsets the advantage of wider seating. Furthermore, if a curved screen is used, I am told that the reflections which result when driving in city streets are tiring to the driver. It may quite justifiably be argued that the total number of hours per annum at which you can drive at 90 m.p.h. in England are so few that these extra complications are not worth while. In other words, one may fairly take the attitude that streamlining for Continental use is proved, but for English use is as yet unproved. Experiment THIS subject is one of so much interest that I think it would be well worth while for one or more of our manufacturers to build a really streamlined car and subject it to tests over a year or so's ordinary running. It is one of those things about which one can argue ad infinitum, but which practical tests should settle once and for all. Naturally, the streamlined car can only appeal to the fast driver, but there are many of these, even if their proportion to the total number is small. Finally, if I may put this in as some afterthought, many people must have wondered why Mercedes-Benz brought out a 3-litre record-breaking car with separate cowlings for the wheels when the all-enclosed type has been proved so efficient, particularly by M.G. and Gardner. The answer to this is that the car was designed particularly for standing-start records in which reduction of weight is of paramount importance. L.J. COMPARISON. A picture showing the difference between a standard saloon and a special low windage type, the chassis in both cases being a Bentley. | ||