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 the engineering principles, benefits, and challenges of streamlining car bodies.
| Identifier | ExFiles\Box 161\1\ scan0077 | |
| Date | 25th January 1938 | |
| The Motor 1144 January 25, 1938. STREAMLINE Contd. limited demand for the streamlined car and if, therefore, it is to be sold at an economic price it must have a foundation that is similar to that of the normal production car. The possibility of using the same basic chassis for normal and streamlined types is well shown by two illustrations in this article. In the first of these a seating diagram and engine and transmission position of the normal car are shown in silhouette. In the second illustration the only mechanical change assumed is the use of a fixed rear axle housing and independent rear suspension. By using this and redisposing the seats on a lower level it is possible to reduce the frontal area of the car by approximately 25 per cent., whilst still retaining four-passenger accommodation. By improvements in the form of the car and the faring in of all wheels, it is not unreasonable to expect a reduction in windage per square foot of area of some 33 per cent. There is, therefore, a 50 per cent. total reduction in wind resistance To achieve such a result it is important that designers should keep in mind the Earl of Stafford’s motto: “I go through.” In addition to streamlining the top of the car it is also essential that the whole of the bottom should be thoroughly fared over so that the flow of air between the underneath of the car and the road is as free as possible. In addition, I think it is logical to place the radiator in a separate cowling ahead of the main streamlined form. This is done on many of the latest racing cars and has obvious advantages. Sacrifices are, of course, necessary if this result is to be achieved. Visibility from the rear seats of the streamlined cars is poor, headroom is restricted and the considerable frontal and rear overhang makes the car difficult to park and awkward to handle in city traffic conditions. METAMORPHOSIS. The streamlined car does not involve a special chassis. The above drawing shows how, by rearranging passenger accommodation and using a fixed axle and independent rear springing, the normal touring car can be changed into a good streamlined form. The one serious engineering problem of the streamlined car is related to its increase in speed range. If one takes the normal minimum speed of a car as being 10 m.p.h. and its maximum as 70 m.p.h., one has to design for a top gear range of 7 to 1, but when the maximum speed is raised to 90 or more we have to think in terms of a range of 10 to 1. If an attempt is made to increase the range of engine speed in proportion severe problems arise with bearing loads because these increase very rapidly as the speed goes up. Gear Ratios and Engine Revs. In point of fact, if the normal gear ratios were left unchanged the bearing loads would be doubled because the engine revs. would have gone up from about 4,500 to 6,500. We should, moreover, be forcing the engine to run in an entirely uneconomical way because we should be running the engine at a greatly increased speed without needing any great increase in horse-power. I think that the problem will be tackled in two different ways. In the first place, the use of a five-speed gearbox with an automatic overdrive will become relatively common; this will mean that the gear ratio will be raised at speed from, say, 4.8 to 1 on direct drive to 3.3 to 1 on overdrive. In this way speeds of 90 m.p.h. to 100 m.p.h. will be realized without forcing the engine above 4,500 r.p.m. The-other possibility is that the normal direct top will be fixed at, say, 3.3 to 1 and the low speed power output of the engine increased by supercharging. Actually, what would be required on a supercharged engine of this type of car is an entire reversal of present practice, for one would use the supercharger only for low speed acceleration and cut it out when travelling at high speeds on the open road. For use on motor roads, however, the advantages make such sacrifices well worth while. Taking as an instance the four-seater Adler car illustrated, I may say that I have timed this on the Avus track to do 100 m.p.h., although it has only a side-valve engine of 1.7 litres capacity. Assuming this to develop 55 h.p., the fuel consumption is about 25 m.p.g. at 100 m.p.h. This statement, and the fact that, given a suitable road, it is now possible for four people to cover the distance between London and Glasgow in 4½ hours with a fuel cost of under 7s. 6d. per head demonstrates more strikingly than any argument the potentialities of modern automobile trans- The Roads that Mould the Car. Every year 600 miles of Hitlerstrasse, such as is pictured above, are built in Germany, thus permitting the full potentialities of the automobile for personal transport to be realized. A26 | ||