Engine Type Wasting Space and Weight
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ONE of our recollections of the Commercial Motor Show of 1935 is that it marked the beginning of the end of the scramble for high ratings in the 30 m.p.h. class. Since then makers have had time to gain more experience of the problems connected with keeping the weight of machines intended to carry approximately twice tons, down to that figure, and the position has become stabilized.
We have no reason to believe that any marked development in this respect will be revealed at Earls Court in November, but it would be logical to surmise that the present state of affairs does not -really represent finality.
When countless designers have racked their brains to find a way of reducing weight still more and, presumably, have failed, it is fairly clear that future advances will be along lines that are not yet open to them. We mean that research and experiment by makers of individual parts and units must be completed before the manufacturers of vehicles can reap the benefit.
Is there a prospect of materially lightening individual units? It is arguable that the weight of a power unit might be reduced by nearly 50 per cent.
Solely because of its cycle of operations, the type of engine commonly used needs an extravagant number of cylinders. It should be practicable to use each for its basic purpose—generating power— at least twice as often in a given number of revolutions; then our engine could be proportionately lighter. In the far-off 'days, when more than a few automobile engineers seriously considered the two-stroke, conditions were very different from what they are to-day. Of chief importance, there was little incentive to cut space and weight to the utmost minimum. Superchargers were almost unknown; scavenging by exhaust-pipe depression was barely a vague theory; aluminium pistons were regarded with deep suspicion, and much else that is available to-day for the advance of the two-stroke was not then to hand.
Pioneers of the Two-stroke Unit.
No maker will readily embark on a new project that breaks entirely fresh ground. That is the main reason why it has been left to a few—the names Trojan and Junkers come to mind—to keep the two-stroke flag flying. There is scope, however, for development in this field and incentive is now• by no means lacking.
Motorcycles and motor ships are successfully powered by two-stroke engines and the fundamental fact that three cylinders of, say, half a litre each, exerting a power impulse once every revolution, are better than six of the same size generating between them no more power than the three, is incontrovertible.