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).
The development challenges and future prospects of evaporatively cooled engines versus water-cooled systems.
| Identifier | ExFiles\Box 178\4\ img072 | |
| Date | 7th May 1932 guessed | |
| -2- It must be recognised that to produce a satisfactory evaporatively cooled engine of low weight/HP. and small frontal area which limits the possible water spacing and size of pipes, is a very big problem. We cannot point to any other Maker of aero engines or car engines who has done it successfully. It has been tried by many firms. We know that the Americans did a lot of work on it before they went over to high temperature cooling with Ethylene Glycol. The only example we know of engines flying satisfactorily under evaporative cooling conditions was the R.101 with C.I. Beardmore engines, but of course this does not compare with what we are trying to do. All the present machines which are flying with evaporatively cooled engines are fitted with tubular condensers. This means that only a small part of the possible advantage of evaporative cooling is being gained. Roughly, the advantage is the saving in weight of the water in the radiator which may amount to 60 or 70 lbs/engine. The machines which are flying weigh ready for flight about 15000 to 22000 lbs so that proportion is very small indeed. The drag is very little altered. The usefulness of the present machines is that they allow us to develop an evaporatively cooled engine. Eventually, if evaporative cooling is going to become worth while, it must be combined with surface radiator. The production of a satisfactory surface radiator installation has still to be achieved but it is difficult to start on this until the engine side has been proved out. The point here we want to make is that when we finish our Type Test and when we have got our satisfactory engine, before evaporative cooling is really worth while there has still got to be produced the ideal condenser to go with it, and there will be any amount of problems attached to that. When we have arrived at the ideal we shall have got something really worth while and we are strong advocates that no effort should be spared to reach that. Going back over the job now the mistake which has been made has been to allow evaporative cooling to get on to machines which were dependent on orders. For instance, the Southampton which did so well with two 'Kestrels' evaporatively cooled, would have done approximately the same with water cooled engines. Looking forward to the future development of the Kestrel engine there is much more immediate prospect of success by keeping it water cooled than there is by pushing evaporative cooling. The immediate prospect of evaporative cooling is to increase the weight of the engine and to reduce the rating. HM.{Capt. W. Hallam - Head Repairs} | ||