Originally Posted by
Bigbjorn
Actually the Merlin was a very ordinary performer at altitude up until the Mk. 20 which was the first to use Stanley Hooker's two stage supercharger. This transformed performance above 20,000 feet. The turbo/supercharger system used on the Lockheed P38 needed a lot of development which it didn't get for a multitude of reasons. Allison were a relatively small company flat out on war production and didn't have the resources for development. Besides which the patents for the turbo system were owned by the USAAC who insisted Allison use them and actually supplied them to Allison after ordering them from GE. Given that the P38 had extraordinary ceiling and altitude performance and speed as was it would have been a real goer if the engine problems were sorted. The Allison and Merlin were the only liquid cooled engine used on US military aircraft in WW2. All others were aircooled radials.
The major problem with the turbos was that they required special alloys that were simply not available in the necessary quantities. Allison was not the only company stressed by wartime production problems - at least they didn't have bombs coming through the factory roof like RR did. Everyone was pushed to the limit, and many companies were doing things they had never done before. To take a local example, during the war, there were about ten thousand Gipsy Major engines built in Australia - by GMH and Tasmanian Railways! Neither organisation had built aeroplane engines before, even small ones like these.
The US did, as you say, largely use aircooled engines in WW2. This was mainly due to experience with the Liberty engine of WW1, which seems to have had major issues keeping water in. Both aircooled and liquid cooled engines were widely used by all the combatants in Europe, with top performers such as fighter aircraft using liquid cooled engines mainly because of their lower frontal area until fairly late in the war when the generally larger size of aircraft meant engine frontal area became less of an issue.
The US had an advantage in the aircooled engine in that a lot of development had continued in these in the two years before the country entered the war - once the war is on there is a strong pressure to stick with what you already have and develop that. A prime example is the Merlin. Developing 890hp in the Fairey Battle in 1936, in 1945, in the Hornet, it was producing over 2,000hp.
Aircooled engines were less able to be increased in power, a good example of a comparable power is the P&W R1830, which produced 800hp initially, but never exceeded 1350hp. It is a lot easier to increase the cooling in a liquid cooled engine!
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
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