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Pratt vs. Wright Axis vs. Allies

Posted by Joe Scheil on Sat Sep 20, 2003 10:44:16 AM

In reply top Maybe inspired by but not copies posted by Christer on Sat Sep 20, 2003 04:05:54 AM

Longwinded Irony....

Kind of an interesting subject, as BMW built the Pratt Hornet for 10 years as the BMW 132. This was the first "big nine" for German industry, and based on this engine BMW built the 139. This was a twin 9 built on a common crankcase, a double Hornet as it was. The engine seemed to come out at the same time as the actual Twin Hornet, the R-2180, a 14 cyl radial, but as a big "18" was unsuccesful. It would be interesting to know how late Pratt&Whitney worked with BMW as the war began to heat up....This engine powered prototypes of the FW-190 and Do-217, but had a better developmental stablemate. The more promising engine that resulted from in house development was the BMW-801 (2562 ci), introduced in production form direct fuel injection and automatic engine control. The BMW 802 continued development from what was learned on the 139, and was 3294 cubic inches, a German R-3350 of sorts. In any case BMW learned with Pratt, and went on from there. Russian engines were Wright based, and this was perhaps a better place for them to be long term.

The two engines that were the departure points for the companies in the USA were the Hornet and the Cyclone. Pratt went back to smaller cylinders and higher RPM around 1932, and the Curtiss Wright group went the other way and enlarged the Cyclone to 1820 ci. Wright got the better engine and the 1820 was in production for 25 years. Pratt and Whitney on the other hand learned the lessons of high speed twin row radials. The (smaller cylinder) bigger twin row Wrights were not trusted upon introduction (R-1510) until they went back to big 1820 cylinders, the R-2600, and then the R-3350 emerged and lasted many years. The Russian industry then had the both successful Wright designs available, the 1820 under production, the R-2600 lend lease and captured R-3350's to be copied by 1944. The russians (Soviets?) called Mikulin M-25 was an 1820 copy, the ASh-62 was 1812 ci and Cyclone based. The 82 was 2513 cubic inches and about 1850 hp. While it was a new engine, the education came from Wright experience. Direct fuel injection and engine control units were probably not considered during the wartime development of the engine. Interestingly the Wright radial probably was the best single engine of the early 30's period unfortunately causing what some say was a reliance on this product. Wright never made it in the jet age and P&W still is a household name. (depending on the household)

In any case, in wartime, just as in peacetime, a similar shape engine can be used to increase performance. (Allison 1710 to Merlin) Well in peacetime it is to lower costs...(Bristol Centaurus to R-3350), well that increases performance too...Unfortunately there aren't many 801's around, so the ASh sould work pretty well. The interesting thing for me is that the design philosophy of the ASh is from the enemy camp considering what hatched the 801! At 2500 cubes there is no comparable smaller diameter Pratt!

Joe

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