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Re: Pratt vs. Wright Axis vs. Allies

Posted by Larry Kraus on Sat Sep 20, 2003 05:06:30 PM

In reply top Pratt vs. Wright Axis vs. Allies posted by Joe Scheil on Sat Sep 20, 2003 10:44:16 AM

: Longwinded Irony....
:
: Kind of an interesting subject, as BMW built the Pratt Hor
: net for 10 years as the BMW 132. This was the first "big
: nine" for German industry, and based on this engine BMW bu
: ilt the 139. This was a twin 9 built on a common crankcas
: e, a double Hornet as it was. The engine seemed to come o
: ut at the same time as the actual Twin Hornet, the R-2180,
: a 14 cyl radial, but as a big "18" was unsuccesful. It w
: ould be interesting to know how late Pratt&Whitney worked
: with BMW as the war began to heat up....This engine powere
: d prototypes of the FW-190 and Do-217, but had a better de
: velopmental stablemate. The more promising engine that re
: sulted 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 developme
: nt from what was learned on the 139, and was 3294 cubic in
: ches, a German R-3350 of sorts. In any case BMW learned w
: ith Pratt, and went on from there. Russian engines were W
: right based, and this was perhaps a better place for them
: to be long term.
:
: The two engines that were the departure points for the com
: panies 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 enlar
: ged the Cyclone to 1820 ci. Wright got the better engine
: and the 1820 was in production for 25 years. Pratt and Wh
: itney 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 in
: dustry then had the both successful Wright designs availab
: le, the 1820 under production, the R-2600 lend lease and c
: aptured R-3350's to be copied by 1944. The russians (Sovi
: ets?) 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 educati
: on 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 e
: arly 30's period unfortunately causing what some say was a
: reliance on this product. Wright never made it in the je
: t age and P&W still is a household name. (depending on th
: e household)
:
: In any case, in wartime, just as in peacetime, a similar s
: hape 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 perfor
: mance 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 th
: e enemy camp considering what hatched the 801! At 2500 cu
: bes there is no comparable smaller diameter Pratt!
:
: Joe


Very interesting and informative.As you say the R3350 has indeed lasted many years.On the Moses Lake ramp right now sits Tanker 05 which is a P2V-5 with two R3350-36's and Tanker 62,a DC-7 with one R3350-EA1 that has been converted to a DA,one R3350-34 from a Navy Connie,and two -93's from Air Force Connies.These are all Turbo-Compound models.With 100/130 fuel instead of 115/145 they are de-rated from 3250 h.p. on the DC-7 (3450h.p. for EA engines on DC-7C's)and near 3700h.p. wet power on the P2V,to 2880 h.p. We are also restricted to low blower and no spark advance,although we still use 10% lean at lower cruise power settings.On the DC-7 we use 50"h.g. or 234 BMEP and 2900r.p.m. as a take-off power setting.Usually we don't get close to the BMEP limit and are closer to 2750h.p. than 2880 using 100LL fuel.Interestingly we had a 100LL sample lab tested a few days ago that the octane/performance rating was 115.2,so it isn't quite as bad a fuel as I had thought.
As to R-1820's there is a world of difference between the -97 on the B-17 and the -80B on the R4D-8/C-117D.The later -80 cylinders look like they came from a 3350,while the much older -97 are far less robust.The -80 was rated at 1475h.p.(using 100/130)at 54 1/2"h.g. and 2700r.p.m. and the -97 was 1200h.p.(using turbos)at 46" and 2500r.p.m.

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