"...On September 29, 1946, a Navy P2V1 Neptune named the “Truculent Turtle” left Perth, Australia and flew 11,236 miles unrefueled to Columbus, Ohio, a
record that stood until the Voyager flight around the world during the fall of 1986. The P2V1 was powered by two Wright R-3350 Cyclones. It is hard to believe
that a record-setting engine such as this had one of the most difficult developments of any aircraft engine ever to see production. This was largely due to an
extremely compressed schedule that tried to do in two years what ordinarily took five...".
"...When the Army requested proposals for a bomber capable of striking targets in Japan, all five bidders proposed the R-3350. The Army ultimately selected
the Boeing XB-29 Superfortress and the Consolidated XB-32 Dominator for production. Wright suddenly found itself with the largest and most important engine
program of the War. More than 30,000 engines would be required for the B-29 program, plus others for the B-32 and Navy. To further complicate issues, many
strategic materials such as mica and core sand were in short supply due to hostilities in India and Madagascar..."
From
enginehistory.org
"Actuarial Analysis of the operating life of B-29 aircraft engines", by O L Altman and C G Goor.
1) R-3350's were in critical supply in 1944 and the first half of 1945. Supply problems were easing around the end of the war.
2) Air transportation was used to fly R-3350's to the US for overhaul, at best 2 R-3350's would fit in a cargo plane.
3) Overhauled engines had around 10% lower "life" before the next overhaul.
4) The -23 was the carburettor and the -57 the fuel injected versions. The -23 was modified to improve reliability.
5) The statisticians noted the standard USAAF methodology for forecasting engine life was only suitable for a reasonably static population. Not where there was a steady arrival of more strength using new aircraft.
In terms of engine life, operations in India were the worst, since each combat sortie required three reasonably rapid climbs, India to China, China to Japan, China to India. Next came training in the US, finally the best were the units in the Marianas.
Expected life prior to first overhaul, early operations from India, 163 hours, -23 engines. Using modified -23 engines this had risen to 280 hours by February/March 1945 for aircraft operating from India and 304 hours from the Marianas.
The figures for B-29s used in training were 221 hours and 310 hours versus the 163 and 280 hours figures above.
Operating from India a comparison between the modified and unmodified -23 engines showed 80% of the unmodified and 95.3% of the modified engines survived to over 100 hours, 33.9 of the unmodified and 81.5% of the modified engines survived to over 200 hours, 0.2% of the unmodified and 47.3% of the modified engines survived to over 300 hours.
In the Marianas, as of 20 November 1944 the average hours on each -23 engine removed was 91, by 20 January 1945 it was 151, as of 30 April it was 234. These figures include removals for engine model changes, modifications, accidents and battle damage. They are also under estimates of the normal engine lifetime because so many of the engines were new. The figures include new and overhauled engines, so it is either the number of hours since the engine was built for new engines or since overhaul for the overhauled engines.
Engine hours before removal as of 31 May was 259 hours, and 31 July 272 hours. These figures are for engines removed because of mechanical problems only.
Even in July the steady number of new B-29s arriving drove down the average engine hours per removed engine.
A study as of 31 July 1945 noted in the Marianas the -23 engines 96.8% of new and 92.5% of overhauled logged more than 100 hours before replacement, 87.5% and 75.7% respectively logged over 200 hours, 62.7 and 43.4 logged over 300 hours, 19% and 8% logged over 400 hours, none logged over 500 hours.
As noted above the training schools in the US went through R-3350 engines quicker than the combat units in the Marianas, for example 57.9% and 36.4% logged over 300 hours, but once this mark was passed the engines in the US held up more, so 24.6% and 10.4% logged over 400 hours, and 1.2% and 0.2% managed over 500 hours.
The fuel injected -57 engine had a higher time between overhauls, so in the above study 31.2% used in training logged over 400 hours, and 4.9% logged over 500 hours.
