Design and development Wright R-3350 Duplex-Cyclone

wright r-3350 turbo-compound radial engine. 2 exhaust recovery turbines shown outside impellor casing area (top (silver) , lower (red blading)) geared crankshaft.

by 1943 ultimate development of new bomber program, boeing b-29 superfortress, flying. engines remained temperamental, , showed alarming tendency rear cylinders overheat, partially due minimal clearance between cylinder baffles , cowl. number of changes introduced superfortress production line in order provide more cooling @ low speeds, aircraft rushed operational use in pacific in 1944. proved unwise, b-29 tactics of maximum weights, when combined high temperatures of tropical airfields b-29s based, produced overheating problems not solved, , engines having additional tendency swallow own valves. because of high magnesium content in potentially combustible crankcase alloy, resulting engine fires — burning core temperature approaching 5,600 °f (3,100 °c) duplex cyclone s magnesium engine crankcase alloys — intense main spar burn through in seconds, resulting in catastrophic wing failure.

early versions of r-3350 had carburetors, though poorly designed elbow entrance supercharger led serious problems fuel/air distribution. near end of wwii, system changed use gasoline direct injection fuel injected directly combustion chamber. change improved engine reliability. after war engine redesigned , became favorite large aircraft, notably lockheed constellation , douglas dc-7.

following war turbo-compound system developed deliver better fuel efficiency. in these versions, 3 power-recovery turbines (prt) inserted exhaust piping of each group of 6 cylinders , geared engine crankshaft fluid couplings deliver more power. prts recovered 20 percent of exhaust energy (around 450 horsepower (340 kw) have otherwise been wasted, reduced engine reliability (mechanics tended call them parts recovery turbines, since increased exhaust heat meant return of old habit of engine eating exhaust valves). fuel burn prt-equipped aircraft same older pratt , whitney r-2800, while producing more useful horsepower. effective 15 october 1957 da-3/da-4 engine cost $88,200.

by point reliability had improved mean time between overhauls @ 3,500 hours , specific fuel consumption in order of 0.4 lb/hp/hour (243 g/kwh, giving 34% fuel efficiency). engines in use limited 52 inhg (180 kpa) manifold pressure, being 2,880 horsepower (2,150 kw) 100/130 octane fuel (or 100ll) instead of 59.5 inhg (201 kpa) , 3,400 horsepower (2,500 kw) possible 115/145, or better, octane fuels, no longer available since many formulations toxic.

several racers @ reno air races use r-3350s. modifications on one, rare bear, include nose case designed slow-turning prop, taken r-3350 used on lockheed l-1649 starliner, mated power section (crankcase, crank, pistons, , cylinders) taken r-3350 used on douglas dc-7. supercharger taken r-3350 used on lockheed ec-121 , engine fitted nitrous oxide injection. normal rated power of stock r-3350 2,800 horsepower (2,100 kw) @ 2,600 rpm , 45 inhg (150 kpa) of manifold pressure. these modifications, rare bear s engine produces 4,000 horsepower (3,000 kw) @ 3,200 rpm , 80 inhg (270 kpa) of manifold pressure , 4,500 horsepower (3,400 kw) nitrous oxide injection.