Design
The resulting design used 9 banks of 4 cylinders arranged around a central crankshaft with each cylinder bank at a 40° angle to each adjacent bank, to form a four-row radial engine. Unlike most multi-row radials, which "spiral" the cylinders to allow cooling air to reach them, the R-7755 was water-cooled, and so each of the cylinder heads in a cylinder bank were in-line within a cooling jacket. Contrast this with the 24-cylinder Junkers Jumo 222, which looked similar from the outside, as both engines used banks of four cylinders each, but ran on a V-style cycle instead of a radial and only used six banks of cylinders. The XR-7755 was 10 ft (3 m) long, 5 ft (1.5 m) in diameter, and weighed 6,050 lb (2,740 kg). At full power it was to produce 5,000 hp (3,700 kW) at 2,600 rpm, maintaining that with a turbocharger to a critical altitude that was apparently never published.
Each cylinder bank had a single overhead cam powering the poppet valves. The camshaft included two sets of cams, one for full takeoff power, and another for economical cruise. The pilot could select between the two settings, which would shift the camshaft along its axis to bring the other set of cams over the valve stems. Interestingly, the design mounted some of the accessories on the "front side" of the camshafts, namely two magnetos and four distributors. The seventh camshaft was not used in this fashion, its location on the front of the engine was used to feed oil to the propeller reduction gearing.
The original XR-7755-1 design drove a single propeller, but even on the largest aircraft the propeller needed to absorb the power would have been ridiculously large. This led to a minor redesign that produced the XR-7755-3, using a new propeller gearing system driving a set of coaxial shafts to power a set of contra-rotating propellers. The propeller reduction gearing also had two speed settings to allow for a greater range of operating power than adjustable props alone could deliver. Another minor modification resulted in the XR-7755-5, the only change being the replacement of carburetors with a new fuel injection system.
Read more about this topic: Lycoming XR-7755
Other articles related to "design, designs":
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... For more design details, see Boeing 747-400, 747-8, and 747SP ... The Boeing 747 is a large, wide-body (two-aisle) airliner with four wing-mounted engines ...
Famous quotes containing the word design:
“I always consider the settlement of America with reverence and wonder, as the opening of a grand scene and design in providence, for the illumination of the ignorant and the emancipation of the slavish part of mankind all over the earth.”
—John Adams (1735–1826)
“The reason American cars don’t sell anymore is that they have forgotten how to design the American Dream. What does it matter if you buy a car today or six months from now, because cars are not beautiful. That’s why the American auto industry is in trouble: no design, no desire.”
—Karl Lagerfeld (b. 1938)
“To nourish children and raise them against odds is in any time, any place, more valuable than to fix bolts in cars or design nuclear weapons.”
—Marilyn French (20th century)