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o n the W r i g h t t u r b o - c o m p o u n d engine, the most highly developed aircooled radial. 46 F igure 4 1.—Pratt & W hitney
W asp air-cooled radial engine,
1 9 2 6 ; 4 25 hp at 1900 r p m , 6 5 0
l b. T he first such United States
e ngine of over 4 0 0 hp to go
i nto general service, it pioneered many technical features
w hich became standard practice for this type. Cylinder
d esign was similar to that of
t he Wright J-5 (fig. 36e) except
t hat rocker-arm supports and
h ousing were cast
w ith the cylinder h ead—an
i m p o r t a n t innovation.
A-3087) F igure 4 2.—Forged a l u m i n u m crankcase of
P ratt & Whitney Wasp engine. Left, complete
c rankcase. Right, forging of one half before
m a c h i n i n g . (Photo
A-3105) F igure 4 3.—Divided c rankshaft, from Pratt &
W hitney Wasp engine. The Gnome (see f i g . 20)
p ioneered this design for radial aircraft engines. (Photo
A-3106) 47 F igure 4 4.—Pratt & W htney
D ouble Wasp R - 2 8 0 0 - C B - 1 6
1 8-cylinder a ir-cooled
r adial engine, 1 9 4 6 ; 2 8 0 0 hp
a t 2800 r p m , 2 3 2 7 lb. Earlier
m odels were extensively used
i n World War I I , and t h i s model
w as widely used in commercial
a nd military aircraft.
A-3103) F igure 4 5.—Pratt & W hitney Wasp Major R -4360 2 8-cylinder 4 -row radial engine, 1948 (cutaway);
3 5 0 0 hp at 2 9 0 0 r p m , 3842 lb. A post-World War II military and commercial engine. (Photo A-4132) 48 Figure 46.—Wright Cyclone R-1820
1 425-hp9-cylinderengine, 1953. When
t his engine first came into use in 1933,
it was rated at 525 hp at 1900 rpm. It
was used in the Douglas DC-3 and
Boeing B-17, among others. (Photo
A-3090) Figure 47.—Wright Turbo-Cyclone R-3350 18-cylinder 2-row radial engine, 1955 (cutaway); 3700
hp at 2900 rpm, about 3000 lb. This post-war engine had three exhaust-driven turbines geared to
the crankshaft, and it was the latest and most highly developed piston type to be widely used in
large military and commercial airplanes. (Photo A-3089) i
rV> .JH m T he following comparison illustrates the development of air-cooled
engines from 1922 t o the present time:
Engine . .
.,..'.'. Lawrance J - l
Number of cylinders
Bore and stroke, in
R pm . .
Brake mean effective pressure,
psi . .
Mean piston speed, ft/min . . .
H p per sq in. piston area . . ... .
Weight, lb, per hp, dry (without oil and oil radiators) . .
As had been true of liquid-cooled engines, improvements in fuels, s upercharging, and cooling systems as well as great improvements in detail
design, were important factors in this development.
T he subject of the air-cooled engine should not be left without mention
of the remarkable development of the light-airplane engine, beginning
w ith the small British 4-cylinder v ertical Cirrus and DeHavilland Gypsy
engines of 1927, and of the 4-cylinder Continental A-40 (fig. 48). Introduced in 1931, this 38-h...
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