enginehistory.org

[lschilling]

Graham White notes that the C-47 was used for Hump missions. I have also seen references to "double blowers' used in C-47's. Are they referring to R-1830-88's with two stage two speed superchargers or 90C's with just two speed blowers which later were locked out?

[admin02]

According to Wikipedia, C-47Bs, powered by R-1830-90 engines with two-speed superchargers with better altitude performance, were used to cover the China-Burma-India routes; 3,364 were built

[lschilling]

So, now I wonder how many -88's were flying on C-47's and where? I think this engine had surging problems, so maybe they didn't last long in the fleet.

[avasko]

There were many R-1830 engine models with two-speed single stage superchargers. However, most C-47/R4D had single speed, single stage superchargers, typically the R-1830-92. The aircraft had no need to fly very high. When the need arose to fly the Hump picking their way through the Himalayas they had to go high and so engine models with two-speed single stage were fitted. Good description follows.

QUOTE from: This Day in Aviation
?The C-47B differed from the C-47A in that it was powered by Pratt & Whitney Twin Wasp S3C4-G (R-1830-90) engines. These engines were equipped with two-speed superchargers for improved high-altitude performance. Following World War II, the second speed (?high blower?) was either disabled or
remove[/i]d. Following this modification, the airplane was redesignated the C-47D?.

Not mentioned in the quote above was that -90 (no suffix) engines were redesignated as -90D. You can see the effect of disabling the high blower below:
R-1830-90 (two-speed) Normal Rating: 1,000-hp (746 kW) @ 12,500-ft, (3810 m)
R-1830-90D (single-speed) Normal Rating: 1,100-hp (820 kW) @ 6,100-ft (1859 m)
The -909D is the -90 with the high blower disabled.
.
The surging you mention was not in the single-stage engine, either one-speed or two-speed. It reportedly occurred in the two-stage models. These engines had the usual engine blower, a single speed 8.08:1 ratio version. An auxiliary stage was fitted, also engine driven, which had a two-speed blower (6.43:1 and 8.48:1 ratios) that fed the main engine blower. The gain is easy to see:
R-1830-76 Normal Rating: 1000-hp (746 kW) @ 19,000-ft (5,800 m)

The two-speed- two-stage engines, the -76 and -86, were fitted to many models of the F4F Wildcat fighters. The -78, also a two-speed two-stage engine was surprisingly fitted to the hulking Consolidated PB2Y-2 Coronado four engined flying bolt. giving it a surprising speed. Quote from USN Historical:
?Powered by R-1830-78 engines with two-stage superchargers, the PB2Y-2's armament was increased to six .50-caliber machine guns. Despite the increased weight, PB2Y-2s achieved a speed of 255 mph at 19,000 ft?.