"Frank Stutzman" wrote in message
...
Bill Daniels wrote:
The prototype Hercules used 8 Pratt and Whitney R-4360 of 3500 HP each -
the
wrong engines. The 5000 - 7000 HP Lycoming XR7755, then under
development,
was the intended engine. The Convair B-36 and the Northrop B-35 were
also
supposed to use the R7755. See:
http://www.aviation-history.com/engines/xr-7755.html
With a total of 56,000 HP instead of "just" 28,000 the "Spruce Goose"
would
have been a outstanding success - don't blame the failure on the
airframe.
Well, maybe.
According to the website you referanced the R7755 burned 580 gallons per
hour at 5,000 HP. For the Goose that would mean 8*580= 4,640 gallons an
hour or 27,840 pounds an hour. Nothing like burning 13 TONS of fuel an
hour!
However, according to http://www.sprucegoose.org/Specification.htm, the
Goose had a payload of 65 tons (130,000 pounds). It also says that the
cruise speed was supposed to be 175 mph. Lets we were going to fly it
from San Francisco to Honolulu (which seems to me to be a reasonable
mission). We've got a fair tail wind and we are going to get 200 mph
groundspeed. We are going to throttle back to 6 tons an hour. Thats a
2400 mile flight that will take 12 hours and burn 72 tons of fuel. Looks
to me like we were going to need fuel about a hour before we got to
Hawaii.
Now maybe the "payload" number on the sprucegoose website is after full
fuel. Maybe the R7755 were lighter than the R4360. It certainly seems to
me that it was doubtful that the goose could have had met its intended
use.
It's interesting to speculate how these huge aircraft would have
performed
with the enormous Liquid cooled Lycoming.
Indeed.
--
Frank Stutzman
Bonanza N494B "Hula Girl"
Hood River, OR
I suspect the 580 GPH is a gross error. Assuming a Specific Fuel
Consumption of 0.42 Lbs./HP/Hr., The R7755 would have "only" used 2100
pounds per hour at 5000 HP output. Assuming 70% power at cruise the fuel
consumption drops to 1470 PPH.
If the engine had been developed to put out 7000 HP and the SFC came in at
0.40, the 70% cruise fuel burn would have been 1,960 PPH. All eight
engines would burn 15,680 PPH or "only" 7.84 Tons per hour.
Given the liquid cooling, variable cam timing and gear box the SFC might
have been even lower.
Bill Daniels