From: Nick Lappos <nlapposNOSPAM@miami.gdi.net>
Subject: Re: Red lines (Sikorsky history time)
Date: 15 Jul 1999
George and Bob,
Great trip down memory lane on the Sikorsky models, let me
toss in my 2cents:
"I wonder what possessed Sikorsky to locate the engine as
they did on these models (S-55, S-58), when both earlier and
later models had conventional engine locations? Any insights
The first turbine helo was the S-59, which flew in 1959 or
so. Before then, the recips were the only game in town for
the entire family of helos prior the S-61 (the H-3).
For turbine helos, the engine weighs about 4 to 8 % of the
gross weight, and so we can park it almost anywhere, as long
as the output shaft lines up with the transmission nicely.
A recip weighs about twice as much for the same power, and
consumes 8 to 16% of the gross weight. Like a big gorilla,
we worry about where a recip will sleep, since the aircraft
must balance with full load and also empty.
For the S-55, with the engine in the nose and the pilots
high above it, try to picture how you'd package the aircraft
otherwise. The engine on a Bell 47 is stacked below the
transmission, and both are right behind the pilot/passenger
area. If you want to pack a big heavy engine, and also have
10 or so passengers, putting the engine on a slant below the
pilots and forward of the cabin, with the shaft feeding the
main gearbox above the cabin allows you to package all the
weights, including passengers, close under the rotor center.
This allows more freedom for loading/CG control, and allows
the engine mounts to fasten directly next to the landing
gear mounts for structural simplicity.
For the S-56 and the S-60 (pre Skycrane recip demonstrator),
with two engines, it was simpler to place them alongside the
None of these aircraft was a candidate for a turbine because
the turboshaft was not yet fully developed. The only other
big helicopters of the 50's were the Mil models that looked
much like the Sikorskys.
Here's a funny tale about the S-60, as told to me by the
test pilots who flew this mission (Jack Peterson and Jim
Kay). Igor Sikorsky had a platform built to carry below the
S-60 and placed 4 seats with seat belts on it. He "invited"
the key department managers of his company to fly below the
helicopter on this platform. For Igor this was a piece of
cake, after all he flew everything you could imagine since
1910. For the managers it was a bit more of an adventure!
Jim Kay told me that he looked back to see how the platform
was riding as they leveled off at 1500 feet, and he
said'Jack, don't get too frisky on the controls."
Jack asked him if the platform was swinging, and Jim said,
"No, but the old man is out of his seat and walking around!"
They said that Igor was the bravest guy they had ever seen,
as he walked up to the edge of the platform, gripped the
support wire and leaned over to look down at the ground. I
get goose bumps thinking about it!