This is a very
unique and little known bit of info from the company that brought such infamous
ships as the “BlackHawk” and the “Super Stallion”. The ABC was a
concept craft built to compete as the RAH-66 program, in part due to its unique
rotor design. Its very hard to find actual photos of this ship. In later years,
Sikorsky also built an S-76 ship (for those of you familiar) that was front/rear
cockpit design. A drastic deviation from the side by side design of the
original. The pilot sat in front and dropped down a bit from the rear allowing
the “backseater’ to have the same field of view. This ship is all but
impossible to find, since Sikorsky only showed this in a company calendar.
“Advancing Blade Concept (ABC)
was a serious contender for the
RAH-66.
However, the transmission weight penalties were too high and so the trade study
decided that the advantages were outweighed (no pun intended although I will
gladly
take credit for it) by the weight disadvantage. In a zero sum game, weight for
the
ABC xmsn would come out of avionics or armor. ABC is in mothballs as it
outlived
the design life of a number of critical components. All who flew it were
impressed
with its capability. We had also envisioned using it in conjunction with a
pusher prop
ala the Cheyene. The Helix is a form of ABC being coaxial but you can see
by the
mast its not weight or design efficient. As we put more effort into
conventional rotors
they get better and lighter. Its going to take a lot of money to catch up
the ABC given
the lack of work in the last 20 years.”---unknown
"The ABC had independent
control for each disk, and very stiff blades (over 25% hinge offset) so tip
clearance was not as big an issue as it is on other co-axials. This meant that
the swashplates could be tilted to wash out lift on the retreating sides, but
keeping it up on the advancing side. The mast was very strong, so the moment
battle between the rotors (one "leaning" to the right, one to the
left) was cancelled at the transmission. This let the rotors blast on out to
high speed, and just as importantly, let the ABC develop very high load factor.
It pulled 2.5 G's at 25,000 feet and cruised at over 250 mph, as the thrust
engines pushed it along in autorotation (it was an autogyro at high speed!) Not
too shabby. Of course the speed was driven by two jets that ate gas like there
was no tomorrow, so the speed was really only good for short bursts. In a
production configuration, the lift engines would drive the prop shafts, so the
cruise efficiency would be much better. One really unique benefit of the ABC was
the purity of the controls. The high offset made the aircraft snap to pitch and
roll commands like a fighter, but with no cross coupling like the Boelkow
family. The couplings were generated by each rotor, of course, but the rotors
developed them in opposite directions so they cancelled at the head, and the
pilot was left with a very crisp clean feel.
I flew it to about 250 MPH and
was really impressed." ~ Nick Lappos, PPRuNe, August 27, 2001
There are
certain circles that say the XH-59A competed against the XV-15. which went on to
become the V-22. The design nature automatically suggests that this wasn’t
true. That the XH-59A was more in line with a fast attack helicopter. The
confusion comes into play when Sikorsky submitted it’s “X-wing” design
that was supposed to compete with the now Osprey. This site, courtesy of Dryden/Nasa
explains the program, http://www.dfrc.nasa.gov/Gallery/Photo/X-Wing/HTML/index.html.
Erik
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