Bell trailing-rotor and folding-rotor projects

hesham said:

Hi,

the Bell T-37 trailing-rotor project.
http://www.flightglobal.com/FlightPDFArchive/1965/1965%20-%200898.pdf

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Bell Trailing Rotor Project

INITIAL DETAILS HAVE BEEN RELEASED of a
Bell Helicopter V/STOL rescue aircraft
project submitted to the USAF. Designs
for other missions have also been submitted
to the US Army and the US Navy. As the
illustration opposite indicates, the Bell
project involves a fixed wing with thrust
turbojets and two rotors at the wingtips
arranged to fold rearwards into a fully
trailing position.
Wind tunnel tests have, say Bell, shown
that rotor drag during conversion is acceptable
and rotor behaviour excellent. In
helicopter flight the rotor axis is tilted
slightly forward and conventional collective
and cyclic pitch changes are applied in the
normal way. Rotor drive is by "off-set
shaft turbine" fed by the two General
Electric CF-700 turbofans under the wings.
The machine would make a helicopter
transition from the hover and, at between
90 and 170 m.p.h., the rotors would be
tilted slightly aft and function as undriven
autogyro rotors. All forward thrust would
be provided by the turbofans. Final
conversion would be by tilting the rotor
shaft progressively rearwards towards the
horizontal, at the same time reducing
collective pitch to a low-drag, windmilling
condition. Negative pitch finally reaches
90° and the blades would fold to trail
behind the nacelle. The reverse of this
process, again with the rotors freewheeling,
would be used to achieve first autogyro
flight and finally the powered hover. Bell
claim that low disc loading of the threeblade,
38ft diameter rotors would allow
effective autorotational landings in the event
of total power failure. The normal conversion
cycle would take 25sec.
The design proposed to the USAF would
carry a two-man crew and ten passengers,
or eight stretchers and an attendant or 15
troops. Gross weight would be 17,000lb,
maximum speed 523 m.p.h., and maximum
hover height 6,000ft in an ambient temperature
of 95°F. At overload gross weight, the
aircraft could make a conventional take-off
with rotors folded, and would then be
capable of a ferry range of over 2,500 miles.
Bell claim that the new design minimizes
vibration and rotor stress problems, offers
far higher speeds than presently available
for pure helicopters and makes particular
use of "advances in engine technology."
Supersonic speeds would be possible with
an appropriate airframe. Bell state that they
have conducted tests with other stoppable
rotor designs; and they are also at an
advanced stage in construction of the
tilting rotor XV-3.

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Triton said:

Summary of Design Studies and Results of Model Tests of the Folding-Proprotor Aircraft Concept by
JA DeTore and EL Brown, Bell Helicopter Textron Inc Fort Worth, July 1972

http://handle.dtic.mil/100.2/AD759534

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