Helicopter Industry #103

HELICOPTER INDUSTRY I LEGACY I
TECHNOLOGY PUZZLE
In order to move forward quickly and cost-effectively, the
design office team makes the greatest possible use of
already existing sub-assemblies. The cell is that of an old
Dauphin previously transformed to give birth to the EC155
prototype. The rotor is also that of the EC155 prototype.
The main gearbox comes from an EC175. It receives two
additional lateral outputs for power transmission to the
propellers at the wingtips. «The transmission was direct, with
no maintenance bearings in the wing» explains Daniel Semioli.
«We carried out a lot of tests on the development of the drive
shafts, which had to meet the requirements of a super critical
shaft». The manufacturing of the propellers was entrusted
to the company MT Propeller, without of course, revealing
the very special use that would be made of them. In order to
go fast and reduce costs, Eurocopter wanted to use existing
propellers with shorter blades and modified twist. The reverse
motion of a propeller while hovering in flight, should allow
the tail to be balanced. The propeller manufacturer remains
perplexed by the requested specifications and explains to
his customer « We don’t know what kind of aircraft you have
but it will probably not work very well with the propellers you
are asking us for...». As far as the engines are concerned, the
TK team has set its sights on the two RTM322 turbines of
the NH90 prototype, whose speed is adapted to the needs of
the aircraft being prepared. The rear of the EC155’s airframe
is profoundly modified with the addition of a large fixed
double tailplane to stabilise the aircraft on the pitch and
yaw axis. The wing is fitted with flaps set to compensate for
asymmetric rotor wash. A «simplex» type autopilot is slipped
under the skin of the aircraft to ensure that everything
functions in harmony. «The most extraordinary thing is that
the X3 was remarkably stable, and it remained fully controllable
throughout the entire flight envelope without the auto-pilot,»
explains Hervé Jammayrac, pilot of the demonstrator.
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