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drive the compressors and a singlestage
free power turbine. It has selfcontained
lubrication with external
oil cooling system and oil tank.
Rotors
The Starflex semi-rigid main rotor
head is made from resin glass fibre,
laminated thrust bearings and selflubricating
bearings. The rotors,
which are made of glass-resin
laminate, go round clockwise when
viewed from above. Pitch variation
is achieved through distortion of
elastomer items. There is a vibration
dampening device in the centre of
the rotor head, which consists of a
weight oscillating between three
springs 120° apart.
A horn sounds when speed drops
below 360 RPM in the B1 (335 in
the B). The maximum RPM speed
for the rotor brake is 170 RPM in
heavy winds (140 in light), with at
least 5 minutes between actuations.
The swashplate is operated by three
mobile cylinder servo controls (two
lateral, one fore-and-aft) whose
piston rod is integral with the MGB.
Control movements are transmitted
to the starflex, which bends to
control rotor pitch.
One operating tip concerns
protecting the starflex when on
sloping ground. Once both skids are
down, centralise the cyclic, as the
machine will be going nowhere and
any strain is reflected in the starflex.
It doesn’t give you any immediate
benefit, but will be reflected in
maintenance costs.
Tail Rotors
Two-bladed, see-saw mounted on
the tail rotor gearbox. They rotate
anticlockwise as viewed from the
right, so are pushers. Be aware that
overstuffing the rear baggage
compartment can affect the controls
as they are routed just above the
compartment.
The extra bit of metal along the
trailing edges of the blades is just to
make the B model's tail rotors able
to work on the BA, B@, etc. (it
saves designing new ones). However,
164 The Helicopter Pilot’s Handbook
they must be checked for cracks
every 10 hours at the ends.
Rotor Brake
When the lever is forward, the rotor
brake is released. When applied, the
lever causes a diaphragm spring to
compress, which keeps the friction
linings under constant load.
Transmission
The main gearbox is attached to the
engine with a coupling shaft that has
a hydraulic pump drive pulley,
through which the shaft drives the
MGB input coupling. The shaft and
flexible coupling turn inside a flared
coupling tube. The gearbox has three
interchangeable modules – an
epicyclic reduction gear module with
five planet gears, a bevel reduction
gear module in two casings, and a
lubrication module attached to the
lower casing. There is a pressurised
lubrication system, with the bottom
of the casing used as an oil tank.
The transmission cannot move
vertically, so forces applied to it will
be transmitted to the fuselage, or go
back up to the head.
There is a two-piece drive shaft for
the tail rotor – the second shaft is
supported by five ball bearing
assemblies.
The tail rotor gearbox is splashlubricated.
The B1 and B2 have higher pedal
force, hence the hydraulic
accumulator on the tail rotors.
Hydraulics
The fluid must comply with AIR
3520 or Mil-H-83282. The total
volume is 3 litres. The rated
operating pressure is 40 bars, and is
the same for all machines, regardless
of gross weight. There is an
accumulator system for each jack to
provide acceptable loading if the
hydraulics fail, rather than providing
a second system which would add
weight and cost. The AS 350 and AS
355 (and Gazelle) suffer from a
condition known as “servo
transparency”, when the jacks may
stall under certain operating
conditions and leave you with frozen
cyclic and collective controls. The
conditions are supposed to be
extreme, but have also been
relatively benign, as when gently
flying round a fire at 4,000 feet ASL
on a warm day. In another example,
the machine was descending from a
mountain top at 110 kts with the
collective fully down and well below
gross weight. Windshear took the
speed up to 155 kts and it snapped
90° to the right. The cyclic froze
solid and both arms could not bring
it back. Although a nippy machine,
the AS 350 should be flown more as
a medium, that is, gently.
When the hydraulics fail, there is
greater force as speed is increased, as
the servos are directly connected
from the main rotors to the top of
the transmission casing. The
　
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本文鏈接地址：The Helicopter Pilot’s Handbook(107)