Post on 14-Apr-2018
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The AS355 - The Rear Structure
The rear structure consists of three frames connected by
beams.
The rear and forward frame support the engine.
The tail boom is bolted to junction frame no. three.( Not to be confused with the rear frame )
The Rear Structure
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The AS355 - The Rear Structure
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Circular frames covered by an outer skin.
Sheet metal stiffeners provide rigidity .
The horizontal stabilizer is attached between two reinforced
frames.
The AS355 - The Tail Boom
The Tail Boom
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The AS355 - The Tail Unit
1. The horizontal stabilizer
2. The upper vertical fin
3. The lower vertical fin
The horizontal stabilizer is
asymmetrical & set at a -2.5 degree
pitch angle.
The upper fin is also asymmetrical &
helps to offset torque reaction incruise
The lower fin is symmetrical and
helps to stabilize the yaw axis
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The horizontal stabilizer
slides through the opening
in the tail boom and is fixed
to the mounting points by
two bolts.
The step, located on the left
side only, serves to increase
the angle of attack on the
left horizontal airfoil . Byproducing more lift, and
drag, this airfoil helps to
bring the left skid down
during cruise flight.
The AS355 - The Horizontal Stabilizer
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The AS355 - The Tail Boom
The Tail Boom FenceDuring hover conditions, reduces the tail rotor workload by
5% (sea level conditions)
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The AS355 - The Tail Boom Fence
Main rotor airflow tends to come at
the tail boom from the left
The airflow accelerates along the
right hand side with causes a negative
pressure of approximately 1 millibar
per cubic centimeter squared
The addition of the fence causes the
airflow to stall. Because the airflow is
stalled, the pressure on the right side
is equal to ambient pressure.
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The AS355 - The Vertical Fins
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The AS355 - Ground Resonance
Ground Resonance
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The AS355 - Ground Resonance
A sympathetic vibration between the main rotor and the
landing gear during light ground contact flight conditions
that grows in amplitude.
the naturally occurring wobble in the main rotor is
transmitted to the airframe.
When the airframe touches the ground, the airframe bounces of
the ground at the same frequency as the main rotor.
The energy from the main rotor combines with the energy from the
ground bounce and the total energy increases with each rotation.
(in other words, the amplitude increases)
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The AS355 - Ground Resonance
The prevention of ground resonance requires that the manufacturer;
Prevents the airframe from wobbling and bouncing on the ground at
the same frequency as the main rotor,
and the energy that is transmitted from the ground bouncing landinggear be absorbed before it reaches the main rotor.
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The AS355 - Ground Resonance
The AS350 achieves the required results by the use of
The flexible steel strip which prevents the airframe from bouncing onthe ground at the same frequency as the main rotor,
and the shock absorber which absorbs the energy that can betransmitted to the main rotor.
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The AS355 - The Landing Gear
The Landing Gear
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The AS355 - The Landing Gear
The landing gear supports the aircraft, protects the structure on
landing, and dampens the vibrations on the ground when the rotor isturning.
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The AS355 - The Landing Gear
The landing gear is attached to the
bottom structure and on the body
structure bulkhead by the use of
clamps. Sandwiched between the
clamps are upper & lower elastomer
linings.
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The AS355 - The Shock Absorbers
During landing, or take-off, and when the gear is in light ground
contact, the shock absorber prevents the energy created by
ground bouncing from reaching the rotor head.
The average movement that is
absorbed by the shock
absorber, when light on the
skids, is about 1 to 2millimeters.
This is about 550 daN .
The forward shock absorber is mounted to the 15
degree forward bulkhead.
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The AS355 - The Shock Absorbers
The dampening rate is the main feature
of the shock. When the load is under
500 daN,
The piston travel is + or - 2 mm.
The speed of the piston is
approximately 35 mm per second
The frequency is 3.1 Hz.
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The AS355 - The Shock Absorbers
When the load isless than 550 daN,
dampening is
obtained by fluid
restriction
through thenormal restriction
orifice (No. 14).
When the load is greater than 550 daN, the over
pressure flexible washers ( No. 12 & 13) bend away &
greatly increase the passage of fluid volume.
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The AS355 - Anti Vibration Devices
Anti-Vibration Devices
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The AS355 - Anti Vibration Devices
There will always be vibrations created by the rotor head in flight.
These vibrations will invariably be transmitted to the airframe and
cabin.
Therefore, because the vibrations cant be eliminated some way of
attenuating the vibration must be developed.
The AS355 attenuates cabin vibrations through the use of a resonator
that is fixed to the bottom structure underneath the cabin floor.
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The AS355 - Anti Vibration Devices
The natural frequency of thevibration depends upon the
weight and elasticity of the
system.
Vibration can be described asa sort of
compression/expansion at a
constant rate.
The manufacturer , knowing thenatural vibration frequency of
the cabin, can use a resonator
to cancel the cabin vibration
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The AS355 - Anti Vibration Devices
A resonator could be
described as a weight thatdoes the shaking for the
component you dont want to
shake.
By attaching a weight of theright elasticity and mass, the
vibrations can pass through
the cabin without actually
shaking the cabin.
The resonator is constructed with materials that provide for the
correct elasticity and mass and will vibrate at the same
frequency of the rotor.
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The AS355 - The Cabin Resonators
The upper illustration shows
the vertical vibration without
resonators
The cabin resonators areattached under the forward
seats.
The effect of the resonator,
which is harmonized with the
rotor frequency, is to cancel
vibrations at the attachment
point.
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The AS355 - The Rotor Head Anti-Vibrator
Instead of allowing excitation
loads to pass through anything,
this resonator acts directly on
the source of the vibration.
The weight is held to its position
by three springs. The ball joint
that supports the weight also
guides the weight in the
horizontal plane.
The weight responds to
vibrations and excitations by
direct opposition. In this way, the
vibrations are absorbed.
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MAIN GEAR BOX
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The AS355 - Rotor Head
Three flexible arms form
the rotorheads basiccomponent & allow the
flapping action of the
blade to occur.
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The AS355 - Rotor Head
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The AS355 - Rotor Head
Distortion of the spherical thrust bearing allows the
sleeve to flap with the flexible arm.
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The AS355 - Rotor Head
All of the
centrifugal &
torsion forces are
transmitted to the
head by the sleeves.The Spherical
Thrust Bearings&
the Frequency
Adaptersprovide
the flexible links for
these forces.
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The AS355 - Rotor Head
All of the rotational forces caused by a pitch
change occur through the spherical bearings.
The flexible arm does NOT rotate on the pitch axis
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The AS355 - Rotor Head
The Frequency Adapters & the Spherical Thrust
Bearing absorb lead\lag forces by distortion.
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The AS355 - Rotor Head
The Spherical Thrust Bearing
Absorbs centrifugal loads
Flapping distortions
Lead\lag distortions
Pitch change distortions
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The AS355 - Rotor Head
If the spherical bearing malfunctioned and
the normal distortions it undergoes were not
to happen, the flight safety of the aircraftwould be seriously compromised
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HYD
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ENGINE OIL SYSTEM
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FUEL SYSTEM
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FUEL TRANSFER
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The AS355 The Fuel System
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The AS355- The Fuel System
If the filter continues
to clog, the bypass
valve will open.
This occurs when thedifferential pressure
is 350 millibars
(+ or - 50 millibars)
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ELECTRICAL SYSTEM
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DC
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AC
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FIRE DETECTORS
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