Intruccion as 355 (1) Power Point

7/29/2019 Intruccion as 355 (1) Power Point

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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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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 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 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 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 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 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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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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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 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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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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Distortion of the spherical thrust bearing allows the

sleeve to flap with the flexible arm.


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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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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 Frequency Adapters & the Spherical Thrust

Bearing absorb lead\lag forces by distortion.


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The Spherical Thrust Bearing

Absorbs centrifugal loads

Flapping distortions

Lead\lag distortions

Pitch change distortions


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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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Intruccion as 355 (1) Power Point

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