Helicopters

  • Created by: stonesy71
  • Created on: 06-11-19 10:23

helicopters

Components of a typical transmission

  • Freewheel unit

  • MRGB

  • IGB

  • TRGB

  • Driveshaft’s

 

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helicopter

Three types of Rotor head

  • Rigid – Mechanically simple, operating loads absorbed in bending rather than hinging. Can’t flap, lead or lag but can be feathered.

  • Semi-rigid – Two movements, flapping and feathering, two blades which are rigidly attached to rotor hub. Allows for blades to flap together or seesaw.

  • Fully articulated – three or more blades. Flap, feather, lead or lag independently of each other.

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Phase lag/gyroscope precession

Resultant action or deflection of a spinning object when a force is applied to this object. This action occurs approximately 90 degrees in the direction of rotation from the point where the force is applied. It is overcome using advance angle

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heli- lateral shift


  • Tail rotors are used to counteract torque of main rotor. Thrust generated by the tail rotor will drift the helicopter in the direction of the tail thrust. To overcome this the main rotor mast can be offset in the opposite direction to the drift or the cyclic controls can be rigged to neutral in the opposite direction.

     


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heli- ground resonance

  • A vibration of large amplitude resulting from a forced or self-induced vibration of a helicopter in contact with the ground. Rotor blades out of phase and unbalanced. Fully articulated head only – lead and lag helps sync the blades. MORE ANSWER REQUIRED


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heli- hazards to personnel

 

Downwash

  • Blade sale

  • Tail rotor

  • Approaching a/c

  • Static discharge

 

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heli-Vibration monitoring systems

Rotor Tune

Rotor track and balance is the process of smoothing vibrations in the airframe, which are caused by the main and tail rotor. Vertical and lateral vibrations are created. Vertical – unequal lift. Lateral – unequal distribution of mass or track.

HUMS

Variety of on board sensors and data acquisition systems.  Hums is used to monitor;

  • Rotor track and balance
  • Limit exceedance monitoring
  • Transmission monitoring
  • Engine and structure monitoring
  • FDR and CVR 

    Benefits are as follows;

  • Data gathering for future maintenance policy
  • Reduced the requirement for track and balance sorties
  • Reduced vibration levels
  • Improved fault diagnosis.
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heli-State the 4 ways to delay surge


  • Change the Duct Characteristics (Move the Running Line)#
  • Blow Off Valve – Rear of the compressor, Duct Characteristic, Bleeds off Volume of air.
  • Variable Nozzle – Reduces pressure in combustion chamber (Opens Nozzle)
  • Chang the Compressor Characteristics (Move the Surge Line);
    VIGVs – Changes AoA for airflow to 2-4 degrees. Improves efficiency.

    Multispooning – Keeps each compressor at 8:1, and can go at different speeds.


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What are 4 turbine material reqs - heli


  • Creep resistance

  • Thermal shock

  • High fatigue strength

  • Cost effective

  • Corrosion resilience


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heli-Name 2 fuel additives and what is

their purpose?


  • FSII – Fuel System Icing Inhibitor – AL41- to prevent the water forming in the fuel

  • Lubricity improvement additive – AL61 – Lubricates the fuel system which helps prevent corrosion

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heli - 4 parameters do the fuel system ctrl?

  • Barometric Control Unit – Keeps the stoichiometric value at 15:1

  • Power Limit – when the engine is trying to work too hard, if pressure in the engine is too extreme

  • TBT Limiter – turbine blade temperature

  • Acceleration Control Unit – Keeps below the surge line

  • Rotation NL & NH – Stop overspeed of Spools

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heli-State Bernoulli’s formula

Dynamic + Static = Total pressure

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heli- purpose of APU and the services

it provides?

The APU starts the main engines on the ground and provides services of the following without the engines on:

  • Pneumatics

  • Hydraulics

  • Electrics

  • Enviromental Control Systems

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heli- describe the fuselage boundary layer

and why it is undesirable?

  • less efficient of compressor

  • Non uniform flow

  • Slow moving turbulent air flow with low energy

  • Could cause stall & surge

  • Reduce performance

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heli-Describe the air spray burner

  • Less smoke

  • Operates well over a wide range of fuel flows

  • System runs at low pressures

  • Lighter gear fuel pumps

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heli-Why do we Lubricate

  • Cooling

  • Corrosion prevention

  • Reduces debris

  • Separates the contact surfaces

  • Lowers friction

  • Reduces wear

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Why are helicopter rotor speeds controlled

with in tight limits:?

Overspeed

  • Prevents tips from going supersonic

  • Excessive stress on pins and blade housing

  • Suffers more drag

Underspeed

  • Blades cone up – Lose lift

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heli- draw and label 4 engines

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heli - draw 2 combustion chambers

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