Helicopter Components and Systems

Study Notes

Helicopter Components and Systems

Droop Compensator: More complex than a correlator, it's a mechanical link between the collective and the throttle.
Correlator: A mechanical linkage connecting the collective and throttle.
Vibration Cancelling Systems: Two types exist:
- Bifilar vibration absorber (using two 4-arm disks)
- Hub vibration absorber (using a weighted drum supported by three springs).
Force Trim System: Returns cyclic to its previous position using a gradient spring. If all controls have force trim, there are 4 gradient actuators (2 for cyclic, 1 for collective, and 1 for anti-torque).
Servo Flap: Located on the rotor blade trailing edge (75% of span). It improves aerodynamic airflow, reduces vibration, and eliminates hydraulic systems. It also allows for adjustable in-flight tracking and infinite life. Hydraulic force required for pitch changes is reduced (from 100 lbs to less).
Hydraulic System Procedure During Rigging: Turn off the hydraulics, bleed down any residual pressure (using hydraulic controls), rig collective first, then cyclic, then anti-torque. Ensure the throttle is rigged before connecting to the correlator. Fixed elevators are inverted airfoils (direct lift downwards).
Elevator Function: Maintains level flight, and moves with cyclic input to create a leveled flight attitude.
Moveable Weights: Part of a vibration dampening system.
Popout Float Aircrafts: Cannot take off or maintain flight directly from water. Flight sequence: ground, hover, then full control flight, then an autorotation test to ensure no over-torque during take-off.
Overspeed (Helicopter): Dangerous for the drivetrain. Caused by large, allowed centrifugal forces.
Chordwise Mass Balance Weights: Located on the leading edge of the blade; typically 35-55% of the span. They are installed by the manufacturer and cannot be adjusted.
Trim Tab: Located 75% along the span; moving it up or down affects the blade's height in the plane of rotation.

Rotor Blade Design and Modifications

Rotor Blade Tracking Weights: Adding forward weights makes the blade fly lower in the plane of rotation. Adding aft weights makes the blade fly higher in the rotation plane.
Trim Tab Function: Helps set blade angle of attack to control pitch and maintain level flight. Twists the blade, with higher angle of attack at the rotor root.

Helicopter Construction and Materials

Uniform vs. Tapered Rotor Blades: Manufacturers prefer uniform rotor blades because they can use the same rib and rib part numbers.
Single vs. Multiple Pockets in Rotors: Single pockets are cheaper to produce than multiple pockets. Bonded construction with no mechanical fasteners is favoured over drilling and bolting holes through bond lines to reduce the weakening of bonds.
Material Selection and Inspection: Common materials include metal, composites, and wood. Special inspections are required after autorotation and hard landings. Additional double plates might be added at the root or tip for increased strength.
Aerodynamic Considerations: Tapered blades accommodate the variation in speed along the span.