Tail Rotor Flashcards
Blade Composition
Composites - carbon, Kevlar, etc.
Construction of the Blades
- longitudinal glass roving spar clamped between 2 elastomeric half-shell bearings
- foam core (with a cavity in the twisting area for the free spar to distort)
- glass fabric skin at +/-45deg (2 layers)
- assembly is molded then hot cured
Length
6.1 feet
Weight
10.14 lbs
Chord
7.3 inches
Airfoil
Symmetric NACA 00.12 airfoil
Spar pre-set twist
10 degrees
Main TR component
- Glass-resin roving spar on which the 2 blades are molded.
- clamped at its center between 2 half shells
- one of the shells has a hole for seesaw-mounting the blade assembly on the rotor shaft hub yoke
How is the spar flexible?
- Thrust (Ty) direction - absorbs the thrust-induced bending loads
- Torsionally flexible over central portion - acts as the pitch change hinge (thrust control)
What does the seesaw mounting do?
Performs flapping function
- blade pivots about the seesaw bolt
- balances every half revolution
- advancing blade lifts above rotation plane and retreating blade drops below
What serves as the pitch/flapping coupling?
The K Link
What component compensates for dissymmetry of lift?
The K Link
How does the K Link work?
The blade horn is offset from the seesaw (flapping) axis, flapping and pitch will couple with each other
- angular offset causes the blade pitch to feather as it flaps
In which ways are the 2 laminated half-bearings flexible?
Stiff in compression
Flexible (deform) in torsion and shear
What’s the purpose of the2 laminated half-bearings?
- pickup the loads as a result of the spar bending
- limit the coning angle
What’s the composition of the 2 laminated half-bearings?
nature rubber/metal bearings
What’s the purpose of the Boss Weights?
- generates a moment counteracting the zero pitch return moment of the blades so that the airfoil is stabilized at all pitch angles
- reduces the pitch control loads
*useful in case of failure of TR servocontrol
What caused the laminated half-shell bearing AD?
Initially, the H125 had larger Boss Weights installed
- they caused premature failure of the laminated half-shell bearings
TR Control System
Pedals
Rocker arm
Rod
Bellcrank
Flexible ball-type sliding control
Servo actuator
Input rod to bellcrank (5 guide bearings)
Control Bellcrank (transmits pedal input to the Pitch Change Spider)
Servo System
Single Cylinder, Hydraulic Servo
Purpose of the Yaw Load Compensator
Assists the pilot with TR Control during a loss of hydraulic pressure
- favors right pedal
- depressurized using the “ACCU TST” button for emergency situations or post-flight procedures
Complete Loss of TR Thrust Symptoms
Left yaw - based on amount of power and forward airspeed at the time
Complete Loss of TR Control
Single Hydraulic Configuration
- Cyclic & Collective - Adjust, 70kts in level flight
- HYD TEST or ACCU TST - ON, load compensator depressurizes
After 5 seconds … - HYD TEST or ACCU TST - RESET to OFF position
Perform running landing
Complete Loss of TR Control
Dual Hydraulic Configuration
- Cyclic & Collective - Adjust, 70kts in level flight
- Hydraulic cut-off switch (on collective pitch) - OFF
- HYD TEST or Pre MOD 07.4719 ACCU TST - ON (load compensator depressurizes
Post MOD:
3. ACCU TST - PRESS for 2 seconds (load compensator depressurizes
Perform running landing
