Chapter 12. Main Rotor. Flashcards
Learn about the Main Rotor installed on the S76D
What is the function of the bifilar vibration absorber?
The bifilar vibration absorber on top of the
main rotor hub absorbs 3-per rev vibrations
prior to their transfer to the airframe.
How is the spindle assembly color coded?
The spindle assembles are color-coded and
numbered in the following counterclockwise
sequence:
• Number 1—Red
• Number 2—Blue
• Number 3—Yellow
• Number 4—Black
The red spindle assembly is always closest to
the rotating scissors
How is the elastomeric bearings lubricated?
The elastomeric bearings are simple and reliable.
They require no lubrication.
What is the function of the flap restrainer?
Each blade has a flap restrainer on its spindle
assemble next to the hub (Figure 12-8).
These spring-loaded cams prevent the blades from
flapping excessively when the rotor is slowing
down or stopped.
At what Nr value will the flap restrainers engage or disengage?
When the main rotor accelerates past approximately
35% NR, centrifugal force pulls the flap
restrainers out to permit blade flapping.
When the rotor decelerates below approximately
35% NR, spring returns the flap
restrainers to the flap-limiting position
What is the function of the droop stops?
The droop stops limit droop of the blades when they are at rest or rotating slowly.
At what Nr value will the droop stops engage or disengage?
When the main rotor head rotational
speed increases to about 55% NR, centrifugal
force swings the weighted cams out, allowing
increased vertical movement of the main blades.
The droops stops engage at about 45% Nr
What constitutes the swash plates?
The swash plate consists of a stationary
and a rotating disc joined by bearings. A
spherical bearing supports it
What is the function of the pitch control rods (PCR)
The PCRs transmit all movement of the flight controls from the swashplate to the main rotor blades.
Each PCR is adjustable
What is the function of the blade damper on the ground and in the air?
When the main rotor is started or stopped, the dampers absorb the shock of the blade movement. The dampers
also control hunting of the blades.
The primary restrictive function of the dampers
is on the ground in starting and stopping. In
flight, when sudden movements of the blades
occur with great force, relief valves in the
piston open in opposite directions to permit
movement of the piston.
What type of vibration does the bifilar tune out?
The bifilar tunes out 3-per-rev
vibrations.
Where are the Nr speed sensors located?
The two NR speed sensors are mounted on the
rear cover of the main gearbox
What causes the ROTOR SPEED LOW warning to illuminate?
A ROTOR SPEED LOW warning alerts the pilot
on the MFD and PFD if NR drops below 91%.
An audio announcement of “ROTOR SPEED
LOW” also sounds in the headset
This signal is disabled when weight is on the
wheels (WOW switch on both landing gear)
How many accelerometers does the AVC use in acquiring measurements?
The active vibration control (AVC) computer
in the electrical compartment acquires measurements
of the vibrations throughout the
helicopter with 10 airframe accelerometers:
seven vertical and three lateral
It also measures the rotational speed of the
main rotor with one of two high-resolution
tachometer (NR) sensors.
What powers the AVC
The AC PRI bus
electrically power the AVC system.
