Vibration Analysis Flashcards
What are the two types of vibration
Describe them
Lateral and vertical
Lateral vibrations are caused by the main rotor being spanwise out of balance
Vertical vibrations are caused by a main rotor being out of track, sweep or having different flight characteristics
Which is done first lateral or vertical balancing
Lateral balance must be perfect prior to moving on to vertical balancing
What is the purpose of the spring mounting on the aircraft battery
The battery is attached to spring mounting and acts as a resonant vibrating mass to absorb vibration from the main rotor blades
It is mechanically tuned by adding or subtracting weights
When removing the CMRB from the retention is it considered normal for a loud bang to be heard?
Yes, hydraulic pressure from the removal kit overcomes the friction of the seating on the morse taper.
What is the technique used to torque the lead-lag pin?
Stretch torquing. More accurate.
. List the functions of the main rotor dampers.
Limit lead-lag travel, maintain smooth lead-lag operation and absorb blade shock on startup/ shutdown.
Under what circumstances would you carry out a main rotor damper check?
When the pilot feels a 1R vibe or excessive ground wallow
How to you check a main rotor damper.
Comparative maintenance between all blades by monitoring each gauge and lead/lagging the blade with the rotor break on.
Why are the tail rotor blades set to a positive angle, as opposed to 0.
A positive blade angle is to counter rotational torque from the Main rotor.
On the retention assembly which components are installed to keep the blades in a safe and neutral position?
Droop stops, Pitch lock.
In the operational checkout procedure for the flight control system there is a requirement for a azimuth phasing check. Why is this check carried out?
To ensure the azimuth was correctly installed and rigged.
What component in the flight control system allows for gyroscopic procession?
90 degree lag of the azimuth rods. (Tower rods)
Describe the construction of the CMRB.
Nickel leading edge and tip cap, Fiberglass composite spar with a nomex honeycomb core and graphite trailing edge.
What are the 2 conditions can the blade tracking system remove to improve the main rotor track and vibration?
One-per-rev and Split cone conditions.
The pilots sign the aircraft in with a 1R vibe. Upon inspection you find that B blade tracking motor is buried in the red. What action would you take.
Double check tracking motor authority, shorten the chordwise rod IAW pubs and re centre the tracking motors.
What is required for the blade tracking system to operate in automatic mode?
Weight off wheels
Name the tracking motors that operate when the pilot is trying to remove a split cone.
B & D.
. What blade tracking motors are used in auto mode?
C and d
What’s the difference between the collective damper assy and the collective bungee?
Damper = ensures slow operation of the collective downwards (and upwards) movement.
Bungee = Spring forces to counteract the centrifugal forces acting on the spanwise rods.
What are the locations for primary stops?
Cyclic = Base of the yoke
Collective = Cantered bulkhead
Directional controls = Pilots input crank
- What is the location of secondary stops?
Cyclic = Idler
Collective = Idler
Directional = Upper tunnel control pulley.
With the aircraft sat on the group running in idle, is it a fault if the collective starts to rise?
No, if it can be overcome by slight downwards pressure.
What components transfer the drive from the main rotor shaft to the azimuth assembly?
Spindle and spindle support.
What component stops the outer half of the azimuth from rotating?
Azimuth link
What are the four mechanical control inputs into the AFCS pack?
Lateral, Longitudinal, Directional and collective.
Does the FCC provide input into the flight controls via the AFCS servo actuators
Yes
Does the FCC receive inputs from the INS & GPS?
Yes
Is the FCC located in the LH nose door?
No rh side
W hat is the purpose of the collective friction brake?
To simulate desired “Feel” for the pilot.
Does the FCC have authority over the friction brake system?
Yes. (Alt hold disables it)
What’s the purpose of the AFCS actuator bobweight assembly
Counteracts flapback.
What is the purpose of the locking springs found in the AFCS pack Boost valve and AFCS actuators?
To return the system to a neutral position when boost is off and acts as a failsafe when hydraulics are lost.
What are the 3 modes of function of the AFCS actuator?
Manual, Boost and Auto.
Name the 2 controls the pilot can use to close the PRSOV and ECS and isolate bleed air from the aircon pack.
Emergency and ECS off.
- With the ECS acting in auto and the cabin temp was to increase, what would be the effect on the torque dual motor valve?
It would close bleed air and provide more conditioned, cold air.
Should the aft avionics compartment overheat, what indication would you see?
Boot temp high warning light
What components work to achieve a cabin temp set by the pilot on the ECS control panel?
Duct temp sensor, Cockpit zone temp sensor, Digital temp controller & dual torque motor valves.
In the event of ditching how would the helicopter stat afloat?
Float bags, Aux tanks & tail boom.
Describe what happens when the helicopter ditches in salt water?
When 2 salt water immersion sensors (One front and one back) are submerged in salt water float bags will deploy.
. Is it possible for the BAU to deploy with the floatation system?
Yes
When would this occur?
When float bags are in automatic mode.
When float bags are deployed, what releases the helium?
Cad’s
Name the different methods of releasing the cargo hook.
Electrically (Cyclic button), emergency jettison handle and externally.
What is the maximum load the cargo hook can carry?
4000lbs
Whats the maximum weight limitation?
Aircraft weight limitations are normally much lower.
What is the construction of the floor panels?
Aluminium sheet sandwiching aluminium foil honeycomb
Can the aircraft be jacked without the floor panels installed?
No
What is the aircraft fuselage construction?
Semi-monocoque, consisting of bulkheads, frames, strings etc.
What’s the purpose of the troop-seat energy absorber?
To reduce forces on personnel during crashes and reduce bodily harm.
How do the troop-seat energy absorbers work?
Wire forced through a bolt matrix causing friction.
What precaution needs to be taken when working around the W-struts?
Strut protective padding.
In general terms, what are the 2 main types of rotor induced vibration?
Later = Blade out of balance.
Vertical = Blades out of track.
What passive system is used to reduce 4R vibration?
Battery shock absorbers.
What principle does this system use?
Resonance
