Ch 9- Tail Rotors Flashcards
Why do we need Tail Rotors?
Allow pilot to compensate for torque and gives directional control
What methods are used to counter-act Newtons 3rd law in regards to a helicopters main rotor? (7)
What is the most common?
- Coaxial main rotors
- Tandem rotors
- rotors located side by side
- Intermeshing main rotors
- Tail rotor (anti-torque rotor)
- NOTAR
- Fenestron or Ducted Fan
Benefit of Fenestron?
Unequally placed 10 blades and Starter for noise suppression
What is the NOTAR system?
NOTAR (no tail rotor) system consists of an enclosed articulated fan driven by the main transmission, a circulation control tail boom, direct-jet thruster, and vertical stabilizers. Low pressure air, forced through 2 slots on the tail boom, causes the main rotor downwash to “hug” the contour of the boom, creating lateral lift that counteracts main rotor torque.
Tail rotors are required for ___ main rotor helicopters, don’t have ___, must have the ability to ____, used for _____, and must have ___ & ___ pitch ability for __________.
- single
- lead-lag system
- pitch change: Positive and Negative
- directional control (movement around the YAW axis)
- negative, positive,
- directional Control an autorotation
T/R system consists of?
- T/R driveshafts
- T/R gearboxes
- T/R blades
- pitch change mechanisms
What does a misaligned driveshaft cause?
And improper shimming cause?
High vibrations
Tail Rotor gearbox (Bell 47) major components
- gearbox housing
- input sleeve
- output shaft and front cap
- pitch change mechanism
206 has a ____ (same as flexible coupling)
Thomas coupling
Intermediate gearbox job
Change direction of shafting. ONLY changes direction NOT rpm
MD500E tail rotor system does not require tracking but requires ____
Static/dynamic balancing
Advantage of NOTOR
Quieter and safer
Where are Datum holes located and what are their purpose?
- long shaft
- if can’t see through them then it means the shaft has been twisted
AS350 short shaft is steel, why?
Because it is located under the engine therefore getting a lot of heat that aluminum wouldn’t be able to withstand
AStar elastomeric bearings functions and how do you clean them?
- allow for flapping
- change pitch
- clean with soap/water then rinse well
AStar T/R blade is ____ filled unlike 206 which is _____
- foam
- honeycomb
Bell mediums
- how many segments on a 212?
- how are they coupled together?
- 6
- riveted on
Bell mediums
-tail rotor gearbox changes ___, 42 degree gearbox just changes ___
-speed, direction
- To change spanwise of bell 212 you ____
- flapping action by 2 ___
- Add washers under blade bolt heads
- spherical bearings
What do the index flats on the bell 206 Thomas couplings indicate?
Grain direction (make sure stack up isn’t taken apart-keep in right order)
When tracking, where do you stand?
Aft of helicopter where tail boom meets fuselage on same side of tail rotor so you can see the reflective tape
How to set up for dynamic balance
Accelerometer cable down back of pylon, over elevator, under tail boom, to observation point (perpendicular to T/R at a safe distance) for balance, with power cable connected to helicopter power.
What do you have to check on flap when you install T/R?
Make sure it won’t hit tail boom
- check pitches and measure distance
- if too close, re-shim
What is T/R pedal creep and when is the ideal time to check? How do you fix it?
- pedals will start moving on own (they won’t stay in neutral)
- no wind condition
Fix with counterweights on pitch horn (by adding or subtracting washers equally on both sides)
