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)
Tail rotor will turn _____ than the main rotor
Faster
42 degree GB location and purpose
Located base of tail fin and used to change direction of shafting as it goes up the tail fin
What connects the 42 degree GB to the 90 degree GB? Where is the 90 degree GB located/ function?
- A single shaft
- mounted at top of tail fin, provides gear reduction and a 90 degree change in direction
Flexible curvic couplings installed with V-clamps. V-clamps have to be in what position?
90 degrees from previous V-clamp
How do we maintain tail rotor alignment?
Hanger bearings are shimmed to obtain correct alignment
Describe the construction of the bell 212 tail rotor drive segment
Total of 6 shafts used (5 same length, 1 shorter) with 4 hanger assemblies and 2 gearboxes
-these are used to deliver power to the tail rotor
Describe construction of the Hughes 500 tail rotor driveshaft
- one piece unit installed between transmission and T/R gearbox
- dynamically balanced tube of bonded and riveted construction with flange coupling on each end
- about halfway down tube a steel sleeve is bonded to tube to act as bearing surface for driveshaft dampener
Describe T/R drive system of Eurocopter AS 350
- driveshafts connected to each other, to engine and T/R GB by flexible couplings which allow for any misalignment that may take place
- short shaft by engine is steel b/c if heat
- flexible discs on fwd shaft larger diameter b/c more flexing occurs near engine/transmission
- rear shaft is aluminum b/c of length and not exposed to heat
- it’s supported by 5 or 6 bearings depending upon engine installation
- bearing packages operate on rubber sleeve to absorb vibrations
What is the construction of a T/R blade for bell 206 Blll?
-constructed with aluminum sheet with a bonded trailing edge and honeycomb core
Methods of T/R tracking
- Stick (small diameter stick with sponge rubber tip has Prussian blue applied. Helicopter at operating speed stick moved til contact made. Blue strips on blade should be same)
- Electronic method (most popular. Strobex unit and reflective tap)
What drives AS 350 pitch change mechanism?
Bell cranks and push pull rods
How is the drive shaft attached to hanger bearings?
?bonded?
What type of airfoil is used for bell 206?
Symmetrical
How do you correct for dissymmetry of lift?
Flapping hinge
