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Helicopters > Ch 9- Tail Rotors > Flashcards

Ch 9- Tail Rotors Flashcards

1
Q

Why do we need Tail Rotors?

A

Allow pilot to compensate for torque and gives directional control

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2
Q

What methods are used to counter-act Newtons 3rd law in regards to a helicopters main rotor? (7)
What is the most common?

A
  • Coaxial main rotors
  • Tandem rotors
  • rotors located side by side
  • Intermeshing main rotors
  • Tail rotor (anti-torque rotor)
  • NOTAR
  • Fenestron or Ducted Fan
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3
Q

Benefit of Fenestron?

A

Unequally placed 10 blades and Starter for noise suppression

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4
Q

What is the NOTAR system?

A

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.

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5
Q

Tail rotors are required for ___ main rotor helicopters, don’t have ___, must have the ability to ____, used for _____, and must have ___ & ___ pitch ability for __________.

A
  • single
  • lead-lag system
  • pitch change: Positive and Negative
  • directional control (movement around the YAW axis)
  • negative, positive,
  • directional Control an autorotation
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6
Q

T/R system consists of?

A
  • T/R driveshafts
  • T/R gearboxes
  • T/R blades
  • pitch change mechanisms
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7
Q

What does a misaligned driveshaft cause?

And improper shimming cause?

A

High vibrations

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8
Q

Tail Rotor gearbox (Bell 47) major components

A
  • gearbox housing
  • input sleeve
  • output shaft and front cap
  • pitch change mechanism
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9
Q

206 has a ____ (same as flexible coupling)

A

Thomas coupling

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10
Q

Intermediate gearbox job

A

Change direction of shafting. ONLY changes direction NOT rpm

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11
Q

MD500E tail rotor system does not require tracking but requires ____

A

Static/dynamic balancing

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12
Q

Advantage of NOTOR

A

Quieter and safer

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13
Q

Where are Datum holes located and what are their purpose?

A
  • long shaft

- if can’t see through them then it means the shaft has been twisted

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14
Q

AS350 short shaft is steel, why?

A

Because it is located under the engine therefore getting a lot of heat that aluminum wouldn’t be able to withstand

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15
Q

AStar elastomeric bearings functions and how do you clean them?

A
  • allow for flapping
  • change pitch
  • clean with soap/water then rinse well
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16
Q

AStar T/R blade is ____ filled unlike 206 which is _____

A
  • foam

- honeycomb

17
Q

Bell mediums

  • how many segments on a 212?
  • how are they coupled together?
A
  • 6

- riveted on

18
Q

Bell mediums

-tail rotor gearbox changes ___, 42 degree gearbox just changes ___

A

-speed, direction

19
Q
  • To change spanwise of bell 212 you ____

- flapping action by 2 ___

A
  • Add washers under blade bolt heads

- spherical bearings

20
Q

What do the index flats on the bell 206 Thomas couplings indicate?

A

Grain direction (make sure stack up isn’t taken apart-keep in right order)

21
Q

When tracking, where do you stand?

A

Aft of helicopter where tail boom meets fuselage on same side of tail rotor so you can see the reflective tape

22
Q

How to set up for dynamic balance

A

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.

23
Q

What do you have to check on flap when you install T/R?

A

Make sure it won’t hit tail boom

  • check pitches and measure distance
  • if too close, re-shim
24
Q

What is T/R pedal creep and when is the ideal time to check? How do you fix it?

A
  • 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)

25
Q

Tail rotor will turn _____ than the main rotor

A

Faster

26
Q

42 degree GB location and purpose

A

Located base of tail fin and used to change direction of shafting as it goes up the tail fin

27
Q

What connects the 42 degree GB to the 90 degree GB? Where is the 90 degree GB located/ function?

A
  • A single shaft

- mounted at top of tail fin, provides gear reduction and a 90 degree change in direction

28
Q

Flexible curvic couplings installed with V-clamps. V-clamps have to be in what position?

A

90 degrees from previous V-clamp

29
Q

How do we maintain tail rotor alignment?

A

Hanger bearings are shimmed to obtain correct alignment

30
Q

Describe the construction of the bell 212 tail rotor drive segment

A

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

31
Q

Describe construction of the Hughes 500 tail rotor driveshaft

A
  • 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
32
Q

Describe T/R drive system of Eurocopter AS 350

A
  • 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
33
Q

What is the construction of a T/R blade for bell 206 Blll?

A

-constructed with aluminum sheet with a bonded trailing edge and honeycomb core

34
Q

Methods of T/R tracking

A
  • 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)
35
Q

What drives AS 350 pitch change mechanism?

A

Bell cranks and push pull rods

36
Q

How is the drive shaft attached to hanger bearings?

A

?bonded?

37
Q

What type of airfoil is used for bell 206?

A

Symmetrical

38
Q

How do you correct for dissymmetry of lift?

A

Flapping hinge

Helicopters (7 decks)

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