Protech ZOOM 425 ccpm Spécifications télécharger pdf (Page 184)

Disadvantage of the Bell-Hiller system include:

• Slightly slower cyclic response than a pure Bell system

• More complexity than either a Bell or Hiller system

The advantage of the moving flybar system is it has fewer parts (no washout unit) therefore

has less slop in the control system.

Three popular helis which use a Bell-Hiller system with a moving flybar are the Hensleit 3DNT,

Hensleit 3DMP and the Century Hummingbird Elite CP.

30.1.5. The rotorhead

There are two types of rotorhead designs commonly used on R/C helicopters:

• Flapping head (technically a fully articulated rotor head)

• Seesaw head (technically a semi-rigid rotor head)

A flapping head allows each rotor blade to flap, lead/lag, and feather independently. This is ac-

complished by having having three hinges per blade:

• flapping hinge, which allows each blade to flap (move vertically)

• lead/lag hinge, which allows the blade to lead and lag (move horizonally)

• feathering shaft, which allow the blade to feather (rotate along long axis)

This is typically used on helicopters with more than two blades, but some two-bladed helis

such as the Corona use this.

A seesaw head typically has the blade grips for two blades connected by a feathering shaft.

This feathering is rigid and only allows the two blades to seesaw as a single unit, e.g. when

one blade rises, the other is forced to sink. The two blades will still feather and lead/lag inde-

pendently, however.

Most R/C helicopters use this system, including the ECO 8, Logo 10, Shogun, T-rex, etc.

30.1.6. Basic helicopter aerodynamics

30.1.6.1. Dissymmetry of lift

When a helicopter flies forward, the rotor blades generate unequal lift. This phenomenon is

called "dissymmetry of lift".

For a clockwise rotating rotorhead, the blade on the left side of the helicopter is moving into the

wind (advancing blade) and the blade on right side of the helicopter is moving with the wind

(retreating blade). The advancing blade generates more lift, and the retreating blade generates

less lift.

(Technically this is dissymmetry of moment, because the center of lift for the advancing/retreat-

ing blades is at different points along the length of the blade, but most most helicopter texts

reference this as dissymmetry of lift.)

Technical Appendix

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Protech ZOOM 425 ccpm Spécifications Page 184