0813

Item 0813

DESIGN: SynchroLite ~ Rotor - Hub - 2-blade Teetering - Layout w/ Coning Hinges

plus feather/pitch delta3 and cone/pitch delta3

Potential Concerns re SynchroLite Rotor Disk:

Lead/lag between the rotors during forward flight.

DESIGN: Rotor - Disk - Lead/Lag for Synchropter ~ 0433

Opposed induced lateral cyclic between rotors during forward flight.

DESIGN: Rotor - Disk - Opposed (Differential) Lateral Cyclic ~ 0717

Opposed induced lateral cyclic between rotors when longitudinal cyclic applied. (wee-wa)

Blade to blade proximity between rotors due to large teetering movements.

DESIGN: Rotor - Disk - Blade to Hub Clearance ~ 0442

DESIGN: Rotor - Disk - Blade to Blade Clearance ~ 0199

Excessive vibration, caused by aerodynamic interaction between blades of other rotor.

DESIGN: Rotor - Disk - Aerodynamic Interaction ~ 0419

An idea for reducing vertical 2P and/or 4P vibration in intermeshing and coaxial helicopters. Will the pitch change be soon enough to arrest the change in conning angle, which occurs at 4P, caused by blade-blade interaction on SynchroLite?

The offset Flapping/Coning hinges will also probably not give a 'sharper' response to cyclic inputs and there by allowing the hub to be located at a lower elevation. [Source ~ RWP2 p.28]. This is because of the teetering hinge that allows the yoke to tip thereby deleting any effective flapping hinge offset. Crazy idea:- If a stiff elastomeric was incorporated into the teetering hinge then perhaps the conning hinges would act a little like flapping hinges with offset.

There will be a pitch/coning action taking place. (See Chuck Beaty's notes on Groen). This may be an advantage or disadvantage. Calculate the amount.

Outside Helicopter

See: DESIGN: Rotor - Hub ~ Notes on Robinson

SynchroLite

Drawing:

This hub will functionally look similar to the Picture of Robinson R--22 Rotor Hub.

Concept:

To retain the delta3 (flap by hinge geometry) teetering hinge rotor hub for lead-lag while at the same time allowing the two blades to freely change their coning angle, by delta3 (control system geometry). The purpose of this change of coning angle is to minimize the transmission into the mast of vertical vibration caused by the blades passing through the "downwash" of the blades on the other rotor. The rational is that if the tip end of the blade, which has the highest loading, is allowed to freely pivot about its root end then the blade will be more inclined to pivot about the root then attempting to move the root (and the mast) vertically. Blade flex probably cancels out some vibration, but this method may cancel out even more vibration plus allow for more rigid blades to be used.

Design:

This hub arraignment requires the pitch horn to be located at the rear of the blades. The current Control - Flight is designed for a pitch horn at the front of the blades.

The yoke consists of 3 parts;

a central block with a central teetering hinge and a coning hinge at both ends,
2 identical end units, each with a coning hinge in their center, a tab on the inside end, to serve as a droop stop (identical to Robinson R22) and a means of attaching to the blade grip at the other.

The two end units are connected to the central block at the coning hinges. This 3-part assembly will rock on the delta-3 teetering hinge.

Options:

Angled Coning Hinges:

Consider rotating the two coning hinges in the horizontal plane in the same direction as the delta-3 teetering hinge. As the blade drops in the increased downwash, caused by the blade of the other rotor, the pitch of this blade will increase somewhat. This should result in it not flapping down so far plus it will give a more even distribution of lift throughout the 360-degree rotation. No. There is already a pitch-cone link because the pitch link is offset from the 90 degree coning hinge.

~ or ~

Pitch - Cone Coupling:

A decrease in the coning angle, caused by the other rotor's blade's down wash, will result in and increase in blade pitch, since the pitch link arm is already located at the trailing edge for reduced hub height. This may be preferred to angled coning hinges and may also be an inherent feature of the hub / pitch-link layout if the coning hinges are offset from the mast centerline. Perhaps the solution is have the flapping hinge normal to the blade span and use control-system-geometry [Source ~ HT p.239] to apply the delta3. This may be able to be done by placing the pitch horn-link connection inline with the other rotors coning hinge. It will of course be in front of the other rotor's leading edge. Calculations will have to be done. A possible disadvantage is that the arm will have to be long ant therefor heavy. Forget control-system-geometry. It does not advance the blade.

Location of Coning Hinges:

They could be located;

at a small distance (say 1.5") from the mast's centerline (i.e. offset), or

on the mast's centerline (i.e. both coning hinges are concentric). I may develop a separate page on this idea. [both blades independently hinged from a central pin with delta3, to give teetering and coning pitch coupling.

Probably go with coning hinges that are perpendicular to the span and offset from the mast.

Change:

Flapping hinge offset (assumed)	2.5"	2.5"
Vertical movement at connecting rod for 1⁰ of flap.	0.0349	0.0349
Pitch link arm length (assumed)	1.9761"	3.5"
Pitch change in blade caused by 1⁰of flap.	1.012⁰	0.571⁰

For the reasoning behind the need for this idea see: DESIGN: Vibration Analysis

Because of the flapping-hinge offset, the pitch link will probably be slightly less then 90 degrees ahead of the controlled blade.

Steps??

Minimize coning angle

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Last Revised: November 24, 2001