Rotor head design

[Si Goodchild]

I've noticed how there are 2 distinctly different approaches to rotor head design. Most, including the Align series, have the flybar set between the swashplate and the main rotor blades with a series of linkages connecting them together. Some others, such as the Belt CP and Raptor series have the flybar set above the main rotor blades necessitating long linkages that loop around the blade grips to connect the flybar to the swashplate.

My gut feeling is that the Raptor-style system keeps the centre of lift close to the CoG thus improving responsiveness to control inputs, whereas the Align-style system with the CoG hanging lower beneath the center of lift should make for a more stable helicopter.

Is this right? are there other benefits of each system and, if so, which one is best? Or are they equally good answers to the same technical problem?

Si

PS - I have both systems in my fleet of 2 helis.

[moyesboy]

Rotor head design is interesting.
The main limit to the distance of the main disc from the c of G is the likelihood of a boom strike.
An over slung flybar is better for bouncing the head button on the hard deck.

The other difference is wether the mixing arms are placed outboard (like the knight), or inboard so they cross over the axis (trex), or if they are mounted on the blade grips (dragonus, aurorra). Some also have the flybar sliding up and down in a groove in the head block.

Then there is if the blade grips have leading or trailing arms (exaggerates or damps the collective and cyclic resonse with damper movement) and how much delta offset they have (exaggerates or damps the cyclic reponse as the spindle moves in the dampers).

Like all complex mechanical systems there is a good result possible from quite different approaches!

Generally with model designs a limited amount of variation is best. Then folks build it and it flies like that. if they want it to fly different then they buy a different version.
The other approach is to make a head with 100s of possible different setups and then nobody has two models the same. So nobody can say how that model flies - but average joe might never get it to fly nice for him, and mr fiddle will never have it fly the same twice in a row...
The Xtreme and aurorra are there for those who like that sort of thing I guess.

[robgt]

You don't _have_ to change the head setup between every flight Gordon
LOL
Cheers,
Rob

[Ashley Davis]

what? oh crap, do I have to put it back how it was last flight?

[Ade_Law]

most of the major dimentions are fixed, the 2 major ones are boom to blades and CG vertically relative to the boom.

if you stick most 50s on a table next to each other you will find that those are all the same accross most models.

the major difference between the different mixer layouts is how easy it is to adjust the ratios. One of the things I liked on the knight was that by moving one ball on the mixer arm you could increase swash input and at the same time reduce flybar input.

with the trex/raptor layout its impossible to do that, moving balls around increases or decreases both flybar and swash input. The only way to reduce the flybar input is to move the whole mixer arm on the flybar carrier but limits of space mean the adjustment is quite small.

the outrage/fury/aurorra layout is much more adjustable you can adjust each ratio pretty much seperatly without affecting anything else. Meaning you can make it fly exactly how you want if you can move the balls on the various arms.

Ade

[Kwickkwack]

Thats a lot of balls you are talking about there Ade



I will take your word for it as you know infinately more than I do.

[moyesboy]

Hey there's a lot of past tense there in Aides knight references!