One for the Techies

[Ashley Davis]

actually looking at your diagram again, the thing I'm calling D is actually C.

The distance the flybar seesaw ball is from the center of the seesaw. If you can move that out further you will get the effect you are looking for but you will need more powerful paddles to maintain your required roll rate (as Mark said).

[mchristyuk]

Looking at it (A) is already all the way out so nothing you can do there. If you reduce (B) that will increase your flybar input but you will also have to increase your swash movement in the TX to compensate.

A low fly bar ratio gives the high roll acceleration that the 3D pilots like.. but this can also be accomplished with light paddles.

Thinking about it this might be where Curtis is coming from with the Stubz paddles. They are very small and light which means high acceleration.. but because of this he can also run a high flybar ratio like the F3C pilots want so as to make the model track nicely and respond well to outside disturbances like gusts of wind.

Personally (and I was talking to Robgt about this the other day) I've never understood the desire for a low flybar ratio in 3D because it although it increases control acceleration it makes the model very unpredictable. High acceleration can be gained elsewhere (such as paddles).

And a flybarless system won't help here either when it comes to outside influences. A flybar can respond to wind gusts that move the model but not its attitude. A flybarless system can not cope as there is no roll movement for it to measure... gyros measure rotation. This is why some people still prefer flybars over flybarless systems and why it will never be used in F3C.

Cheers

Mark

[moyesboy]

Here links to colin mills techie articles published a long time ago

Model Aircraft and Model Flying - W3MH - Home Page basic heli aero dynamics
Model Aircraft and Model Flying - W3MH - Home Page throttle and pitch curves
Model Aircraft and Model Flying - W3MH - Home Page tail rotor mixing (out of date really)
Model Aircraft and Model Flying - W3MH - Home Page gyros
Model Aircraft and Model Flying - W3MH - Home Page mixing rations explained

Incidentally I wonder how long those old pages from a defunct mag will still be avaiable on t'int hair net?
I wonder if colin mill of CSM might be willing to have them hosted on helliaddicts for safe keeping?

[scallybert]

Here links to colin mills techie articles published a long time ago[...]

Yes, there are some really useful, fundamental truths in there.

It's where I got the idea from that the flybar disk will precess to 'follow' the mainshaft. (Because the paddle pich is set realtive to the mainshaft.

Also interesting is the section on Bell/Young flybars in The Art Of The Helicopter. The book overall does a pretty good job of making pretty complex dynamics accessible, while still being useful to people with a theoretical background. (Rusty as it may be...)

[scallybert]

FWIW, here's my take on the big picture.

Fact: the heli can't sustain a roll faster than the flybar can be made to precess.

The rest is theorising/opinion.

Therefore the agility is going to be limited by how fast the flybar can be made to precess.

I think this ought to be the limiting factor - as that's arguably what flybars are for.

If the flybar is going to be an effective stabiliser: the rate at which the mainshaft axis rotates towards the axis of the flybar disk, in response to flybar input, must be significantly greater than the rate at which the flybar disk precesses towards the mainshaft (due to effect in previous post).

So for agility, you need things like a light, long flybar with fast paddles. The ratio from the wash-out arms can also increase the pitch repsonse of the paddles wrt cyclic input. Whilst not effecting how fast the flybar disk precesses towards the mainshaft.

To maintain stability the response of the heli to flybar input must more than keep up with this. The flybar ratio, precesion rate of main blades (eg light main blades) are factors. Also, how heli as a whole follows the main rotor disk. Stiffness of blades, moments of inertia of heli (in pitch and yaw axes - smaller is better (interesting)) , head dampers, etc.

Hopefully, what you want to do with the mixing ratios will fall out of this - or at least some ideas. Hopefully this is also consistent with what people have already found to work...

You may also want to look at mass distribution of heli.

[moyesboy]

What you are after is fast roll/flip but not too sensitive to sticks in the middle.
What you don't want is too much instability in the hover and in forward flight.
I presume you tries a combination of light paddles and some expo on the cyclic controls?
Perhaps the stability from the flybar ratio is actually ok and its just too sensitive to the stick unput arround centre?

My 500 is the ojne thats fastest in roll and flip, but its still no problem with stability for me in the hover and fff no matter how gusty the wind. But it depends on what you are trying to do!