One for the Techies

[Gareth-71]

Hi

I posted a thread quite some time ago asking the same question, but got now replies, so I'll try again:

HEAD SETUP

Okay, being that way inclinded, I have studied the setup of the head, and understand how everything works, and can easily setup any 120 head near perfect, the questions I have relate the mixing ratio's

i.e. What ratio affect what?

The way I see it, there are three primary michaincal ratio's as shown in the picture:




Now I understand that a higher ratio makes for a more responsive heli (exept the FLybar ratio which makes the flybar have more of an effect), but exactly how do these interact with each and what is the effect. They are all different and all have their own effects?

I have owned and flown many heli's, and have tried many different setups and have learned a lot, however despite all of this messing around, I am still stuck......

An easy example:

Some of my heli's are incredibly stable around centre stick (easy to hover and fly gently) but also have incredible cyclic speed when given big stick movements. e.g. I have a trex450 with Stuby paddles, the roll and flip rate is off the scale, yet it is gentle and easy to fly unless you put in big stick movements.

On the flip side to this, I have a few helis that are the opposite, nearly impossbile to hover neatly (my Srimok is like this) as it is so twitchy, yet given a full stick roll input is slowly rolls over. WTF?

This has to be a setup thing, and these ratio's are key. I have tried different things (paddles, flybar lengths, programmable positions) and have realised huge changes, but still cannot get it the way I want. i.e. If I change the setup to make the roll rate quick, then it is even more twitchy around centre stick.


Any help would be very much appreciated because I have hit a brick wall....

Gareth

[mchristyuk]

Hi Gareth,

First the easy ones:

C - I'm not sure what this is relating to.. but suffice to say the ball for the flybar arm always has to be in the centre of the flybar pivot point.

D/E/F - All these do is change the amount of flybar angle change for a given swashplate movement. Adjusting any one of these will change the amount of swashplate input into the flybar. Generally you want the flybar arm to start hitting its limits at the same time the blade grip mixers start hitting their limits. Therefore (E/F) are generally set so that at 0 pitch and with the washout level there is a 90 degree angle between the washout arm and the link connecting to the swashplate/flybar. If (D) is reduced then the long arm of the washout is also reduced to keep everything 90 degrees. Changing all of these will have no effect on stability just the control response. So the more flybar angle change per swash angle change the faster the ultimate roll rate.

Now the harder ones:

A/B (and the one you haven't marked.. the ball with two positions on the flybar) - These combined effect the amount of blade angle movement per swash angle movement AND the amount of flybar input into the blade. The greater the flybar input the more stable and nicer tracking the model. The roll rate shouldn't change dramatically but the responses will be a bit slower initially.

Therefore the smaller you make (A) the more direct swashplate input and the less flybar you will have into the blade grip. This will make the model respond faster to a given input.

Reducing (B) will have the opposite effect. It will reduce the swashplate input into the blade grip and increase the flybar input.

However the tricky bit is that reducing (A) by 1mm is not the same as increasing (B) by 1 mm owing to the geometry at play. This is why both are adjustable to tailor things to your liking.

So if you have a model that just won't hover or track nicely the chances are the flybar ratio is too low (A - too short B - too long).

Remember though that increasing your flybar input with this mixer design also reduces your swash input.. therefore to keep the control responses the same you will need to increase your swash throws on your transmitter.. INCLUDING PITCH.

So if you want a model that tracks nicely AND rolls fast with the rotor head you have shown you need to:

Make (A) as long as possible and (B) as short as possible. Move the link on B to the outer ball on the flybar carrier too. Run powerful paddles (either light or big.. or both!).

Remember.. the more flybar authority the less swashplate authority.. you can still get the same ultimate roll rate near as damn it so long as you increase your swash throw as you increase flybar input. Obviously there will become a point where the swashplate and mixer arms foul and you can't get anymore...

Hope that helps some!

Cheers

Mark

[trillian]

I wish I knew the answers to all that. I have yet to twist my melon around it.

I just about have a handle on the flybar side in terms of ratio and weights / paddles etc.

Ideally I'd like all my helis to be rock solid hovering and then snappy cyclics when the stick input is there.

I would think if you have very fast response but too twitchy in the hover maybe some expo would smooth that out.

At the moment I don't use any expo but none of mine are twitchy.

[Gareth-71]

Hi

Phew! Just what I was looking for, thank you!
BTW, the C measurement is the flybar carrier ball postion (the one you said I left out) ??? I just shows it the other side.

So what effect do E and F make?

Gareth

[mchristyuk]

Hi Gareth,

Ah ok.. I see what you mean now with (C). That one increases the flybar ratio the further out it goes but has a less detrimental effect on reducing swash input compared to changing (A) or (B).

On your diagram it seems (E) and (F) are both marked (F). I will assume the shorter side is (E) and the longer side is (F).

I have never seen (E) adjustable on any helicopter. That has to make the link 90 degrees to the swashplate so is not a "tuneable" item.

(F) is adjustable on some machines. The longer you make it the more swashplate input into the flybar. In theory lengthing (F) will increase the roll rate and response rate. It has no effect on stability. Stability is generated by the flybar tilting on its seesaw and that action being changed into degree movement on the blades through the mixer arms.

BUT

You just can't go lengthening (F) as the flybar arms will hit the the rotorhead before you get full stick movement.

Therefore you could shorten (F) and wind up your swashplate movement in the transmitter. This will give you more overall blade movement too and therefore faster responses and roll rate.

BUT

Your blade mixers will probably bind before any real difference is made...

That is why (F) is generally not adjustable as the length has been careful chosen to give you maximum flybar movement with maximum blade deflection for a given swashplate input.

Cheers

Mark

[Ashley Davis]

can the ball that is pointed to by D (and connects to B) be moved either further away from the rotor hub or closer to it along the flybar seesaw? If so that ball being moved outward would increase flybar input and increase stability. If you can move that one on it's own you can improve stability without as much interaction as adjusting the other controls but as with all rotorheads changing one thing also changes others.

[Gareth-71]

Hi

No. D is fixed. I only out this in there because this length, although fixed, define the ratio of the other adjustable part.

Gareth

[scallybert]

I've not waded through this all yet; but I don't think this has been mentioned:

You can't sustain a roll rate faster than your flybar can precess.

[Oh, and there's a G5 upgrade to give variable washout arms, I believe.]

[robgt]

You can if you have a virtual flybar
LOL
Cheers,
Rob

[Gareth-71]

I've not waded through this all yet; but I don't think this has been mentioned:

You can't sustain a roll rate faster than your flybar can precess.

[Oh, and there's a G5 upgrade to give variable washout arms, I believe.]

Hmmn! Roll rate and roll acceleration are different. You accelerate a roll faster than the flybar and precess, but you can increase the roll rate.

Right???

[derrick]

I've not waded through this all yet; but I don't think this has been mentioned:

You can't sustain a roll rate faster than your flybar can precess.

[Oh, and there's a G5 upgrade to give variable washout arms, I believe.]

O no here we go again.
Del

[scallybert]

You can if you have a virtual flybar

Indeed. But he hasn't...

Hmmn! Roll rate and roll acceleration are different. You accelerate a roll faster than the flybar and precess, but you can increase the roll rate.

Right???

That's why I referred to the sustained roll rate.

I reckon that two of the main things of interest are the sustained roll rate, and how the heli responds to a disturbance.

[brin]

[quote=scallybert;369822





I reckon that two of the main things of interest are the sustained roll rate, and how the heli responds to a disturbance.[/quote]

hi mark. i know i shouldn't ask but what sort of disturbance are you referring to, some outside force or stick input

[scallybert]

hi mark. i know i shouldn't ask but what sort of disturbance are you referring to, some outside force or stick input

Not sure why you shouldn't ask...

No stick input. If something disturbs the heli, consider how it responds.

[Ashley Davis]

hmm, pity D is fixed, that's probably the one I'd have gone for to fix the problem you are describing, move that out a bit to increase flybar input whilst maintaining the other linkages. The outrage head lets you move that ball hence my question. Without being able to gain some independence over the flybar input (as described above) you are probably left with fiddling with different paddles or blade weights to try to change the head response as the others aren't really changing the ratios in the way you need.

The other option I guess is to use expo to soften the stick response around center but that won't make it more stable, just less sensitive to commanded inputs around center.