Rotor tuning

[Chopper Reid]

Birdy, the reason the AK's have little shake is that they have about .75 % pitch compared to Robs which can have around 2 %, the more pitch. I reckon if you pitched the extruded blades up to 2 % you might find they shake a lot more.

I will hopefully be able to tell you more info shortly as I am sending a set of 27 ft Ricks to Jeff for a new hub bar and I want him to put 1.5 % pitch into them. They are extruded and have done approx 2000 plus hours but are still in reasonable condition ..except for a few dings on the trailing edge where a very helpfull soul shifted my gyro and didnt watch where the rotors were hitting in the shed...grrrrrrrrrrrrrr!!!!

I agree with you in regard to starter motors, if everything is balanced and right then it doesnt matter how much weight is up the mast.

 

[Aussie_Paul]

I agree with you in regard to starter motors, if everything is balanced and right then it doesnt matter how much weight is up the mast.

Unfortunately it is not that simple Brian.

Aussie Paul.

 

[Chopper Reid]

Unfortunately it is not that simple Brian.

Aussie Paul.

mmmm.....I sort of agree with you Paul but its so close to the truth that I will stick with what I have said, just based on my findings. I have been down the path of even taking the starter motor off and going for a fly and that only relieved the problem by a smidgeon [bees dick] so it wasnt weight up the top causing the problem. Now, when I put another set of blades on same gyro, smooth as silk, the same blades with a new hub bar and rough as guts.........

 

[Mike G]

Birdy
I'm sure you've already excluded this as an explanation.
I assume you string the blades by going from one blade tip to another.
If so then are you sure that the marks you have on the blade tip as a reference for the stringing are actually aligned with the C of Gs of each blade?

The attached sketch explains it better, what I'm trying to show is that of you have a perfect rotor (with two identical blades) with the C of G of each blade and the axis of rotation all in a straight line then it will be perfectly balanced from a mechanical point of view (ignoring coning and aerodynamic effects).
If you string this rotor from the tips and the points on the blade tips you've chosen are not in line with the C of Gs then your perfect rotor will give the impression that you have a problem.

I hope this isn't an insult.

Mike G

 

[birdy]

I get wot your sayn Mike, and no, sugestions never insult me

These blades come with string line holes in um, and i strung um the same as i have with every set of AKs i'v had. Only, every other set were perfectly centered.

 

[Mike G]

Birdy
I suppose the only way to check if the string line holes are correct woud be to take each blade off and find its C of G. Since your rotor is so sweet at the moment that would appear to be risking making it worse just to satisfy your intellectual curiosity.
Again I'm sure you know all this but the easiest way to find the C of G is to find the centre of the blade by balancing it twice on a straight edge that is at 45° to the longitudinal axis of the blade. Picture attached it's easier than words.

Mike G