balancing

[tiketyboo]

hi

 

i have a three bladed composite fibre Aero-sail prop set that has one blade out 20 grams. i have talked to the factory (poland) and they want me to ship it back and they will balance and charge me and ship back. the props are in good shape with no damage and rather than pay $200 plus balancing i am wondering does any one know how to or have experience in changing the weight of composite blades?

 

 

[Guest Escadrille]

Hey tiketyboo. Ring around your local A and P shops and see who does the dynamic balancing on props for their customers. The chadwick helmuth 8500 equipment can balance your prop and spinner assembly easily and uses washers fitted under the spenner screws. see this website for really good info on prop balancing.

 

DynaVibe - Dynamic Propeller Balancer

 

 

[facthunter]

Where is the 20 grams?

 

If you weigh the 3 blades separately, the difference in weight does not tell the whole story. IF the weight variation is close to the tip it will have much more effect than at the hub. The weight correction at the hub could be a few X 20. (A few being a lot, possibly).. Like a see-saw. LITTLE boy at the end , balanced by BIG boy closer in to the turning (hinge) point. Nev

 

 

[JG3]

I don't know about 20 grams, but we always balance props by spraying clear lacquer paint on the back side of the lighter blades, particularly toward the tips. This is with the prop mounted on a low friction spindle. Small ball bearings with no oil or seals work well. Or a solid spindle set on absolutely level, smooth, steel rails. Have to wait for the lacquer to dry after each application of course. Keep at it until the prop stops at random orientations after a gentle push. Must be in a draft-free room, very sensitive. Works really well, and sure makes a difference to smooth running.

 

JG

 

 

[tiketyboo]

brilliant idea, simple but i am sure it works well, i will try it.

 

thanks

 

 

[facthunter]

More..

 

JG3 has covered it. The point I was making is that comparing total weight of each blade does not determine whether the assembly is balanced. The solid mandrel , with the prop assembled as it will run. on a pair of smooth level surfaces (ideally knife edges), with NO drafts,(wind) will give a good result. Nev

 

 

[jetboy]

There is also the method using a plug that fits inside the exact centre of the hub and the prop is suspended by a string so that any out of balance is revealed by both tilt and tist of the blades. Such and adaptor can be purchased or made.

 

I've statically balanced props both methods and prefer the hang way. with Warp drive blades I had to cut 10mm off one blade tip to get the brand new set in proper trim. Just drilling (the prefered fix) into the end of the heavy blade was not enough. The coning angle was then checked on the plane and that blade was repitched a further 0.3 deg to match the thrust.

 

Ralph

 

 

[tiketyboo]

yes, the one blade is out of balance at the stub end when i balance them off that is what it shows but maybe by laquering that end only a few times will add weight to that blade and change the centre of balance to match the other two.

 

also adding laquer another good way to change the centre of balance of uneven blades.

 

for sure you have to have the weight right plus the balance right for it to work right and have no vibration. t

 

thanks

 

tony

 

 

[Guest Andys@coffs]

There is also the method using a plug that fits inside the exact centre of the hub and the prop is suspended by a string so that any out of balance is revealed by both tilt and tist of the blades. Such and adaptor can be purchased or made.I've statically balanced props both methods and prefer the hang way. with Warp drive blades I had to cut 10mm off one blade tip to get the brand new set in proper trim. Just drilling (the prefered fix) into the end of the heavy blade was not enough. The coning angle was then checked on the plane and that blade was repitched a further 0.3 deg to match the thrust.

 

Ralph

Question not a statement of fact:-

 

While cutting 10mm off the blade will get the static balance correct doesnt it then mean that when the blade is spinning, doing its job, that the shorter blade will now generate less thrust that the other blades, which in turn will mean that the whole thing runs as though its now out of static balance?

 

I always thought that balancing was a result of adding or moving weights around, not by changing aerodynamic profiles of the blades.

 

Andy

 

 

[jetboy]

Andy I covered that in 2nd paragraph, indeed the shorter blade has slightly less thrust so the pich is adjusted accordingly to get the blades in line (coning angle as observed side on to the disc) just mark one blade with white dot for ID

 

I know it sounds all backyard but this is what I was taught from an RC model helicopter guru and similar Bantam owner at the end of the day it worked perfectly well vibration gone and this was on a NEW aircraft with NEW prop so no point in arguing with the suppliers they really didnt know any better just a waste of time and $

 

Ralph

 

 

[Guest Andys@coffs]

ooopps....if only I had read the entire post before bursting into type...

 

So the change in pitch works at all speeds?, again I would have thought that the pitch required would be different at different speeds....but then perhaps that is getting down to microbalance...

 

Anyway...Ive learned something today and that's the daily requirement

 

Andy