Balance of Align blades

[helimadness]

Hi All.
ok so first time I have balanced blades. I have never worried as most people have said the align ones are fairly good out of the box. These blades are about 30 flights old and not a mark on them.
I started to notice on the Vbar the vibrations level were rising. To the point just about every entry was "raised vibration" with some high vibrations.
Started looking at all bearings etc and nothing obvious.
Had brought a super cheap blade balance so decided to give it a go. Just a simple bolt with pins to sit on something. Turned out the best I could find was a couple of glasses on the tile floor. Looked a bit rough but I marked the light blade and tested in 4 orientations all with the same result so the glasses must have been fairly level. Also pulled apart flipped the blades and bolted back together in case there was something funny there. Still the same result in all 4 orientations.
Started putting 3cm x 1.2cm bits of tape on from the middle out. Ended up with 13 bits all the way to the end and could have done with one more. They now sit fairly perfect. I noticed they obviously "hang" with both leading edges facing up so seemed the easiest way to get to balance. Leading edge is obviously heavy. Tried flipped so one up one down and they would stay in the middle but if any one was low it would drop. But not consistent so went back to both leading edges facing up.

So now the front edge is plastered with temp bits of tape. Don't want to fly like that as want something better. What is the best to use to balance? I know a dynamic balance is better but haven't got that far yet. Is this basic technique ok? Should I just find some heavier tape and stick on the middle?

Any advice appreciated.

Some pics of my slightly rough but seemingly effective technique.

Blade Balance 1.JPG Blade blanace 2.JPG

[Mark_T]

Do you have a way to weigh them accurately?

I would expect them to be within 0.1g of each other and with that much tape I'm guessing yours are not.

The other thing I would have checked before adding tape is to find the CoG of each blade to see if that was dramatically different.

If either the weight or CoG is significantly out then I'd be returning the blades as they are supposed to be balanced.

[nobbycopter]

Have a look at Finless Bob's setup videos....they're brilliant...blade balancing 101 is what you want.

Heli Skills and Setup 101 - LOOK here first! - HeliFreak

You should get the C of G correct then only add tape to the lighter blade on the C of G, not all the way down.

[cjcj1949]

Does he explain why? I thought that balancing was sufficient from my simple understanding of the forces involved. The conditions required for balance are the same as the conditions for the rotational forces to be equal. I originally used a bolt and glasses and made things worse. I bought a secondhand proper balance and took off all the tape I'd put on. Then I set the head links equal (on a clone sport 450) and blades track flat. Or rather tracked as they are now in bits.

[helimadness]

Ah COG is important I think. That's the bit I am missing. The blades at the tip are going faster so the mass greater.. does that sound right????

Ill get some scales and a better balance. The balance I had was a bolt but with machined ends so there wasn't thread where it rested on the glass. I tried it in 8 different orientations and was the same every time so fairly sure it was right. Was only a 50p investment for the balance so will get another one to compare :-) just saw it when I was ordering stuff and thought I should have one. Now just have to work out what to do with it :-)

Wow thats a gem of a link with all those setup.

Cheers

[r4nd0m]

hm, I thought you would need to mount the blades accordingly how they are fitted on the rotor so leading edges facing the same direction if you use a balancer like that?

like so?
k10289a_3.jpg

[pgkevet]

If you have need to worry about the balance then you also should consider the head itself.
I'm pretty lax over such issues after messing about with balancers and such and rarely finding new blades 'out'.. so tend only to do it if balancing up leftover broken blades on my beater helis.
At the siplest level just bolt the two blades together and balance the bolt between two glasses..pretty accurate and saves messing getting the blade balacer out. Follow that by assessing matching CoG by teetering the blade pair over a table edge.
If you want to get fancy then consider a stand to lay your heli horizontal and clamp it down and use it's own mainshaft and bearings as your teeter point..over the edge of a bench..balance up the head then add the blades after marking/balacing their CoG and work from there

[cjcj1949]

My understanding is that you are trying to make sure that the forces generated by the blade due to rotation are equal and opposite. The force of each element is given by its mass X its speed of rotation squared X the distance from the centre of rotation. If mass is in kilos and distance in metres and rotation is in radians per sec then the force is in Newtons. When you balance a blade you are comparing the moment of each element that is the mass of each element X acceleration due to gravity X distance from the centre of rotation. In other words you are doing the same integral. The mass distribution is critical and balancing is all that is necessary. This ignores aerodynamic forces which will come into play when the blade is not horizontal.

This is basic Physics and there may well be effects that I have not accounted for. If CofG correction is necessary but not explainable that is fine. Perhaps it makes a difference under angular acceleration?

My post was started before the previous two. I agree that using the head could well be important. Things will get very complex as well with main shaft flexure as that will generate an out of balance force which will tend to generate more flexure and more out of balance.

[helimadness]

All good ideas and things to think about. The perfect world you would do a full dynamic balance in the heli so you blanace everything not just the blades. Maybe pulling the main shaft / head out and putting horizontal in another set of bearings is the go. Would take the head into account as well. May also bring some others gremlins into play as well.

Anyway main goal was to check I was in the ball park as having vibes show up more than I would like on the vbar log so just checking everything. Having a good way to check blade balance I think will be very handy for the future.

All good learning.
Cheers

[Bronek]

Are you sure the problem is with balance and not with tracking?

I would first do the balance best I can (first CG of each blade individually, then them both). If the balance is right then the problem must be somewhere else.

It is possible that one blade is slightly warped (slightly different pitch along the length of the blade), this would cause bad tracking even when CG is perfect. Also I imagine the links may "give" a little, thus causing bad tracking.

[helimadness]

ok have pulled all tape off and done the finless bob balance method. One bit of tape on the end of one blade to get the CG right. Well bit hard to judge exactly between the thickness of the line and judging the center of the rod but I think closer.
Then the balance was about 5 laps of tape around the CG point on the light one. About the same amount I had on before. Only using thin light tape.
Have ordered a 500g .01g scale so should have in a few days and will check the actual weight.
Ended up with a fair bump of tape on the light blade. Might have to find some wider heavier tape.

I check the tracking all the time when doing some hover practice at the start of each flight. Is very close. Will watch the finless bob video on that while im at it :-) Warped blades now that brings up a new set of problems. I think they are fairly good. Nothing obvious.
I also have another set of blades I just did a quick check on. I trust them less as I have had to re glue the bushes back in. Still not a scratch on them, never touched the grass. Basically about the same result. CG marks are about 4mm different but the amount of weight I had to add was similar. I guess align have consistency :-)

I don't really have a major problem just think the Vbar log could show a few more green ticks opposed to vibration warnings.

Cheers

[jimheli]

yes i have found this with a fair few blades , of different makes that i have & fellow club members have & it does make a difference to the vib levels shown on vbar log , but also you can sometimes see it in the heli via the tail fin from what i have seen , i have found one make after 8 sets 600 size tested to be spot on ,no tape needed , cg bang on .
i personally would always check each new set i get .

[nobbycopter]

Basically about the same result. CG marks are about 4mm different but the amount of weight I had to add was similar. I guess align have consistency :-)

If both sets are about the same amount out....can't you make 2 sets that are the same by swapping one blade from each set? I'm assuming tho that they are both the same type of course!!

[helimadness]

Doh. why didn't I think of that. Kinda obvious.
Ok so bolted the 2 heavy ones together and put on the balance and it went thud one way. Way off. Did the 2 light ones and the same as you would expect. There is obviously a big difference in weight between these 2 sets. Should be able to tell you when my scale turns up.

[nobbycopter]

Hah.....nothing's ever straightforward eh!!