Extreme vibrations with RCP 500mm CF blades

[hoffa]

Hi all
I've been running my Hurricane 550 since this summer with the stock rotor blades. No problems with vibrations. But when I fit my new RCP 500mm CF blades on the Hurricane and try them out on the basement floor, at around 20% throttle, I get the famous chicken dance from the vibrations.
I don't have a dedicated blade balancer but have tried both to check the CG of the CF blades by balancing the blades on a screwdriver and I've also tried to screw the blades together and hold them up with a pair of strings. Complete with all bolts and nuts I've found that the CG only differed by some 2mm and nomatter how I twist the blades when they are tied together they always return to balanced level.

Have anyone come across this before, Hurricane working OK with regular blades but not with CF blades? Makes me wounder if CF blades are more sensitive than regular blades.

Regards
Hoff

[istandalone]

with a 450 sized heli, running woodies a blade balancer isn't really needed. but when you get to 500 + size helis it's a must. weird though, my rcp 515's were dead-on-balls balanced out of the bag. have you tried loosening and/or tightening the blades in the grips?

[mjdee14]

I agree with the above statement from istandalone....about the blade grips.

The blades are more likely heavier than the woodies and therfore will move diferently in the holders. i had to really tighten mine more than the typical "just enough to hold the blade from falling",

Make sure they are both the same tightness...and try tightning...then loosening a little, etc.

One blade lags behind the other on spool up or down and you get the "chicken dance"...assuming all other parameters are ok.

Do invest in a good balancer, even if for piece of mind, i have to use as little as 1 piece of scotch tape to balance cf blades, bit it's nice to know they are perfect.

Remember that 2mm is being accented by 1800 - 2000 RPm's

[ukgroucho]

It's funny but after my last rebuild I stuck some GoQuick 515s on and went out for a test hover... vibed horribly. I had not balanced the blades but when I checked weight and CofG they were very close.

So I got paranoid and swapped out the (just replaced) main shaft in case I'd stuck a bent one in (although it proved to be straight). Threw some more RCP 500s on (had to add 0.2grams of tape to one to get the weight the same but CofG was identical) and took it to the field Sunday with some trepidation... and it flew beautifully.

Right now I'm thinking it was a couple of things - blade tightness and tracking. The GoQuick blades were noticeably out of track (RCPs are perfect) and they are also quite a bit heavier - 90 grams a blade vs. high 70 - low 80s for the RCP 500s. I suspect that heavier blades need different tightness...

When I get around to it I'll swap the GoQuick blades back in... but the RCPs fly so nice I cannot be bothered to mess around in the cold tracking and tweaking.

[mjdee14]

UK...i had the opposite...the 515 GoQuick's balanced almost perfectly (1 small piece of scotch tape)....and tracked perfectly...no vibs.

Liked them so much a ordered a second set....I hope they are as good.

I LOVE the sound they make "beating the air"....it is much better than the woodies....even just hovering in the front yard. Can't wait to actually fly them.

Weather here stinks...and when it's nice I have to work....!! Bummer