P500 Chicken dance from Hell.

[KSKen]

Got a carbon P500 that on occasion on spool-down does a chicken dance from hell that has stripped the first set of cyclics I put in it.
I installed new JR DS3717's in it and the first couple of flights went well, then it done it again yesterday. It never does it on spool-up, flys great, but on spool-down, I have 3 flat throt curves N, 1, 2..I always stay at zero thrust after landing and flip hold on. I never move pitch down until it's about stopped. Vibe download from Brain 2 shows no vibes even close to being an issue. Pitch set at 11.5, Cyclic at about 10. I installed a true metal gear servo to eliminate the stripping but yesterday broke 2 servo arms (plastic) when it went ape-shit on spool-down. It happens at a point about half way between norm HS and stopped..
Any insight??

[Number]

resonance?

[Number]

some blades cause weird resonance that can't be solved otherwise. first make sure tracking is spot on and the blades are perfectly balanced. otherwise, try different blades.

[HarryR]

You might have your blades TOO LOOSE so they start flapping when the traction / power is cut ( shut-down).

I fly Protos 500 and the blades need to be pretty tight. In fact .. soo tight that it is very difficult to move them. Forget the voices that tell you that they should be kinda' loose.. WRONG!!!

[KSKen]

I tightened the main blade bolts a bit and I "think" that was it. 2 flights out front with several landings and spool-downs with no problem.
I hope that was it.
Thanks!

[HarryR]

Originally Posted by Blade550X

I tightened the main blade bolts a bit and I "think" that was it. 2 flights out front with several landings and spool-downs with no problem.
I hope that was it.
Thanks!

Goooodd!. They should almost be totally rigid so much so that it takes good effort to adjust them. I am assuming you will have the same requirement for your Protos 700.

[Number]

It shouldn't be anywhere near as tight as on a 700. Otherwise they won't be able to fling out when it gets up to headspeed.

[cquillen]

There is a lot of force when up to speed. You'd have to make them very tight indeed to prevent centering.

I think Harry's point is that the typical "loose enough they move when you shake the heli" advice common on micros is too loose. I feel victim to the same advice and had problems with both spooling up and spooling down. Tightening them down till they require some effort to move fixed it.

[Number]

Yes there is a lot of force when up to speed, but if they are too tight the head will have to be turning very fast before they fling out, and vibrating all the while until it gets there...

[KSKen]

According to Brain Vibe scan it's about 1000rpm. It does it just a tad on spool up but about twice as bad on spool down-as far as vibes show but just at limit and it's transitioning through that spot and settles down to a very acceptable level.
I believe I can live with it.
p.s. never had an issue with the 700, 770 or 800...smooth as silk.

[DoubleCH]

My general rule of thumb is to have the main blades tight enough that when heli spools up the blades perfectly straightens (from hand-straighten which almost never gets it perfect) by around half the flying headspeed (or half of the spool up time period). You should notice the slight vibration suddenly goes away at around half the flying headspeed. If perfectly straightened too soon blades are too loose. If perfectly straightened almost at full flying headspeed blades are too tight.

Also check if the belt is too tight in which case it acts like brakes to shift loose main blades off perfectly straightened positions on spool down. Plus also check main rotor for even slight out-of-balance which will also cause chicken dance on spool down even though it seems to fly fine.

[cudaboy_71]

I had a set of revolution 425s that worked fine on the black dampers. put on a set of red dampers and I stripped out 2 servos on two separate spoolups. it just got this shudder at about 1000 RPM, like you said.

I put on another set of the same blades and it was fine. I think the 500 is so light it is super sensitive to balance. Balance and CG your blades and see how it goes.

FWIW, I ended up balancing and CG'ing the 'shudder set' and they worked fine. But, I kept them as a backup set since they were ugly now with balance tape all over them.

[HarryR]

Originally Posted by cquillen

There is a lot of force when up to speed. You'd have to make them very tight indeed to prevent centering.

I think Harry's point is that the typical "loose enough they move when you shake the heli" advice common on micros is too loose. I feel victim to the same advice and had problems with both spooling up and spooling down. Tightening them down till they require some effort to move fixed it.

[HarryR]

One more suggestion. If you use blades with a spacer on the blade grips you will find that they can be tightened up more ( they are just smoother when you move them by hand ). Blades that are just stuck in the grips without spacers seem to have a little more resistance and should be run a little looser.

[DoubleCH]

Originally Posted by cudaboy_71

FWIW, I ended up balancing and CG'ing the 'shudder set' and they worked fine. But, I kept them as a backup set since they were ugly now with balance tape all over them.

I use clear packing tape to balance my blades that need quite some weight. More than a foot away I won't notice the tape.