Just did the first flight on the new Corona, finally. The only problem was a vibration most noticable looking at the tail. The frequency seems to be that of the main rotor. It is pretty smooth on the ground but the second that it lifts off , it vibrates pretty bad. I have tried all combinations of dynamic balancing. Is it perhaps a bent shaft?
Thanks,
Kip
http://www.springeraviation.net/

Mine had a bent shaft, either from the factory or during assembly. I did as the manual suggested, and the straightned shaft was much smoother and it was easier to fly.

I had a vibration but not any more.
I found out that the rotor head it self WAS out of balance.
I took off the rotor head and put it on an extra 5/32 shafts I had (piano wire) put it on a high point or prop balancer, WITH OUT BLADES and found it was way off! I drilled a hole in each pitch grip.
One to make it liter and put a screw in the other to make it heavier. Then I made a blade balancer and balanced the blades.
Not only did it take out the vibration but crashes don't seem to bend the shaft as much as before. I think being out off balance made things worse in crashes.

I'll be rebalancing the head on a high point today. I did that the first time and put some little washers under the grip bolt and it balanced pretty good. My vibration must be from somewhere else so I am reassembling the thing.
Thanks,
Kip

Sometimes the source of vibrations on this little bird can be hard to locate, I have had everything balanced (including the main gear) and still got vibrations, it turned out to be the drive wire in the tail boom, one of the plastic inserts (bearings) has moved and the slight bent in the wire was making all the trouble

N111kx, your's sounds like blade tracking problem, I've had this happen to me before.

Good Luck!

Joe K,

When you balanced the rotor head on the high point, did you have the subrotor on or had you taken that off? I have some vibration I am trying to track down and have never been truly satisfied with the head / subrotor / main blades balance job...

Also, what type of balancer do you recomend. I have seen several styles and know little about it.

Spiro

I found that the rotor head with out the blades was way off.
I ended up drilling a hole in both grips and putting in a screw and nut on it to get it in balance.
I just took the whole rotor head and putting it on the highpoint.
If you have a spare main shaft use it. Or you can use a piano wire the same diameter.

The problem that I had was that one of the subrotor blades was way out of balance. I didn't think that it was possible to be that much difference in something that is semmetrical. Apparently I need to put the head back on the balancer.
By the way, how vibration-free can you get these little things?

N111kx,

After viewing your looping video, it appears to me you must have solved your vibration problems. That, or the vibrations don’t show up on the video very well. If things are running smoothly now, what did you do to get the vibration ironed out?

Spiro

Unfortunateley, I cannot pinpoint exactly what smoothed things out, but...I am betting on the cf boom with ball bearings. The vibes went away right when I put that thing on and others have had the same result. I would highly recommend it. Also, after about 5 aluminum booms, it will have paid for itself.
Kip

Kip,

Could you describe any bend you may or may not have in the main shaft? I desperately want to know how much is acceptable and your setup seems rock solid and vibration free. If you have a minute, take off the rotor head and slap the ol’ paper clip and cloths pin on. I am sure a great many people would appreciate it

Also, I see all kinds of talk about the CF boom and bearings for the 120, but nothing for the short stubby 100/116/117 tail boom. Does anybody make one? Can the long electric boom and drive wire be cut shorter?

Spiro

Funny you should ask about shaft straightness. I have a theory, for the moment anyway, that a perfectly straight shaft is not the answer to complete smoothness. I think that having a smooth Corona involves cancelling different imbalances. For example, I have had a perfect shaft and yet I could rotate it 180 degrees, insert the Jesus bolt and cause more vibration. Therefore an imbalance existed somewhere other than the shaft but was somehow related. And, my smoothest operation has been with a noticeably wobbly shaft. So... a bent shaft may be able to actually cancel an imbalace somewhere else (perhaps in the design!!!) This may not make sense and I am still trying to master dignosing the vibes. Perhaps my next Corona will be the educational tool that helps me pin down the causes of all of this.
As for the drive wire, I don't know. I have never seen a gas LMH and am not sure if they are identical.
Kip

I would recommend trying music wire to replace the main shaft. It is cheap, and I wonder if it's flexibility allows it to damper some of the vibrations. I have been using it for a while now and love it.

Also, watch for the uneven blade tracking issues, you need to check the blades on all sides to be sure..

I have made some main shafts out of music wire. I have not been able to make the music wire any "straighter" per say and still have my vibration. I don't really know if it helps any or not. I suspect this is essentially an identical product as what LMH uses.

Spiro