Tail bounce

When checking my logo 500 today in hover mode I noticed that the tail is not wagging but rather now bounces up & down!
What could be causing this? I could only do a hover in the back yard today so could not the the effects while flying.
Anyone have any ideas? Belt tension seems to be ok and servo arm position is correct, tail gain on vbar /neo is set at 58 in bank 1, bank 2,3
Are set higher.
Thanks for any help

Hi,

up and down could be an effect between the dampening of the main rotor and the tail, some kind of resonance, or it could be related to the tail rotor/tail blades not running true or not being balanced properly (also causing some kind of resonance.

Ambient temperatures could play tricks ... I would be curios if it's in all your head speeds the same, and I would be curios if you find something obvious in the vibration analysis.

Was it working before, or were there any changes?

Kind regards

Eddi

Born to fly ...
forced to work.

Hi eddi, thanks for the reply, I had installed new tail blades (95mm from 550) and retightened the belt so was doing a check flight at our field. I will have to check the log to give you exact times, events but in general this is what happened: flying was really fine then suddenly I heard a strange noise so I turned to land and then it went into a flat spin out of control. Power was shut off and it landed in the cabbage patch. What I found at the crash site was that the tail assembly had turned 90 degrees so that the blades were on top. Other minor damage was the landing gear was broken, a link to one of the blades was broken (pulled apart), and the riemen pulley hat slipped. Checking the log it said the cyclic was out of range. Post check of damage showed that the boom had also turned.
To be safe I replaced the main shaft, blatt welle, tail assembly, riemen pulley, and of course the landing gear.
The first post flight actually run up, the tail again started to twist. Once again retightened the boom and tail assembly (why is there not a pin system in the chassis and at the tail which prevents this twist?), and took it off into a hover in my yard. This is where I found this bobbing action and cannot find anything as to why this happens. I thought maybe it has to do with the elevator servo or swashplate but all seems ok. Bearings and dampers are ok and regreased and checked that the bearings are not reversed. Main blades were not damaged.
I’ll try again to look at the log and see if anything strange was recorded. In the meantime I am going to again replace the entire tail assembly. Then when weather permits I’ll try again to test it.
Thanks for the help.

Eddi, here are a few entries from the logs.
1. Ambiguous value on TailRC channel at Init
2. Aileron sensor value out of range - this was the log at the crash time.
3. Cyclic ring is active
Maybe this helps?
Dennis

Hi,

OK, a guess would be that the new tail blades are out of balance and create vibration. This vibration can lead to the otherwise firm mounting of the tail rotor housing to twist. Had that myself once or twice, during my career, once it was a new set of blades, once it was a minor touch with the tail, to the ground, upon landing or an auto, both causing the tail to run untrue.

If you use the anti static kit, you automatically secure the tail boom in front, in the chassis, with the metal screw.
On the tail, you could also use a small screw to set the tail rotor housing, the clamps, just make sure it does not interfere with the belt inside (at both ends).

Kind regards

Eddi

Born to fly ...
forced to work.

Ok, thanks for the hints. I’ll give it a try soon and let you know if there is a difference.
Dennis

Hi eddi, It seems I have solved the problem using your hints; here is what I did:
Checked tail rotor blades – weight was the same but changed them to a chk type instead f the white plastic ones.
While I was at it, I changed the entire tail unit for an upgrade. It now does not slip pr twist.
Then checked the edge main rotor blades and found them to be out of balance by 3 grams. I did not like the idea of adding 3 grams of tape to the blade so I changed them for a set of Fun Tech( ?). these are in balance, also checked to be sure the rotor welle was exactly placed.
When the rain stopped for a few minutes I was able to get a quick check flight in and wow, it´s flying great again!
Thanks for the help!

Hi Dennis,

glad to hear. It's often the small things ...

Kind regards

Eddi

Born to fly ...
forced to work.