Problem after tail belt change

[A.W.]

Looking for some problem solving help.

I've just had to change the tail belt after it went mid flight, luckily I was only a couple of foot off the floor and got it down in one piece.

So I changed out the belt, fixed the gyro back down and re set the travel limits for the tail. First flight was absolutely fine, no problems at all. Just held a steady hover for 5 minutes, tail nice and solid.

Then for the following 5 flights right before take off and during the first minute of flight I had real bad tail wag/shake, then it would disappear and fly fine for the next 4 minutes of flight?

The only thing I changed was the new belt and fixing pad for the gyro. Everything seems ok with everything, but somethings up? Prior to the belt change it was flying great.

Could it just be the new fixing pad for the gyro, its a foam one the old one was the one that came with the kit which was more dense and not as springy?

[Gladius]

How tight are your main and tail rotor blades? If they are too tight, and aren't able to properly position themselves, it will cause vibes? Are you flying back-2-back?

[A.W.]

Yeah today was back to back for the 6 batteries as really short on time. Think all my blades are ok, not too tight and are pretty much the same as before the belt change.

I thought it might be vibes but puzzled why the shaking and wagging would go away after hovering for 30 secs or a minute? Everything I've checked seems fine.

[Gladius]

Yeah, if you're flying back-2-back, then once your blades center, you shouldn't have vibes on subsequent flights.

[A.W.]

Quick update -

First time out today since the problems I was having with the bad tail wagg. Checked everything over again, nothing seemed wrong so went ahead with the first flight.

No issues at all, tail was rock solid the entire flight. all subsequent flights exactly the same no problem during spool up, take off or normal flight. Really don't understand what was causing the issue for it just to vanish completely without anything changing???

[Ron_R]

I get this, too.

Not sure why, either. Tail is fine for one flight, and the next it wags a bit. Then fine for 2 packs, wag comes back next time. Weird.

[Gladius]

Are you guys using a governor, and if so, which one? In A.W.'s case, it could be a resonance vibration caused by the headspeed with a fully charged pack. As the pack's voltage drops off, the headspeed comes down out of the resonance range, and the wag stops. To test this, you could try raising your headspeed a little and see if the wag returns. It is just a theory though...

[A.W.]

I'm not using a governor, I have the throttle curve set to 0-55-80-80-80% in normal mode - haven't dared switch to IU1 which is a flat 80%. Thats not changed since I first set the heli up.

Thanks for the suggestion, should I try upping the throttle curve a bit to see if the tail wags? If it does what does that mean needs looking at? Sorry but not really sure what a resonance vibration is or caused by?

[Ron_R]

Originally Posted by A.W.

Sorry but not really sure what a resonance vibration is or caused by?

Any sound causes a certain type of vibration, even if the frequency of the vibration is very, very small.

"PHYSICS
the reinforcement or prolongation of sound by reflection from a surface or by the synchronous vibration of a neighboring object."

Once the sound is reflected off any surface, it causes a vibration that is steady and this is what can cause interference with radio signals, etc. This is what can cause gyros to glitch as well as the actual vibration from movement.

Gosh, I hope I explained that correctly!

[Gladius]

First off, I highly recommend flying in idle up. If you need to lower the heli somewhat quickly, and you drop you throttle below mid-stick, you are going to lose rpm, which will make control more difficult at a moment when you probably need all the control you can get. If you have a sim or a micro, use that to practice hitting TH. I remember how intimidated I was to use IU the first time, but as soon as I did, I never looked back.

Next, a vibration is the rapid movement of an object back and forth. The number of times the object moves back and forth within one second is the frequency. An object tends to vibrate at a specific frequency, depending on what it is made out of, and it's shape. You can make objects vibrate, by exposing them to a vibration at just the right frequency, called the resonance frequency. For example, if the boom of your heli naturally vibrates at 1000 Hz (1000 times/sec), and you use a motor that spins at 1000rpm, your boom will begin vibrating in sync with your motor.

Resonance causes things to vibrate a lot, which is bad for your heli. Ordinarily, the designers that built your heli will have engineered out resonance in your heli, but if something isn't right, or you've modified the heli away from their design specs, you could introduce some resonance into your heli.

Raising your TC to 85% will allow you to see if a slightly higher rpm could be causing resonance somewhere. Even if that is the case, I would still want to track down what is causing the vibe and fix it.

[A.W.]

Thanks for the explanation guys.

I will certainly try taking the throttle up to 85% and see if there is any re occurrence of the wag. If there is will try and track down the cause.

I do have a micro (MCPX BL) and a sim, in both I switch to IU1 and use TH as suggested, I've just been a bit apprehensive with the 500. Its fair to say I can do miles more with the MCPX than my 500. With the MCPX I've got all upright orientations well, circuits, figure or 8's and a little bit of inverted.

With the 500 I'm just a lot more cautious due to its size I guess, can hover well tail in and side on, and move it about tail in and a bit of forward flight side to side. With each trip to the field I get a bit more confidence.

Will keep working at it, I've a lot to learn! Early days yet, still only 4 months into my heli flying.

[Gladius]

That's what it's all about. Just getting out, expanding your flight envelope, and having a blast!