500 3d tail vibration

[AusAnt]

I have been chasing a small tail vibration for a little while now. It is not that bad, but seems to me to be big enough to be worth fixing. First I thought it was the stock tail blades, so I replaced them with Radix 92mm so they would be more precisely balanced than the stock blades.

The vibration continued, and then I saw that the two rear boom stays (the carbon rods) were resonating and slapping around in flight. I checked them and they were a bit long, so they were a bowed at rest, and this bow was slapping around in flight. So I tightened them up (or so I thought). The problem was much better, but the left stay was still slapping a little in flight.

Do you think the movement of the rear stays is the problem, or is it merely a symptom of another problem? Any suggestions on how I should adjust the rear stays, and any other typical things I should check for?

Thanks,

Ant

[Mercuriell]

Think you've been unlucky - my overwhelming liking of my two Logos is the absence of twitches, wags and miscellaneous vibrations that characterise the Rexxes and so you can get on and fly .....:fly

Judging by the lack of responses to your thread I guess I'm not alone :)

[AusAnt]

Thanks John,

It wasn't there for the first 20 or so flights, so I am assuming that something has come loose or moved, I'm just having a little trouble finding it!

So the problem is not with my rear boom stays? There is nothing special I need to do to make sure they are tight enough/ not too tight?

I'll go over it carefully and see if anything else has come loose.

I agree it is good that not many people are chiming in with similar experience:lol:

Ant

[LITHIUMSTATIC]

I was watching Andy Rummer at the Mt. Pleasant fly in a few months back. He had a small piece of carbon fiber plate between the two boom support rods conecting them together. It was zip tied and glued with epoxy the as to fuse the boom struts together. I don't remember if it was on his 500 or 600. Anyways it's worth a try.

[th3tick]

I wouldn't think the boom struts to be a cause of a vibration, just some good bits to really show it well.

When chasing something down on my 450, I bought a Dubro Tru-Spin balancer and hung my head minus blades on it. That helped me track down an odd flybar paddle imbalance. I would suppose putting your entire tail on it might help as well.

The only other thing I'd check is whether those two inner pulleys for the tail belt are still spinning freely with no bearing notchiness. Most of the rest of the components are along the axis, and I wouldn't think could do much.

These are all just guesses, mind you ;)
John

[OICU812]

High vibrations as you suggest usually are from a bearing going or gone bad. Have you inspected the tail rotor case bearings as well as the main bearings? Did you ever touch the ground with your tail, meaning there could be a possibility of the tr shaft having a small bend in it or the tail hub having damage?

Hmmmm just trying to offer some roads to take..

[AusAnt]

Thanks everybody,

I'll work my way through the things suggested. You may be onto something Shawn, I did touch the tail rotor once in the longish grass, may have been enough to give the TR shaft a slight bend.

The other thing I thought of today is my training gear. I am still using my training gear, and I do notice that the plastic balls on the end of the carbon rods sometimes get a bit of oscilation in them due to rotor wash. Although I can't see that most of the time in flight, it may be there enough to cause a bit of vibration. What do you think?

Thanks,

Ant

[cptsnoopy]

The reason I have not replied is that I usually don't know what finally fixes the problem but I have battled it several times. Sometimes it gets fixed, sometimes I give up. I just got my brother's Logo14 reassembled and found it has a nasty vib from about 1700hs up to 2200 hs. fairly smooth below and above those speeds. I changed the tail shaft to a new one and put my 600 tail hub/blades on it to see how it did. No change, still the same vibes. Next thing is to take the whole head assembly and main shaft off and put it on the Du-bro balancer. If that does not help, new pulleys front and rear along with new bearings and last would be the belt. Then everything has been balanced and or replaced. If it still vibes, give it away.. :(

[AusAnt]

Well I hope it doesn't become so serious that I decide to give it away :shock: Especially seeing as it hasn't even been crashed yet!

I'll check it over carefully around the tail hub and shaft and see how I go.

Thanks,
Ant

[th3tick]

Then everything has been balanced and or replaced. If it still vibes, give it away.. :(

Back to my 450 story, I forgot to tell you the ending. I never did find the cause, but one day, of course, I crashed it. After the rebuild, the vibration was gone...

[cptsnoopy]

Back to my 450 story, I forgot to tell you the ending. I never did find the cause, but one day, of course, I crashed it. After the rebuild, the vibration was gone...

Ok, that is a great idea. Do not give it away! My bad... Just go hammer it good and start over... :D

I have found that that tail vibes are the most frustrating part of working on the heli's. Can you tell?

:)

[rscamp]

Vibration will always be an issue in something like this with fast rotating parts.

No two parts ever have exactly the same dimensions, no rotating parts have zero runout and the fit of parts is never perfect. A near perfect static balance can be negated by components that do not run true.

Until someone develops a rotor dynamic balance that doesn't cost a fortune and is easy to use we will always have some vibration to deal with. Fortunately, most of the time in good kits it is acceptable but when it is not, I have found some trial and error with tape on the blades can work wonders. Just be prepared to spend an hour or two fiddling... :)

Rob

[NTM]

Well I hope it doesn't become so serious that I decide to give it away :shock: Especially seeing as it hasn't even been crashed yet!

I'll check it over carefully around the tail hub and shaft and see how I go.

Thanks,
Ant


The tail hub will do this, and they bend very easily on a tail touch. Just get a new one, they're tough to eyeball for a bend.

Cptsnoopy, I chased a vibe problem in my logo 14 that almost drove me nuts, turns out the alloy motor mount was imperceptably bent. Last thing I swapped was the motor mount and all vibes were gone.
It was a high frequency vibe that manifested itself in the vertical tail fin, and really seemed to resonate in a certain head speed range.

Regards,
Nathan

[cptsnoopy]

Thanks Nathan,

This one is showing on the horizontal but just in case I have two spare alloy mounts I can swap in to see if it helps.

Just a question about the vibes and which fin you see them on. Is it a true statement that if you see it in the vertical it is most likely in the main rotor system and if you see it on the horizontal it is most likely in the tail rotor system? For now I will consider it an "old wives tale" unless someone really has confirmed it.

Charlie
:)

[rscamp]

An out-of-balance rotor will have a rotating force vector in the plane of rotation. This being said, the main clue regarding the excitation source is the frequency of rotation. Since the tail rotates 4-5 times faster, it will impart rotating forces at a much higher frequency than the rotor head. If it is a fast wobble (around 30 RPS), its from the head. If it is more of a buzz (around 150 RPS), it is from the tail.

We also know the excitation force from the rotors is radial in nature and located at the ends the shafts. This is another clue as to the effect they will have. The main rotor will tend to wobble the heli and the tail rotor will tend to vibrate the boom up and down.

To add further complication, the vibration excitations will transfer though the heli mechanical structure. The input will have different effects in different portions of the heli due to excitation of natural frequencies as the head and tail rotor speeds vary. This makes it more difficult to determine exactly what will happen. It is particularly nasty though when the tail rotor speed coincides with the first modal frequency of the tail boom. I think in this case the tail boom would act like a pinned-free beam so the boom would have a node nearer the tail rotor.

Rob

[AusAnt]

Thanks everybody,

Nathan, I think I will follow your advice and just replace the tail hub.

I put in two flights today, and the vibration bas basically not there- makes me wonder if it is my training gear, and maybe I just strapped it on a bit better this time?

Anyway, I will check the head again - I just had a suggestion on another thread that my 'pre-balanced' carbon main blades may not be that well balanced at all, and I will check that soon.

But my favourite theory so far is the training gear (also my favourite because it is the easiest to fix :lol:) So when I migrate out of that in the next couple of weeks I will know whether that was it.

If all else fails, I think I will follow the advice of th3tick and cptsnoopy, and fly it really hard until I crash it big time, then the rebuild should sort it out! I think I need to start flying a bit harder now anyway, because even my wife tells me I fly like a girl ;) !

Ant

[th3tick]

My second piece of advice is: lose the training gear ASAP. I decided to never use them, and feel it got me further faster, with no mishaps related to not having them ;)

John

[OICU812]

If you can hover decent and steady why do you need the trainging gear? Get rid of it seriously. You should be hovering a foot off ground out of the wash, by then the training gear does nothing anyways. Just a thought but I find the training gear for most is more of a hinderance and brain blocker than anything. Training gear is good for 6 inches and under and that is it, after that it is useless.

[AusAnt]

OK, I'll lose it next time.......

But I must say it has saved me from a few tipovers, but none lately I must admit so I'll move on

Ant

[OICU812]

Well if you feel you can land and take off without them then they are not needed. It is no race to get good, just get comfortable is the most important. Take your time to do well and to be in control, that is the key.

[helicraze]

I had a vibration on a E550 that i could not find! You know what it was? In the end i found the main gear had worn on an angle due to the pinion not being high enough on the motor shaft.
This may not apply to the logo 500 but think outside the square.

[Mercuriell]

Funny I've been chasing an intermittent oscillation of the tail rotor for a few weeks on the 500 - changed tail servo - belt - did a tail grip flip - changed belt and tail casing - changed gyro to the V-Stabi system - improved - and blow me, saw exactly what Ausant was describing the left boom strut vibrating away like a string on a double bass - changed the hor stab mount for a QUK one (Hirobo) and lost the KB blades and now it's gone - seemed like the tail blades flexing set up a resonance in the strut - only apparent at higher HS

[LITHIUMSTATIC]

Mikado needs to make a bridge to fuse the two tail boom struts together. I've seen this done on other Mikados by top pilots.

[AusAnt]

Well it seems I never reported back on the solution to my problems here :oops:

I basically replaced everything in the tail - bearings, hub, shaft and blades, and the problem was not solved.

Then very soon afterwards dumb thumbs solved it for me by making me tip over on landing in the snow. I did a fair bit of damage to the head, and bent the tail boom. After repairs, it was as smooth as glass again. During the crash there was absolutely no damage to any of the tail parts, so I re-used them all. I put in a new tail boom, tail boom struts, yoke, flybar cage, flybar etc.

So afterwards I figured that we had recently moved house, and the heli may have got bumped in transport and I would guess bent the flybar, and that this was showing up as a vibration in the tail. If it wasn't the flybar, it was definitely something in the head.

Since the rebuild it has flown absolutely flawlessly and I have now put in another 50 or so flights on it without issue. There is no need for any reinforcement at least for my style of flying (which is very basic).

There was a really good post earlier on in this thread by rscamp which I had to read about 5 times before I kind of understood it, but when you finally get it, it is really helpful.

So thanks again guys on the Freak for solving all problems - I don't know where I'd be if I had to try and work all this stuff out on my own! :hug:

Ant

[th3tick]

Then very soon afterwards dumb thumbs solved it for me by making me tip over on landing in the snow. I did a fair bit of damage to the head, and bent the tail boom. After repairs, it was as smooth as glass again.

So I was right! Smooth flight is one crash away! :thumbup: