Mini Titan e325 Tail Vibrations During Spool Up

[SpeedVision]

:hug: See 2nd post on page 2 for final update!

Hello All:

Getting my new beast set up and have a strange occurance while I am spooling up. Here's my setup for ease in diagnosis:

TT e325 (duh)
GY401
DX7 tx
6100E rx
9650 on tail
Z-10 3300 Motor
Align 325 Pro's
Metal upper and lower mixing arms for tracking
Reinforced (new style) plastic blade grips
65mg for cyclic
13 tooth pinion
Castle Phoenix 35 and Bec 10
Kong Power 2100, 25c
Blades Balanced (checked and rechecked)
Tail belt tension is moderate without being loose

Throttle curve is linear from zero to 100%
Negative pitch starts at minus 2 (newbie)
Pitch curve starts at 43.5%, then to 50% and 100%

Problem (finally) - Around mid throttle I get a pretty good shake that is very noticable in the tail fin (this is long AFTER the blades have straightened out). If I continue to increase throttle the shake will subside and the heli start to ease off the ground. If I lay on the ground and spool up to the shake point, the tracking is still dead on! Once in the air, no apparent vibrations...

Tried various pitch and throttle curves with no improvement. Also, I get the vibration when spooling down as well... Seems to appear between 35 and 40% throttle.

Is this normal? I assume not. Mechanically everything looks right... Any "been there, done that" feedback would be much appreciated!!

[redvtr1000]

I get the same vibration sometimes. Everything on my bird is balanced, no bent shafts b/c they are all new. I am thinking that some of this problem may be coming from the dampers. Sometimes pulling the feathering shaft and lubing it up real good seems to alleviate it. I usually just throttle through that area now, I won't spend a bunch of time at that rpm. In flight I don't see the vibe either so I guess it is ok.

[mkoutnik]

I agree...lube up the flap dampeners and feathering shaft with a high quality silicon oil (like used in RC car shocks) or Vaseline petroleum jelly.

[SpeedVision]

I agree...lube up the flap dampeners and feathering shaft with a high quality silicon oil (like used in RC car shocks) or Vaseline petroleum jelly.

Fortunately (or unfortunately), I did lube them up during the build. I used Vaseline and everything moves easy. If all else fails, I do have some shock oil that I could give a try.

Come to think of it, I haven't balanced the stock tail blades yet. I guess I'll add that to the list as well.

Hopefully, I'll get to the bottom of it. I'm pretty particular about my stuff and this will bug me till it's gone (either the shake or the bird). Or I'll have to "upgrade" :wink: to a T-Rex... Did I say that?

[SpeedVision]

Well, I balanced the tail blades, lubed up the dampeners and feathering shaft with "extra virgin" silicone oil, made a few adjustments, found a few "build flaws" and got everything in tip top shape.

Result - EXACTLY the same vibration as before. Based on the extent of changes I made, I was almost positive that all would be well. Not so.

Arrrrrr....

Am I expecting too much? Any other Mini T owners please chime and and tell me that you get no vibration during spool up so I know it's possible.

[mkoutnik]

I don't get any vibration during spool-up...are one or both of your main blades too tight in the grips? Just a thought...Have you tried to rebalance the main blades, just to make sure? Are the blades tracking perfectly?

[redvtr1000]

Ibcynya,

I have had that vibration as well and no matter how many times I balance, swap shafts to new ones, etc I can still find it once in a while. I'm starting to think it is time to pull the tail assembly and replace the shafts. Possible that one of them was damaged in a crash. I am leaning towards the shaft coming off the main gear for the tail drive but it all looks ok without the main gear when I just spin the tail.

What happens if you power through the vibration on spool up??

With mine, I will often have the vibration the first time I spool up and once I get past that rpm it is gone. As long as there are no tracking issues, it seems to be nice and smooth in flight. I will see a vibe in the skids during a hover. Not much and not steady. It will come and go. I dropped my pitch curve slightly around the hover and that seemed to help.

I'm like you though, everything has been replaced except for the tail drive assemblies.

This may or may not be related but it is something to look at. Pinch your main gear and tail gear between your thumb and forefinger with one hand. Grab the rotor head with the other. See if you can twist the main shaft in the gears. I have noticed with some of the main shafts I have bought as replacement parts that the hole machined down bottom for the bolt that goes all the way through the shaft/gears is a bit too large. This allows play in the setup down bottom which allows the whole thing to twist a bit. May affect the head geometry a bit but I haven't been able to see any real bad flight characteristics out of it.

Others have told me that they don't have this play. I have taken everything apart and looked at it. The play is clearly from the difference in size b/t the hole in the main shaft and the bolt that is meant to pass through. It is tight on clearance for the gear and the one way shaft but there is too much space IMO in that main shaft.

[SpeedVision]

I don't get any vibration during spool-up...

Super. Now I know my quest is not a waste of time.

are one or both of your main blades too tight in the grips? Just a thought...Have you tried to rebalance the main blades, just to make sure? Are the blades tracking perfectly?

Blades are only tight enough to keep them horizontal if I pick up the heli and point the nose in the air. If I then lower the heli and stop abruptly, the blades will cant towards the ground. I would assume that's loose enough.

Checked and rechecked the Alighn 325 Pro's. Might throw on the never used TT blades to see what happens.

What blades are you using?

Tracking is pretty darn good. The shake only happens at only during the tail end of spool up and goes away just before the heli lifts off the ground.

Just out of curiosity, even though it's soo subjective, can you explain how tight you have your belt? That's one of the few items I haven't addressed. I would say my is moderately tight.

Thanks for the questions and insight.

[SpeedVision]

Ibcynya,

What happens if you power through the vibration on spool up??

It goes away... The vibration is harsh for a few seconds then everything smooths out... All this happens long after the blades have properly centered themselves...

I'd say the lower end of tail fin flex's a good 1/2 inch during the vibration period.

This heli is new and never crashed. This is really my final portion of the build...

I'll try some of your other ideas as well. Thanks.

[mkoutnik]

What blades are you using?

Just out of curiosity, even though it's soo subjective, can you explain how tight you have your belt? That's one of the few items I haven't addressed. I would say my is moderately tight.

Originally I used the original TT blades that came with the MT...They look cool, but were horribly out of balance. Since then, I switched to Align wood 315 mm and 325 mm blades. But after the blade switch I had to replace the upper mixing arms with aluminum in order to get the blades to track. (See attached pic) If you have a spare set of blades you may want to give them a try. Are you using blade spacers in the grips with the Align blades?

As far as the tail belt...I would say that it's moderatley loose - just tight enough were it won't slip. I'm still in the beginning stages of learning, so I'm not doing any insane 3D that would require a tight tail belt.

I hope that helps?! :D

[dynodude]

Try changing your throttle curve and see if it moves the point of vibration. You may be experiencing a condition of mechanical resonance that is manifesting itself through your CF fin. Personaly, if it smoothes out at full power, and is'nt present when you fly, I wouldnt worry about it or try to fix it unless you want to drive yourself crazy trying to isolate and dampen every rotating part on your heli. Just my 2$(inflation)

[SpeedVision]

Ok, here's the update I've been hoping to give everyone.

The vibration is gone. At this point I can attribute the vibration to an imbalance in the rotor head, more specifically the flybar and paddles.

I bought a Du Bro balancer that allowed me to balance the entire head via the main shaft - http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXD712. I removed the swash and any other part that does not rotate with the blades andd first balanced the head without the main blades. In order to get the head to balance, I needed to acutally offset the flybar by about 6/10 of a millimeter. Doesn't sound like much, but this balancer is so sensitive and the heavy side would drop like a rock. Once balanced I could rotate the assembly to any increment and it stay exactly where I put it (think of a clock, flybar at 9 and 3, 12 and 6, 2 and 7, etc).

Next I added the Align 325 Pro's. I removed the balance tape from previously blade only balancing. Trying to balance the head with blades attached proved to be quite tedious. The size of the blades and the sensitivity of the balancer meant that every little disturbance caused the assembly to wander. (just the air disturbance from moving your hand have an effect...). Also, getting the blades perfectly straight also took some patients. This balancer has zero forgiveness, so the better the accuracy of the setup contributes to the end result more dramatically.

After playing around for a couple hours, the final outcome was NO tape on the Aligns and NO further adjustments to the flybar offset. I couldn't get it perfect enough to stop at any increment around center, but the tendancy for one side to drift was sooo slight that it was probably more to do with air disturbances than balance. The blades would hold when set horizontal and vertical, just not increments in between.

Finally, I put everything back together and no vibration during spool up. Tracking was spot on, life was good. Now I can sleep at night.

Thanks to everyone for your input.

PS - If anyone has more experience with these Du Bro balancers and can give us some tips on balancing a rotor head, please chime in and share your experience.

[mkoutnik]

That's really good the hear!! Good work...:D