300X - the HOW TO GET RID OF VIBRATIONS tread

[thruster]

Originally Posted by bobbygz

I had some old grip parts and found another beveled spacer and slapped it together and now I'm flying without any tape on the tail blades. .....

So....does this mean the tail is working good and vibrations are gone? Suh-weet!

[bobbygz]

Yeah, it flies perfect with no vibes at all. Ran 4 packs yesterday, hopefully two packs today at lunch time......and possibly more after work since it will be light out till a little after 7.00 pm

[Tim Wolff]

Originally Posted by Tim Wolff

I'm fixing to do a full teardown on mine. My IU TC is flat 85% and I have a loud and very visible vibration that comes and goes. Snugged everything up. Loosened the tail case screws. Tightened/loosened the belt. etc. Fine for flight or two and buzzin' like hornet's nest the next. Replaced the tail hub and grips with a Align 450 setup and thought I had it licked. Flew great yesterday morning. 8 hours later and it started buzzin' and shakin' as soon as I switched to IU.

Shortly after the post quoted above the vibes caused a death roll and a minor crash. At least there was no damage to the CF main blades. I used 2-56 nylon screws to act as a breakaway mount for the landing gear and they worked as intended too. I boxed the whole mess and threw it on the shelf. A few weeks later, I purchased a unused complete airframe less electronics off eBay for a pittance intending to move the electronics from my original to the new frame. Tossed that on the shelf too.
Fast forward to this year...purchased a Lynx one-way and slant gear setup and lynx main shaft from a fellow freaker here and decided the 300x had been punished long enough.
Attempted to install a Lynx frame stiffener on the new frame, but the 12mm long cap screws are just too short for the job. Ruined the frame attempting to drill the holes deeper for the short screws. Same fit on the org. frame. Screw the frame brace. Pressing on...
Decided to replace everything that spins with parts from the "new" airframe that included the entire tail boom back. Installed the new Lynx on-way and mainshaft. Used the whole head assy. off the new airframe. HK Parkfly motor and 10t slant pinion. Spun it up w/o the mains and the tail buzzed like mad.
I had a NIP Align 450 tail hub that I purchased back in '13, actually a pair of them one of which failed to help with the vibes back then. These were very inexpensive and came with plastic grips. Back in '13 I swapped the org. blade grips and weights etc. to the Align hub. This time I just installed the tail blades and ball links off the org. tail and stuck it on. Adjusted the tail throw on the AR7200 BX setup to keep it from moving too far toward the boom and possibly jamming the blades at full deflection. No weights, just the screws that came with the hub. Spun up really nice w/o the mains for a change. I rebalanced the mains and gave it another try...
Happily, it has never been smoother. It has resonance shake as it spools up that smooths out as the head speed increases. Idle up with a 100% flat throttle curve is smooth like buddah! I can finally enjoy flying this heli. Put 3 packs through it in the front yard yesterday w/o issue.
Ordered some longer fasteners so I can install the Lynx frame brace. It will be nice to finally be able to do some fine tuning on it. I already have a Talon 35 that I'm going to setup to run governed. I want to do a complete setup on the AR7200BX, but will leave it mounted underneath. The set of Boca bearings that have been sitting in the box for two years will be going in. All one at a time and this problem child won't start vibrating again (I hope). The slant gear and one-way bearing setup is nice and quiet. I'm gonna have to get the slant gears for the 450x now.

[thruster]

Tim, great to hear you got her going after all that. I had similar issues a year ago.

[SHYguy]

Bit silly but now almost 2 years later I'm back

The heli's been lying on the desk in my man cave in pieces all this time... now put back together. I'll try and get a test flight in tomorrow
I did notice some lateral play for the main shaft/gear (using the Lynx frame), so I shimmed it a bit.

[thruster]

Welcome back ShyGuy! They say (who ever THEY are) while trouble shooting you should change only one item at a time then test, that way you can pinpoint the real problem. But sometimes this can take almost forever. So remember if needed, just go for it and change everything at once.

[SHYguy]

Thx Thruster!

Good points there!

[SHYguy]

OK, first test done. I spooled it up on the bench w/o main/tail blades - fine.

In the field I get massive tail wag. I see the belt moving a bit from side to side, but quite slowly,

So it's back to the shop:

1) test w/o main blades

[mustangflyer]

300X vibrations only with fiberglass canopies! No vibrations with stock plastic canopy. Any ideas ?

[SHYguy]

Originally Posted by mustangflyer

300X vibrations only with fiberglass canopies! No vibrations with stock plastic canopy. Any ideas ?

My guess is you have vibes, and the stiff fibreglass canopy enhance them to the level of it becoming a problem.

[mustangflyer]

Originally Posted by mustangflyer

300X vibrations only with fiberglass canopies! No vibrations with stock plastic canopy. Any ideas ?

Lowered trottle curve to 85% / 75 / 70 / 75 / 85 % AND vibrations with fiberglass
canopies went away. Can use 100 / 100 / 95 / 100 / 100 with stock plastic canopy
without vibrations. Probable cause = stock wooden blades (?)

[SHYguy]

Ah yes woodies are a no go with high HS, get carbons and balance them!

[PilotPin]

I had trouble with the stock head dampeners wearing out fast and causing vibrations. I added a couple more shims to tighten thing up. That has taken care of the problem.

[Tim Wolff]

Originally Posted by PilotPin

I had trouble with the stock head dampeners wearing out fast and causing vibrations. I added a couple more shims to tighten thing up. That has taken care of the problem.

Lynx dampers will take care of it too. Hard as rocks compared to the stock dampers.

[SHYguy]

OK guys, almost too embarrassed to say this... but my 300X has been grounded for like 2 years now due to a vibration problem I never did figure out (and I have lots of other helis to fly).

Now that the rest of the fleet is operative I though it was high time to try and cure this oldie



After lots of elimination testing I've localized the source of the vibes. It's in the tail. At lower speeds it's all good but at max headspeed (Scorpion motor 2313-14) the tail shaft starts to vibrate like crazy. See illustration with the red line. It's insane how much the shaft flexes!

I've tried:
-Two different shafts
-New Boca bearing in the tail
-Three different sets of tail blades
-Balancing the entire tail assembly and dynamic balancing

When I remove the blades it's ok. Any ideas as to what to do?

Here's info on my tail grip setup:
https://www.helifreak.com/showthread...=543119&page=3
-maybe I should try to go back to the stock tail hub...

[chuteopn]

Hey Shy, what tail shaft are you using and is there any lateral play in the shaft?
I had to go thru 4 stock tail shafts to find a straight one.
Put one in without the hub and spin it up with pitch slider in middle. ( Mains removed) Most look fine at lower HS, but at high HS you can see how bad they are.
I've since changed the whole tail setup to Lynx with the Align tail grips.
Has been flying great for over 2 yrs now.

[PilotPin]

Void

[PilotPin]

SHYguy

Make sure that the inner races are snug on the shaft and the outer race is snug. Take a tooth pick and put some loctite on the races. This will take up any slop and keep the races from spinning and causing any vibration.

[SHYguy]

Hi guys! Thx to both of you - will check/try!

Tried with Lynx and stock shaft.

[SHYguy]

Sorry for the long wait. One of the really smart guys on here (dCH) noticed in the pics that one of the pins in the tail pitchs arms had come out - this could very well be the cause!...

But sadly no... ok, so the final attempt will be:
-Get a new std plastic tail case + a new tail shaft... if that doesn't fix it then it's retirement...