RunRyder - T-REX 450 low rpm vibrations

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e-Align T-REX 250-450-500-600 > T-REX 450 low rpm vibrations

nmrs
Senior Heliman
Location: Austin, TX

I am getting some medium vibrations at low RPM. I only see them when the heli is spooling up. Once it's up to speed, vibrations are gone and the heli is stable. Just wondering if it is normal or something I need to track down.

A friend suggested I try balancing the tail blades. I tried to with this tool http://www.readyheli.com/K10289A_Ma...0_p/k10289a.htm which I use to balance my main blades, but my tail blades won't fit on the shaft of it. It says it's a tail balancer so I guess I should be able to... Just wondering if it's safe to drill out the tail shaft holes a bit to get them to fit on it, but worried that will just make the vibs worse rather than better...

06-03-2008 03:39 PM

sinte
Senior Heliman
Location: Tacoma,WA

...dampers...play between pinion and main gear...play between mast collar and top bearing block?

.....97% Adrenaline...3% Skill.....

06-03-2008 05:22 PM

nmrs
Senior Heliman
Location: Austin, TX

So it sounds like this is not normal behavior and I should start trying to track it down.

Any advice on drilling out the tail blade holes? My gut tells me not to, which is why I haven't yet. Has anyone else tried to balance their tail blades with that align balancing tool?

06-03-2008 05:23 PM

helimatt
Elite Veteran
Location: Lafayette, IN

That tool looks like its meant to be used for balancing the entire tail hub/grip assembly including the blades. I am not familiar with it, but it would need to be very sensitive. Might work well

What I do is spool up the heli with the main blades and flybar paddles off, (carefully) feel the tail for vibrations. They would be high-frequency. Add some clear scotch tape to one blade about mid-span (not much tape needed), and spool up again to see if the vibration is better. If so, add a bit more tape there. If it then gets worse, take a bit of the tape off.

If originally adding tape makes the vibration worse than when you started, then add the bit of tape to the other blade, etc. Trial and error.

Its one of the more tedious things about tuning a 450, and I don't enjoy it, but you can resolve the tail-sourced vibrations very nicely that way.

If the vibes are stubborn, look for a bent tail hub or grip bolt. All this presumes the tail shaft if straight.

Never, ever, ever, ever give up.

06-03-2008 06:53 PM

nmrs
Senior Heliman
Location: Austin, TX

Quote
That tool looks like its meant to be used for balancing the entire tail hub/grip assembly including the blades.

Eureka. Thanks for that. I just went back and looked at the photo on that page again and you are right, they have the whole assembly on there. Thanks for that. Glad I didn't drill out my tail blade holes now

06-03-2008 07:41 PM

nmrs
Senior Heliman
Location: Austin, TX

Ok, I tried to balance the entire tail hub assembly, but I can't figure out how to get the tail rotor off of the tail shaft. I took the blade grips off, unscrewed the grub screw and pulled at it as hard as I could and it seems pretty well permanently mounted on there. Anyone know how to remove it?

06-03-2008 08:43 PM

kcass518
Veteran
Location: Manhasset, NY - USA

I'll jump in on this one, too!

Minor vibrations on spool up can be caused by the grips being a bit tight. When the head starts spinning and the blades are seeking their proper place, a tight blade grip will cause a bit of vibration until you reach full speed and the blades are settled. I wouldn't worry about it, if that's what's happening. You want the grips snug, but not too tight (both main and tail).

DO NOT 'drill out' your tail blade holes (I'm confirming what you already know).

To balance my blades, I use a scale and add tracking tape to the light blade until they weigh the same. I take it a step further with a Koll Rotor Pro and put that tape in a place that will give me matching centers of gravity, but that's a bit overkill for what you're doing. I use an Ohaus Cent O Gram for the big blades, and a gunpowder scale for the tail blades. I'm not saying you need any of these things, but that's how I do it. After I know that the blades weigh the same, and that they have the same CG, then I put them on the head and make sure the whole thing balances on a High Point balancer (Dubro or Robart). OR, you can do it dynamically as Helimatt suggests.

06-03-2008 08:52 PM

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e-Align T-REX 250-450-500-600 > T-REX 450 low rpm vibrations

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