Bad vibration

[Jerrymac]

Last fall, at the end of our flying season here, I finished my 'low cost' Hurricane 425 build. I only got a couple of test flights in before the weather turned sour and never really had a chance to perfect the set-up.
Last weekend I finally got the first chance to get out to fly this year. I spooled up the new 425 and noticed that the vertical tail fin is vibrating badly, about 15 or 20mm at he lower tip. This is a totally new build from a new kit. I have checked the belt and found no problems with it. I removed the tail shaft and chucked it up in a drill press, then placed a dial indicator on it and spun it. It showed no signs of being bent. I put the tail blades on a balancer and they were fine. I checked the tail boom supports for loose screws and all were tight.

I am at a loss. Any ideas of what else to check? At this point I am thinking that it might be the main blades that are out of balance and just transferring the vibration to the vertical tail fin, I dunno. I think I might swap the main blades out with the ones on my other 425 to see if it makes any difference, although I might have to adjust the blade tracking then. I really hate taking one helicopter apart to test the parts on another one, especially when the "donor" helicopter flys great.

If you guys think it might be the main blades causing the vibration in the tail fin, I think I will just try another set of blades first before robbing parts from my other 425. If you have any other suggestions, I am all ears because at this point, I am a little baffled.

Thanks,

Jerry

[dunkonu23]

Jun 13, 2012 2:28:58 GMT -5 Jerrymac said:

Last fall, at the end of our flying season here, I finished my 'low cost' Hurricane 425 build. I only got a couple of test flights in before the weather turned sour and never really had a chance to perfect the set-up.
Last weekend I finally got the first chance to get out to fly this year. I spooled up the new 425 and noticed that the vertical tail fin is vibrating badly, about 15 or 20mm at he lower tip. This is a totally new build from a new kit. I have checked the belt and found no problems with it. I removed the tail shaft and chucked it up in a drill press, then placed a dial indicator on it and spun it. It showed no signs of being bent. I put the tail blades on a balancer and they were fine. I checked the tail boom supports for loose screws and all were tight.

I am at a loss. Any ideas of what else to check? At this point I am thinking that it might be the main blades that are out of balance and just transferring the vibration to the vertical tail fin, I dunno. I think I might swap the main blades out with the ones on my other 425 to see if it makes any difference, although I might have to adjust the blade tracking then. I really hate taking one helicopter apart to test the parts on another one, especially when the "donor" helicopter flys great.

If you guys think it might be the main blades causing the vibration in the tail fin, I think I will just try another set of blades first before robbing parts from my other 425. If you have any other suggestions, I am all ears because at this point, I am a little baffled.

Thanks,

Jerry

Could be the main blades, gear mesh, etc. I would first check the boom supports to make sure there is a little load on them and glue the mounting points in with JB Weld.

Scott