Rudders fluttering

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rcm243
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Rudders fluttering

Post by rcm243 » Tue Apr 19, 2016 8:09 pm

I just put an old hull back in operation with a 0360 that a friend wasn`t using, I built the rudders out of thin paneling and glassed both sides, they flutter like hell when I throttle up, what could be wrong . RCM
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Deano
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Re: Rudders fluttering

Post by Deano » Tue Apr 19, 2016 8:51 pm

Not enough information given to narrow down the list of possibilities.

How do you define 'thin' paneling? What exactly did you do when you 'glassed' them?
Do they have some kind of framework? If so, how robust? what spacing?
What size are they and where is the pivot point (front to back)?
What kind of steering (cable / mechanical)? Do you have a drawing or
Can you post some pictures?

I am in no way meaning to be a smartass . . . I salute your ingenuity. :salute:
Trouble is that you know what you mean, how they were built and what they look like, but we don't.

Just a wild ass guess, but is the skin (surface) flexing when it flutters?
If so, maybe filling them with sprayed foam would provide the rigidity that they currently lack? :dontknow:
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rcm243
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Re: Rudders fluttering

Post by rcm243 » Tue Apr 19, 2016 8:57 pm

Deano wrote:Not enough information given to narrow down the list of possibilities.

How do you define 'thin' paneling? What exactly did you do when you 'glassed' them?
Do they have some kind of framework? If so, how robust? what spacing?
What size are they and where is the pivot point (front to back)?
What kind of steering (cable / mechanical)? Do you have a drawing or
Can you post some pictures?

I am in no way meaning to be a smartass . . . I salute your ingenuity. :salute:
Trouble is that you know what you mean, how they were built and what they look like, but we don't.

Just a wild ass guess, but is the skin (surface) flexing when it flutters?
If so, maybe filling them with sprayed foam would provide the rigidity that they currently lack? :dontknow:
They`re made of 1/4 in. plywood and fiberglassed on both sides with 1oz chopped strand mat, the pivot point is 6 in. back from leading edge, they are spaced 26 in. apart. Mechanical steering, the rudders are 24x48in.
Politicians are like whores,as long as the money`s available they`re there for you.

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Waggs
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Re: Rudders fluttering

Post by Waggs » Tue Apr 19, 2016 9:15 pm

6" seems like a lot. Not sure what mine measure from leading edge but I don't think it's 6", prolly more like 4". Do you have "hat" bushings installed? Is the linkage twinced the two good and tight. Good hiem joints and what not.
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Deano
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Re: Rudders fluttering

Post by Deano » Tue Apr 19, 2016 9:18 pm

OK. So they are not hollow then, my bad.

When you say 'fluttering', is that to say that when the stick and associated steering is
held stationary under power that the trailing edge of the rudders is moving left and right?

If this is the case, is the front edge moving as well or is it staying stationary?
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

rcm243
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Re: Rudders fluttering

Post by rcm243 » Tue Apr 19, 2016 9:41 pm

Deano wrote:OK. So they are not hollow then, my bad.

When you say 'fluttering', is that to say that when the stick and associated steering is
held stationary under power that the trailing edge of the rudders is moving left and right?

If this is the case, is the front edge moving as well or is it staying stationary?
You can feel the steering stick moving back and fourth
Politicians are like whores,as long as the money`s available they`re there for you.

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Re: Rudders fluttering

Post by fladan » Tue Apr 19, 2016 10:24 pm

I just read through some old post about trim tabs and they were talking about the setup of the rudders with the pivot points 6" or less from the front so it seems that might not be your problem. I had to install trim tabs on mine because it wanted to pull to the left all the time. Once they were installed, my stick would stay straight hands off. Back to your problem; during my search to solve my problem, someone mentioned the distance between the front of the rudders should be just a little bit WIDER than the measurement between the rear of the rudders. This would cause the air to channel through a smaller opening at the rear putting pressure on both rudders and not letting them search for center independently. Maybe someone else can chime in here with their opinion. Good luck!

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Re: Rudders fluttering

Post by Whitebear » Tue Apr 19, 2016 11:49 pm

With the tie rod between the nose of the rudders you can set in a little bit of toe-in or toe-out. Either should go a long ways toward preventing flutter.
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Re: Rudders fluttering

Post by Gary S » Wed Apr 20, 2016 7:40 am

What are you calling fluter? Is the stick vibrating in your hand when your running? Layup on rudders sounds light, are you able to flex the rudders by hand? I would be concerned about delimitation especially with such a light layup and the amount of wind hitting it on the edge. Were the edges glassed as well?

AceNtheHole
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Re: Rudders fluttering

Post by AceNtheHole » Wed Apr 20, 2016 7:01 pm

hehe...... he has 'rudder flutter'......... :wink:

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Re: Rudders fluttering

Post by rcm243 » Wed Apr 27, 2016 2:04 pm

[quote="AceNtheHole"]hehe...... he has 'rudder flutter'......... :wink:[/quo Problem solved, I put a set of air foil rudders on .
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Re: Rudders fluttering

Post by Gary S » Fri Apr 29, 2016 7:48 am

There you go.

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