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Old Aug 22, 2015, 05:27 PM
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Zipper wing wagging problem

I have, what looks like, an original Goldberg Zipper with an Astroflight 05 geared electric motor. The problem is that the wings wag (oscillation about the roll axis) with a period of two to three seconds, which is annoying. The balance is about right (6" back from the LE and it glides very nicely with a little down elevator) Any ideas on how to stop the wagging?
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Old Aug 22, 2015, 11:48 PM
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Sounds like a poorly damped dutch roll mode. Increase the size of the fixed vertical stabilizer and it will stop oscillating.

Steve
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Old Aug 23, 2015, 04:24 AM
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Yes, sounds like dutch rolling. If the model has the original dihedral (i.e. as a free-flight model) then some designs, when flown under radio, do demonstrate this characteristic, in these case an increase in vertical tail surface area can help. I note that you say that the glide trim needs some down elevator; if you re-trim so that the glide is right with neutral elevator by moving the CG forward, you might find that also reduces the dutch rolling.
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Old Aug 23, 2015, 10:36 AM
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Quote:
Originally Posted by Toodle View Post
I have, what looks like, an original Goldberg Zipper with an Astroflight 05 geared electric motor. The problem is that the wings wag (oscillation about the roll axis) with a period of two to three seconds, which is annoying. The balance is about right (6" back from the LE and it glides very nicely with a little down elevator) Any ideas on how to stop the wagging?
A classic case of Dutch rolling! Lots of these vintage polyhedral models do this, and the suggestions made will go some way to curing it. Let`s not forget that most if not all of these vintage type models were designed for free flight with maximum endurance, and some don`t take kindly to having their normal flight path interfered with! It`s the price worth paying for the elegance of these models in the air!
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Old Aug 23, 2015, 11:18 AM
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And, of course, I forgot to say - keep the rudder movement down and have some exponential. The secret is to fly them with very gentle rudder inputs to avoid the rocking starting up in the first place.
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Old Aug 23, 2015, 11:30 PM
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Had a Mcoy 60 in mine ,Dutch rolled all over the country first few flights ,couldn't keep up with it and had to shutoff after about 5 secs engine run . My friend Lionel said to put in more washout in the outer panels ,instant fix . Beautiful aeroplane , just to hard to build as against a Playboy . Will build another one day. .
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Old Aug 24, 2015, 12:18 AM
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Quote:
Originally Posted by Geoff Potter View Post
Had a Mcoy 60 in mine ,Dutch rolled all over the country first few flights ,couldn't keep up with it and had to shutoff after about 5 secs engine run . My friend Lionel said to put in more washout in the outer panels ,instant fix . Beautiful aeroplane , just to hard to build as against a Playboy . Will build another one day. .
Geoff,
This probably worked because it unloaded the wingtips where dihedral was the largest resulting in less effective dihedral for the entire wing. Reducing dihedral or increasing fin area are the 2 major factors in stabilizing the dutch roll oscillation.

Steve
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Old Aug 24, 2015, 03:28 AM
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Yes Steve, it most definitely did work like that . That is the only option available. Out here in Aus we are not allowed to deviate from the plan ,ie ,fin ,diaheadral alterations . So one has to make the model fly as it should ,looking like it should ,and built like it should be .
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Old Aug 24, 2015, 04:22 AM
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I must say I hadn't thought about adding washout to the tips, but it makes sense. A good fix where rules prohibit reduction in dihedral or increase in fin area, or for an already completed model where these changes would be hard to implement
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Old Today, 04:14 PM
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First, I want to thank all of you who have taken the time to respond with helpful suggestions. I tried to put in some washout with a heat gun, but the old covering is so brittle that it won't hold a preset. So, at the suggestion of Jerry P. (a real pro and nice guy), I added the TE thickeners shown below to achieve some washout.

With the thickeners, Jerry's tutoring, and a soft touch on the rudder, the plane flies OK now. Thanks again!
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Old Today, 07:52 PM
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I'm glad you got it sorted out Toodle,

I was talking to a mate of mine the other night. He has a large Zipper with an OS 91 surpass.

He has it trimmed for the climb and let's it fly free flight style, spiralling up to altitude. There's no way he can touch the controls during the climb, but it's fine in the glide which confirms what others have said and what you've found.

He uses the model for competition work so it's fine like that, not so good for a sports model though.

Cheers,

Dave H
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