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 Sunderland S-18 (T-18CW)
 Convertible Wing
 Wing Flutter
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jlevi

USA
5 Posts

Posted - 08/23/2010 :  16:07:05  Show Profile
I just got my plane backi the air after painting. I was coming back from Brown field and hit a little turbulence so I back down on the speed and at 160mph the wings started to flap. They were going about 4" at the tips. I slowed and it stopped.

During the first 2 years of flying, I had no issues. The plane was primed but not painted. I checked the ailerons yesterday and found a little play which I fixed. In addition I had shifted them up to match closer to the tips, So I rerigged them down to match the bottom of the wing where they were before. I took it up yesterday evening and didn't feel anything. I banged the stick and got nothing to over 190mph.

Anybody seen anything like this on a Thorp?

Jon
N165JL
Fallbrook, Ca

Rich Brazell

USA
911 Posts

Posted - 08/23/2010 :  16:56:24  Show Profile
4 inches ! I can't see how that is possible on a stiff wing like this A/C. Unless your S-18 wing pins are loose ? Even then there should be very little play. In turb. it may appear that the wing tips are moving more in relation to the rest of the A/C. It is also possible that while at Brown Field you ate one of those wacky Fish Tacos with Hot Sauce, causing temporary spatial disorientation !

I am surely (don't call me Surely), that you checked the wing tip play when you got on the deck ? You didn't mention that ?

PS...When I flew King Airs (stiff wing), the same type of "wing tip movement" could be observed. A little unnerving for a "new co-pilot!" ME!

RB
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admin

USA
168 Posts

Posted - 08/23/2010 :  18:17:53  Show Profile  Visit admin's Homepage
John,
I have been through extreme turb in my Thorp. My wing tips never moved. At one point I had full forward stick and was doing 1500 fpm climb. What you describe does not sound like flutter. As Rich suggested, check your pins for play. Don't fly it with play!
Cubes

** admin posted for Cubes **
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jlevi

USA
5 Posts

Posted - 08/24/2010 :  11:45:40  Show Profile
There is no play in the wings. The pins are tight. Shaking the wing and looking to ensure the whole plane shakes is part of my preflight. It is definately a vibration since it went away when i slowed. I have not seen it before while flying in turbulence.
I have been concentrating on the ailerons since something must be moving. There is no indication of stress on the wing (inspected after landing). What I have done is take all slop out of linkage. I have reset them to match the bottom of the wing which is where they were originally. The flight I took Sunday after these mods was good up thru 190mph. It was dusk, so the air was smooth, so I banged the stick to try and cause any vibration. Didn't feel or see any.
I still plan to add some extra weight to the counter weights to bring them close to balanced. They have always been heavy.

Jon
N165JL
Fallbrook, Ca
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Bill Williams

USA
336 Posts

Posted - 08/24/2010 :  11:55:44  Show Profile
Levi, if you have riveted trailing edge aileons, you will have a heavy stick as speed increases. I have found folded trailing edges decrease the heavy stick as speed increases.
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Rich Brazell

USA
911 Posts

Posted - 08/24/2010 :  14:51:07  Show Profile
Jon: The fact you took all the "slop" out of the linkage, may have cured your problem. Where exactly did you take it out ? Bell cranks (at the wing joint ?) ? Push rods ? Walking beam ?

RB
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jlevi

USA
5 Posts

Posted - 08/26/2010 :  12:31:27  Show Profile
I took out the play by adding a small spacer at the wing joint bell cranks. I used Micarta for the spacers. I have ordered some RC model lead weights. I will add these to the existing weights to balance for the paint since I know they got heavier.

Jon
N165JL
Fallbrook, Ca
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