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Old 07-07-2019, 08:57 PM   #1
DaveV
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NORSEMAN Unionville wing support?


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Got myself a used 86" Norseman, converted it from floats to wheels, installed a Saito FA100 and did the maiden.
The maiden lasted about 10 seconds and the wings folded up; First one side, followed immediately by the other side. The four 1/4"dia wing support struts all broke right in the middle. Damage to the fuse and both wings is now fixed except for the Monokote but I'm still scratching my head over why the struts broke and how to make it stronger for the next flight. Other similar planes with high wings usually have an alu tube connecting the two wing halves, passing through the fuse. The Norseman drawings don't call for that and doing a retro fit would be a lot of work redesigning and rebuilding the wings and the fuse.
I'm sure the previous owner of the plane flew it with only the external struts supporting the wings and would think that most others do the same since that is what the manual calls for.
Has anyone done anything extra to give the wings better support?

Dave
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Old 07-07-2019, 10:28 PM   #2
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Re: NORSEMAN Unionville wing support?

You did not state if the wing struts gave way. I would suspect that is the case if the wings folded as they were the only support. The fuse attach points were not designed for torque. Nor were they designed for full support of the AUW if wing tubes were modded to fit. Along with altering the wing structure the same would be required for the fuse sides if you wanted to build it fully cantilever with struts just for appearance sake.

Personally, I would make use of what is there, just a bit more substantial. The original struts you can see in the pics were not really all that strong, even when the brass tubing was pinned to the wood. I intended to replace mine with more scale alloy tubing with some form of straight bar to attach each end and form the attach fitting. This is how full scale are done.

ps. I regret ever selling mine and if encountered one again would make several changes to build it both lighter and stronger. There was really no requirement for the bulkheads and stabs to be built from slabs as they were. Wings would have individual servos and the firewall moved back to fit a larger engine.

Other than that, would be nice to see another large Norseman kit from any maker.
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Old 07-08-2019, 12:41 AM   #3
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Re: NORSEMAN Unionville wing support?

DaveV
Sounds like a few problems there without seeing just how the struts were connected to the wing and fuse and how the attachments were done to the 1/4 inch dowls.
Good choice would have been 1/4 by 1/2 inch square.., straight grained pine, spruce or beechwood with the leading and trailing edges rounded , could be one choice. First choice could be stainless steel pipe strapping from hose clamps ....solid type for the end pieces. To strengthen the longitudinal wood would be to grove the inside our outside piece of strut wood enough to take a length of 1/16 music wire bent 90 degrees at the ends to slip into matching holes of the ss strapping . Make sense without drawings ?

Problems these days , there are hardly any kits around for guys to learn how to built and modify like the old days when all we had were magazines and builders/modifiers articles on how to do things better. Called “hints and “kinks” or something like that.... Gary would remember.
By going through those building years fellas pick some good knowledge by themselves and talking to other builders .

Last edited by stegl; 07-08-2019 at 12:50 AM.
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Old 07-08-2019, 08:36 AM   #4
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Re: NORSEMAN Unionville wing support?

You did not say what gave way! Did something break? Did a glue joint separate? What caused both sides to fold? Did they fail at the same spot? Did you do a sharp turn that caused the failure? If we knew where it failed and the design of the item at that point it would be easier to help.
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Old 07-08-2019, 09:55 AM   #5
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Re: NORSEMAN Unionville wing support?

I said: "The four 1/4"dia wing support struts all broke right in the middle."
Pics will follow.
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Old 07-08-2019, 10:02 AM   #6
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Re: NORSEMAN Unionville wing support?

Thanks for the quick replies. Here a few pics showing the before and current. The pics from Gary reminded me that my struts didn't have the half way supports to the wing. This plane never had them (no holes in the wings for them) and I had looked at some other pics on the net showing this plane without them. I can see how perhaps harmonic vibration on full power take-off may have played a roll and will definitely install half way strut to the wing supports.
I had already bought the 1/4x1/2 flat stock suggested by stegl (my big Cub has those) but am hesitant because of the 90deg offset for the fuse connection.
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Old 07-08-2019, 10:43 AM   #7
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Re: NORSEMAN Unionville wing support?

From the close ups of the broken struts it looks like a wide span bending failure similar to what you would get if trying to flex them over your knee. The fact both are mid span would make me suspect stress from prop pulses and/or airflow. The latter would be less on my list since the Saito likely does not pull it that fast. Like full size, this is a high drag airframe.

Also, the fact this happened on your maiden hints to me there may have been other problems, such as bending stress on the struts set when bolting everything together. That all 4 failed would not really indicate some hidden flaw in the wood itself, unless the first caused a cascade. If that were the case the breaks would likely be different.
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Old 07-08-2019, 11:15 AM   #8
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Re: NORSEMAN Unionville wing support?

Looks like we're on the same page with what I call harmonic vibration. Previously the plane was flown with a smaller 4stroke (72).
Here is what the manual calls for, showing a 1/16 wire support half way up the strut. Mine didn't have that and it would have prevented the pulsing and therefore the break. You've got to love how well manuals used to be illustrated and worded.
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Old 07-08-2019, 11:23 AM   #9
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Re: NORSEMAN Unionville wing support?

The break appears ( to me) almost across the grain so they could have broken even with the
Wire support. Definitely not straight grain wood.
Also I would not have glued the dowels into the brass tubing as indicated . If it had to go that route I would have used at least two stick pins thu the brass tubing and dowel at 90 degrees to each other. Sort of a rivet effect. Would require a very tiny drill and glue in with ca and snip off the long end, allowing a little to protrude. Minimizes the weakening of the wood vs a small screw.
The wire makeup would still hAve to be used to minimize vibration.

Last edited by stegl; 07-08-2019 at 11:34 AM.
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Old 07-08-2019, 07:38 PM   #10
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Re: NORSEMAN Unionville wing support?

My impression was the dowel was a poor choice of material and unless very expensive woos that has perfect.grain from end to end is just about guaranteed to break without the 1/16 wire.

I would use a tube of metal or composite and still put the mid support in.
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