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Permalink Reply by Clint L Gosch on May 21, 2018 at 5:14pm

Hi Loren,   I have a fifth option for you, countersink both sides and set a double flush rivet.  A pancake drill with either a deburring bit or a very shallow counter sink bit should be able to countersink the top hole.

http://www.vansairforce.com/community/showthread.php?t=118615

This website has a discussion that may (or may not) describe it better.

For what it's worth, I'm considering not installing it.  The bolt seems to be doing most of the work in this joint.

 

You may get many different opinions on this, go with the one that makes the most sense to you.

Hope this helps!  Good luck!

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Permalink Reply by Loren Warner on May 21, 2018 at 5:42pm

Thanks Clint,

I've never seen a pancake drill or double flush rivets.  Something to look into even if we don't use it. 

I'm hoping someone who has been flying their aircraft for a long time, after performing one of the other options will chime in.

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Permalink Reply by Clint L Gosch on May 21, 2018 at 9:03pm

Understood,  I look forward to hearing how other builders have approached this.

Just for reference, here is the setup I might use to perform the countersink for the top hole, not much clearance in that location, the pancake drill attachment is available at yardstore.com.  I've also attached a picture of a practice piece I used to try out the double flush technique.  First try was a complete failure, countersink was too deep.  Second try was better.  Still need more practice before I try it on the real part, if I decide to do it at all.  

 

Attachments:

• 20180521_204530.jpg, 2.9 MB
• 20180521_204819.jpg, 2.3 MB
• 20180521_204833.jpg, 2.3 MB

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Permalink Reply by David J. Beaulieu on May 21, 2018 at 9:27pm

Loren, this is not a newly discovered problem among the builders. The necessity of the rivet has been discussed previously. If I recall correctly, Caleb (aero engineer formerly associated with Zenith)was insistent that the rivet be installed. Seems it acted as some sort of stress relief?
Anyway, Clint has the answer, do a double flush traditional bucked rivet. There is room for a bucking bar on the backside, but it does take a bit of practice to set the rivet. If you get most of it in there and set, it's just a matter of shaving or taking it down flush with a file or sander. There is plenty of material to countersink into.

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Permalink Reply by Loren Warner on May 21, 2018 at 11:38pm

David, this may be a long known problem to some Zenith builders, but it completely escaped me.  Our 750 STOL is the latest version, and it's incredible that the builders guide and plans continue to require a rivet that we later need to replace. 

I just got email from Roger suggesting we "replace with a countersunk flush rivet and notch the backside of the strut fitting."

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Permalink Reply by John Austin on May 22, 2018 at 6:20am

I agree with David.  The rivet IS necessary and apparently acts as a stress relief.  I recall a simplistic explanation that "stress flows to the path of least resistance, just like water, and the rivet controls where that stress flows."

On my build, I pretty much installed the rivet per plans.  I had to slightly radius the fitting's edge to clear the rivet and it seemed to work OK ... or at least has worked OK for 500+ hrs!  ;>)

John

N750A

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Permalink Reply by Loren Warner on May 22, 2018 at 8:47am

Ok, so doing as Roger suggests by replacing with a flush rivet and slightly notching the back side to fit the rivet should suffice, although not as clean as Clint's double flush rivet.

Thank you guys for the information.

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Permalink Reply by Clint L Gosch on May 22, 2018 at 11:59am

Actually, I stole the idea from David.  I've been trying to keep my workmanship standards on par with David's, John's, and Joe H's planes (along with a bunch of others on this forum).  I figure if my plane turns out half as nice as their's I'll be happy.  Keep up the good work!

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Permalink Reply by Loren Warner on May 22, 2018 at 5:13pm

You guys left me in the dust a long time ago, following the rudder build.

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