nzrv8
Well Known Member
Afternoon all,
I've been having trouble with #40 dimples cracking on the rear wing spar flanges. Initially, I noticed these only on the RH wing top flange. They were visible with the naked eye, and most (but not all) would clean up with a #30 hole. Approx 15 cracked dimples were identified.
All dimples were done with a hand squeezer and Avery spring back dies. All holes reamed and deburred as I usually would.
I made up a test piece out of the same thickness material, and ran some tests including different dies and deburring techniques (including not deburring at all). The results were inconclusive - the only dimples that had any similar cracking were the ones that weren't deburred first, and even these cracks were much more minor than the ones on the spar flange - they polished out with a pass or two of scotchbrite.
A quick visual check of the LH rear wing spar was made under good lighting led me to believe that the problem lay with the RH spar only.
The decision to replace the wing rear spar was made, and parts ordered.
Fast forward to today. I was getting ready for the final wing assembly on the LH wing. I thought I would inspect each dimple under 10x magnification on the rear spar flange, just to be 100% sure. You guessed it - cracks. Much smaller than the RH wing, and difficult to see with the naked eye. Once again, approx 15 or so, but on both the top and bottom flanges.
Interestingly, every single crack is in the approximatly 5:30 position when viewed with the wings vertical in their stands. So regardless of flange bend direction, or squeezer orientation, every crack runs down towards the floor.
I'm curious to see if anyone else has had a similar issue, and what did they do to fix it? Hopefully the photos attach.
Cheers,
Hugh
I've been having trouble with #40 dimples cracking on the rear wing spar flanges. Initially, I noticed these only on the RH wing top flange. They were visible with the naked eye, and most (but not all) would clean up with a #30 hole. Approx 15 cracked dimples were identified.
All dimples were done with a hand squeezer and Avery spring back dies. All holes reamed and deburred as I usually would.
I made up a test piece out of the same thickness material, and ran some tests including different dies and deburring techniques (including not deburring at all). The results were inconclusive - the only dimples that had any similar cracking were the ones that weren't deburred first, and even these cracks were much more minor than the ones on the spar flange - they polished out with a pass or two of scotchbrite.
A quick visual check of the LH rear wing spar was made under good lighting led me to believe that the problem lay with the RH spar only.
The decision to replace the wing rear spar was made, and parts ordered.
Fast forward to today. I was getting ready for the final wing assembly on the LH wing. I thought I would inspect each dimple under 10x magnification on the rear spar flange, just to be 100% sure. You guessed it - cracks. Much smaller than the RH wing, and difficult to see with the naked eye. Once again, approx 15 or so, but on both the top and bottom flanges.
Interestingly, every single crack is in the approximatly 5:30 position when viewed with the wings vertical in their stands. So regardless of flange bend direction, or squeezer orientation, every crack runs down towards the floor.
I'm curious to see if anyone else has had a similar issue, and what did they do to fix it? Hopefully the photos attach.
Cheers,
Hugh