Ongoing spar tunnel annoyances
Posted: Tue Dec 27, 2011 5:38 pmHey all...
The saga of my spar tunnel build continues. I've completely rebuilt it now, and I'm pretty happy with it, EXCEPT...
Some of the holes in the tunnel sheet metal and the angle crosspiece are larger than I'd like (I riveted the aft part together before realizing that I shouldn't do that until the gear attach points are in place, so I had to drill out all the rivets again). The largest holes are about #27 in size, there's perhaps 6 out of 50 that size. I tested on some scrap and the rivets will still grab on that size hole, but since this is a structural area I want to make sure it's as strong as it should be. So I have three options:
1) Shrug, assume it's fine, and carry on;
2) Updrill the holes to 5/32 and install larger rivets;
3) Do the whole back side of the spar tunnel over again.
Here are some pics...first, one of the most enlarged holes in the angle (top), next to a normal hole:
Here's the same hole with a rivet stuck through it so you can see the degree of space around the rivet (some of that darkeness is the deburred area though, you have to look close at the innermost black ring that is the gap):
Finally, here is a rivet stuck through the tunnel sheet metal so you can see how enlarged those holes are (all of those are roughly the same size):
I'm actually more concerned about the tunnel holes than the angle holes. All of the tunnel holes are larger from stretching during dimpling, in spite of using a #32 drill bit as recommended by Sonex. Some in the Yahoo group have said that as long as you have enough material for the countersunk head to grab, it's enough, but I'm not sure I'd agree with that.
To do #2 I could use these rivets:
http://www.rivetsinstock.com/rivets/blind-rivets/basic-structural-blind-rivets/q-rivet.html
They have tensile & sheer strength over 1000 each, and so the joints should be stronger than the factory specified rivets, but probably have larger heads and that means removing some additional material to countersink them. I'm guessing the additional rivets will cost about $100.
If I remake the aft tunnel again, the parts will cost $61 + shipping. The good news is I've re-made the tunnel before, and I can do it pretty quickly. It's just demoralizing to have to keep making the same parts (and paying for them!)...
Okay...suggestions, recommendations, recriminations? Am I just being too picky? Is all this "good enough"? Will my Sonex disintegrate in flight if I even think of using these parts? Inquiring minds want to know!
If you got this far, thanks for reading all this!
The saga of my spar tunnel build continues. I've completely rebuilt it now, and I'm pretty happy with it, EXCEPT...
Some of the holes in the tunnel sheet metal and the angle crosspiece are larger than I'd like (I riveted the aft part together before realizing that I shouldn't do that until the gear attach points are in place, so I had to drill out all the rivets again). The largest holes are about #27 in size, there's perhaps 6 out of 50 that size. I tested on some scrap and the rivets will still grab on that size hole, but since this is a structural area I want to make sure it's as strong as it should be. So I have three options:
1) Shrug, assume it's fine, and carry on;
2) Updrill the holes to 5/32 and install larger rivets;
3) Do the whole back side of the spar tunnel over again.
Here are some pics...first, one of the most enlarged holes in the angle (top), next to a normal hole:
Here's the same hole with a rivet stuck through it so you can see the degree of space around the rivet (some of that darkeness is the deburred area though, you have to look close at the innermost black ring that is the gap):
Finally, here is a rivet stuck through the tunnel sheet metal so you can see how enlarged those holes are (all of those are roughly the same size):
I'm actually more concerned about the tunnel holes than the angle holes. All of the tunnel holes are larger from stretching during dimpling, in spite of using a #32 drill bit as recommended by Sonex. Some in the Yahoo group have said that as long as you have enough material for the countersunk head to grab, it's enough, but I'm not sure I'd agree with that.
To do #2 I could use these rivets:
http://www.rivetsinstock.com/rivets/blind-rivets/basic-structural-blind-rivets/q-rivet.html
They have tensile & sheer strength over 1000 each, and so the joints should be stronger than the factory specified rivets, but probably have larger heads and that means removing some additional material to countersink them. I'm guessing the additional rivets will cost about $100.
If I remake the aft tunnel again, the parts will cost $61 + shipping. The good news is I've re-made the tunnel before, and I can do it pretty quickly. It's just demoralizing to have to keep making the same parts (and paying for them!)...
Okay...suggestions, recommendations, recriminations? Am I just being too picky? Is all this "good enough"? Will my Sonex disintegrate in flight if I even think of using these parts? Inquiring minds want to know!
If you got this far, thanks for reading all this!