Wednesday, March 13, 2013

Received a Package of Goodies Today

I finally ordered my SafeAir1 Pitot/Static plumbing kit and the Pitot Mast, and both of these arrived in the mail today. I also ordered my Dynon Pitot tube from Steinair. I believe that the pitot tube is supposed to arrive tomorrow.


The pitot mast gets mounted to the bottom left wing skin, in the bay just beyond the inspection panel for the aileron belcrank. The air lines are color coded. Green for the pitot line, blue the angle of attack (if you use it), and white for the static line. You also get a bag of nifty fittings. The airlines just slide into these fittings and they lock in place. Pretty nifty setup as long as it works, but there are probably thousands of folks using this kit in their already-flying airplanes and I have heard hardly anything about any issues with it.

I also managed to match drill the holes in each rib to the spar flanges on both sides. I spent yesterday reviewing a whole bunch of posts about this particular seemingly simple operation. The instructions in the manual tell you to match drill ALL of the attach points of the ribs to the main spar web, and the builder must assume,since they do not call specific attention to it in the manual, that this includes the 4 holes on the top and bottom forward section of each rib that slide underneath the main wing spar flanges. Then they tell you to remove, debur, scuff, clean, and prime the ribs. Only problem is that these top and bottom rib-to-spar flange holes are the most forward attach points for all of the wing skins, and when you fit the wing skins to the frame the one thing that you are trying to do is get them to line up nicely to avoid any gaps between the main wing skins and the leading edge skins, etc. SO the typical preferred thing to do is to attach all the parts, including the wing skins, with clecoes and then match drill through ALL the layers at one time, including the wing skins, so that the holes are all truly matched to each other.

One question that arises from this centers on the fact that if you match drill the wing skin-to-spar-to-rib holes WITHOUT having the skins on the frame, as the instructions imply, you might not get a proper match hole in the wing skin if you finish match drilling them to the frame AFTER the ribs have been riveted to the spars. If you match drill only the ribs and spar flange holes first, without match drilling the wing skins, and then prep and rivet the ribs to the spars, you risk not getting a good matching hole fit of the wing skins. So the issue for this is if you should attach the frame and skins entirely with clecos and THEN match drill all the holes together, or should you wait until after the ribs are match drilled and riveted to the wing spars before you fit and match drill the skins, having already match drilled the holes in the spar flange and the rib? Clecos are a bit more flimsy, and may cause flexing or twisting of the parts, whereas rivets would not allow as much of this to occur, so the better option for fitting the skins is to have the frame solidly riveted in place, which is consistent with the way that all other skinned parts have been put together up to this point.

Then next part of the problem is deciding exactly when to match drill the rib-to-spar flange holes. If you rivet the ribs to the spar web, and wait to match drill the top and bottom holes to the wing skins until after you fit the skins to the frame, there is no way to remove the ribs to debur the newly drilled holes in the ribs or the spar flange. So this turns into a large discussion about waiting to dirll these holes until after you fit the wing skins, and risk not being able to debur the holes, or drilling and deburring these holes BEFORE riveting the ribs to the spar and then fitting and match driling the wing skins later.

Turns out different builders are doing it both ways. SO I chose to go ahead and drill and debur the holes before attaching and match drilling the wing skins. I can reduce or eliminate the tendency to mis-align the wing skin holes by back drilling through the rib and spar flange holes that I match drilled tonight, instead of drilling through the wing skins first. To further mitigate these issues, I used my #40 reamer that I got with the tool kit years ago, instead of a #40 drill bit, to keep the holes as smooth and accurate as possible. I did this to try to further reduce the burs around the holes.

I had some problems with inserting a few clecoes in some of the holes, but managed to work through that. Otherwise, all the rib to spar flange holes are now match drilled. I will debur them tomorrow and also mark and drill the additional wire run holes and pitot air line holes through the forward portion of the ribs. Should have more pics tomorrow.

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