Lower Longerons, LWX and LWY

I had to put the lower longerons in one at a time, and lost a day in the process, because it required so many clamps to hold the thing in place.  I did not nail the longerons in place with pre-drilled holes, as per the plans, as I had a great deal of trouble removing the last set of nails that I put in through flox.  Here’s what the right side lower longeron looked like being floxed into place:

Ok, so that’s not really what it looked like, this was my pre-flox test fit.  For the real deal, I used twice as many clamps to ensure there were no gaps.

As other people have had happen, in order to make my lower longerons match the dimensions for the fuselage sides from Fig. 5 in the plans, the longerons overhang the lower edge in some places.  This is because you cut the masonite to the correct dimensions, and build up the foam on top of that.  the common error that people make is lining up the lower edge of the foam as they go.  because the jigs are putting a curvature into the sides, the top edge of the foam (where the longerons eventually go) can be as much as a 0.1″ inside the required dimension.  It shouldn’t be a problem, it just means I’ll have a little gap to fill when contouring the fuselage exterior in chapter 7.

Here’s where I made a big oops!  I came out to the hangar after the lower longeron on the right side had cured overnight, and found that I had left the excess length on the FORWARD end of the side! Doh!  The longerons need to overhang the aft end by at least 0.5″ so that they can penetrate the firewall.  So, I got to try my first scarf joint!  I cut the excess off from the front at about a 45 degree angle, and then cut the aft end back a couple inches at the same angle:

And here you see the repair floxed into place:

The repair came out pretty nice, and I had it curing at the same time as the left lower longeron, so the next day I was free to move on.

I cut the remaining spruce that I had to the required dimensions for LWX, LWY, and the lower longeron doubler.  Prior to floxing those in place, I made some molds for the upper part of the electrical conduit, as seen below:

This was my second mistake of the week, because after making the upper half of the conduit out of fiberglass, and installing the remaining wooden pieces, I found that the upper conduit piece needs to extend all the way to LWY, so as to not leave a gap over the conduit cutout.  Ah well, should have followed the plans in order a little more carefully.  To fix that, I took the upper conduit pieces that I had, and simply extended them by glassing on a bit more BID over the molds.  I didn’t get pictures of any of this, but I did get a picture of all of it installed, including the foam cut out and micro’ed in to fill the void around the conduits.

Once the micro cures, I’m going to sand the whole thing level, and fiberglass the whole area with 6 plies of bid.  It may be a few days though, as I ran out of micro today.  Decent timing, as I’ll be playing Halo Reach for the next few days anyway… that’s right, games are my other weakness.

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3 Responses to Lower Longerons, LWX and LWY

  1. Dad says:

    Looks complicated – Good thing you’re an engineer and can do a stress analysis to see if the shortened longeron will have structural impact, huh?

    Any TriPac news?

  2. Matt says:

    Naw. There was a bunch extra hanging off the front end, and that end is going to get squared off anyway. I’d put money on the joint at the other end being stronger than the original wood.

    Not much Tri-Pacer news. Hope to be putting the panel back together soon, and get a turn coordinator that works installed.

  3. Mike says:

    Hi Matt; A great website and fantastic that you’re sharing your build experience with others. Very useful to someone like myself who is still in the process of considering what type of aircraft to build. In reference to your longeron splice, the following link is useful. http://www.aviation-safety-bureau.com/aircraft-wood-structures4.html. If going below the standard splice, it may be worth a stress analysis.

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