Wednesday, May 14, 2014

23-02 Longerons

I bet you thought I had gone on vacation or something.  Well, you’re half right.  There was the usual “work is interfering with my life” for a week, but I did go out of town for a quick 24 hour vacation.  When I got back, I grabbed the new longeron piece that had arrived while I was working and went out the the garage to pound metal.

Take a moment and go back to read the 1st paragraph of  23-03.  OK.  As you can surmise, I botched up the longerons the 1st time I tried it.  I actually did the Left one properly, but it took the better part of a day to get my courage up to hit the damn thing hard enough to bend it properly.  It was a very tedious day with multiple clamping-beating-unclamping-clecoing the part-measuring-cussing and repeating the cycle.  Eventually, I got the thing done.

I didn’t trust my ability to hold pieces in my hand for delicate measurements, so I got a piece of 0.025” scrap and clamped on the arm rest appropriately and match drilled hole #1 and #8 (from the front).  These became my anchors and I took the time to cleco the arm rest on every time I wanted to evaluate my progress.

Suitably emboldened, but also tired and not realizing how tired, I fearlessly clamped the Right longeron in my vice and proceeded to whack the hell out of it.  I was very impressed that I had a patently obvious curvature when I finished the first pass.  It bent in two planes, as expected.  What wasn’t expected is that the two planes were not the intended one.  I didn’t pay attention to the orientation in the clamp and proceeded to bend it down (and it bent out) instead of in (and down).  Well, damn and double damn.  Swallowing my pride, I simply placed an order for the replacement ($20 + $20 S&H).  That’s when I went to do other chapters.  Returning to our saga...

Like the 2nd piece, this one bent much easier than the 1st.  Unlike the 2nd piece, I triple checked the orientation prior to applying hammer to aluminum.  The open-&-twist maneuver went very well, as did the introduction of the curvature.  I actually got the curve just about perfect with one pass of hammer blows at each inch (just like the book said to do.)  I ended up with about 4 or 5 inches of unwanted deviation downward.  

My bench vice has a feature to permit rotation of the jaws.  Unfortunately, that means that it’s got a tendency to rotate and no matter how much I tightened it down, trying to bend the longeron back into level by hand didn’t work because the vice would rotate.  I ended up taking it into the kitchen and (1) used the granite top as a level surface and (2) using the corner of said top as a fulcrum and just applied hand pressure until I got the longeron within 1/4-1/2” flat.  Bending the tail went a bit too far—about 6°, but it went back just as easily.  I used the trig trick from Homebuilt Help and calculated that 4° deviation over 6” was about 7/16”, and used a straightedge & ruler to determine what I needed.

IMG 0001 2

Bent Longerons, with attached arm rests

IMG 0002 2

Close up of Longerons with Arm Rests


In the top photo, you can see the atypical tools used in this operation: the protractor, the skin shim and the dead blow soft hammer.  Quite the adventure!

I’m going to stop on this chapter for now and do the installation of the rudder and fuel system, possibly also some wiring.  I could attach the vertical portions of the skeleton, but that would expose things to being bent or poking me in the eye as I work around the bottom of the fuselage.  For now,  I’ve conquered the longerons, which was a major emotional milestone, thus I’m content to move elsewhere for now.

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