Contouring the Fuselage Bottom

Here is a most exciting step.  Contouring the fuselage bottom felt like a huge milestone.  Previously, the fuselage has been looking a little… square. Yeah, I know the sides have some complex curvature to them, and the bottom is slightly curved, but all the joints are these ugly sharp corners.  After this step, no more!

I was lucky enough to be tackling this post when my parents were up for a visit, so Dad and I tackled the airplane while the ladies were out shopping or talking about girl stuff or whatever it is they do. 😉  I tell ya, it’s great to be doing work on the plane with another engineer around!  Dad’s always got a good perspective on these things.

Anyway, when first setting about carving the sides, the bulk of the material is supposed to be carved away with a jig saw set at 45 degrees.  Problem is, the area it has to cut through is about 6″ to 7″ wide.  The little 2″ jigsaw blades I had would never get it done.  So I took a hacksaw blade, traced the end of a jigsaw blade in it, and cut it out with a dremel and my permagrit tools.

Making my Own Jigsaw Blade


It Fits!

The problem with using a jigsaw blade, while it’s long enough, is that it is rather flexible.  In order to make it come out where it was supposed to, and maintain a 45 degree cut, dad had to walk along with a scrap piece of metal and keep pressing the blade one way or the other to keep it straight.  We had previously drawn the lines on the bottom and sides of the fuselage to mark the cuts, so it wasn’t really a big deal, but like the plans say… GO SLOWLY.

Here goes nothin'

It’s also nice to have the Dad man around to take picture of me working… most of the pictures have been just the pieces and parts, or heather working.

Rough Cut Almost Complete

Once the rough cut was done, I decided to take the simple route for sanding the bottom shape.  I simply took my 2 foot permagrit sanding board, and went at it, checking against the template every once in a while.  For some reason, I find this type of work immensely satsifying, which is probably a good thing considering the amount of finish sanding these planes take!

Sanding Away

A lot of people have put a lot of thought and effort into contouring their fuselage bottoms, and make sanding blocks from the templates, or use a specially made tool that has been passed around the community for years.  I found that all to be overkill, and just stuck to the plans. At any rate, I’m quite happy with how mine came out doing it the old fashioned way, and I got it done very quickly.

As many builders have, I had a gap back near the landing gear bulkheads between the sides and bottoms, outboard of the longerons.  This is where we get a bit of foreshadowing of the contouring process to come.  I mixed up some dry micro, filled the gap with it, and came back and sanded it to the right shape.  After three rounds of this, it was perfectly smooth, and close enough to the right shape for me!

Contouring the back third of the plane is the trickiest part of the procedure, and I don’t have any pictures of it, unfortunately.  I just imagined a hotwire cutter pivoting around a forward point, and pinned up against the firewall (as is called out in the chapter 7 FAQ on, and sanded away.  The big part that confuses people is the way the foam is supposed to be cut out around the spar cutout. (I cut out the spar cutout at this point, which was dead simple.) The plans are a bit confusing on this point, but I found the pictures at the following link most helpful:

The only thing I did differently at this point was leave the section cut next to the vertical part of the spar perpendicular to the fuselage, instead of sloping it.  Later on, when I was getting ready to glass the sides, I made some rounded slopes down to the glass at LWX and the longeron, but I didn’t see much point in sloping the foam down to nothing in the spar cutout.  The idea behind sloping in this area is to allow you to make a glass to glass bond with the glass that was laid on the inside of the sides back in chapter 5.  All will be clear by the end of the chapter.

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One Response to Contouring the Fuselage Bottom

  1. Dad says:

    Yaah! Progress!

    That was a lot of fun; thanks for including me!

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