Step 10.7, Roll bar

I don't know if I was having as much fun as my puppy, but it sure was good to get back to some basic construction.  In this post I am fabricating the roll bar.

The roll bar is designed to protect the noggin in the unlikely event of an unplanned inverted dirt landing.  The basic construction is a curved U-channel of pressed aluminum spaced apart by narrow strips of 0.063" sheet aluminum.  Here are the basic parts:

Some access holes are cut into the aft sides at the base and then the parts are laid out on the bench where the splice plate can be match drilled and then riveted to the center of the arch.

A splice plate is fabricated for the aft piece as well.  The aft piece also gets a bit of angle to mount the roll bar support that ties the top of the bar to the top to the fuselage.  This is probably thought to prevent the bar from laying over -- With any luck, I'll never have to find out if it is up to the challenge.

The narrow strips are cut to length and and then match drilled to the forward arch piece

Match drilling.

And riveted.  The inside strip is next.

Followed by the other half of the roll bar to complete the tube.

There are a number of flanges that are fabricated from various thicknesses of angle that are needed to attach the roll bar to the fuselage.  Carol has come down to bang out a few..

Here are two that will hold the outside of the base.

The bar is canted aft so the attachment flanges are cut back to reflect that angle.

The bottom of the bar has to nest within the inside of the angle brackets, so the corners are radiused with a Scotch Brite wheel.

Here the two brackets on each side are shown clamped in place prior to match drilling.

Oops.  The L-shaped brackets are the wrong way around.  The smaller of the two should be on the bottom.

That's better.  I should have known something was wrong when I felt a blissful surge of intuitive correctness about the assembly.  That just never happens.  Oh well, better off correct than aesthetically pleasing.

The U shaped channel at left attaches to the top of the roll bar and keeps it from folding over.  I have elected to add a bottom piece to it to give me a place to mount a baggage compartment light and for a more finished appearance.  I found some left over 0.025 sheet aluminum that was large enough and the thickness seems about right.  I'm going to mount the cover inside the U channel so that I can put the nut plate fasteners on on cover instead of inside the channel.  This will probably be easier although either way is do-able.

Now I'm back to the L brackets.  The outside piece has to be tapered down to match the curve of the fuselage.  I start out with the Vixen file because there is quite a lot of material to remove.  It turns out that on this particular piece, the filing is making a very loud high pitched noise.  I decide I'd better move it over to the belt sander before my puppy files a grievance.

I finally get the taper right and begin the final installation with counter sinks for two attachment screws.  You can see the taper in the edge of the counter sink.

Then the U channel is attached to the roll bar.

Then a quick run through the pait booth.  Here is the roll bar drying on a pile of interior panels.  

Here is the custom bottom piece.  I put it in place temporarily so that I could get the proper spacing on the two rivets on the sides.  The top is also riveted to the top skin.

And now...  The roll bar is finished.  Painted and bolted down.  Ain't it purdy.