Cowling and Extension - Part I

 For weight and balance purposes due to the mass of the UL engine, it has been pushed out 10.5".  Francois did a lot of calculations to come up with that number.  It should allow full loading of the baggage compartment.

But this means that the cowling needs to be extended.

After thinking about this for a long time, the plan will be to cut ~4" off the cowl on the aft end, bridge the gap with and aluminum mold, and then add 4 layers of cloth it to bridge the gap.

First step in that process is to center the cowling on the crankshaft.  The inner diameter of the cowling at the crank is 8", and the crank itself is just over 2.75".  Make a disk out of MDF, split it in half, and then temporarily attached it to the prop flange.

Because it is not supported at the back, there is no way to line it up properly, so I dont see any way around just cutting off the back and hoping for the best.

3.5/8" marked off to cut.

On the bottom, I left the scoop in tact with the hope of extending it.  So in the bottom, I only cut off the sides, plus about 4" off the bottom.

Initial test fit.  The back 3 5/8" of the cowl is clecoed to the fuselage, using the holes on the cowl flange intended for the firewall mounting.

Unfortunately it does not line up. the corners on the top half are pushing out and not following the correct line.

So I believe the solution is the overlap the seam between the top and bottom halfs (temporarily) to get the right profile on the edges.

I mounted all of my 22" long aluminum braces.  The theory behind 22" long...

• The gap to fill is ~10"
• I need 2" of scarf on each side (14")
• 2.5 additional " on the back side to pick up the fuselage to carry the line.  16.5"
• Another 6" forward to support the cowl to get an even transition.

Starting in the middle and working my way out on each side.  All of the braces are numbered, as is both the fuselage and cowl.

Using this method, I successfully followed the curve.  And my pushing the forward cowling piece down, the whole curve is lining up.

The trick will be redoing the goggle - but that is a problem for another day.  This shows the amount of overlap to get everything to line up.

The plan:  do the top cowling and fit it back on the airplane post fiberglass / scarf joint.  Then use the same method on the bottom (starting at the bottom and moving my way up.

For the mold, I am going to follow Ted's advice.  Aluminum.  I bought a 60" x 16" piece of .032.  Lined it up in the center, and took off the two center braces and drilled the first, and worked my way out again.  Had to trim the aluminum a bit.  17" wide would have been better in hindsight.

The only issue is the .032 does not want to bend, so its pulling out on the sides.  Plan will be to made a frame for it to sit in while I glass it.

Next is to take it apart and scarf the joints as close to 50:1 as I can get.  Going to put peel ply on the aluminum to try and get a decent finish.