Lower Cowling

Lower Cowling

Cut it off, so you can screw it on...

Making the lower cowling was an interesting and ingenious task...

I had been waiting to do this ASAP, since starting this build.  The size of my garage meant that the full length fuselage only allowed enough room for me to pass in front, or behind, and with little extra room.  So I was eagerly awaiting the extra room!

The concept is quite simple: Cut the back of the fuselage off and make it into the lower cowling, by adding a flange.

As always, the first step was to sand and clean the bonding surfaces.

I sanded a full 6" out from the firewall, to account for the widest layer of fiberglass.

Next, was to measure the cut-line.  Of course the factory cut-line was way too far off to work; therefore, I laid out a new cut-line.

 The problem with the concept, is that you have to cut the cowling section off the rest of the fuselage, but the flange needs to fit perfectly.  Here in lies a catch 22.  The cowling needs to be cut off, but the flange needs to be made in place.  Originally, the factory suggested making the flange first, then cutting just through the outer skin, without cutting into the newly created flange.  This precision cutting would have been very difficult, with probably less than perfect results.

The new process is nothing short of ingenious...

As per the instructions, I first cut 6" down the side, and hot glued a tongue depressor across the middle of the cut.

Notice the huge deviation of the correct cut-line, to the factory marked cut-line.

This process was repeated every 6".  To give sufficient time for each stick's glue to cool, I worked back and forth between the left and right sides.  I found by the time I returned to a side it was fully cooled, and ready to continue.  In this way, I never had to wait for the hot glue to cool.

I was much more concerned with creating the strongest bond, than the cleanest hot glue application!

 Eventually, I worked all the way around the lower cowl.

It was more than a bit creepy having the cowling supported by nothing more than popcicle sticks.

Next was to cover the fuselage side from the cut-line to the firewall with duct tape.  Fiberglass will not adhere to the back of duct tape; therefore, any fiberglass laid over the duct tape will mold to the shape of it, but not stick.  This is how the flange is created.

With the duct tape in place, I was ready to make the flange.

When making this flange, and any similar layups, I highly recommend using foil tape instead of duct tape.  It is much thinner and very smooth, so the resulting flange will come out much nicer.  Another thanks to the VOBA group for that trick!

I then did the fiberglass lay-ups, as directed in the manual.  I found the plastic transfer method of applying fiberglass, not practical for such long of lay-ups (~84"); therefore, I did the traditional method of laying dry glass down and wetting it out in place.  By starting with narrow layers and ending with the widest layer, it results in a smooth surface with only one exposed edge.

The downside of using a felt marker to mark glass cut lines, is it REALLY shows.  Notice all the black lines, showing different width layers.

I left the flange to sit and cure for 2 days.  Partly to ensure a totally full cure of the epoxy, and partly because I was out of town all day the next day.

Once fully cured, the first thing was to drill 1/8" holes around the flange, which will later be the locations for attaching the cowl to the fuselage.  The next step was to remove the sticks holding the cowl in place.  Due to my desire to be sure my cowl did not prematurely fall off, while still curing, I completely covered the sticks with hot glue.  This did however, mean removing the sticks was a bit more difficult.  I found a putty knife and hammer made quick work of them though.

The putty knife worked well, but lots of glue will have to be scraped or sanded later.

With a few "taps" from a rubber mallet and a helping hand, the cowling quickly released.

With the cowling off, the fuselage is now over 3' shorter, meaning its much easier to get around, when working in the limited confines of a 2 car garage!

The finishing touch, which is not in the instructions, but is on the old video, is to trim the flange down to about 1/2" beyond the holes.  This makes for a cleaner finished product.

AND... as always... sand, sand, sand!  Always gotta sand the fresh fiberglass nice and smooth!

With all the extra room, it is now time to get back to working on the fuselage.  

On to the main spar supports!