Thursday, August 9, 2018

FlatCat Boost/Glider Build, Part 3 - The Fuselage.

Now it's time to tackle the component that holds all the other parts together to make something that resembles a glider - the fuselage.

The first step is to cut the two lengths of 1/4 x 1/2 balsa that will make up the fuselage.  The main piece is a king's foot (12") in length and the nose section is cut to 4".
In reality, the fuselage could be made of one continuous 16" piece, but I wanted to stick with how it was done in the original design.
I didn' t take a pic of this process, because it's just a couple of 1/4 x 1/2 balsa sticks. Not overly exciting.
The next process is to cut a couple of pieces out of the short 4" nose section, per the plans.
One of the cut-outs is the 'Piece-X' attachment pin that will later be glued to the pop pod pylon. 
The dimensions are marked on the nose section and carefully cut out using a sharp X-Acto blade.


Next, a small piece is cut out of the center of the nose section tip.  This will provide a cavity for inserting trim clay later on when the glider is completed.


I used a couple of various shaped needle files to clean up the cuts.

Now the two fuselage sections are glued into one long piece.  The end-grain surfaces absorb a lot of glue, so it's best to thoroughly pre-glue them before actually attaching the pieces together.
It is important that the two pieces are perfectly aligned.  A straight edge ruler helps here.

The fuselage is set between a couple of small sheets of wax paper, then covered by a piece of plate glass and weighted down with a couple books for drying.


In the mean time, the two 1/2" x 6" fuselage sides are cut from 1/32" thick plywood. Again, no pic necessary here.        

Once the main fuselage is dry, the side pieces can be glued into place. 

 

Important Tip:  It's best to spread the glue on the fuselage rather than on the side pieces to avoid getting glue in the Piece-X cavity, as it might interfere with the smooth operation of the pop pod.
For the same reason, once the side pieces are glued and clamped in place, it's a good idea to use a Q-tip to swab out any glue squeeze-out from inside the Piece-X cavity.

 The clamps used to hold the assembly together to dry are actually clips cut off from department store trouser hangers! They make perfect utility clamps for a lot of applications.

Once, the fuselage assembly is completely dry, it's time to make a taper cut to reduce the fuselage height from 1/2" at the wing trailing edge location to 1/4" at the rear, as shown in the plans.

 

The next modification is not in the published plan, and that is to form a very slight forward slope on the bottom of the fuselage rear where the horizontal stabilizer will be glued.  I marked the fuselage tube 2" from the rear (the width of the horizontal stab).  Using a fine sanding block, I carefully formed a 1-2 degree forward slope, being careful not to angle the block side to side.  Here's an illustration for better clarification.



This procedure introduces a little bit of negative incidence to the horizontal stab.  I won't go into the details of aerodynamic stability here, suffice to say that doing this step will aid greatly with glide trimming and performance later on.  For an explanation of negative incidence, refer to Estes' technical report TR-4 covering boost/gliders.

The next bit of work for the fuselage is to sand the front tip to a rounded profile. This is a drag-reduction measure.  It is easier to start with cutting off the front corners at 45 degree angles with a razor saw.  This makes for a little less work with a sanding block.

 
The final step is to taper and round the rear end of the fuselage as shown in the instruction diagram.  Sand only the top and side surfaces.  I did not round the bottom because that is the tail section gluing surface.
 Later on, after the wings and tail section are attached, the entire fuselage will be sanded to round over all the square edges along its length.  Again, this is a further drag reduction measure.

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