Airfield Models - Fuselage Construction Example

Laying Out the Fuselage Sides

May 03, 2015



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Airfield Models (http://www.airfieldmodels.com/)Laying out the Fuselage Sides

Creating the fuselage sides is as critical as joining them together.  It is not difficult to do, but it requires a methodical approach and accurate measuring and cutting methods.

If you are building from a kit then you will not need to cut out the sides, but you may need to draw in the locations of formers and other internal structural members unless they use some type of interlocking construction.

Also see

 
 
Select straight-grained, medium density wood for the fuselage sides. Before doing anything else, select the wood to use for the fuselage sides.  I like straight-grained wood that is firm and light.  Contest balsa can be pulpy so I generally do not use it here.

This model is receiving a natural finish so I also selected pieces that have a nice mottled appearance and matched the overall tone of the wood.  In fact, I sorted the wood by color first and found that I had five different stacks by the time I was finished.

I went through each stack until I found three pieces of wood (sides and top) that matched in color, grain-pattern, weight and flexibility.

After the two sides each have one true edge, locate the reference line.  Normally it will be parallel to the trued edge.  In this case I will use the bottom of the fuselage as the reference line so another line is not necessary.

Start by marking the location of the firewall. This is one of the original fuselage sides that was scrapped.  I have drawn in the firewall location.  The thrust line will be 0 right and 0 down (0-0), so it is perpendicular to the bottom of the fuselage having no right or down thrust.

The new set of fuselage sides has the cowl as part of the side so the firewall is located further back.

Locate the leading edge of the wing and draw in the former located to the rear of the tank compartment.  Draw in the former location at the rear of the wing saddle.

Next I measure back to the leading edge of the wing.  Normally I determine where the leading edge is by measuring the fuel tank length and adding 1/2" to 1" to that measurement.

Measure the chord of the wing without the ailerons and draw the location of the former aft of the wing.

Locate the wing centerline.  I normally set up a symmetrical wing with a very slight amount of positive incidence.  This is because at 0 the wing has zero lift.

When I say a slight amount of positive incidence, I'm talking about the leading edge being about 1/32" higher than the trailing edge.  In this case, that amounts to a fraction of one degree.

Draw the centerline of the wing at the proper incidence.  Place the wing over the line and trace around it for the wing saddle cut-out.

Carefully locate the wing over the centerline and trace around it.

Now you can see why I have left the wing tips off.  Once the saddles are cut (and you are sure you will not be cutting another set of fuselage sides) the tips can be glued on the wing.

The Leading Edge of the wing centered over the line. Here you can see the leading edge of the wing located over the centerline drawn on the fuselage.
The Trailing Edge of the wing centered over the line. Ditto for the trailing edge of the wing.
The horizontal stabilizer location. The same method was used to locate the cutout for the stabilizer which was built up using a method similar to the wing.
Mark all other locations of internal components. Thin fuselage sides tend to take on a concave shape (the middle caves in) when the tail is pulled together.  To prevent this I glue vertical support pieces in the aft end of the fuselage.  The lines drawn here represent the locations of these supports.  Their weight is negligible, but they really help keep the fuselage sides flat.

The fuselage sides are taped together using double-sided tape.  Cut the sides and sand them carefully to shape while ensuring the edges remain square.

Leave the sides joined and transfer the former locations to the edges of the sides.  These lines are used to mark the former locations on the fuselage side that has not been marked.

Tape the sides together and cut them to shape.  Transfer all lines to the second fuselage side before taking them back apart. The fuselage sides are carefully cut out using straight edges and a scroll or jig saw.  Because this model will receive a natural finish I took extra care cutting the wing and stabilizer saddles.  Using putty and filler will not be an option so the fit has to be good.

I made a sanding block from a scrap of 3/8" x 1-1/2" x 6" balsa.  One of the faces was gently rounded over and fine sandpaper was used to shape the saddles after they were initially cut oversize.  The wing and stabilizer were checked against the saddles several times during the shaping process.

Taking care when making cut-outs ensures a good fit. Here you can see the final stabilizer fit.  The excess wood aft of the trailing edge of the stabilizer will be trimmed away later.
The forward fuselage showing the adjusted thrust line. After the thrust line was initially drawn it was relocated 1/4" lower to position the engine properly in relation to the fuel tank.
 
 

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How to Build a Fuselage for a Model Aircraft
Building the Inner Fuselage-Side Structure

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Copyright 2003 Paul K. Johnson