Airfield Models - Fuselage Construction Example

Preparing the Formers for a Model Aircraft Fuselage

May 03, 2015



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Airfield Models (http://www.airfieldmodels.com/)Making and Preparing the Formers for a Model Aircraft Fuselage

Most formers that come with kits are not ready-to-use.  Various holes need to be drilled and if the formers were die-cut they may need to be replaced entirely if too much of the edge was crunched.  If you are building from scratch then take your time to ensure the formers are as precise as possible.

A good set of formers makes construction much simpler and goes a long way toward ensuring the fuselage is straight.

Most sport kits have rectangular formers for their box fuselages.  In this case all you need to do is take a height and width measurement and then use a good square to mark the cut lines.

I always laminate critical formers from wood of half the finished thickness.  For example, if the former is to be 1/8" balsa, then I laminate two pieces of 1/16" balsa cross-grain.  This ensures the formers are flat and allows the use of thinner formers while increasing the strength.  The intended purpose of a former dictates the material it is made from.

Laminating formers is a little extra work, but I do all the laminating at the very beginning of the project so the blanks are ready when I need them.

 
 
Always cut former outlines slightly over-size and sand to final shape.  Internal cut-outs lighten the formers as well as making it easier to move things around inside. Interior cut outs should always have radiused corners.  They look better and are stronger than sharp corners.  I use a 1/2" sanding drum on a Dremel to make the corners.

First mark the center of the corners and drill a hole smaller than the finished radius.  I normally use a 3/8" bit in a drill press to get started.

Next, use a hobby knife, scroll saw or jeweler's saw to finish the cut-out.

Finally sand the inside to smooth it out and use a Dremel or a dowel with sandpaper wrapped around it to finish the corner.

Here I am showing my anal-retentive nature by using a sanding drum on my Dremel in my router table to clean up the inside cut-out.

Always set up the firewall before gluing it into the fuselage structure. The front face of the firewall.  It has been drilled for the engine mount, fuel lines and throttle linkage.  This aircraft will have a tail wheel so there is no nose gear mount.

Notice that the fuel line holes have been chamfered using a counter-sink to soften the edge and help prevent the plywood from cutting the fuel line.

Radius fuel-line holes to prevent sharp edges or splinters from cutting the fuel lines. The rear face of the firewall.  Again, notice the chamfered fuel line holes.

Also note that the holes for the engine mount screws have been enlarged slightly on the rear face to receive the blind nuts.

The blind nuts for the engine mount are easy to install before the firewall is glued in place.

The blind nuts have been tapped in place with a small hammer.  The smaller blind nut is made by a different manufacturer but they all have the same thread (6-32).

I used a small blind nut so that I would not have to grind away part of the flange to prevent it from blocking the fuel line holes.  However, if you run into this problem you can grind away part of the flange with a Dremel.  The blind nut will still be strong enough.

A plywood blank for a nose ring to match the spinner. It is easy to make a perfect nose ring.  Start by selecting a piece of plywood of appropriate thickness.  Draw the centerlines and the outer diameter of the spinner.

The diameter of the nose ring should be slightly larger than that of the spinner assuming the fuselage tapers normally.  Add about 1/32" to the radius of the spinner before drawing the circle.

The inner circle only needs to be large enough to pass the thrust washer with a little margin for error.

Drill a hole in the center to thread a bolt through. Drill a 1/8" hole in the center of the former.
Cut off excess material leaving enough left to sand to final shape. Trim off most of the excess using whatever method you like.  Leave enough material so the former can be sanded to final shape.
Thread a bolt through the center hole and use a nut to tighten it securely. If you have a drill or a drill press you can make final shaping really easy.

Thread a 6-32 bolt through the former with a washer on each side.  Thread a hex nut on and tighten it securely.

Do not chuck this assembly into your moto-tool unless you want to learn how cheap the bearings in these tools really are.  They will not last long with an unbalanced load such as this.

Mount the nose ring assembly in a drill or drill press and sand to shape. Chuck the assembly in your drill or drill press.  Use a sanding block to take the former down to the line.  Notice that the bolt is threaded through so the lines are visible.

Do not continuously press the block against the former.  Instead, push the block up to the former until it just touches.  Then hold the block still until the high spots are knocked off.  Keep doing this until the former is to the line.

Turn off the drill and check the spinner backplate against the former.  Keep sanding until they match well.

You can also sand a slight taper into the former by tilting the block so that the former matches the taper of the fuselage.

The nose ring should be very slightly larger than the back of the spinner to allow the ring to taper. I leave the ring slightly over-size so I can finish sand it after it is glued on the fuselage.  Here you can see that the former is a hair larger than the spinner backplate.
When the outside is finished, remove the inside. Cut out the inside of the nose ring when you are satisfied that the outside edge is correct.
All the formers are ready to use, having all necessary holes and cut-outs. The complete set of formers from the nose rearward shown in order from left to right, top to bottom.

The center former in the bottom row goes in the center of the radio compartment.  The cut-out at the bottom is to pass wires from the servo compartment to the receiver/battery compartment.

Note the former at the bottom left.  This former is located at the leading edge of the wing.  The holes for the wing dowels are already drilled to simplify mounting the wing.

Note that the dowel holes are as far apart as possible.  The farther apart these holes are, the more stable the wing mount will be.

After the formers are made is a good time to start working on the radio installation.

 
 

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Building the Inner Fuselage-Side Structure
Jigging and Dry-Fitting

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Copyright 2003 Paul K. Johnson