Airfield Models - Wing Construction Example

Build Ailerons and Flaps for a Model Airplane Wing

May 02, 2015

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Airfield Models ( Ailerons and Flaps for a Model Aircraft Wing

Building the ailerons and flaps was not difficult, but they did require care to ensure they are as closely matched in size and shape as possible.  The first decision was to determine the area for the flaps and ailerons.

The ailerons will be mixed to flaps the (flaperons) so as far as ailerons go it does not matter how the area is split.  I do not plan to use flaps alone, but I will use Crow mixing.  In that regard I have no idea how much the area should be split.  I decided not to tax my brain too much and made the flaps and ailerons the same size.

Next I had to figure out what the actual size is.  I gave the flaps 1/4" clearance from the fuselage side.  The flaps and ailerons have 1/16" clearance between them and the aileron has 1/16" clearance from the tip.  That allows room for the finish without the controls binding against each other.

A little measuring followed by simple math gave me the span of the flaps and ailerons.

Make a kit first.  It makes construction move along more smoothly and enjoyably. Parts for each of the flaps and ailerons.  Common double-stick cellophane tape is used to hold the skins together for shaping.  The only parts not shown here are the plywood control horn mounts.

The leading edges will be prepared for hinges as shown here before beginning assembly.

In the lower left is the plywood template used to cut the ribs.

Sheeting is stacked together so it can be cut all at once. The balsa wood skins have been taped together and squared.  Lines have been drawn on the leading edge to be transferred to the inside of the skin after they are separated.

The scallops are cut roughly to shape using a scroll saw and then sanded using a drum in a moto-tool or sandpaper wrapped around a bottle.

If you use double-stick tape on thin wood then be gentle when peeling the wood apart.

A lower sheeting on the building board.  A straightedge is used to align the leading edge. A skin is placed on a flat building board.  The end ribs are carefully positioned over a line drawn parallel to and spaced back from the front edge of the lower skin to allow for the leading edge to be glued inside the skin as can be seen in later photos.  The tip ribs establish a straight line for the leading edge.

A  straightedge is used to ensure the leading edge is absolutely straight.  A piece of hardwood provides a stop at the trailing edge so the leading edge remains under clamping pressure.

All the ribs are glued in place. The remaining ribs are glued in place and allowed to dry.
Don't forget to add hinge support blocks. The hinge support blocks are centered behind the pre-drilled hinge holes and glued in place.
Carefully sand the top of the flap so that the parts are flush. After a careful sanding to get the ribs and leading edge flush the upper skin is glued in place.
The upper sheeting glued in place using a flat board as a clamp. A scrap of particle board is used to clamp the upper skin in place on my glass workbench.  If the flaps and ailerons are not straight the airplane will not ever fly straight.
The upper sheeting glued in place using a flat board as a clamp. Another view of the upper skin being glued in place.  Notice the skins and leading edge have been left over size.

Again, Hayes clamps are being used.  The jaws swivel and are perfect for situations like this.

Sand the ends of the flaps so they are square and all wood is flush. When laying out the flaps and ailerons I took into account the thickness of the end cap.  I really do not like the unfinished look shown here and always cap these parts.

It is not as important when an opaque finish will be used, but it is more difficult to get iron-on coverings to stick to end grain so I always use caps regardless of the finish.

Add balsa end caps. Two scraps of hardwood and a rubber band are used to clamp the end caps in place.  To prevent the control surface from bowing under pressure I even up the tension by adjusting the band.  The band was removed after about 15 minutes to relieve pressure on the control surface.
A large rubber band and a piece of hardwood makes an effective clamp. Another view of the end cap being glued and clamped in place.  After the caps dry the control surfaces will be rough sanded.
A hard point is inset to provide a control horn mount. The skin is cut out to receive 1/16" plywood control horn mounts.  The servos are positioned in the wing so that the control horn is located close to a hinge.  This also means that there is a hinge support block in the area which provides a solid anchor for the plywood plate.

Due to the size of the control surface and the amount of taper, the horn will be mounted well behind the hinge line.  After the surface is fiberglassed a hardwood wedge will be epoxied onto the plywood plate to rotate the horn forward.

All four flaps and ailerons nealy complete. All four control surfaces ready to have the control horn mounts glued in place.  The mounts were glued in place using Carpenter's glue and then clamped back to the table with Hayes clamps as shown above.

The flaps have the control horns mounted in the middle and the ailerons have the control horns mounted on the inboard end.  This decision was made to reduce the length of the servo extensions as well as keep weight as inboard as possible.  Weight towards the tips reduces roll response.

A small gap at the trailing edge needs to be addressed. One small detail remains.  Due to the taper of the control surface the scallops create areas where the trailing edge of the skins do not meet.
A little glue and some small clamps resolves the problem. I squeezed a small amount of Carpenter's glue in the joint and used small spring clamps to hold the skins together until the glue dried.

You may have noticed that the scallops have sharp corners.  I left them like this because the square edge between scallops provides a place to measure from.  Also this area is prone to being dinged during handling.  I rounded these edges during finish sanding.

The flaps and ailerons mounted to the finished wing.

Put the control surfaces in a safe place until it comes time to apply the finish.

For now the wing will be set aside while the fuselage is constructed.  The wing will be needed without the wing tips attached to use as a pattern for the wing saddles on the fuselage sides.



Build Model Airplane Wing Servo Mounts & Hatches
Mounting the Wing to the Fuselage

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Copyright 2003 Paul K. Johnson