Installing Hinges

I saw this post from Pat McCurry from PCM Models on a forum I subscribe to and I liked his method of installing Robart hinges. His post was informative and had several detailed pictures as you can see below.

Here is a shot of one of the main wing outer panels. Using a three view, the exact seperation line between wing and aileron is determined. From there, the thickness of the aileron determine the amount of solid stock I will need to add to the front of the aileron. The amount of trailing edge material is determind and all of these dimensions are added. Together these dimensions represent an amount of material that must be removed from the wing. Lines are drawn on the wing at these positions.

All cuts to the various panels are made only while the panel is in position on the blocks from which it was cut. This ensures that all cuts will be made true vertical, even when the other wing is upside down. As you can see I chose to complete the outer panels with leading edge and wing tip. I did this because the outer panels will have their ailerons made seperate from the center section. And the flaps will be cut away in a similar fashion. It is important to ALWAYS maintain the true trailing edge position in order that when the outer panel and aileron are joined to the finished center section. If carefull attention is not paid, it would be all too easy to have a sloppy transition between wing, flap aileron and wingtip. These items should line up perfectly with each other and form a straight line when completed. By adding the wingtip WHILE the aileron is attached, I have a reference when hinging to realign to.

You will note that I cut away the aileron section first and then come back and cut the rest away. If you were to cut the front line first you would have less control over the thin piece of aileron.

Once cut away, A Long sanding block is used to take the cut right perfectly to the line. This is important. If the face of the bare aileron is not true and square, the solid leading edge, when added, will warp the aileron. A solid piece of balsa stock is then attached to the front of the aileron. While I always use 5 or 30 minute epoxy to adhere wing skins to a core, I prefere to move along much faster during construction phases such as this. For this reason I use and oderless or "foam" freindly CA such as Pacer's PT25. (Not and add here, just think it is important).

A razor plane and sanding block are used to bring the balsa stock just added into "Plain" with the surrounding aileron. As mentioned earlier, the aileron was final sanded while still attached to the wing, meaning that it matches the wing as it is. It is important to maintain this shape. Once the stock is flush and in plain with the top and bottom skins as well as the ends, I lay out the actual shape I desire to give the control surface. This little step gives me total control over the shape by giving be guidlines that can be accurately followed. It would be faster and easier to simply put some 80 grit in my hand and knock of the edges until it is close but that is all it will ever be - close.

The raw aileron leading edge, marked and ready for shaping. A cicle template gauge found at any office supply house is used to get the end semi circle shape while a straight edge is used for the long lines.

A razor plane and sanding block are used to quickly get the leading edge into shape.

On this model I am able to use a scale hinge type and location. This means I will only use three hinges for an 18 inch aileron. To do this I need to ensure that the hinges I use are up to the task. I have used Robart hinge points on countless models and trust them and chose to use them here. An added bonus is that I can make the aileron removable using Robart's Hinge Sleeve.

As shown here the sleeve allows you to insert the hinge and a set screw holds it in place. I have used these on High perfomance jets and they work.

You will notice that I "Cap" all ends of the surface I am building with 1/64th ply. This gives a finished mechanical edge so critical not only to ridgidity but also to the finished look of the model. It also make glassing so much easier. I never glass ends or edges but rather finish them in the primer stage. This method make the control surface very durable. You can also see that the hinge point in the aileron is set into a solid balsa wedge at the end of the aileron. The other hinges are also set into wedges. This gives absolute rigidity that is so important to tightly controled, slop-free hinging and control runs.

The trailing edge of the wing is first blocked to the line much like the aileron was.

Next a 1/4 think piece of stock is added and brought into plain. The location for the hinge point sleeves is marked and drill and the aileron is glued put into place. After setting the set screws can be loosened and the aileron removed. Due to the fact that the hinge closest in the photo is at the very edge of the foam core, a piece of 1/64th ply is temporarily placed on the foam so that when the hinge is glued in place, the glue is kept in place.

A point of note is the amount of throw available to this surface. Also note the position of the actual pivoting point of the hinge and the surrounding "ball" of the leading edge. Even with the shouds in place later I will be able to get far more free throught than this aircraft will ever need.

The shrouds that will finish the trailing edge of the wing are installed. 1/64th ply (yes I use a lot of this stuff) is cut perpendicular to its grain. I want this shoud to be flush with the surface of the wing skin so a slight amount of balsa needs to be removed to allow this to happen. Using a straight edge and a purpose built sanding block, a trough is quickly cut into the skin. In this shot you can also see the Robart hingepoint sleeves.

A strip of the ply is placed into position to ensure the depth of the trough, when correct, the strip is cut to coorect length and width and then glued to the balsa skins using thin CA. Note the orientation of the grain of the 1/64th ply

This picture show how with the deflection of the control surface, the shroud keeps the gap minimized and perfect. If you decide to glass the wing, the glass cloth can be applied right to the edge of the shroud. This would also keep everything together.

Shown here are the aileron and flap control surfaces down in the manner described above. Makes for a nice clean look. Thanks Pat for sharing this knowledge with us!