Easy CA Hinges: Control-surface installation in eight simple steps

Model Airplane News, Jun 2003 by Royer, Erick

Almost-ready-to-fly (ARF) models are more popular than ever. They are available for just about any type of aircraft you can think of. Whether you build an Extra 300 or a P-51 Mustang, many of the assembly steps are the same, and that includes control-surface hinging.

Several types of hinges are available, but CA hinges are by far the most popular. A CA hinge is a thin piece of Mylar covered with cloth (wick) that is most often held in place by thin cyanoacrylate (CA). CA hinges are inexpensive, easy to install and do not require any special tools or modeling skills.

To illustrate how easy it is to install CA hinges, I'll describe how I hinged the ailerons on my Model Tech Magic ARF. Let's get started.

1 Here are all the items you'll need to successfully install CA hinges. In many cases, these hinges are included with the model. I use four hinges for each control surface. In addition to the wing, the control surfaces and CA hinges, you'll need T-pins, thin CA (I use Great Planes thin CA), a high-speed rotary tool with a 3/32-inch drill bit and a hobby knife with a sharp no. 11 blade.

2 The first step is to push a T-pin through the center of each CA hinge. This ensures that the hinge fits equally into the control surface and the wing. It also serves as a spacer.

3 Determine the positions for the CA hinges on the wing and the control surface. As is the case with many ARFs, the Magic comes with the hinge slots already cut. Use the hobby knife to remove any excess balsa or covering that might prevent the hinge from fitting properly.

4 This step is optional, but it does help to ensure that the entire hinge will absorb the CA. Use a high-speed rotary tool (I used a Dremel) with a 3/32-inch bit to drill a hole in the center of the hinge slot on the wing and the control surface. The hole should be no deeper than the depth of the hinge. You could use a power drill instead of a rotary tool, but the rotary tool's high rpms will make a cleaner hole with less risk of damage to the balsa.

5 Slide CA hinges into the slots on the control surface until the T-pins rest against its leading edge.

6 To attach the control surface to the wing, carefully insert the hinges into the corresponding slots on the wing until the T-pins touch the wing's trailing edge. Go slowly, and make sure that everything fits properly.

7 Put thin CA on the hinges to permanently secure them. I like to leave the T-pins in the hinges until after I've applied the glue. This creates a small gap between the control surface and the wing's trailing edge to allow for maximum control throw; this is essential for a highly aerobatic model. On some models, removing the pin and pushing the control surface tightly against the wing will restrict the control-surface throw and could put too much stress on the hinge. On the other hand, a large gap will allow air to pass between the control surface and the wing instead of over it; this might cause flutter in flight. On larger models, I seal the hinge gap with transparent covering material to avoid having flutter problems.

Apply 4 or 5 drops of thin CA to each hinge, then flip the model over and apply 4 or 5 more drops to the other side. You may need to bend the control surface a bit to gain access to the entire hinge.

8 After a few minutes, remove the T-pins and flex the control surface up and down to its maximum deflection. This will help keep the Mylar flexible while the CA fully cures. Notice how much surface deflection the small gap that I left in the hinge line allows.