CA hinges have been the topic of many discussions here at RCU. It seems that everyone has their favorite way to install them, and there are many people who won’t use them anymore due to problems they have encountered with them in the past.
I’m going to attempt to show not only how they should be installed, but I also would like to make some comments as to what you should NOT do when installing them.
For this example, we will assume that we are hinging an elevator to a stab.
The first thing you need to do is to cut the slots to accept the hinges. This can be done with an Exacto knife, or an electric slotter. Be sure to keep the slots straight, and in line with each other.
Once the slots are cut, drill a small hole that is centered on each of the slots and just about as deep. Then, using an Exacto knife or razorblade, carefully remove a small area of covering around the slots.
Next, push a straight pin through the centers of all of the hinges. This will keep any of the hinges from pushing into the stab while the elevator is being attached.
Insert the all of the hinges into the stab until the pin touches the trailing edge.
Next, slide the elevator onto the hinges. Once it is completely in place, remove the pins.
Flex the elevator down. Be sure to flex the elevator MORE than it will move in flight! (See notes). Then add 4 to 5 drops of THIN CA to each hinge.
Now flip the stab over and repeat this step on the other side.
Many people have experienced problems with CA hinges. I am not one of them, however I have seen a few bad installations, and I hope to point out some “Do’s and Don’ts”.
It is my experience that there are 3 main reasons why CA hinges fail. The first is caused by using anything other than THIN CA. Thick or medium CA cannot “wick” into the slots the way it needs to in order to effectively attach the hinges to the wood. THIN CA MUST BE USED!
The next reason is poor penetration of the CA even when using THIN. This can be caused by a variety of reasons such as not using enough CA, or by not having removed the covering in the area of the hinge, or even by a tight slot or dense wood (also be sure the CA hasn’t gotten thick with age). The CA can’t work if it cant get in there. This is the reason for drilling the hole. It is a way to let the CA flow deep into the slot where it can wick sideways across the hinge.
And finally, the next type of failure is when the hinges break. Ok, maybe there are some bad ones out there, but many times, hinge breakage is the fault of the installer. So much emphasis is placed on the all important “gap” that many modelers go through extreme lengths to keep it to a minimum, including not giving their hinges enough room to flex. Let’s face it, no matter how small the gap is, it still needs to be sealed. So while it is still important to keep it small, it is EVERY BIT AS IMPORTANT to let it be large enough to allow the hinge to flex freely! This is why you must flex the control surface MORE THAN IT WILL MOVE IN FLIGHT when applying the CA.
One final thought… NEVER use accelerator when using thin CA. It only causes the CA to foam up in the gap area and cause undue stress to the hinge.
here are other precautions that some people take as well, including drawing a line in the center of the hinge with a crayon to keep the CA from hardening in the flex area. I have never done this, and quite frankly, the idea doesn’t sit very well with me. But if you’re comfortable with it, by all means go ahead and do it.
But by just following the steps listed above, I am still flying planes with CA hinges that are over 10 years old! So the next time you’re installing them, give this method a shot!