I've used all 3 makes of hinges mentioned here over the years, (CA, Pin and Point) and here's my take.

CA hinges are by far the easiest and least expensive to install, the reason they are so common on ARF's. Unfortunately if not installed correctly, (such as too large a hinge gap and/or, more commonly, too little glue wicked in to do a full bond) then they can work loose.

They also have the problem of fatigue with repeated flexing. Yes, they can fail over time, especially if flown in cold weather

Your typical pin hinges are still my favourite. I normally go a bit overboard with both number and size since this not only makes for a good rotation axis, it stiffens up the control surface and transmits your control input better. On the larger hinges I throw away their cotter pins and fab my own pins from piano wire. Very easy to do.

The Robart hinges can also be a good option, with drilling a hole sometimes easier than a good slit for the previous two options. I found on surfaces with hard edges you also have to profile the hole for the center of the hinge as that is a square outline. What I find is the Robarts best feature is the ability to more easily offset the hinge axis to change where the pivot point occurs. The simple system has the hinge line directly between the two. If you offset it either way you change the geometry and how the surface moves. Hard to explain, but you can accomplish the same type of thing with the entire surface that you would get with a counterbalance ahead of the control surface, (the part of the elevator or rudder that is ahead of the hinge line, normally on the outer or upper portion of the surface). You can also make simulated Fowler Flaps by offsetting the hinge point below the centerline of the flap and wing. When deflected the surface travels aft and down.

With all of the above the key is to ensure all the hinges are in an absolutely straight line. Even with the CA hinges you can have problems when the surface is deflected if they are not and binding and surface flexing, the deflection of the stab or control surface if moved one way or the other, can occur. Not only will it require more energy to flex, it can eventually lead to hinge or flight surface failure over time.

The other key to a pin hinge is to properly glue only where its needed. With CA hinges this is simple as the hinge is fully seated before application and there really is no "Hinge Axis". You can use thin CA if there is a relatively tight fit to the slot and perhaps medium if not, (if too large then a CA hinge is not the best option). You need to flex the hinge while the glue is drying to help set the flexible hinge area. If you wait till the glue is fully set then it can create too much stress when first flexing and start micro cracks in the plastic that will lead to failure.

I normally take the effort on the larger hinges to individually grease the pin and pin receptacles before bonding them in to ensure no glue intrudes or bonds the area that needs to move. It is time consuming and dreary, (some may say ) but it is the only way I know to do it right.

In the past I have used epoxy, then mixing in FLOX to add structural strength and body to the epoxy, (to prevent too much flow until set), but in the last couple of planes I opted to try Gorilla Glue, mainly since the original hinge slots were gaping holes no other material would fill properly. The advantage of the GG is it expands when curing from exposure to atmospheric moisture. You just have to keep watch as it expands it does not actually push one surface away from the other. To prevent this I tape them together, held at the proper distance.

In my own opinion CA hinges are perfectly acceptable on smaller models with smaller surfaces and light control loads. When working on something I expect to fly hard or will encounter significant loads(I try to build it only once......crashing does not count) then I opt for pin or Robart Hinges. Once complete I can almost guarantee I will never have to touch them again. With CA hinges I regularly do a security pull check.

p.s. At the first sign of failure I will and have replaced CA hinges with pin style. In may cases the smaller hinges are almost a direct replacement with very little hinge slot work required.

ORIGINAL: lopflyers

Thx Bob. I'll try that