Tools for the job – Robart centre finder for pin hinges and drill, the other is a Dubro hinge slotting kit. The 3mm spruce is a most useful tool for slotting (see text).
Presently (as you may be aware from my build blogs) I have three models ready for fitting out – an Evolution Enigma, a Super 60 and an Astro Hog.
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The Enigma will use Mylar as per the instructions, whilst the Super 60 and Astro Hog will use pin type hinges. Rather than go into detail in the build blogs I though a quick article on hinging might be useful.
For most hinges to work properly, the hinge has to be on the centre line of the control surface. I say most because for things like flaps you may want to hinge towards the bottom of the trailing edge.
Some hinge types – top left – my preferred hinge type for most models. Bottom Left – typical Mylar hinge cut off from strip. Notice the score lines where I have keyed the surface. Right shows pin hinges the top being Robart and the bottom a cheaper alternative from Giant Cod.
Control surface hinging is probably one of the most important things to get right – if the hinges aren’t secure enough there is a risk that they could come apart in the air. If too tight or binding then you'll run the risk of adding an extra load on the servo/s, this can increase the current draw and impacts battery and servo life. Not only that but if the control surface has large gaps around it, so control surface effectiveness can decrease.
So what we are looking for is…
- Good alignment
- No gaps between the moving surface and wing/tail
- Free and easy movement with no binding
Without doubt the hardest part to get right and I suggest you don’t attempt this freehand is the hinge positioning. The hinge has to be positioned centrally and in the same position on both surfaces. If using Mylar or any flat hinge you do have some leeway, but if using pin type hinges you have to be very accurate.
Careful marking on both the fixed & moving control is essential. I bring the 2 surfaces together and mark both with a small dot. If you are building the model yourself it’s a good idea to make the hinge holes /slots before shaping and covering the control surface whilst it is still square, I find it easier, you can then trial fit the surface and make sure everything fits nicely. This also has the advantage that the hinge holes/slots become the datum to shape to.
If the model is already covered no matter you just have to be extra careful in finding the centre line of the control.
Glue selection must also be considered. I use thin cyano for Mylar because there is a good tight fit between the actual hinge and the slot and as a rule cyano is not good at filling gaps. It also goes off too fast and I like some working time.
If I’m using pin type hinges or the flat type where there is more of a gap around the hinge I use a slow setting epoxy (30 min is good) , but I think that Gorilla glue might be a good alternative.
I did not follow my own advice here and shaped and covered the ailerons before cutting the slots. It’s not so easy to use one of my tools to find the centre line, but this handy piece of wood, half the thickness of the control surface does the trick. Most control surfaces are 6mm so a piece of 3mm scrap is ideal for finding the centre.
Marking the wing is simple with the correct tool for the job. I suggest you have some sort of centre finder for this job. Alex Whittaker had details of how to make one in his column in a recent issue of RCM&E.
I tend not to trust just gluing the hinges in place, I like to pin as well. Now the last thing this rather neat job needs is a 3mm hole drilled through it and a cocktail stick pushed in so I use metal pins. What I do is from the bottom, push a pin through until I can feel the Mylar, and cut the pin off about 1mm above the surface. I then continue to push the pin in through the Mylar, so the pin is just below the surface of the covering.
Completed hinge line with minimum gap, full deflection and the securing pin ready to be pushed in.
ROBART STYLE HINGE POINTS
The Robart hinge point drilling jig is an essential tool if you intend to use this type of hinge.
There a couple of things to be aware of with pin hinges – they require a deep hole to fit, so a 6mm trailing edge isn’t quite enough, you have to plan ahead where the hinges are going to go and double up the trailing edge in these areas. This is true also for foam wings. The hinges are tapered and get slightly larger as you get to the hinge point, so you have to make provision for that. I've found the easiest way to do this is to remove material rather than counter bore the hole.
What make these hinges so versatile is that they're strong enough to have the hinge line offset from the edge so they're ideal for flaps or scale hinge lines.
Before gluing pin hinges into place, I run Vaseline into the hinge joint to prevent any glue from getting in and seizing-up the hinge. The best way I've found is to heat up the Vaseline with a heat gun and, when molten, dip the hinges and give them a wriggle. I’ve also found it better to run glue into the hole, but don’t use too much. I prefer epoxy and a little heat will help it flow. Gorilla glue also works well. Remember that any glue forced out will have to be cleaned away quickly. A slow setting cyano could also work, but any excess might be harder to remove.
That's it! A little careful preparation, the right tools and you'll soon be hinging like a pro!
