Monday, 2 April 2012

DS Style Horns

Let’s explode a few myths about control horns on wings: If you want the strongest and best wearing then look at the horns used on DS planes. They don’t use brass or aluminium metal ‘rod’ horns, why, because they have very little gluing area and can be pull out in flight (with sufficient force)! They all use composite horns with a triangular shape with a big foot for lots of gluing area. With a syringe you can pump in lots of epoxy inside the surrounding area of the flap or aileron skin and that in itself makes a huge difference when attaching horns. 
DS style horns aren’t just for DS models of course, standard Opus horns, well, could be improved! and some of these types of planes like Paces don’t come with horns at all!
You would imagine then carbon horns would be the best, they are not. Carbon wears very quickly in the clevis hole, you’ll find very quickly the hole enlarges and you have play and a sloppy surface.
Real G10 horns are the best, not the cheaper type of fibreglass board that splits and breaks easily you’ll find used in control horns from some far eastern manufacturers. The proper stuff is awful to CNC as it wears milling tools out so quickly but that means they are good and tough for horns! Of course they will wear (but a drop of cyano will cure) and they can break but I doubt you will ever pull them out in flight!
I’ve been using them for a while in high load situations, like DS planes or front side heavy wind stuff. Here we don’t care about hidden linkages under the skin. You want decent gearing which means relatively large horns and servo arms that will protrude from the skin surfaces. However, you don’t need ridiculously outsized horns and arms like the ones we were finding in DS planes a few years ago. The bigger the arm the less torque you’ll see from your servo and 10mm-15mm arms seem to be the optimum for most applications for these types of planes.
You can make and design your own with a bit of time but to save you the effort we have 2 designs horns that I’ve found will cover most situations. One is 10.5mm tall and ‘Raked’ 1mm in front of the hinge line and the other 16.5mm tall with the hole ‘In line’ with the hinge line. You can of course trim them to reduce horn height for that special application (or just to keep under the horn shrouds!). It’s milled from 1.6mm G10 and perfect thickness for standard M2, M2.5 or M3 clevises (any wider would spread the clevis and the pin will not engage fully on the opposite retaining hole).   
They are available now in pairs of Raked or In line at £3.50 include 1st class post (and packing) in UK or + airmail letter for overseas.

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