Hi,

I'm brand new to the forums, and relatively new to RC flying. I'm currently building a semi-scale DHC-3 Otter from a kit, so I have the occasional odd question as I make progress.. I don't know very many modelers yet in my area, so I'll ask here...

Here's one - how come hinges on control surfaces get glued and pinned, but control horns are typically a two piece affair, with the horn, and a backing plate that gets bolted together? Why not use bolts on all the hinges? Do horns need it because of the greater shearing load on the control horns?

Thanks,
Scott

Hinges are inserted internall to the wood in a "layered" manner and don't require bolting because of the direction of the loading. Simple pulling for the most part.

Control horns are attached to the EXTERNAL surface and because of the type of load "angular" needs the load distribution effect of the backing plate. A couple of drops of thin CA is often also used to harden the balsa too. Drill the holes first.

OK, so it is because of the pulling forces, for horns...Not all hinges are internal though - I'm not using CA hinges on this model, but rather the regular external ones that you glue and pin. No bolts on those either, correct?

-Scott

Correct. Like Burce said, the hinges are sandwiched between two layers of wood, so just gluing them in place is good enough.

Also, do this..........

Lay all the hinges that're going into an aileron side by side. Pretty wide, right? With all that area, no need for bolts.

BTW, since this is a beginners forum, some advice about the horns...............
ARFs are put together by people who mostly have no modeling experience. So the wood that they choose for surfaces that get horns bolted to them, is just whatever wood is in front of them. When you build your own models from kits or scratch, you know what wood is going to be used for. And you can pass on punk wood and choose good solid wood. You can also choose quarter grain (but that's another topic) to be almost warp free. So..........

When you're about to bolt the next horn to it's surface, take a close look at that surface. Does it feel soft to you? When you tighten down the bolts, does the horn easily dig into the wood? The covering give a lot? If so, and you're building anything larger than a park flyer, think real hard about doing a very simple toughening up step or two. CA into the holes really doesn't hack it on a hard charger. May be good enough for some, but false security for others. The decisions are ones you will gain more experience to make as you go along. But you need to think about them now as a beginner. A very small "patch" of thin plywood could be the answer. Look how small the base of the horn is. Think about how much force the surfaces are going to see. Might not need any patch, might need more.

Wanna learn if this matters? Walk around the flight line next time you're at the field and look at all the airplanes. Look closely at every horn you can see. Bet you find at least on loose one. Hope it isn't on one of yours.

Beauty of this hobby is that we learn a bunch as we go along.

Except my hinges aren't...these aren't CA hinges...but I still don't think it matters for hinges, from what I gather

I detect a potential gross conceptual error here. You're referring to "external" hinges. The hinges DO NOT lay on the outside of the control surface. Rather, you cut a slot on the mid-line of the control surface, put the glue on the hinge, and insert the hinges into the slot.

After the hinge glue has set, many people will drill a small hole down through the hinge in the control surface, and insert a wooden toothpick down through the hole. This "pins" the hinge in place.

Brad

TOOTH PICK GOOD >>> CRASH BAD
I drill a hole on the bottom of the wing and tooth pic each hinge.(follow kit directions for hinge SLOT placement) a drop of thin and a final small drop of med on the toothpic after its cutoff to keep the surface smooth. Some guys like straight pins but after a while I always wonder where they went

TIP: a tiny drop of salad oil on the hinge to keep the CA from locking it up don't ask me how I know!

On the control horn soft wood issue good advice to AT LEAST harden the screw holes on any kind of model. Sometimes I poke alot of pin holes into the wood under and around the area the horn will cover and run thin CA on that to toughen up the wood. I dont fly any thing much over 60 size birds....but I would add ply to any 3D type for durability.

No hinges I know of that are glued to the outside of a wing and then pinned.

Flat nylon hinged hinges are about the size of CA hinges, and go into slots just like CA ones do. Learn to install either of them and they don't need pinning. And with Hinge Glue, it's almost foolproof installing the nylon ones.

I agree but the pins are still an added safety feature and not a bad idea for first builds.
OK[sm=what_smile.gif] school me here what is hinge glue? Your never to old to learn something new

da Rock is correct. The only hinges that don't get inserted INTO the material but are mounted EXTERNALLY would be those used for gear doors or bomb bay doors or the like. Oh, and some flap hinges. Specialty stuff. All others that I can think of are "internal" and fit into a slit cut into the wood and then MAY be pinned.

Hinge glue
http://www2.towerhobbies.com/cgi-bin...&I=LXCX67&P=ML

Good stuff, easy to work with.

COOL,
[sm=idea.gif] thanks Bruce

I'm just curious here, do you fly a trainer at all or is this Otter your first plane

Not a hinge problem.....Does anyone know where I can find mini screws such as servo mounting screws
but a little longer sorta like an inch.Many thanks to ya.

pappy

[link]http://www.microfasteners.com/catalog/products/TWSSHWHMS.cfm[/link]

I have a trainer as well...

"the regular external ones"??? Can you provide an example of this? Picture or link please. Or mfg and model of hinge. I don't think I/we know what "the regular external ones" are.

My misunderstanding...having only seen the thin CA hinges before on the trainer, I didn't realize the nylon ones went internal as well...glad I asked before I glued

I did a quick bench test on some scrap wood, and yeah, you wouldn't want them laying flat on the control surface, you can peel them off pretty easily.

Thanks,
Scott

OK, as long as it's settled.

Those nylon ones are almost as easy to install as CA hinges. If you use hinge glue that is. They are a pain if you install them with epoxy, and you can wind up with a disaster. Hinge glue solves all that.

There is a trick that makes any glue hold those hinges very solidly. The holes in the hinge flats. Make sure those holes are filled when the flat is being pushed into the slot. Actually, make sure you got some glue into the slot first, and that you smeared the flats both sides, but those holes are the clincher (pun intended). When they carry a plug of glue in with them, the glue winds up drying and creating a bridge from one balsa face to the other. In a sense, the glue becomes a pin sticking from one side to the other.

Hinge glue that squeezes out into the hinge or hinge gap is easily wiped away. Epoxy isn't. And epoxy that seeps into the hinge ruins it. Hinge glue doesn't. And if you wipe with a wet paper towel, is diluted and removed.

If you've ever fought epoxy this hinge glue will amaze you.

Hinge glue
http://www2.towerhobbies.com/cgi-bin...&I=LXCX67&P=ML