My ca hinges have a rectangular slot cut in the middle of them like in this picture (very hard to see but above the right wheel, .

Question is do I install the ca hinge with that slot parallel or perpendicalar to the joint?

Perpendicular

Ken

when installing them if you haven't already a tip is to stick them in the aileron and just put a little bit of CA on it and pull on it lightly to make sure it stays in. Then go ahead and fit it and when glueing them don't bend the aileron just find the hinge and put some CA there then when you finish that on all the hinges go ahead and fold the aileron and add some more CA

Think about it....if you installed the hinges with the slot parallel, you wouldn't
have a hinge....except for the small cloth area at the ends.

FBD.

Well I was thinking it would be stronger installed perpendicular but it would flex more freely parallel so I wasn't sure. I thought the slot might alow it to flex better but now that i know its suppose to go the other way, I'm guessing the slot is a channel for the ca to penetrate better?

Yes....the CA will "wick in" along the edges of the hinge, as well as flow with
the effect of capillary attraction along the surface and through the hinge.

Dave.

My tip for CA hinges:

Take 2 thin straight pins and put them through the hinge at what will become the hinge line. Do all the hinges this way

The insert all the hinges into the aileron, for example.

Then, slide the hinges into the hinge slots in the wing, for example

The pins will keep the hinges from sliding too far into either the wing or aileron.

Remove all the pins and slide the joint tightly together.

Now, AND ONLY NOW, bend the joint and put several drops of thin CA on the hinge. Let it wick into the wood and the hinge.

Flex the joint a few times, turn the piece over, bend the joint again and put a few more drops of thin CA on the hinges.

Let the structure sit for a minute or so, then flex the joint a few times. It may creak and groan, but it'll be just fine.

Elevator to stab and rudder to fin hinges are done the same way.

this is probably late but here is some good info for installing ca hinges. i use this on all my planes. [link=http://www.rcuniverse.com/magazine/article_display.cfm?article_id=55]RCU Magazine How-To - NA Installing CA Hinges[/link] this info was written by minnflyer.