Hi folks,

I've just finished hingeing the elevator on my Venture 60 and have used Robart hinge points for the first time. I unfortunately don't have access to a drill press, so to drill the hinge holes I use a combination of my Dremel and a 50/50 mix of caution and concentration.

After some very careful measuring and drilling, and reading through the excellent [link=http://www.airfieldmodels.com/]Airfield Models[/link] Robart installation instructions, I got the six 1/8" hinge points installed. The hinges all pivot at 90 degrees to the plane of the stabiliser and the elevator and stabiliser mate together with very little pressure so I think the hinge holes are correctly aligned (does need
a bit of extra pressure for the last few millimetres of the hinge points due to the flaring around the hinge.)

OK - enough of the history and on to my question. Visually the elevator attachment seems to be spot-on. The hinge gap between elevator and stabiliser is tiny and consistent. The top and bottom surfaces of the elevator align perfectly with the top and bottom surfaces of the stabiliser when in the neutral position. The thing that concerns me is the 'stiffness' of the hinges. The elevator isn't binding - I can move it between maximum up and down deflection with no sticking, and the amount of force required to move the elevator is constant throughout the full travel - but the amount of force required to move the elevator is a bit more than I expected. While I expected the elevator to be 'stiffer' than my previous model (where I used Great Planes plastic pinned hinge tabs) I wasn't expecting it to be THIS stiff. I can place the elevator in any position and it'll hold that position regardless of whether I flip the stabiliser assembly right-side-up, upside-down or even gently shake it!

I guess my first question is, is this normal? If not then where have I slipped up and how can I rectify the problem?

Thanks for the assistance,
Neil.

Hm-m-m. I'm guessing that there's nothing to be concerned about, providing that the "stiffness" is not severe enough to strain the servo.

Did you oversize the outer most point of each hinge hole to allow for the wider flange at the hinge pin? It could just be that they are binding slightly, which will ease up as they wear in.

Did you taper the leading edge of the elevator(s) to a fairly thin line? (45 both the top and bottom.)
Dennis-

I don't think the stiffness is enough to stress the servos too much - it's probably me being paranoid, plus I'm used to the 'floppiness' of CA and GP pinned hinges.

That's a great suggestion about oversizing the fitting holes. I didn't so much oversize the hole as push the hinges in until they were snug - it's entirely possible that the balsa is pinching the sides of the hinges just hard enough to increase the friction between the two hinge halves. I'll try flaring out the holes with a little file or my trusty Dremel plus grinding cone and report back here with the results.

The elevators come pre-tapered in the Venture 60 kit and, thanks to the care that Bruce Tharpe obviously lavishes on his kits, was as close to perfect as I'd ever want

Thanks for the help Dennis,
Neil.

No problem, hope the thoughts help.
Dennis-

Few questions...

I thought CA hinges were tight enough

What is a drill press?

How do you make sure that the holes are not slanted? To me it sounds amazingly difficult.

Thanks!!!
David

Mindwarp,
What type of glue did you use? It does sound as though the problem has been caused by not enlarging the outer portion of the holes to clear the hinge point knuckles. This along with possibly some glue in or close around the hinge. Work the surface back and forth by hand 100 times or so and see if it gets better. To answer your question of this being normal for hinge points, no it is not. A surface that is installed correctly with hinge points should fall bevel to bevel under it's own weight. Robart also makes a small jig for drilling the holes which works very well, no drill press needed.

This tool is a "must have" item, in my opinion.
Either that... or you can make something like it from scratch. Simple, yet very effective.

I pretty much only use the Robart hinges and the above tool really helps. It is best to drill your hinge holes before you bevel the hinge line. This way the jig works better to ensure you are drilling exactly on the hinge line.

As for the stiffness. Sometimes, the hinges will be a bit stiff out of the package. They will loosen up. It is also possible that one or more hinges are not perfectly aligned. One could be in a different hinge plane (fore/aft or up/dn a little) or twisted/rotated slightly. It doesn't take much error... even 1mm is enough to make the surface feel stiffer. If the control surface is not perfectly true (warped/slanted), this can put pressure on some hinges making them bind a little. It is also very easy to get a dab of glue in the hinge or next to the hing or in the hinge line that will cause surface movement to be a bit stiff. If the surface moves without jerking or catching, and is just stiff, I'd say you are probably fine. You can try to work a little Vaseline into the joints if it really bothers you, that should help.