I can't emphasize how important it is to seal the hinge lines on any CL Stunt model from which you expect to get even decent performance and consistency. And not just flapped models; even those Pukey Profiles with elevator-only controls need this treatment.
This came to mind during the recent Fall Follies. There was entered an ARC Oriental which had a strangely configured tab fitted to the outboard flap. I don't doubt that it cured some problem, especially as the model was sorta decent in flight. It did, as I remember, seem to go a bit loose on outsides**, but as the tab was radically bent down and against the airflow, more of the same didn't seem a likely option.
And we have seen lots of Orientals in this area; none have required anything nearly this drastic during the trim process.
Bruce Hunt--who is pretty sharp when analyzing trim problems--and I spent a fair bit of time trying to figure out the problem. Warps? Nothing remarkable. Tip weight? Pretty close, which in my world means "Too much." A jig-built model, of course, so basic structure was assumed to be at least close enough.
Yes, we ran the list. Ah, ha! Too late to actually do anything about it we found the hinge lines to be open, not sealed in any way.
Our failing, simple as that. Bruce and I were once party to trimming a SIG Banshee that was absolutely horrible in outside maneuvers.** I had a Banshee years and years ago, Bruce flew one in Advanced not so long ago. But we were stumped. Looked like Swap Meet Material.
Noticing the hinge lines were unsealed, we flopped the sucker upside down and performed an impromptu--and not very good, truth be known, the surfaces being difficult to get really clean while at the field--sealing of all hinge lines.
While not all models will benefit to such a degree, this particular Banshee was literally a different model. Instantly. It was as if we had a piece of junk one moment, pulled the glow plug out and slid an entirely new model in place, installed the plug and flew a much more than merely competent PA model the next.
First thing needed is the right kind of tape. And that is Scotch (3M) "Multitasking" tape (used to be called "Crystal Clear"). The stuff I use is purchased at any good office-supply retailer, and I buy the commonly available 3/4" wide tape.
One can deflect the surface fully open, run one strip of tape along the full length of each hinge line, press it place, wiggle the surfaces vigorously and fly. Which is what we did with that ornery Banshee.
There is a better way. I have taken to only sealing the areas between each hinge. This is more work in the beginning, but when a piece comes loose it's easier to replace small seals.
First, clean the surfaces. Now clean them again. Wash your hands while you're at it.
The idea is to center a cut-to-length piece of tape between the hinges and centered on the open hinge line. Touch it to one surface and press in place. Continue off the edge of the surface, down into the hinge line, back up the edge of the opposing surface and to the flat of this surface.
Simple. Well, not so fast. I find it to be helpful to first apply the sealing tape to a non-stick surface, half the width of the tape hanging off the edge. I use scraps of the backing for FasCal for this purpose, although 1/64" ply might work, maybe a strip of thin but rigid plastic.
With the tape applied to this temporary holding fixture it is a fairly easy task to get the seal applied to one surface, sliding the fixture out of the way, completing the sealing operation.
After flying and cleaning the model a few times, handling and oil residue will begin to lift the edges of the seals. To a great extent this can be eliminated in rounding the corners of the seals by trimming them with finger nail clippers just prior to installation.
Should you prefer one-piece seals--the hinges themselves do leak a little air after all--run the seals from one end to the other of the surfaces, press in place. The controls will have stiffened a little bit to a lot. With the model back right side up, squirt some WD-40 into a small container. Using a Q-tip apply a small amount of WD-40 to each hinge barrel. Wiggle the surfaces with the leadouts. They should free right up.
Having said all that, I will admit that once in a great while we do come across a model or two which do not seem to benefit from having the hinge lines sealed. But that only proves the rule, in that one cannot possibly know if such is the case until the hinge lines are sealed and the model flown in back-to-back tests with and without seals.
Truly, there is no option here. Sorry...
Well, there is an option. Let's say you are into real, real fine tuning, you're flying a flapped model, the hinge gaps are minimal to begin with and you don't have easy access to the controls. Let's also assume your name is Don McClave.
Assuming no real bad habits with and without seals, it is possible to fine-tune the actions of elevators and/or flaps by experimenting with them sealed and unsealed. I have, for example, seen Don do this to apparently good effect with the flap hinge line unsealed, but the elevator hinge line sealed. The former was slightly less effective in action, the latter more effective.
So. That new or old model of yours, the one which doesn't respond to control input the way you expected? Seal the hinge lines. You may well come back from your next flying session feeling as if you have been gifted a brand-new, improved model. For very little investment in time or money.
Dan
** Having completed above I noticed one could misconstrue sealing hinge lines as correcting problems in outside maneuvers. This not the case, it was mere coincidence that the Banshee and Oriental both suffered in outsides. Besides, simply sealing hinge lines can have quite a lot of effect on how the model flies in level flight, let alone during maneuvers.
This page was updated April 13, 2006