gaps between control surfaces
 

I bought an old but flying Thunder Tiger Skylark 40 trainer. I am a newbie. This winter I completely stripped and re-covered the plane with Ultracoat, and made new slightly larger ailerons and elevators.

My question is, because I was struggling with the hinges and the CA drying, instead of a snug fit of the ailerons against the wing and the elevotor to the stabilizer, there is a gap ranging from one-sixteenth to one-eghth inch between the moving surface and the wing/horiz. stab.

Will this be OK? I thought I read somewhere if air can move through the gap it will cause flutter, but I thought flutter was caused by something else.

I would have to cut the hinges and start over if it has to be tighter.

RE: gaps between control surfaces
 

I've seen planes fly with some pretty huge gaps. Sometimes it's ok, and it's not like the world will end. However, you are better off cutting off the hinges and doing it again.

While you may or may not have flutter, there are several other problems that will occur with big hinge gaps.

First, the controls will not be as effective as they would be with smaller or even sealed hinge gaps.

Second, you can have problems with the plane holding trim consistantly. This is worst on the ailerons if one side has more of a gap than the other. What happens is that depending on the amount of lift being generated, the amount of air going through the gap changes, resulting in the lift changing at different rates on the two wings, and that results in a rolling tendancy. For example, you might notice that the plane starts to roll a bit as you slow to land, or if you pull a loop, the plane might always want to roll a little.

Remember, when installing CA hinges, put the hinges in dry, put the control surface on, and when everything is in place, then apply the thinnest CA you can. Don't put CA on the hinge first and try to insert it in the wood, and don't try to attach the hinge to one side then the other.

RE: gaps between control surfaces
 

Ahh great advice already! Thank you Montague! The roll issues make perfect sense.

But I have two other issues: 1) I have already cut and re-done the hinges about 3 times and I'm running out of room for new holes, worried about weakening the trailing edges of the wing and stab with all this cutting.
2)Lets say I re-cut and get a snug dry fit, seems I would have to put the thin CA right onto the moving part of the hinge to get it to seep down. These are nylon hinges with a metal pin. How do you do a snug fit and apply the thin CA without gluing the hinge frozen??

I also have a brand new Hobbico Superstar trainer that has flown once at the hands of an experienced flyer I talked into flying it at one of our local fields to trim it out. I suppose I should I learn with the Superstar, until I take the rebuilt Sky Lark in the air.

One more questioin and perhaps this belongs in the beginners forum, but all the control surface pushrods on the Sky Lark are attached to the servos with a "set screw" tightened down on the pushrods, but just wondering if I should make them into Z-bends that can't come loose.

Thanks for the help for a newbie!

(Got my first tastes and love of flight as a kid flying u-control, no flying for 30 years, just now spreading my wings at age 44 with some RC.)

RE: gaps between control surfaces
 

Oops, sorry, if you are using hinges that have a pin, then what I said about installing them is totally wrong. What I said applies only to CA hinges, which are little bits of plastic with a fuzzy coating designed to wick in CA.

If you have conventional hinges with a couple of bits of plastic and a pin, then you're best off installing them with epoxy or in any number of ways. When I've used those hinges, I usally cut a recess in to the moveable surface to get the gap nice and small. I dry fit everything to make sure it all works. Then I put vasilene on the moving bits and work some slow setting epoxy in to the hinge slots and insert the hinges. In this case, I usually do one side at a time, and use some masking tape to hold the surface on.

RE: gaps between control surfaces
 

G'day Mate,
No wonder you are having trouble, they are NOT CA hinges, use 30 minute epoxy to secure them, remember you must have a double bevel on the control surface, to allow it to move, & you should have the hinge pin centre line on the exact centre of the hinge line. Meaning you must cut some of both sides away to allow the hinge centre section, the thick part, where the pin is, to be inline with the point of the bevel, that is the pivot point of the hinge.
When I use these hinges, I fold them together, & dip just the centre section, where the pin is, into some melted industrial while grease, it will get into the hinge pin joint, & stop the glue from sticking up the hinge. DON"T GET ANY ON THE FLAT PART OF THE HINGE.
Do it with clean hands, let it cool on some paper towel, & then mix your epoxy, & use a thin spatula, I use an old butter knife, ground square at the end, to push some epoxy into the slots on one surface only, & some on the hinges, Eg, an aileron, mark exactly where they must fit, & push the hinges into the slots one at a time & line em up square, leave em to dry, & if you have enough time you can do the other aileron, & so on, don't be in a hurry, & it will work out fine.

RE: gaps between control surfaces
 

My Goodness! No one's suggested sealing the hinge gap! Search for this subject and find how to seal the gap with covering. It's been posted many times.

I don't know what a Skylark is, or how big, but avoid using the set-screw connectors for control linkages. They may be OK for small park flyers.

RE: gaps between control surfaces
 

G'day Mate,
No point sealing a hinge gap when the hinges will probaly fall out because they were glued with the wrong type of glue.

RE: gaps between control surfaces
 

I agree with some of the others.

Remove the hinges and use 30-minute epoxy to re-glue them AFTER you're sure that they will seat properly.

As for the EZ connectors, you can put a Z bend, but only on one side of the pushrod because you will need a way to adjust the length. And I have used EZ connectors on larger planes than a Skylark, so don't worry too much about them. Just be sure they are tight

RE: gaps between control surfaces
 

Alan- Are you saying nylon hinges glued with CA will eventually come loose? I tried and tried to remove one that dried crooked, and if I pulled any harder, I was going to pull the leading edge off the back of the wing. My hinge slots were very tight to begin with.

RE: gaps between control surfaces
 

Nevermind Alan, you were right. I popped off the ailerons tonight all too easily, and now I need advice on re-hinging by the best method. Any advicve?

Also, I plan to cover the gaps with covering once they're done, based on Ken's wonderful build thread.

RE: gaps between control surfaces
 

I might as well chime in. If you have been using nothing but CA on your hinges, then just choose a good location and reinstall using epoxy as others have already advised. Make sure and protect the pins from the glue. Montague uses vasaline, I prefer a toothpick dipped in 3-in-1 oil. Just light coating is needed. If your wing is in to bad of shape due to all the hinging and re-hinging attempts, why not try the Robart hinge points. They make small ones that would work great on a trainer. It's all I use anymore. Simply drill a hole corrosponding the pin size countersink a little and glue with either epoxy or what I use, polyeurathane glue (Gorrilla Glue). Key is to get both surfaces lined up well and drill the holes straight. Robart makes a drilling jig for about $5.50 that make it fool proof.

Good luck.

Greg

RE: gaps between control surfaces
 

But as far as worrying about sealing the aileron hinge gaps on a 40 trainer..... Bag it. You will have little to no effect with this type plane ..... Greg

RE: gaps between control surfaces
 

Well, that depends... IF the gaps are fairly large, you could benefit greatly from sealing them - especially on a trainer

RE: gaps between control surfaces
 

I try and keep the gaps close, but have also sealed the gaps in some cases. Can't really say I noticed a difference, but just about everybody agrees its a good idea. I have a couple of fast planes that I make sure and seal the gaps--would hate to loose and elevator or elevon due to flutter.

I handle training for our club and have seen some pretty large gaps in the planes some guys bring out. We always give the control surfaces a pretty good tug before flying a plane for the first time--its interesting how many times we have had epoxy hinges installed with CA, or CA hinges installed with epoxy. I have had some surprised looks when I tear off an airelon but then it's better to loose on the ground than in the air. It's better to be on the ground wishing you were up there, than being up there wishing you were on the ground.

Greg

RE: gaps between control surfaces
 

I can't envision a reason not to seal the gap other than the time it takes- which really isn't much if you use clear covering. Sharper response, lower stall speed- it's all good.