Paper Flaps for Aileron and Rudder?

[TSOlympian]

Hey guys,

I was wondering, is anyone using paper flaps to make ailerons and rudders for their plane? I know they were often used with Elastic Launch Gliders a while ago, back when it was still around, but I noticed in a lot of rubber-powered plane designs they're absent. Not sure, but I was thinking they would help the plane go in a circle, because the ailerons could help the plane bank slightly and the rudder would help it turn on the yaw axis (is that the right one?). I also thought it might make the plane easier to trim.

I've also seen ELG models that are apparently called "flapper designs"; the aileron is large and flexible enough that it slightly changes angles based on the windspeed. So the trailing edge might go up or down during a flight, so it supplies an appropriate amount of lift for the plane. Could it maybe apply here?

Thanks!

[jander14indoor]

Next statement not official, etc...
I suspect many ES would consider the flap as part of the wing or stab chord so be careful how you use them.

Now, not official, but based on experience, lets talk about the practicality or use of paper flaps for aileron and/or rudder.
Frankly, they aren't a very efficient way to make these planes turn. You don't turn these planes the same way you do a man rated plane. In addition, paper tabs don't hold their settings well.

WS planes fly over a wide speed range, but must maintain a constant turn radius. It turns out that different inputs work better at different speeds.
At high speeds, you turn radius is controlled by the direction of thrust, so you tilt the prop SLIGHTLY left. But as torque drops, this becomes less efficient and the turn will open out.
Next in the speed range is the vertical stab. Using rudder to turn is actually pretty draggy, so instead of a rudder, its better to angle the whole stab. Most of the time this is set by angling the whole tail boom, not the stab alone. More sensitive control and what you are really trying to do is to keep it from causing drag by setting it to match the turn radius set by the other controls.
Finally you can control the turn by tilting the stab. This is a pretty low drag way, but works best at lower speeds.
If you mix these correctly, you get a nice, constant turn radius throughout the flight.

What you DON'T want to do is to turn the plane by banking it. This causes turn by causing some of the lift towards the center of the turn. If you want to keep flying you have to speed up and that causes more drag and burns up your rubber faster. It turns out that most efficient flight is by keeping the wings fairly level. That's why most designs have longer left wings than right, and have the angle of attack of the left wing higher than the right.

So the best way to have a constant/low drag/efficient turn is to bend your plane in seemingly odd ways. Yes you need to be able to adjust things when you are first trimming a new plane, but the best way to do this is to set up a good first approximation and then strategically break (crack) and reglue elements to adjust.

Example, I was trimming out my plane at a clinic this morning to demonstrate this to students. I had my plane set up with left wing 1.5 cm longer than the right, left wing slightly washed in, tail boom offset about 1/2 inch left, horizontal stab tilted with left side 1/2 inch higher than the right, prop a couple of degrees down and left. Plane would circle steady, but not climb. It also looked like the plane was tilting too far left bank. I slit the leading edge near the center about halfway, cracked it, applied superglue (thin) and while holding the left tip higher that it had been set the glue with insta-set. Same winds, the plane climbed strongly to the ceiling.

Jeff Anderson
Livonia, MI

[TSOlympian]

Ah thanks! but about trimming, if the whole trimming process involves breaking and regluing, then how do we get to trim at the competition? Aren't we to allowed to trim our plane right before before/during our flight period to get it's path to match the room? When you said you cracked your plane and made the left tip higher, were u adding a new dihedral to the plane?
Also how exactly do we crack it? Is it sort of just sort of bending the wood without ever breaking it in two pieces, or do you cut them apart?

[jander14indoor]

You should have the bulk of your trimming done BEFORE a contest.
You should have time to practice at a tournament not part of your competition time. Doesn't happen everywhere.
That's why we recommend room dimensions be available before the tournament.

<SNIP>When you said you cracked your plane and made the left tip higher, were u adding a new dihedral to the plane?<SNIP>

No, not adding dihedral. Twisting the wing so the left wing tip has a higher leading edge than the right. Crack is only in front spar and the outer left tip of the front spar is lifted maybe 1/8 inch from straight. The idea is to increase the angle of attack of the left wing to fly level (or more so) in a left turn.

<SNIP>Also how exactly do we crack it? Is it sort of just sort of bending the wood without ever breaking it in two pieces, or do you cut them apart?

A couple of ways to do it, depending on how much change is needed. Small changes can some times be bent or warped in. Problem with that is getting it to stay.
What I typically do is to slit the part I want to crack about 1/4 to 1/2 through to control the exact spot and direction of the bend, then crack the remaining part without causing it to fully separate. While holding the change where I want it I have (or sometimes do it myself) someone add a VERY small amount of thin cyanoacrylate in the crack and immediately hit it with setter. Can be done in a couple of minutes with practice. Most of my planes have a number of these adjustments added when I first trim them out as I adjust for errors in manufacturing.

Jeff Anderson
Livonia, MI

[TSOlympian]

That makes a lot of sense! I was planning on doing the trimming before the competition, but since I'm going to other competitions like invitationals, I knew there would be some adjustments from one to the other.

Also, do you use diluted superglue? Is this what you meant by "thin cyanoacrylate"?

[Less_Incidence]

As far as I know there isn't any thinner that can effectively "dilute" CA glue.

Any hobby store will sell CA glue in various viscosities - thick, medium, and thin. I buy Insta-Cure (thin) and Insta-Cure+ (medium) brand CA from HobbyTown USA. I believe it's available at other places as well.

[bernard]

As far as I know there isn't any thinner that can effectively "dilute" CA glue.

Any hobby store will sell CA glue in various viscosities - thick, medium, and thin. I buy Insta-Cure (thin) and Insta-Cure+ (medium) brand CA from HobbyTown USA. I believe it's available at other places as well.

Yes, don't try to thin your CA with water (like our coach tried last year)! If I remember correctly, it makes it gooey and sets it a little, weakening it.

[jander14indoor]

The others are correct, you buy the CA thin, you can't thin it. CA is a glue that sets by crosslinking smaller molecules into longer molecules (that's why you can't practically dissolve it after the fact). Mixing in something else just leaves the stuff mixed in locked in or weeping out of the now winker cross linked matrix when the glue sets.

The advantage of thin CA is it wicks into the wood that' you've cracked to reconnect it.

Jeff Anderson
Livonia, MI

[TSOlympian]

Ah that makes sense! I noticed that superglue burns a bit when it dries on you...because it's a formation of bonds, exothermic reaction! (sorry, I'm taking chem this year) I read that acetone is sometimes a CA solvent/is used to remove it...is there any way it might dilute CA glue without interfering with the crosslinking?

If not, I guess I'll just head to the store for thinned glue and setter

[Less_Incidence]

Trying to use any kind of thinner on CA glue is a bad idea. All it will do is weaken the bonds formed by the glue. If you need thin CA, you'll need to buy some thin CA.

Acetone is OK at debonding CA but it still takes a lot of effort. CA is very, very difficult to chemically alter once it's set.

If you want a glue that can be thinned and debonded, try Duco cement - it's an acetate-based glue that can be thinned & debonded with acetone. To my knowledge, though, stores generally don't sell Duco and I've only ever bought it from Amazon.