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What am I doing wrong on my control surfaces

jhitesma

Some guy in the desert
Mentor
#1
Ok, I've built a couple of planes now (Nutball, Flyer, Delta, Baby Blender v2, Axon) and have two more I'm just finishing up (Old Fogey and Bloody Wonder) and I keep having the same problem on all of them.

Namely my control surfaces don't deflect well. By deflect I mean move towards the side with the bevel. They move towards the paper side just fine. But none of them move well towards the bevel.

I'm cutting my bevels with a knife. I do a score just through the paper about 5mm away from the hinge line and peel the paper off to help guide me. Then use a fresh blade to slice as close as I can to the hinge and the paper. I then go back with a sanding sponge and make a few passes to even it all up. The result usually looks great...and seems to move really well.

But then I do one of two things. On the Nutball and Axon I put tape over the hinge - it still seemed to move well by hand. But when I hook up my servos my control rods end up bending and I get very little deflection. I've checked that the holes in my horns are directly over the hinge line (I've used cut up gift cards, zip ties, grayson hobby laser cut horns and now the FT laser cut horns for my horns) and it all looks good, and I can't feel any binding...but the servos just don't want to push.

Instead of tape I've been trying Chad's hot glue trick that's been mentioned in the show a few times - just running a thin bead of hot glue right down the hinge line and then scraping it into the foam and removing any excess. But after doing this my surfaces don't feel nearly as free - and my hot glue seems to stay sticky for a few days which leaves me worried about the surfaces sticking if I move them to full extension.

I'm using .032" music wire from my LHS for my control rods. The Flyer has the best control surfaces I've made yet - but only because I used a BUNCH of zip ties to constrain the control rods:
IMG_8006-L.jpg

And even then the rods tend to flex more than I'd like.

On the delta I figured they were short enough rods it wouldn't be an issue...but I think I'm going to have to add some zip ties on there as well because they're bending and I'm getting more travel in one direction than the other as a result.

The baby blender I used linkage stoppers finally instead of z bends and the triangular bend for adjustment - but again my elevator barely moves down (it always seems worst on my elevators for some reason.)

Last night I added servos to the BW and used the next size up on wire for the elevator (.047") and it seems great. no zip tie supports required at all. But that wire seems MUCH heavier and bulkier. On the ailerons I used the same .032" wire I've been using - and I get basically no downward deflection at all, the wire just bends. I'm debating whether to switch to the heavier wire on the ailerons as well or if I should just add some zip ties and see if that helps.

Maybe I'm not making a big enough bevel? I'd try with no glue and no tape...but I'm really worried about how well that would hold up since I do nick the paper while cutting the bevel sometimes.

I'm having a blast building and flying...but it's getting really frustrating having the same problem over and over - and it's always worst on the elevator it seems.

Any ideas?
 
Last edited:

Liemavick

New member
Mentor
#2
032 is the lightest wire I use and when i do I sleeve it with the tubing and use zipties as you have done. The 047 gauge wire is by far my favorite as it doesnt flex much. As far as your hinges, are you beveling both sides or just one? I like to slice back 1/4" of the paper as you mentioned and use a sanding block to make the bevels. Make sure your getting at least a 45 degree bevel and its clean all the way across, no high spots to stop the travel of the flap. From what you've said that they move freely before hand. I would guess its the thinner wire or the servo's not centered prior to installing the horn. Glueing the edges of the flaps does give them more resistance, but if everything else is OK it won't affet the travel as the servo is strong enough to lift/lower them.

Good Luck and let us know what you find.

Brian
 

CrashRecovery

I'm a care bear...Really?
Mentor
#3
If you don't have all the foam removed from the underside it won't flex. Just making sure you have that done. The 45* should be right up against the paper
 

aiidanwings

Senior Member
#4
I like to completely remove the hinged surface before cutting the bevel, then reattach it with hinge tape (colored duct tape from Walmart). It can be frustrating to align, but is well worth the effort as it is much more flexible and durable than the paper hinge.

Any fine powder will kill the sticky hot glue surface.
 

jhitesma

Some guy in the desert
Mentor
#5
Thanks for the feedback so far guys. I have been making sure to center the servos, just forgot to mention it. I have only been cutting the bevel on one side - but I do sand both sides. When I do the sanding I make sure there aren't any high spots and that it's a nice smooth flat surface on both sides with the paper exposed down the hinge line.

Before doing the glue trick or tape they are SUPER loose and just flap from me lifting the board in either direction way farther than required.

Even with the glue or tape they still move easily by hand.

I guess it's just the .032 wire isn't quite strong enough. On my Axon I had to tape a BBQ skewer to the elevator rod and that got it working...but I did break that servo in a crash and had some goofiness in the air that felt like the elevator just wasn't working properly. But I had a number of issues with that plane and have already retired it (I like the general idea of the axon and do plan on building a second with what I learned from this one) so it's hard to tell what the primary problem really was.

I'll go ahead and try the .047" wire on the BW ailerons tonight to see how that works. Was also hoping to setup the fogey tonight...but I haven't found anything good to use for sleeving the wire and it turns out I don't have enough .032" wire to finish it anyway...and my LHS won't be open for at least another week thanks to permit issues they're experiencing with the city over their new location :( (Same reason I haven't been able to finish the landing gear for my Blender!)
 

FlyingMonkey

Stuck in Sunny FL
Staff member
Admin
#6
A few points that I didn't notice being made...

1) Make sure that the hole for your control horn lines up exactly over the hinge line.

2) The further out on the servo arm, and the closer in on the control horn, the more deflection you'll have. Kind of like the big gear in front, and the little gear in back makes you go the fastest on a bike.

3) I use the metal rods from irrigation marking flags. They weigh more, but if you find the right ones, they're just enough thicker that they don't flex anywhere near as much as that music wire will.
 

jhitesma

Some guy in the desert
Mentor
#7
A few points that I didn't notice being made...

1) Make sure that the hole for your control horn lines up exactly over the hinge line.
Yep, thought I had mentioned that I checked and double checked that. (Side note: That's one of the reasons I haven't dusted off the balsa glider I built a few years ago again - need to reinstall the horns and just don't want to work on that beast!)

2) The further out on the servo arm, and the closer in on the control horn, the more deflection you'll have. Kind of like the big gear in front, and the little gear in back makes you go the fastest on a bike.
I'm horrible about gear ratios :D Always get those messed up. Most of the planes I've built so far I used the farthest hole on the servo arm and then just dialed back the limits in my TX. But on the BW and the Flyer and Delta I used the 2nd hole in from the center and on the BW I'm using the 3rd (Flyer and Delta didn't have linkage stoppers - and 3rd hole was the closest in that it was easy to fit the stoppers on.)

3) I use the metal rods from irrigation marking flags. They weigh more, but if you find the right ones, they're just enough thicker that they don't flex anywhere near as much as that music wire will.
[/quote]

I've been keeping my eyes open for those, keep forgetting to actually look for them at the hardware store though.

I went ahead and put the .047" wire on the BW ailerons tonight and they work MUCH better now. One side is still has slightly less movement than the other when deflected - but I think it's just due to the servo being mounted slightly crooked, I evened out the servo arm with subtrims and it's better but still slightly less on one side. But I'm pretty it's deflecting more than necessary before reaching that point so now I just need a bit of time to test fly!
 

jhitesma

Some guy in the desert
Mentor
#8
Thanks for the feedback guys. Got to maiden my BW this morning and it was a blast. Unfortunately I didn't have any landings that didn't result in a broken prop due to the lack of landing gear so I only tossed it into the air 3 times - but 2 of the landings were at least controlled and gentle :)

Need to pick up another bag or two of props and get it it back in the air. Flew well and survived the one unplanned landing great. But I need to adjust my aileron linkages just a bit more it seems as it's pulling in one direction and I can see that the ailerons aren't quite level at neutral. And with it breaking a prop each time I landed I figured I'd rather use the rest of my flying time to enjoy my FT Flyer and Delta a bit more and stretch my props ;)

Just need to figure out a way to get it out of the air and back on the ground without going through quite so many props :)