Author Topic: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing (Read 3917 times)

RknRusty · « **on:** March 02, 2017, 11:07:19 PM »

I got a little wild with the thin CA on my new Twister wing. I've always used traditional glues, but for the sake of speed, I deceided to use thin CA for a lot of this new wing that replaces the one I busted back in October. It's all finished except for making the flaps now.

My question is about the 1/16" center sheeting. On the bottom sheets and, the front top sheet I covered the insides of the sheets with thin CA. First, I molded them to make them fit the curve of the ribs. I also left the 4 strips un-hardened where they contact the ribs so the Titebond can soak in and make a strong joint.

My thinking was to harden them, but now that I've done it, I wonder if I just made them too stiff and possibly brittle. Anyone ever done this? What do y'all think, was it a mistake to coat the insides of the center sheeting with CA? I'm a little worried that now if I donk it, it'll shatter worse than if I had left all the balsa center sheeting alone and not hardened it with the CA.

Ya think this is something I'll regret?
Rusty

Don Jenkins · « **Reply #1 on:** March 03, 2017, 06:56:16 AM »

Its too late now! Finish the plane and lets go flying!

Don

Brett Buck · « **Reply #2 on:** March 03, 2017, 07:40:42 AM »

Quote from: RknRusty on March 02, 2017, 11:07:19 PM

I got a little wild with the thin CA on my new Twister wing. I've always used traditional glues, but for the sake of speed, I deceided to use thin CA for a lot of this new wing that replaces the one I busted back in October. It's all finished except for making the flaps now.

My question is about the 1/16" center sheeting. On the bottom sheets and, the front top sheet I covered the insides of the sheets with thin CA. First, I molded them to make them fit the curve of the ribs. I also left the 4 strips un-hardened where they contact the ribs so the Titebond can soak in and make a strong joint.

My thinking was to harden them, but now that I've done it, I wonder if I just made them too stiff and possibly brittle. Anyone ever done this? What do y'all think, was it a mistake to coat the insides of the center sheeting with CA? I'm a little worried that now if I donk it, it'll shatter worse than if I had left all the balsa center sheeting alone and not hardened it with the CA.

No, it's probably OK. Finishing it on the outside works more-or-less the same way.

What you probably want to avoid is stuff like covering the wing with silkspan after its installed, rather than covering it first. The end of the silkspan near the fuselage creates a stress riser that has been known to cause structural problems later. In the early-mid 80s, when people first started using ST60's and 4045FSRs, the New Jersey guys had a bunch of problems with wings folding. Part of it was the better cornering you could do with more powerful engines, but the root cause was not covering the wing through the center section. So they broke near the root time after time. They started beefing up the center sections, but all that really needed to be done was to silkspan it from tip to tip before assembly. Now, with vastly higher cornering loads yet, with much better engines than an ST60, it's even more important.

On full-house airplanes, the ability to stay together is still a big issue.

Brett

tom hampshire · « **Reply #3 on:** March 03, 2017, 07:58:37 AM »

For the same reasons, my last 3 stunters have had carbon veil doped to the rib side of the sheeting before assembly. Gives a noticeable increase in stiffness, and better support to the planking for sanding.

RknRusty · « **Reply #4 on:** March 03, 2017, 10:17:42 AM »

Thanks, guys. Tom, that's a good idea I wish I'd thought of. I do have carbon veil too. Brett, I never thought about that being a stress riser, as I'm still Monokoting wings, but it makes good sense.
Don... I'll deal with you later Lol.
Rusty

Brett Buck · « **Reply #5 on:** March 03, 2017, 11:11:55 PM »

Quote from: RknRusty on March 03, 2017, 10:17:42 AM

Brett, I never thought about that being a stress riser, as I'm still Monokoting wings, but it makes good sense

Ted Fancher diagnosed that one, I merely relay the information.

Brett

RknRusty · « **Reply #6 on:** March 03, 2017, 11:47:16 PM »

That's okay, Brett. As long as you know something, you know it. I do like to assign due credit too, so thanks for passing it along. This is also the first sheeting I've shaped curves at each end, for the same reason, rather than just cutting it off square, preventing a sharp stress riser. Can't say for sure which builder(s) to attribute that too, but it also looks good. I have only built a few PA ships, but I'm getting pretty good at it.

I have a couple of nice old hand-me-down planes from Bob Z. that I'm going to honor with the traditional old ways of covering, and if I have to cut the wings out, now I'll know about your tip. I usually overlap a 1/4" of epoxy/microballoon filet over the edge of the iron-on covering whenever I cover it after the wing installation. I guess that's better than nothing, but I suppose the edge of hard dope contributes as much or more sress than the silkspan.

As long as I have your ear, I've been wanting to ask you about your posture and arm position. After seeing a video of you flying a pattern I see some changes I've thought of making since I'm lately(and suddenly) unable to turn my head and look up higher than 45 deg. anymore. Your style that I saw might get me back into competition, so I may send you a PM or maybe a phone call about that.
Thanks,
Rusty

Shug Emery · « **Reply #7 on:** March 04, 2017, 08:51:13 AM »

Quote from: Brett Buck on March 03, 2017, 07:40:42 AM

No, it's probably OK. Finishing it on the outside works more-or-less the same way.

What you probably want to avoid is stuff like covering the wing with silkspan after its installed, rather than covering it first. The end of the silkspan near the fuselage creates a stress riser that has been known to cause structural problems later. In the early-mid 80s, when people first started using ST60's and 4045FSRs, the New Jersey guys had a bunch of problems with wings folding. Part of it was the better cornering you could do with more powerful engines, but the root cause was not covering the wing through the center section. So they broke near the root time after time. They started beefing up the center sections, but all that really needed to be done was to silkspan it from tip to tip before assembly. Now, with vastly higher cornering loads yet, with much better engines than an ST60, it's even more important.

On full-house airplanes, the ability to stay together is still a big issue.

Brett

So, are you saying that it is good to cover the wing on a profile with silkspan...maybe doubled over in middle and then glue into fuselage? Not a wood to wood joint but a wood to doped silkspan joint? Been curious about this.
Thanks.
Shug

Chuck_Smith · « **Reply #8 on:** March 04, 2017, 10:33:53 AM »

Quote from: Shug Emery on March 04, 2017, 08:51:13 AM

So, are you saying that it is good to cover the wing on a profile with silkspan...maybe doubled over in middle and then glue into fuselage? Not a wood to wood joint but a wood to doped silkspan joint? Been curious about this.
Thanks.
Shug

Shug, that's how I do it. I overlap the center. I'll add a fillet on the inside of the fuse. I used to overlap to past the fuse sides but some of my ships have aged and now and as the finish sinks over time you can now see the seam.

Brett Buck · « **Reply #9 on:** March 04, 2017, 03:26:26 PM »

Quote from: Shug Emery on March 04, 2017, 08:51:13 AM

So, are you saying that it is good to cover the wing on a profile with silkspan...maybe doubled over in middle and then glue into fuselage? Not a wood to wood joint but a wood to doped silkspan joint? Been curious about this.
Thanks.
Shug

Not just a profile, any model.

Brett

Mike Griffin · « **Reply #10 on:** March 12, 2017, 11:43:10 AM »

I don't want to be redundant but just wanted to reiterate what Brett said. When I started using Polyspan (when silkspan got impossible to find) I happened to be having a conversation with Tom Morris and he always would cover the wing before installing it and would overlap the Polyspan on the center sheeting. In other words, cut a piece long enough to go from the wing tip on the outboard wing to the outside edge of the center sheeting towards the inboard tip and do the same thing when you cut the polyspan to cover the inboard wing. You then have the entire center sheeting piece double covered. I hope that was not confusing and made sense.

Mike

RknRusty · « **Reply #11 on:** March 12, 2017, 12:37:24 PM »

That makes perfect sense, Mike. Thanks for the clear explanation, I'll add that to my knowledge-base.

In the "What did you do in your shop" thread, I posted about having finished cleaning out the epoxy and broken wood from the wing cutout in the fuse and getting ready to install the new wing. I'll be Monokoting this one again, possibly disappointing the traditionalists, but I'm good at it, so I just haven't done a lot with fabric and dope on wings.

http://stunthanger.com/smf/open-forum/what-did-you-do-in-your-shop-today/msg479224/#msg479224

Rusty

Mike Griffin · « **Reply #12 on:** March 12, 2017, 03:52:56 PM »

Absolutely nothing wrong with the plastic type coverings. I use Ultracote and have gotten pretty good at applying also. I used dope and silkspan when you could still get it and now I use Polyspan and dope, when I use dope. When I first started with the shrink type coverings, I really was bad at it but I kept at it and with some practice over the years I got better and better. We have "purist" in the hobby that would never think of using anything but dope and/or automotive top coats and that is perfectly great if you have the place and equipment to get those kind of finishes. I don't. I have no compressors or guns to spray with mainly because I have no place to do it. My wife nearly kills me when I use dope in the house and the fumes are not real friendly to my body either. My paint comes from a spray can. I also paint over Monokote/Ultracote and have never had it come off. There are lots of ways to do things.

Mike

phil c · « **Reply #13 on:** March 15, 2017, 08:26:27 PM »

Quote from: RknRusty on March 03, 2017, 10:17:42 AM

Thanks, guys. Tom, that's a good idea I wish I'd thought of. I do have carbon veil too. Brett, I never thought about that being a stress riser, as I'm still Monokoting wings, but it makes good sense.
Don... I'll deal with you later Lol.
Rusty

A stress riser is ANY place where one part of the structure stops. That's why the FAA specifies a 1:10 splice with plywood cover plates for joints in spars, longerons, etc. When you have multiple discontinuities, such as at a wing root, small stress risers are even more important, as Brett pointed out. Other popular spots are the ends of engine mounts(often near the leading edge), stabilizer mounts(not enough wood in the fuselage, glue joints in the stab root). That's why many planes use a stab cut from one piece of wood and then has rounded open bays cut out and ribs inserted, or a spar/rib structure completely sheeted with thin balsa.

You know you've got a well balanced design when you fly it straight into the ground and all that is left unbroken are the wing tips, the rudder, and the outer parts of the stab.

RknRusty · « **Reply #14 on:** March 16, 2017, 05:50:17 PM »

Haha, thanks for elaborating on that, Phil. I can claim to have had at least a couple of planes that were structurally "well balanced," as you say.

Are you coming to Huntersville in a few weeks? I met you at Watt's one time a year or so ago.
Rusty

Chris Fretz · « **Reply #15 on:** March 16, 2017, 06:13:46 PM »

Is the wing done and back in yet Rusty?

RknRusty · « **Reply #16 on:** March 16, 2017, 08:07:54 PM »

Quote from: #Liner on March 16, 2017, 06:13:46 PM

Is the wing done and back in yet Rusty?

Hey, Chris
The wing is done, and I started slotting the flap hinges today. Cleaning out the root in the fuselage was done with a razor knife and finished with a Dremel sanding drum. I'm being careful not to induce any incidence, and it looks like it lines up nicely so far. To make for good epoxy joints, I'm lining the inside of the root in the fuse with 1/64" ply, which will be epoxied in place and make for an even fit all the way around. It'll need some minor shimming underneath where I got a bit wild with the Dremel, but I think it's going to be indistinguishable from its pre-wrecked condition. Fillets will cover any minor roughage.
Here it is dry-fit:

Author Topic: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing (Read 3917 times)

RknRusty

Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

Don Jenkins

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

Brett Buck

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

tom hampshire

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

RknRusty

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

Brett Buck

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

RknRusty

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

Shug Emery

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

Chuck_Smith

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

Brett Buck

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

Mike Griffin

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

RknRusty

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

Mike Griffin

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

phil c

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

RknRusty

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

Chris Fretz

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing

RknRusty

Re: Did I do a bad thing?...I CA hardened the inside of center sheeting on my wing