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Mar 28, 2019, 05:13 PM
A man with a plan
Balsaworkbench's Avatar
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Build Log

another 25 size Corkscrew build log


I have a few reasons for doing this project. One of them is that I always liked the looks of the Corkscrew, and then I sold Mike a short kit and he did a build log. It looked like he was having so much fun, maybe I should try one.

Another reason is that my son is a pretty good pilot now. He takes off, flies inverted, lands, etc. I thought he would find this plane entertaining, so I should build more than one.

Additionally, I have three OS 25 SF engines. I know the Corkscrew would be good enough with a 25 FP or similar, but these engines are just sitting around doing nothing, so what if I cut out three kits and build one each for me, my son, and our flying buddy Xu. We can learn formation flying and aerobatics.

The last piece of the puzzle fell into place this week. There was a swap meet on Saturday, and perfect flying weather on Friday. I decided to sell a particular 40 size low winger that hadn't gotten any air time in the last year. I wanted to take it out on the last day, have some fun, and then sell it. In case you haven't heard this particular law of thermodynamics, any plane that's taken out for "one last romp" before being put up for sale is in fact taking its last romp. The muffler screw backed out, it lost pressure on takeoff, the engine died, and I couldn't get it back to the runway. It hit a tree and smithereened itself in the adjacent pasture. This has happened several times to me over the years. I should know better. Anyway, I can use the battery for a new plane now. The next day I sold one plane, freeing up another battery and receiver, and a few days later my son strained his PT 40 through a tree during a failed attempt to do a low inverted pass, thus freeing up another battery and receiver. If I counted correctly, that's three sets of airborne gear for the new airshow team.

Now all I need is a bucket with three Corkscrew short kits in it. Fortunately I have one of those here:
Last edited by Balsaworkbench; Mar 28, 2019 at 09:46 PM.
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Mar 28, 2019, 05:20 PM
A man with a plan
Balsaworkbench's Avatar
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Since I'm building three of the same plane, I think it's a good idea to make them slightly different, for comparison.

For efficiency the fuselage side is in two pieces to be joined by the builder. The first plane has the sides joined with my old favorite method, thin CA glue. One side is chosen to be on the outside of the plane, and the two pieces are placed so they are flush on this side. The easiest way is to lay them flat on the table. The glue is applied to the other side of the joint. It may or may not be flush, but that doesn't matter because it's on the inside. This is the fast way to join parts. On the other two maybe I'll use masking tape and Titebond II or the Ambroid clone that's available on ebay.
Mar 28, 2019, 05:54 PM
A man with a plan
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Even though I've been building planes for decades almost every project has at least one big stupid mistake. Maybe I can make an exception this time. So far so good...

The fuselage side pieces were matched for flexibility and weight to avoid warping the fuselage when the tail post is joined. Then I went one step further and put the lightest top with the heaviest bottom, and vice versa, to make the three planes more consistent in weight.

The selected pieces were joined tightly with tape.
Last edited by Balsaworkbench; Mar 28, 2019 at 09:48 PM.
Mar 28, 2019, 05:57 PM
A man with a plan
Balsaworkbench's Avatar
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Then the joints were folded open on the other side and glued. I glued one pair with Titebond II and the other with Ambrulose. Then like sides were stacked with the tape side down and weighted with home made pickles. There's nothing like home made pickles.
Mar 29, 2019, 08:02 AM
AndyKunz's Avatar
Yup, pickles work! I use home made grape jelly (for weight, not for glue ). I grow the grapes and make the jelly - my other hobby.

Andy
Mar 29, 2019, 09:14 AM
A man with a plan
Balsaworkbench's Avatar
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There's also a bottle of home made wine holding the parts flat. A friend of ours makes that. He gives us a bottle every other year when we raise new hens for his laying flock. The wine is good but we're not huge alcohol enthusiasts, so we use it for cooking.

We've planted grapes a few times but they always die. We have tons of native grape vines growing in the woods, so I'm not sure what the problem is.

Edit 6 months later, September 19th: I opened the jar of hot peppers to the left of the wine bottle. Wow, those are good! I canned these 3 years ago and they just keep getting better. I have a ton of jalapenos in the garden now. I'll be canning those this month.
Last edited by Balsaworkbench; Sep 19, 2019 at 10:49 PM.
Mar 29, 2019, 09:35 AM
A man with a plan
Balsaworkbench's Avatar
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What is Sigment glue good for?


The fuselage glue experiment demonstrated that all three kinds of glue produced excellent results. The CA fuselage doesn't need much sanding because I held the outside flush while gluing, and the other two glues are easy to sand. I didn't even spend more than 10 seconds dressing the edges to be glued. They still have a tapered kerf and a bit of char, and they stuck together really well.

Next I have to laminate the 1/32" ply doublers to the fuselage sides, and I thought maybe I would do another experiment. Water based glues are not my favorite for laminating because the wood sometimes warps when it absorbs the water. So I was going to leave Titebond II out of this operation. Ambrulose comes in a little bottle, and mine is getting pretty low, so that's out. That leaves epoxy, CA and Sigment, which I have a big nearly new tube of.

I glued a small block of balsa to a scrap of plywood over night with Sigment to test it before making a commitment on a pair of fuselage sides. I put a blob of glue down, squidged it around with the scrap of balsa, and weighted it with a jar of screws. 14 hours later the bond seemed pretty strong, so I tested it. It resisted side force very well, but I was able to pull the balsa loose easily, and it came away with no breakage of balsa wood. The only thing that broke was the glue joint.

Now I'm wondering if Sigment is not good for laminating balsa to ply, or if I just didn't leave it long enough. I certainly like the smell of Sigment. I've used it to glue balsa to balsa once or twice, and now this laminating experiment. So far I'm not super excited about the bond strength. Did I do it wrong?

And what about laminating with Titebond II? Any of you guys have a warpage problem when laminating with it?
Mar 29, 2019, 02:53 PM
The runway used to be longer
Mad_Mike's Avatar
Glad to see you've started on your fleet of CorkScrews!
I used Lepages express PVA to laminate the fuselage sides and had no warping issues. I think Titebond is also PVA but I'm not certain.

Anyway, one mustn't select glue based on how much one likes the smell. Bad engineering.
Mar 29, 2019, 05:21 PM
UAS Pilot - FAA# *******HRK
CryHavoc's Avatar
Quote:
Originally Posted by Balsaworkbench

Now I'm wondering if Sigment is not good for laminating balsa to ply, or if I just didn't leave it long enough. I certainly like the smell of Sigment. I've used it to glue balsa to balsa once or twice, and now this laminating experiment. So far I'm not super excited about the bond strength. Did I do it wrong?

And what about laminating with Titebond II? Any of you guys have a warpage problem when laminating with it?
I'm surprised too about the Sigment. I've never used it but was going to get some for myself as I've always wanted to try it. I've never seen anyone write anything bad about it. All those old build articles praise it.

I've also always read about yellow glue warping the balsa but honestly have never experienced that. I use Gorilla brand and think that it dries too fast to induce warping. Especially if heavily weighted down. Maybe it was the old original formulas or the white Elmers types that they had warping experience with. Most small planes these days I just use thick CA though and make sure to use guide pins to ensure it sets down in the right place and I don't have to "hunt" the doubler into place. For bigger planes or profile control liners I fall back to good 'ole epoxy.

Mike
Mar 29, 2019, 06:00 PM
A man with a plan
Balsaworkbench's Avatar
Thread OP
Are you using Gorilla polyurethane glue, or some other formula? I've used Gorilla polyurethane for laminating. You have to put a lot of weight on it because it makes foam. I don't have any at the moment, though.

I decided to get really crazy and read the instructions on the Sigment tube. It says to put some on both surfaces, allow to dry for 2 or 3 minutes, then put the pieces together with more fresh glue, and allow to set with clamps, pins, rubber bands or weight. It didn't say how long, though. I flipped my test piece over and tried it again. This time I'll let it set for a whole day before I disturb it.

I'm thinking I'll go ahead and use Titebond II on one plane, epoxy on another, and either CA or Sigment on the third, depending on how the test piece turns out.
Mar 30, 2019, 10:32 AM
A man with a plan
Balsaworkbench's Avatar
Thread OP

Much better!


The Sigment test scrap is stuck on much better after drying for 24 hours. I'm happy. Now I'll go ahead and glue all three sets of doublers with different adhesives.
Mar 30, 2019, 04:58 PM
A man with a plan
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Laminating


I gathered the epoxy, scrap paper for mixing it on, balsa stick for mixing, expired debit card for spreading, Titebond II, plastic Monokote backing sheet to keep the glue off the table, and a bunch of weights. At the last minute I decided I really didn't feel like mixing epoxy, so I started with Titebond. The 1/32" ply doublers have a significant curl, and they're both cut in the same direction. So when I put the glue on, one of them flattened out and the other curled more. The plan was to spread the glue, put the doubler in place, and tack the back edge with medium CA and a shot of accelerator, then weigh it down. That operation went rather well.

Then I fell back into my old habits and did one set of fuselage sides with medium CA glue, which is a lot faster and easier. I think I'll do the third one that way, too.
Mar 31, 2019, 09:46 PM
UAS Pilot - FAA# *******HRK
CryHavoc's Avatar
Quote:
Originally Posted by Balsaworkbench
Are you using Gorilla polyurethane glue, or some other formula?

I decided to get really crazy and read the instructions on the Sigment tube. It says to put some on both surfaces, allow to dry for 2 or 3 minutes, then put the pieces together with more fresh glue, and allow to set with clamps, pins, rubber bands or weight. It didn't say how long, though. I flipped my test piece over and tried it again. This time I'll let it set for a whole day before I disturb it.

I'm thinking I'll go ahead and use Titebond II on one plane, epoxy on another, and either CA or Sigment on the third, depending on how the test piece turns out.
Not the Poly. Its the Gorilla brand yellow wood glue. Its dries faster than others I've used and is strong but still sandable. This stuff but I get it at Lowes - https://www.amazon.com/d/Wood-Glue/G...021/B001NN5T22

The Sigment sounds like Ambroid.

Mike
Apr 01, 2019, 10:08 AM
A man with a plan
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I've heard that the Ambrulose glue sold on ebay by an RC Groups member is an Ambroid copy. Sigment smells different, it dries slower, and the bonding is not the same.

I ended up doing two fuselages with medium CA and the other with Titebond II. The Titebond fuselage sides warped noticeably. I'll be able to get them straightened out, though.
Apr 10, 2019, 11:58 AM
A man with a plan
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I knew from the start that I wanted to use nylon engine mounts, so I cut the firewalls out on the laser cutter with holes for blind nuts.

I flip flop a lot on the wing mounting question. I swore off of rubber bands a long time ago, but then I used them again because it's so easy. Then I swore off of them again, etc, etc. It seems I usually have at least one rubber band plane in my fleet. Currently I have a Q-Tee, a 15 size float plane and a Buzzard Bombshell with rubber band wings. I was going to build bolt-on wings for the Corkscrew, but now I'm thinking that if I have a rubber band holding the fuel tank I might as well have more rubber bands holding the wings.

I figure it's a good idea to drill the holes for the wing dowels first before closing up the compartment under the fuel tank. I got the bottom in place, and the landing gear plate. Now it just needs some nice clean holes drilled, and then I'm ready to add the tank floor. I'm going to fuel proof the inside of that compartment first, though.


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