2018/19 Balsa Build Along Sig J3 Cub


Aviation Enthusiast
Definitely do it, flying from floats is a great experience, I love it. Check out my brand new Super Dragon I just finished, here's the video, but it is a flying hull/boat, not floats...
I saw that one!

Question about the hull, is it Balsa or another wood? If you were building floats would you build them out of balsa? Do they get sealed with glass?


Aviation Enthusiast
Its balsa and just simply covered with Ultracote which seals it completely, if you make sure to overlap everything. When I build my 1/4 cub floats I will glass them as I feel glass would better seal everything on a bigger build.
Its balsa and just simply covered with Ultracote which seals it completely, if you make sure to overlap everything. When I build my 1/4 cub floats I will glass them as I feel glass would better seal everything on a bigger build.

That's what I was thinking too, even if you just sealed it with epoxy without any fiberglass. I suppose you could use a thinner 1/16th Balsa sheeting, and a layer of thin fiberglass. would give you rigidity and strength. maybe a gel coat.

You could probably do the whole floats with Samples from Total Boat or a West Systems
Got to start on the tailfeathers today, made a couple of changes the build manual specified 3/32 balsa for the ribs and after putting the horizontal stabilizer together it seemed really weak, even with notching the leading and trailing edges (which the plans don’t specify either. so I reinforced the elevators with 1/8th x 1/4 for the ribs and that made a huge difference. I used the same construction on the rudder and vertical stabilizer, makes for a very stiff surface pretty pleased with the results so far.


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Been a few days, got a little bit of time in, but my day job has been keeping me busy. I finished gluing up the tail section, had to strip some more balsa because the kit was a couple sticks short.

Started assembling the fuselage and broke out the plans for the float kit, I laughed a bit when I realized the floats are a left fuselage plan and the aircraft is a right fuselage plan! Haha can’t be easy eh!

I also finally received a replacement plans set, and noticed extra support in the fuse that’s not on the older plans! There’s several differences in the plans actually, so I’m adopting a hybrid of this and that. Since I’m including the supports for floats I don’t want to leave out something that could help to reinforce the structure


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Still going strong I got a lot of progress on the fuselage over the last couple days both the right and left sides are framed out.

As a tip, for anyone who hasn’t figured this out, but the rubber bands have been pretty awesome to hold parts down when using t pins, if you insert at an angle it pulls the bands down tight to the building board and puts tension on the pieces holding them together. I did an okay job cutting all the angles I used a file in places where I needed to clean the angles up. There were a few sticks that I ended up shimming because they were a little loose in the glue joint. I’m going to clean those up and likely replace them altogether. We’ll see how it goes in the next few days.

I was able to completely glue up the fuselage sides, and I couldn’t help but mock it up! It’s beginning to look like an airplane!

I didn’t get a picture of it today, but if you lay the completed fuselage over the new plans you’ll see that the model has definitely been revisited, there several extra fuselage supports that are not in the older drawings I’ll make a point to get a picture of that.

Also the kit seems to be short a bundle of spruce sticks. The spruce was called for to frame out the cabin, unfortunately I wasn’t able to find spruce but I was able to find pine at the hardware store today, would it be a bad idea to substitute pine for spruce in the cabin frame?


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So alot of work has been made this week,

I've begun assembling the frame sides, and its starting to turn into a real fuselage!

As always I've made a few mistakes here and there, but nothing that isn't easily overcome. I accidentally installed the aft cabin bulkhead 1/8" too far aft. So I installed a shim to the front section of the bulkhead which actually helped to stiffen the ply bulkhead.

I also began installing the cabin frames, one thing I noted from other build threads is that it was a flimsy structure and people suggest doubling the frame. One thing I noticed in the drawings is that you are supposed to double the top of the frame which I think other build threads might have overlooked. so I installed the 1/8" in doubler across the top to help with the flimsiness of the frame and then cut the vertical supports into the bottom of the window frame (top of the fuselage) to give a better joint to glue into. This combined with the ply sheeting should help tie everything together and make for strong construction.


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Hello build along,

It’s been a while but I haven’t given up!! I Had some family in so I had to put up my airplane to make room for guests. I got a few things completed before that happened, I finally built the Nose section, and epoxied it to the front of the cabin. I had been waiting to get the spar material in, because I wanted to use it to build the landing gear blocks and float mounts which I’m still going to do, but I realized I didn’t need to wait to complete the nose section.

I also completed the capping of the wing rib sections, which I had put off due to lack of interest as I was getting closer to completing the wing sections. This is in preparation of building the center section in order to attach the wings. I’m a little confused on the build up of the center section trailing edge, the instructions say build it up as you would the wings, but the plans show a larger triangle block, as well as the center section of the wing appears to be about 3/8” shorter than the rest of the wing.

Any Ideas??

I sanded the frame down where the nose attached to get the lower nose plow block cut to fit, it steel needs to be shaped to form the lower nose shape but I think I’ll wait until I sheet the cabin to shape it so I can match the body lines without filler.

Today I worked on the hinges for the rudder, I have three types I have the Robert pin style, a dubro ca style hinge with a pin, and a ca style hinge without a pin. I put the ca hinge in first and didn’t like the way the rudder was lining up, so I installed the Robert style hinges they seem to be easier to line up and the movement of the rudder appears to be more scale like.

Another thing I worked on was the horizontal stabilizer installation, the plans call for a 3/8 dowel and the feathers glued in prior to covering, this is one of the main things people seem to be dis satisfied with, to fix this I bought a 5 MIL CF rod with a 4 MIL ID, and bought a second CF rod with a 4 mil ID. Instead of gluing the dowel in, I will install the 4 MIL CF rod to the fuselage and glue the 5 MIL rod to the tail feathers this way I can install both Horizontal stabilisers independently after the fuselage has been covered. This approach will give me the option to make the tail feathers removeable if I choose.

It seems like I’m spending hours working and achieving little in the way of visual results. So mocking up a tail feathers and seeing the rudder installed is quite rewarding!!


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Also in other news, my babe-bot glue bottle had a catastrophic failure!! I’ve been using it for a couple months and I really enjoy it, I’ve used the full size glue bot in my shop for a while and have had zero issues so I’m confident this was a one off thing, I’ve purchased a replacement and will scrutinize the quality of it for future use. (See attached pics)

I’ve also settled on a motor,

I’ve purchased an OS 3825-750kv motor. According to the charts I should be able to swing a 12x6 SF prop @ 8k RPM on a 4s battery at 40 amps. So with that in mind I’ve purchased a 60 Amp ESC

Choosing a motor/esc and battery combo is completely foreign to me, so this might be a flop, however I feel that it will be easier to retro fit an IC engine to a fuselage that hasn’t been already hacked up. So with that in mind if the electric motor doesn’t give the performance I want, then I’ll go back and Retrofit an IC engine. This way The fuselage won’t be hacked apart for an engine.


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Joker 53150

Mmmmmmm, balsa.
Hopefully the broken bottle didn't get too much glue on the plane/plans. I'm guessing it's due to a weak seam and all the squeezing the bottle gets.
Hopefully the broken bottle didn't get too much glue on the plane/plans. I'm guessing it's due to a weak seam and all the squeezing the bottle gets.

Got a little bit on the plans, yeah it was a bad seam, I really like the bottle and it’s only 6.00 so I’m more than willing to give it another shot.


Skill Collector
I like the CF tube on the stabilizer approach - making that removable could really help when it comes to storage and transport options!
Yeah the tube will work out great, plus after a it’s assembled I think it will be stronger than just the wooden dowel alone.


Aviation Enthusiast
The power system looks good, 12" prop on 4s is good. Ecalc is a good method to check everything out and then a watt meter when you put it together to double check. 60 amp ESC for a 40 amp draw is good.
Well there’s no going back,

Wings are assembled into one piece. Still a lot of finishing work to go, and the fuselage obviously has more to be done but having the wings together is a huge milestone!


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