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1/4 Scale Cubs - Sig and Balsa USA, Rescue and Re-Build

Joker 53150

Mmmmmmm, balsa.
Mentor
#1
A month or so ago my dad and I went to a swap meet, and I ended up with a new (to me) toy, a Sig 1/4 scale J-3 Clipped-Wing Cub, complete with floats as well as the standard gear. No motor was included, but for $100 I couldn't pass it up. The plan is to hold this one as a build for the near future, as it doesn't need any real structural work, the covering is decent, etc. The picture is photographic evidence of the rare time I was able to coax my son away from his xBox for a few minutes. Kind of like getting a picture of Big Foot at a Chinese restaurant.

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So a little time goes by and I go to visit my dad for Thanksgiving. He also invited one of the members of the flying club we belong to. Obviously, a lot of discussion was on planes, and the guy mentions he knows somebody selling a 1/4 scale cub for $50, but there are no electronics and the covering needs a lot of attention. The seller inherited it somehow and doesn't want it. I figure it is worth the chance, so my dad and I call the seller, hop in the car, and drive an hour to his place. As soon as we saw it, we knew it was going home with me. The covering did need some work, but it had all the servos and included old 72mHz radios. I didn't know what brand kit it was, but it didn't matter.

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Looking at it as we were loading it up, it looked a lot like the Sig I got a few weeks back, but the wing was a 2-piece instead of 1-piece, and it has suspension in the landing gear. There are a few companies out there who make 1/4 scale Cubs.

When I got home and compared against the Clipped Wing Cub, I found this is also a Sig 1/4 scale Cub, but the full-size wing version, which is 104". Score! :)

But now what am I going to do with two huge planes? The plan right now is to completely re-cover this plane in an older military scheme and update electronics as needed. I talked to my dad a bit about how it could be done. He's always liked the CAP version of the cub (yellow body, silver or blue wing) so I'm going that route for the new design. Motor choice is up in the air for now - electric, gas, or nitro.

A brief conversation with EarthSciTeach online gave me the jolt to start tearing into it. The covering didn't look bad (if you don't look at all the little holes poked in it), but a couple things bothered me and I wanted to see what kind of quality was hidden under the sea of yellow.

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The first thing which confused me was the servo mount for the aileron. It's done in a fairly clean manner, but not the same as the first Cub. I like this style more because it's cleaner than having the servo arm poke through the mounting plate, but there is a problem... As you'll see in a later picture, the servo mounting screws are all extremely hard to reach once the covering is installed! I'll change this to the "correct" way to do it as I get further into the project.

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The ailerons were also attached with CA hinges. While these do work, they don't move as freely as I'd like, so I'll update them with standard hinges.

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On this wing, this was the biggest damage. Nothing too major, it'll be a fast fix once covering is removed. There are also a lot of dimples in the balsa which I'll fill before re-covering it.

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I'm not sure what happened here, but it looks like the builder tried applying the leading edge sheet without wetting it down first, which made the balsa crack. There are a number of little issues like this I've found on the first wing, so it should be interesting to see what I find as ALL the covering comes off!

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Here's another not-so-good idea, using multiple servo extensions without anything to help make sure they don't come undone! The vertical webbing between the spars could have been done better, but this isn't a high-speed plane so it'll do.

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Here's how the servo was mounted. An extra plywood plate was added inside the wing and it was mounted to the plate. I don't know why, but it'll get changed and the extra weight will be removed.

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...and this is what the wing looks like with 98% of the covering removed! I won't be too worried about small bits that don't come off, as the new covering is darker and will hide it well. The builder did an OK job it it. Not great, and not horrible.

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#2
Nice scores! I'm a new guy to balsa building and RC but I have figured out that I enjoy building and as much, repairing and saving old planes that I find. Your Cubs look like really good projects for some cold winter nights. Enjoy
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#3
Thanks Nate. Building is certainly fun, and there are some very worthy planes out there to be rescued!

Here's the scheme I'm leaning towards for this re-build. The wings appear silver, although my dad thinks they were really blue. I haven't found a lot of documentation either way to know for sure. Blue looks better, but if silver is correct...

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#5
Awesome photos! As someone who is currently building a SIG 1/4 scale cub, the pictures inside the wing really help. The instructions are pretty good, but it is nice to see what the finished product is supposed to look like.
 

aeroncalover

It shouldn't do that....
#6
Looks good! I am working on a Sig 1/6 scale cub as well. From what I can tell, the construction is pretty similar.

From what I know about cubs, the wings can be silver or blue. I have seen both. I would tend to think they would be silver if the cub was a later year model, and blue if it were built earlier. Either way, I think it will look right.

Have you though about extending the wings on the clipped wing version? I can't for the life of me figure out why somebody would cut up a perfectly good full size cub wing. It gets you a higher stall speed, higher wing loading, faster approach speed, longer takeoff and landing runs, less ability to carry weight (read: Can't fly floats!) and all you get in return is a faster roll rate.

Best of luck with the two projects!
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#9
Awesome photos! As someone who is currently building a SIG 1/4 scale cub, the pictures inside the wing really help. The instructions are pretty good, but it is nice to see what the finished product is supposed to look like.
Thanks. Let me know if you need any specific shots of the construction. There should be plenty of time since I need to finish tearing it all apart and fixing various things before covering.
 

aeroncalover

It shouldn't do that....
#10
blue wing cub.jpg

Figured out how to upload pictures!

Found a blue winged cub, Its a Nitro planes foamie, so who knows if its accurate or not. But there you go! They exist!
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#11
Looks good! I am working on a Sig 1/6 scale cub as well. From what I can tell, the construction is pretty similar.

From what I know about cubs, the wings can be silver or blue. I have seen both. I would tend to think they would be silver if the cub was a later year model, and blue if it were built earlier. Either way, I think it will look right.

Have you though about extending the wings on the clipped wing version? I can't for the life of me figure out why somebody would cut up a perfectly good full size cub wing. It gets you a higher stall speed, higher wing loading, faster approach speed, longer takeoff and landing runs, less ability to carry weight (read: Can't fly floats!) and all you get in return is a faster roll rate.

Best of luck with the two projects!
I've heard the 1/4 and 1/6 scale aren't too different overall, but that's just what somebody said on teh Interwebs, so it MUST be true!

I won't change the structure on the clipped wing. Having the more aerobatic version should be fun, especially if I "accidently" over-power it! :) As for floats, it came with the Sig floats and I was told the previous owner flew it extensively like that.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#12
I think silver is correct. I've done extensive research (googled Piper Cub in military colors) and find no examples of blue wings.
The only one I could find for sure with blue wings is a Hobby King foamie! I personally think it looks better in blue than silver. Granted, this build won't be stand-off scale, but I can't help feel that if I'm going for a certain "look" I should do it as close as reasonably possible. My dad has some friends who were in the CAP, and is making some calls to see what they remember.

This is the foamie from HK mentioned above. My dad actually purchased this ARF a few years ago and the wings are blue, not silver. Maybe "creative license" on the part of our Chinese overlords, or maybe there WAS a blue-wing version...?

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Joker 53150

Mmmmmmm, balsa.
Mentor
#13
With the wings mostly stripped (little scraps here and there need to be addressed), attention was turned towards the fuselage. My work table is an old dining room table with two extension sections in it, and this plane takes up most of it!

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From what I could see, this was the worst part of the damage. But who knows what's hiding under the covering?

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I do like how the builder handled the cowl, compared to the other 1/4 scale Cub. It was altered (or maybe it's a replacement?) to allow the top and bottom to come off independently of each other. So without removing the prop, half the cowl could be removed for work.

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This is another area that wasn't done too well. The plastic windows were simply held in place with hex head screws, all the way around. I could see adding them as details once the windows are properly installed, but this just seems lazy.

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A couple hours later and most of the covering is removed. No big surprises to be found, and only a few spots which need some TLC. Overall, a decent fuselage.

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Here is where things get interesting again. I knew the tail wheel assembly was different/better than on the other Cub, and that this plane came with suspension landing gear which are not part of the original kit. After doing a little research I was surprised how flipping expensive this gear can get! The gear that came with mine MIGHT be Robart, which run about $150 or so. They're the closest in design I could find, with only a few minor differences. There are spring or bungee styles, and it seems that bungee (like this set) are preferred.

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Once the elevator is removed it's time to do some repairs, which shouldn't take long. Getting the old covering removed as much as possible will be a pain, but it doesn't need to be perfect - the new covering will hide the remains.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#16
The plane was missing the wing struts when I bought it. Technically, I could make them, but I'm lazy and also want it to look right so I spent as much as I did on the entire plane buying the struts and a set of original plans from Sig! :) Also dropped an extra $20 for a cowl since at least one of the Cubs will get a new one.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#17
Hmmmm... :) I'll have to make sure to add the structural supports in the fuselage for these floats before covering it. The floats came with the other Cub which as modified to work with them.

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There was a hole in the bottom of one wing, near the leading edge. As I inspected the damage inside I saw the rib was also damaged, so I cut off enough material to give me access to fix it. There didn't seem to be any extra flex in the sheeting with it broken, but since it's inboard on the wing it needs to take more stress, so it is being repaired properly.

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As mentioned previously, I don't like how the aileron servos were installed. I'm removing some of the material and adding some back that was removed. The actual tray the servo sat on is heavily epoxied in place and would take a lot of effort to remove, so I'll just leave it there - it shouldn't cause any interference.

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In one of the earlier pictures there was a crack visible along most of the leading edge sheeting. I thought about trying to just squeeze some glue in, but I didn't know if there were any hidden problems so off comes the broken sheeting! There wasn't anything hidden, but taking the sheet off helped me find a couple bad glue joints which can now easily be fixed. I also noticed a couple of the rib bays don't have the webbing between upper and lower spars, so I'll add that as well.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#18
The 1/4 scale Clipped Wing Cub uses a one-piece wing design, while the standard wing is 2-piece for "easy" transportation. To hold the two wing halves together the design calls for a front spar 17" long and a rear locating plug. A single screw goes between the wings to keep them together, and the wing struts also keep everything in place.

At least twice in the past the big front spar was broken. There is evidence of patch work on the sheeting and you can easily see where the front spar was too short to extend into the wing. That spar is also broken where the two wings join.

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I want to make the wing strong, and this is a crucial spot. It was an easy decision to simply cut out all of the old spar and install a full-size one again. Lucky for me, I've got a jigsaw to make short work of cutting out the old stuff. There was quite a bit of epoxy in there so I removed slightly more than the width of the spar, but that won't matter once I get it all reassembled.

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The spar should be 1/4" thick and about 17" long. My on-hand plywood was limited to 12" pieces so I'm laminating a couple pieces together with epoxy, and making it slightly taller for some extra strength. Once dry I can do the final trimming, cut out the holes for the locating pins, and start re-building the front of the wing.

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