I would have been happy to store them for you. 
1/4 Scale Cubs - Sig and Balsa USA, Rescue and Re-Build
- Thread starter Joker 53150
- Start date
aeroncalover
It shouldn't do that....
I have a 1/4 scale Hipps Kitten (basically an ultralight version of a cub) with a split cowl as well. The main difference is that mine splits down the top of the cowl and the bottom is left open. There is a small hook that hooks onto a screw at the bottom to hold it closed. The side doesn't come off, it just swings up.
As for the windows, my kitten also has the glass screwed in, but with small screws and black trimming it looks pretty good, and allows for them to be removed if you like. The trimming is just 1/4x1/16 wood colored black with a sharpie and screwed in under the screws that hold the windows in.
As for the windows, my kitten also has the glass screwed in, but with small screws and black trimming it looks pretty good, and allows for them to be removed if you like. The trimming is just 1/4x1/16 wood colored black with a sharpie and screwed in under the screws that hold the windows in.
The new spar is a success. It was made to the size listed in the manual and some scrap balsa was used to fill in across the top edge. Balsa filler helps make it smooth, but I need to mount the wing to the fuselage and really focus on getting the transition smooth between the wing and the blocks at the top of the windshield (3rd picture). The spar got three holes drilled into it which locate the front of the wing securely. It was a little tricky getting the placement right since this is much easier to do when the plane is under construction, but it all fits well and has a lot less slop than the previous spar. Plus it's not broken, which is also good. I also had to work around the two main bolts that told the back of the wing down, but it all worked out.
With the spar done I could mount the wing on the fuselage for the first time. Damn this thing is big! I'm not convinced that the single bolt holding the wing halves together is strong enough (although it as designed by people much smarter than me, so it probably is) so the plan is to add another bolt just to be safe. The wing struts which I ordered should also help keep the wings together, but I'll feel better with a little extra strength. Note that the wings aren't matching sizes - the port wing also includes the center section and the main spar, so the joint between the wings is just starboard of the top of the cabin.
A little tweaking is still needed between the leading edge of the wing and the blocks that transition to the windshield. The port side is good while the starboard has a small gap. Some gap will be needed to account for covering, but the larger gap on the one side will probably get a layer of 1/32" balsa that can then be sanded down as needed to give me even gaps
3/32" balsa sheet was needed to patch the leading edge sheeting I removed yesterday. Of course I only had 1/32", 1/16", and 1/8" on hand... An order with National Balsa or Balsa USA was almost placed until I remembered my local ACE Hardware carries a limited supply of balsa. Score! They had 36" sheets 3" and 4" wide. 3" would have been the better choice but it is pretty hard wood. The 4" was ideal, so I got a couple sheets of each since you never know when you'll have a balsa emergency!
With the spar done I could mount the wing on the fuselage for the first time. Damn this thing is big!
I'm not convinced that the single bolt holding the wing halves together is strong enough (although it as designed by people much smarter than me, so it probably is) so the plan is to add another bolt just to be safe. The wing struts which I ordered should also help keep the wings together, but I'll feel better with a little extra strength. Note that the wings aren't matching sizes - the port wing also includes the center section and the main spar, so the joint between the wings is just starboard of the top of the cabin.
A little tweaking is still needed between the leading edge of the wing and the blocks that transition to the windshield. The port side is good while the starboard has a small gap. Some gap will be needed to account for covering, but the larger gap on the one side will probably get a layer of 1/32" balsa that can then be sanded down as needed to give me even gaps
3/32" balsa sheet was needed to patch the leading edge sheeting I removed yesterday. Of course I only had 1/32", 1/16", and 1/8" on hand... An order with National Balsa or Balsa USA was almost placed until I remembered my local ACE Hardware carries a limited supply of balsa. Score! They had 36" sheets 3" and 4" wide. 3" would have been the better choice but it is pretty hard wood. The 4" was ideal, so I got a couple sheets of each since you never know when you'll have a balsa emergency!
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Trying to think a few steps ahead, I'm about to do some tests to see how I want to cover this bird. The common covering material is too shiny and wouldn't look right on a plane this size. In fact, that's what I removed after getting it home - shiny Cub Yellow, and it looked pretty out-of-place. What is really needed is something that looks like fabric, with a grain and matt finish. There are shrink coverings that achieve this look, but they're $55 per roll, and the wing alone would take about 1.25 rolls.
Looking at other solutions I found many people use fabric attached to the structure, which is then shrunk, primed, and painted. It's a few more steps, but the cost is MUCH lower and since paint is available in thousands of colors I can get more creative. So yesterday I hit the fabric store and got 6 yards of 100% polyester "dress lining". It's off of a fabric bolt, so 9' of it is wide enough to do the top and bottom of the wing compared to the regular covering material that is only wide enough to do one side of the wing.
To see how the process will work I'm going to cover a smaller wing that I built last year with it. It's much smaller, but should at least give me a good idea before starting on the Cub.
Looking at other solutions I found many people use fabric attached to the structure, which is then shrunk, primed, and painted. It's a few more steps, but the cost is MUCH lower and since paint is available in thousands of colors I can get more creative. So yesterday I hit the fabric store and got 6 yards of 100% polyester "dress lining". It's off of a fabric bolt, so 9' of it is wide enough to do the top and bottom of the wing compared to the regular covering material that is only wide enough to do one side of the wing.
To see how the process will work I'm going to cover a smaller wing that I built last year with it. It's much smaller, but should at least give me a good idea before starting on the Cub.
Flyingninja
Senior Member
This is a really neat project. I'll be following it! Will you have a 2 cylinder engine or just one? Maybe something like this: http://www.osengines.com/engines-airplane/osmg1320/index.html
It would look more scale if it was a 2 cyl and not a 4, but the larger engine could allow for more intense aerobatics. :black_eyed:
It would look more scale if it was a 2 cyl and not a 4, but the larger engine could allow for more intense aerobatics. :black_eyed:
My trial attempt at fabric covering didn't work out so well, maybe because the covering was pre-shrunk I'm guessing. It wasn't marked as such, but with heat applied it didn't budge. I'll try again with another material soon.
In the meantime, the wing struts, plans, and cowl arrived from Sig on Friday and there was finally time to check it all out. It turns out that the cowl on the Cub with the full-size wing (the yellow Cub) isn't an original Sig cowl, but the Cub pictured on floats on Page 1 does have an original. It comes without any holes drilled for the prop shaft, cooling, or cylinder heads so those will all be cut as needed once a power plant is decided on.
The plans are impressive at four large pages, which should be standard for a good. There are detailed pictures of the struts and supports, which I need to build for this plane since they didn't come with the original purchase. Looking at the pictures it looks fairly straight forward. Cut the brass tubes to length, crimp the ends flat, drill the holes, and bend ends. It all needs to be done very closely following the directions as the four vertical braces are all unique. Looking at the drawings I was confident I had it all figured out, but once I compared against the other Cub I found out I was making the parts backwards.
With the vertical parts made I did the horizontal pieces and did bolted it all in place. Everything lined up properly so I was able to move on to the next step, making the struts.
The struts include hardwood material for the actual struts and pre-cut metal for the ends. The metal gets epoxied in place and then reinforced with a little fiberglass cloth. Before going that far it all needs to be test fit on the fuselage to make sure it's all aligned properly. Additional holes are also drilled into the metal which give the epoxy something else to grip.
Everything lined up nicely and the wing should get plenty of strength from the struts. Unlike some planes, these struts are functional so all the hardpoints they attach to need to be plenty strong. The wing's points all look good, but the two screws that hold the fuselage in place are a bit weak so they will be upgraded a bit. Once finished, the struts will be a pain to install/remove so the tentative plan is to just leave them installed. The wing has two main bolts on top, and the struts each have one bolt where they meet the fuselage. Then the screw that holds the wings together can be removed so the wing breaks into two parts. It won't be a quick process, but until I get a trailer to haul my toys around in..!
In the meantime, the wing struts, plans, and cowl arrived from Sig on Friday and there was finally time to check it all out. It turns out that the cowl on the Cub with the full-size wing (the yellow Cub) isn't an original Sig cowl, but the Cub pictured on floats on Page 1 does have an original. It comes without any holes drilled for the prop shaft, cooling, or cylinder heads so those will all be cut as needed once a power plant is decided on.
The plans are impressive at four large pages, which should be standard for a good. There are detailed pictures of the struts and supports, which I need to build for this plane since they didn't come with the original purchase. Looking at the pictures it looks fairly straight forward. Cut the brass tubes to length, crimp the ends flat, drill the holes, and bend ends. It all needs to be done very closely following the directions as the four vertical braces are all unique. Looking at the drawings I was confident I had it all figured out, but once I compared against the other Cub I found out I was making the parts backwards.
With the vertical parts made I did the horizontal pieces and did bolted it all in place. Everything lined up properly so I was able to move on to the next step, making the struts.
The struts include hardwood material for the actual struts and pre-cut metal for the ends. The metal gets epoxied in place and then reinforced with a little fiberglass cloth. Before going that far it all needs to be test fit on the fuselage to make sure it's all aligned properly. Additional holes are also drilled into the metal which give the epoxy something else to grip.
Everything lined up nicely and the wing should get plenty of strength from the struts. Unlike some planes, these struts are functional so all the hardpoints they attach to need to be plenty strong. The wing's points all look good, but the two screws that hold the fuselage in place are a bit weak so they will be upgraded a bit. Once finished, the struts will be a pain to install/remove so the tentative plan is to just leave them installed. The wing has two main bolts on top, and the struts each have one bolt where they meet the fuselage. Then the screw that holds the wings together can be removed so the wing breaks into two parts. It won't be a quick process, but until I get a trailer to haul my toys around in..!
And a little more time results in the rough fabrication complete. Next up is rounding off the hardwood before the ends are all epoxied in place. The struts really help strengthen the entire wing, more than I expected.
Struts are coming along slowly. The hard stock I got from Sig needs to have the edges rounded and shaped, along with a little final trimming to length. It's nothing difficult, and only takes some time to do it right. To make the wing as easily removable as possible the previous owner used a bolt with a wing-nut. To remove the wing completely there are two large nylon bolts in the wing and two simple wing-nuts to remove at the base of the struts, making it a pretty quick process.
The next step for the struts is giving them a thin layer of fiberglass at the ends and where the strut braces are located. I'll need to source all new hardware first, since this plane had a crazy assortment of hex-head, phillips, and standard screws. I'd like to change it all over to one style, preferably all the same size where possible.
Something else that's been bugging me since I removed the covering is the upper side stringers on the fuselage. I'm pretty sure this plane has been recovered at least once, and these two pieces were sanded pretty aggressively in the past so they are now quite a bit smaller/weaker than they should be. That may be why one of them was broken when I got the plane. It's not as easy as I hoped to remove them as the previous builder wasn't shy about using the glue! It looks like the fuselage formers have been modified a bit over the years as well, so I'll need to watch that as I replace wood over the next few days.
The next step for the struts is giving them a thin layer of fiberglass at the ends and where the strut braces are located. I'll need to source all new hardware first, since this plane had a crazy assortment of hex-head, phillips, and standard screws. I'd like to change it all over to one style, preferably all the same size where possible.
Something else that's been bugging me since I removed the covering is the upper side stringers on the fuselage. I'm pretty sure this plane has been recovered at least once, and these two pieces were sanded pretty aggressively in the past so they are now quite a bit smaller/weaker than they should be. That may be why one of them was broken when I got the plane. It's not as easy as I hoped to remove them as the previous builder wasn't shy about using the glue! It looks like the fuselage formers have been modified a bit over the years as well, so I'll need to watch that as I replace wood over the next few days.
In the previous post I mentioned some concern on the fuselage formers at the rear of the plane. It looked really half-assed how the stringers were attached with big globs of brittle old glue (you can see how it was applied so heavily it was running down the formers!) so I decided to replace them. It's extra work, but this is the time to do it... It's hard to tell for sure, but it does appear some repair work was done towards the tail. There are marks where balsa was removed and replaced, and some of the formers are weirdly mis-sized now. So all 5 upper formers are removed!
Removing the formers leaves only the center stringer, which is in good shape. There is some clean-up needed of all the old glue which will leave me with a good, flat surface to install new formers.
Here's a perfect example of what I'm trying to fix. F10 has a big chunk missing from the right side when compared to the outline on the plans. I'm also not a big fan of how the stringers have very little contact area with the former, so I'll change that slightly. I'm not sure why, but only F10 and F12 formers are shown on the plans, so I had to use the removed pieces for the other 3 formers as templates and make changes from there.
This is my version of F10. All I really did is add some extra material to support the stringers. The lightly drawn lines on the new pattern are outlines of the original former. In theory, the new style should give more support with only a minuscule weight penalty. Heck, by removing a lot of old glue I may still come out ahead!
Original F12 and my re-design behind it. Again, you can see all the old glue that dripped down the former. Even with the extra material I'm adding, the entire former will be recessed far enough so it doesn't show up through the covering material. Only the formers will be in contact with it.
I wasn't sure what I was going to do for servos. The plane came with them, but they didn't work when I hooked them up to my servo tester. They're a good name, and I wouldn't expect ALL of them to be fried, so maybe it was just an error on my end...
It turns out that old servos like this were wired differently than they are today. The power wire was at one end with the ground in the center. Now the power is in the center, so by simply swapping two pins they all work! Unfortunately for me, I already took delivery on new replacement servos. While the temptation is to simply use the new ones, I'd like to re-use the original equipment when possible and save the new ones for another project.
Removing the formers leaves only the center stringer, which is in good shape. There is some clean-up needed of all the old glue which will leave me with a good, flat surface to install new formers.
Here's a perfect example of what I'm trying to fix. F10 has a big chunk missing from the right side when compared to the outline on the plans. I'm also not a big fan of how the stringers have very little contact area with the former, so I'll change that slightly. I'm not sure why, but only F10 and F12 formers are shown on the plans, so I had to use the removed pieces for the other 3 formers as templates and make changes from there.
This is my version of F10. All I really did is add some extra material to support the stringers. The lightly drawn lines on the new pattern are outlines of the original former. In theory, the new style should give more support with only a minuscule weight penalty. Heck, by removing a lot of old glue I may still come out ahead!
Original F12 and my re-design behind it. Again, you can see all the old glue that dripped down the former. Even with the extra material I'm adding, the entire former will be recessed far enough so it doesn't show up through the covering material. Only the formers will be in contact with it.
I wasn't sure what I was going to do for servos. The plane came with them, but they didn't work when I hooked them up to my servo tester. They're a good name, and I wouldn't expect ALL of them to be fried, so maybe it was just an error on my end...
It turns out that old servos like this were wired differently than they are today. The power wire was at one end with the ground in the center. Now the power is in the center, so by simply swapping two pins they all work! Unfortunately for me, I already took delivery on new replacement servos. While the temptation is to simply use the new ones, I'd like to re-use the original equipment when possible and save the new ones for another project.
aeroncalover
It shouldn't do that....
The wires being swapped on the servos would explain why older servos sometimes don't work for me. Strange that nobody else has figures that out yet.
Question about the struts- On my 1/6 scale Cub I epoxied the metal strips to the struts at the fuselage end. At the wing attachment point I drilled straight through the wood strut with no metal. Do you think this will be strong enough, or should I go back and use the metal strips on the wing end? I've had fears of the air loads splitting the struts but I feel like that would be unlikely if you compare the weight of the model to the strength of the strut material.
Also, my jury struts are preformed from bent music wire (since this is a smaller kit) and I have them epoxied to the struts so that they will just plug into the wing. As far as I know, only the lift struts are functional on this model, but do you think I should go back and make the jury struts functional too?
Question about the struts- On my 1/6 scale Cub I epoxied the metal strips to the struts at the fuselage end. At the wing attachment point I drilled straight through the wood strut with no metal. Do you think this will be strong enough, or should I go back and use the metal strips on the wing end? I've had fears of the air loads splitting the struts but I feel like that would be unlikely if you compare the weight of the model to the strength of the strut material.
Also, my jury struts are preformed from bent music wire (since this is a smaller kit) and I have them epoxied to the struts so that they will just plug into the wing. As far as I know, only the lift struts are functional on this model, but do you think I should go back and make the jury struts functional too?
So the jury struts just stick up into the wing for appearances? If that's what Sig planned, I'd probably just go with it like that unless you plan on over-powering the plane.
What does the plan show for the strut attachment at the wing? I assume it's a hardwood strut like the 1/4 scale (but smaller). I'd be a little worried about it splitting at the wing attachment point as well unless there was something in there to strengthen it somehow. Unless it's purely for looks and not designed to transfer forces down to the fuselage? The 1/4 scale version is certainly functional for both the struts and jury struts. Even sitting on my workbench it makes a huge difference adding the strut assemblies.
What does the plan show for the strut attachment at the wing? I assume it's a hardwood strut like the 1/4 scale (but smaller). I'd be a little worried about it splitting at the wing attachment point as well unless there was something in there to strengthen it somehow. Unless it's purely for looks and not designed to transfer forces down to the fuselage? The 1/4 scale version is certainly functional for both the struts and jury struts. Even sitting on my workbench it makes a huge difference adding the strut assemblies.
The wife wasn't amused at all the balsa shavings I've been tracking around the house, so time to clean the shop. In the process of moving planes around both Cubs ended up on the bench at the same time, which wasn't easy to do. I think more room for planes is going to be needed!
The rebuilt fuselage turned out well. Once glue is fully cured I'll give the edges a very light sanding and that part will be done. Even though it won't be visible once the covering is on, knowing it's done makes me feel better about the project since the warts are being removed, not just hidden from sight.
The rebuilt fuselage turned out well. Once glue is fully cured I'll give the edges a very light sanding and that part will be done. Even though it won't be visible once the covering is on, knowing it's done makes me feel better about the project since the warts are being removed, not just hidden from sight.
Work on the wings should go pretty quickly. First up is replacing the leading edge top sheet. The original sheet had a long crack going across most of the wing, so I removed it to make sure the structure inside wasn't damaged. There was also a hole punched through the sheet, which also hit one of the ribs. That rib was damaged in front of the front spar so I cut a replacement piece and glued it in before attaching the new sheeting.
Here's a trick I like for installing a piece like this sheet. It's too long and awkward of a piece for clamps, and I'll avoid pin holes if possible. Electrical tape comes in a couple different widths and has a stretchy property which works well at keeping pressure applied better than other tapes. I grabbed a small roll and went down the length of the wing twice to make sure the sheet was stuck down as well as possible across the spar, ribs, and leading edge. Once dry it'll require a little sanding, but no filling of holes will be needed.
The other wing had a damaged rib which wasn't visible through the original covering. The rib cap is pretty firm and hid the damage, while the covering kept the broken pieces with the wing. There were three small pieces that made up the missing area shown. I could have cut a new rib, but that would have been substantially more work and this area can be fixed with the original wood.
Once the original pieces were glued back in place a small paintbrush was used to remove excess glue. No sanding or other touch-up is needed on this repair, it's good to go!
Here's a trick I like for installing a piece like this sheet. It's too long and awkward of a piece for clamps, and I'll avoid pin holes if possible. Electrical tape comes in a couple different widths and has a stretchy property which works well at keeping pressure applied better than other tapes. I grabbed a small roll and went down the length of the wing twice to make sure the sheet was stuck down as well as possible across the spar, ribs, and leading edge. Once dry it'll require a little sanding, but no filling of holes will be needed.
The other wing had a damaged rib which wasn't visible through the original covering. The rib cap is pretty firm and hid the damage, while the covering kept the broken pieces with the wing. There were three small pieces that made up the missing area shown. I could have cut a new rib, but that would have been substantially more work and this area can be fixed with the original wood.
Once the original pieces were glued back in place a small paintbrush was used to remove excess glue. No sanding or other touch-up is needed on this repair, it's good to go!
ScottyWarpNine
Mostly Harmless
Could you please show a close up picture of the cowl on the tan cub? I'm wondering if I attached the dummy engine cylinders correctly. I cut my cylinders out along what I thought was a cut line that as a little bit away from the cylinder itself. t fits the curves of the cowl but I think it looks a little strange that what really should be a hole in the cowl is actually a raised plastic lip. If that makes any sense.
Here you go. From what I can tell, this is an original Sig cowl, but I don't know if the dummy motor is from Sig or not. To me it looks too large. I ordered a replacement from Sig, but it's just the cowl without the dummy cylinders to compare against.
BobK
Banned
This is very cool..nice score and nice work on the rebuild! I can't wait to see how it goes Always wanted a sig 1/4 scale Cub, I had the old 1/6 scale many years ago which flew fantastic I can't imagine how these fly. I might possibly have some Cub wheelcaps that would be perfect size for your plane and if I can find them they are yours if you want them..let me do some digging. I love when people take the time to fix/rebuild old planes and make them fly again.
Not trying to steal your thread at all but just be glad it wasn't covered in silk, I scored this baby..a Goldberg Skylane 2 for free..it was in the back of a co-workers truck on its way to the dump so I couldn't say no. Problem is I have no idea how to get the silk off, the wing is easy but any sheeted areas is horrible..if anyone has any helpful ideas I would appreciate it. It is so old the windows are yellow and it had slide-type servos installed lol.
-Bob
Always wanted a sig 1/4 scale Cub, I had the old 1/6 scale many years ago which flew fantastic I can't imagine how these fly. I might possibly have some Cub wheelcaps that would be perfect size for your plane and if I can find them they are yours if you want them..let me do some digging. I love when people take the time to fix/rebuild old planes and make them fly again.Not trying to steal your thread at all but just be glad it wasn't covered in silk, I scored this baby..a Goldberg Skylane 2 for free..it was in the back of a co-workers truck on its way to the dump so I couldn't say no. Problem is I have no idea how to get the silk off, the wing is easy but any sheeted areas is horrible..if anyone has any helpful ideas I would appreciate it. It is so old the windows are yellow and it had slide-type servos installed lol.
-Bob
Wow, hopefully that wing isn't as rough as it looks! The fuselage looks good, is there any major damage there? I can't help you on the silk, but if the fuselage is OK maybe it can be painted over to match a re-constructed wing?
For some reason, seeing your salvaged plane makes me think about a 63" span J-3 Cub I have, which took a nose dive after a brown-out. The entire nose is crushed, but fixable. Minor wing damage as well. Maybe after the big Cubs I'll look at the "little" one!
For some reason, seeing your salvaged plane makes me think about a 63" span J-3 Cub I have, which took a nose dive after a brown-out. The entire nose is crushed, but fixable. Minor wing damage as well. Maybe after the big Cubs I'll look at the "little" one!
BobK
Banned
The actual structure of the Skylane is fine, built a bit heavy but isn't broken up..I plan to lighten it up quite a bit. it's the torn covering that makes it look a lot worse. I am to the point of taking my palm sander and just going at the sheeted areas and see what I have left when I am done lol. The silk covering has basically become one with the wood. The wing and stab are open structures and can be salvaged, the fin is sheet and I will just rebuild it, but the fuse is another story. If I have to rebuild the fuse I wll but I plan to cut lightening holes where I can without weakening the structure then sand the covering off the rest..maybe lol.
-Bob
-Bob
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