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

[roversgonemad]

Don’t know how much the CA chemistry has changed. I suspect the foam safe and thick adhesives may not be subject to the issues. As a caution, I’ve always used plastic cement for my vac formed parts. I crack them enough with bad landings, I don’t need glue helping me crack it

 

[Joker 53150]

Only 3 nights away from home this coming week so I get a little extra time to play in the shop! I grabbed the left wing so I could start the repairs. I knew it needed the inner-most rib replaced but had done no other real digging to see if there were any other bits needing attention. Right away I found the aileron servo was either broken or damaged, so I pulled the 10(!) screws from the cover to see what happened. It turns out only the servo arm is broken, and I probably have spare parts to fix it - hopefully. The fabric around the cover plate needs some tweaking as well, not from the crash, but because I don't like how it was built. In the pic you can see the front and rear of the servo hole have some loose fabric. That'll get fixed when I get the real work done as it's only cosmetic.

Moving to the primary damage found on both wings, this original rib can be re-used after a little tweaking. A little bit of sheet was also cracked so I've got the yellow clamp holding it while the glue dries. You can see how the original fabric (SolarTex) covering only goes up to the edge of the wing where it meets the fuselage, and doesn't wrap around and inside. I'll do some tweaking here as well which should help hold the covering in place on those hot sunny days.

Last, I'm going to replace the wing struts. The original pieces work just fine, but they're very plain and not scale. I've got the metal tube with an airfoil shape to replace the wood pieces, and will also update the jury struts. Hopefully I can make the struts into a folding design, which will make the plane and wings easier to transport. Updating to these new struts will also give me a chance to make big changes to how the struts attach at the fuselage. Currently they bolt on underneath. While that gives a clean look and hides the hardware, it does complicate assembling the plane at the field. The tentative plan is to have visible hardware that is also more scale looking.

 

[heli-pilot]

I’m doing a similar attachment for my 1/6 cub with the metal airfoil shape So I’m interested to see how you tackle this!

 

[Joker 53150]

My new wing strut hardware has arrived, so on with more wing work (while not working on a couple other planes...). This stuff is fairly expensive for what you get, but it should be money well spent in making this plane look that much better.

It's also time to take care of a problem with the original covering. It was trimmed right up to the edge of the wing which meant it could come loose in the hot sun. Wrapping around the edge gives that much more material to secure the covering, plus it hides the balsa completely where the wing meets the fuselage. Any small imperfections (and there are plenty) would leave small gaps where you could see the structure.

The top of the wings have pinking tape to simulate what was used for rib stitching on the original, a very nice detail. I used some of my left-over Cub Yellow for the purpose, wrapping a small amount around the edge of the wing. It's not perfect, but will certainly help hide the balsa.

A quick spray of paint and it quickly blends in with the original pinking tape. The paint isn't a perfect match to the original SolarTex, but it's close and helps give the plane a "weathered" and field-patched appearance.

The fuselage wing location also needs the extra covering added, that'll be done after I do some more wing work.

.......Aaaaaaaaand, back to the wing! Another detail which I wanted to fix is the mounting location for the wing struts. They were installed farther out on the wing than they should be, meaning the struts are quite long. I'm going to move the mounting points in 2" which should give it a better look (to me, at least. Nobody else will notice the difference!). A pair of captured nuts are installed inside the wing. To add new nuts requires access inside the wing, so out comes the Xacto knife <GULP>! Unfortunately I need to add some new structure for the captured nuts, so the pieces are being glued in. Once done the covering can be heated up to glue it back down. I'll get a little creative later on to hide the surgery. Eventually I'd like to re-cover the entire plane so I'm not 100% worried about a few visible scars at this time.

 

[Joker 53150]

One thing I forgot to mention - the broken servo control arm was easily fixed with new pieces I had on-hand. I've never purchased a HiTec servo, but had a lot of spare parts from an estate sale I went to last year. All kinds of different servo parts, cables, etc are in my stash now, which is very handy for just such an occasion.

Patching the first wing up is pretty much done now, so attention tomorrow will be on building the new struts. As mentioned previously, the covering around the servo hatch was pretty janky. To fix it (until the entire plane is re-covered) I simply took a rectangular piece of Cub Yellow Solar Tex and pinked the edges so it was big enough to completely cover the hole and also stick to all surrounding covering. Once installed the excess inside material was removed and the servo re-installed. Below you can see it with the first paint applied. I'm also going to touch-up the two small patches over the old strut mounting holes. A little clear flat paint will eventually be applied to dull the finish on the stripes.

Extra covering was also added on the fuselage where the wings mount. Like the wings, the covering here only went right to the edge with no extra to overlap the corner. I use a special trim tool to cut the covering close and even like this. It's perfect when overlapping covering on a squared surface or fuselage.

 

[Joker 53150]

Other than being a bit too glossy (for now) the repairs are done and strut work can start.

To mount the struts at the wing I'm following a trick I found online, and using butterfly bolts. Well, *part* of them... I drilled out the center bolt which holds the two pieces together, and....

...after a little work the butterfly bolt is now used to mimic the full scale Cub's design. More work is needed to line the parts up better, but it looks like it'll work as expected! Plus, using components like this will also allow me to fold the struts for storage if needed.

 

[Joker 53150]

Back at it again after 5 days on the road. Again. Probably doing that again this coming week as well, yay... My goal by the end of this short weekend is to make some big progress on the wing and jury struts for the first wing. Here's where I'm at after a few early morning hours while everybody else sleeps in.

The original struts get fabricated into a single piece which works, but lacks detail. Here you can see how the individual struts will now connect at the fuselage with plenty of visible hardware. The piece they attach to at the fuselage is salvaged from the original struts and will be trimmed down for a better look soon. Some JB Weld will be used to fill the ends of the airfoil strut ends.

Where the struts attach to the wing again will be plenty of visible hardware. Some paint will really dress it up. Soon... Also visible is the cord used to hang the wing from the ceiling while I build the struts.

Here is where it gets tricky - connecting the jury struts to the wing struts. I found the ideas for this entire design on the Cub Den, and really like how it adds plenty of visible hardware and interest to the overall look. Thin brass is cut to 1/4" strips and bent around the strut, then drilled to accept the torque-tube connector. This creates a hinge that will allow the struts to fold down against the wing. Now that I've tested and verified my hardware will fit I need to cut a buck to form a couple final pieces around. Or I may just take a short section of tube and fill it with JB Weld so it doesn't deform easily while I form the straps!

 

[FDS]

That is rapidly turning into a real work of art.

 

[Joker 53150]

Here's a tool I'm glad I purchased about 20 years ago - a spring-loaded center-punch. If you try and drill a hole in metal without first punching it, the drill bit can wander all over. Use the punch first and it puts a dimple in the metal which "holds" the bit in place as it starts cutting. It works great on the soft-ish brass, and it also works great for shattering tempered glass.

A couple early morning hours and the jury struts are mostly fabricated. I need to re-arrange the pieces and direction the screws are facing on some parts, but that's just detail work. At this time I'm not sure if I'll glue or screw the straps to the struts. I could just leave them to be held in by the clamping force, but the vibration from the engine will probably cause them to move slightly which would scratch the paint. I'm tentatively planning a single tiny screw thru each piece with a touch of epoxy. Maybe...

 

[FDS]

I would put a locator screw in there to hold the brass mounts in place. They look great. I love scale detail, on something the size of that Cub “real” aviation solutions made smaller will always look best.
Brass is hard to glue, as I am sure you know. Centre punches are an essential tool. The spring loaded ones are really handy for one handed marking of screw positions too.

 

[Joker 53150]

Holy cow, this is a fiddly project! I've taken the new struts off a dozen times today working to get it all lined up properly. Now some JB Weld and balsa are curing to make sure the rods inside the struts are lined up properly at the top ends. After that cures it all comes off so the bottoms can be worked on. I'm also considering filling the strut tubes with something to help make sure the rods inside don't rattle. Sand would be nice since it's cheap, but it's also fairly heavy. Gotta give that some more thought... Maybe epoxy mixed with microbaloons and then thinned so it'll pour easily would work.

 

[FDS]

You could try expanding insulation foam? The stuff that comes in a can, maybe narrow the delivery tube diameter?

 

[Joker 53150]

You could try expanding insulation foam? The stuff that comes in a can, maybe narrow the delivery tube diameter?

I've been thinking about that as an option. Getting it all the way into the tube would be an issue as one end is already sealed. I'd have to drill a hole to give it an exit (or to fill it from). Along that same line, maybe I should consider Gorilla Glue. With a little ingenuity I could get GG in the length of the strut and it would hopefully foam up enough to fill the tube solid.

 

[FDS]

I have never tried GG. The idea of expanding super glue and me trying to work together is not a good one!

 

[Joker 53150]

It takes some time to set up, but once it does it’s solid stuff.

 

[nhk750]

I have seen the wing strut mounting method on the Flying Giants website, oops, I mean the Cub Den, and I think it looks great. I may try it when I build my 1/4 scale cub someday, after moving and everything else...

 

[Joker 53150]

My first big Cub used wingnuts to secure the struts at the fuselage, which works great and doesn’t require special tools.

 

[Joker 53150]

One wing is about 98% complete, FINALLY! Limited work time has really made this project drag on longer than expected, but it really makes a big difference in the appearance of the plane.

Here is a side-by-side of original Balsa USA struts next to my scratch-built struts. (minor filling, sanding, and painting are still needed at the ends)

The original jury struts were made from a single wire that was attached to the main struts. Very functional, but pretty plain.

The new jury struts have a lot more detail and can be folded for transport, although folding them requires removing two more small hex-head screws. I've beefed up the structure from the original wire diameter as well, using brass tube.

This is the mounting plate which attaches to the bottom of the fuselage with a single bolt. Nothing wrong with it other than it lacking some good detail.

And here's the new version. The original mounting plate was used (for now) so there are extra screw holes in it. I'll continue to use this style as it's quick and easy to mount the struts to the fuselage and I don't have to worry about losing those tiny screws which hold the strut to the mounting plate. These pieces need a small amount of filler and sanding still, which became super obvious once I painted them!

 

[rockyboy]

Excellent work! Love the little details on these!

 

[heli-pilot]

How did you end up securing the threaded rods into the aluminum profile? Is it just a glue? Does the rod go all the way to the other end or is it just inserts at each end?