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Funtana S90 Wing Repairs

Joker 53150

Mmmmmmm, balsa.
Mentor
#1
It appears that balsa planes are getting more of a cult following here on the FT Forum, with multiple people taking on their first balsa builds, and I'm thrilled to see that! Building a plane that actually flies from a box of sticks and planks is a great feeling of accomplishment.

However, some people (like me) also find a lot of satisfaction in re-building (rescuing) planes. There are tons of cheap planes out there at swap meets, on Craigslist, from friends, etc that would be flyable with a bit of work. Since flying season is well underway and I've got plenty of flyable planes to keep me busy I decided to do a quick-ish thread on repairing a balsa wing.

Enter the Funtana S90 I picked up a couple years ago. It's had a hard life and needs a lot of TLC to get it air-worthy again. The fuselage will require a ton of work and will have to wait, but for now the right wing will be used to show how I go about fixing a plane. I picked this wing because it has a lot of common damage, and it's also not a huge project like the fuselage will be. This will also feed my hunger for building without starting an entire new project in the middle of flying season! :)

So to start, here's the wing. The covering looks a little saggy at the wingtip, but overall doesn't look too bad. Or does it.....?

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You can't see it in the picture, but underneath this covering and a couple layers of packing tape on the leading edge the balsa sheet is soft and broken. The tape was probably used to give it a little strength without actually fixing the problem.

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Next, the aileron rubs against the wing. On a humid day I'm betting that the wood would swell a bit making aileron movement even worse. The hinges are all ok and move freely.

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Moving to the bottom of the wing we have some very visible problems, all covered with more packing tape. :rolleyes:

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The wingtip is where most of the damage is found, and the last wing rib is fairly well destroyed.

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There is some damage in the aileron pocket which should be easy to repair.

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Here's an interesting "fix". The rib was damaged in the past and instead of splicing in properly sized balsa someone just glued the bits across the rib to bridge the gap. While it's technically functional, it's certainly not an elegant repair. The torn covering was also simply covered with more packing tape. The last problem (that I know of so far) is the servo mounting tray. To mount the servo, the previous owner held it in with drywall screws. o_O The screw holes are now too hogged out to handle "normal" servo mounting screws, so that'll have to be fixed as well.

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And I expect to find more problems as I start digging into the wing. So this is my next project (after finishing up a couple details on other planes in flying condition). My plan is to re-cover the wing with the same color scheme. The transparent blue really shows off the structure inside and I hope to make it look as though it wasn't run over by a truck. :) I'll probably kick off the work next weekend after I clean off the bench.
 
#7
I'm thrilled at this idea too and I'm only about two-thirds finished with my first balsa kit. I haven't had any luck yet finding bargains on CL or FB though. I've just joined a local club and hopefully that will turn up some things as I start going to their meets. Finding bargains is a long-term play. Patience is especially difficult when you don't have any flyable planes, but I'll get there eventually.

Thanks for the inspiration.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#8
Home a day earlier than expected, so let's get started on the wing re-build!

To separate the aileron from the wing I had to cut through each of the hinges. I was hoping that the hinges would have the removable pin which would make the task easy, but wasn't that lucky. A bandsaw made the job quick and easy. When the control horn was removed I found two wood screws and a machine screw, which doesn't work too well on wood. :confused: The screw holes will be filled and then re-drilled for matching screws later on in the project.

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Before taking the covering off I measured the yellow stripes and noted their placement on the wing.

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The covering came off pretty easily once it was heated up a bit with my covering heat gun. A couple small bits of color stuck to the wood but were easily removed. Other planes I've done had problems with removing the covering, but so far so good on this one.

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Here is where I started removing covering without adding heat first. Notice the color separated from the covering film and stuck to the wood.

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Here's a trick that removed most of that color from the wood - I applied packing tape over the color and heated it up a bit with the heat gun. Most of it came right off with the tape, and the remaining little bits were easily removed with a fingernail or by lightly scraping the surface with my X-acto knife blade.

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Next was a quick job of removing the original hinges, which were still glued in the aileron's leading edge. I used the saw blade shown to cut across the top & bottom edge of the hinge and the pieces then just fell out. The remaining holes in the aileron will be sanded, filled, and then re-cut for new hinges. At this time I'm not sure which type of hinge I'm going to use - probably a style similar to the original ones, but with a removable pin.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#9
Moving over to the rest of the wing now, since this is the "quick" part of the re-build. Again, taking some measurements of the graphics on the wing. I'll probably re-create these colors to keep the design close to original, but we'll see what happens when all the repairs are done. Like the aileron, the covering came off pretty easily after a little heat was applied.

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On the original post I mentioned some of the sheeting was damaged. It's not too bad and all the pieces are still there. A couple different methods can be used to fix this, from cutting it out and replacing it to simply wicking in some thin CA. Blue "X"s mark where the sheet is broken.

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Also on the original post you saw the bottom covering was torn and "repaired" with tape, and one of the ribs had some janky repair work done. When the rib was glued it was done with thin CA and excess dripped down and stuck the balsa to the covering. I'll do a little cleaning up here as well.

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This area was saturated with CA as well, and the covering is stuck tight to the balsa. It'll be a fairly easy fix as well.

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Here's the servo tray with the holes wallowed out by drywall screws. I'll leave the tray in place and plug the holes with hardwood. Later on they can be re-drilled for proper servo screws.

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The biggest damage is the wingtip rib. I've got most of the wood, at least enough to make a template to cut a new rib. I'll probably use a slightly thicker piece of balsa for this rib as it is subject to more damage than ribs buried inside the wing.

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And last, a shot showing 3 of the 4 ribs with damage to be repaired. The second rib will be easy as it's just a split along the grain of the wood. All remains of the original hinges are also now removed, and like the aileron I'll clean up the old pockets and glue in some new wood.

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TooJung2Die

Well-known member
#10
This is interesting. I never thought about buying someone else's airplane until just now. Now I can see the fun of buying a broken airplane and fixing it. I love restoring old stuff. I also do old air rifles, antique clocks and furniture among other things.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#11
This is interesting. I never thought about buying someone else's airplane until just now. Now I can see the fun of buying a broken airplane and fixing it. I love restoring old stuff. I also do old air rifles, antique clocks and furniture among other things.
Planes like this can often be found far cheaper than trying to build from a kit or scratch, and I personally find a lot of satisfaction in saving a plane from the landfill. This plane cost me around $75 and included a glow engine that I re-sold for $75. The other wing is in better shape than this one, although the fuselage will really be a chore to fix! :)
 

L Edge

Well-known member
#14
With the price of nitro fuels running about $30 gallon, more and more are either switching to either gasoline or electric. Even the 4 stroke fuel is getting to be overpriced.
There will be always a market for nitro, but is is dwindling.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#15
First up for the repairs is fixing the old hinge slots. They got chewed up a bit from removing the old hinges and I want to replace the voids with all new balsa. New hinge slots will then be cut so the hinges have a good, snug fit.

I took a balsa stick that was thick enough to fix any of the hings slots and used it to mark the outline for the new plug.

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Using an X-acto knife I trimmed up to the lines before test-fitting the new plug. To smooth out the edges on the hinge hole I took a popsicle stick and stuck 120 grit sandpaper to it. This was just thin enough to fit into the hole and allowed me to get it nice and even.

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When the hole and plug were a good match I used some Titebond II glue to make it permanent. My balsa planer and a sanding block finished off the repair. It's smooth enough that no balsa filler will be needed. Now to repeat the process 9 more times... :poop:

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Joker 53150

Mmmmmmm, balsa.
Mentor
#16
I may change the control horns so I felt it would be smart to plug the holes from the original horn. In my stash of supplies I've got various size hardwood dowels. I grabbed the smallest one I had and measured it as .130" in size. I've got a huge assortment of drillbits from when I did a lot of metal work, and grabbed a .136" bit to drill out the original holes. A little glue was squirted in the hole, the dowel was inserted, and cut off. When the glue cures I'll sand it smooth. Pretty quick and easy, and with this done all the aileron will need is a little finish sanding and it's ready for covering.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#17
While working on the wing I noticed an additional small problem. This surface on the aileron pocket is a bit beat up, which is where the aileron was rubbing. I'm guessing this was part of an attempt at making the aileron move more smoothly? Either way, it won't be super obvious, but I still want to even it out a bit, and I have a very simple method.

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To fill the gap I'm simply gluing a small piece of 3/32" balsa to the void. Once the glue dries I'll shape and sand it to match the surrounding surfaces. It may get a drop or two of thin CA to harden the balsa after shaping, but the scrap I used was medium density and it'll probably be fine without.

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Earlier I showed you where the aileron pocket had a big divot taken out of it. That wood was saturated with CA glue all the way down to the hinge. To fix this problem I start by cutting it out with a razor saw. Notice I cut the pieces at an angle. When I glue in the new wood I'll have more surface area for the glue meaning a stronger glue joint. Fixing this will also fix the old hinge pocket at the same time.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#18
Here is the sanded and shaped filler on the aileron pocket, now nice and straight. As I'm going over the wing more and more I don't think there is any way to avoid covering it with balsa filler later on if I want to get a good smooth finish. There are plenty of little dings and dips from a hard life. I'm hoping to use some techniques to limit the amount of filler once I get that far along - we'll see what happens.

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The rib that was broken had the broken pieces glued in sideways to "fix" the break. I'm not sure why the guy who did that didn't just glue them back in the way they originally were....? There is still some CA residue on the rib, but it's back in one piece. I originally planned to cut the rib out and replace it with a new one, but there is so much glue holding it all together it would be a nightmare to do. I think I can pretty this mess up enough to not be too noticeable once finished.

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The hogged out servo mounting screw holes are also plugged now with a small hardwood dowel. Once the glue dries I'll go over it with a sanding block to even it all out.

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The outside rib was crushed pretty badly, and the repair job was even worse! However, I had enough of the original broken pieces to form up the proper shape of the wing tip. The design of the wing had this last rib exposed at the end, and I don't care for how it looks with the holes in it visible through the covering. To change this, and strengthen the repaired rib, I'm covering the rib with a 3/16" piece of balsa.

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This will also give me a full flat surface to apply covering onto. I'll probably have to do the same to the aileron so it fits properly, which will be a quick task.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#19
This repair is to a very common type of damage on balsa planes - broken sheeting. Its hard to see in the picture so I traced where the major cracks were, and then outlined the entire area with a flexible metal ruler. I was lucky in that the ruler was just as wide as the damage so I could simply trace both sides of the ruler without moving it. That made the patch panel easy to cut as I just made it about 1/32" wider than the ruler, so I could simply plane it down for a good, snug fit.

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With the damaged sheet removed, the next task was cleaning up the tops of the exposed ribs. Notice that I extended the section to be cut all the way to the next rib so the patch would have something solid to be glued down to.

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With the tops of the ribs scraped clean of old glue I ran a sharp blade across them to allow glue to soak down into the rib when the patch is applied. I also used sheet that is about 1/32" thicker than the original sheet for my patch which will give it a little extra strength. Since the thicker sheet would normally sit proud of the rest of the sheet and require tons of sanding (and defeating the purpose of using a thicker sheet) I sanded the back of the patch slightly where it would sit on the ribs. Doing this will allow me to fine-tune the final height of the patch and minimize sanding.

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With the sanding on the back done it sits very nicely without the help of pins, tape, or clamps. The surface does have a minor curve that will be dealt with using a few pins...

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...like this. The pins both hold the patch down and also help hold the new and old surfaces even with each other to again minimize sanding.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#20
Time for hinges! Cutting hinge slots can be a real pain, as you often find harder balsa stock in these areas for strength. A while back I got this tool from an estate sale which makes the chore MUCH easier - the "Slot Machine" by Great Planes. You simply put it up against the wood where you want a hinge slot cut and pull the trigger. The two blades slide back & forth and cut a slot as you push the machine deeper. Very quick, very easy, and perfect for CA hinges.

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However, I'm not using CA hinges on this plane. :) On bigger planes I prefer using a 2-piece hinge with removable pin. Often I'll not use the supplied pin and instead use a long piece of wire the same diameter to run through all hinges in a line, which is what I'll probably do here as well. But for now I'll use the stock pins. The advantage with this style hinge is that you can pull the pins and remove an aileron/elevator/rudder for service if needed without destroying the hinge in the process.

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To make the thin slot from the Slot Machine big enough to handle these hinges I used the knife and a slot cutting tool. It takes a little time, but eventually the slot is big enough to hold the hinge with a little resistance.

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Test fitting the aileron, and everything lines up nicely. I usually cut the slots just a hair wider than they need to be. Nobody will see it and it gives me a little wiggle room to make sure the aileron lines up with the wing slots.

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The gap between the aileron and the wing is pretty even now that I filled the small gap at the end. A little sanding will make it better. When fitting pieces like this don't forget to leave room for the covering! A bigger gap is better than having a control surface rubbing.

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