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

Joker 53150

Mmmmmmm, balsa.
Mentor
A small update on the Taylorcraft: the wing is too short to be 1/4 scale, but the fuselage is too big to be 1/5 sale. A little more digging and I think it may actually simply be a 1/4-ish scale Clipped Wing Taylorcraft. With a 83" wing it would actually be a touch smaller than 1/4 scale (88"). Close enough. I cleaned it up, temporarily mounted the landing gear, wings, and struts. It'll be fairly heavy for the wing size but with a 26cc gasser it should really perform well. Kind of strange how the two planes I picked from the lot were both clipped wings.

To make some room in the hangar I sold the Bud Nosen Trainer to my buddy for the $60 I paid for it. He giggled the whole time he was loading it into his truck! :)
 

nhk750

Aviation Enthusiast
Ya, sounds like a 1/4 scale clipped. I should have a New Sig 1/4 scale clipped wing Cub on the way today for a future build. I'm going big finally...or going home...or staying home to build it...
 

Joker 53150

Mmmmmmm, balsa.
Mentor
Picking up where I left off with the Balsa USA Cub, it's last flight was rather scary. The engine died as it was flying away from me, but it was fairly low and I was flying at a sod far, so no worries about trees! Because of the distance I had a hard time judging altitude above the turf and I ended up stalling it from a few feet up. It came down fairly hard, but with relatively limited damage. The entire fuselage sustained only a few simple breaks - the opening side window broke off, the silicone exhaust extension was broken, the windshield cracked, and a landing gear bungee mount broke. The wings took a little damage, but only at the root ribs where the wings attach to the fuselage. These broke fairly cleanly right off. No other visible damage to the wings, and even the struts survived intact.

To get it back in flying shape I've got a little work to do, starting with removing the remains of the ribs that were still attached to the fuselage. Balsa USA sold me just these replacement pieces, although I could have tried cutting them from scratch. These will be taken care of after I get some work done on the fuselage.

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The windshield was cracked fairly bad, which is no big deal as I wanted to replace it anyway. The old one is scratched up and I just didn't like how it was installed. It'll take a little time removing the excess glue used to hold it in place, but the new clear windshield will be worth the effort.

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Nothing major with the engine, although I'm putting a new muffler on it, new spark plug, new fuel tubing, etc. It's still got a lot of dirt from the sod farm crash on it, although amazingly it didn't break the prop! As I was going through the fuel system I found out why the engine died - it was out of gas! I'm not sure how that happened as I was only flying for maybe 8-9 minutes and I normally stop flying at 11, with 2 minutes of reserve. I'll have to watch it for the next few flights and tweak my flight times as necessary. Also a little carb tuning could help as it does run a little rich. The plan is to install a new cowl as part of the re-build. The original one is still usable, but I don't like the design of the fake Continental engine and am going with one that is a bit more realistic.

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This didn't cause the power loss, but it certainly doesn't help fuel flow - note the kink in the line leading to the carb. The clunk is stuck forward in the tank, probably from the force of the extra hard landing. The clunk line will be replaced with a different type of fuel line that is supposed to stay much more flexible than the yellow Tygon line. A new bung will go in as well - maybe I can sneak a bigger fuel tank in the fuselage, I'd like to extend my flight times if possible.

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And here's the biggest headache to fix, mainly because I can't fix it myself. One of the lugs that holds the bungee in place broke off, but I was able to rig it temporarily so it could at least sit without needing to be propped up. The crash put a lot of stress on these little lugs so I'm sending the parts back to the guy in Idaho who made them so he can either re-build the parts or simply sell me new ones. Either way I don't want to trust the original lugs after they've been stressed like this.

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4 screws later and the struts are off and ready to be packed up. When I got these pieces they were painted (horribly) with thick yellow paint which is visible in spots from wear. Considering the impact forces I'm amazed at how well these pieces survived the crash.

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Since this has been my favorite plane to fly and it doesn't need *THAT* much work I'm trying to get it done ASAP so it's ready for Spring. Unless something else jumps in front of it! :)
 

Joker 53150

Mmmmmmm, balsa.
Mentor
A few weeks of waiting and my replacement struts are here. He says he just put new bungee pins on them, but I'm fairly sure these are new units. I guess it's possible he stripped all the paint off my original units for the repairs and then painted them...? It appears he used nails for the pins, which should be far stronger than the original wires. They're pretty grungy from the exhaust blowing over them for a season, but it does help give the plane a more weathered appearance. For anybody needing articulated Cub gear for anything from the E-Flite Carbon Cub all the way up through the 1/3 scale Cubs I can't recommend this company strongly enough! www.cublandinggear.com is the place - their prices are good for the quality of the product, and they work great at smoothing out your landings on rough ground.

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I also started doing some work on my 1/4 scale Citabria (from Bud Nosen plans). It suffered some minor damage last season due to a poor landing in tall grass and needs the wing center section repaired. I've stripped the covering and the top & bottom sheeting. One of the two bolts which holds the left wing on is a bit wallowed out and needs some repair. I think the job should be fairly easy (hopefully) and quick, and that plane will then be ready for action once weather warms up again.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
Work is moving along at a snail's pace. Last week and this week I'm scheduled to be on the road Monday thru Friday, but at least this week is MUCH warmer than last week's -25F! I spent a few hours getting some work done on the Cub, including painting and re-installing the repaired landing gear. The forward window pillars were both broken loose in the crash, so I removed the pieces and cleaned up the mounting surfaces. The covering on top of the nose was also removed as it was in pretty rough shape.

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The replacement pillars were cut from basswood and painted before installation. The visible surfaces around the top/front of the windshield were also painted as they are starting to show some age/hangar-rash. A new sheet of clear plastic from Balsa USA is in transit so I can cut a new windshield - the old one was cracked from the crash and was fairly ugly from age, bugs, etc. hitting it for years.

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The side window still needs to be re-installed after checking the glue joints for damage. When that happens I plan to also update the door. Currently it is held closed by a pair of magnets, one at the front and one at the rear. They hold fairly well, but the door has still popped open a few times during flight. The plan is to make a rotating handle for the center of the door, with pins that will secure the door properly at the front and rear. I'm really looking forward to getting some more time so I can work on the new wing struts. The original pieces work well enough, but just don't look as good as I'd like. The struts are an area I could go nuts with scale detail, but I'll leave that kind of stuff for Joshua! My plan is to simply make them look much better than before while not going clinical with work. :)
 

Joker 53150

Mmmmmmm, balsa.
Mentor
The nose will be re-covered and then painted to match since I can’t get the proper OD Green Solar Tex anymore. The cowl will be replaced since I’m also replacing the muffler with a different style (which needs a different size hole cut into the cowl). The new cowl will also get a more realistic Continental engine installed, and I may also make the cowl 2-piece for easier engine access.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
So the Cub is covered with SolarTex, which has now been out of production for a year or two. If I had the money (and brains?) I'd have bought a bunch of rolls including the Olive Drab for this plane while it was still available, but.... What I *DO* have for SolarTex is Cub Yellow and Light Blue scraps from my first 1/4 scale Sig Cub re-build. Since I've got spray paint that is very close to the Olive Drab needed for this plane I'm going to use it to paint the Cub Yellow to match. While the paint isn't a perfect match it's darn close. Plus, a real military plane that is seeing action will have patches and uneven paint anyway. :) So on goes the Cub Yellow. If you look closely you can see where some of the paint has been used around the door, which was covered in Light Blue shortly after I bought the plane.

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Along with the new covering is a new windscreen. I used the original plastic as a template and cut a template out of card stock. I'm not a fan of how the original windscreen was installed so I'll tweak the template a bit before cutting the plastic.

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Joker 53150

Mmmmmmm, balsa.
Mentor
...And with a little tweaking the template fits nicely - better than the previous windshield. I'm going to make a second template and tweak it some more to make sure it's right before cutting the plastic. The original plastic was cracked and had quite a bit of gunk on it that wouldn't clean, but it also bowed in from the prop blast. I measured the original windshield and it was .015" thick while the new one is .020", so hopefully that extra thickness will help it keep it's shape. On my bigger planes I've gone with .030" for windshields, although that thickness really doesn't want to bend for tight curves without heating it up, and heating it introduces all kinds of other warping potential.

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Joker 53150

Mmmmmmm, balsa.
Mentor
The paint is on and dry enough for me to test-fit the new windshield. It's still got the plastic film on it which makes it blue (for now). When the old covering was coming off I took the fuel gauge off and gave it a new coat of paint as well. On the Cub the cap is red, not sure if the military would use it in that color or not, but I like adding a touch of color to the nose. It'll be glued in place after the windshield install is completed. For those who aren't familiar with it, the Cub uses a simple float to show the fuel level.

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Here's a very handy tool for cutting plastic sheet, scissors made by Kyosho. I got them 30 years or so ago for trimming bodies for electric cars. They've got a slight curve which helps cutting the curves on the windshield. For straight lines I use a bigger "normal" pair of scissors.

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Joker 53150

Mmmmmmm, balsa.
Mentor
I started a thread a while back about balsa building while "on the road". Last week I traveled Monday thru Friday and this week I'm doing that again. Probably next week as well.... :( Last week was all kinds of bad weather and a roommate for the week to keep me busy, but this week I'm solo and making some balsa dust! :) I picked up the Balsa USA 1/4 scale Continental engine kit and and finally making some more progress on it. The main pieces are vacuum formed with balsa sheet inside for strength. Cylinders are each built from 2 halves glued together. There is currently a visible seam down the sides which I'm hoping to minimize by use of spot putty and sanding. Realistically, only part of these pieces will actually be visible once mounted and a big air shroud will also cover part of it. The rocker arm covers seem a bit small, and I may decide to 3D print them for a little better detail.

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Joker 53150

Mmmmmmm, balsa.
Mentor
Here is the process for building the Balsa USA Cub dummy engine cylinders. The kit comes with the balsa, vacuum formed cylinders and rocker covers, dowels, screws, and metal for the air shrouds. 1/8" sheet is cut to size to fit inside the backs of the parts as shown, and glued in with thick CA.

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The parts are then cut and trimmed with a scissors, but this trimming is just to get the bulk of the excess material removed.

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Sandpaper is laid on the work surface and the pieces are sanded on the flat surface, which eventually removes all the excess and leaves you with nice flush-sanded parts ready to glue.

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Here is a finished piece ready to glue next to an unsanded half. I've had some cowls in the past that are sanded like this after removing extra material, but without the balsa inside. The balsa really does a lot to strengthen the overall parts.

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Here's a quick mock-up of the overall design, less the intake and exhaust , shroud, plugs & wires. :) The screws in the rocker cover are just for show and don't actually hold the cover in place. A little medium CA will be dripped into the holes before re-installing the screws.

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Be careful with CA on vacu-formed parts. The plastic used for vac parts doesn’t play well with CA. It will make the plastic brittle and cracking will occur. I typically use canopy glue or some other glue besides CA for vac parts.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
Be careful with CA on vacu-formed parts. The plastic used for vac parts doesn’t play well with CA. It will make the plastic brittle and cracking will occur. I typically use canopy glue or some other glue besides CA for vac parts.
Interesting... I'm following the directions which call for the CA, but I normally don't use it often and am fairly ignorant on potential problems like this. At least it's not a structural part! :)
 

Joker 53150

Mmmmmmm, balsa.
Mentor
It’s something I became aware of when I started building Pat Tritle models. Thin CA is the worst. Here’s a link to some instructions from Pat Tritle. Vacu formed instructions. The thick may not have the crystalizing effect.
I wonder if that is for all current types of CA or if it’s dated. I’ve had Omer models built with CA where the glue is crystallized and fairly brittle, but supposedly that was an older style of adhesive.