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

Joker 53150

Mmmmmmm, balsa.
Mentor
Rebuilding the door and window on the Cub is heavily underway now. If the original pieces were more usable I'd have just used them and not bothered, but the way the pieces were hinged kept both pieces from opening properly. This made it hard to reach inside to screw in the wing bolts, to get at the battery plugs, etc. The original hinges were simple pin-style hinges that were installed straight through the center of the wood. At first glance the problem may not be obvious, but the issue is that as the door/window is opened the hinge doesn't allow enough room for that to happen and the door/window hits the frame. I'm doing it a little differently, which will allow full movement.

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Here's the original side window and frame. It was very solidly built and strong, but the window was in pretty sad shape and it had a ton of excess glue all over it. It could have been re-used, but I have the plastic sheet on-hand and decided to just build a new one. Plus, the window was glued to the inside of the frame which I don't like. It leaves the frame exposed which is harder to keep clean and much less aerodynamic than having the plastic on the outside. Eventually I'll re-do the front and left side windows as well.

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The door was solid, except for where I removed the old hinges, so that was just patched up and re-hinged. The window is being mocked-up before final gluing and trimming. Instead of the birch that the builder probably used, I'm using some very hard balsa.

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Here is how the builder did the windows. It works, but I want the window on the outside, which will be an easy fix in the future. The windshield is also serviceable for now.

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The door was re-painted on the inside and re-covered on the outside, and now it operates as it should. You can see the hinges at the bottom of the door (they aren't painted yet). While having those hinges visible isn't ideal, I'm going with function over form for this quick fix.

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With the new window installed, it's almost invisible. The hinges need to be attached to the fuselage still, this is a trial-fit. Note the canopy adhesive hasn't completely dried on a few spots. For those who haven't use it, canopy glue is an incredible adhesive for this kind of work!

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Joker 53150

Mmmmmmm, balsa.
Mentor
Some strange force is trying to keep me from flying this Cub. I got the door & window done, painted the landing gear, and did some programming on the Taranis. Since I'm off today I installed the wings and planned to fire it up to tune the engine.

Well, the electric fuel pump doesn't work now. Maybe, since it'll suck gas out of the tank... So I did a little work trying to figure it out and have decided it's something with the tank, maybe a line is pinched. Either way, I want to re-do it and this gives me a solid reason. So I connected the fuel line from the carb directly to the gas can (with only about 8 oz of gas in it) and got it to suck gas. It fired pretty quickly after that, and surprisingly enough I think the carb settings are just about perfect!

Now the list is fairly short before a maiden. Re-plumb the gas lines, finish programming the TX, set up the fail-safe, add one more magnet to keep the door closed, re-install the cowl, and find a better way to install the wings.

The wings... Seriously, these are a pain in the butt to install! Between Sig and Balsa USA you have two good options for 1/4 scale Cubs. The Balsa USA is the better/more scale looking version according to most people, but the Sig is MUCH easier to set up at the field! Just bolt the wing on the top of the fuselage and you're set. This one has two bolts per wing that have to be reached from inside the cockpit, and there just isn't an easy way to do it. It took me a good 20 minutes or more just to attach both wings.

But she's close, oh so close to being ready! :)
 

Joker 53150

Mmmmmmm, balsa.
Mentor
A little more testing, and the fueling problem is in the tank fill line, which is also the main line to the carb. It's probably kinked somewhere, although it's a pretty straight shot from the tank to the carb, but it's either that or a plug in the line. Oh well, either way it's an easy fix. While I'm at it, I'll run a better vent line that is less likely to leak gas during flight. I'm tempted to do away with the fill system already in place in favor of a fuel dot. That'll be a game-time decision.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
Maiden flight report!

Today looked like goo weather to get the Cub into the air, so yesterday the batteries go on the charger and the plane is given a one-over. Once at the field I filled the tank before installing the wings, just to run the engine a bit to make sure it's behaving.

No love, it wouldn't start. A little checking found that I'm still having problems with the fuel line being kinked, so no gas was getting to the engine! A little field-surgery and I confirmed it was now able to flow freely. A few seconds with the starter and it sprang to life. Controls were checked and everything appeared good, so it was shut down and the wings were installed.

If I haven't said this for a while I'll say it now, the Balsa USA Cub wings are a pain in the butt to install! Two bolts per wing inside the fuselage (reaching through the window & door) and a third at the base of the struts. The inside bolts are tough to get at, and I'm probably going to make a tool to try and make it easier. Either way, it's a 2-person job. The Sig 1/4 scale Cub wing simply drops down onto the fuselage top and bolts into place, followed by the lower wing bolts. Quick & easy. Balsa USA's Cub is apparently more scale, but given the choice I'd still go with the Sig.

So the wings are on, the tank is full, the sky is clear, and the winds are calm. Only my dad and a guy who lives near the field are there to watch as I do some taxi testing. She's responding nicely, so I aim it into the light breeze and give it the throttle. The tail pops up immediately, and with some elevator management it stays on the ground picking up speed. The 23cc Zenoah has NO problem motivating the Cub, and it eventually is allowed to lift off into a steady climb. Surprisingly, the only trim needed was a little down elevator to keep it level at 1/2 throttle. Otherwise, it flies like a Cub is expected to. Some changes to the throws are needed, but nothing to worry about.

But then.... About 20 seconds into the maiden flight I heard the two words every pilot dreads... "LOW BATTERY!" coming from my Taranis. I was about 1/2 way through the first lap of the field when the warning was announced, so I throttled back, made my turn into the wind, and it came down smooth and controlled for a nice landing.

I'm not sure what happened with the transmitter battery since it was on the charger yesterday. That was the only transmitter battery I had, and I was 3 hours from home. :( However, I have an electric starter for the gas planes, and the field box has a charger on it that will handle the stock Taranis battery, so I modified some cables and was able to put 30 minutes of charge into the transmitter battery.

By that point I had an audience as other club members were showing up. Nothing like a little pressure! The Cub didn't disappoint, as it again took off in a very Cub-like manner, flew for 10 minutes, and then settled down for a decent landing.

I ended the day with three flights and about 20 minutes of air time with it today, and the only issues are a broken solder joint on the landing gear and the need for another magnet on the door. Both easy fixes. Hopefully I can get a little flight video tomorrow.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
Another nice day to go flying! Three flights today, at 9-10 minutes per flight. That drains the tank to about 1/4 full, which isn't too bad, but I may try to swap in a slightly bigger tank.

With about 45 minutes of flight time on it, here are my observations and my (unfinished) to-do list:

This plane is an absolute joy to fly. The Zenoah G23 gasser has plenty of power compared to the 20cc I had in my previous full-wing 1/4 scale Cub. That could just be the tuning of the engine, prop choice, or maybe even the weight of the plane. Either way, it flies great and lifts off so nice & smooth it makes me look like a much better pilot. Landings are no problem, although the tires may get swapped out for slightly bigger ones to handle rough ground better. My first two landings today ended up tipping forward onto the nose (not a full flip, just ass-up) which resulted in a cracked prop. The more I use it, the more I like the fill plug that came on the plane. I re-built the original piece and it seems to work pretty well and doesn't pop off during filling like I was expecting.

To be done:
  • The interior will get re-done and a pilot added. I couldn't find a good WWI era pilot for it, but found a 60's era pilot that should look good. Heck, it's a J-3 with invasion stripes which isn't correct, why not throw the wrong pilot in as well?
  • It spits out a lot of exhaust goo which leaves a hard-to-remove sludge across parts of the bottom. Xylene & water mixed does a great job removing it, but I ordered a diverter that is hopefully going to fit that should take care of the problem.
  • The wheels should be bigger - these are stock size for a J-3, but a bumpy grass field calls for bigger ones.
  • Fuel tank plumbing still isn't right, I think the foam surrounding it is pinching the line slightly.
  • A full nut & bolt inspection should be done. While I haven't found anything loose it's always a good idea to do periodically, and since this plane hasn't flown for close to a decade you never know...!
  • A solution needs to be found to make installing the wings easier. Maybe some type of wingnut on the bolts? It's easily a 20 minute job installing them right now. I hate the wings as much as I love how the plane flies.
  • New exhaust gaskets should be installed, as these are leaking a bit and making a mess inside the cowl.
  • A way to kill the motor from the transmitter is needed. The engine doesn't have a choke so I can't simply choke it to death, and even with the throttle fully closed it will still idle. It has a magneto instead of the electronic ignition, so grounding out the coil wire is the goal. Right now there is a switch on the side of the cowl, but that doesn't help me if I'm not standing next to the plane. To handle the task I ordered a reed-switch that will be operated by a servo. That switch will take care of killing the engine as needed, and as a fail-safe it will be set to kill the engine if I lose signal for any reason. Now that's a happy thought...!
  • The windshield looks like crap and will be replaced. The one on it now just isn't done as I'd like it and really looks it's age.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
I'm slowly knocking a few things off the to-do list for the Cub. First, like the 1/4 scale Citabria I'm working on I installed a 2S LiPo battery for the receiver pack, along with a 6 volt regulator. It's snug down in the bottom of the fuselage and will be hidden by the floor which I'm now building. Once the floor is done most of the RC components will be hidden, including the RX, the RX battery pack, most servo wires, and the servos. Only a few pieces will be visible, giving it a much nicer, scale look. I've printed a pilot for it, but have to finish it before deciding if it'll be installed or not.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
Those of you with good memories may remember how I was having fuel problems early on in my re-build of this plane. I figured a gas line was kinked while installing the gas tank, but was able to make it work without tearing it all apart. Well, I finally pulled the tank so I can re-do the lines and install a kill-switch, and I confirmed that the gas feed line WAS kinked as shown below. After I pulled the tank out a bit the kink was cleared, but it was still never able to flow as freely as it should have. These lines will be replaced, and the vent/drain line (top line) will be have a few loops added to it which will make it harder for gas to simply flow out of it.

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New interior flooring has been cut and painted. Only the elevator pushrod is visible on the left, and I may cut some additional material to cover this as well. Why? When I install the wings I need to feed four bolts in through the cabin, and twice now I've dropped either a bolt, the allen wrench, or both, and the parts always find the most difficult area to get 'em out of!

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With the flooring removed I've got easy access to the receiver (big green foam), flight battery (white foam), and receiver battery voltage regulator (small green foam). The tentative plan for the servo-actuated kill-switch is to mount it in the open space to the right of the receiver.

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Joker 53150

Mmmmmmm, balsa.
Mentor
Work on the kill switch has started. It's basically a simple reed switch with a servo stuck to it. As the servo arm rotates it presses down on the switch, which completes the circuit and grounds the magneto killing the engine. The switch has 3 poles, allowing for a normally open or normally closed condition. I'll set this one up as normally open, with a fail safe setting to move the servo arm and close the circuit. The assembly will be mounted under the floor, hidden from view.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
The internals are all buttoned up and done now. The kill switch works nicely and gives me the ability to kill the engine with the flip of a switch or via failsafe if I lose signal - kind of important, I guess. :) The floor is installed which really cleans up the interior, and now I just need to decide if I want to do anything else with the interior. I've already printed a pilot, but the big issue is that installing a pilot will make it harder to get at the wing mounting bolts. The pilot could be removable, but that just creates more work. All things considered, I may just clean up and re-use the original pilot that came with the plane. It's super lightweight and flexible so it won't be in the way too much, plus it's part of the plane's history. Even if the pilot doesn't go back in, I will re-install the original seats that came with the plane as they just give it an extra level of detail.

New tubing is installed on the fuel tank, and during the inspection I found the rubber stopper was splitting! Good thing I noticed it before the interior of the plane got soaked with gas! A new bung was installed and it's back in and ready to go. While the cowl was off I took the opportunity to clean it up with Xylene and water, which does a fantastic job removing the old engine residue (and paint, if you're not careful).

Also to-do is fixing the landing gear wires. One of the cross braces is broken and I want to re-do it in a stronger manner to hopefully avoid future problems. Weather is very promising for Saturday, so the plan is to get out and fly!
 

Joker 53150

Mmmmmmm, balsa.
Mentor
It was a beautiful day for flying, and the Cub went up five more times for 54 minutes of flight time. Once again, I broke a solder joint on my landing gear...! :( The ground isn't too rough and my landings weren't harsh, so I'll assume I just had a bad solder joint. Again. It'll be an easy fix, but one I don't want to keep doing, hopefully I finally get it right soon!

I checked the new LiPo receiver battery a few times to make sure it had plenty of charge, and after almost an hour of flying and at least 30 minutes of re-programming time it was only down to about 75% charge, so I should easily have enough battery for 2 hours of flight time on a single charge.

Most flights are limited to 10-12 minutes which would give me a safe fuel reserve. The last flight I pushed it to 15 minutes as I was having fun doing some aerobatic maneuvers. At least as aerobatic as a Cub is going to get. It was the only plane in the sky so I was able to hear the engine burble a bit and speed up after doing an aileron roll, so I figured it might be running out of gas. Quickly it was brought down for a landing, and I found the tank was almost dry. I pumped about 1/2 ounce of gas out and ran the engine to finish what was left in the carb, and packed it up. That was too close for comfort, and future flights won't exceed 12-13 minutes. :)
 

Joker 53150

Mmmmmmm, balsa.
Mentor
It was a beautiful day for flying, and the Cub went up five more times for 54 minutes of flight time. Once again, I broke a solder joint on my landing gear...! :( The ground isn't too rough and my landings weren't harsh, so I'll assume I just had a bad solder joint. Again. It'll be an easy fix, but one I don't want to keep doing, hopefully I finally get it right soon!

I checked the new LiPo receiver battery a few times to make sure it had plenty of charge, and after almost an hour of flying and at least 30 minutes of re-programming time it was only down to about 75% charge, so I should easily have enough battery for 2 hours of flight time on a single charge.

Most flights are limited to 10-12 minutes which would give me a safe fuel reserve. The last flight I pushed it to 15 minutes as I was having fun doing some aerobatic maneuvers. At least as aerobatic as a Cub is going to get. It was the only plane in the sky so I was able to hear the engine burble a bit and speed up after doing an aileron roll, so I figured it might be running out of gas. Quickly it was brought down for a landing, and I found the tank was almost dry. I pumped about 1/2 ounce of gas out and ran the engine to finish what was left in the carb, and packed it up. That was too close for comfort, and future flights won't exceed 12-13 minutes. :)
 

Joker 53150

Mmmmmmm, balsa.
Mentor
I finally got some pics of the Cub in the air, months after it's first flight with me. Today was a perfect day for flying, no wind, clear sky, and cool temps. The Cub continues to fly great, but once again I broke a solder joint on the landing gear even though I didn't have anything close to a hard landing. :mad: The wires have been heated and cooled numerous times now due to the breaks, so I'm worried about the integrity and strength of the wires, and think I'm going to hit the hardware store to buy new wires to bend up my own gear.

The kill switch I made a while back also continues to work very well, and I consider it a must-have with a magneto based engine. Today I flew the plane for about 40 minutes, plus another 5-10 minutes on the ground. With the 2 cell LiPo installed earlier this year I still had about 95% of the charge left! As much as I like that type of performance I'm still going to switch the LiPo out for a NiMh over the winter. Doing that will allow me to use a simple charge port with a kill switch, which will likely be mounted inside the plane. Not that charging a LiPo is difficult, it's just that the NiMh is easier. The windshield is also bugging me due to it's flimsy design, but that probably won't get changed until I eventually re-cover the plane and update the look. Certainly there is no hurry, as there are already too many projects on the bench right now and the plane looks decent as-is.

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Joker 53150

Mmmmmmm, balsa.
Mentor
An on-going theme with the Cub has been landing gear failures. I've taken it apart and re-soldered a few times, but it just won't stick. Granted that's probably my own fault for a poor solder job, but I'm man enough to split the blame with Balsa USA on this one. :)

Instead of trying to save this landing gear yet again, I ordered a new set of wires - they're fairly cheap. Instead of going with the Balsa USA wires I instead ordered the landing gear wire set from Sig. Their wire is slightly thicker, which hopefully helps. More care will be taken to get the wire clean & prepped as needed before soldering, as I really REALLY don't want to do this yet again!

While the Cub is laid up getting her legs worked on I'm also going to do some cleaning of the engine and cowl. The previous owner did some weird modification work to the muffler so it would fit inside the cowl, but it leaks exhaust juice all over which makes a mess down the side of the cowl and nose of the plane. I'm going to see if I can find a good replacement for the Zenoah G23 gasser instead of just living with the problem. Hopefully.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
I'm making this into a 4-day weekend, burning a few days off while the weather is still decent and trying to get a few projects done. First up is soldering the new Sig landing gear wires for the Balsa USA Cub. You can see in the first picture that they're designed for a slightly narrower fuselage, but they'll still work just fine.

First step was cleaning the wire with warm water, a mild detergent, and a scuffing pad. The wire comes with a healthy film to keep 'em from rusting, and a bit of scrubbing was required. With the two main wires in place I added the front lower bar and put a ziptie around them to hold them in place while I secured the other side.

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Copper wire was then wrapped around the wires as tightly a I could do by hand. Flux was then brushed all around the joint to get the solder to wick in properly. For solder I used silver solder, not the rosin core version. This wire is THICK, so a regular soldering iron won't provide enough heat. I've got an 80 watt soldering iron and an even bigger old soldering iron with a big flat tip on it. I plugged them both in and let them heat up for a while before proceeding.

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With hot irons, I put the larger old iron on the bottom and the smaller 80 watt on top of the joint to be soldered in an attempt to get it up to temp more quickly. A single 150 watt-ish iron would be better, but this is what I had and I made it work. :) With the joint absorbing the heat, I removed the smaller iron and started applying the silver solder, making sure to get it in all over. Melting flux and excess solder were dripping all over the work bench and floor - this is NOT something you want to do over carpet! After the joints were all soldered I went back and did a little touch-up, followed by a deep clean with more mild detergent. A coat of OD Green was next.

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This is a step I previously didn't do with the landing gear, and it was bugging me. The struts should be filled in and covered as shown below. I've read about a few ways to do this, and am going with a balsa sheet epoxied in place which will be covered with Solartex covering. Too bad I'm out of Solartex! :( Since this plane may be done flying for the season I'll finish a couple other details on it before hanging it up until I order the OD Green Solartex to finish the gear. I could use some regular Monokote, but the glossy film would look like crap when the rest of the plane has the nice fabric look.

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I just read this entire thread... Hole E Crap! Wow man, I hated to read the blue winged one went down, but this OD green one is super nice as well! Cant wait to see more from you!
 

Joker 53150

Mmmmmmm, balsa.
Mentor
Thanks, it was a rough day when it happened, but it's all part of the hobby. The engine and electronics were all harvested and are currently waiting to be installed in a 1/6 scale Stinson Reliant, a project I might start this winter.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
Kicking around future ideas for the Cub, eventually I want to re-cover the entire plane and add some scale details. The invasion stripes would also probably go away as they aren't correct to the J-3, although there is still the option of turning the J-3 Cub into an L-4 Grasshopper.

Regarding the covering, it's currently wearing Solartex, which is a fantastic product. However, I'm thinking about using a bare fabric that would be sealed and then painted, as it would give me a more realistic/scale look, especially if I add rib stitching detail. Balsa USA (and other companies) sell some interesting products I've been wanting to try. Poly-Tak is the first product, and it's brushed around the edges of the structure to be covered and allowed to dry. The bare fabric (Planetex) is then placed over the structure and the edges are ironed which sticks the fabric down to the balsa structure. The iron is then used to shrink the fabric, and a couple coats of Poly-Brush "Magic Primer" follow that. The Poly-Brush seals the fabric and allows the use of just about any kind of paint, and it gives a very nice and durable finish. It's more work than Solartex, but the finished product can look much better once it's done. I'm thinking of getting the supplies and trying them out on a small area, such as the balsa fillers I added to the recently-repaired landing gear. If I like the results I can look at doing an entire plane with this method.