Balsa Build Along 2017/18 - Hobbico 300S, Thinning the Herd
- Thread starter Joker 53150
- Start date
Setting up the fuel tank and hoses is next on the agenda while I wait for the epoxy on the ailerons to dry. There are a lot of ways to do this, and no matter who you ask you'll find out you're doing it wrong. 
Many people use a simple 2-line setup, with one line going to the carb and the other line to the muffler. The muffler line pressurizes the tank and acts as an overflow line, while the carb line is used to fill & drain the tank. To use this type of setup you need to unhook the fuel line so you can fill the tank through that line.
Since I've got a full cowl installed and don't want exposed fuel lines I'm going with a 3-line setup. One line goes to the carb, a second line is the vent & pressure line from the muffler, and a third line is for filling & draining the tank. To do this I'll have two clunk lines in the tank, which some people don't like. I haven't had any issues with this configuration and am not really worried about the two lines interfering with each other, so I'm moving forward with it.
The fuel tank will be buried in the nose and surrounded by foam, making leaks hard to find. To minimize the chances of leaks I'm going a little overboard with my fuel line setup. Each brass line into the tank will have a barbed end soldered on which will help hold the fuel line. Additionally, either the compression clamp or a stainless wire will be added to each to further secure it as the hose ages. In theory, this will help keep leaks from developing at the tank from age and vibration on the line.
Many people use a simple 2-line setup, with one line going to the carb and the other line to the muffler. The muffler line pressurizes the tank and acts as an overflow line, while the carb line is used to fill & drain the tank. To use this type of setup you need to unhook the fuel line so you can fill the tank through that line.Since I've got a full cowl installed and don't want exposed fuel lines I'm going with a 3-line setup. One line goes to the carb, a second line is the vent & pressure line from the muffler, and a third line is for filling & draining the tank. To do this I'll have two clunk lines in the tank, which some people don't like. I haven't had any issues with this configuration and am not really worried about the two lines interfering with each other, so I'm moving forward with it.
The fuel tank will be buried in the nose and surrounded by foam, making leaks hard to find. To minimize the chances of leaks I'm going a little overboard with my fuel line setup. Each brass line into the tank will have a barbed end soldered on which will help hold the fuel line. Additionally, either the compression clamp or a stainless wire will be added to each to further secure it as the hose ages. In theory, this will help keep leaks from developing at the tank from age and vibration on the line.
Here's how the fuel system is laid out. It's pretty similar to how I prefer to set up gas engines (one line to the carb, one line to vent, and one line to fill). As mentioned previously, I'm soldering barbs to the fuel lines to help keep the fuel lines from sliding off.
This is the vent/pressure line that'll be connected to the muffler to pressurize the tank. It also acts as an overflow line during filling, and therefore needs to be at the highest point of the fuel tank. Notice the tank has a little "bubble" on top that you try and get this line up and into, to maximize the amount of fuel you can get in the tank. To bend the line I use a spring-bender. Simply slide the spring over the tube and bend it by hand, and the spring keeps the tube from kinking. Because of the soldered on barb the line needs to be bent AFTER it's through the rubber bung - doing the bend before makes it very difficult to get through the bung.
Fast-forward a few minutes and the assembly is ready to install in the tank. The vent is trimmed to length and fits just inside the tank's bubble, and the fill & carb lines move freely getting close to the rear wall of the tank without touching it. You can also see the stainless wires wrapped around the ends of the fuel lines to secure them in place. Some people swear by small zip ties for the same purpose. With the assembly complete I was barely able to fit it all through the hole in the tank. Tightening the screw on the cap then compresses the white rubber bung which (hopefully) makes it leak-proof.
The tank was then installed and packed in with foam to help keep vibration to a minimum. A voltage monitor by Hobbico was also installed on the "dash" of the cockpit so it's visible through the canopy. Next up is making a battery and receiver tray. Things are coming together quickly now, and the engine will be ready to test soon!
This is the vent/pressure line that'll be connected to the muffler to pressurize the tank. It also acts as an overflow line during filling, and therefore needs to be at the highest point of the fuel tank. Notice the tank has a little "bubble" on top that you try and get this line up and into, to maximize the amount of fuel you can get in the tank. To bend the line I use a spring-bender. Simply slide the spring over the tube and bend it by hand, and the spring keeps the tube from kinking. Because of the soldered on barb the line needs to be bent AFTER it's through the rubber bung - doing the bend before makes it very difficult to get through the bung.
Fast-forward a few minutes and the assembly is ready to install in the tank. The vent is trimmed to length and fits just inside the tank's bubble, and the fill & carb lines move freely getting close to the rear wall of the tank without touching it. You can also see the stainless wires wrapped around the ends of the fuel lines to secure them in place. Some people swear by small zip ties for the same purpose. With the assembly complete I was barely able to fit it all through the hole in the tank. Tightening the screw on the cap then compresses the white rubber bung which (hopefully) makes it leak-proof.
The tank was then installed and packed in with foam to help keep vibration to a minimum. A voltage monitor by Hobbico was also installed on the "dash" of the cockpit so it's visible through the canopy. Next up is making a battery and receiver tray. Things are coming together quickly now, and the engine will be ready to test soon!
This is a part of the build I haven't been looking forward to, forming a canopy. The original that came with the planes is about 75% complete, but it's broken into a few pieces, cracked, etc. The best solution would be to simply buy a replacement, but they're long out of production. My plan is to build a balsa form which I can use to mold a replacement.
There are numerous ways to make the form, from clay, plaster, etc, but I'm going with a couple large blocks of balsa glued together. Turns out they're almost the perfect size once glued together. After the glue dries I'll draw the outline, cut the big pieces from the form with the bandsaw, and then start the more delicate carving. The balsa form would then need to be prepped and made super-smooth for the plastic to be pulled over the top. Hopefully I can do this without having to make a full vacuum forming table, but I'll go that route if needed!
There are numerous ways to make the form, from clay, plaster, etc, but I'm going with a couple large blocks of balsa glued together. Turns out they're almost the perfect size once glued together. After the glue dries I'll draw the outline, cut the big pieces from the form with the bandsaw, and then start the more delicate carving. The balsa form would then need to be prepped and made super-smooth for the plastic to be pulled over the top. Hopefully I can do this without having to make a full vacuum forming table, but I'll go that route if needed!
I'm planning to give that a shot, although I'll need to get a good clean bottle to work with. This canopy should work well with a 2 liter size I'm guessing.
The canopy mold is coming along nicely. I've cut, carved, sanded and filled numerous times, and it's almost ready for final prep work. It'll get covered with a layer of fiberglass & resin, followed by filler primer, spot filler, sanding, filling, priming, sanding, priming, filling, sanding, rinse & repeat. To be safe, I'll probably add a little extra "meat" to the mold first just so the canopy can be made slightly larger than needed, which should give me a little extra wiggle-room for final trimming.
Also, the ailerons are finally done so the punch-list is getting very short, and about 1/3 of it isn't really necessary before a flight:
Program TX rates and throws
Keepers on pushrod ends
Finish tail wheel installation
Glue control surface hinges
Fabricate canopy and install
Test run engine
Prep & paint cowl
Add FAA #
Make some vinyl graphics
Add a little color
Install wheel pants - maybe?
Also, the ailerons are finally done so the punch-list is getting very short, and about 1/3 of it isn't really necessary before a flight:
Program TX rates and throws
Keepers on pushrod ends
Finish tail wheel installation
Glue control surface hinges
Fabricate canopy and install
Test run engine
Prep & paint cowl
Add FAA #
Make some vinyl graphics
Add a little color
Install wheel pants - maybe?
Tench745
Master member
If you do, be cautious. Those bottles can really shrink, often to the point of crushing soft balsa. Most tutorials I've seen for the technique use something like pine for the forming blank.
Fiberglassing of the canopy mold has started. I laid down a layer with Zpoxy finishing resin and left it to cure for a day, and then followed with another skim coat of epoxy to help fill in the weave.
This is after trimming the excess off and giving it a quick sanding to remove bumps from dust.
The original canopy fits nicely over the mold. It's not perfect, and honestly I don't expect it to ever get perfect. The canopy shape is not the easiest to do, but it'll get some extra help from putty as needed.
Spot putty is then applied to fill the weave and any small dimples. After it dries most of it will be sanded off and a coat of filler primer will go on. At that point I should be able to better see the raised or lowered spots so they can be addressed with more putty or sanding. Then more primer, sanding, filler, primer, sanding, filler, rinse & repeat. I won't get to that till next weekend due to work. I didn't win the Powerball jackpot, so work is still in my future.
This is after trimming the excess off and giving it a quick sanding to remove bumps from dust.
The original canopy fits nicely over the mold. It's not perfect, and honestly I don't expect it to ever get perfect. The canopy shape is not the easiest to do, but it'll get some extra help from putty as needed.
Spot putty is then applied to fill the weave and any small dimples. After it dries most of it will be sanded off and a coat of filler primer will go on. At that point I should be able to better see the raised or lowered spots so they can be addressed with more putty or sanding. Then more primer, sanding, filler, primer, sanding, filler, rinse & repeat. I won't get to that till next weekend due to work. I didn't win the Powerball jackpot, so work is still in my future.
After the filler dried the canopy mold was sanded, primed, sanded, filled, sanded and primed again. It looks a little bumpy in the pic due to the uneven drying of the paint, but it's pretty darn smooth. It'll get a final sanding with fine wet/dry sandpaper before being finished and ready to use. Maybe tomorrow I'll have a little time to go out and get a 2 liter bottle of soda.
The cowl was also given a shot of color. Before painting it was scuffed with 300 grit, washed with dish soap in hot water, and dried. The color is a primer/paint combo that I've used before with good success. The first coat showed me a few spots in the gelcoat that needed attention, so they were filled with spot filler and sanded smooth. Another two coats of paint followed and I'm pretty happy with the result. Next up is adding some color to the fuselage. Currently I'm thinking of adding most of it (in white) to the bottom, with maybe some vinyl lettering on top. That'll be a game-time decision.
The cowl was also given a shot of color. Before painting it was scuffed with 300 grit, washed with dish soap in hot water, and dried. The color is a primer/paint combo that I've used before with good success. The first coat showed me a few spots in the gelcoat that needed attention, so they were filled with spot filler and sanded smooth. Another two coats of paint followed and I'm pretty happy with the result.
Next up is adding some color to the fuselage. Currently I'm thinking of adding most of it (in white) to the bottom, with maybe some vinyl lettering on top. That'll be a game-time decision. 
I picked up a 2 liter bottle of soda today so I could try shrinking it over the canopy mold. Dr. Pepper bottles are nice & smooth, and they only have a thin stripe of glue which is good.
However.........
The canopy is way too long for a 2 liter bottle, so it won't work.
Back to the drawing board. I've got some ideas, ranging from building a vacuum forming bed to making a fiberglass canopy. I'll give it some thought as I work on other planes for a while. Otherwise it's pretty much done other than setting up my rates and expo in the transmitter!
However.........
The canopy is way too long for a 2 liter bottle, so it won't work.
Back to the drawing board. I've got some ideas, ranging from building a vacuum forming bed to making a fiberglass canopy. I'll give it some thought as I work on other planes for a while. Otherwise it's pretty much done other than setting up my rates and expo in the transmitter!
I haven't forgotten the build-along! The big delay (other than the canopy which still isn't done) has been waiting to fire up and tune the glow engine. This weekend has been some of the better weather we've had in Wisconsin in a while for such shenanigans, so I took the nitro fleet out for testing. So far only the Zero has been started or flown by me.
First up was the Mustang with a 4-stroke Saito 100 glow engine. The biggest problem is the plug is hard to reach. It's got a remote glow plug setup, but it didn't come with the rest of the harness to make it work. Either way, it still fired up easily and was surprisingly quiet. It needs quite a bit of tuning and the valves are a bit out of adjustment, but it runs.
The Zero was fired up to warm it up so I could get some after-run oil into it, as I didn't do that yesterday after flying it.
When it came time to fire up the Extra 300S things didn't go too well. First the fuel didn't want to flow into the tank, so I'm figuring there is a kink in the line somewhere which will be easy enough to fix. After getting some fuel into I wasn't able to get it to pull into the engine by hand or with the electric starter. Hmm, maybe the glow plug was bad? So I pulled out my plug wrench and found the plug was loose. Heck, that must be it! I tried to tighten it only to find the plug threads are stripped! It's an OS engine so parts should be easy to get, but that'll keep me from doing much more with it for a while unfortunately.
More to come!
First up was the Mustang with a 4-stroke Saito 100 glow engine. The biggest problem is the plug is hard to reach. It's got a remote glow plug setup, but it didn't come with the rest of the harness to make it work. Either way, it still fired up easily and was surprisingly quiet. It needs quite a bit of tuning and the valves are a bit out of adjustment, but it runs.
The Zero was fired up to warm it up so I could get some after-run oil into it, as I didn't do that yesterday after flying it.
When it came time to fire up the Extra 300S things didn't go too well. First the fuel didn't want to flow into the tank, so I'm figuring there is a kink in the line somewhere which will be easy enough to fix. After getting some fuel into I wasn't able to get it to pull into the engine by hand or with the electric starter. Hmm, maybe the glow plug was bad? So I pulled out my plug wrench and found the plug was loose. Heck, that must be it! I tried to tighten it only to find the plug threads are stripped!
It's an OS engine so parts should be easy to get, but that'll keep me from doing much more with it for a while unfortunately.More to come!
Thanks. Not only has the Balsa Virus taken over with me but now I’ve got Glow Fever!
It's been a while since I updated this log, so here's an update on the Extra 300s. The new head for the glow engine arrived about a month ago and after some effort I got it running pretty well. I didn't run much fuel through it as weather was cold, but all appeared well. That left only the canopy as the big remaining project.
I'd done a lot of work building a mold to form my own, but never got around to actually trying it. The more I looked at it the more I didn't want to do it for some reason (probably just laziness). So recently when I was looking at various parts on the Tower Hobbies website I noticed an Extra 300 that was about the same size as mine, and they offered a replacement canopy for it. My dream was that it'd be a perfect fit, but really just didn't want it to be too small. Too big was fine, it could be trimmed. Probably...
It arrived today and as hoped it was a little over-sized. Some time test-fitting and cutting eventually got it to a pretty nice fit and the glue is now drying. The edges I didn't cut still have the original silver paint on them (mainly the front edge), so I'll have to get creative in either painting or covering the edges once the canopy is secure. Is it perfect? Heck no, but it's far better, smoother, etc., than I could do myself so I'll chalk it up as a victory.
Now if we could just finally get some decent flying weather....!
I'd done a lot of work building a mold to form my own, but never got around to actually trying it. The more I looked at it the more I didn't want to do it for some reason (probably just laziness). So recently when I was looking at various parts on the Tower Hobbies website I noticed an Extra 300 that was about the same size as mine, and they offered a replacement canopy for it. My dream was that it'd be a perfect fit, but really just didn't want it to be too small. Too big was fine, it could be trimmed. Probably...
It arrived today and as hoped it was a little over-sized. Some time test-fitting and cutting eventually got it to a pretty nice fit and the glue is now drying. The edges I didn't cut still have the original silver paint on them (mainly the front edge), so I'll have to get creative in either painting or covering the edges once the canopy is secure. Is it perfect? Heck no, but it's far better, smoother, etc., than I could do myself so I'll chalk it up as a victory.
Now if we could just finally get some decent flying weather....!
roversgonemad
Member
Grab some silver striping tape and you'll be in like Flynn!! It's great stuff and will bend around a corner on a canopy really well.
Those two corners are the only poor fitting areas, the rest turned out well. The glue is almost cured (finally) and I'm happy with the decision to go this route. Another option for fixing those spots would be to simply take a knife and carve down the edge sticking up. Not sure I'll do that or not yet, at this point I just want some good weather so I can try flying it! 30mph gusts today with rain, and now it's calm winds and snow...
I fired the Extra up again today to do a little more tuning on it, and it's running very well. The maiden flights will be done without the cowl, hopefully within the next few weeks if the weather cooperates. It's kind of strange starting this plane compared to some of the other glow-engines in my fleet as it doesn't want to cold-start unless it's got at least 1/2 throttle, but after that it's fine.
