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Balsa Build Along 2017/18 - Hobbico 300S, Thinning the Herd

Joker 53150

Mmmmmmm, balsa.
Mentor
#41
Hopefully we both keep up the pace! I’ve got a couple projects that could be “next” to keep my wife happy-ish... A 1/6 scale Stinson Reliant with a 20cc gasser, a Great Planes F-4 Phantom that needs a .60-.75 glow engine, or even a PT-40 trainer with an OS .40 glow engine. Or any number of other projects that need to be finished! :)
 
#42
I’ve been buttering up the wife to lessen the blow when I order the new PT-19. I’m trying to sell it as a plane that the two of us can take to giant scale meets for more time together. So far she’s not really buying it, lol. I get the “Don’t you already have all those boxes of airplanes that you don’t do anything with now?” every time I bring it up.

I vote you build the F-4!
 

Joker 53150

Mmmmmmm, balsa.
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#43
I laughed out loud at the line about "more together time", well done. Not believable at all, but you tried.

The F4 would require the most work of the three listed, and it's the only one I don't have an engine for yet. It needs roughly a .75 glow or equivalent, and I'm planning to stick with glow simply because a similar sized electric would require too much battery space. The wings are about 80% done and the fuselage is maybe 75% done, although the finish work on a plane is usually 90% of the job 70% of the time! :) I'd love to go EDF with it, but that would open up a major can of worms trying to re-engineer it to work.

As of now I'm leaning towards doing the Stinson Reliant next. All I need for it is covering material and the receiver and receiver battery pack. Most of the electronics and engine were harvested from a 1/4 scale Cub that lost it's battle with gravity.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#44
The engine is mounted, temporarily at least. The entire firewall needs a coat of epoxy and a little extra bracing to prevent damage from vibration. The engine and motor mount both came from a recent swap meet, from different sellers. With the motor mounted I could start the process of fitting the cowl and cutting it as needed so everything fits.

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There is still some clean-up to do to even out the cuts and gaps, but the cylinder head now clears the fiberglass cowl. I'd like to have the spinner about 1/8" closer to the cowl, but with the vibration and tuning needs on the glow engine I'll be content with a little extra gap. If this were getting an electric motor I'd get that gap much closer. The cowl is just held on by friction on the fuselage right now, but with the installation this far I can now focus on making mounts for it to make it official. Then I'll install the muffler and see what kind of work is needed to make that fit as well.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#46
Closer looks better, but with an IC engine I'm worried about movement from vibration or from handling it to tune the engine while it's running. The only support for it will be where it's attached at the fuselage, and the fiberglass has some "give" and movement to it, so a little extra gap simply makes it less likely that the spinner will ever touch the cowl. It's not a big issue, and I'm probably the only one who'll ever notice once it's done. As I move forward I can always adjust the engine on the motor mount if needed to change the gap.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#47
It's a long and fiddly process, but the cowl has now been cut so the muffler fits. There is minor trimming needed, and a couple mounting screws still need to be added, but it's getting close. At the end of the muffler a bit of firewall needed to be cut away for clearance. I'll have to fabricate some material to patch around it now, which should be fairly easy to do.

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Around the prop you can see a couple random strands from the fiberglass. These will get hardened with some thin CA before getting sanded to remove them and smooth the cuts out. The cowl fits a little loose across the top & bottom of the fuselage, but I still really like how it's starting to look!

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Joker 53150

Mmmmmmm, balsa.
Mentor
#48
Moving right along, more parts are needed so I can eventually finish this project. I've been robbing parts from other builds, so those need to be replaced as well. Orders were placed with Tower Hobbies, Hobby King, and Aloft Hobbies for a receiver, fiberglass cloth, pushrods, fuel tank, etc. Hopefully the orders arrive on days I get home before my wife! :)
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#49
The tail needs some fabrication for two reasons. First, I'm not using the tailwheel that came with the kits, and instead am using a Sullivan product. Second, the tail is supposed to include a plastic cover assembly which didn't come with the kits. No big problem, the work shouldn't be too involved.

The Sullivan wheel fits well enough over the ply block, but instead of simply running screws down into the ply to secure it I wanted to go a little stronger. T-nuts needed to be installed on the inside, so I peeled away a couple layers of original balsa. The nuts could have been installed by removing less material, but I wanted to take the opportunity to re-glue some of the pieces at the same time as a few joints were coming undone. With the T-nuts installed I found a piece of darker balsa to match the piece I cut out and made a patch. It's hidden under the tail so it won't be very obvious, even with a clear finish over the wood.

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Since the plastic cover that originally came with the kit is MIA I'm going to re-create it in balsa. 1/32" sheet was cut oversize and then soaked with Windex to soften it. This was one of the softer sheets I had, so it took the bend very easily. I'll leave it clamped till tomorrow, or the next time I work on the plane. It can then be trimmed and glued into place, and it should hold most of the shape it's been bent into.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#51
Here's something I've really been wanting to do for a while now, test my idea for finishing the plane! As mentioned previously, the plan is to fiberglass & epoxy the plane and leave it mostly clear/natural. I'm using a very lightweight fiberglass for this, which will hopefully limit the amount of epoxy needed. The test is being done on an extra wing I got with the Extra 300s kits. Actually, I got two extra wings, both left sides, and one of them was in such horrible shape I just threw it out. This one was kept to perform tests on.

Step one is to cut the 'glass to the approximate size needed. This is a leftover piece that'll do half the wing, good enough for me! :)

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The epoxy being used is Z-poxy finishing resin, which I'm thinning with denatured alcohol so it is easier to apply. The mix stats off 50:50 resin to hardener, and then I thin that by about 50% with the denatured alcohol. So the final ratio is 1/3 : 1/3 : 1/3. The denatured alcohol gets mixed in after the resin and hardener are completely mixed.

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With this stuff, a little goes a LONG way! I poured it onto the middle of the wing and then worked from the center out with a brush. After it's started I switch to an old playing card as my squeegee and keep working it farther and farther from center. Excess material is scooped up and moved to thin areas. You really don't want ANY excess material, and the goal is to get as much wetness out as possible. Any excess is removed, and I run the 'glass and epoxy just past the edges. I may try the other half of the wing with a little stain on the wood first, although I'm thinking that would be hard to apply evenly and the wetness could cause other problems - something I need to look into...

Note: I did this first test without adding any extra balsa filler to the wing panel. It was only sanded smooth and the extra balsa dust was removed. Assuming I do this to the entire airframe it'll all be covered with balsa filler and sanded just to make sure any small dings/dents/scrapes/seams are filled and smooth.

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For anybody wondering what that black line is across the wing, is the hold-down strap on my "Wing Station", a handy device I got from a vendor at Flite Fest 2016. It'll hold wings, fuselages, etc pretty securely so you can work on the part easily. In my case it's perfect for only 'glassing 1/2 a wing! :)

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Here's their owner's manual, it's worth checking them out online if you do a lot of balsa work. Covering a big wing becomes much easier when it's held securely.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#52
A quick (or a bunch of them) are required before the resin sets up. Part of the reason you don't want excess resin in spots is that it'll allow the 'glass to "float" and not stick down to the balsa. This also creates lumps that have to be taken care of later on, not to mention the extra weight the extra resin adds. After this cures overnight I'll sand and/or scrape the surface and apply another very thin coat to fill any remaining voids. If it works as planned, scraping the surface with a regular razor blade will do most of the smoothing, and will allow the final coat of resin to be ultra thin. But I haven't tried that yet, so we'll see what happens! In the past I sanded and then filled the weave with thinned body filler and primer. This was ok for a painted plane, but that isn't the plan here.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#53
I checked the wing this morning and it looks like the 'glass was done right. I didn't find any streaks, bubbles, or runs in the epoxy. It cured nicely and the excess should be quick & easy to remove. It'll sit for another 7 hours till I get home, at which time I'll scrape it with a razor blade and follow that with another very thin layer. In theory it should then be "done". Maybe? This is a new technique for me, as normally it'd be scuffed up, primed, and painted.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#54
Hmm, mixed results so far. I started off today's work by trimming excess fiberglass off the wing, and then scraping the surface with a razor blade. For scraping it, I simply took a razor blade and scraped it back & forth quickly across the surface. This knocked down a lot of the higher spots to even the surface out even more. While there aren't any bumps or thick spots of epoxy, there are still very tiny high and low spots. After scraping I had quite a bit of epoxy dust, and the surfaces felt smoother and less like the grain of the fiberglass.

As this is my first time trying this, I didn't know where or when to stop, so I did 2 scrapings and wiped the wing down. Another very small batch of Z-poxy finishing resin was mixed up and thinned with the denatured alcohol, and then applied to the previous layer. I spent some extra time with a new playing card going over it a few more times until there was no excess being removed. My hope is that enough epoxy will remain in the low spots to fill them in level with the high spots. Hopefully. At least I'm hoping it'll be smoother than the previous finish! The picture shows the reflection of my shop lights, and it doesn't look quite as glossy as I'm wanting. Maybe a coat of clear gloss paint will help, although I don't know how well it'll stick to the epoxy finish. Just more stuff to test, I guess! :)

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Joker 53150

Mmmmmmm, balsa.
Mentor
#55
Aaaaaaand, I think I have a NEW plan! :) Looking at options for painting the plane I thought about adding some tint to the epoxy, which led to Google searches, which led to a recommendation of using regular Testors enamel paint. So I tried it. And I like it!

This was a very small batch of resin, with two drops of red paint, also thinned out with the denatured alcohol. The color isn't very vibrant, but is still subtle enough to clearly show the grain of the wood. I'll need to test a few different ratios of paint to make sure it doesn't throw off the epoxy so much that it doesn't harden, as that might be considered a "problem".

There is also a concern as to how the paint will tint the balsa filler, so that'll need to be tested as well. But I'm stoked about the possibilities! :)

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Joker 53150

Mmmmmmm, balsa.
Mentor
#56
Pushrod work is now underway (when I'm not screwing around with the tinted fiberglass). There are two slots on each side - one side gets the elevator pushrod and the other side gets the rudder. I'll fill the extra holes so they don't stand out too much when the finish work is done. You can see how rough the cut-outs are, as I'm assuming this was all die-cut wood. There is also a bit of balsa filler spread over this area which is only rough-sanded and it makes it look like the balsa is a bit scaly. For the pushrods I'm using Sullivan Goldenrods, which I've used on a number of projects, and they should be plenty strong enough for this job.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#57
The tail has taken more work than expected, but the major work is pretty much done. Some material had to be added to fix the transition from the fuselage to the vertical stabilizer, a couple excess pushrod holes had to be filled, and more balsa filler was needed than I'd like to smooth it all out. Luckily most of the filler will be hidden under the vertical stab so it won't be super noticeable once it's fiberglassed. The balsa filler also took care of the gaps between body panels, which makes the plane look much better overall. Those gaps were big & ugly, and either the balsa sheet has shrunk over the years or the original pieces were cut fairly inaccurately. Since it was all very rough die-cut material I'm leaning towards poor cut quality. Some pieces look like they were cut with a butter knife! Since the plane was sold with covering on it already, all these issues were hidden from the consumer.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#58
Just a quick observation about this project so far, it's requiring a lot more work than I expected! None of it is too difficult, and I'm certainly making it more work than it would otherwise need if it were just being covered with film. For some silly reason I was picturing this being a very quick project! :p

Moving ahead to the gas tank installation, I wasn't sure which size tank would fit best so I ordered an 8 ounce, 10 ounce, and 12 ounce DuBro tanks. They're different shape than what the plans show so a little guesswork is in order to make sure there is room for the hoses and fittings. Whatever doesn't get used now will be useful in the future, and tanks are only about $6/ea in these sizes so at least I wouldn't have to run back to the hobby shop or order from Tower again!

Not so fast...

I took delivery on the three tanks and started checking out which would fit best, only to find all three were too wide, as there is some internal structure I didn't notice that blocks a fair amount of room. I could simply cut some of it out, but hesitate to do so as I really want the strength in the nose to handle the vibration from the glow engine. So I did what I should have done the first time and measured the opening more accurately so I could re-order a tank. I'm still going with DuBro, but a different style this time. Again, the tanks are cheap, and shipping from Tower is also extra cheap, and there is plenty of work to keep me busy while I wait.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#59
The entire firewall assembly needs to be painted with epoxy to fuel-proof it, so I thinned some 30 minute epoxy with denatured alcohol and brushed it on. The exterior is easy, but getting the inside fuel-proofed is going to be extremely difficult due to all the braces and bulkheads in there. No way will I be able to get 100% coverage, unfortunately. As long as I don't have any fuel leaks I should be ok, and I'm more concerned with getting the epoxy in there to brace the structure against vibrations.

In this pic you can also see the hardwood strips I've added that the cowl mounts to. Seven screws total are used to hold the cowl, and there are enough gaps between the cowl and fuselage to allow for good airflow, so I'm not concerned with the engine overheating.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#60
Servos are installed, along with the pushrods to the tail. I gave the entire servo tray a quick coat of epoxy to help make sure it holds together, and the pushrods were placed inside a brace made from scrap sticks. They're epoxied in place at both ends and cross each other inside the fuselage to keep the runs as straight as possible.

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While I was doing the epoxy work I also 'glassed the bottom of the horizontal stabilizer. The balsa filler is still noticeable , but it's a trade-off - smooth finish or better looks. The top has only a few tiny spots of filler so it should end up looking better. The filler can also be hidden a bit with the paint that will eventually go on. I probably won't do anything with the tinted epoxy, as I just couldn't decide on a way to do it that I'd like compared to what I can do with paint. Oh well, it was a fun experiment!

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