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Aug 20, 2017, 12:39 PM
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Basic balsa & mylar F3P-ish model

Recently I found a nice group of guys who have monthly access to a small gym for indoor flying, and I showed up with my Clik! clone. With a 30" span at 133 grams, it met the requirements of F3P planes 15 years ago, but in reality was still way to fast and heavy and I quickly found a wall right after take-off. I fly this plane outdoors on calm mornings, but never having flown in an enclosed space - and in this case a pretty small one - it made me realize just how important slow flying planes can be.

Moving forward, I really wanted to build something lighter but without spending too much money on a special coaxial motor or 0.5mm CF rods since I'll only have access to this location once a month, give or take. I've seen some examples online of some very light balsa & mylar planes at around 40 grams, but they look extremely fragile. I wanted to build something simple and one that I wouldn't have to repair as it was being built... It needed to be a little more durable, although not necessarily crash-proof.

So I decided to go with square 3/32" balsa sticks, in medium to light weights depending on the strength I felt the part needed, along with smaller square 1/16" lightweight balsa for cross-bracing. I'll use some stiffer 1/16" balsa sticks and kevlar fly-tying thread for bracing, and a few sticks of CF for the landing gear. I found some cellophane at a local store (Texas Art Supply in Houston, a great place) that isn't the lightest but should work fine. My target AUW is around 75g, and the spreadsheet below has the vitals.

I'll apply the covering in a bit and see where I'm at...
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Aug 20, 2017, 01:13 PM
Risto Hölttä - F3A/P Team FIN
Finnspeed's Avatar
Looks pretty good to me. But if possible, try to find a much lower Kv motor that can turn larger props. The motor you listed may be able to fly the plane but is most likely a bit too small without any gearing.
Aug 20, 2017, 03:03 PM
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Finnspeed, I can go to an Eflite Park 180 motor with an 8x4 prop, at a cost of about 6 grams, if needed. That would get me right to the 75g mark. But still barely over half the weight of the depron model I flew into the wall...

I've read the little AP05 3000kV motor will produce 90g of thrust on 2S, but I agree in that it may be a bit too aggressive for lightweight model. But this first one is all about figuring things out, especially equipment placement now that the airframe is much lighter, so not taking it too seriously.
Aug 20, 2017, 08:09 PM
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I ended up using blue cellophane, and I think it turned out pretty nice. I had to re-cover a few pieces, since I didn't use enough 3M77 spray, and I stuck the parts to the more matted side of the cellophane and it didn't stick very well.

But once I figured out the issue I re-sprayed the parts and it was easy to finish covering the parts. 3 light coats seemed to do the trick. I also used a tiny drop of thin CA on the corners to make sure the cellophane won't peel off. I might also use thin CA along the hinge lines to make sure the hinge tape doesn't peel the covering.

So far, the covered weight of the parts is 22g, so I managed to save 3g off the estimated covered weight. With the AP05 I'm looking at 65g, or with the Park 180 it could be 71g. Either one would probably fly nicely. I also need to come up with some simple air-brakes.
Aug 21, 2017, 02:25 AM
Risto Hölttä - F3A/P Team FIN
Finnspeed's Avatar
That all looks quite promising - your current weight is not too bad at all. You could fairly easily shave off some 10 g or more by stripping the servos and using dynamo wire, replacing the heavy propeller and receiver and getting a lighter BEC (or some small diodes to drop the voltage a bit).

The airframe is now about 10 g heavier than my Rane 2016 which is a fairly competitive carbon/mylar model with total AUW of 43 g. So the potential is there.

Aug 21, 2017, 12:32 PM
Registered User
Thank you, sir.

I can really see where chasing the grams starts to become part of the fun, but for now I'm content with how relatively easy it's been to build a plane at roughly half the weight of my first F3P style model. 12 or so years ago, for me that was 154g if I recall it correctly. And I think my lightest unmilled depron plane was 127g. So something around 75g would be awesome, for starters.

The only thing I'm not too crazy about is that this model will be pretty fragile... But you can't build them for crashing, just for flying, right? I suppose the CF & mylar places are way more durable than the balsa & mylar ones, but the CF planes also seem much more time consuming to build.

I hope to start assembling the horizontal fuse and lower vertical, building it upside-down as long as I can before I have to flip it over and figure out optimal placement for the rudder/elevator servos, receiver, ESC, and battery. That's the part I always like the least on one of these little models since having to add weight to balance would be awful.

Depending on the final weight, I also still want to consider spending a gram on some air brakes and maybe even another on some canalizers...
Aug 21, 2017, 11:51 PM
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Tonight I glued together the horizontal and lower fuselage parts. I'm surprised at how rigid it is. It will still need bracing but maybe not as much as I thought.
Aug 22, 2017, 12:58 PM
Risto Hölttä - F3A/P Team FIN
Finnspeed's Avatar
Yes, that's the big difference between balsa/film and carbon/film planes. They can both be built competitive but the carbon plane is almost indestructible while it takes 10 times longer to build...

I bet you have read this thread for various building tricks and pictures of different planes (my Rane included):
Aug 23, 2017, 07:10 PM
Registered User
I might make a few balsa versions but if I can develop some indoor flying skills I'll probably switch to CF just for the durability. I've also read that the CF versions can be built with medium CA and no thread, with no weight penalty and much faster than thin CA wth tied joints. I was also thinking about making a contra-drive setup, but that's getting ahead of myself...

I've read that article and there is certainly some good stuff in there but I'm not ready to abandon the convenience of plugs and the factory wiring just yet. But out of curiosity, what does that typically save in weight when you go to magnet wire and no connectors (direct soldering)?

Anyway, I also still haven't given up on trying the little AP05 3000 kV motor and I now have one in my hands so hopefully I can test its ability to power a 65-ish gram model vs. the Park 180 and a slightly bigger battery powering a 75-ish gram model.

But then either one will still be way better than the 133g version....
Aug 24, 2017, 09:45 AM
Risto Hölttä - F3A/P Team FIN
Finnspeed's Avatar
I'd say the weight saving from removing all the plugs and normal servo wires is roughly 4 - 5 grams, including the RX end. Additionally you can save about 1 g by lightening the servo covers and further 0.5 g by eliminating servo wheels and using only carbon tubes. Removing RX cover also gives about 1 g advantage, unless you use an ultra light RX already.

Good luck! Looking forward to see your results. It is always refreshing to see someone experimenting with new materials and alternatives.
Aug 25, 2017, 10:29 PM
Registered User
Based on some more info I've read the little AP05 3000kV motor on 2S probably won't have the muscle to get the job done, adequately. And when using the Eflite Park 180, I'll need batteries with more than just 150mAh, something more like a 280mAh 2S 30C pack to be able to deliver the amps it needs... Something along the lines of 4 amps, based on this post.

So far I have all the parts and electronics, and even with the P180 and a 2S 280mAh battery, I think I'm still on track for a 75g plane. Hopefully I'll be able to finish it this weekend, as long as my house doesn't float away in this storm from Hurricane Harvey.

All kidding aside, Corpus Christi is currently getting pounded by a Category 4 hurricane... I rode out Hurricane Ike in Houston in 2008 and that was a miserable experience. I feel for those in the middle of it right now.
Aug 27, 2017, 03:24 PM
Risto Hölttä - F3A/P Team FIN
Finnspeed's Avatar
OT: I've seen some images of Houston today and the flood situation looks pretty bad. Let's hope the damage is not as bad as it looks like and nobody is floating away in their houses.
Sep 11, 2017, 11:37 PM
Registered User
I finally got to fly my plane tonight, and I was very happy with the results.

AUW ended up being 78g... Part of that has to do with having to use epoxy to glue the upper fuse once I discovered that CA attacks the cellophane I used. Before I realized that, I was going to pin-prick the top of the horizontal fuse and CA the upper vertical. But instead I was forced to use some epoxy since it's all I had on hand. In the future I'll make slots that the upper / lower / horizontal fuselage will key together with, similar to how you'd do it with Depron. I could also stand to use a lighter pack, like a 200mAh or maybe a 180mAh if I can find suitable ones. I could also probably cut back on some of the balsa diagonal bracing and use smaller dia. CF wing and fuse bracing. Maybe even use thread instead of CF rods in some places.

Attached are some pictures on my dirty carpet, and a youtube video with me doing some very erratic and un-smooth flying while feeling a little claustrophobic. It's not easy flying inside a small gym for the first time. A little nerve wrecking, really. But I'll get used to it...

Basic balsa and mylar F3P plane (1 min 35 sec)
Sep 12, 2017, 12:32 AM
Registered User

Looks and flies great!

Sep 20, 2017, 09:15 PM
JosephSzczur101's Avatar
Happy to see more people trying out balsa!

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