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Old Mar 23, 2016, 11:36 AM
Zemi is offline
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Build Log
Piper J-4 Cub coupe 1/10

Hello modelers,

After taking so much inspiration from internet and RCGroups in particular I thought it is time to give some of it back, so I am presenting my first serious scratch built model.

As it is my first design I wanted something about 1m in wingspan. I decided to go with nice slow high wing monoplane and I run across Piper J-4. It is still a Cub with all that means (some would say it is not, I know, no tandem, no bungees...), but it looks so much more sofisticated and dignified that I simply couldnt resist it.

My build is going to be to scale of 1/10 made of 5mm and 2mm depron-ish foamboard I got from my local DIY store. Power will be provided by Emax 2812 "small red" 1540kv outrunner turning 8x3,8 propeller (for now at least). I will be using 2S Li-po. Servos are some generic 9g cheapos I found in spares.

5mm depron construction is laser cut along with some plywood parts (firewall and reinforcement for undercarriage). Cowl is
3D printed using ABS. Everything else is conventional building...

P.S.: If you are wondering why there is no ESC, reciever and battery holes in the construction it is because i didn't make any. I will make them in the second build (hopefully) when I will no where they need to be to keep the CofG where it belongs.

P.P.S.: Please forgive me any english mistakes, I am Czech, and crappy pictures... I really need to learn photography...
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Old Mar 23, 2016, 08:16 PM
BHOFM is offline
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United States, AR
Joined Nov 2014
3,670 Posts
Welcome to the forum, your English is fine. And the pictures are very nice.

Looking good.

With the 2812 you may want to go to a 8X6 on 2s. The 8X3.8 will be good with a 3s.
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Last edited by BHOFM; Mar 23, 2016 at 08:22 PM.
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Old Mar 23, 2016, 10:13 PM
springer is online now
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SE MI
Joined Oct 2004
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Pix are fine, and so's your English! Welcome to the forum too.

My fave prop for the 2812 is a apc style 7x6 with 3s lipo. Gives excellent performance. If you need the 8" prop to get the correct scale look, then BHOFM's suggestion is right on.
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Old Mar 24, 2016, 06:56 AM
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Thank you both for the propeller advices. I looked into it and found this site with some test results:

http://www.headsuphobby.com/Emax-CF2...otor-C-423.htm

I don't have means to perform such tests at home to verify kvs of my motor, but I will stick with what you guys said. I will keep the 8x3.8 APC for use with 3S and get some 8x5s or 8x6s for 2S use. BTW it is surprising how powerfull this little thing can be with 3S and appropriate prop...

Bit more to the construction. I decided not to incorporate any dihedral into the wing for ease of construction, as it is a high wing that "should" by itself provide some effective dihedral, or so I have read. The original had about 1 of dihedral. Is it fine if I go with none? I still have one extra set of wing parts, because I predict this is where problems will be...
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