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        Build Log Mountain Models J-3 Cub -- Beta Build

#1 buzzltyr Sep 05, 2006 02:27 PM

Mountain Models J-3 Cub -- Beta Build
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Brian Eberwein at Mountain Models/Laser Arts was kind enough to offer me a beta kit of his new J-3 Cub. I'm always excited to have a new project, and even better, a new scale project, to tackle. :D

This one is a little larger than the usual MM kit, with a 48" wingspan, and 332 sq in. Weight on Brian's alpha is 12.6 - 13.4 oz depending on the battery, with a wingloading in the 5.5 - 5.8 oz/sq ft range. The model is obviously light enough to be flown with a lot of different power systems, from small outrunners to geared inrunners. I haven't picked a power system yet, but have a couple of GWS Pico servos for the ailerons, and a couple of Hitec 55's for rudder and elevator.

Brian has been terrific about getting me started, and answering a ton of emails. Keep in mind that this is a beta, being built without plans or a manual.
I'm sure that production kits will have some changes as Brian tweaks the design, so future builders should note that their kit may vary slightly from my build pics.

The first pic is the obligatory shot of the contents of the kit.


#2 buzzltyr Sep 05, 2006 02:33 PM

Tail feathers
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Because nothing screams "J-3 Cub" to me like the tail feathers, and because I knew they'd be easy to do, that's where I started. Everything, of course, is laser cut, out of quality wood. Part's fit was smooth and tight.


#3 buzzltyr Sep 05, 2006 02:44 PM

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The fuselage was next. The center area formers are tabbed/slotted into one of the sides, glued (hopefully perpendicular to the fuselage side), and then the other side added. The cabin top is also inserted at this point, creating a sturdy "box" in the center of the fuselage. The other formers are then put in place. The very tail area is sanded, using laser-scribed lines, so that the fuselage sides mate nicely. Everything is tabs, slots, and laser cut joints, so building a nice straight fuselage should be an easy task.

More to come later!


#4 mle2tie Sep 05, 2006 06:21 PM

any idea on price?
when it will be ready to ship?

#5 Mountain Models Sep 05, 2006 06:34 PM

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I might have some kits at NEAT. I just hope I have the instructions done by then. (Plastics may or may not be done for NEAT though because I was late in getting things shipped off.

Price is still to be determined after the cut files are finalized.

The Alpha is flying as listed below:

WingSpan: 48"
Area: 332 sq in
13.4 oz AUW
Loading: 5.8 oz/sq ft.

Equipment used:
Motor: GWS 2205-15T Outrunner w/8x4.3 prop
(Pulls about 11.5A at our altitude - 6000')
Battery: 2S 1200 mAh PolyRc
ESC: Thunderbird 18
Receiver: Berg Microstamp 4L
Servos: 2 ea HS-55, 2 ea. GWS Pico

Flying around at 1/2- throttle is enough. I need to get the aileron differential figured out, because as a real Cub, it has a bit of adverse yaw. The differential helps, but some rudder really smooths it out nicely. It's been a lot of fun to fly around so far... completely relaxing.

A couple teaser shots ...


#6 Tram Sep 05, 2006 10:42 PM

I'll be watching this one.. :)

#7 sj3cub Sep 05, 2006 11:08 PM

Pictures? How scale are we talking? Dummy Engine, scale gear? If its anything like your other kits Brian, I'm sure it will be a winner.


#8 buzzltyr Sep 06, 2006 10:24 AM

Scott, I'll let Brian chime in with the "how scale" issue, as I'm really not sure.
From what I've done, it certainly looks scale, but I'm no scale expert or Cub fanatic. My understanding is that there is a cowl and engine detail coming in plastic, but even Brian doesn't have one yet.


#9 Mountain Models Sep 06, 2006 02:07 PM


Originally Posted by Scott Morgan
Pictures? How scale are we talking? Dummy Engine, scale gear?

I posted a couple teaser pictures above. It does have scale gear on it. I still have to design the "simple" gear today or tomorrow for those who don't want to bend so much wire. It's wrapped in Kevlar thread soaked in CA. It works like a charm. The center section is kept untied so the gear still has plenty of flex in it. I suppose a rubber band piece around that center joint would work as well, I'll have to try it out.

I should have some plastics in a day or 2 and Iíll post the pictures of the cowling and engine details as soon as possible.

Itís been a mad rush, and I just flew a different wing this morning to check a couple minor changes, but I like the first wing better.


#10 boomerace Sep 06, 2006 02:22 PM

Sound Like a kit I would want but first need to build the Mott P-38 with brushless and the P-51. I figure by then the kit ought to be ready! :cool:

#11 buzzltyr Sep 06, 2006 04:32 PM

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The fuselage build continues with the rest of the formers, sanding the rearward tail area, and mating the ends of the fuselage. Here's a pic of the rest of the formers installed.


#12 buzzltyr Sep 06, 2006 04:34 PM

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Here's a pic of the basic fuselage completed, from the top. Looks pretty good to me! :)


#13 buzzltyr Sep 06, 2006 04:36 PM

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Next the cabin sides are installed. Easy to do with everything tabbed, slotted and laser-cut joints. It's starting to look like a J-3!


#14 buzzltyr Sep 06, 2006 04:41 PM

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To finish up the basic fuselage construction, the tailpieces are installed along with the fuselage longerons on both sides and the top. There are also side longerons that stick out from the side of the fuselage, to give the appearance of the original's structure. The second picture shows the detail of the tail area. If you enlarge the picture, I think you can see the side longerons.

I forgot to take a picture of it, but the nose area forward of the dashboard is sheeted with some 1/32" balsa.


#15 sj3cub Sep 06, 2006 10:28 PM

Sounds Great guys. Can't wait to see the finished product and cowl/w dummy engine.
Looks like a nice and easy straight foward build!

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