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Old Sep 30, 2012, 12:16 AM
wood is good
loNslo's Avatar
United States, CA, Marina Del Rey
Joined Jun 2012
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Build Log
#21 model building clinic >> Great Planes J-3 Cub .40 <<

Reference clinic and kudos to Murocflyer for encouraging model building:
http://www.rcgroups.com/forums/showthread.php?t=1704076



SPECIFICATIONS
Piper J-3 Cub 40
Stock Number: GPMA0160
Wingspan: Standard Wing: 76.5 in (1945 mm)
Wing Area: Standard Wing: 820 in˛ (52.9 dm˛)
Weight: 6.5-7.5 lb (2950-3400 g)
Length: 49 in (1245 mm)
Requires: 2-stroke .40-.60 cu in or 4-stroke .48-.70 cu in; 4-channel radio; 2+ rolls MonoKote

This is the model I've chosen as a first step to get back into model building following a ~50 year hiatus. It will incorporate a glow to electric conversion as well as the capability to use floats or landing gear. It is my intention that this build will provide an opportunity for me to tune up my model building skills and tools in preparation to build a 1/5-scale Monocoupe, from plans, and to provide an advanced 4-channel trainer for me to transition from learning R/C on a foam ARF Cub to prepare me for flying the Monocoupe, and to provide a platform for water flying.

Why a Cub? Because I've always admired their simple and honest, no-nonsense design.

Why electric? I'd like to say for its simplicity, but the challenge of getting started in E-power has proven to be much more complicated than I had imagined. So I will just say that this choice was made for the greater potential flying sites available to this quiet power system and for the enjoyment of learning another set of skills in a rapidly evolving technology.

There are plenty of build threads which cover the gluing and sanding, and include many photos of wing structures and tail feathers being assembled. So I thought I would try to begin with some of the other considerations which are sometimes simply taken for granted, like how I wound up choosing this particular model, power, landing gear, floats, radio gear, ... ; what I have done to prepare my shop and modeling supplies for this build. And open for discussion alternatives to building this strictly by the plans and manual .

Comments and questions are welcome and encouraged.

'til the next installment...
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Old Sep 30, 2012, 12:27 AM
Promoting Model Aviation...
Murocflyer's Avatar
United States, CA, Tehachapi
Joined Nov 2005
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Looking forward to it and along for the ride.

Frank
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Old Sep 30, 2012, 12:29 AM
AMA 910957
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United States, WA, Hoodsport
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Subscribed with all enthusiastic and support!

EJWash
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Old Sep 30, 2012, 06:28 AM
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United States, MD, Elkton
Joined Oct 2011
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And I promise to be right there,as usual....The season is fast approaching..

I'm glad to see you starting the Cub...

We'll be only too happy to offer encouragement,and BASHING,if necessary,lol

Enjoy the construction....we will.
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Old Sep 30, 2012, 08:49 AM
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USA, NH, Alstead
Joined Oct 2007
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Me too. I've been waiting for you to get started on this.

It is always a bittersweet moment for me when I break into a pristine new kit and start building. I know there is a limit to the time and money I can spend, and I savor the moment for a long time, but once I break out that first piece of balsa it is like a book I can't put down.

I will offer the controversial opinion that personally on a plane this big I would be tempted to consider nitro power if you have a club available where you can fly nitro. It is not that electric won't be fine, but it is getting to a size where batteries start to get expensive. And flight times are fairly short with a typical setup. Plus, if you Monocoupe is going to be nitro, this would be a good plane to get familiar with nitro.

Don't get me wrong, I like electric just fine, but more in the size of your foam Cub. Plus, there is just something about the sound of a Saito that really "makes" a plane like a Cub seem realistic. An electric Cub is just kind of going to "swish" through the air, while the nitro Cub will sound more Cubbish, if you know what I mean. Electric is almost "too quiet". I have a somewhat smaller Sig 1/6 Scale Cub I converted to electric from nitro, and I miss the sounds and smells and don't fly it. I know, call me old fashioned, cause I am I guess.
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Old Sep 30, 2012, 09:22 AM
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Here is another perhaps controversial thing to think about: flight stabilization.

I have been kind of a "purist" since I made my belated start into this hobby, you know, the old fashioned thing again. While I have a computer radio, I don't use any mixes. I just was of the opinion I should "fly the plane" and use the sticks rather than the computer.

Well, recently I have totally reversed course when I bought a DJI quad copter. This thing is pretty much flown by its onboard computer and the pilot is just there for guidence. I have just been having a total blast because it is so easy to fly. I can hover it, go in the house and get a cup of coffee, and come back and it be waiting in the same spot ready to fly. Just kidding, but I could.

Now that brings me to my heli. I thought I would try a heli a couple of years ago. The learning curve on a heli is very steep. It is pretty much stay on the cord or crash and repair. I have not gotten very far with the heli.

Well, after my quad experience I decided to look at "stabilization" for helis and came across the FMA Co-Pilot II. While this is based on thermal imaging rather than gyros like my quad, the result is similar: you can fly the heli but if you start to lose it and relax the sticks to center, it will recover and stabilize the heli in a hover.

The reason for this long winded story is that this system works equally well in airplanes. Basically if you get disoriented and relax the right stick it will level the plane. You can adjust the "gain" to get the amount of stabilization you want.

From what I understand these systems work very well, are simple to install, and cost less than $200. Less than the cost of a crash for sure. I think it might simplify the learning curve. And you can set them up on a switch if you want so they are "off" until you have one of those "uh oh" moments.

Just thought I would mention it.
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Old Sep 30, 2012, 12:41 PM
wood is good
loNslo's Avatar
United States, CA, Marina Del Rey
Joined Jun 2012
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Imagine my delight this morning when, logging in to get my emails, I find that some reliable friends have shown up to offer their support and ideas for discussion on my new build thread! (my best happy face). Well done, fellas!

For me, it is the dynamic aspect of these threads that makes them interesting--the interaction of the subscribers--not some dry monologue describing how two pieces were sanded and then glued together, but the discussion which leads to a design improvement in the two pieces and the right choice of glue, or a different approach, entirely.

To illustrate, since U2 mentioned the power system (I had lots of glow experience as a kid), and although I've already purchased the motor and speed control, the power source, the batteries, and a place and method of mounting and accessing for changing and charging, have not been chosen.

As a reference, though there were many sources of information which led me to the choices I've made, here is the single thread which made it all come together for me:
http://www.rcgroups.com/forums/showt...136470&page=48
along with the truly generous help of Flieslikeabeagle who created WebOcalc for the benefit of all of us. Using this program, I was able to develop enough of an understanding of the basics such that I could make a pretty well informed guess at what size motor would be required to sufficiently power this ~7 lb model once a ~2 lb set of floats were attached (more on those later).
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Old Sep 30, 2012, 12:51 PM
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Well, now that you've bought the stuff I am sure it will be a good learning experience and fly fine. There is a very long time modeler who has flown every type of power at my club who has an electric this size. While the cost of his batteries kind of kills it for me, he really likes his setup. I am sure you will too!
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Old Sep 30, 2012, 12:58 PM
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United States, WA, Hoodsport
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Quote:
Originally Posted by u2builder View Post
I will offer the controversial opinion that personally on a plane this big I would be tempted to consider nitro power if you have a club available where you can fly nitro. It is not that electric won't be fine, but it is getting to a size where batteries start to get expensive. And flight times are fairly short with a typical setup.
A couple of years ago I was in a "right time/right place" situation and attended an electric-only fly-in in Central Florida. I was expecting to see mostly smaller park flyer size models, but I was surprised to see models all the way up to quarter-scale.
Your point is taken on flight endurance. There were a few models that bored-holes in the sky, just not for too long. There were plenty of Cub-like floaters that gave their pilots plenty of time to have a fun flight.

Electric is definitely a paradigm-shift. Will modelers *have* to make the switch? Not now, and maybe not in the future. But electric is more community friendly, and for some the only option they have to enjoy the hobby.

I have a Sig 1/-6-scale Clipped Wing Cub I'm planning to build as my entry into electric-power, so I'm all eyes and ears on loNslo's this project. I also have the plans and a few bit-n-pieces (gear, cowl) for a Hostetler 1/4-scale Stinson 108 that is primarily designed for electric.

If you really want some inspiration, check-out this 1/4-scale electric Cub build:

http://www.rcuniverse.com/forum/m_88..._1/key_/tm.htm

I'm onboard with the sound matching the aero-machine, but it is just another aspect of the hobby to enjoy.

EJWash
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Old Sep 30, 2012, 01:27 PM
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Joined Oct 2007
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Quote:
I'm onboard with the sound matching the aero-machine, but it is just another aspect of the hobby to enjoy.

EJWash[
Yeah, and you can get a little electronic gismo that makes engine sounds I think. Heck, they probably have one that makes exact CUBBIE sounds. LOL
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Old Sep 30, 2012, 04:38 PM
Promoting Model Aviation...
Murocflyer's Avatar
United States, CA, Tehachapi
Joined Nov 2005
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Quote:
Originally Posted by loNslo View Post
Imagine my delight this morning when, logging in to get my emails, I find that some reliable friends have shown up to offer their support and ideas for discussion on my new build thread! (my best happy face). Well done, fellas!

For me, it is the dynamic aspect of these threads that makes them interesting--the interaction of the subscribers--not some dry monologue describing how two pieces were sanded and then glued together, but the discussion which leads to a design improvement in the two pieces and the right choice of glue, or a different approach, entirely.

To illustrate, since U2 mentioned the power system (I had lots of glow experience as a kid), and although I've already purchased the motor and speed control, the power source, the batteries, and a place and method of mounting and accessing for changing and charging, have not been chosen.

As a reference, though there were many sources of information which led me to the choices I've made, here is the single thread which made it all come together for me:
http://www.rcgroups.com/forums/showt...136470&page=48
along with the truly generous help of Flieslikeabeagle who created WebOcalc for the benefit of all of us. Using this program, I was able to develop enough of an understanding of the basics such that I could make a pretty well informed guess at what size motor would be required to sufficiently power this ~7 lb model once a ~2 lb set of floats were attached (more on those later).
Speaking of online calculators, check out this one I discovered. I spoke about it here: http://www.rcgroups.com/forums/showthread.php?t=1733569

Frank
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Old Oct 01, 2012, 05:05 AM
Flying Low
cbarnes0061's Avatar
United States, VA, Petersburg
Joined Mar 2012
615 Posts
Love a good Cub I'm in.
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Old Oct 01, 2012, 09:36 AM
wood is good
loNslo's Avatar
United States, CA, Marina Del Rey
Joined Jun 2012
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Since we've already begun discussing the power system, and since the power system represents a huge payload to carry, and a major piece of engineering to install properly, let me begin by fleshing out the major components.

Here is the motor I've purchased ($115 delivered):
http://www.hacker-motor-shop.com/e-v...&t=3&c=23&p=23
(Hover your cursor over the thumbnails to see a readable size image.)
Specs are:
Peak Watts: 1500
kV(RPM/V):410
Diameter: 1.64 in
Length: 2.01in
Weight:9.71 oz
Shaft Diameter: 5.00mm
Shaft Diameter W/ GB mm
Idle Current: 1.50
Operating Current: 45A
Peak Current:55A
Resistance: 0.0250ohms
Poles: 14
Orientation: Out

The ESC (electronic speed control) I've purchased ($89 delivered) is:
http://www.castlecreations.com/suppo...Ice_75-100.pdf
Specs can be found here, towards the bottom of the page:
http://www.castlecreations.com/produ...oenix_ice.html
In addition to providing and controlling power for the motor, this ESC contains a BEC (battery eliminator circuit) which provides up to 5 amps of the low voltage (~5V) required for operating receiver and servos.

Details of how and why these were chosen appear in this thread, as previously mentioned:
http://www.rcgroups.com/forums/showt...136470&page=48

Another large and heavy component of the power system, and perhaps the most challenging to provide easily accessed space for mounting, is the battery. While providing space and mounting details for it will be important topics for discussion, here, it is probably best to try to keep discussion of the technical electronic details in the power system thread just mentioned, for anyone who cares to follow. This will include preliminary propeller selection, so more on this later.
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Old Oct 01, 2012, 09:49 AM
ARFs Are Me
TomCrump's Avatar
Traverse City, Michigan
Joined Dec 2005
11,888 Posts
Although I'm currently without one, I love Cubs. I'll follow along, too !

My last Cub was the GP 60 sized, built by a friend, abd re-built by me. She flew very well, but the landing gear was weak. I replaced it with an aftermarket unit.

Good luck with your build. Most importantly, HAVE FUN !!!
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Old Oct 01, 2012, 10:02 AM
wood is good
loNslo's Avatar
United States, CA, Marina Del Rey
Joined Jun 2012
1,361 Posts
Welcome aboard, Tom! Awfully glad you're joining us.

That may be the first Cub I've seen with wheel pants.

The Landing gear I've purchased for this build is this one from an E-flite 25 Super Cub:
http://www.horizonhobby.com/products/aux-EFL460016
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