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Old Feb 20, 2012, 10:50 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
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Skeleton Citabria (now with video, Post #1)

Here's what's on my workbench. I haven't been able to do any model building since right before NEAT. Finally I'm getting started again.

I did a semi-profile 13-inch Citabria with printed tissue back in 2004. Here's the thread: http://www.rcgroups.com/forums/showthread.php?t=203468
That one used a JMP actuator receiver, a 6mm pager gearbox, MiniActs (BSD hadn't come out with the MicroAct's yet) and a CF prop that I molded. Weight was 16.8g.

Since the Citabria has always been one of my favorite planes I thought I'd do another one, but a cartoon skeltonized version with painted mylar instead of printed tissue. Wing span will still be 13 inches. Here's what the plane should look like when done. The fuselage has been distorted vertically quite a bit to get that cartoon look. On the 2004 version I had stretched the chord from scale. On this one I've stretched it a bit more.

Equipment is a pair of Nick Leichty's 0.70g servos (just rudder/elevator like the 2004 version), a DT receiver, Vapor 6mm gearbox with a Cub motor, and a FR 60mAh cell. Final weight without the wheel pants is 12.6g weight. Thrust is 19g so it should be amore spirited flier than the 2004 version which had only 10g of thrust.

{edit #2}
The Citabria has now flown. I've added a video below. Final weight without wheel pants came in at a satisfying 12.6g. It flew like a high wing cabin plane without ailerons would be expected to fly, sedately. It has silly thrust and will climb like crazy. I may swap a 4-inch CF prop for the 5-incher next time out.

Citabria (1 min 45 sec)
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Last edited by Gordon Johnson; May 01, 2012 at 07:03 AM.
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Old Feb 20, 2012, 11:00 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,427 Posts
Previously on other models I've made painting templates by lasering them from regular printer paper and spraying them on the back side with Delta Stencil Magic adhesive. But, I tended to get bleeding when I painted it. On this plane I'm trying something new. I got something called "frisket paper", which isn't really paper, it's a plastic film with sticky adhesive on one side, and a peel off paper on the other side. It's really flexible and flimsy. So, I adhere it to some heavy paper stock and then cut openings in a larger sheet of paper and drop this frisket/paper sandwich in the opening, tape around the seam, and paint with my usual Krylon Short Cuts spray paint.

The result: virtually no bleeding and a much crisper edge to the graphic. The downside is multiple steps on the laser to do this, and it takes some time.
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Last edited by Gordon Johnson; Feb 21, 2012 at 09:06 AM.
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Old Feb 21, 2012, 07:26 AM
Registered User
Minneapolis, Minnesota
Joined Jul 2007
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Cute! I've been planning to make a tiny foam Aeronca for Classroom Fighter gear. The cartoony aspects look particularly nice on a small plane, imo!
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Old Feb 22, 2012, 11:35 AM
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Oxford, Michigan, United States
Joined Aug 1999
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So are you bonding the frisket paper with it's backing paper to the card stock Gordon? Then peeling off the stiffened backing to actually use the mask? End result being a laser cut mask vs hand cut?
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Old Feb 22, 2012, 12:28 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,427 Posts
Pete,
the frisket paper has a thin wax paper like sheet that is designed to peel off on the side which will go against the surface to be painted. The top side is just a plastic sheet. So, I spray the card stock on one side, and apply it on the top side of the frisket paper. Then, I cut through all three layers, which are in this order:
Top: Card stock
Middle: plastic frisket layer
Bottom: thin sheet to be removed

I remove the thin sheet on the bottom, leaving a nice sticky surface, and press it down on my RA Microlite sheet for painting.

To conserve frisket paper, and because this stuff takes some work to remove, I cut openings in a large sheet of construction paper equal in size to each frisket sandwich. Then, I dop these frisket sandwiches into their respective openings, run masking tape around those openings to cover up the seam, and then I paint.

Gordon
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Old Feb 23, 2012, 02:21 AM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,427 Posts
A couple of long nights of work. First, I soldered up the equipment. I changed my mind and skipped the BL motor due to the space problems with fitting a YGE controller on the side of the nose. I used a Vapor gearbox with a Cub motor instead. Quite a while was spent soldering everything up.
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Old Feb 23, 2012, 02:26 AM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,427 Posts
I took a detour and tried an alternate fuselage. This one is made from 6mm thick bead foam. I enlarged the thickness of the internal bracing, which can be seen by comparing to the Depron version at the top. The bead foam skeleton dropped the weight from 1.2g to 0.7g. Covering one side with some scrap mylar demonstrated that it would be stiff enough, especially after covering the other side. In the end I decided I didn't like the bumpiness of the mylar over the bead foam. However, I may revisit this in the future for other planes as a weight savings technique.
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Last edited by Gordon Johnson; Feb 23, 2012 at 08:05 AM.
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Old Feb 23, 2012, 02:32 AM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,427 Posts
Multiple steps later the fuselage is done (using the Depron skeleton). Final weight for the fuselage including covering and paint is a satisfyingly low 1.7g.

Here are all the parts so far. At 3am I messed up one of the mylar coverings for the rudder when it tore when I was starting to pry up the edge of the frisket paint mask (they really don't want to get started). That was a sign I should go to bed. I'll have to do that mylar covering again and then proceed.
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Old Feb 23, 2012, 02:40 AM
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Minneapolis, Minnesota
Joined Jul 2007
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Looks good! How about building me one? :P
Jay
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Old Feb 23, 2012, 01:11 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,427 Posts
Quote:
Originally Posted by Faethor View Post
Looks good! How about building me one? :P
Jay
Jay,
Glad you like it. I can't find much time to build my own models, let alone for others. I know you were kidding. However, feel free to build one. Pretty much the plans are in the first post, just enlarge to 13 inch span. The painting templates are shown superimposed over the skeleton framework.

Gordon
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Old Feb 23, 2012, 10:04 PM
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Minneapolis, Minnesota
Joined Jul 2007
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I'll take you up on that Gordon - when time permits! I now know what I'm going to build and have basic plans, and that's (ready now?) "Half the battle!" LOL I'll be covering it in tissue so will probably go with a bland yellow w/black trim..

Jay
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Old Mar 02, 2012, 10:23 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,427 Posts
A week and a half later ...

I finally have time to work on the rudder. Just gluing the two different colors of mylar together, then two different colors of painting, cutting it out, etc took over an hour and half.

Anyway, now I have the rudder, from 2mm Depron, which matches up nicely with the 6mm Depron fuselage. Now I have all the airframe pieces.
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Old Mar 04, 2012, 11:50 AM
Aircraft Designer Guy
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Melrose, MA
Joined Jul 2005
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Looking good Gordon.

-A
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Old Mar 22, 2012, 11:27 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,427 Posts
It's been three weeks with no progress. Well ... I tend to work on planes in small 15 minute bits of time between kids homework, shuttling kids to activities, etc. However, this is the most complicated mylar covered skeleton plane I've done yet because of joining two different colors of mylar together, two different colors of trim painted on the tail, etc. So, I kept making mistakes late at night or when rushing to quickly do a step between family duties, etc.

Yes, what you see are four rudders. The first was fine, but the stripes didn't line up on the two sides. So, one side would not have lined up with the stripes on the fuselage. The second one I got the stripes on both sides wrong and neither lined up with the fuselage. The third would have been ok, but I accidently printed the previous step and cut out openings through the mylar.

Tonight my wife had her book club, and I actually got some uninterrupted time to work on on the Citabria after I got the kids in bed ... and managed to make a rudder with no mistakes.
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Last edited by Gordon Johnson; Mar 22, 2012 at 11:42 PM.
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