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Jan 12, 2021, 01:03 AM
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Build Log

1/4 scale Citabria - Bud Nosen "kit"


Over the next few days, I'll be posting the build log for my 1/4 scale Bud Nosen Citabria from an A & A Industries kit. This build log was originally created back in 2007 and was documented on my website but several years ago I removed those pages to make room for other content, so now it will live here. Since then, the Citabria has flown several times until its last flight that same year which ended in an unplanned off-field "landing" with moderate damage. More on this towards the end of the build log. This build log will be followed by a repair log that is finally happening now, 14 years later...

This A&A Industries kit was discount "lumber yard" of what I would call wood scrap seconds. You've all heard of die-smashed wood, and this kit had plenty of that. Most of the ribs looked like they were cut out with an over-grown fingernail. But that's not the worst of it. All the 3/32" ply pieces were die cut half way through on the back with some other pattern, so all of that ply was DOA. I ended up replacing at least 50% of the kit wood if not more.

The basic fuselage structure is a straight forward build. Left and right fuselage sides are framed up and then brought together with the cabin bulkhead, formers and cross members. The structure becomes very rigid once the tail end is brought together and the firewall is added. The bulk of the truss fuselage is 1/4" balsa stick, but in hindsight, I should have replaced the fuselage longerons with 1/4" x 1/4" spruce. I did however add 1/32" ply gussets to tie the vertical and diagonal sticks to the longerons.

The kit manufacturer provided two pieces of 3/32" cheap door-skin plywood (to be laminated together) for the firewall. This was replaced with a single piece of 1/4" birch aircraft plywood (5-ply).

Unfortunately the first few photos are pretty low rez from the original website archive - I haven't found their higher rez source files yet.
Last edited by Mucksmear; Yesterday at 02:45 PM.
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Jan 12, 2021, 03:40 AM
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After completing the fuselage per plans, I had second thoughts about the strength of the cabin side frames so I ran carbon fiber tows through the wing saddle rails and down the cabin uprights FC1 and FC2. The forward pair (left and right) are tied through the upper left and right corners of fuselage former F2, while the aft pair run to the bottom of the fuselage sides. The carbon tows are sandwiched between the vertical members of the cabin sides and an extra set of Lite-ply doublers
Jan 12, 2021, 04:07 AM
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The attachment points for lift-struts are on top of the 1/4" ply LG mounting plate. The lift-strut ends are 1/16" sheet brass and slide into a pair of boxes made from a stack of 1/4" aircraft ply. The strut is secured with a bolt that goes up through the LG, the 1/4" ply LG mounting plate, and ply box. The ply boxes extend through the aft corner of ply LG gusset and fuselage sides and end flush with the outside surface. The kits stock dural LG are not scale and have an overly broad chord where they meet the fuselage. The non-scale LG puts the lift strut attachment point above the LG in an equally non-scale manner.
Jan 12, 2021, 01:53 PM
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Wings


The wings are very straightforward. I cut lighting holes in most of the ribs. I had to modify the wing tip a little. Following the plans resulted in a wing tip with a high angle of attack with respect to the rest of the wing (the L.E. sweep that occurs between the last two wing ribs as shown on the plans is excessive).

Standard aileron servos, 1 in front of each aileron, fit nicely and completely within the wing when mounted on their sides. These are removable through a hatch on the lower surface of the wing. The pushrod to the ailerons have a nice straight run with no bends or kinks

I wish I had added flaps although they are not needed.
Jan 12, 2021, 02:22 PM
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Removable Stabilizer


I decided to go with a two piece removable (plug-in) horizontal stabilizer and an integral fin. The vertical fin's TE was replaced with a longer one that extends down to the bottom of the fuse, sandwiched by the two large triangular gussets that form the aft end of the fuselage sides.

The plug-in stabilizer uses load bearing 1/8" steel rod to support the stabilizer halves. Wood dowels at the stabilizer LE and TE plug into 3/8" brass tubes. Functional tail bracing is from 2-56 rods with threaded clevises that attached to through-mounted brass tabs on the fin, stabilizer and fuselage underside.

2 standard servos and pushrods, one for each elevator half, and 1 standard servo with pull-pull cables for the rudder.

In practice it seems to work pretty well. My shop is small and I don't have an SUV or a trailer. I store and transport the Citabria with the stabilizers and wings removed. To remove the stabilizer I only need a flat screwdriver to pry the clevis off of the stabilizer mounted tabs. The tail bracing stays attached to the fin and fuse and just swings forward from the fin or backwards from the fuse bottom. A bit of tape keeps them stowed and out of the way.
Jan 12, 2021, 03:08 PM
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Folding Wing Struts


The plans call for simple but functional hardwood lift struts (without jury struts). While researching this project I stumbled across Cub Man's article on folding struts for his 1/4 scale Cub. Citabria struts are a bit different in the details, but for me these were close enough, functional and good looking. Go to www.thecubden.org and look for the "Folding Struts 101" link under the "J3/L4 Related" tab on his site. The photos below show the fuselage and wing mount ends of the struts without the streamline aluminum tubes
Jan 12, 2021, 06:13 PM
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3 piece wing


The stock 3-piece wing consists of the left and right panels plus the center section that bolts to the top of the fuselage. I used another tip from Cub Man's site was using a storm door turnbuckle brace for wing retention. A threaded rod is permanently mounted in each wing sticking out the root and into the center section. One has left handed threads and the other has right handed threads. A threaded coupler joins the two, pulling the wings in tight against the center section.
Last edited by Mucksmear; Jan 12, 2021 at 06:20 PM.
Jan 12, 2021, 06:35 PM
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Power


The original plan was to use a Zenoah G-23 and I had in fact completed the engine installation as shown here. With my little kids in tow, I found myself flying more "grab-n go" electric and revisiting the slope soaring sites. So.... I sold the G-23 and a few other things on eBay to help pay for the new power system: Torcman TM430-30 10pole outrunner / 30 x GP3300 NiMh / Jeti Advanced 77-3p Opto esc / APC 20x8.
Jan 13, 2021, 04:31 PM
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Ready to cover


Windshield pattern is fine tuned in cardstock. Fully framed and Torcman outrunner mounted, ready to cover with my last rolls of Super Coverite. Still on the stock gear which btw, are not strong enough once the flying weight gets up near 18 pounds. I ordered new LG from TNT to support the 18-20 pound flying weight as well as provide a little more clearance for the 20" prop.
Jan 13, 2021, 04:44 PM
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Ready to paint


...And this brings us up to date with the beginning of my Citabria Conversion thread from 2007:
https://www.rcgroups.com/forums/show...ria-conversion

New LG from TNT installed, Strut's completed with streamline tubing and jury struts. Ready for paint.


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