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Old May 28, 2004, 01:36 AM
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Hobby Lobby Super Cub--clipped wing

Hi guys,

Finally gave in and ponied up all of $32 for the kit. Really nice for the money, as the die-cutting for the ribs is nice and clean, and all the wood is really straight.

I figured it might be a little sedate for me, but I thought a clipped-wing version with big ailerons and a good brushless might be just the thing. My favorite gas plane (still hanging in the garage) is a 6' span Carl Goldberg Clipped Cub with a .91 4-cycle that was an absolute giggle to fly, and I want to re-create that in a smaller electric version.

Plans are for a Razor 400 in a GWS "C" gearbox swinging a 9x7 prop, powered at first by 3s1p Etec 1200s (thanks again, Shaun, over in Power Systems). A set of Trexler wheels/tires are a must too.

I've read all the horror stories about the wing folding, so I'll mount the struts more securely and go with either carbon-fiber dihedral braces, or just a stronger grade of plywood (the ones in the kit are light but flimsy). Looks like the cabin will need some beefing up, so I'll back the balsa pillars with bass wood. I'm going to really make an effort to strengthen only where necessary.

Here's progress so far. I'm going to use one aileron servo per wing. Outboard strut mounts will be plywood tabs that will glue in perpendicular to the ribs...you can see the balsa mounts I've glued in to accept them. Struts will connect to tabs with steel clevises, most likely. Wing feels nice and strong, even without LE sheeting.

I'm thinking of zero dihedral with the ailerons. Do you guys think this is good, or should I give it just a touch?

--Doug

P.S. I "clipped" it by one rib per panel, which takes the wingspan from 46" to about 41".
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Old May 28, 2004, 02:03 AM
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Here's my photo for inspiration. It belongs to Giles Henderson of Illinois:
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Old May 28, 2004, 10:30 AM
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Newton, NJ
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Very nice solution to the aileron addition. It looks like it was meant to be built that way. Personally, I'd give it about two degrees of dihedral, but I'm no aeronautical engineer. A flat wing would be a little easier to build true and straight, though.
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Old May 28, 2004, 11:16 AM
Around the World
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Scottsville, KY
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Very nice job on the wing mod. Keep us informed.
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Old May 28, 2004, 11:56 AM
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Thanks for the words of encouragement

I suspect a lot of the wing failures were due to inadequately secured struts, or people just leaving them off entirely, so a few simple mods here will be just the ticket.

Matt--good call. I took a good look at my gasser Cub, and it looks to have a couple of degrees.

I like how the little mid-strut thingies (I know there's a more precise term) plug into little pieces of aluminum tubing glued to the spars. Pat Tritle, if you're out there, nice engineering job!

I'll try for better pictures in the future. Whenever I photograph balsa against a blue background, it makes the wood look old and stale...but it's not!

--Doug
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Old May 28, 2004, 02:29 PM
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Doug,

Nice job, and an interesting mod for the dear old Super Cub! I second the 2 degrees of dihederal. Think it looks better, and should add just a touch of stability if you ever want to slow her down and relax a bit. I like your aileron installation, and ideas for strut mounting. Keep us posted!

Happy Flying!

AmpAce
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Old May 28, 2004, 02:35 PM
Lookin' Good. Real Good.
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London, Canada
Joined Aug 2002
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Nice work!

Also, when you have no dihedral and the plane is flying away from you or towards you, it looks like there is anhedral, which if other people see it will accuzse of of building upside down!! Putting in a few degrees eliminates that look.
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Old May 28, 2004, 05:04 PM
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Okay, a couple/few degrees it is. Rather than dust off the ol' college trig textbook, I'll just block up each wingtip by the same amount till it looks "right."

BTW, the laminated wingtips are both light and strong. Hadn't used this technique before in a build, so I researched it and decided on using 3/4" insulation foam as a template for forming. Once I soaked and glued the strips together, I was able to just Scotch-tape it to the foam until the glue set up. Also put tape on the cut surface of the foam so the white glue wouldn't stick to it. Worked like a charm.

--Doug
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Old May 28, 2004, 05:09 PM
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One more shot of Henderson's plane, inverted with the engine off!
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Old May 28, 2004, 07:30 PM
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Amazing photo's! I had the opportunity to see a pilot perform a kind of "flying farmer" routine with a real clipped wing Cub several years ago. Did lot's of loops, rolls, inverted flight, bouncing one or both wheels off the runway, flying sideways, flying like a beginner, etc. I don't think he ever got more than 300 feet above the ground! Very impressive!

AmpAce
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Old May 29, 2004, 12:40 AM
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That sounds completely cool, AmpAce. I would love to see a routine like that in person. These Cubs do things they just shouldn't do!!!

Here's tonight's subassembly, the wing center section. Using c-f rods as dihedral joiners, and the one for the main spar extends to the second rib, where the kit's ply joiners only go to the first. I know the diameter of the c-f rod looks spindly, but the stuff is so strong that it will be more than enough, esp. with the sturdy struts.

Since I'm only going to have a little dihedral, I can get away with the straight rod joiners. No skylight for me, as I want the extra strength here.
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Old May 31, 2004, 06:40 PM
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More progress. Building the second wing half is a little monotonous, but at least it goes faster because you know the drill, and I didn't have to contemplate sizing the ailerons etc.

The wing turned out really strong! The one substitution I made was replacing the 1/16" leading-edge sheeting with some different wood, as the stuff in the kit was kinda heavy and fibrous, though hugely stout.

I blocked the tips up about 5/8", which gives maybe half the kit's recommended dihedral. Anybody remember trig? Each wing panel is about 18" I'm just curious what is is in degrees.

Little trays for the servos are 1/64" ply glued to 1/32" balsa sheet. Put the servos a little inboard, rather than right in the middle of the aileron to lower polar moment about the roll axis. With these big ailerons, she should roll nice!

Close-up of spar shows how c-f dihedral brace fits inside spar. I put little blocks of wood at the ends for a snug fit against the upper main spar, which preloads the whole thing for positive g's.

Oh well, back to building!!

--Doug
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Old Jun 01, 2004, 12:49 AM
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Welp, got one side of the fuse framed up, and I'm a little disappointed in the cabin header for the wing. It's the same light, cheesy plywood as the stock dihedral braces, and it kinda de-laminated when I punched it out of its home.

Actually, it's a piece I wanted to modify, as the lower section needs to be 1/16" narrower on each side, to allow for the bass wood strips I'm going to put on the inside of the front cabin pillars. So I made a new one of heavier ply, and its "fingers" extend a little farther down the pillars too. It's a little overbuilt, but I may put some lightening holes in it once I find out where the wing dowels go.

Happy Memorial Day!
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Old Jun 04, 2004, 12:40 AM
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A little more build progress on the hyper-Cub.

Fuse is coming together nicely, and I'm really pleased with the strength of the header assembly. The bass wood strips extend down to a strong junction of 1/8" pieces, which I've further reinforced with a gusset. I'm going to use cabin doors on both sides, which will shore it up even more.

If this thing breaks during some wild aerobatics (giving new meaning to the term "snap roll" ), I won't hold the kit designer responsible!

The bottom of the fuse really lends itself to a large hatch just aft of the landing gear blocks.

Whole assembly in last picture weighs in at about 4.2 oz. With any luck I can keep her AUW to 18 oz.

--Doug
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Old Jun 04, 2004, 01:00 AM
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Looks great. My kit (ok, my girlfriends) arrived today. I plan to build it completely stock. Olympus GB, sp400, lipos. Does anyone fly this bird with the sp 400 and olympus?
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