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Old Jul 16, 2016, 12:25 AM
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United States, WA, Snohomish
Joined Mar 2001
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Build Log
50+ Build Off-- Sterling J-3 Cub (.15-size oldie)

I normally don't build much in the middle of summer, but I missed some seriously good benchtime this spring due to a medical sabbatical, so I'm going to play catch up now and build during the twilight hours of our long summer days up here in the northern lats of Seattle. Hope the late afternoon sun doesn't lure me outside too often, lest my build project languish neglected-- I've been known to fly until right up to 10PM this time of year!

My entry for the "50 Plus" build-off is this musty old kit I dug out from under my teetering kit stack, because it has waited over half a century to get cracked open, and it's high time this old bunch of sticks got made into an airplane. It's a Sterling J-3 Cub, with two-function controls, balsa spars and functional struts, and enough dihedral to keep the wingtips out of trouble on a crosswind landing. Tonight is the unboxing, and sorting all the parts for the build.

I plan on powering this one with an old Fox .15 I have been hanging on to for far too long. It's a good runner, on the bench, anyway. I hope it doesn't turn out to be too much power for this 54 inch span model. I was half-tempted to try it rudder-throttle only, but the field I fly at has tall trees in the vicinity, so to stay out of trouble I will add a small elevator tab just to be safe. Covering will be.... doculam and tissue? I haven't tried that yet. This may be a good opportunity to try it out, and I do want that tissue look for this one.

Now to see if I can finish this project in the remaining time left for the build-off! Think I can do it? Let's find out!
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Old Jul 16, 2016, 02:14 AM
Sundancer is offline
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I like real wooden aeroplanes!
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Thanks Don; entry posted, should be interesting to see all those sticks and die cuts finally getting stuck together after all those years in the box.
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Old Jul 16, 2016, 07:12 AM
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Ilkley, West Yorkshire, UK
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Hey Don, you've hit on about the greatest therapy to assist recuperation - model building! Low on physical strain, high on mental exercise.

I'm really interested in this build, as it will be good to compare the Sterling design to the Jack Headley version I am building for the Complete A Project Build Off: http://www.rcgroups.com/forums/showthread.php?t=2647430

The Headley version is 2" smaller on span, and I have fitted ailerons partly because I wasn't convinced that 1" of dihedral on each panel was enough (and I'd built the wing before I thought that) and because the club field has a fairly constant and gusty wind and I have found that ailerons make a model infinitely more comfortable to fly in those conditions.

So pile on ahead with it!

Which reminds me, I really need to update my log now that covering has commenced.......
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Old Jul 16, 2016, 06:05 PM
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The Sterling J3 is a very nice semi-scale model that flies extremely well, like most other Sterling models. I made one in 1966 with a Command Master RC and a Cox .15. But beware of weak wing center section. It wasn't designed for modern engines or high speeds so some reinforcing is a nice thing to do before is too late. Also Sterling used the cheapest plywood then available which was very weak.
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Old Jul 17, 2016, 12:18 AM
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I built this one from an original kit in 1995 and an OS max 15 engine. You might want to use aircraft ply on the wing spar near the wing center section, I have some recollection of mine having a questionable plywood doubler. The rudder area is small relative to the dihedral they recommend, a typical FF arrangement that had good stability as a rudder only model with small rudder inputs for control. When you fly with servos you'll want to be careful with that small rudder and gobs of dihedral, my model was barely dutch roll stable and a sharp rudder input could easily flip it over.

Steve
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Old Jul 17, 2016, 01:58 AM
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@ Colonel Blink: Couldn't agree more.... model building is the greatest therapy on earth! Relaxing, enjoyable, and unlike full-scale homebuilts, you can do most of it while seated comfortably at the building bench. I did see your thread on the Headley Cub, and there are some similarities (like the extensive use of sheeting). Mine will not need ailerons, with a whopping 3" of dihedral in each panel. Our weather here in the Pacific Northwest is usually calm to light breezes, so I can get by with nudging it along down final without getting knocked about too much.

@Eduardo: I did notice the pithy plywood in the kit, and I will be swapping out the wing joiners with some quality aircraft ply. Also, the spars are balsa, so I also plan on making my wing struts functional. No loops or snap rolls with this model! I plan on tooling around at partial throttle in slow cruise mode, and steering it gently around the sky. The elevator will be on the left side only and will be small like a trim tab, and if I have my way I will not need to touch it for much of the flight... just use it when I have to carve a tight turn.

@Steve: I saw your earlier post in this thread, where you cautioned about the small vertical tail, which makes total sense to me when I look at it in pictures. The stab is enormous (like a free-flight model should be!), and it would just look more "right" if I enlarge the vertical tail a bit. All that dihedral will want a larger TVCvert to compensate, I'm sure. I'll also program some dual rate on the rudder, in case it dutch rolls too much with rudder input. BTW, thanks for including pictures of your model here. Nice job!

Tonight I built my wing panels. I cut some new ribs to replace the missing ones, and fussed a bit with lightening the wing tips as much as I could, to keep the polar moment of inertia down as much as possible (this can also contribute to dutch rolling, I have found). Tomorrow I will build the center section, and join the wing panels. I gotta say, the die cutting on this kit is not too bad! Are you surprised to hear that? I am!! Must have been an early kit in the production run, when the dies were still sharp.
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Old Jul 22, 2016, 01:14 AM
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I got the wing panels joined tonight. The ply spar joiners were a bit of a fiddle, having to guide them through the rib cutouts each time I installed the outer panels to the center section for a check fit. 3" dihedral under each tip doesn't look too ridiculous at this point, but should be plenty for quick rudder response in the turns.

I plan on making a bolt-down wing, with plug-in dowels up front and nylon bolts at the trailing edge, so I will leave off the center section sheeting until that is done.

On to the fuselage!
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Old Jul 22, 2016, 01:40 AM
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Good progress there Don.....seeing that the Sterling Cub has 3" dihedral in each panel, and the Jack Headley version has only 1" makes me glad that I decided to convert mine to ailerons! I must admit that I am seriously considering also converting mine to a bolt on wing, even though the wing is complete and covered - the work will have to be carried out from the underside. Will your trailing edge bolts be going straight through the TE?
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Old Jul 22, 2016, 11:02 AM
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Colonel,

The bolt-on wing will require a plywood hard point at the trailing edge (can't trust the balsa TE stock to do the job). On my Velie Monocoupe, I got away with just sheeting the TE stock with some 1/64th ply, and it has held up well. The nylon hold-down bolt needs a ply plate in the fuselage to receive the bolt.

I haven't had a chance to advance-engineer this yet-- hoping it will be made obvious to me once I get the fuselage built and I see what the wing saddle has to offer.
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Last edited by dgliderguy; Jul 22, 2016 at 11:13 AM.
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Old Jul 22, 2016, 11:39 AM
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The cub looks to be sized about right for a single 10/32 bolt on the center line.With some 1/16" ply for a top plate.
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