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Oct 06, 2014, 12:38 PM
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Build Log

OneSheeter #17 OSC140 Cessna 120/140


The genesis of this build was the Aeronca Scamp, which got me into building the OSA Aeronca chief. While doing research on it, I stumbled across the early Cessnas, and was intrigued by the rounded fuselages. I had had good success in doing the rounded bottom fuse for the OSMulligan based on Howard's Mr. Mulligan racer, so figured I could take learning from that plane and do another. Plane was designed in Sketchup, first for another half sheeter at 24" span, but when I built it, I found that rolling the Readiboard was just too tough for that small a plane and shelved it. Recently, I was in the mood to tinker again, so upsized it to a full Readiboard size, at 33.5" span. This size was much better. Rolling the foam was easier, more room for gear, and works with the gear I used for most other onesheeters: 1700 kv 24gm motor, 7x6 prop, 2s 800-900mah packs, etc.

Finally got video on flight day #3. (first two were definitely developmental days! by day 3 I had it all sorted out for flying) Since then I have put more time on her, and find her a really pleasant flyer. She loops, aileron rolls easy as pie, and I even flew her inverted for a while. (Not very scale, I suppose as I doubt any were ever acro certified!)

osc140 10-10-14 (3 min 25 sec)
Last edited by springer; Nov 10, 2014 at 10:25 PM.
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Oct 06, 2014, 12:49 PM
Jim
I likey
Oct 06, 2014, 12:51 PM
Jim
Do a Aeronca C3! A fuse only a mother could love!
Oct 06, 2014, 01:00 PM
treefinder
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Jim: I have looked at the C3, and just can't bring myself to do it, it's just too ugly!
Oct 06, 2014, 01:00 PM
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Here are the templates I used to do the build. Please note that I added a couple of parts in the build process, and haven't incorporated them into the sheet yet, so there will be updates (assuming I can find space for them!) They are all small; two longerons between former 2 and 3, and a cap for the windshield mounting to fuse.
Last edited by springer; Oct 06, 2014 at 01:28 PM.
Oct 06, 2014, 01:00 PM
treefinder
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build log 1 layout
Oct 06, 2014, 01:00 PM
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build log 2 fuse

The fuse build up starts with laminating two formers that are doubled (first pic). Then glue the former #1 to former#2 subassembly. The connecting pieces for 1-2 form a T, while the ones from 2-3 have two verticals and a horizontal, like the letter pi. (the two verticals are not in the templates - they were added to make the subassembly self supporting, and if required to be a place for the battery to fit.) Once the subassembly is done, roll/form the skins and glue them to formers. (with current templates, the skins will be about 1/4" too long (circumference), so you will want to fit and trim as required. I will fine tune lengths later - but probably better to be long and trim than short!) The skins are fore/aft long enough to fit at former center of thickness. A bit tricky to glue up, maybe I should have doubled the formers, eh? I use lots of tape to hole everything together tightly as well as strategically placed T pins! While that is curing you can laminate all the layers of the gear mounting. and eventually glue them up to the sub assembly. Note the distance from the second skin joint to the slot for gear wire, as you will be cutting through the mid fuse skin to expose that slot once it's all glued up. I just marked the location of slot on fuse skin.
Last edited by springer; Oct 06, 2014 at 01:56 PM.
Oct 06, 2014, 01:00 PM
treefinder
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build log 3 aft fuse glueup and tail empennage

The aft fuse lower skin is rolled into the half cylinder, then tapered at aft end to a 180deg fold which is then glued together. This is glued to the fwd fuse assembly at the former #6. I used lots of tape and pins to insure that things stayed in place as the GG cured. the partial former (#7) gets glued to the fuse side along with the horizontal piece. Once the fuse lower is cured, I ran the guide tubes which are two pair of coffee stirrers. I twisted a skewer into one end of a stirrer, to bell it out and slipped another stirrer into the flared end. you can push this one into the other about a quarter inch. This is then long enough to run the entire length. I hot glue them in place at the correct location for each of the servo arms at fwd end and to point to rudder and elevator horns at aft. The tail wheel assembly is a bent .062" wire with "L" bend at fwd end which i sandwiched between two pieces of cardboard and slathered with GG and let it foam up and lock everything in place. Wheel was recycled from another model. Fuse aft top is now glued to the bottom. pins and tape hold everything tight. Next the H stab is glued in place (elevator is preglued/hinged to it) The V stab and rudder assembly is fitted into a slot on H stab and then glued in place. Once it's all cured, sand the square corners of top to round the section.
Last edited by springer; Oct 06, 2014 at 10:14 PM.
Oct 06, 2014, 01:01 PM
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build log 4 wing:

The wing halves and KFm5a step pieces are rolled (I used a bendfoam fixture, but they can be rolled over a table edge) to approximately the same radius. Then they are glued together using the technique first used with the OSG. (A pic showing it done is in that thread) The two halves are glued together and LE and main spars glued to the wing. Once cured, the LE airfoil shape is sanded into the wood and foam. Ailerons are marked and cut out. LE of ailerons are beveled. Wing LE and TE reinforcing members are glued to the wing assembly. I debated tabbing the wing at LE, but decided to just use screws at LE and TE, so the reinforcements are necessary. Torque rods are bent and sleeves slipped over them (the sleeves are plastic "Qtip sticks" perfect for .062 wire) A groove is cut and sanded in wing to accept them. I also glued a short length of tube to inside of each aileron for the torque rod to fit into for aileron actuation. Once the tubes are cured, the ailerons are fitted onto the wires, and the hinges (ribbon) are glued with several coats of WBPU/minwax polycrylic. More to come here as centeral servo is fitted and short control wires are made and installed.
Last edited by springer; Oct 06, 2014 at 10:30 PM.
Oct 06, 2014, 01:01 PM
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build log 5 gear:

The main gear is bent up from .078 wire (need template for this) and fitted into the slot provided . (note that the fuse bottom must be cut at the marked location to expose the slots). This took a bit of time fiddling and fitting the gear wire into the slot. I put a screw through the gear assembly and a triangular piece of 1/16" ply that I fit into the pocket after the gear wire installed. This holds the gear in place.

Rudder and elevator servos are located and installed. Popsicle sticks used as mounts. A battery hatch is cut in lower fuse. RX installed. esc wires are fed through hole in motor mount through the area on top of the longitudinal pieces in fwd fuse and into the battery compartment.
Last edited by springer; Oct 06, 2014 at 10:44 PM.
Oct 06, 2014, 01:02 PM
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build log 6 misc
Oct 06, 2014, 01:02 PM
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build log 7 misc
Oct 06, 2014, 07:49 PM
Doink-not again :)...aka Greg
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Mike, how to you find the time!
I still have the Rolston Beta to build.
Looks great! Did you maiden yet?
Oct 06, 2014, 09:52 PM
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did a semi maiden tonite, not finished with ailerons, so taped them and did a hand launch. I learned that she either needs more down thrust, less wing incidence or more fwd CG (probably a mix of all the above. With the dead straight wing, she really needs ailerons, though, so no more flying til they are done!
Oct 08, 2014, 09:24 AM
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Second flight with functional ailerons this morning before the wind came up. Reduced wing incidence, a washer's worth of down thrust. ROG was fine in about five feet, but still wants to nose up adding max down trim made for decent flight, power off glide ok but still tends nose up. CG is at the step (40%) which is aft of my liking. Gonna make new forward battery hatch and get CG to 25% and retest. The ailerons are working well, though! (Flat wing realllly needs them!)


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