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Building Tips and technical articles. => Building techniques => Topic started by: Keith Miller on June 14, 2013, 09:55:20 PM
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Getting back into control line and looking for a good transition into stunt, I came across the Hobo (Model Aviation Aug 2012) . I wasn't prepared to drop $150 on a kit, and it looks similar to a Tower Uproar kit I've got. Hmmm.
So here starts the bash of an Uproar into what I'll call my Misfit. The Uproar is boxy and gives me a starting point with a fair supply of wood…
Oh, and this will be electric powered.
Since the Uproar's dimensions aren't suited for stunt (stubby), I started measuring some other CL stunt plans that I'd collected to see how I would modify the wing and tail to set the aspect ratio and tail moment. The goal is to use the wing as-is, changing only the flaps and tips. I also referenced Wild Bill Netzeband's "A SUMMARY OF AERODYNAMIC AND GEOMETRIC DATA FOR 101 C/L PRECISION AEROBATIC OR STUNT DESIGNS, ACTIVE BETWEEN 1946 AND 1996" which seems to be an excellent design tool.
Using SolidWorks, I overlaid a simple sketch on top of an Uproar scan and started adding tips, reducing flaps, and moving the tail around until the dimensions and factors fit within many of the averages that Wild Bill summarized. SolidWorks can take a simple sketch and provide a quick surface area, so coming up with "K" (Tail Volume Coefficient) was quick. My "K" comes smack dab in the middle of Wild Bill's average.
Next came the chore of figuring out how to modify the Uproar into a Misfit.
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Doing some research in these forums, and using MotoCalc, I settled on an ePower setup of an Arrowind 2832-05, 4-cell LiPo (2700 mAh), a Castle Ice Lite 50A ESC and a Hubin FM-9 timer. MotoCalc has proven a perfect prediction tool in the past. In this case, on a 12x6 prop, this combo should give me 5.2 sec laps on 60' lines (give or take…).
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The first bashing step was to figure out how to fit and mount the ePower systems up front.
Using a pdf of the plan (amazing how accurately a scanned pdf can be used to measure parts!), I modeled the fuselage and key formers.
I wanted a way to insert batteries (yellow) without taking too much apart, so this tray will fit just above the wing LE, and the battery will butt up against the spar with the center wing sheeting cut away.
A big ol' carved canopy will snap down with rare earth magnets to cover the hatch. The Hubin Timer (green) was positioned to access the programming port (top connector). The "start" button will mount towards the bottom. The Ice Lite 75 (not the 50 I first posted) is in pink.
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The control linkage took me quite a while to figure out. One decision was whether or not the elevator horn would be internal or external. Nice thing about 3D CAD is that I could see that the elevator linkage simply wouldn’t fit inside the stock Uproar fuselage with the elevator set to tail moment that I needed (just too skinny back there).
I'll also have to modify the former that originally butts up against the wing TE. It will have to be hogged out to clear the flap horn and torque rod. Another nice tool in SolidWorks is the ability to determine where parts conflict.
Tom Morris made my flap and elevator horns custom to fit the dimensions that fit the Uproar solution.
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Started piecing things together. I fitted up the bellcrank mounts between the existing R1's. Odd shapes, but it fits between the ribs and clears the ball link.
Basic wing assembly is started.
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One picture at a time, I guess...
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First attempt at a magnetic building board - I like it!
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The adjustable leadout guide is together.
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I suppose it depends on how sensitive you want it to be, but I'd think about moving the bellcrank to flap control horn in a bit closer to the pivot.
Looks like a fun project.
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I suppose it depends on how sensitive you want it to be, but I'd think about moving the bellcrank to flap control horn in a bit closer to the pivot.
Absolutely! Controls are seldom too slow (can fix with a wide spacing at the handle, which hurts nothing), but very often too quick. A narrow handle spacing is not good, because you lose precision. n1 Steve
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Keith,
Looks good. I have a copy of Solid Works but haven't had the time to get into it.
Thanks for the free publicity for the "Hobo". As you know, I encourage kit bashing and I show either internal or exterior controls, but I recommend the external controls because it makes changing controls ratios simple.
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I suppose it depends on how sensitive you want it to be, but I'd think about moving the bellcrank to flap control horn in a bit closer to the pivot.
Good point - thanks!
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Thanks for the free publicity for the "Hobo". As you know, I encourage kit bashing and I show either internal or exterior controls, but I recommend the external controls because it makes changing controls ratios simple.
Keeping your concept in mind, I kept the elevator external, and I'll have access to the bellcrank and flap through the top of the fuselage. The canopy will be removable, and I'll have a cut-out above the flap horn.
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Well, finally some progress....
Finished the wing a couple of months ago. I employed a single-wire hinge for each flap to ease with covering and painting. Saw that idea in this forum under the "finishing" section. It also makes alignment of the entire hinge set a lot easier with a single wire. The tip plates are probably a little on the fat side, but I wanted to make sure I could get my hex wrench in to adjust the leadouts. I'll go thinner next time around to save weight.
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Those fat tips with the hinge wire captured ...
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Removed a plug from each fuselage side through which I could pass the flap horn and bellcrank as I slide the wing into the fuselage.
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Those fat tips with the hinge wire captured ...
Hinge wire? In the wingtip?
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Using SolidWorks to lay out the control linkages (last year sometime during the "design" phase), I was able to actually model the control movements. I can grab a leadout or the pushrod and move the entire control system. This allowed me to place the pushrod exit hole and account for the up/down translation as the elevator moved. Once assembled, the pushrod actually exits the hole exactly as planned with clearance all the way around.
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Hinge wire? In the wingtip?
Yeah - poor description there, I know.
The hinges are all pinned with one wire running the length of the flap. The wire exits the wing tip at which point it's bent back into a hook and pushed back into the tip to hold it in place.
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The biggest pain in the rear was figuring out how to put an access panel on the top of the fuselage to allow for future "changes" of power systems and controls. The Hobo (from which this bash was conceived) keeps the control linkages accessible.
So I made a top deck which is semi-permanent (pinned into the firewall, screwed into the fuselage sides at the rear above the wing TE, with magnets in between to keep the center section firmly stuck down.
The battery access hole is in the front section of that top deck, and the balsa block canopy covers that up with a tongue and magnets.
Between flights I need only pop the canopy off and strap in a fresh battery.
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Beautiful CAD work! ...and with color and texture.
My dream is a vintage Drafting machine and table with a drawer full of accessories.
I'm such a Luddite, I could never keep up. :-\
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Framework is complete, ready for some Ultracote on the wings and Rustoleum on the wood.
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Finally finished
Took it out for maiden flights today. While the motor power is perfect for 5.2 sec laps, there was some trimming to be done with tip weights, line rake and such.
I think I'll keep it...
When I get it trimmed out right, I'll spend some time on a cowl and an actual color scheme.
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What was the final weight My RC uproar is a porker.
Steve
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Steve - it came out 3 lb 10 oz (58 oz) with battery installed. The fuselage sides and ribs are heavy. The wing loading came out just under 13 oz/sq ft which falls in between my Cardinal (11.9) and my Tutor II (15.5). I'm happy with it.
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You did a nice job, I like it.
Steve