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| Giant Scale Aircraft Discuss Giant RC Scale Aircraft. |
Topic Review (Newest First)
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| 12-09-2013 03:06 PM | ||
| mwavesdave |
Re: 33% J3 Cub to be restored and modified... I'd fly with no washout. Don't stall it low, get it up high, and see how it recovers. If, and I'm 99% sure, it recovers just fine, all on it's own, great. If not, you can induce either with the slight up ailerons on both, as the weblink I sent suggested, or shorten the forward struts just slightly, which will induce the washout as well. Doesn't really matter who's kit it is, and no manual required. Look to any other builds of Cubs, and see what makes sense for wing attachment, which I've previously discussed. CG on any constant chord wing, start with 33%, and go from there. Use washers for inducing 2 degrees down thrust, and right thrust, and experiment from there. Fly without a cowl, till you're totally happy with the setup, then build cowl to suit that! The slight undercamber is normal, and more scale. Even the Hawker Hurricane had a very slight undercamber the last 18 inches or so of the trailing edges, and while not totally flat bottomed, it's still a Clark-Y, with an H designation after. Remember, the whole point of the washout is for a smooth stall, at the root first, nothing to do with producing additional lift. Low speed aileron effectiveness on something like a cub, especially that big, isn't a whole lot. That's what Rudder is for!! I've flown the real Cub enough, along with Citabria's and Decathelon's to know, you'd better have good feet and keep on the rudder! |
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| 12-09-2013 11:54 AM | ||
| Struts1 |
Re: 33% J3 Cub to be restored and modified... Thanks Dave for all this neat aerodynamics 101 info, case with my Cub is that, I still haven't been able fully establish who's kit or plans it's actually built from, as you know 99% of the times all this info is on the plans or in the instruction manual of the kit. Most models have built in washouts In there wings and you are right Clark Y airfoil wouldn't need it if flown as supposed to be in this Cub's case but again but by looking at the airfoil it looks close to Clark Y yet it's different as it seems to have tiny bit of under camber on the bottom near the trailing edge. I also looked at the 1/4 Cub wings I have from BUSA Cub n it does have 2 degrees of washout built into it. So just to be on safe side I'll add 2 degrees of washout on both wings so this way it's there. I remember when Connie's wing was being designed it's scale tip airfoil generated enough lift with out need of adding any washout but it was still added by 2 degrees just to prevent it from tip stalling if it may ever occur. I will be ordering few books on aerodynamics and aircraft designs plus one on fluid mechanics to keep as reference and to read and learn more from through Amazon.ca |
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| 12-09-2013 10:58 AM | ||
| mwavesdave |
Re: 33% J3 Cub to be restored and modified... http://www.modelaviation.com/washout Perfect link for RC birds, specifically dealing with washout. Great info. |
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| 12-09-2013 09:57 AM | ||
| mwavesdave |
Re: 33% J3 Cub to be restored and modified... You're worried about tip-stalling a 1/3rd Cub? If you're flying it all all like the real deal, it will never be an issue. I built and flew a real Pietenpol Aircamper, no washout, and couldn't even get the damn thing to stall. If it wasn't forcefully held into a stall, the second you let pressure off the stick, nose would drop, and she'd fly again, never dropping a tip. This is aerodynamics 101, everything in aviation is a compromise in design, in order to meet a set of performance requirements. Read up on the development of the Spitfire wing, for example, you'll learn a lot of good info. I've heard RC guys complain about RC Spitfires tip-stalling badly. That's why they need washout, the wing was designed for speed, not puttering about just over stall. A thick Clark Y airfoil, with a thick chord, doesn't need washout. You can put 2-3 Degrees in Max, if you really really wanted to, or were doing a clipped Wing Cub for aerobatics, maybe, but I doubt you'd ever notice the difference, unless for some reason you forced it into a prolonged stall, didn't let go of the sticks, and fiddled with the ailerons. A caution, if you're scratchbuilding performance aircraft, you really need to know all this stuff inside out, to best ensure successful flights and handling. "From the Ground Up" is a great book that can get you started, and there's tons of good info out there on Aerodynamics. The world of designing and building aircraft, RC or full sized, is all about doing tons of research first, cutting parts after. Air, unfortunately, isn't scale, it's just air, and behaves the same no matter how big or small the aircraft is, so that's an added factor when it comes to RC. Hence why a lot of the really good flying scale kits, such as Top Flite, have made concessions to scale, in order to ensure it actually flies. |
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| 12-08-2013 12:21 PM | ||
| Struts1 |
Re: 33% J3 Cub to be restored and modified... Will be restarting resto on the wings again, will be getting some wood today for spar segments, some triangular stocks, some hard wood blocks for aileron hinges. Does these big Cubs have any wash out built into the wings?, reason is, I doubt these wings have it.... |
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| 12-08-2013 12:17 PM | ||
| Struts1 |
Re: 33% J3 Cub to be restored and modified... Quote:
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| 12-05-2013 04:34 PM | ||
| machzx |
Re: 33% J3 Cub to be restored and modified... Post from your cell anyway People can blow up on their screen |
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| 12-04-2013 03:43 PM | ||
| moo |
Re: 33% J3 Cub to be restored and modified... Quote:
better yet install Ubuntu instead of windoze or make the machine dual boot |
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| 12-04-2013 03:27 PM | ||
| machzx |
Re: 33% J3 Cub to be restored and modified... Cookies and old files Erased programs |
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| 12-04-2013 02:50 PM | ||
| machzx |
Re: 33% J3 Cub to be restored and modified... My PC gets so full of bs sometimes I have to clean it out Is that the case here? I have it formatted and start over |
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