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View Poll Results: What do ya think of Urban Kaos?
What a hunk of hooey!
1
16.67%
You'll be lucky if it doesn't tip stall.
1
16.67%
Eh, it may fly alright.
2
33.33%
You're a genius!
3
50.00%
Multiple Choice Poll. Voters: 6. You may not vote on this poll

My 1st scratch build, Urban Kaos.

Old 01-05-2009, 08:22 AM
  #1  
UglyNet
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Default My 1st scratch build, Urban Kaos.

I only recently got back into R/C after a nearly 20 year hiatus. Holy cow how it's changed! I first forayed into helis which I've enjoyed immensely then to flat foamies. I had a left over geared S-370 so naturally I had to build something around it. I did a quick look and found a couple of DXFs of various S400 models which looked enticing, did a couple of quick calculations, played with some scaled guestimates of models and decided to go ahead and dive in. Worst case it's radically underpowered and I just get a S400 class brushless and another ESC.

I finally decided on a model that I was familiar with from my youth. I remember seeing a couple of guys at the RC club flying Bridi Kaoses back in the 70's. Of course by then it was already a classic design and good designs are classics for a reason. I found a 65% scaled version by Joe Jopling that I decided to build. I downloaded a couple of demo versions of various CAD software and decided that TurboCAD worked mostly like I think from my days fiddling with a less than legal version of AutoCAD many many years ago. For the record, I now own TurboCAD 15.

This is the first balsa model I've built in literally 20 years and the first scratch build I've ever done. Of course I changed a couple of things and learned a lot along the way. I moved the horizontal stab up a little bit and made the elevator a little deeper to give me a little shorter moment. I also changed the design to have convetional rather than the original tricycle gear. I thought about leaving the tail wheel freely castoring but decided to use a pull-pull system through the rudder when I failed at bending wired. Along the way I prototyped a section of a thinner wing (10%) to hopefully reduce the load on the motor by reducing drag but though better of it and opted to go back to the original 14% thickness. I'm still not 100% certain where Mr. Jopling got intake air from but I built a thin chin scoop to introduce outside air into the battery compartment. Air still exits the airframe at the TE of the wing per Mr. Joplings design. When I built this wing I built it with a straight LE and tapered TE with wingtips raked back sharply. I don't have an aerodynamic basis behind that, I just think it looks cool. I think I'm going to call it Urban Kaos.

I later read about how a swept leading edge helps stability so I hope I didn't shoot myself in the foot too badly. I had to add 3/4 oz of lead to the noze to get it to balance so a future version will likely have a shorter tail. Hopefully I won't crack it up too badly on it's first flight. Now if only the weather will cooperate. A little more time with the tachometer and calculator will decide if I use the 10x7 or 10x4.5 prop on this guy.

Thanks to Joe Bridi for the base design and Joe Jopling for scaling it for electric power.
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Old 01-05-2009, 08:37 AM
  #2  
xuzme720
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I'm glad you decided to pull the stab forward, that is a looong tail! I love the wings, but like you said, i hope the are stable enough. speaking of, did you happen to add any washout to the wings? that would help with tip stalls...
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Old 01-05-2009, 02:21 PM
  #3  
starcad
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Nice job UglyNet, welcome back. It is true the original had a couple of degrees of washout in the tips. I can't remember how much and it would take me several hours to find those plans. Maybe someone else here will chime in. Great looking bird and hope you get the weather you need to maiden. Looks like it will be a fun flying plane.
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Old 01-05-2009, 06:35 PM
  #4  
UglyNet
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Thanks. I was anxious to get some pictures and do some taxi testing, get balance done, etc. so I haven't added any washout to it yet. I didn't build any into it figuring that I'd do the same thing I did with the first trainer I built (Goldberg PT25) and put in the washout by warping the wing and shrinking the covering. One of the nice things about heat shrink covering vs the tissue and dope I used on my FF and CL models before then. I doubt I'll add more than a degree or two of washout. I've also contemplated building a wing with fixed slots or a sawtooth which would look cool but be kind of a PITA to build. The swept LE is also supposed to abate tip stalls some. It can't be any worse than any of the flat foamies I've flown, right?
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Old 01-05-2009, 06:39 PM
  #5  
UglyNet
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Originally Posted by xuzme720 View Post
I'm glad you decided to pull the stab forward, that is a looong tail! I love the wings, but like you said, i hope the are stable enough. speaking of, did you happen to add any washout to the wings? that would help with tip stalls...

Thanks. If the straight LE doesn't work out I'll just build a double taper wing with a straight spar rather than a straight LE. I drew both wings and decided I liked the look of the straight LE better. I figure this one is a prototype so I expect to build at least another wing and fuse either by choice or through re-kitting.
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Old 01-06-2009, 11:55 PM
  #6  
carlosponti
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add another option "I refrain from calling you a genious but it looks like a great little airplane" then ill vote ha ha
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Old 01-07-2009, 05:48 AM
  #7  
UglyNet
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Hehehe.. Thanks Carl. I'm concerned that the little S370 won't pull it around very well but I've prototyped it in Real Flight as best I can with a scaled down version of the Super Sport, gotten the prop and motor RPM about right in Real Flight and it should at least haul itself through the air.

I'd like to get a brushless but I'm still debating of a geared inrunner or an outrunner. It seems the geared inrunners can swing a bigger prop which would make it more efficient. Since I'm not going for an all out 3D machine it shouldn't matter much. I also think that big ol' piece of windmill out front looks pretty cool. One problem that I'm looking at with a geared brushless is that I'll have to get another ESC. I've got a 12A E-Flite ESC on my RCU Bipe behind a Park 300 but that just don't think that one will feed a bigger motor.
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Old 01-07-2009, 05:27 PM
  #8  
Alpea42
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I had a 60 Kaos in the early 80s it had Rohm Air retracts flew great . When I crashed it I bought another kit. Which I never built but I robbed balsa outta it, still have the box and some of it. The rudder behind the elevator is a good design. The Click, foamy 3Der is designed that way.
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Old 01-07-2009, 09:34 PM
  #9  
UglyNet
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I intend to put retracts on this one but I wanted to keep it simple since this is my first ground-up build. When I build the next wing I'll incorporate the GWS Micro retracts that I have into the design.

The Kaos design is super simple which was a big attraction to me. I think v0.2 will have a shorter tail and a big-ish outrunner but that's hopefully a while from now. I guess that depends on how well the prototype flys.
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