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Urban Kaos maiden flight. w00t!

Old 01-11-2009, 09:42 PM
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Join Date: Nov 2007
Location: Dallas, TX
Posts: 161
Default Urban Kaos maiden flight. w00t!

Another possible title might be "Spare Parts, the Ultimate Bad Thing(tm)!"

My modified version of Joe Bridi's Kaos, scaled to 65% by Joe Josling has now officially had it's maiden flight!

It's powered by a brushed S-370 in a 5:1 gearbox left over from a Great Planes FlatOut Cap 580 run through Electrifly c-12 ESC and an E-Flite 15C 800mAh 3s LiPo scavenged from my now unused Blade CP+. I also use that battery on my RCU Bipe but that's another story. Both the battery and the ESC max out at 12A so I figure they'll protect each other. Since the run time for my 370 powered heli was about half of what I got in static testing I figured I'm safe with that prop on a geared 370.

I have a 10x4.7 prop on it and it lifts the tail almost immediately upon application of the go-fast stick. Yes, I know it's already geared way down but I figure it was originally designed to run a 10x3.8 on the FlatOut. I burned up one motor static testing a 10x7 prop and was going to make my second flight on a 10x7 but doofus forgot to pack extra props. I'm still not 100% convinced that the prop was to blame but it is nearly twice that of the intended design of that motor and gearbox. Wing level stalls didn't exhibit any ill tendencies and the flaperons worked well though I'll add more deflection once I mount a more powerful motor. I made approaches with and without flaps. With the flaps down the approach was slightly slower and did obviously require a little more power but with as much headwind as I had it really wasn't necessary.

The wind was a bit gusty so it made it hard to tell but I didn't notice and tendancy to ballon when applying power. Obviously with a 370 I didn't have much power to begin with but it did climb without any power. I'd estimate that it's climb was about like that of a trainer, nothing to be excited about but at least it can pull itself out of the way of immediate danger.


Urban Kaos did fly pretty well on a 10x4.7 but I think a 10x6 or 9x7 on a geared S-400 or a brushless motor would be pretty awe inspiring. That's just another $100 that I didn't care to shell out on an unproven model. Now it's proven.

The wing brace broke free on a hard landing. In mid flight it started to act like it lost a lot of power but if the brace failed in flight it may have been a lot more induced drag since it's behavior was much changed from the first approach. The first landing was straight into the wind and was completely uneventful and looked about as picture perfect as you could get. I could *not* have been more pleased. The second landing I was fighting with stalls the whole way down and it kept trying to balloon once it got into ground effect. I will need to change the wing saddle/brace/mount design to improve that stressed member.

The kludged together stick mount I made was a bit lacking. I'll need to replace that with a firewall mounted something or other. Either a brushless motor or another stick mount. While I'm tuning the design I think I may use a brushless motor stick mount in reverse mount a stick to the firewall directly and use that to adjust shims and get the thrustline where I want it.

I have a lack of elevator authority that needs to be addressed. I'm concerned that the micro pushrods I'm using just aren't stiff enough. I'll probably make some from carbon tubes and use those instead. Failing that I'll change the horizontal stab design to increase the percentage of area given to the elevator. I may decrease the cord and increase the span of the horizontal stab at that time as well. The rudder and ailerons seemed to work just fine.

On to v1.01!
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Old 01-12-2009, 02:09 AM
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Join Date: Sep 2005
Location: Tucson, Az
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Good job Ugnet, glad to here it at least flies. Sounds to me like you learned a lot from this design and what it takes to build from plans. Next, the real fun is when you design your own or draw something from a 3-view, your really going to love that part.
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Old 01-12-2009, 02:31 AM
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Join Date: Nov 2007
Location: Dallas, TX
Posts: 161

I have plenty more learnin' to do from this one. I'm sure that it'll be an evolution more than a flat out design for now. I'm converting Joe Jopling's plans from 3-view to 3D mostly as an exercise to learn the software I'm using. I've got the E-Flite S75 servo in 3D already so my battery pack and reciever are next. I did the servo this morning while I was waiting for the sun and temperature to come up. I'm using CompuFoil3D to do the dirty work on rib design for me and TurboCad to do the bulk of the work.

I have a couple of ideas for ground-up designs but I want to finish getting my feet wet on this mod to the ever popular Kaos. I doubt I'll do a 3D machine, there are tons of those already. I do enjoy the pattern ships but the current breed is too big for my taste and too dependant on composites, which I'm not ready to tackle yet. For that matter, I don't care much for their asthetics either. I do like the models of the 60s through the 80s so we'll see what I come up with in the coming months and years.
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Old 01-12-2009, 07:09 AM
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Join Date: Nov 2007
Location: Dallas, TX
Posts: 161
Default Real Flight G3 approximation

If anyone is interested in how this mess of balsa and monokote flies on a S-370 I have a fair approximation based on the SuperSport. I can approximate it's performance based on what my UrbanKaos did today and I think I've got it pretty close. I doubt anyone would be interested but I thought I might offer it up anyhow.
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UrbanKaos - (4.8 KB, 130 views)
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