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Old 01-11-2009, 08:42 PM
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UglyNet
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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.


Problems:

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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