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Old Jul 20, 2012, 10:48 AM
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roo_ster's Avatar
United States, TX, Dallas
Joined Mar 2011
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Wicked Jr Powered 24" Flying Wing

Hardware:
Don's Wicked Jr outrunner, 29g, 3300kv
http://donsrc.com/cart/index.php?_a=...&product_id=27
30amp ESC
APC 4.5x4.1 prop
2x HXT900 9g servos
1000mah 3S 25C+ lipos.

When I get CG nailed down after maiden, I will enclose all the hardware for the sake of speed. I am hoping for 70mph+ after enclosing the electronics.

The wing has the usual 3x thickness of KFM4 wings made from bluecor. Also, the leading edge is reinforced, it has a 1/4" sqaure wood dowel fore & aft, and a round 1/4" dowel side to side. I used coroplast for the winglets and "laminated" the elevons in packing tape to stiffen them up.



Hardware located as to achieve theoretical CG:




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Old Jul 20, 2012, 06:05 PM
Wonderfully Wicked
The Don's Avatar
Willoughby, Ohio
Joined Jan 2002
13,218 Posts
Looking good! Let me know how it goes on that model. I have never used one of those airfoils before.

Don
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Old Jul 22, 2012, 11:56 PM
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roo_ster's Avatar
United States, TX, Dallas
Joined Mar 2011
640 Posts
Maidened it this evening, dirty like the photo in the OP, but with the winglets extended below the wing proper. Lots of vert stab, but I can cut it back.

10-15mph winds & gusts, but hey, it is a foamy scratch-build. Suck it up & drive on..

The winds buffeted it, but it cut through them pretty darned good (too much winglet?). It would only show its light weight when I got it underbelly to the wind, going up. I think I need to give it a bit more control movement, pitch-wise. Roll rate is good & smooth. Needs some reflex. Or maybe I instinctively made it a bit nose-heavy due to the winds.

I have gotten used to having some slop in the controls when yanking the sticks at WOT with bluecor control surfaces, but this critter had none of that. I think the packing tape-wrapped blucor elevons made the difference. It cut a pretty darned precise path. That was an experiment. If it didn't work, I was going to move to balsa. At this size & speed, no need for balsa.

Half-throttle handling was exceptional, still had plenty of giblets for aerobatics. Could be flown half-throttle all day in that wind. Slow speed handling was good. I think the "winglets of doom" kept me from wobbling. No tip stalls at landing speeds.

I'll have to wait until it is calmer to get a good recording, but I doubt I will get close to 70mph dirty and lucky to get 70mph clean with a canopy over the goodies. It was the second-fastest plane in the air, but I think it was doing 50mph, according to my eyes. Most the big stuff was 3D or otherwise not optimized for velocity. I recall a hotliner at that field in past days that would have blown it away. I think it just has too much frontal area relative to critters like the HK Parkjet. My lipos got warm, but not hot (HK Nanotech 3S 1000mah 45C). 30amp Hurc ESC was loafing. Motor was a little hot. I could touch it without pain, but if I kept doing so, it might have hurt. Cooled off fast, though. I hammered it pretty hard, alternating WOT passes with 1/2 throttle passes.

I may not get 70mph, but I am not displeased. It is faster than anything else I have built and will help train me to fly faster birds that cost real $$$. Also, this is an answer to "what plane do I fly in the wind?" 15mph + gusts no problem. Two other guys with real pricey planes ate turf this PM. One a big honking gas-powered 3D beastie and another a smaller, 50" WS or so nitro 3D or aerobatic bird. My little wing found a nice patch of long grass and skidded/flopped.

As far as the kfm4 airfoil, I think it is the real deal. I have built kfm3 and kfm2 and appreciated their properties ( kfm3 oodles of lift, kfm2 good all-around & settles down a flat foamy). It just so happens that I built a lighter-weight kfm2 true-parkflyer version of this wing. It flies pretty good, but it has more pitch reaction when I hammer it to WOT. My wicked jr powered kfm4 has less or none of that. I'll see just how much less in calm air, soon. This critter is more "it goes where the goofball behind the stick points it." Also, the kfm2 wing will tip stall if you get it out of position. Not this kfm4wing, so far.

Oh, and the sound of the motor at WOT was sweet. Rrrrrrriiippp! It was like a barracuda among tuna. Smaller, faster, more agile...predatory.

Don:

I have another one of these Wicked Jr motors. What air frame / plans has you gotten the fastest plane with one of these motors?

I think I have been bit by the speed bug. Oh, I'll rationalize by saying I mean to improve my flying skills, but I admit I was enjoying the WOT passes with a goofy grin on my mug.
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Old Jul 23, 2012, 12:14 AM
Wonderfully Wicked
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Willoughby, Ohio
Joined Jan 2002
13,218 Posts
Glad the maiden went well. if you want more speed, buy one of these mine goes about 80-85mph. Goes just fine in wind as well.

http://www.rcgroups.com/forums/showthread.php?t=1565475
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