KFm airfoil 48" Flying Wing - Page 2 - RC Groups
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Aug 25, 2011, 07:49 PM
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gatorlynch's Avatar
Originally Posted by stumblebum
I have an equitable 450 I had purchased for a HOT version of rcrich's
cheap-n-easy so I think I have everything I need.
hxt 500 servos be good enough for this bird?
I can't comment on your motor, as I'm unfamiliar with it. If it's a 450 size, it should be fine.

Although I've never used a 5g servo, I personally think the 9g would be a more appropriate choice for this model. These are big, long control surfaces on a 1.5 lb. bird .....
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Aug 25, 2011, 09:52 PM
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gatorlynch's Avatar

V2 pics & notes

AUW is 26 oz. - including the bomb drop base.

Some of the things I did differently on my second wing -

The original elevons had a lot of flex or twist in them. The horns were attached far inboard, and the outboard portions did not move in conjunction with the inner portion. To combat this,
I Moved the servos further outboard, to about midpoint on the elevons.
I added CF strips to the trailing edge of the elevons.
I cut slots in the hinge line (no more continuous hinge).
The combined effect seems to have helped. There is still flex in the elevons, but not near as bad. The CF strip I used is 0.8mm thick - next time I would go with at least a 1mm thickness. I think the results would be even better.

I ran the motor mount spar all the way thru to the tip of the nose, as the original wing had some longitudinal flex. I also zip tied the wood in a few spots, in addition to CA. This has helped.

To combat the lateral flex or flutter, I inserted 3 CF rods into the flutes for spars. 4mm is a nice, snug fit. The rearmost one is located in the very last flute. You can see the outlines of 2 of them in the pic of the wing underside. The jury is still out on this mod. In the very limited time I have flown this wing, I was still getting some flutter at very high speeds. It is certainly better, as before it was acting like the wing would tear itself apart if I let it keep going. This might just be inherent with a 48" coro wing and no strong center brace. I think I might try a 42" WS next time, to see if it's any better.

I don't know yet what a good CG is for this wing. I need to get some more air time to dial it in. I maidened it @ 7.5" from the tip, but she was acting nose heavy. I now have her balanced to a 8" CG - but I need to get her up & flight test her. I'll post the results when done ......
Last edited by gatorlynch; Aug 25, 2011 at 10:18 PM.
Aug 26, 2011, 09:50 AM
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New Updates

Made a typo on the servos. Mine are 900's.
Thanks for the info for cutting the fold and the mods.
Was wondering about the folds being at an angle. All I have
fooled with to now has always been parallel or 90 to the flutes.
Trying to get started on mine. Other stuff getting in the way.
What is the cover looking thingy at the cross pieces of the spar?
Will keep you posted.
Last edited by stumblebum; Aug 26, 2011 at 09:56 AM.
Aug 26, 2011, 12:40 PM
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gatorlynch's Avatar
Originally Posted by stumblebum
What is the cover looking thingy at the cross pieces of the spar?
If you're talking about the green piece on the underside, it's the base unit for the Quanum Bomb Drop System. - http://www.hobbyking.com/hobbyking/s...dProduct=10624 There is a pic & vids on this back on page 1.

As far as cutting at an angle - it's a little more difficult to get a straight cut, as the cutting tool wants to wander a bit. I just go slow & keep the tool turned into the straightedge a bit.
Aug 29, 2011, 12:06 PM
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gatorlynch's Avatar
Well, I learned 2 things about this wing -

She flies best balanced to a CG of 7.75"-8"

She doesn't fly with a glider strapped to her belly .........

RC Wing - Glider Launch FAIL (2 min 2 sec)
Aug 31, 2011, 11:00 AM
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JohnsPop's Avatar
Out of curiosity.... why wouldn't you mount the shuttle facing forward? Cool video, though.
Aug 31, 2011, 12:33 PM
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gatorlynch's Avatar
Originally Posted by JohnsPop
why wouldn't you mount the shuttle facing forward?
We started off that way - and it was even worse!

Due to its' vertical stab, the glider needs to be mounted upside down on the bomb drop mechanism. The bottom rear of the fuselage angles up at an angle. When you mount it upside down & facing forward, the main fuse & wings are pointing down at about a 30 degree angle.

As we learned, this configuration acts as a down force during launch - the operative word being force. Thankfully, no video exists ....

The rear facing configuration was an attempt to keep the glider's wings parallel with the KFm wing. Apparently, there was enough slop/movement in the mounting bracket to allow the glider to move up & down, thus acting as a control surface.

It was worth a try ....
Aug 31, 2011, 05:13 PM
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earlwb's Avatar
Interesting experiment with the glider add on. I guess the NASA folks had it all worked out with they bolted the shuttle on top of the 747 like they did. of course they had wind tunnel simulations too. it would only work on the bottom, if you could accommodate the tail fin somehow and mount the glider right side up.
Oct 21, 2011, 12:38 PM
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gatorlynch's Avatar
I have added LED's for night flying.

Using the HK strips, I have Orange/Amber & Blue on top & bottom. The bottom lights are just behind the step but they still show up from the front.

I also have small 3 light segments of white at the nose (2 each, top & bottom) - they look like landing lights in the air.

To help with visual up/down orientation (it was hard to tell when/if inverted), I added an outboard horizontal strip right on the very top on the winglets. I used white lights, but ended up covering them with red tape for a better look.
Oct 28, 2011, 10:52 AM
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killercando's Avatar
I like your wing. I have built a couple but they seem to come out a bit on the heavy side. What thickness coroplast are you using? Here is a pic and video of my 36" ds wing It is epp though. I used about 72" of assorted HK LED strips.
Oct 28, 2011, 12:35 PM
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gatorlynch's Avatar
Originally Posted by killercando
What thickness coroplast are you using?
She's made from 4mil.

Yes, it's a heavy bird - but it's also bulletproof!
I did upgrade to metal gear servos, as I kept stripping the HXT 900's. Now It really is indestructable.

I ran into trailer mounted generator the other day at full throttle - she just bounced off the metal enclosure & threw the battery.
I just walked over, reattached the battery & threw 'er back up!
Jan 07, 2012, 08:30 AM
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gatorlynch's Avatar

New Motor - new life

My wing had been sitting on the shelf, and I had "borrowed" the 450 motor for my SPAD Stick.

My buddy brought out a 2200 kv motor yesterday, so we brought the wing back to life with his motor & Rx.

She flies well with the faster motor & 6X4 prop. You do need to watch the speed, as she will develop flutter at top end speeds.

New motors for the Wing & the Stick (1 min 53 sec)
Jan 07, 2012, 05:48 PM
Watch This!
Corocrumpler's Avatar
Looks like I have to get new piece of 4mm that is 48" and start building.
Jan 14, 2012, 02:17 PM
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Corocrumpler's Avatar
Finished!! Well almost, I have to put some stripes or something so I know which side is up!!! Very windy today, but she flies, pretty well. I like it, its my first true flying wing, I have a mod'd Mugi delta that is very fast, I think I like flying this wing better, it can go pretty slow if you want to. It's like a flying wing version of a Slow Stick.

48" wing span 8% overall thickness KFM wing, 4 carbon fiber rods, AUW 19ozs, 10X6 prop, 1450 motor, 7.4/2 cell 1800 lipo, Plenty of power, no problems with flapping
Last edited by Corocrumpler; Mar 13, 2012 at 10:29 PM.
Jan 14, 2012, 06:23 PM
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gatorlynch's Avatar
Coro -
Nice looking wing. How did you attach the motor mount spar to the wing? I can't tell from looking at the picture.

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