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Old Nov 19, 2009, 07:58 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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SpaFFFnutz 48" KFm4 Flying Wing - Electric FFF/Coroplast Hybrid

I modified Tony65x55's 48" KFm Zagnutz flying wing from KFm1 to KFm4 in FFF, now I have it modified again as a Coroplast and FFF hybrid to further improve the durability of the plane. And it has not hurt the flyability and fun factor at all. I gave it the name SpaFFFnutz so that Tony can distance himself from my tampering if he would like.

The build details are here:

http://www.rcgroups.com/forums/showp...postcount=3778

The maiden flight report and link to a video are here:

http://www.rcgroups.com/forums/showp...postcount=3781

and the plans are here:

http://www.rcgroups.com/forums/showp...postcount=3790

I just finished modifying it a little because of elevon fluttering. I moved the servos outboard on the wings and the horns are now in the center of the elevons.

I'm a newbie to SPADs, I built an electric SPADET LC-40 recently and that first encounter with coro inspired the SpaFFFnutz build.

Jack
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Old Nov 24, 2009, 03:26 AM
BEX
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Nice one Jack , what glue did you use between the coro and the foam?

I am going to try a 2mm folded one soon , I made a spar for it a year ago and never got round to finishing it.
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Old Nov 24, 2009, 07:38 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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I used the 4mm coro for the center panel and with that sandwiched between the FFF with the plastic skin still on, did not add a spar. The wing has a nice stiffness but will still flex down 2-3" across the span if you hold it by one wing tip. I think it is strong enough without a spar with the 4mm coro. I figure there is only about 4-5 oz. more weight in this build than there would be an in all FFF build with spars.

I glued the FFF to the coro with Gorilla Quick PU. I sanded the contact patch with 80 grit paper, them woodpeckered it hard enough to get small holes, cleaned it with alcohol, misted the coro, spread the PU on the FFF and weighted them together for good full contact. That is holding well so far.

I've put it in the trees and crashed it hard a few times too. The leading edge is a little wrinkled and dented but the colored package sealing tape is holding up OK there.

The servos had been hot glued into pockets in the FFF but popped out on an impact. I tried double sided tape and that did not hold well enough either. In the end I cleaned the servo pockets up down to bare coro, roughed them up a little with 80 grit, and hot glued the servos on by puting them on a full servo sized bed of the good Arrow BSS6-4 hot glue. That is holding but has not been really hard impact tested yet.

Moving the elevator horns from near the inner ends out to the center of the elevons (I had to relocate the servos too of course) has stopped the elevons from fluttering in full throttle dives and even level flight. The elevons could be made smaller, they don't need to be wider on the ends as I have them. I have a lot more pitch and roll rate than I need, I could give some of that elevon width up.

All in all it has been a good quick build and strong too.

I'm using 4S A123 1100 mAh battery packs (180 grams) so I added a larger 80 gram DAT-750 motor. My AUW is about 27 oz. That motor is using a Great Planes Powerflow 10x4.5 Slow Fly (GPMQ6660) prop.

That prop is like an industrial strength slow fly prop compared to the GWS slow fly props. It static tests to 6,600 RPM at 11V and 17.3A for 190 Watts. The pitch speed at that RPM is 28 MPH and I think I am getting most of that as the KFm4 is a pretty thin wing. I like and prefer lower flying speeds and this is as fast as I would want it.

Your 2mm build with be with an airfoil like a Clark-Y or similar, right? Or symmetrical with ribs?

Jack
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Old Nov 24, 2009, 09:17 AM
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Quote:
Originally Posted by jackerbes View Post
I used the 4mm coro for the center panel and with that sandwiched between the FFF with the plastic skin still on, did not add a spar.
Why not just go "industrial" and route a groove in coro wide enough to wrap around the center panel and put coro on the outside too? That would provide even less wrinkling when you hit a tree! I guess it would add a little more weight than the foam, but I know how you like those industrial strength builds.
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Old Nov 24, 2009, 09:32 AM
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Oh yeah, about the servos.... you remember when we were talking about mounting them in the wings? Did you see those photos over on Spadworld of how those guys mounted their's in the wing with that little hatch? Looked pretty simple and might do the trick for you. If I've got the link right it's: http://spadworld.net/forum/viewtopic.php?t=17228 That guy glues in wooden mounts and then screws the servo to the mounts. Villa just glues his servo directly to the coro flap with CA and zip ties it for security. If I ever build a "pretty plane" I might try that. LOL Maybe when I get to my Corsair......
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Old Nov 24, 2009, 10:56 AM
BEX
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"Your 2mm build with be with an airfoil like a Clark-Y or similar, right? Or symmetrical with ribs?" Jack , that last sentence cracked me up , man you havent been in SPADS long enough yet , but we will get you there

i have no idea what a Clark-Y airfoil looks like. and have no intention of ever using ribs in any of my spad wings, its just not neccesary.
AFter building about 10 wings i worked out what i had to do to get a specific shape airfoil . After about 30 wings i managed to work out what the properties of each airfoil shape is. You can say ive been reinventing the wheel and i wont argue that , but ive been having fun doing it and i have learned a lot.
In this process I discovered that if done right gluing up a spad wing will automaticaly give you washout. I played with the discovery a bit and now I can put in washout in my wings for great stability. i posted a thread on it somewhere , cant rememeber, too long ago.

I am pretty sure it is possible to build one using 2mm folded coro with spar at about the same weight, and it will be stonger. remember the 4mm coro weighs almost double what the 2mm coro does , so the coro weight will be the same. the weight for the foam and glue should just about balance out with the spar weight as you can do it with a very light spar . Ill finnish up mine as slope soarer soon so we can compare them by just subtracting the weight of the power system.
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Old Nov 24, 2009, 04:50 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Jack wrote:

"..Your 2mm build with be with an airfoil like a Clark-Y or similar, right? Or symmetrical with ribs?..."

BEX wrote (my comments interspersed):

"..Jack , that last sentence cracked me up , man you havent been in SPADS long enough yet , but we will get you there ..."

I try to be entertaining and I am learning thanks to guys like you and the other folks over at STTB. I saw a build of something somewhere (a glider wing?) that was 2mm coro, symmetrical IIRC, and that also had ribs inside it that were made from coro. It was basically a technique that was similar to balsa stick building but in coro. I'll see if I can find that again.

"..i have no idea what a Clark-Y airfoil looks like. and have no intention of ever using ribs in any of my spad wings, its just not neccesary..."

A Clarke-Y is a flat bottomed rounded top wing, pretty much half of a symmetrical wing. It can be build on a flat surface easy and flies well. Like it or not, you SPAD guys are building that or something very much like it in the SPADET and similar wings.

"..AFter building about 10 wings i worked out what i had to do to get a specific shape airfoil . After about 30 wings i managed to work out what the properties of each airfoil shape is..."

Right. I am *not* an aerodynamics guy of any depth or even very interest3ed in it. I use what I find in plans and mess with it too when I feel it serves my needs. We are like minded but I don't have anywhere near the experience or depth of knowledge you do.

"..You can say ive been reinventing the wheel and i wont argue that , but ive been having fun doing it and i have learned a lot. In this process I discovered that if done right gluing up a spad wing will automaticaly give you washout. I played with the discovery a bit and now I can put in washout in my wings for great stability. i posted a thread on it somewhere , cant rememeber, too long ago..."

That would be interesting to read if you can find it. I'm not at all focused on building anything but flat and square at this point and my SPADET is flying nicely enough that way.

"..I am pretty sure it is possible to build one using 2mm folded coro with spar at about the same weight, and it will be stonger. remember the 4mm coro weighs almost double what the 2mm coro does , so the coro weight will be the same. the weight for the foam and glue should just about balance out with the spar weight as you can do it with a very light spar . Ill finnish up mine as slope soarer soon so we can compare them by just subtracting the weight of the power system..."

I look forward seeing how it goes. I'm visualizing "..2mm folded coro with spar..." as a "V" shaped piece of coro wrapped back over and fastened to a spar at the thickest part of the wing. I see that as two curves coming back from the leading edge, over the spar, and meeting at the trailing edge. That is what prompted my remark about symmetrical wings. A wing like that would have a symmetry of sorts at least. Maybe my minds eye has it wrong?

I am thoroughly addicted to the Kline-Fogelman air foil as it works so well with my favorite material, FFF. I know that FFF is not as plentiful in some areas as it is here in the U.S. but it is a wonderful material. My initial impression is that if you are building for electric power and in smaller and lighter planes, FFF is hard to beat. And if you are building in FFF the KFm airfoils are hard to beat for quick and simple builds.

I moved on to coro in the interest of having a bigger electric plane to fly after demolishing my electrified SIG Rascal 40. Coro is definitely a better material for fuelies (although I am not likely to ever build another fuelie).

Jack
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Old Nov 24, 2009, 04:54 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,802 Posts
JohnPop wrote:

"..Oh yeah, about the servos.... you remember when we were talking about mounting them in the wings? Did you see those photos over on Spadworld of how those guys mounted their's in the wing with that little hatch? Looked pretty simple and might do the trick for you...."

I did something like that on the SPADET because it is a hollow wing. The SpaFFFnutz wing is pretty thin and I wanted to fasten them to the top as I've had good luck with that in numerous builds. I fly hand launched and land in tall grass and weeds so I like to keep the wing bottoms clean of snags if I can. It will work hot glued to the top I think, I tested them today and they are holding OK.

Jack
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Old Nov 25, 2009, 08:55 AM
BEX
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Hi Jack
"A Clarke-Y is a flat bottomed rounded top wing, pretty much half of a symmetrical wing. It can be build on a flat surface easy and flies well. Like it or not, you SPAD guys are building that or something very much like it in the SPADET and similar wings."

I have done a lot of wings like that , my problem with it is that when you remove the wing from the jig the top skin always pull the bottom skin a bit up just in front of the TE . This results in undercamber giving lots of lift but increase drag , which is fine for a slow flyer or trainer . I want cleaner airfoils these days , so I put a dowel of about 4mm under the LE in the wing jig. the raises the LE to give a very nice semisymetrical airfoil with good lift and some aerobatic capability.

Ill see if i can find that washout thread , otherwise ill just type it up again, feeling a bit lazy though.

"I look forward seeing how it goes. I'm visualizing "..2mm folded coro with spar..." as a "V" shaped piece of coro wrapped back over and fastened to a spar at the thickest part of the wing. ..... ..... Maybe my minds eye has it wrong?

You got it just about right there . Anything speedy i always make symetrical , it just flys more stable in my opinion. There is a Corozag thread on Spadworld that shows how to do it , but i cant work from plans and instructions , I like to figure it out myself.
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Old Nov 25, 2009, 10:14 AM
BEX
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I found that washout post I did , http://spadworld.net/forum/viewtopic.php?t=15918
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Old Nov 25, 2009, 02:41 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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"..I found that washout post I did..."

Interesting reading. I knew the basics of washout but have never tried to build any in.

I uploaded a couple of video of the SpaFFFnutz

Ground camera -
SpaFFFnutz Demo - Ground Camera View (3 min 26 sec)


Air camera -
SpaFFFnutz Demo - Air Camera View (4 min 17 sec)


The plane is really turnng out to be a nice flier. Needs little to no reflex when the cg is right, flies very neutral. Not too bad a roll rate and not even grossly barrel shaped rolls. Needs a little down elevator to fly inverted but will loop under easily enough with a reasonable amount of ground clearance. It likes smaller elevator inputs for loops and hard turns better than a full pull yank and bank. But will respond to either way.

Looks like centering the horns on the servos will stop the elevon flutter.
That is with 9 gram servos, slightly better quaility servos might help with that too. I saw just a trace of flutter pulling up into a ti8ght loop from a fairly steep full throttle dive. I'm cool with that because I'm smart enough to not fly that way most of the time.

Jack
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