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Old Nov 14, 2009, 08:21 PM
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Jack
USA, ME, Ellsworth
Joined May 2008
18,088 Posts
SpaFFFnutz 48" KFm4 Flying Wing - FFF/Coroplast Hybrid

With my full apologies to tony65x55, let me introduce you to the latest variant on the Zagnutz. I even gave it a name that is derived from it's roots:

SPAD = Simple Plastic Airplane Design, the popular Coroplast planes

FFF = Well, we all know what that is.

and I transliterated and mutated that to "SpaFFFnutz" and if the plane flies maybe I'll give it a thread of it's own.

Here are the build details for now though.

Wing span: 48"
Weight: 770 grams/27 oz.
Wing area: 377 sq. in.
Wing loading: 10.3 oz/sq. ft.

Battery: 4S A123 1100 mAh (180 grams, 13.2V nominal)

Motor: Turnigy DAT-750 brushless outrunner, 750 Kv, 80 grams, 180 Watts

Prop: Great Planes Powerflow 10x4.5 Slow Fly

ESC: Atlas Black 20A

Servos: two generic 9 gram micros

Material: Coroplast 4mm center panel sandwiched between Dow PB III FFF to make KFm4 strips. Factory folded edge of two FFF sheets was used for the leading edge of wing, no spars or other stiffening was added to the wing.

This is a fast build because the Coroplast center panel does not have any spar on it or in it.

The five sided center filler panels were added to the center of the wing, top and bottom. These extend back to the prop slot cutout. The filler panels are also PU glued to the coro for a little additional stiffening in the wing center.

With the FFF KFm strips on the top and bottom of the wing wrapping the coro back to the 50% mark, the filler panels in the center, and all of the FFF being glued to the coro for it's full contact area, the wing stiffens up nicely while still retaining some gentle spanwise flexibility. I think this wing will flex a little under load in flight but that might turn out to be a good thing.

The wing is .670" thick at the KFm strips and the wing thickness and step height is constant across the wing span. The KFm steps are about .230 high (a single layer of FFF).

The elevons were made from FFF and clear package sealing tape was used to make full length hinges. The elevons were later covered with a second layer of colored package sealing tape for additional strenghening and stiffening.

Motor was mounted with a 3/8"/9mm square stick. The square stick rests on the top of the coro center panel and is held in place by two screws from the bottom. The screws go through doubler was made from a paint stirring stick.

Coro is quite a bit heavier than FFF, it weighs 70 grams per sq. ft compared to FFF's 20 grams sq. ft. The change to coro center panel probably increased the weight of this build by 3 or 4 oz. over an all FFF build with spars. But I'll bet this build has made the center section pretty much indestructible too.

The wing is 378 sq. in., the loading is about 10.3 oz/sq. ft, and the plane will be flying at about 106 Watts per pound at full throttle.

Maiden report to follow...

Jack

22 March 2010 - Added Note: I have added a working drawing of the SpaFFFnutz to this post, it should help with construction.

27 March 2010 - Added Note: Do to popular demand, SpaFFFnutz now has a thread of it's own. Please seek answers and post comments about SpaFFFnutz there:

http://www.rcgroups.com/forums/showthread.php?t=1217861

Jack
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Last edited by jackerbes; Mar 27, 2010 at 05:55 AM.
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