"UFO Pinata" 48" EPP combat wing - RC Groups
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Apr 10, 2007, 05:32 PM
Lee's Avatar

"UFO Pinata" 48" EPP combat wing

Meet the new UFO Pinata!!!

I had trouble with the last cut of WWMs so I went back and retooled the cutter and redesigned the jig. The new airfoil is neither the SD6060 or the trainer airfoil but a good looker somewhere in between. The wing shape will be the same but the airfoil will be different.

The new cutting table has the wing pattern drawn on it and will be more versatile for cutting alot of different wings than a cutter that is specialized for one cut only. It is made out of a 3/4" x 15" x 72" partical board shelf. The anchor points can be moved up and down the table to change the angle of the leading edge cut. The side of the board is used for the alignment of the TE. The right wing is cut on one side of the table and the table is turned around to cut the left wing. The jig is designed so that the same jig can do both the right and left wing cuts just by turning it around.

I'm using a different airfoil so I wanted a new name. "UFO Pinata" seemed an appropriate name concidering the plane is intended for combat.

Here are some pictures of the new taable with anchor point and jig.
Last edited by Lee; Apr 11, 2007 at 08:45 AM.
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Apr 10, 2007, 10:54 PM
Registered User
It's always fun to see someone willing to change an idea for progress. I always wonder
why so many just push along the same old way, without thinking about how something
might work better with a little tweeting. Congratulations Lee, you should go to the head
of the class. I always work to improve my designs. It makes life so much more fun. I love
when I have to say, " now why didn't I think of that ". Thanks for being there for all of us. Carlos Venson
Apr 10, 2007, 11:05 PM
I can fix it.
nageotte's Avatar
Well Darn! Now my new wing is obsolete already.
Apr 11, 2007, 10:52 AM
Utah Flyers
natetanr's Avatar
Thanks for sharing Lee. Im going to give this a try. I have ruined lots of foam trying to cut the WWMax. This looks like a great improvement that should prevent those losses. Is the Pinata the same sweep as the WWMax?
Apr 11, 2007, 01:30 PM
Lee's Avatar
The plane will look the same to the untrained eye. I like the angle of sweep we have and tried to preserve it.

I know this airfoil will work well but due to the distortion I had to cut into it it won't be exact with the old airfoil. I have a 12" jig making a 14" cut because of the angle.

I wanted to maintain the thickness and blunt the nose a little to slow down the low speed flying. Top end characteristics should be good too.

I'm hoping to do a little slope soaring with this plane.

Jim don't feel too bad, this plane is still untested, we know yours flies great.
Apr 12, 2007, 12:01 AM
Lee's Avatar
There is more to it than just the jig.

I have been playing with the cutting wire and it needs to be ultra tight. The rubber bands have tensioned the bow but have also allowed some vertical movement that is hard to control on a 70" bow that I didn't see until now. All it takes is 1/8" over 70" which isn't much to distort and ruin the wing.

The suspension from the ceiling is also critical.

I have 2 of the UFO Pinatas cut and one other half cut that isn't good enough to use.
Apr 12, 2007, 10:23 AM
Lee's Avatar
I think I understand more of the problem. The cutting wire is longer and so it stretches more when it gets hot. The fact it is has the right tension when it is cold doesn't mean it has the right tension when it is hot. The rubber bands have enough movement on a 40" wire but not enough to maintain the tension on the 70" wire. I need to stretch the rubber bands even more on the cold wire to maintain the tension on the hot wire.

In other words.....I think the wire is too loose when it is hot and tends to sag during the cut.
Apr 12, 2007, 11:12 AM
Hit Me! Please!
jwjohnson's Avatar
Sagging is a big problem when you are too long or too old.
Apr 12, 2007, 12:21 PM
Lee's Avatar

I just tightened the wire so that 8 of the #64 rubber bands are stretched over a full 6" gap. The difference is amazing. The wire stretches over 1/2" over the 70" when the power is turned on. I did have the gap at 4" previously. I expect the wire will break more frequently with this kind of stress on it.


Sorry about the sagging problem.

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