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Old Jun 27, 2012, 05:56 PM
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Joined Jun 2012
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Presenting the Uh... Oh!

My dad designed this cool little foamy on his work bench and we've been having a blast with it.

It combines the best elements of two planes we love: the Firefly and the Nutball.

It's an octagonal plank with a thin kfm1 step hot glued to the bottom. Hook up a 130 watt Blue Wonder motor, a $6 Hobbyking orange RX, a 1000 mah battery and two 9 gram Hextronic servos and you have yourself a VERY nimble little sport plane with forgiving stall characteristics. It rolls like a madman, hence the name "Uh... Oh!". Dad thought it was more polite than "Oh Sh**!".

Here's a picture of the plans (measurements, really), and a couple pics of the finished product. Flight video to follow soon, of course.

We're calling this one the Mark I.

The whole thing is made from a sheet of Dollar Tree foam. It has a verticle stab but no rudder and uses elevons.

We covered it with packing tape a la Experimental Airlines (thanks Ed!), and so far there's no need for a cf spar or any reinforcement. It makes for a really strong airframe.

Mk II is on my workbench. I thickened the Kfm1 step and added a functional rudder. We'll se how she flies.

Hope you like it. We sure do.
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Old Jun 27, 2012, 08:28 PM
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WombatControl's Avatar
United States, MN, Minneapolis
Joined Jul 2011
306 Posts
Looks like a nice little plane! Looking forward to seeing the flight video. Looks like an incredibly easy build too. Nothing like those $1 airframes...
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Old Jun 28, 2012, 12:01 PM
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Joined Jun 2012
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Thanks! 4 hours all in and I have an airplane built from scratch.
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Old Jun 28, 2012, 01:21 PM
This is kid stuff.
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USA, AR, Harrison
Joined Aug 2010
966 Posts
I'm intrigued and have a couple of questions.
1. How high is the motor thrustline above the wing/fuze?
2. Why are the servos staggered fore and aft.? It looks like there's room to mount them equidistant from the control surfaces .Although it may not really matter, when in doubt, ask the designer.

I'm subbed and will be watching for MK II report. Flight video(s) would be appreciated as well.
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Last edited by Mazzepa1; Jun 28, 2012 at 01:22 PM. Reason: Correct typo
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Old Jun 28, 2012, 03:21 PM
I wanna fly!
Pacific Northwest
Joined Jun 2008
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Looks interesting.
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Old Jun 28, 2012, 03:23 PM
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1. About an inch? We build light ply L-shaped mounts, with the firewall about 2 inches tall, and mount the motor in the middle. When we attach the motor mount we screw it on cruciform style and stick a washer under the top and left arms to create some down/right thrust.

2. He had a reason for this, but I forgot. I just finished the Mk II and I put the servos forward of the CG equidistant from the control surfaces. We'll see how she flies.

Thanks very much for your interest!
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Old Jun 30, 2012, 01:30 AM
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Flew the Mk II today and it was very tail heavy. Put another dead battery on top of the good one and it flew better, but still tail heavy. Balanced at 6 inches. The Mk I balances at 5 3/4 inches and weighs 240 grams without the battery.
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Old Jun 30, 2012, 04:54 AM
This is kid stuff.
Mazzepa1's Avatar
USA, AR, Harrison
Joined Aug 2010
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Mk I & II CG measured from front of motor mount?

Seems as though locating the servos forward of the MK I locations should have made up for the weight added by the rudder addition.

Good luck getting it figured.

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Old Jul 25, 2012, 01:02 AM
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United States, OR, Salem
Joined Sep 2011
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MkI and II CG measured from front of the motor mount, 1/4 inch light ply.

The pattern was drawn on the foam itself, so all measurements are valid.

Motor mount measurements ;
base (battery tray) 4" X 2 1/2".
firewall (front), 2 1/2" by 2".
sides, cut one each 1 3/5" X 1 1/2", then cut diagonally for two sides.
Last piece is a bulkhead added just behind the firewall to keep battery fron being punctured by motor mount screws. Add AFTER MOTOR IS MOUNTED or you'll never get to the screws! size for bulkhead is1 15/16" X 1 1/8".

Front piece (firewall) is ca glued in front of the battery tray (base)
sides are glued to back of firewall and top of base.

Servos are in present location because I mounted control horns at right angles to elevons, so servos attached where they fit for a straight control throw. Keep weight foreward and don't be tempted to add servos close to elevons or weight may have to be added to nose.
Hope this helps.
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Old Aug 02, 2012, 01:27 AM
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Joined Jun 2012
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Video!

Here's a link to the Youtube video showing a bit of flight footage. I mean a bit, because it was REALLY windy when we flew.

Miracle Air Presents the "Uh... Oh" (1 min 47 sec)
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