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Old Aug 29, 2012, 06:20 PM
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Nodd's Avatar
United States, CT, Fairfield
Joined Mar 2012
712 Posts
Careful!
Tip-stall prone Cub

I'd been flying this Piper Cub (from Nitroplanes) for eight months now. She entered a spin around 60 feet up, this was the result...



She was a nice looking plane, lots of scale detail, fair quality parts. She always felt a little on the heavy side though, flew like she had a moderate wing-loading, not very Cub like IMO. She also had a real nasty tendency to tip stall. I played around with the CG, that didn't help. Looking at the wings, there appeared to be zero washout built into the wingtips. That combined with the weight & a short coupled tail meant she was a real handful if stalled. Probably didn't help that I botched a stall turn (hammer head) at around 60', sent her into a nasty spin. As expected at that altitude there wasn't enough room to recover. Also didn't help that I nailed the throttle in hopes of powering out... CRUNCH... right into the dirt.

Oh well. I probably could repair her but I think I'm going to lay her to rest. If she was a nicer flying plane maybe I'd break out the glue but I think I'll salvage the parts & use them in another project.

...and another one bites the dust
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Old Aug 29, 2012, 07:13 PM
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cfircav8r's Avatar
United States, IA, Hampton
Joined May 2012
307 Posts
In the future on a plane that can't have washout added by warping the wings, if it has barn door ailerons, you can raise the ailerons a few degrees. This will give you sufficient washout to tame most planes. The other thing to keep in mind is with barn door ailerons is you need to use them less as speed decreases and use more rudder as you approach stall, but it is best to avoid stalls at low altitude.
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Old Aug 30, 2012, 07:22 AM
Thailand
Joined Aug 2010
521 Posts
Most people in that situation just hold in full UP elevator hoping it will pull out.
You have to release the UP and let the speed build up before trying to pull out or most aircarft will stay in the spin until they hit the ground.
I was demonstrating the very same thing to a flyer who was complaining about his model.
He had too much elevator throw which would hold it in a spin so we reduced it which cured the problem and there was still enough throw to fly it ok.
Use long horns on the moving surfaces and shorter horns on the servo.
Around 3 to 1 ratio is a good starting point and then you can use 100%ATV.
i:e 1cm servo horn and a 3cm moving surface horn.
Jim
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Old Aug 31, 2012, 02:41 PM
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United States, OR, Portland
Joined Jan 2008
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bummer...
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Old Sep 21, 2012, 03:42 PM
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United States, CT, Fairfield
Joined Mar 2012
712 Posts
All is not lost! I've decided to make a new plane from the remaining parts. You can read about that project here...

Piper Cub Sailplane
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Old Oct 01, 2012, 01:42 PM
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BE77 Pilot's Avatar
Joined May 2010
422 Posts
Sorry to see that. I have a e-Flight Super Cub I fly and am real careful with tight slow speed turns. Just curious, are you using a rudder aileron mix?
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Old Oct 01, 2012, 02:06 PM
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United States, CT, Fairfield
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Yeah for most of my planes I use an aileron to rudder mix (around 40%). I also fly the left stick & stay on the rudder while turning.

It was a full-on, deep stall that did her in though, not a turn. I botched a hammer-head at around 60 feet. She never recovered, just spun on in.

I see where you're going with this though. A properly coordinated turn will reduce the possibility of a tip stall while turning. Interesting to hear from other Cub owners, that they've had similar experiences with tip stalls.

My Cub was fine as long as I flew her with respect. As soon as I started pushing her she'd turn around & bite me. The low level stall-turn was the final straw it seems.
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Old Oct 02, 2012, 06:43 PM
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BE77 Pilot's Avatar
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Quote:
Originally Posted by Nodd View Post
Yeah for most of my planes I use an aileron to rudder mix (around 40%). I also fly the left stick & stay on the rudder while turning.

It was a full-on, deep stall that did her in though, not a turn. I botched a hammer-head at around 60 feet. She never recovered, just spun on in.

I see where you're going with this though. A properly coordinated turn will reduce the possibility of a tip stall while turning. Interesting to hear from other Cub owners, that they've had similar experiences with tip stalls.

My Cub was fine as long as I flew her with respect. As soon as I started pushing her she'd turn around & bite me. The low level stall-turn was the final straw it seems.
Interesting you say your situation happened with a botched hammer head. I did the same the other day and although I didn't fall into a spin it tried. Lucky I had lots of power on and I guess more altitude than you did. I think the long wing on the cub has so much mass when it gets turning it does not want to stop. I fly clipped wing Cubs too and they are more forgiving in that aspect.
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Old Oct 02, 2012, 07:48 PM
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Oops, your longer wing theory may have dire consequences for my Piper Cub sailplane project then. I'm extending that same wing nearly a foot LOL
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Old Oct 02, 2012, 08:12 PM
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cfircav8r's Avatar
United States, IA, Hampton
Joined May 2012
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More of a combination of a large span short tail moment and no dihedral. A little wash out will make a world of difference though.
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Old Oct 04, 2012, 10:09 PM
Thailand
Joined Aug 2010
521 Posts
Spinning is nothing to do with dihedral or the lack of it.
If the model normally flies ok then it is the pilot who is holding in "up" elevator that makes it spin. Holding in rudder doesn't help much either but we assume he wasn't doing that.
Piper Cubs do not need washout and impossible to add to an already constructed model.
A rearwards CG will make it easy to enter a spin.
I doubt a piper cub would spin easily with a cg at 25percent of the root chord but would be marginal at 35 percent and probably unstable.
Reducing the amount of elevator movement is the answer. Not just on the ATV in the TX either but do it properly by using a shorter servo arm and/or a longer elevator horn.
Jim
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Old Oct 19, 2012, 06:52 PM
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United States, CT, Fairfield
Joined Mar 2012
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UPDATE
Well I've completed my recycled Cub project. I built this cute little Cub sailplane using the Cub's wing & tailfeathers...



If you're interested here's the build log & video...

Cub Sailplane - Build Log

Cub Sailplane - Flight Footage
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