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Author Topic: Breakaway fin ideas wanted.  (Read 704 times)
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Kevbo
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« on: August 11, 2013, 12:25:09 PM »

I built a lil' Wizard from a NOS kit so I would have something to allow beginners to fly.

Though the design is specifically intended to survive crashes, the fin seems to be a weak point.

In nose-overs, the pointed rudder grabs the ground and tries to stop the airplane, and the fin is not up to the task. The current fin has been repaired twice, and that is probably the limit.

I can make new fin of 1/16" ply, as the design is so nose heavy the added weight would be welcome.  I worry though that this will just kick the can down the road and break the fuselage.   I am willing to change the shape so I doesn't dig in to the ground.

It seems to me, though, that this airplane should have a fin that can depart the fuse with no damage. My first idea was to glue it on with silicone RTV.  I think this would work fine except the long cure time means that once the fin is off, you are done flying for the day.  Something I could have back in the air quickly would be much preferred.

So I am wanting a clean way to attach a 1/16" ply fin to a 1/4" Balsa fuse.  The fin is offset to be flush on the line side, so that the offset rudder is supported by the fuse.

I like the idea of rubber band attachment, but can't think of any way to make that work.

Small nylon bolts seem pretty workable, but removing the broken off bolts can be a chore at times.

Magnets?  Velcro?  Scotch tape?

I can think of ways to do this, just none that seem like a GOOD way to do it.


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sweepettelee
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Simplicate & add more lightness. Keep sanding!



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« Reply #1 on: August 11, 2013, 03:01:23 PM »

I will posit the neodymium magnets will do the trick.  Several(many?) scale FAC builders use this method currently, which has made its way into
useage on several other classes of aircraft.
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Leeper
Kevbo
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« Reply #2 on: August 15, 2013, 06:43:46 PM »

How does this idea sound:

Make a new fin and rudder of plywood.  Cut it in two with a wavy line about where the original broke.  Join the two parts with scotch tape on each side.  The wavy line is to stiffen the joint which would tend to hinge on the tape if straight.

I am pretty sure this will do what I want... Anyone ever try similar?
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sweepettelee
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Simplicate & add more lightness. Keep sanding!



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« Reply #3 on: August 15, 2013, 06:59:15 PM »

Not sure why, but that seems wrong to me.
Consider this: 3/32nd balsa fin attached by the neodymium magnets.
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Leeper
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« Reply #4 on: August 15, 2013, 08:36:29 PM »

Being a controliner, its probably not fussy about the shape or even having a rudder. Make it rounder (like maybe a Ringmaster). You could use 1/32 ply and glue it to the side of the fuselage for more support.

Hey Leeper! What are you doing over here in the ukie stuff?

NormF
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sweepettelee
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Simplicate & add more lightness. Keep sanding!



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« Reply #5 on: August 15, 2013, 08:46:29 PM »

Guess I had a 'Roseanne Roseanna Danna' moment and
didn't notice the subject matter.
Soooo, "Never mind".
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Leeper
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« Reply #6 on: August 16, 2013, 01:13:14 PM »

Hi,
If you were to add two vertical pieces of balsa that formed a vertical slot you could slide the vertical stab into the slot and secure it with a single rubber-band around the whole assembly.  The vertical stab would need a slot at the rudder "hinge" point to clear the rubber-band.
If you made the slot tight enough it may not need a rubber-band at all.  Attached is a drawing.

Just an idea, I hope I've helped.
Attached files Thumbnail(s):
Re: Breakaway fin ideas wanted.
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lincoln
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« Reply #7 on: August 17, 2013, 07:01:43 PM »

Hi,
If you were to add two vertical pieces of balsa that formed a vertical slot you could slide the vertical stab into the slot and secure it with a single rubber-band around the whole assembly.  The vertical stab would need a slot at the rudder "hinge" point to clear the rubber-band.
If you made the slot tight enough it may not need a rubber-band at all.  Attached is a drawing.

Just an idea, I hope I've helped.


You could just use a magnet at the base of the rudder and this slot idea. For a bit of extra work, you could make the slot in the middle of the fuse, not sticking up, and use a longer fin. That way it wouldn't show. Just make sure the fin is free to slide out backwards and frontwards.
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