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Post by gregstone on Jun 28, 2012 9:29:51 GMT 1
After a horrific spiraling in I discovered the cause - damage from an earlier crash I had missed where the elevator had become brokem so that on one side it was perpetually raised!  So - I have a new horizontal stab, but I'm wondering if the old one can be rescued and what's the best way. It has a 5-inch long crease that runs from near one tip to near the center - and from the front to the rear. I assume this crease means that the foam is broken, but everything is still held together by the covering. My thoughts at the moment are to take a razor blade and slit the covering along the crease, then glue the foam back together, then put tape on the covering. My question - does this make sense? Is there an easier way? A better way? (I've been using something called "Foamtastic" that seem to do a good job with the gluing.) Attachments:
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Post by flydiver on Jun 28, 2012 15:34:51 GMT 1
The structural integrity is shot. Glue and tape are not likely to hold it as the glue surfaces are too thin.
Get some 2mm flat carbon.
Make 1 or 2 slits parallel to the hinge and crossing the crease. Look like you'll need 2 since it is creased across the hinge.
Make them almost full elevator width. Try to only slit through 1 surface.
Glue the carbon in edge-wise with your favorite glue. Have the elevator pressed down FLAT on a FLAT surface while curing.
Is all that worth it?
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Post by larkshead on Jun 28, 2012 15:47:16 GMT 1
Flydiver is probably right, but if it's a lost cause anyway, try the gentle application of a hairdryer. I was able to resurrect one once that way. (Of course, I also destroyed one that way too.) The heat softens the plastic covering and seems to release the crease in the underlying foam.
Have a book handy to lay on top of it while it's still warm.
Good luck,
-Peter
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Post by flydiver on Jun 28, 2012 15:55:47 GMT 1
Peter's trick 'may' work. It's easier but less reliable. The load on the elevator is not like a wing so structural integrity requirement is lower.
OTOH, if it fails in flight you risk the whole plane. ....so.....choose....
This type of damage was common on the old Aerobird type planes, which I still have, both the wing and V-tail. The plastic skin would hide the crease damage so you would overlook the problem after a seemingly minor crash. The foam would crease, then the wing would fold up under stress (say a loop) and you got to watch it lawn dart. Been there-dramatic for sure. Tape and glue alone would not hold it. It's been tried and found wanting a bunch of times by lots of people.
Not as tidy or pretty, bamboo skewers are easy to get and cheap, and they come in different sizes. Great repair product. They will work in place of carbon (often called poor man's carbon) but you'll have to kind of gouge out a place for them. I used them on the Aerobird wing and it is stronger than original, but heavier of course.
For a friend's SC tail I did as above with carbon-came out great and is almost invisible. He's a lousy pilot, crashes all the time so doesn't buy parts unless forced to. His Cub looks awful but still flies.
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Post by gregstone on Jun 28, 2012 21:22:03 GMT 1
Thanks folks - that's very helpful. You've convinced me that: 1. I'll put the new one on. 2. I'll then experiment with repairing this one just to learn more about the material. And thanks for the story about not noticing the crease - I actually saw it and it didn't seem to be doing anything bad and so I got to watch a lawn dart - and on a hard baseball infield to boot! But it's good to know I'm not alone.  |
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Post by flydiver on Jun 29, 2012 6:25:30 GMT 1
The Aerobird has a pointy plastic fuse and is a pusher. Mine actually did 'lawn dart' - stuck about 2" into the dirt with the tail pointing up. It happened to most owners after awhile.
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Post by gregstone on Jun 29, 2012 23:17:31 GMT 1
Well, i admit the Cub wasn't much of a "lawn dart" - but it sure tried. That baseball infield is hard as concrete and it went straight in. The good news is I glued the motor mount back together, repaired the fuselage and attached the motor mount, glued the guts back into the plane ( battery compartments, etc.) , repaired the crack in the fuselage where it half broke in half, put on the new tail feathers and had several successful flights this morning with one perfect landing on the infield.
Now when we have a rainy day I'll play with repairing the old stab as suggested and if it looks strong, I'll keep it as a spare. Again - many thanks for the sound advice. And, incidentally, I can't tell you how delighted I am to find that thes eplanes can be rapired and do put some demands us on to do just that - I was feeling guilty buying an RTF ;D
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Post by flydiver on Jun 30, 2012 3:33:00 GMT 1
Repairng the plastic motor mount is about as dicey or worse than fixing the elevator. That plastic doesn't take any glue very well. The firewall mount becomes a mess if you glue it, compromising future proper fixes. The gearbox stresses play havoc on structural repairs to that part. Best to just replace them.
Like most folks, you learn these things the hard way.
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bdg
Flying officer
Posts: 17
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Post by bdg on Jun 30, 2012 17:57:06 GMT 1
Would a little foam-safe CA help to strengthen the horizontal stabilizer? It is not a perfect solution, but should add some strength. That all said, a new horizontal stabilizer with tail is (I believe) less than $12.
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Post by flydiver on Jun 30, 2012 18:57:41 GMT 1
Help? Probably.
Enough? No idea. Try it....then try to bend it.
You are butt gluing 2mm worth of crushed foam. Seems that's like butt gluing a couple of 2X4 together and wondering if you can use it for a structural application.
You want to risk a crash on it?
IMO, fix it right or get a new one.
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bdg
Flying officer
Posts: 17
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Post by bdg on Jul 1, 2012 5:16:48 GMT 1
Again - a $12 solution is possible. Regarding the strength - to me it depends upon whether the crease is *just* a dent or all of the way through.... butt gluing is extreme, for sure.
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Post by flydiver on Jul 1, 2012 15:31:57 GMT 1
The foam has little bending strength at that thickness. It does have some crush resistance.
Skin the foam with plastic and it stiffens it with an I-beam kind of effect. Ruin that I-beam with a crease crushing the foam and the strength is largely gone. It creates a hinge point.
Think of cardboard > simple paper that has been corrugated. It's resistant to bending until you crease it. Try gluing the area of crease on some folded cardboard and see how much it helps.
If you have a dent in the plastic and you cut it open to glue it you've now further weakened the structure. Seems to me complete reinforcement is the only really viable option besides replacement.
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Post by gregstone on Jul 1, 2012 23:58:31 GMT 1
So far so good - replaced tail feathers and glued motor mount back together - and in place - with five minutes epoxy. I'll check it frequently, but so far it's stood the stresses of a few batteries worth of flying. Meanwhile, I have a whole new fuselage and new wing and new cowl - I just figured I would continue to learn on the beat up one. I know the repairs may not hold, but I'll keep a close eye on them.
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gspan
Flying officer
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Post by gspan on Aug 23, 2012 18:48:14 GMT 1
I was about to throw away an old beat up cowling and thought about this thread. I wonder if it could be cut to fit over a crease like that and epoxied in place. It would give it strength and it's not thick at all.
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Post by luvofthagame on Aug 23, 2012 22:11:17 GMT 1
I've got a crease very similar, just not near as deep...more of a surface bend...its had no affect to many hours of flight, but I am always checking and so far, so good...but, if you try to bend it a liitle and it kind of hinges there, I would let it go...its really not worth it when a replacement is 10 bucks...I've got the replacement waiting in case...
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