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Building Tips and technical articles. => Building techniques => Topic started by: Tom Vieira on August 06, 2018, 06:23:10 AM

Title: foam wing advice
Post by: Tom Vieira on August 06, 2018, 06:23:10 AM
Hi all,

I'm building a Gotcha Streak RST from Core House, and I put the wing together last night, no issues, I thought...

Went down this morning, and apparently it shifted a little, and what looked like a nice tight joint at the leading edgehas opened about 1/8 inch, and the Titebond I was using for its assembly ran out.

I do have extra cores, but would rather save this if possible.  just wrap the center joint with some fiberglass and call it a day?
Title: Re: foam wing advice
Post by: Jim Mynes on August 06, 2018, 07:37:03 AM
Fill the gap with epoxy/microballoon mix, then use the same mix to glue some reinforcing glass cloth to the wing joint. Squeegee off as much glue as you can to save weight.
Title: Re: foam wing advice
Post by: Tom Vieira on August 06, 2018, 09:15:13 AM
cool, thanks!
Title: Re: foam wing advice
Post by: Brett Buck on August 06, 2018, 09:16:49 AM
Hi all,

I'm building a Gotcha Streak RST from Core House, and I put the wing together last night, no issues, I thought...

Went down this morning, and apparently it shifted a little, and what looked like a nice tight joint at the leading edgehas opened about 1/8 inch, and the Titebond I was using for its assembly ran out.

I do have extra cores, but would rather save this if possible.  just wrap the center joint with some fiberglass and call it a day?

    I would be sorely tempted to cut out the glue, square it up, and then try again.

      Brett
Title: Re: foam wing advice
Post by: Tom Vieira on August 06, 2018, 09:24:07 AM
Brett,

tough to do with the top and bottom spars glued in...
Title: Re: foam wing advice
Post by: Mike Haverly on August 06, 2018, 10:22:01 AM
If you ignore the problem it won't go away.  If you have trouble making fly the way you want, you will always wonder.  I would fix it before it is complete. 
Just my opinion of course, but I have experience in the "ignoring" part.
Title: Re: foam wing advice
Post by: john e. holliday on August 06, 2018, 10:44:27 AM
I too had a problem with Core House foam core having a gap either leading edge or trailing .  Checked wing and it was straight,  Filled gap with filler and finished the wing according to instructions and had no problems with the planes not flying right.   D>K
Title: Re: foam wing advice
Post by: Tom Vieira on August 06, 2018, 11:17:57 AM
the first time I was dry fitting things, there was a huge gap in the back, but the LE was straight.  understandable, as it's cut out of a big block, and no guarantee that was straight.  so, I measured and cut...

looked pretty good, so I propped it up, but I must've biffed it somehow, thus the small gap.  it looks tight from the spar back, but the spar fwd it a little wonkey.  a few quick checks (I noticed it this morning while getting ready for work), and it looks straight and such, just this annoying gap.  I also tried to flex the wing, I couldn't make it spread.

I think a 2" wide strip and some epoxy may be in my future....
Title: Re: foam wing advice
Post by: Tim Wescott on August 06, 2018, 12:04:14 PM
I built a couple of trainers using the Gotcha Streak wing cores.  I started with epoxy + microballoons, but have moved to using clear Gorilla Glue.  It's lighter, and much closer to the strength properties of the foam, so you don't re-fracture the wing right where the glue joint is, and you don't add much weight.  I've even been using it to fill holes when there's chunks missing after I gather up the pieces and glue the wing back together.  Just don't use it for wood to wood joints.

Spritz water in the hole, inject some glue, poke it in with a stick, then wait.  When it's solid (about an hour or two) take a sharp wood chisel* or a single-edge razor blade and carve off the excess.  Then proceed.

* Really sharp, not from-the-store sharp
Title: Re: foam wing advice
Post by: Fredvon4 on August 06, 2018, 12:35:34 PM
Gotcha streak and RST are pretty much same.... Narrow Bass wood fuselage and 1/64th 1 inch wide by 23 inches long glued inside of wing cut out...The bell crank is under the wing attached to the Fuselage

I have two that I Use Gorilla tape to hold the wing in the fuselage....quite frankly this is about the easiest stuntable plane to make alignment on

The wing basically is warp free... NO flaps
Tail fathers are keyed and not hard to get Zero Zero on all planes
Skewing the wing and alignment are easy with shims, and once taped or glued, it is level level level to the thrust line and tail

Problem for OP is did the wing shift out of good alignment...Epoxy is easy to soften and with heat gun..BUT NOT on a FOAM wing!!! and because of the 1 inch wide 1.64th opening the wing is in....NOT a whole lot an be done without major surgery

I say fly the sucker...have fun and build another...I have three...about the best bang for the buck semi ARF there is

Title: Re: foam wing advice
Post by: Will Hinton on August 06, 2018, 08:44:52 PM
Ahh Fred my friend, I have softened epoxy in a foam wing with no adverse effects.  Just don't plaster the gun down on the wing but pass it back and forth slowly until the epoxy softens up and give it a twist to staright, or seperate it if that's your goal.
Title: Re: foam wing advice
Post by: Tom Vieira on August 07, 2018, 06:03:04 AM
I'm sure this thing will see the dirt soon enough...  I took another look last night at the wing, and it all still looks pretty freaking straight and true.  I'm wondering if I didn't pay close enough attention to the spars, and one or both had an ever so slight curve that pulled it just enough to make a gap.

I think i'll wrap it and go nuts.  the wing will be taped in, not glued.  so, if it proves to just be a flying pile, I have extra cores.

or, I'm also building a second one at the same time for my nephew. something a little more sturdy than the 1/2a jobs.  His will probably smack the ground quicker.  Perhaps just make this wing his  LL~
Title: Re: foam wing advice
Post by: phil c on September 09, 2018, 05:18:38 PM
I'm sure this thing will see the dirt soon enough...  I took another look last night at the wing, and it all still looks pretty freaking straight and true.  I'm wondering if I didn't pay close enough attention to the spars, and one or both had an ever so slight curve that pulled it just enough to make a gap.

I think i'll wrap it and go nuts.  the wing will be taped in, not glued.  so, if it proves to just be a flying pile, I have extra cores.

or, I'm also building a second one at the same time for my nephew. something a little more sturdy than the 1/2a jobs.  His will probably smack the ground quicker.  Perhaps just make this wing his  LL~

Really TJ you can just fill the slot with some light weight filler and proceed.  That portion of the wing has no real structural or alignment function that a little vertical gap is going to mess up

As FredVon4 points out, the ply saddle for the wing provides a ton of strength for the wing/fuse joint, and makes it easy to shim into alignment with the rest of the plane.
Title: Re: foam wing advice
Post by: Tom Vieira on September 19, 2018, 11:41:57 AM
Hi phil,

both planes I have built are flying great!  even trying a few new moves now ;)