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Old May 24, 2011, 05:26 PM
Building with TLAR precision
Zenmaniac's Avatar
near Madison, WI
Joined Jan 2009
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Originally Posted by DudleyLeRoux View Post
While i'm in the mood to type : I read in the Modelling Science forum that a sharp leading edge can cause pitch sensitivity, with one member having built a flying wing with a sharp leading edge that was unflyable until the LE was rounded correctly.
Thanks for the help, guys. Yeah, I made this exact newbie mistake with this wing -- thinking a sharp edge would penetrate better. Wrong. Sally was totally unflyable until my friend dope-slapped me and said "You call this an airfoil? Let's start by sanding it flat"

It's not the leading edge that is my concern, Dudley -- I did what you (and Thepasty) said, with some 6 oz fg on the LE. It's the rounded corner of the LE and the tip. Layer, it sounds like you use something thinner than mylar, if I'm understanding you correctly.

Maybe I'm making a bigger deal about it than there has to be. I should just throw a wing in a bag and see what happens.

I've been playing with a combination of PU glue and fiberglass, rather than epoxy and fiberglass. One of my building friends has a terrible sensitivity to epoxy after years of exposure. He's pretty fired up about my first trial of PU/FG on a sample of a Sally tail. Now that the weather's warm enough to paint, maybe that will be a weekend project.


-= Dave
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Old May 25, 2011, 07:25 AM
certified insomniac
ziggx's Avatar
Durban SouthAfrica
Joined Feb 2007
584 Posts
that tail looks awesome did you vak bag it and is it a lot lighter than epoxy and have you tried painting the mylars to see if the paint transfers to the part
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Old May 25, 2011, 06:23 PM
Building with TLAR precision
Zenmaniac's Avatar
near Madison, WI
Joined Jan 2009
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Originally Posted by ziggx View Post
that tail looks awesome did you vak bag it and is it a lot lighter than epoxy and have you tried painting the mylars to see if the paint transfers to the part
Vac bagged: Yes
Lighter: Maybe a little (but I guess it depends on how much you put on...). This tail weighs 10.5gm, but could have used a little more glue along the edge to make a stronger seam.
Paintable on mylar: We'll see this weekend, weather permitting.

-= Dave
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Old May 28, 2011, 08:49 AM
Building with TLAR precision
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near Madison, WI
Joined Jan 2009
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Originally Posted by Thepasty View Post
in good time my friend... we got a run of 3 blue foam Swingers taking up the workshop atm.

The weather is cooling again this week, as soon as the nights are warmer I'll get the wings glassed... I'm even going to paint these bad boys!
Hmmm... April 11. Must be a really late summer in Cornwall this year...



-= Dave
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Old May 30, 2011, 10:51 AM
Building with TLAR precision
Zenmaniac's Avatar
near Madison, WI
Joined Jan 2009
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A new Sally wing is born!

This is for my friend Darryl, and was a test using PU glue instead of epoxy (since he's highly sensitive to epoxy).

Here's the wing, just out of the bag with minimal trimming it's at 111 gm (50 gm less than my first wing!)

The PU glue we used is Elmer's Glue-All Max, which says "lower foaming" -- though I've seen good results posted with standard Gorilla Glue. It held the paint really well, and we had no bubbles in the finish. Used Krylon plastic paint. Really pleased -- I might have to make another for myself!!!

Hopefully completed plane and in-flight pictures soon!

-= Dave
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Last edited by Zenmaniac; May 30, 2011 at 12:20 PM.
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Old May 30, 2011, 10:55 AM
scratch build everything
DudleyLeRoux's Avatar
South Africa, KwaZulu-Natal, Botha's Hill
Joined Aug 2009
1,219 Posts
fantastic. 111g gawd is that the 810mm wing?
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Old May 30, 2011, 12:18 PM
Building with TLAR precision
Zenmaniac's Avatar
near Madison, WI
Joined Jan 2009
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Originally Posted by DudleyLeRoux View Post
fantastic. 111g gawd is that the 810mm wing?
Ha! Yes sir! I think that's pretty close to what Steve gets on his <200gm AUW glass Sally. We used 1.5oz glass straight on the top and the same on a bias on the bottom, with 6 oz on the LE.

-= Dave
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Old May 30, 2011, 12:27 PM
.....till the wind drops.
Sean Oelofse's Avatar
Port Elizabeth, South Africa
Joined Oct 2006
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Fantastic Dave!!
Keep going!
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Old May 30, 2011, 12:47 PM
Building with TLAR precision
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near Madison, WI
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Originally Posted by Sean Oelofse View Post
Fantastic Dave!!
Keep going!
It's all in Darryl's hands now. I gave him a pod, finished tail, and the wing we worked on together, dimensions for the ailerons and template for placement of the servos.

He's built some big 100"+ thermal ships in the past, like 15 years ago, before his issue with epoxy started. So he's giddy as a schoolgirl knowing that the PU method works, and he can get back to building!

He's promised a maiden flight by the weekend! Stay tuned for pix and vids (I promise, not as long as my last one )

Guess it means he might want his vacuum pump back...

-= Dave
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Old May 31, 2011, 04:33 AM
Fly fast, Dont crash.
Thepasty's Avatar
Cornwall, UK
Joined Sep 2006
2,459 Posts
Wow Dave, I had no idea you could bag with PU... and get great results too!

You got my mind wurling now, I need to find out more about bagging with PU.

great job.

Glass and Carbon Sally are still going strong btw... I've been a little side tracked with building speedy electric things for FPV recently but unless I stuff this one in too I should have a clear bench for bagging wings to go with the Zally fuz J kindly sent me.

steve
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Old May 31, 2011, 08:14 AM
Building with TLAR precision
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near Madison, WI
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Originally Posted by Thepasty View Post
You got my mind wurling now, I need to find out more about bagging with PU.
Simple, actually. No measuring, no mixing, not that much different than epoxy for application. We wetted the mylars with PU, laid on the glass, rolled and wetted the glass where we saw dry spots, a little on the cores, and most importantly misted the PU surfaces with water before bagging. As you know, PU needs water to activate. I don't know how much working time you have with PU -- it must have taken us an hour or so to do the layup (maybe a little less), but I think the critical time is once you've misted with water.

We kept it in the bag overnight. I don't know what the actual set time should be. I took a test piece out of a bag after 3 hours, and it kept foaming . Could have been not enough water, or whatever else.

The PU we used is a little bit thinner than the standard Gorilla Glue, but I think guys use standard PU straight up.

-= Dave
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Old May 31, 2011, 08:31 AM
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Cornwall, UK
Joined Sep 2006
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Thanks Dave, defo going to give this a go, I got some PU at home thats thin and see through and not really man enough as a parts joiner but should be cool for this application.

I presume it gives a more flexible finish than glass?
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Old May 31, 2011, 09:31 AM
Building with TLAR precision
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near Madison, WI
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Originally Posted by Thepasty View Post
I presume it gives a more flexible finish than glass?
I would guess. but it's a little hard for me to judge based on the layup. But the glass hanging over the edge of the foam that got PU glue is definitely not as stiff as I would have expected with epoxy.

The crash-resistance is yet to be tested -- seems to me that it would be a less brittle finish, tho.

BTW, I flew my Sally for almost a 2 hr flight on a tree/bush-covered hill yesterday. Darryl's Alula got knocked down 4x from being pushed back toward the hill and the dirty air above the scrub. But Sally was able to penetrate out in front of the hill to the clean air, and when heavy thermal sink came along was fast enough to cruise the length of the hill to find lift zones. Not any issues that you guys on the sea ever encounter, but works well for us!

-= Dave
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Old May 31, 2011, 09:33 AM
Building with TLAR precision
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near Madison, WI
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Originally Posted by Thepasty View Post
..., I got some PU at home thats thin and see through ...
The depron tail, above was done with the "brown" PU, and it does impart a bit of a tint to the true white color of the foam (you might not see it in the pix). I haven't tried this with the new fast drying clear Gorilla Glue.

d.
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Old May 31, 2011, 09:41 AM
Fly fast, Dont crash.
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Cornwall, UK
Joined Sep 2006
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The thing I like about my Sally most is its wide flight envelope, it'll fly great in anything from 4 to 40mph... one hell of an efficient airframe.
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