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8ft Zagi Sloper - DIY / Hot cutting / Fiberglass

thenated0g

Drinker of coffee, Maker of things
Mentor
#1
*********I wasn't going to do a build thread but i had some free time last night so typed it up in case anybody was interested.

Last week i finished building another plane and wanted something to do and i got inspired to do a "quick" hot cut wing. This is in comparison to the over year it took to do my last big build ha! Hoping to have this done in a month time total so kind of hurrying and trying not to let my anxiety and "is it perfect" get in the way.

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www.zagi.com

I want to move my hot cutting away from the home depot white rigid insulation foam, which is kinda squishy, to the pink foam which is very rigid and easy to sand. So my thought process was "how do i get rid of all this foam at once?". I didn't want to do a 16' as it would be pretty hard to reinforce this already flimsy foam and that would be really hard to fit in my jeep. So that meant the other side of the foam was my size limit (4x8 sheets), so 4ft wing cores it was, for a total of 8 ft, as i know that will fit in my jeep even if i make a one piece wing. Plus i was wanting to do a hand cut wing which i hadn't done in a while.


One thing i decided to do different this time was try galvanized flashing instead of my usual aluminium flashing for my templates. It worked out great. It is more rigid than the aluminium and keeps it shape much better as its getting moved around on the workbench, but it is still easy to cut with desk scissors. I also moved to my banggood adjustable bench power supply. Previously i had used either a 3s(12v) or 4s(14v) battery. Being able to crank it up to 30v made a noticeable difference on the steel fishing wire i was using. Plus it was very nice to reach over to a dial and adjust it as needed. Since i was in a hurry i temporarily mounted the other end of my hot wire to a shelf bracket screwed into studs. Worked great, would do again. I also had to laminate two sheets together to get the needed thickness. I used super77 spray adhesive.


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After the cores have been fiberglassed i am going to add some carbon fiber rods that interlock on each other at CG. This will be the only internal spar and what takes all the G load. There will be "something" in the nose and tail that keys into eachother to stop the cores from rotating on that spar. Some wooden blocks or dowels or something simple. I need a way to center the hole for the carbon so i traced out and cut some matching balsa templates and glued them to the root of each wing.

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I realized that i will need the wingtip stabilizers to also be removable so i added some balsa dowels to the wingtips as a point to screw into later.

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This morning i applied DAP light weight spackle to the entire bottom surface. This will create a more even surface and act as a sealer for the epoxy so it doesn't soak into the foam (get heavy).

Next steps are to apply one layer of 6oz S-glass fiberglass to the bottom of the wing cores. This will be cut flush, no overhang/overlap. I will squeegee out as much of the epoxy as i can. The weave will be filled in later with epoxy and phenolic filler. The top will also be cut flush where it wont wrap around the curve well. Later i will come back with a thin strip of fiberglass to connect the two pieces.

Also finalized the art for one side...probably the top.
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oh yeah, i also made a custom sticker for it lol
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thenated0g

Drinker of coffee, Maker of things
Mentor
#4
Sanded back the spackle this morning and layed out the fiberglass cloth only to realize that i won't have enough. I also realized that 6oz s glass is HEAVY! So since i need to order more fiberglass i am going for some standard wing fiberglass which is 3oz. So be a week before i can apply it but should be a lot lighter. Guess I can work on scaling up the winglets and cutting them out of coroplast to see if they will be rigid enough.

Also finalized the other side graphics.
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Piotrsko

Active member
#5
Since the major structural direction is stretch on the skin, have you ever tried dress makers dacron? Comes anywhere from 1/4 oz to 3oz sq ft. I used to use it for my "silk" covered wings, and also on parts of my 1950 pacer airplane. Do have to wash it first to remove the greige. It heat shrinks also.
 

bracesport

Well-known member
#9
@thenated0g - exciting times with the fibreglass, I really enjoyed glassing my vista wing - I used too much resin so next time I was thinking to use a vacuum bag - something simple like a kitchen vacuum bag sealer!

I think I used a similar cloth - I think mine was 2.5oz - worked well!
 
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thenated0g

Drinker of coffee, Maker of things
Mentor
#12
I forgot to weigh the wing cores before epoxy and fiberglass. Currently one wing core, with one side done, weighs 515g. Still need to add spackle, epoxy/fiberglass, epoxy and filler to fill in the weave, paint, and spars. If i could keep it in the 1k-1.5kg range per side i would be happy.

I wanted to add some leading edge protection and stiffen it up a little so i used hot glue to tac in place some carbon tow on the leading edge. This will be epoxied in place. Than the top will get 3oz fiberglass. After that i will put one long strip of 6oz s-glass on the leading edge nose area so it overlaps about an inch or 2 on top and bottom. This should really toughen it up and make it more rigid.
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Currently i am worried about the stiffness of the elevons. I may need to wrap them in 6oz to get them rigid enough. But wont know until this first layer of 3oz is done and i cut them loose.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#13
Topside got a layer of 3oz fiberglass immediately followed by a 4 inch piece of 6oz s-glass from tip to root. Weight is currently 830 grams per wing. I still need to cut the elevons off and than take small, probably 2 inch, piece of 6oz s-glass tip to root on both the elevon and trailer edge of the main wing to stiffen them up. I also decided to try vinyl as the top covering, so aside from some sanding that may be the next step. I dont think i need to do filler and sanding. I have asked ninjawraps1 how much it would cost to do some custom vinyl on the top.
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CapnBry

Active member
#14
That's awesome. I wire cut my first test piece of foam using some 28awg stainless "art wire" I had on hand and have been scratching my head about how complex a system I wanted to make to try to cut my first wing. Your first post is inspiring in its simplicity-- I already have a power supply, wire, foam and a nearby wall! I'm excited to see how this comes out because I love how giant you're going.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#15
That's awesome. I wire cut my first test piece of foam using some 28awg stainless "art wire" I had on hand and have been scratching my head about how complex a system I wanted to make to try to cut my first wing. Your first post is inspiring in its simplicity-- I already have a power supply, wire, foam and a nearby wall! I'm excited to see how this comes out because I love how giant you're going.
I actually have a CNC hot wire cutter that i made, but i really enjoy the hand cutting process. It does require some "finishing" work, ie spackle or something else to fill in your mistakes though. The larger wings are much more forgiving of mistakes, thin wings you can very easily make unusable. Here's a video i made a while back:

 

mayan

Well-known member
#16
I actually have a CNC hot wire cutter that i made, but i really enjoy the hand cutting process. It does require some "finishing" work, ie spackle or something else to fill in your mistakes though. The larger wings are much more forgiving of mistakes, thin wings you can very easily make unusable. Here's a video i made a while back:

Great video thanks for sharing :).
 

CapnBry

Active member
#17
I actually have a CNC hot wire cutter that i made, but i really enjoy the hand cutting process. It does require some "finishing" work, ie spackle or something else to fill in your mistakes though. The larger wings are much more forgiving of mistakes, thin wings you can very easily make unusable. Here's a video i made a while back:
Nice, you cover everything in that video. I'm going to try tonight with some pink FOAMULAR bits I have in the closet!

I was wondering last night thinking about the pivot point cuts, what's the height of the pivot point in relation to the foam? It seems to me that if you have templates on both ends, that all the pivot point needs to be is below the cut point. If it is too far below then you can't cut the bottom surface because the wire won't be pulled into the template properly. Do you find that the pivot height has to be exactly in the middle of the airfoil shape to get good shape on both sides? Or should I flip the foam over once the top is cut so the cutting isn't as sensitive to the height of the pivot?

EDIT: Forgot to say that I love the FliteTest TV in the background. Excellent post-production touch. ;)
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#18
ha, yeah i forgot about that little tv. I ripped out the guts and put some 12v leds inside. Think i ended up tossing that this year, it fell and broke.

Yes the pivot point height. I usually make that exactly the same height as the very bottom of the root airfoil template. This means the bottom of the wing is flat and the top of the wing slopes down from root to tip. I made a cap232 which was a symmetrical airfoil i think and i put the pivot point in the middle to make it the same on top and bottom. I havent researched this much, but i also havent had any issues always using the bottom flat method. I am actually going to be picking up one of those laser line levels to make this leveling process way way faster.
 

CapnBry

Active member
#20
Man, that is one big fat piece of lift right there. Half your plane is bigger than most of what I build. :-D How does one launch an 8ft slope soarer with no motor? Do you go running at the ridge with it over your head and give it a chuck?

And off-topic but I couldn't wait until after work so I did it during lunch. My first clark-y hot wire cut airfoil. Just 130mm chord because that's the size of the scraps I have sitting around. Just 3D printed the airfoil in PLA (with a 26 degree bead chamfer on the edge so the wire doesn't dig in), screwed it in the side, and turned on the power supply. The PLA didn't melt at all and if I didn't have to stop halfway because the foam started to scoot away it would have been perfect!
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Thanks for your helpful videos and inspiration and I'll return to just oohing and ahhing at your work.