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4 meter Plank - Build thread

thenated0g

Drinker of coffee, Maker of things
Mentor
#1
A few months back i randomly came across this beauty of a plank:​

2019-12-05.png

Heres some links to the original model, no longer being made:
http://www.wing-tips.at/Portraet/Modelle/modelle.htm
Nice video of the control surfaces:


So i immediately started a file in inkscape to start planning out how to make this work. Also started tickling the ear of James Hammond who manufactures a lot of popular slope soaring and racing slope soaring planes.

overview of original plan..JPG


Right away i was nervous as its a pretty thin and narrow wing with a wide wingspan. My plan is a 2 piece wing, so 2x 80" wings that join in the middle for transport. At 80 inches they are only about 11 inches deep at the root and barely thicker than an inch. This is not much material to keep 80 inches rigied out to the wing tip. Thats a lot of leverage being placed in the center of that wing. So started asking more experienced people about that as well.

As an example here is how the plane will compare to my 5'11 height:
2019-12-07 (1).jpg

Ill save the back and forth and just get to the end plan that i decided on. Just wanted to say that this was not entirely me coming up with this, more like listening to the experts and just choosing which path to take.

The wings will be blue high density foam vacuum bagged with epoxy and fiberglass. I am choosing to go with 4oz S-glass. S-glass is stronger and stiffer than standard e-glass by 25-30% but a lot people don't know that it is also stronger than carbon fiber while also at a significantly cheaper price. Carbon of the same weight cloth would be stiffer and lighter, but would break well before the fiberglass would.

While it will have an internal spar, this is mainly to hold the wing joining tube. The strength of the wing will come from overlapping fiberglass layers. So while on the wingtips it will have 2 layers of 4oz (8oz total) in the center area it will get up to 20oz total. Here's a diagram of my current layup plan:

fiberglass plan..JPG

In the above picture i show the different layers. One thing to note is that parts 1-4 will be twice as deep as in the picture as the wrap around the top and bottom layers the same amount. Every 25% of the leading edge another layer is added. Than after all those layers are added the final piece, 5, is added which covers the entire wing surface top and bottom tying everything together. The Center of gravity, at least in the center of the wing, will be within that leading edge thick layer of fiberglass.

Also in the picture is the Mandrel wound carbon fiber tube that will go 30" up into each wing and hold the joining tube. The inside of the root will be a piece of plywood. Also drawn is a peg to keep the wings from rotating.

The control surfaces are actually 2 elevators on the inside and Ailerons on the outer parts of the wings, not elevons as you normally see on planks/wings. This will allow things like crow braking if i want in the future.

The fuselage, at this point in time, is going to be a gifted fuselage from a rcgroups member. He has fuselage from a big xplorer sail plane that broke behind the wing saddle. This will work well enough as i don't need the tail boom at all.

The reality of physically cutting the wing and shipping it via usps means that some things have to change. After some back and forth here is the cut plan i decided on with the same guy that cut my booby planks:
daniels plan.png


PW51 airfoil with the internal spars cut already.
Each core will be cut in 3 sections. 2x 30 inch sections and the wingtips in 20". I will manually add the sweep back on the wingtips and sand to match the airfoil later.

Instead of a constant sweep back the center will have a straight leading edge. This will allow the spar to be straight across the join. Than the outer 30" section will sweep about 11mm and the wingtip another 29mm. If you have watched any cockpit views of full scale high performance gliders it actually is pretty similar, the broken section look.

Im sure i missed some stuff. I will continue to add as the build goes on.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#9
Heres another thing i do with Inkscape to help me see exactly how much materials i need to purchase. As i build everything full size in inkscape i can get the dimensions of fiberglass cloth for example and lay the parts on it and see how many yards i need to purchase:

1578517843517.png
 

FoamyDM

Building Fool-Flying Noob
#10
I have an idea for building a rigid foamwing, like a torsion table. The are coveted by woodworkers because they have a high capacity and yet remain extremely flat. Honeycombing might be a better fit.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#11
For coloring i have decided to try painting the inside of the mylars.

I have tried two other ways on other planes. One is using chiffon cloth under the fiberglass like i did on my booby build. This looks amazing, gives it an almost carbon fiber look, but it would add an additional $60 to the cost in materials, its heavy, and makes wetting out all the layers much more difficult.

On the glass rat i just finished i tried using pigment. I just wasnt happy with it. It was not opaque and given that ill probably be doing even one wing in multiple epoxy batches, getting the ratio perfect both times would be irritating.

Bonus 3rd option! I forgot, after i wasnt happy with the pigment on the glassrat i than tried painting it. This really shows all the pinholes on the fiberglass and would require some work but as far as the plane flying wont really matter. This will be my plan B if painting the mylars doesnt work.

The problem with painting mylars is that you wax them first so the paint doesnt stick but .. well wax and paint is basically oil in water. They dont like eachother and fisheyes are pretty common if you do it wrong. But its pretty much the gold standard of finish for "moldys".

The idea as i have read is to do a bunch of very light coats building up on the wax. Once the epoxy sets the paint and epoxy mix and become a super hard coat.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#14
I have the scat cat 500 build so finishing up on my workbench so going to be a week or 2 before i have room in my shop. I also plan on doing another booby. when i ordered the cores for my original vacuum bagged booby i ordered 2 sets. The second set was always going to be my "heavy" build with a ballast tube. I have some 12oz carbon fiber for it. So i think i will do one more vacuum bagged plane before this big one to give me some more experience. But the nice thing about this big wing coming in 6 pieces is that most of the internal work to be done before bagging is just on those central 30" sections. so i can do a lot before i even get close to bagging, so may get some work on it here and there. But man 14' or so is a pretty big area to have to assemble a plane. i really need to clean my shop.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#15
I need to get back into the forums...this seems like a good place to start. :)
It would be about a 5 hour drive, but you are always invited the annual Sunset Beach camp n fly. Its about a 4 hr drive for me and so much fun. 4 days of standing looking at the beach flying with others. Going to try and have this ready for maiden at this years on may 2nd. you can even camp for free if so.

 

thenated0g

Drinker of coffee, Maker of things
Mentor
#16
I am going to upgrade my vacuum bagging setup a little bit this time. Not that i have noticed any deficiency in my current setup, but i guess to get the highest strength out of your epoxy you have to follow a heating schedule. Like the initial 8 hrs in the vacuum bag maybe at 80f and than for the next 12-24hrs you put it in a 'hotbox' at 120f. Each recipe of epoxy has a schedule that it "likes". Some guys build a box out of insulation foam with lights inside or a heater. But i came across the easiest setup, which i will try, and that is just wrapping the wing in an electric blanket on low and than wrapping that in another blanket or putting in a sleeping bag.

I have an old electric blanket so i picked up a $35 temperature controller from amazon to complete the setup:
1578597683456.png
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#18
@thenated0g - the sunset beach looks like a very cool event! You will have to turn pro soon with your epoxy skills! :D
I burned out my vacuum switch on my medical pump. Didnt realize that the pump pulled more than the 5 amps the little switch liked. Oh well, got a new one on the way and a 110v (our house voltage) relay so it wont happen again.
 

Mid7night

Jetman
Mentor
#19
It would be about a 5 hour drive, but you are always invited the annual Sunset Beach camp n fly. Its about a 4 hr drive for me and so much fun. 4 days of standing looking at the beach flying with others. Going to try and have this ready for maiden at this years on may 2nd. you can even camp for free if so.

I'll look into it, might be fun!
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#20
I'll look into it, might be fun!
its a nice campground. My spot is literally 10 feet from the hill, its like a 2 minute walk to the top. Beach access is just a short walk down the road. Camp bathrooms, but they do have showers. We have basically taken over the entire south camp loop where the glider port is. Saturday night they have a big potluck. Last year it was basically show up friday afternoon and fly until it got dark. Next morning get up and have breakfast and to fly something light,(6-8mph) by lunch and rest of the day it was 12-20mph. Do that again sunday and Monday. Mostly foamy's, lots of dreamflight stuff. The hill is pretty long so guys that have nicer planes would take a short walk to get some distance or stay up high.


https://www.google.com/maps/place/36°53'04.8"N+121°49'41.8"W/@36.8846683,-121.8304617,894m/data=!3m2!1e3!4b1!4m6!3m5!1s0x0:0x0!7e2!8m2!3d36.8846642!4d-121.8282732
 
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