That looks perfect!
4 Metre Glider Scratch Build
- Thread starter Jackson T
- Start date
That looks perfect!
Most of the carbon tow I've purchase online was either from a US distributor or an eBay source out of the Ukraine. From AU it might be cheaper to pick up from Japan, but in any case cheap is good. For something ribbon like, go with 10k or higher tow. You'll also want to use a thinner epoxy, preferably with a longer working time (15 minutes, minimum, 60 minutes prefered), and do your layup/prep on wax paper, then transfer to the model.
To do the layup, I'd do three layers of the tow, in tapering lengths -- longest spans ~2/3 the span, next 1/2 span, and last 1/3 span. It doesn't need to run all the way put to the tips.
As you cut the lengths, 3m77 (spray adhesive) them to keep the strands more or less under control, then lay them, one on top of the other over the wax paper. Mix your epoxy, wet out the carbon, squeegee out as much as you can (credit cards work well for this) then blot the carbon with a paper towel . . . Twice.
Once blotted, the layup is done, its time to apply. cut the wax paper around the carbon, and use that to apply the carbon to the wing -- line it up with the paper down, then flip it over. Press down on the wax paper to stick it down. Leave the paper on until cured, and for better results cover the whole surface with wax paper/saran wrap, and sandbag it (sugar in a ziplock works in a pinch) to hold it pressed down while it cures improve the bond strength. Top is sufficent. Top and bottom is better.
To do the layup, I'd do three layers of the tow, in tapering lengths -- longest spans ~2/3 the span, next 1/2 span, and last 1/3 span. It doesn't need to run all the way put to the tips.
As you cut the lengths, 3m77 (spray adhesive) them to keep the strands more or less under control, then lay them, one on top of the other over the wax paper. Mix your epoxy, wet out the carbon, squeegee out as much as you can (credit cards work well for this) then blot the carbon with a paper towel . . . Twice.
Once blotted, the layup is done, its time to apply. cut the wax paper around the carbon, and use that to apply the carbon to the wing -- line it up with the paper down, then flip it over. Press down on the wax paper to stick it down. Leave the paper on until cured, and for better results cover the whole surface with wax paper/saran wrap, and sandbag it (sugar in a ziplock works in a pinch) to hold it pressed down while it cures improve the bond strength. Top is sufficent. Top and bottom is better.
Wildthing
Legendary member
Check out Jackson T link post https://forum.flitetest.com/index.php?threads/4-metre-glider-scratch-build.57736/post-467704
Price per foot is the same on ebay and shipping appears to be cheaper plus you can order as much as you want.
Jackson T
Elite member
So it looks alright? I'm not sure what to look for.
Jackson T
Elite member
@Craftydan and @rockyboy, it's a 3 piece wing, going off wing joining breaks and dihedral joints, where would be a good place to start each layer? Pic below illustrates the wing dihedral and 3 piece wing breaks. The bigger lines are wing breaks, the smaller ones dihedral. Going off dihedral, each semispan has 1m flat, 0.5m dihedral, then another 0.5m dihedral. Going off wing joining breaks, the centre section is 1.4m, and the outer sections are 1.3m each.
How's this CF tow: https://www.ebay.com.au/itm/TORAY-T...3aa6be80ef:g:Q6kAAOSwBahVID16&frcectupt=true? What does blot mean? Would 30 min epoxy be alright? How much working time will I get, and how much do you think I'll need? Thanks again for all of your help!
How's this CF tow: https://www.ebay.com.au/itm/TORAY-T...3aa6be80ef:g:Q6kAAOSwBahVID16&frcectupt=true? What does blot mean? Would 30 min epoxy be alright? How much working time will I get, and how much do you think I'll need? Thanks again for all of your help!
If the cost/shipping is right for you, that tow looks like what you're looking for.
Since the CF's strength will be broken at each wing break (the wing will only be as strong as the joint there) id run the longest length out to the ends of the center pannel, then size the tapering layers to fractions of that span(1/2 mid span and 1/3 mid span?). You could run an additional length 1/3 the way down the wingtips, but all of the force concentrates at the center, so only one layer of that should be sufficient on the tips -- your call.
Blotting, like squeegeeing is a process of removing excess epoxy -- you need to fully wet the epoxy to ensure all the fibers are well coated, but then you'll likely remove more than half of what you applied. Blotting involves taking a paper towel and patting it down on the wet carbon to soak just a little bit of the carbon into the paper towel. Yes, you will go through a lot of paper towels doing this, but this is how you get a good light layup. It will start to look too dry, and thats usually just about right.
30 minute will do, and unless you heat it to further thin it out, you should get most of that time. You will still have to work quickly -- 1.3 m is a lot to work -- but you should have plenty of time to go from wetting to pressing. I prefer 60, mostly because that gives me time to think and react sensibly if (when) something doesn't work like I expect it to. This is a good, simple layup to start with, so you should have plenty of time, but take a break just before you mix the epoxy and make sure everything is laid out where it needs to be and rehearse what you plan to do in your head to keep surprises to a minimum.
Keep in mind, For each patch of tow, everything must be done at one time, but you can/should do each patch in a separate sequence -- don't try to do a top spar and bottom spar on the same wing at the same time.
Finally, curing time: Unless the bottle says longer, give it a full 24 hours before you think about touching it again. You can always let the stuff cure longer, but never unpack a layed-up part early. The resin may be simi-solid fairly quick, but it can still be flexible (easy to damage) a lot longer than you'd expect. Keep a small cup of the excess to the side to know how the cure is coming along on the part, but give the part all the time it needs . . . And maybe then a little bit more.
Jackson T
Elite member
Thanks! That should get me out of trouble. By the way, what are some of your favourite personal builds that I could check out? It sounds like you must've built heaps of cool and inspiring builds!
Piotrsko
Master member
Wow this thread is moving..... my comment was more about tieing the two spars together so the loads on one has to get transferred to the other and reducing bending to failure the non structural members, ie ribs and planking. Thin spars compress then either fracture or In my experience, the glue fails outward first using CA. Wood sucks on loads applied across grain.
a lot of fiberglass repair material shops have carbon tow, some even prepreg. Second place, aircraft spruce ships worldwide but they are pricey. String tape might just work. On the 3 1/2 meter Grand Espirit I built, I used dacron & cheap epoxy paint over the planking.
a lot of fiberglass repair material shops have carbon tow, some even prepreg. Second place, aircraft spruce ships worldwide but they are pricey. String tape might just work. On the 3 1/2 meter Grand Espirit I built, I used dacron & cheap epoxy paint over the planking.
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Jackson T
Elite member
Cool plane you got there! How did you launch it? When you mentioned about doubling the thickness of the shear webbing, did you mean so it would act like another spar? I was planning on using the shear webbing with the grain oriented vertically to resist twisting of the wing. Would I get any spar effect with a vertical grain?
Piotrsko
Master member
1: stock online photo, didn't have the net back in '84, cant find my poloroid picture. Sucks to be old. Mine was black with chrome (which pisses off hawks for some reason)
2: flew at CSUDH using their 1500ft heavy duty gas winch, also tossed off my front porch on no wind days when I owned a slope. Landing was ALWAYS a challenge, it didn't stop flying even with spoilers out. Way too big and scary to catch. Needs a HUUGE field 1/2 mile square. hope you are thinking of spoilers of some sort.
3: use the webbing as a modified box spar. All balsa Grain vertical. Slows fluttering, adds major strength stiffness with little weight penalty. horizontal grain is a pain to accomplish for little benefit. Down side is 2 piece ribs.
Jackson T
Elite member
The birds don't chase me, I chase the birds! It's really fun FPV! I'm flying in a nice big farm paddock, so I should be right landing wise. I haven't even made a balsa wing with two aileron servos (just one at the centre) before, and I was kinda hoping to keep tricky new things to a minimum with this build, so no spoilers or ailerons this time around. I'd be pretty keen to see one of those winches in action! Bunnings only sells 91cm long by 7.5-10cm wide pieces of balsa, so I can't make long vertical grain shear webs. Could I orient the grain horizontally, maybe? How much does your plane weigh? I have no idea what weight is normal for a project this big.
Jackson T
Elite member
I just ordered 80ft of CF tow from ebay. It is really cheap per unit length, so while I was paying for postage, I may as well stock up good and proper! It estimates the shipping to take the best part of a month though 
. Meanwhile, Hobbyking is literally out of stock of every thin-ish pushrod thickness, thin CA glue (except one), folding prop, and 30 min epoxy! They drive me so crazy with all the out of stock stuff. You'd think they try to sell their products!
. Meanwhile, Hobbyking is literally out of stock of every thin-ish pushrod thickness, thin CA glue (except one), folding prop, and 30 min epoxy! They drive me so crazy with all the out of stock stuff. You'd think they try to sell their products!
Jackson T
Elite member
@Craftydan, how much extra thickness will the two layers of CF add to my spars, and can I cover straight over them, or would the heat do weird stuff to it?
Jackson T
Elite member
Did the birds cause any damage to the plane? Thanks for the weight. I can't make a one piece shear web with vertical grain because my balsa sheets are only 75mm-100mm wide. Could I make the shear webbing with a horizontal grain?
Jackson T
Elite member
Ok. Would 1/16th be enough for the shear webbing? Can I cover straight over the CF, or will the heat from the iron do weird stuff to it?
Mostly DLG repairs, but I've built a few kit DLGs That use these techniques. I've also rebuilt and reinforced a Bird of Time, and I'm currently working up the nerve to bag a 3m composite foam-core wing. Not to mention some of the indoor Free flight planes I've gotten to build, but that's an entirely different scale of strength and weight.
Any single I'm proud of? Well . . . The more you build, the more you realize your past projects are mediocre. I've gotten to the point of taking pleasure in the plane I'm flying or the parts I'm repairing . . . So more or less, not one in particular.
1/16 should be fine. It's the box-spar spacing that the thin webbing wood picks up it's strength -- two pieces of 1/16" spaced 1/2" or so apart is MUCH stronger than a single piece of 1/8"
The c.f. tow will hardly be a wrinkle under your covering. Do your best to keep the tow from folding/rolling up as you do your layup, and the three layers will be crazy flat.
As far as the heat of an iron . . . Carbon fiber on its own is good to over 300c, so unless the iron is used for soldering, it'll be just fine.
