You need to get a pinwheel to make tiny holes in the balsa before applying the glass/carbon and resin. This technique (in conjunction with vacuum-bagging) causes the resin to impregnate deeper into the wood so you get far better adhesion and greater resistance to delamination. Another consideration is the fact that when only supported by foam your spar will be more inclined to twist (thus further encouraging delamination) -- which is why an I-beam is commonly used -- the pieces on each edge which run at right angles helping prevent that twist. Material science and engineering is fun eh?
If using this as one main spar rather than an I beam I think the real stress test will be the bond between the foam and the spar itself..? That bond is likely to break before the spar does? :)
@@DavePinnock The spar is just along for the ride in composite construction I would guess (considering the minimal contribution to the area moment in torsion or bending), but it would be helpful in attaching the wing halves or the wing to the structure.
I don't know what you want to achieve, but you loaded the composite in the wrong direction. What you want to do to get a bending load carrying beam is fiber in the layers that get most strain, i.e. on top and bottom of a wing panel, binding them together with a lightweight material that can transmit shear. (That would be your balsa, ideally laminated with a composite oriented at +/- 45°)
Balsa (vertical orientation end grain about 6mm thick) spar with woven carbon sandwich and pre-stressed unidirectional carbon spar caps worked very well on my 2.2 metre wing weight of 500 grams for an older style F5B 3.2kg total airframe. Used in very high speed pylon turns without failure at 1990 world championships.
That was really interesting! I've played around a bit with similar methods at a smaller scale - I made a spar for a high-ish-aspect-ratio motor-glider model that was the same setup, a vertical slot cut in the hotwired foam wing core, so essentially making the whole wing an I-beam where the spar is the web and the foam is effectively the flange/s. My spar was VERY low tech, it was thin strips of cheapo-pine, craft-size (20mm long) popsicle sticks CA-glued together to get enough length, then hot-glued into the slot, but it had a ridiculous amount of strength for how light it was; the model's wing flex vanished, regardless of wind speed and battery weight. So I can safely say the concept is sound! I agree with the people saying you'll get much higher strength if you wrap the composite all the way around the balsa spar, especially as the self-peeling of the composites seemed to be the main failure mode (though Bruce's pinwheel suggestion will help that a lot too.) It also means less waste cloth for you to trim off. I'd love to see another test done with full-wrap composites. Also curious, have you calculated any approx. realistic in-flight torque loads for the wing root? Even with plenty of improvements to go on the spar design, if we just take the numbers you have so far, 2kg at each wingtip seems like a lot if we assume a roughly elliptical lift distribution along the span. How heavy is the finished craft likely to be, to nearest kg? RE: the slipping of the moving part of the test rig, would it help to have the moving part attached to the desk by a bolt, right by the fulcrum point, that it could rotate around?
@@iforce2d Ah, then I overestimated the size you were going for by a factor of 10. In that case, fully or partially wrapped spars aside, this should be a very durable aircraft. :D
If you run the balsa through a sewing machine, with or without kevlar thread....the epoxy will wick down into the channels. This is just some research paper I read. I'm looking to try it out with depron skinned with glass or carbon. I can see the idea behind this is to create the bone structure of a bird, there were some nice images of slices through samples with the channels at the same angles as found in bone. I did some little bits by hand and it is really effective, stops the weave skin from ripping the first layer of fibres off the balsa. I can imagine that's just the kind of thing that would appeal to you, and a little test project. How to get a needle in at 45 degrees....
With a tall and thin spar like that in your tests the strong material is most effectively placed far away from the central axis. You’ve effectively given the balsa spar really strong shear webbing but no spar cap. Put both on and make a sturdy box spar, or I beam.
3:19 "A little bit more is better than a little bit less (of the hardener) I think." Not with epoxy. You should hit the stoechiometric ratio as precisely as you can. Anything in excess will remain sort of unbound in the structure and soften it up. That is true for both the resin and the hardener.
Yes obviously as precisely as you can is the desired outcome, but we're not always perfect. So the question is whether a little more hardener is better than a little less. In my experience a little more hardener just means it cures quicker and you wasted some hardener. A little less hardener and it barely cures even after 4-5 days, still a little tacky and not really hardened. Perhaps this is different for different types of epoxy but that's what I get with this one. In my first mix I added waaaay too much hardener and it got so hot I couldn't touch it, after just 15 minutes I already couldn't pull the mixing stick out, and the heat distorted the pot - and the next day it was so rigid I could hardly believe it. But I think that would result in a more brittle result, so not ideal, but still better than never curing.
@@iforce2d It's just that coming from UP (polyester) resins a user might be misled. There the hardener ratio is elastic, and one can adjust curing time to a degree with more hardener. With epoxy there is no such elasticity. Deviation to either side is bad. As for not completely curing: That is best alleviated with slightly elevated temperatures. Though these resins are marketed as room temperature curing, they definitely can do with some thermal boost. Especially when used in thin layers, where such a boost doesn't come naturally from the exothermic reaction.
Interesting stuff! The test shows that UD weave doesnt farewell in shearstress, 90-0 weave does bit better. Adding UD fiber to the top and bottom flanges where it is stressed in tension( or compression) would give greater stiffness.
The test setup is pretty good for a reasonably good comparison test. Well done. The main point that is not made in the use of composite materials is that you need to understand the plane of strength that the product is strongest in and design around that. For example, the CF spread tow is strongest in tension and not so much in compression. Knowing this, you would not use it as a shear web as you have but place it on top (double strip) and below (single strip) and place a fibreglass shear web in between. I bet that would test better. I too am learning the best way to use these materials. Fibreglass may not be as sexy as CF or Aramid (kevlar) but it is much cheaper and used well with CF provides a super strong and much cheaper alternative for the mug builder who is not trying to squeeze past 99.8% in performance. Keep up the good work.
Is there really much difference between say a 6.5mm wide strip on top, and the uppermost 6.5mm on the side though? Seems to me that just because the carbon strip is rotated 90 degrees doesn't mean it's not undergoing tension.
@@iforce2d if placed on the 6.5mm face, the load is pressing the carbon against the balsa instead of on the 20mm face where it peeling the carbon off the face of the balsa.
I took a piece of oak wood and a thick piece of stainless steel fishing leader and made a loop similar to one coil of a spring with two straight legs off of it and ran the legs through the oak. Attached my dc power supply to it and used a straight edge to cut out a perfect circle with an thin open line to the outside. Works great!
@@lloydprunier4415 you are right. I was thinking that same thing as I was typing it. I don't know if I can add a picture here. But I will see if I can put one on my UA-cam page.
My interpretation is that your composite samples are poorly designed for the bending moment you apply. The balsa provides nothing but a slight prevention of plate buckling -limited by the poor adhesion to the balsa. If you go back and measure the thickness of the composite in each sample you will see correlation to the maximum force. The correct design for a bending load is composite on the tension side, end grain balsa, composite on tension. 10 to 1000X stronger than this result.
I would make you jig so that the two mounts are actually clamped and you can't let the the two touch each other on the lower part as they are in your tests as then you introduce another aspect that is not true bending, but also has the price in tension and a leverage effect
hi there... instead of balsa you should use PVC foam... you can find it with several thicknesses AND add kevlar to it. part os the failure is due to the lack of mechanical bond between the balsa and resin, PVC foam will solve it right away and the kevlar will prevent the carbon to snap so fast
I suppose I could add kevlar to the balsa too :) The bond problem is that the balsa can't stick to itself very well - the bond between balsa and resin is good.
@@iforce2d yes, the bond is good but the resin doesn't impregnate it deep enough to offer you a reasonable mechanical attachment which causes it to peel. PVC foam is made for that type of purpose and will you'll get a rock solid sandwich with it.. I would try with carbon unidirectional + kevlar + carbon unidirectional layers in both sides of the foam. You can also try with Polyurethane foam, it is not as good as the PVC but always better than balsa.
What about multilayer tinner balsa wood peaces? They do that with wood in construction. They just replaced someone huge wooden beam that holds off roof with plywood style wood beam fraction of the size and weight. Maybe it can work as well on small scale. It would certanly help prevent fiberglass or carbon fiber to bend as much and hold straightness if there was another peace of balsa on other side.
You laminated wrong sides. You should laminate thin sides. So one side will work for tension, another for compression. Also you should give some time, like 1-2 weeks, to allow the laminate to completely cure. Unless you post-cured the resin in the oven with Tg (T glassing). Not sure what would be a post-curing schedule for WS 105 though. Also, if balsa expands with Tg, the hot post-curing will destroy your laminate. So post-cure in room T, just wait week or 2.
That's what I did last time, but what I was trying to say at the beginning of this video is that the next design will not have the wing made from stacked slices (only the fuselage section).
@@iforce2d lmao, so i did misunderstand you, but what I suggested wasn't even consistent with my understanding of what you wanted to do, so double wrong. I thought you were making the wings with profiles cut parallel to long axis of the wing
you could try just cutting you wing core with hot wire from root to tip where you want your spar to go. and glass or carbon on the vertical section and an inch or so back top and bottom then stick the front back on and the glass over the lot. like a rutan style full size???
Good that you compress the excess resin out. there is little strength in the resin, only the composite . the correct ratio is 40% resin 60% fiberglass by weight.
There are two questions..1. Is the design suitable for purpose? 2. Is the design optimal? This design might work out for purpose of an R/C application. It is not an optimal (strength/weight) design geometry (Optimal = I beam). When mixing materials in a composite design, each materials elongation must be matched...including the adhesive. The beam can stretch only to the beam material with the least elongation. Should point out, too, the carbon fiber is ~ 1000000 stiffer than balsa. Last, beams carry bending AND shear. The later in countered by +/- 45deg layups or 45deg plywood web. Cheers
A monocoque design uses the skin as tension strength typically for the spars, empennages etc. The filler material is *support*. Therefore you need to use the balsa grains at right angles to the fibers. Think of the top and bottom of an I beam - that's the carbon. The middle of the I-beam is the material under compression so it needs to be strong in that direction. Balsa is not great, as you now know, under compression *along the fibers* but it is, unsurprisingly, strong in compression as a tree would stand. Also you need to take care not to have the glue sopped up as it goes down the grain easily. Google it - there's a few methods.
I read your post a few times but I still couldn't figure out if you're saying I did something wrong or not. The grains were running along the 15cm dimension. I have never seen balsa for sale with grain going along the shorter dimension of the sheet, and the widest sheets I can find around here are about 10cm wide. So if I want to make a wingspan of say 60cm it's gonna have to be done the way I did it in the video.
Ths is one example, but you can use thin glass fiber at 45 cut at 45 deg, to wrap the spar instead of kevlar,www.espritmodel.com/explanation-of-the-d-box-build-technology.aspxyou can search for Mark Drela Supra wingspar.
@@iforce2d Sorry, I was being terse as one never knows if these will be read. State of the art (ish) is apparently: Nomex core: www.fibreglast.com/product/Nomex_Honeycomb_1562/Vacuum_Bagging_Sandwich_Core . Think of this as just balsa with many holes drilled in the same direction is the grain. Here's a company that provides a balsa core www.fibertek.ca/shop/fiberglass-materials/foams-balsa/end-grain-balsa-core/#&gid=1&pid=1 . Think of the two vectors that are tangent to the fabric surface. The grains of the balsa should orthogonal to those. I think you're doing great - just thought I'd share my experience from building a carbon/foam kayak and my to-date analysis into one day building an composite / electric plane. If you're looking to collab, LMK. CHeers!
@@iforce2dBoats built with this technique are (where, I expect they use foam today) built as Garth describes. Think of it as the fibres stand between the two layers. They are not only stronger in this direction but the open pores allow for deeper penetration of the resin. Also the main final strength comes from the completely closed structure, with open sides you introduce breaking points. Would be very interesting to see the same test again but with weave and resin wrapped around the whole spar to create a box around it.
@@rgarthwood3881 Aircraft Spars, composite or otherwise, all have similar attributes. The shear web is oriented such that balsa end grain is normal, ie, perpendicular, to the spar caps, in compression. www.jstor.org/stable/27826109?seq=1 ua-cam.com/users/philiplardnervideos For those of you who wish to use the same skillsets to perhaps build a bigger wing: www.aryjglantz.com/p/blog-page.html www.kitplanes.com/?s=corvair+engine Have fun :)
Would be interesting to see the results of cutting a slice in the narrow section of the timber (both sides) and pressing in say a 10mm x 1mm ( or whatever) pre-made carbon fibre strip coated in epoxy. Would make no difference to any sideways force but in the first tests I imagine it would work just as well and be much lighter given much less epoxy used.
I've been thinking about attempting this kind of project myself. I'm curious if the frame was perhaps too stiff? (not enough absorption of bumps). Also how was it's weight to strength ratio compared to a metal bike?
@@chmedlychmedenstein916 Hey, I just saw your comment. Glad to give you any info I can. As for too stiff, I don't think so. Wood flexes a bit more than metal usually. I was replacing a worn out aluminum frame with suspension and the balsa wood frame ended up about the same weight. Now that I know how stiff the frame is I would make it a lot slimmer and less side panel. Here is a link to the blog I did of the build, www.tapatalk.com/groups/unclezapaudiozap/viewtopic.php?p=875#p875 If you have any questions email me @ larryzap@gmail.com
I will be comparing the wingwing and nano-talon soon, with basically that type of setup. For scratch builds though I think that scale might be a bit tricky, the 1-1.5m wingspan seems to be the sweet spot for ease of construction and yet still not using too much foam.
yes diffidently scratch build and Yes agreed im thinking 1.4m from my quick crude tests seems like over propping a miniquad motor around the 1700kv with 8x4 has a better efficiency and just restricting full throttle than running a smaller prop faster for the same cruise speed,and maybe a 4-5s pack , once built send it on a top secret mission ;-)
There are various products designed as core materials. One springs to mind called core-mat.. a white porous plastic material with dimple holes that is flexible - rolls up in a roll. Comes in varying thicknesses. It's designed to soak up the resin, the trick is to not apply too much resin (to avoid over weight). On an industrial scale (boat building) we'd apply the resin with paint rollers and used them to also soak up and remove excess resin. We would chopper gun a layer of glass 0.5-1oz or so, apply and wet out the core-mat, then spray on another glass layer. On that scale it's a bitch to fully get the air out. To use something like that for hobby scale, I'd be inclined to layup some sheets/strips as raw material and let it cure. Some molding boards below and above with weight on top makes for a neat finish and helps to squeeze out surplus resin. (Window) glass sheets make excellent molding surfaces if you want mirror smooth finish. Or on large scale we'd often use dark brown Masonite sheet heavily waxed with Johnson traffic wax - multiple coats. The sandwich sheet material will easily cut like butter using a 4" angle grinder fitted with a diamond blade.. safe to use, rarely break skin when touching the spinning blade. However you'd probably need to surface the wing foam with glass (glass tissue would do), so that you can finish the surface afterwards.. the edge of the embedded sandwich will be 100 times tougher to sand than the adjacent raw wing foam. Might be possible by continually removing the sandwich strip to sand it, then refit until perfectly flush all round. :) You're reminding me of some good times from the past. I still miss using the chopper gun - so much fun. Cheers.
Yeah I'm thinking I will have to continually remove the sandwich strip to sand it a bit. Sandpaper tears through the XPS foam too easily to try and sand it in place. I'm planning to fully surface with glass this time too, hoping this will spread the strength of the spar a bit further, and the wings will probably be thin enough that it won't work without it anyway.
@@iforce2d Sounds good, looking forward to seeing it fly. Was thinking after commenting above; I'd at least consider skipping the spar completely, and instead rely on a full surface skin of f/g above and below, so that the complete wing itself becomes the foam sandwich structure. Would depend on the exact scale (wing span to wing thickness [chord?] ratio) though. With the f/g skin, the trick might be to not make it too heavy. Check out f/g tissue if you've not already seen it.. very useful for super light weight work, can always use multiple layers.
Actually my first plan was as you say, no spar and just rely on a strong glass skin. Then I saw a video about this sandwich idea... I might try both and see how they go.
All you need to do is saturate the wood. The same method used in boat building. You saturate the timber so it absorbs into wood. The reason the Carbon came off faster is it is stronger so its pulling off the ply where the glass will have more flex. But saturtion of the wood and you be amazed at the strength. Epoxy is more expensive that's why boat builders use polyester and Viynlester resin. Plus poly doesn't react with some foams I believe, so won't melt i But that's coming from boat building.
@@iforce2d lol..... hence qualifying statement 'I believe'. One of them is good for foam dam it! Alotof people use the light glass and instead of resin use varnish as the hardener, that is one thing I do know works. I think the theory is ifyou saturate a timber that is prone to peel it stops it. Although you are right may be to heavy. Also if you use builders plastic or plastic sheet on top of glass it's a great way to get a smooth finish and the resin doesn't stick to it. I'd get some proper glass rollers if it's what your doing, if you don't have any, as in infuses the glass/carbon evenly. Hey fan boy a 47 who'd have think it hey! :-)
My understanding is epoxy is not really suitable for balsa because it doesn't absorb enough into the material. Poly or vinyl I believe is what's used, that's why you got delamination.
Comment: if you properly bond plain old woven fiberglass prepreg to a balsa wing core, your only worry will be how to keep the wing on the plane, not about its strength. As for material choice, uni graphite is best because you can tailor the layup to accomodate stress requirements, but it's harder to work with than graphite cloth. Fiberglass is not as strong, but it's cheaper and not as stiff as graphite woven, the latter making it easier to work with. For what you're doing, the way to go might be to build the lightest wing possible, with just one ply of fiberglass cloth oriented 45° spanwise, and then test it by static loading with 5g's worth of sandbags (as you did with Big Red) while simulating actual wing-attach methods. To get a better feel for what the bond line between the outer skins and inner core is doing, stack three yard sticks (meter-long might even work, but haven't tried it) on top of each other face to face, and set them on a table with supports under each end. Set enough weight mid span so you can see and measure a significant deflection. Then repeat the experiment after gluing them together. Close observation reveals that the ends of the unglued sticks are offset from each other when the assembly is deflected, while they remain in one plane in the bonded structure. The bonded assembly is radically stiffer than the unbounded one, the inhibition of horizontal slippage between the faces making the difference. The type of stress between the layers in the bonded assembly is pure sheer. Looking back at the clever testing you did in the video, it's now easy to see which results were relevant, which were just interesting, any involving bond-line failures being the most relevant. Cheers, mate!
Okay, lots of mistakes here but at least you are trying to be quantitative in your tests. 1) the first tests are completely irrelevent to the composite material, you are testing deflection and stress in the axis perpendicular to the sandwich composite, that is, the only relevent factor in deflection is the moment of inertia of the beam which is essentially the thickness of the balsa in all cases. 2) the second tests are actually testing the composites (but using the broken pieces compromises the test) 3) a solid piece of balsa is not an ideal core material in sandwich composites. In sandwich composites under deflection, the skins are under tension and compression, therefore the core material's compressive and shear strength become paramount. Balsa as a core matierial, has its greatest compressive strength when the fibers are vertical between the skins. In your example, using a solid piece of wood and skinning with composites, is not actually taking advantage of the core material's properties. If you want to use a solid piece of lumber you would be better off using a dimensionally identical piece of cedar with no composites. 4) the peeling of the composites stems from two issues: a) you likely did not prep the surface properly, the wood needs to be freshly sanded right before the wet out, and b) you need to first saturate the core surface with resin and then apply the composite. 5) Another trick to avoid peeling at the edges is to make a much larger piece and then trim the sandwich composite to size. Composites do not like to bend and when they hang off an edge they tend to create air pockets right at the edge as they lift away from the core while curing.
Interesting, that's the temporary title I gave it while it was uploading. But then I changed it, changed the thumbnail etc, and saved my changes almost an hour before actually publishing. Will keep in mind not to put anything stupid in the temporary titles in future :)
I don't get why you are bending the pieces in that direction. It's hard to explain, but the way you tested it you only get the "strength" of the balsa added to that of the expoxied fiber mats. If you would test the balsa on it's own and than the mats on their own and added the values, you should end up with the same number. This is theoretical of course, because the fiber mat alone would crumple when you'd try that. But that was pretty much the only thing the balsa added: it kept the mats from crumpling. Your test in the end on the other hand was the "correct" way to load the piece (in relation to where you put the fiber mats). The strong material has to go on the inside and the outside of the bend to add any strength. The farther apart those outer layers are the better, the strength increases with the square of the distance from the center line. That is a reason why you see steel I-beams everywhere. Exaggeratedly, the only job of the thing in the middle (in your case the balsa, in a steel beam the vertical part of the I, also called the web) is to keep the outer layers apart, because they do the lifting.
I tested bending in that direction because that's how it will be under stress in the real application. That's what I was trying to explain at the beginning. Yes, the "strength" of the balsa added to that of the expoxied fiber mats is exactly what I wanted to check.
I'm not real sure what your objective is, here. Fibers such as glass and carbon are useful for their tensile strength, so if you want to strengthen a spar, you don't bond fibers to the sides of the spar, but the top and bottom. As we can see in your first carbon fiber test, the fiber was just torn off of the balsa, which it did because this was the easiest path for the carbon fiber to take. This failure mode was similar to what you observed in trying to remove the non-stick backing material: the failure wasn't due to either the fibers or the epoxy failing, but the wood fibers separating. This is further indication that your lamination was not at all effective. And finally, by the time you figured out that the lamination may be of more use on the surfaces that are actually going to be under tension, rather than repeat the experiment from the start, with fresh materials, you tried it with already failed balsa. What the heck was this supposed to prove? From what I can see, all this proves is that broken balsa isn't a very good building material.
I think that the breaking point or the stres was never 2 kg. At this angle ist the nm mutsh higher. The position and the length of the bord makes the strength. An Boat or a plain Wing will never bekome that stres in a normal Situation. I m sure that this kind of lamination is very strong and flexible, but the direktion and the way you laminate can make the difference . Especially the overlap is the key to success 💪👌
Polyester resin which is to say polyester resin with styrene monomer does smell bad but it isn't particularly dangerous at least in the normal concentrations that you might encounter in a build situation like yours. A boat Factory would be a different story of course. Epoxy resin on the other hand which is to say epoxy resin plus a particular curing agent may be very poisonous. In the case of West system you are actually smelling the curing agent which is triethylenetetramine, one of the most toxic curing agents known. The fumes from this are actually quite toxic even though they don't smell too unpleasant. All the amine curing agents smell OK even while being quite toxic.
you probably cannot replicate that test, because of every balsa wood piece is made differently, I wonder what if you sandwich foam with fiber glass in 4 layers
The main thing I wanted to test was the relative strength, I just measured with absolute values for the video. The wood was cut side-by-side from the same large piece. I have a belt sander but if you're meaning I should have used that to sand all of the edges off, no way I would want to fill my garage with that much nasty particles.
Wood pecker for better adhesion: www.amainhobbies.com/top-flite-woodpecker-covering-tool-topr2190/p609877 You can also increase the performance of the unidirectional by pretensioning it. Lastly, *never* cure resins in an oven you use for food prep. Yes even Epoxies.
I dont think your method of testing is repeatable. You might reconsider orientation of balsa in your layup. I highly advise you to check out the Tech Ingredients YT channel and their playlist: ua-cam.com/play/PLzrI14lOlSqfR9lOz-3dgf7fQaD6C9_bW.html specifically this video: ua-cam.com/video/tiS8ArzEA58/v-deo.html Thanks for posting!
It doesn't need to be repeatable, I'm just comparing these materials. I'm subscribed to that channel actually, hadn't seen that video though, good stuff thanks :) What do you mean by reconsider orientation of balsa? If I want a 600mm long spar, there is only one way to orient it (at least with the balsa sheets I can find in shops here...)
"Composite" means the combination of multiple materials, such as glass fiber or carbon fiber and epoxy. Carbon fiber and glass fiber are not composites on their own - it's the sandwiching and bonding of of a matrix material (the balsa here) and a reinforcing material (the carbon or glass fiber) that makes a composite.
I see, and what units measure "bending"? sigh If I used a piece of titanium instead of the balsa and applied a force of 1kg to the end of the lever, there would be no bending - so what would we call the 1kg of force being applied? "A force applied at a right angle to a lever multiplied by its distance from the lever's fulcrum (the length of the lever arm) is its torque." Whether something bends as a result is not relevant.
@@iforce2d That type of load is called a bending load. If we're trying to twist the wing, we'd apply a torsional load. For deflection analysis, we multiply the bending load times the distance to the reacting support, and it has the units of newton-meters, foot-pounds, etc., and the value is referred to as "bending moment." In the end, it's just semantics.
You need to get a pinwheel to make tiny holes in the balsa before applying the glass/carbon and resin. This technique (in conjunction with vacuum-bagging) causes the resin to impregnate deeper into the wood so you get far better adhesion and greater resistance to delamination. Another consideration is the fact that when only supported by foam your spar will be more inclined to twist (thus further encouraging delamination) -- which is why an I-beam is commonly used -- the pieces on each edge which run at right angles helping prevent that twist. Material science and engineering is fun eh?
well... bruce said exactly what I was going to say so.... :D
If using this as one main spar rather than an I beam I think the real stress test will be the bond between the foam and the spar itself..? That bond is likely to break before the spar does? :)
xjet Even sanding with course grit sandpaper will help with adhesion. Sometimes oil in the wood will affect it also.
also you can use the adhesive micro-balloons to secure the cloth to wood or foam. they are very light to the point it of negligible weight impact.
@@DavePinnock The spar is just along for the ride in composite construction I would guess (considering the minimal contribution to the area moment in torsion or bending), but it would be helpful in attaching the wing halves or the wing to the structure.
I don't know what you want to achieve, but you loaded the composite in the wrong direction. What you want to do to get a bending load carrying beam is fiber in the layers that get most strain, i.e. on top and bottom of a wing panel, binding them together with a lightweight material that can transmit shear. (That would be your balsa, ideally laminated with a composite oriented at +/- 45°)
Yes exactly what I was thinking
Exactly. The fiber is the strong part. The balsa is the filler. This test is close to meaningless.
Balsa (vertical orientation end grain about 6mm thick) spar with woven carbon sandwich and pre-stressed unidirectional carbon spar caps worked very well on my 2.2 metre wing weight of 500 grams for an older style F5B 3.2kg total airframe. Used in very high speed pylon turns without failure at 1990 world championships.
fiberglass or carbon fiber layers should be on the other side to have a maximum bending resistance
That was really interesting! I've played around a bit with similar methods at a smaller scale - I made a spar for a high-ish-aspect-ratio motor-glider model that was the same setup, a vertical slot cut in the hotwired foam wing core, so essentially making the whole wing an I-beam where the spar is the web and the foam is effectively the flange/s. My spar was VERY low tech, it was thin strips of cheapo-pine, craft-size (20mm long) popsicle sticks CA-glued together to get enough length, then hot-glued into the slot, but it had a ridiculous amount of strength for how light it was; the model's wing flex vanished, regardless of wind speed and battery weight. So I can safely say the concept is sound!
I agree with the people saying you'll get much higher strength if you wrap the composite all the way around the balsa spar, especially as the self-peeling of the composites seemed to be the main failure mode (though Bruce's pinwheel suggestion will help that a lot too.) It also means less waste cloth for you to trim off. I'd love to see another test done with full-wrap composites. Also curious, have you calculated any approx. realistic in-flight torque loads for the wing root? Even with plenty of improvements to go on the spar design, if we just take the numbers you have so far, 2kg at each wingtip seems like a lot if we assume a roughly elliptical lift distribution along the span. How heavy is the finished craft likely to be, to nearest kg?
RE: the slipping of the moving part of the test rig, would it help to have the moving part attached to the desk by a bolt, right by the fulcrum point, that it could rotate around?
I'm expecting the plane will be around 2kg so any of the materials I tried here should be capable.
@@iforce2d Ah, then I overestimated the size you were going for by a factor of 10. In that case, fully or partially wrapped spars aside, this should be a very durable aircraft. :D
Fascinating. Love watching stress tests
If you run the balsa through a sewing machine, with or without kevlar thread....the epoxy will wick down into the channels. This is just some research paper I read. I'm looking to try it out with depron skinned with glass or carbon. I can see the idea behind this is to create the bone structure of a bird, there were some nice images of slices through samples with the channels at the same angles as found in bone. I did some little bits by hand and it is really effective, stops the weave skin from ripping the first layer of fibres off the balsa. I can imagine that's just the kind of thing that would appeal to you, and a little test project. How to get a needle in at 45 degrees....
With a tall and thin spar like that in your tests the strong material is most effectively placed far away from the central axis. You’ve effectively given the balsa spar really strong shear webbing but no spar cap. Put both on and make a sturdy box spar, or I beam.
I will probably have to sand down the upper and lower edges of the beam to fit, so not really an option to put anything on top/bottom.
3:19 "A little bit more is better than a little bit less (of the hardener) I think."
Not with epoxy. You should hit the stoechiometric ratio as precisely as you can. Anything in excess will remain sort of unbound in the structure and soften it up. That is true for both the resin and the hardener.
Yes obviously as precisely as you can is the desired outcome, but we're not always perfect. So the question is whether a little more hardener is better than a little less. In my experience a little more hardener just means it cures quicker and you wasted some hardener. A little less hardener and it barely cures even after 4-5 days, still a little tacky and not really hardened.
Perhaps this is different for different types of epoxy but that's what I get with this one. In my first mix I added waaaay too much hardener and it got so hot I couldn't touch it, after just 15 minutes I already couldn't pull the mixing stick out, and the heat distorted the pot - and the next day it was so rigid I could hardly believe it. But I think that would result in a more brittle result, so not ideal, but still better than never curing.
@@iforce2d It's just that coming from UP (polyester) resins a user might be misled. There the hardener ratio is elastic, and one can adjust curing time to a degree with more hardener.
With epoxy there is no such elasticity. Deviation to either side is bad.
As for not completely curing: That is best alleviated with slightly elevated temperatures. Though these resins are marketed as room temperature curing, they definitely can do with some thermal boost. Especially when used in thin layers, where such a boost doesn't come naturally from the exothermic reaction.
Interesting stuff! The test shows that UD weave doesnt farewell in shearstress, 90-0 weave does bit better. Adding UD fiber to the top and bottom flanges where it is stressed in tension( or compression) would give greater stiffness.
So that would help all of his sample pieces...right.
The test setup is pretty good for a reasonably good comparison test. Well done. The main point that is not made in the use of composite materials is that you need to understand the plane of strength that the product is strongest in and design around that. For example, the CF spread tow is strongest in tension and not so much in compression. Knowing this, you would not use it as a shear web as you have but place it on top (double strip) and below (single strip) and place a fibreglass shear web in between. I bet that would test better. I too am learning the best way to use these materials. Fibreglass may not be as sexy as CF or Aramid (kevlar) but it is much cheaper and used well with CF provides a super strong and much cheaper alternative for the mug builder who is not trying to squeeze past 99.8% in performance. Keep up the good work.
Is there really much difference between say a 6.5mm wide strip on top, and the uppermost 6.5mm on the side though? Seems to me that just because the carbon strip is rotated 90 degrees doesn't mean it's not undergoing tension.
@@iforce2d if placed on the 6.5mm face, the load is pressing the carbon against the balsa instead of on the 20mm face where it peeling the carbon off the face of the balsa.
I took a piece of oak wood and a thick piece of stainless steel fishing leader and made a loop similar to one coil of a spring with two straight legs off of it and ran the legs through the oak. Attached my dc power supply to it and used a straight edge to cut out a perfect circle with an thin open line to the outside. Works great!
I had to read it twice, but I got the idea. I will have to give this a try! This is one of those situations where a picture is worth a lot of words.
@@lloydprunier4415 you are right. I was thinking that same thing as I was typing it. I don't know if I can add a picture here. But I will see if I can put one on my UA-cam page.
@@lloydprunier4415 I am putting a video of it on my channel. It should be done soon. Check it out.
My interpretation is that your composite samples are poorly designed for the bending moment you apply. The balsa provides nothing but a slight prevention of plate buckling -limited by the poor adhesion to the balsa. If you go back and measure the thickness of the composite in each sample you will see correlation to the maximum force.
The correct design for a bending load is composite on the tension side, end grain balsa, composite on tension. 10 to 1000X stronger than this result.
Thank you for your time well done 🇨🇦
Pearl makes drums called Carbonply
outside and inside are carbon, 2 plies of maple inside
I would make you jig so that the two mounts are actually clamped and you can't let the the two touch each other on the lower part as they are in your tests as then you introduce another aspect that is not true bending, but also has the price in tension and a leverage effect
hi there... instead of balsa you should use PVC foam... you can find it with several thicknesses AND add kevlar to it. part os the failure is due to the lack of mechanical bond between the balsa and resin, PVC foam will solve it right away and the kevlar will prevent the carbon to snap so fast
I suppose I could add kevlar to the balsa too :)
The bond problem is that the balsa can't stick to itself very well - the bond between balsa and resin is good.
@@iforce2d yes, the bond is good but the resin doesn't impregnate it deep enough to offer you a reasonable mechanical attachment which causes it to peel. PVC foam is made for that type of purpose and will you'll get a rock solid sandwich with it.. I would try with carbon unidirectional + kevlar + carbon unidirectional layers in both sides of the foam.
You can also try with Polyurethane foam, it is not as good as the PVC but always better than balsa.
you have the same scale as when i made my kayak. had to write the initial volume on paper as the display kept timing out
What about multilayer tinner balsa wood peaces? They do that with wood in construction. They just replaced someone huge wooden beam that holds off roof with plywood style wood beam fraction of the size and weight. Maybe it can work as well on small scale. It would certanly help prevent fiberglass or carbon fiber to bend as much and hold straightness if there was another peace of balsa on other side.
You laminated wrong sides. You should laminate thin sides. So one side will work for tension, another for compression.
Also you should give some time, like 1-2 weeks, to allow the laminate to completely cure. Unless you post-cured the resin in the oven with Tg (T glassing). Not sure what would be a post-curing schedule for WS 105 though. Also, if balsa expands with Tg, the hot post-curing will destroy your laminate. So post-cure in room T, just wait week or 2.
to put a spar in, couldn't you put holes into each piece as you go, rather than having to make a very long hole right at the end?
That's what I did last time, but what I was trying to say at the beginning of this video is that the next design will not have the wing made from stacked slices (only the fuselage section).
@@iforce2d lmao, so i did misunderstand you, but what I suggested wasn't even consistent with my understanding of what you wanted to do, so double wrong. I thought you were making the wings with profiles cut parallel to long axis of the wing
No end grain balsa?
Very interesting test, thanks for do and share with us!!! 👏👏🔝🔝😜
you could try just cutting you wing core with hot wire from root to tip where you want your spar to go. and glass or carbon on the vertical section and an inch or so back top and bottom then stick the front back on and the glass over the lot. like a rutan style full size???
Indeed, I might try that sometime.
Good that you compress the excess resin out. there is little strength in the resin, only the composite . the correct ratio is 40% resin 60% fiberglass by weight.
Vintage composite construction, might be something useful here. I use the west system pumps being lazy. ua-cam.com/video/mBfnaNYmJZI/v-deo.html
There are two questions..1. Is the design suitable for purpose? 2. Is the design optimal? This design might work out for purpose of an R/C application. It is not an optimal (strength/weight) design geometry (Optimal = I beam).
When mixing materials in a composite design, each materials elongation must be matched...including the adhesive. The beam can stretch only to the beam material with the least elongation. Should point out, too, the carbon fiber is ~ 1000000 stiffer than balsa.
Last, beams carry bending AND shear. The later in countered by +/- 45deg layups or 45deg plywood web. Cheers
Helpful video. Very good 👍
A monocoque design uses the skin as tension strength typically for the spars, empennages etc. The filler material is *support*. Therefore you need to use the balsa grains at right angles to the fibers. Think of the top and bottom of an I beam - that's the carbon. The middle of the I-beam is the material under compression so it needs to be strong in that direction. Balsa is not great, as you now know, under compression *along the fibers* but it is, unsurprisingly, strong in compression as a tree would stand. Also you need to take care not to have the glue sopped up as it goes down the grain easily. Google it - there's a few methods.
I read your post a few times but I still couldn't figure out if you're saying I did something wrong or not. The grains were running along the 15cm dimension. I have never seen balsa for sale with grain going along the shorter dimension of the sheet, and the widest sheets I can find around here are about 10cm wide. So if I want to make a wingspan of say 60cm it's gonna have to be done the way I did it in the video.
Ths is one example, but you can use thin glass fiber at 45 cut at 45 deg, to wrap the spar instead of kevlar,www.espritmodel.com/explanation-of-the-d-box-build-technology.aspxyou can search for Mark Drela Supra wingspar.
@@iforce2d Sorry, I was being terse as one never knows if these will be read. State of the art (ish) is apparently: Nomex core: www.fibreglast.com/product/Nomex_Honeycomb_1562/Vacuum_Bagging_Sandwich_Core . Think of this as just balsa with many holes drilled in the same direction is the grain. Here's a company that provides a balsa core www.fibertek.ca/shop/fiberglass-materials/foams-balsa/end-grain-balsa-core/#&gid=1&pid=1 . Think of the two vectors that are tangent to the fabric surface. The grains of the balsa should orthogonal to those. I think you're doing great - just thought I'd share my experience from building a carbon/foam kayak and my to-date analysis into one day building an composite / electric plane. If you're looking to collab, LMK. CHeers!
@@iforce2dBoats built with this technique are (where, I expect they use foam today) built as Garth describes. Think of it as the fibres stand between the two layers. They are not only stronger in this direction but the open pores allow for deeper penetration of the resin.
Also the main final strength comes from the completely closed structure, with open sides you introduce breaking points.
Would be very interesting to see the same test again but with weave and resin wrapped around the whole spar to create a box around it.
@@rgarthwood3881
Aircraft Spars, composite or otherwise, all have similar attributes.
The shear web is oriented such that balsa end grain is normal, ie, perpendicular, to the spar caps, in compression.
www.jstor.org/stable/27826109?seq=1
ua-cam.com/users/philiplardnervideos
For those of you who wish to use the same skillsets to perhaps build a bigger wing:
www.aryjglantz.com/p/blog-page.html
www.kitplanes.com/?s=corvair+engine
Have fun :)
Adversed Test Pressures can tell any of the findings
plane weave at 45 deg?
Pointless. Putting the fibers at a 45 degree angle just makes the fibers shorter. How would you expect this to help?
What is the name of software for drawing in the first part of the clip?
openvsp.org/
www.blender.org/
Would be interesting to see the results of cutting a slice in the narrow section of the timber (both sides) and pressing in say a 10mm x 1mm ( or whatever) pre-made carbon fibre strip coated in epoxy.
Would make no difference to any sideways force but in the first tests I imagine it would work just as well and be much lighter given much less epoxy used.
What is that software you are using just says Thrust Tester?
ua-cam.com/video/PfVJmci9IQQ/v-deo.html
Unidirectional fabrics are stronger than standard weaves in epoxy, especially when layered with a 45 degree rotation of subsequent layers
How is the test equipment made?
github.com/iforce2d/thrustTester
ua-cam.com/video/PfVJmci9IQQ/v-deo.html
interesting comparison. I built a mountain bike frame from balsa and fiberglass. stiffest and strongest frame I have ridden
I've been thinking about attempting this kind of project myself. I'm curious if the frame was perhaps too stiff? (not enough absorption of bumps). Also how was it's weight to strength ratio compared to a metal bike?
@@chmedlychmedenstein916 Hey, I just saw your comment. Glad to give you any info I can. As for too stiff, I don't think so. Wood flexes a bit more than metal usually. I was replacing a worn out aluminum frame with suspension and the balsa wood frame ended up about the same weight. Now that I know how stiff the frame is I would make it a lot slimmer and less side panel. Here is a link to the blog I did of the build, www.tapatalk.com/groups/unclezapaudiozap/viewtopic.php?p=875#p875
If you have any questions email me @ larryzap@gmail.com
Can you make the smallish plane using a mini quad motor that cruisers at about 1.5- 2 amps and using 18650 battery’s
maybe similar to the nano specs
I will be comparing the wingwing and nano-talon soon, with basically that type of setup. For scratch builds though I think that scale might be a bit tricky, the 1-1.5m wingspan seems to be the sweet spot for ease of construction and yet still not using too much foam.
yes diffidently scratch build and Yes agreed im thinking 1.4m
from my quick crude tests seems like over propping a miniquad motor around the 1700kv with 8x4 has a better efficiency and just restricting full throttle than running a smaller prop faster for the same cruise speed,and maybe a 4-5s pack , once built send it on a top secret mission ;-)
There are various products designed as core materials. One springs to mind called core-mat.. a white porous plastic material with dimple holes that is flexible - rolls up in a roll. Comes in varying thicknesses. It's designed to soak up the resin, the trick is to not apply too much resin (to avoid over weight). On an industrial scale (boat building) we'd apply the resin with paint rollers and used them to also soak up and remove excess resin. We would chopper gun a layer of glass 0.5-1oz or so, apply and wet out the core-mat, then spray on another glass layer. On that scale it's a bitch to fully get the air out.
To use something like that for hobby scale, I'd be inclined to layup some sheets/strips as raw material and let it cure. Some molding boards below and above with weight on top makes for a neat finish and helps to squeeze out surplus resin. (Window) glass sheets make excellent molding surfaces if you want mirror smooth finish. Or on large scale we'd often use dark brown Masonite sheet heavily waxed with Johnson traffic wax - multiple coats. The sandwich sheet material will easily cut like butter using a 4" angle grinder fitted with a diamond blade.. safe to use, rarely break skin when touching the spinning blade.
However you'd probably need to surface the wing foam with glass (glass tissue would do), so that you can finish the surface afterwards.. the edge of the embedded sandwich will be 100 times tougher to sand than the adjacent raw wing foam. Might be possible by continually removing the sandwich strip to sand it, then refit until perfectly flush all round.
:) You're reminding me of some good times from the past. I still miss using the chopper gun - so much fun. Cheers.
Yeah I'm thinking I will have to continually remove the sandwich strip to sand it a bit. Sandpaper tears through the XPS foam too easily to try and sand it in place. I'm planning to fully surface with glass this time too, hoping this will spread the strength of the spar a bit further, and the wings will probably be thin enough that it won't work without it anyway.
@@iforce2d Sounds good, looking forward to seeing it fly. Was thinking after commenting above; I'd at least consider skipping the spar completely, and instead rely on a full surface skin of f/g above and below, so that the complete wing itself becomes the foam sandwich structure. Would depend on the exact scale (wing span to wing thickness [chord?] ratio) though. With the f/g skin, the trick might be to not make it too heavy. Check out f/g tissue if you've not already seen it.. very useful for super light weight work, can always use multiple layers.
Actually my first plan was as you say, no spar and just rely on a strong glass skin. Then I saw a video about this sandwich idea... I might try both and see how they go.
All you need to do is saturate the wood. The same method used in boat building. You saturate the timber so it absorbs into wood.
The reason the Carbon came off faster is it is stronger so its pulling off the ply where the glass will have more flex. But saturtion of the wood and you be amazed at the strength.
Epoxy is more expensive that's why boat builders use polyester and Viynlester resin. Plus poly doesn't react with some foams I believe, so won't melt i But that's coming from boat building.
Saturating sounds heavy though. Polyester makes a nice mess of this foam, I tried that a while ago :)
@@iforce2d lol..... hence qualifying statement 'I believe'. One of them is good for foam dam it!
Alotof people use the light glass and instead of resin use varnish as the hardener, that is one thing I do know works.
I think the theory is ifyou saturate a timber that is prone to peel it stops it. Although you are right may be to heavy.
Also if you use builders plastic or plastic sheet on top of glass it's a great way to get a smooth finish and the resin doesn't stick to it. I'd get some proper glass rollers if it's what your doing, if you don't have any, as in infuses the glass/carbon evenly.
Hey fan boy a 47 who'd have think it hey! :-)
My understanding is epoxy is not really suitable for balsa because it doesn't absorb enough into the material. Poly or vinyl I believe is what's used, that's why you got delamination.
What do you mean at the beginning CLASSIFIED? Is just a straight wing for a plane there’s nothing classified on that your plane is pretty simple.
en.wikipedia.org/wiki/Joke
@@iforce2d nice
im interested in how you did and made your load cell device. ever think of doing a video on it? what operating system did you use?
github.com/iforce2d/thrustTester
Comment: if you properly bond plain old woven fiberglass prepreg to a balsa wing core, your only worry will be how to keep the wing on the plane, not about its strength. As for material choice, uni graphite is best because you can tailor the layup to accomodate stress requirements, but it's harder to work with than graphite cloth. Fiberglass is not as strong, but it's cheaper and not as stiff as graphite woven, the latter making it easier to work with. For what you're doing, the way to go might be to build the lightest wing possible, with just one ply of fiberglass cloth oriented 45° spanwise, and then test it by static loading with 5g's worth of sandbags (as you did with Big Red) while simulating actual wing-attach methods.
To get a better feel for what the bond line between the outer skins and inner core is doing, stack three yard sticks (meter-long might even work, but haven't tried it) on top of each other face to face, and set them on a table with supports under each end. Set enough weight mid span so you can see and measure a significant deflection. Then repeat the experiment after gluing them together. Close observation reveals that the ends of the unglued sticks are offset from each other when the assembly is deflected, while they remain in one plane in the bonded structure. The bonded assembly is radically stiffer than the unbounded one, the inhibition of horizontal slippage between the faces making the difference. The type of stress between the layers in the bonded assembly is pure sheer.
Looking back at the clever testing you did in the video, it's now easy to see which results were relevant, which were just interesting, any involving bond-line failures being the most relevant.
Cheers, mate!
Okay, lots of mistakes here but at least you are trying to be quantitative in your tests. 1) the first tests are completely irrelevent to the composite material, you are testing deflection and stress in the axis perpendicular to the sandwich composite, that is, the only relevent factor in deflection is the moment of inertia of the beam which is essentially the thickness of the balsa in all cases. 2) the second tests are actually testing the composites (but using the broken pieces compromises the test) 3) a solid piece of balsa is not an ideal core material in sandwich composites. In sandwich composites under deflection, the skins are under tension and compression, therefore the core material's compressive and shear strength become paramount. Balsa as a core matierial, has its greatest compressive strength when the fibers are vertical between the skins. In your example, using a solid piece of wood and skinning with composites, is not actually taking advantage of the core material's properties. If you want to use a solid piece of lumber you would be better off using a dimensionally identical piece of cedar with no composites. 4) the peeling of the composites stems from two issues: a) you likely did not prep the surface properly, the wood needs to be freshly sanded right before the wet out, and b) you need to first saturate the core surface with resin and then apply the composite. 5) Another trick to avoid peeling at the edges is to make a much larger piece and then trim the sandwich composite to size. Composites do not like to bend and when they hang off an edge they tend to create air pockets right at the edge as they lift away from the core while curing.
i like how the notification just said "new video: balsa sandwich"
Interesting, that's the temporary title I gave it while it was uploading. But then I changed it, changed the thumbnail etc, and saved my changes almost an hour before actually publishing. Will keep in mind not to put anything stupid in the temporary titles in future :)
@@iforce2d don't get me wrong, i enjoy these stupid titles
Composite materials have come a long way since chewing gum and string.
You mixed the wood grater with fiberglass material. New method
not just using Carbon fiber but you must also try using ordinary fiberglass and compare it with fiber glass... the difference will not be that BIG...
Your lever clamp thingy seems to flex at about 2kg, maybe thats why you were having trouble reading bigger values
I don't get why you are bending the pieces in that direction. It's hard to explain, but the way you tested it you only get the "strength" of the balsa added to that of the expoxied fiber mats. If you would test the balsa on it's own and than the mats on their own and added the values, you should end up with the same number. This is theoretical of course, because the fiber mat alone would crumple when you'd try that. But that was pretty much the only thing the balsa added: it kept the mats from crumpling.
Your test in the end on the other hand was the "correct" way to load the piece (in relation to where you put the fiber mats). The strong material has to go on the inside and the outside of the bend to add any strength. The farther apart those outer layers are the better, the strength increases with the square of the distance from the center line. That is a reason why you see steel I-beams everywhere. Exaggeratedly, the only job of the thing in the middle (in your case the balsa, in a steel beam the vertical part of the I, also called the web) is to keep the outer layers apart, because they do the lifting.
I tested bending in that direction because that's how it will be under stress in the real application. That's what I was trying to explain at the beginning. Yes, the "strength" of the balsa added to that of the expoxied fiber mats is exactly what I wanted to check.
Sweet... apparently my UA-cam login has sufficient clearance. I could totally see it. Yep.
You need to wet out the balsa wood and let it cure - make it a two step process to solve the delaminating problem
I'm not real sure what your objective is, here. Fibers such as glass and carbon are useful for their tensile strength, so if you want to strengthen a spar, you don't bond fibers to the sides of the spar, but the top and bottom. As we can see in your first carbon fiber test, the fiber was just torn off of the balsa, which it did because this was the easiest path for the carbon fiber to take. This failure mode was similar to what you observed in trying to remove the non-stick backing material: the failure wasn't due to either the fibers or the epoxy failing, but the wood fibers separating. This is further indication that your lamination was not at all effective.
And finally, by the time you figured out that the lamination may be of more use on the surfaces that are actually going to be under tension, rather than repeat the experiment from the start, with fresh materials, you tried it with already failed balsa. What the heck was this supposed to prove? From what I can see, all this proves is that broken balsa isn't a very good building material.
Great video
great vid
I think that the breaking point or the stres was never 2 kg. At this angle ist the nm mutsh higher. The position and the length of the bord makes the strength. An Boat or a plain Wing will never bekome that stres in a normal Situation. I m sure that this kind of lamination is very strong and flexible, but the direktion and the way you laminate can make the difference . Especially the overlap is the key to success 💪👌
I think you need to sandwoch more laqyers on top of another, like actual carbon fiber frames
Polyester resin which is to say polyester resin with styrene monomer does smell bad but it isn't particularly dangerous at least in the normal concentrations that you might encounter in a build situation like yours. A boat Factory would be a different story of course. Epoxy resin on the other hand which is to say epoxy resin plus a particular curing agent may be very poisonous. In the case of West system you are actually smelling the curing agent which is triethylenetetramine, one of the most toxic curing agents known. The fumes from this are actually quite toxic even though they don't smell too unpleasant. All the amine curing agents smell OK even while being quite toxic.
Yep, polyester is stinky but the epoxy fumes are far more insidious. Great video though!
very nice video stress test my frent
you probably cannot replicate that test, because of every balsa wood piece is made differently, I wonder what if you sandwich foam with fiber glass in 4 layers
use belt sander to clean edges man
The main thing I wanted to test was the relative strength, I just measured with absolute values for the video. The wood was cut side-by-side from the same large piece. I have a belt sander but if you're meaning I should have used that to sand all of the edges off, no way I would want to fill my garage with that much nasty particles.
Wood pecker for better adhesion: www.amainhobbies.com/top-flite-woodpecker-covering-tool-topr2190/p609877
You can also increase the performance of the unidirectional by pretensioning it.
Lastly, *never* cure resins in an oven you use for food prep. Yes even Epoxies.
AU AUAUAUUU HEAVEN
I dont think your method of testing is repeatable. You might reconsider orientation of balsa in your layup. I highly advise you to check out the Tech Ingredients YT channel and their playlist:
ua-cam.com/play/PLzrI14lOlSqfR9lOz-3dgf7fQaD6C9_bW.html
specifically this video:
ua-cam.com/video/tiS8ArzEA58/v-deo.html
Thanks for posting!
It doesn't need to be repeatable, I'm just comparing these materials. I'm subscribed to that channel actually, hadn't seen that video though, good stuff thanks :)
What do you mean by reconsider orientation of balsa? If I want a 600mm long spar, there is only one way to orient it (at least with the balsa sheets I can find in shops here...)
Oh, Oh, Oh! I have a level two National Security Clearance that will get me into the Vault at Boeing. Cant I watch? Please?
"Composite" means the combination of multiple materials, such as glass fiber or carbon fiber and epoxy. Carbon fiber and glass fiber are not composites on their own - it's the sandwiching and bonding of of a matrix material (the balsa here) and a reinforcing material (the carbon or glass fiber) that makes a composite.
It's not torque, it's bending... sigh.
I see, and what units measure "bending"? sigh
If I used a piece of titanium instead of the balsa and applied a force of 1kg to the end of the lever, there would be no bending - so what would we call the 1kg of force being applied?
"A force applied at a right angle to a lever multiplied by its distance from the lever's fulcrum (the length of the lever arm) is its torque." Whether something bends as a result is not relevant.
@@iforce2d That type of load is called a bending load. If we're trying to twist the wing, we'd apply a torsional load. For deflection analysis, we multiply the bending load times the distance to the reacting support, and it has the units of newton-meters, foot-pounds, etc., and the value is referred to as "bending moment." In the end, it's just semantics.
First!