chasingmars

Be careful with using Kevlar in an application like this. Kevlar has good and bad points, for example, it has excellent tensile strength to weight and absorbs a lot of energy in the process of failing, but, it has terrible compressive strength (worse than E-glass even), and large parts of the bow structure are in compression during landing. Basically, the structure of kevlar has a "kink" in the molecule that basically in compression make weak spots each fibre - an oversimplification, but generally that's what it is. Moreover it's failure mode is such that you could see gradual degradation in strength over time (basically these until ultimate failure hits unexpectedly, so unless your friend with the kevlar bow is a composites engineer, and took this into account, I'd be very cautious following in his footsteps even if his kevlar bow works fine now.

I bought my fibreglass (note, their BID/UNI is made by BFG rather than Hexel, but it is the same spec, you do need to mention the cloth style numbers rather than just BID/UNI for them to know what you mean though), also all my epoxy, my vac bag supplies and such. Can't get the core foams there for the most part (they only sell densities other than H80 by the full box as special order), although they did have the friable polyureathane foam which is spec'd in the plans in a couple places. My last experience with them was two years ago, so it may be dated, after you consider shipping and such, especially for epoxy (and sometimes even before for MGS as their distributer for N.A. is next door in Hamilton, I gather) they are cost competitive, perhaps less so for glass cloth depending on who you compare with. I've had quite the opposite experience with Composites Canada. The guy I spoke with took an interest in the specific needs of my Cozy projects, they stock a couple of the approved epoxy (or did last time I was there two years ago), including both MGS, and were frank about what they could get and what they couldn't. A lot of the volume in composite sales is for boats, so I can't blame them for having their business oriented towards them to some extent, but they did, at least of two years ago, consider the niche markets like us. Noah's Marine was very much as you said however, perhaps you are thinking of them?

Well, I have to find some explaination... so I'm going back to recalculate it all... if I haven't done some dunderheaded math thing, I need to figure out why the numbers are so different and if it's a problem, then it's a big problem because my plane is probably the same. I suspect I'll be back with at least a little more discussion on this, but deferring to C&R, in another thread.

What's wrong with dividing measured weight by published density? We're only talking two significant figures here. My understanding is that volume fractions are used because it"s far less sensitive to fibre type when speaking generally (because it's insensitive to fibre density)

The numbers we're talking about of 50% (or worse) and 40% by weight for hand and vacuum layup concern me relative to my own experience. I'm seeing substantially lower numbers based on tests I did early in the build process. Basically, what I did when trying to learn the vacuum bag (not lovac) technique is build the six-ply flat sample piece in chapter three about a half dozen times. One was a hand layup for reference, the others were at various vacuum levels. I weighed the cloth after cutting to ensure that I was accounting as best I could for the actual vice nominal cloth weight (this came out at 8.5 oz/sq yd for the BID), then after completion trimmed the edges (for a consistant piece) down to 16 x 10 inches. Six plies means 6.3 oz of glass in each sample, and then I weighed the sample to find out how much resin was in each. My hand layup weighed 10.35 oz, which is 61% glass / 39% resin by weight. A moderate vacuum (10.5inHg) drew down to only 8.85 oz, for 71% glass / 29% resin, unless my math is terribly off. These were done with MGS 285, which I find fairly low viscosity, though I haven't worked with any of the other approved systems for comparison, and of course this sample has no core so there's no micro or epoxy in an interface layer. Still, the "achievable numbers" being talked about here, what is that based on? Have these been measured, are they perpetuated conventional wisdom, or based on previous research? Specifically I'm wondering if we aren't getting volume fraction and mass fraction mixed up here. My copy of Composite Materials for Aircraft Structures uses volume rather than mass fractions nearly exclusively with Vf of ~60% for unidirectional reinforcements (we won't see close to that if only because BID won't lie that flat, but the point remains). As a further sanity check, with E glass at a density of 2.6 (from the same ref) and MGS 285 at 1.2 (from datasheet), my Volume fractions on those two test samples are 0.42 (glass) for the hand layup and 0.53 (glass) on the vacuum layup. Either my samples are lying to me (or are hugely dry, which they don't appear to be), or the mass fractions stated of 50%+ epoxy best effort for hand layups and 40% for vac bagging are in error. I think we're mixing mass fraction with volume fraction, and thereby coming to wrong conclusions. My thought is that good hand layup is in the Vf 0.40-0.45 (glass) range (i.e. 55-60% resin by volume or only 36-41% resin by weight), good vac woven reinforcement bagging is in the Vf 0.50-0.55 range (i.e. 45-50% resin by volume or 28-32% by weight), and prepreg uni or filiment gets down into that unobtainable "ideal" (for uni/filiment) Vf 0.60 range. OF course the respective mass fractions are valid only for E-glass (and approximately for S-glass) as both carbon and kevlar are much less dense than glass driving their respective epoxy mass fractions substantially higher. This would mean your vacuum bagged portions might have about 1/3 less epoxy weight in them than your hand laid parts... and that's still not going to save that much weight... personally I think we scrap a lot more than 25% of the 17 gallons, but even if we do, that's still only 43 lbs if *everything* is perfectly bagged, and that's not acheivable. In the end, although I disagree with his ratios, Marc is right that aggressive, thorough vacuum bagging of the whole plane can at best save you about thirty pounds. Probably less... some of the largest areal layups are hard to bag effectively, and there are uses of epoxy that simply aren't part of a composite glass layup where there's no saving (e.g. flox, fairing micro, etc) Vacuum bagging is not a weight cure all... it helps greatly for part quality control in my opinion, but that's about it.

TMann, Are you sure you vac bagged *all* parts? To be fair (as someone who's vac bagged pretty much everything through to the outside of the fuselage), given that the plans don't account for needing to seal things up, vac bagging some things is very tricky... Vac bagging the flat stuff is quite doable, if expensive. My take is that given the amount of epoxy used on these planes, you're not going to save a huge amount of weight (maybe a couple tens of pounds at best), and probably not even. The cost is substantial to do it right, and if you're not doing it right, you shouldn't be doing it. Anyhow, TMann, by now your bird (if you're keeping your early pace) should be looking pretty nice... how did you skin the outside of the fuse, and if you vac bagged it, any tips on procedure?

I wonder if one could build a smoothing tool that incorporated a butane powered soldering iron (catalytic?) to heat the base? Might make the smoothing job easier if one could adjust the temperature and keep it there without reheating it or having wires or whathaveyou? As to alcohol, I'm not really inclined to potentially mess with the curing chemistry of my fairing and paint interface layer, even if it is non-structural.

Don't slink too far, we've all been new before, and most of us didn't fess up as quickly as you when we realized it...

There are cheaper "wood" blades for the fein. Don't use them for FG work, I trashed mine in short order when I couldn't find my HSS and said "just once won't hurt it". My HSS is the original one with no signs of wear. I used it to cut a hole in the floor of my house too, for a laundry chute installation, cutting drywall, all sorts of stuff.

(oops... double post)

I'm up in Ottawa. I get my MGS (285, but it's getting ridiculously expensive so considering going to the cheaper approved MGS) and my 7715/7725 from Composites Canada, I buy the cloth by the bolt. Got my bagging supplies there too and most of my vac stuff and tools, etc. I use phenolic balloons for micro, but glass or phenolic you can get it (and flox, etc) from Composites Canada. Sometimes, it's pricier than the same item from the states, but once I figure in shipping and all that, it's usually pretty competative *as long as* you get stuff by the roll, they are not reallycompetative with ordering from the states in cut lengths usually (but to their credit, when I'm making a big purchase, they'll sometimes give me roll pricing on smaller quantities) - My last big buy was about a year ago mind you, so this is a bit dated. The 7715/7725 cloth I got from them is of BGF Industries manufacture (ACS is supposed to be Hexcel, but they are both the 7715/7725 standard style), with "504 - Volan Chrome complex finish compatible with polyester and epoxy resins" - I always check that it has that though as the BGF datasheets for this cloth inexpliably list "no finish"). I used to get my nitrile gloves there too, but I've since found them at Costco (though the price is similar) and I get them there now (just cause I tend not to plan ahead enough on consumables to line them up with my Toronto trips). Metal stuff I get from the Cozy Girls. If they make it, that's where I get it/plan to get it. Divinycell foam (and the small amount of wood) I ship from Wicks or ACS, whichever is more reasonable. I try to get this several chapters at a time to save on shipping. Composites canada only sells H80 by the sheet (last I checked), any other density you have to buy by the case. They had some Last-a-foam at one point, but were trying to sell off the stock and I don't think they carry it any more. Poly urethane (the really fragile friable stuff) you can get there. I'm doing some substitution of the lightweight Last-a-foam using Corecell, Noah's Marine in toronto often has off-cuts of the right density for this (forget what it was, I got it some time ago). Note that I'm *not* recommending you make material substitutions out of sourcing difficulties, I did this because I don't much like last-a-foam's friability (and crunched the numbers on the change first). Brakes and tires/tubes I got from Infinity, his package deal is good (and his reputation for interminable turnaround time applies apparently to this retracts, not his brake packages, the matcos get shipped direct from matco anyhow), and Landing Gear from featherlight (long lead time on this). Speaking of long lead time, order your antenna kit from RST as soon as possible, took about 4 months before mine showed up in my mailbox one day. Customs doesn't seem to worry about the low value USPS shipped little things like the RST kit, so that can just be mailed directly without worrying about running afoul of the taxman. Stuff from the US is often easiest if you live nearish the border to find a UPS store in the states that does package receipt, the one in Ogdensburg (across the boarder from the 721 km mark on the 401) does this for $5/box. I ship stuff there, then pick it up and bring it through customs at the border myself, pay my GST/PST, and go on my way, takes 5 minutes (and an hour drive each way, but I usually do it when I'm going that way anyhow). Saves a ton on courier "brokerage" fees for customs clearing that get added if you use a non-priority (i.e. less expensive) shipping method like UPS ground. That's my supply chain, hope it's helpful.

Due to a minor "oaf moment" I broke one of my upper longeron doublers, so I was faced with the same dilemma, of expensive shipping for one piece of wood. I ended up using poplar, which worked very well, and was easy to get in clear straight grained pieces (which is not often true for pine round here). There's little volume in the lower longerons, so as long as strength is similar, a little bit higher density wood makes only a trivial difference to weight - in my case it was about 20 grams (less than half an ounce) for poplar doublers on both sides. The US forestry services has a good free publication, "Wood Handbook Wood as an engineering material. General Technical Report 113." online if you want to compare a candidate to Sitka Spruce.

Lets make a separate thread for the brominated stuff if there's any continued interest in it perhaps? I'm not trying to be the post police or anything, but the on-topic discussion (and the lessons that might be learned from the unfortunate experience gained) is I think important enough to be kept so? Didn't mean to veer off topic by ending my previous post with a question. My bad.

Jack, condolences on the loss of your aircraft, I too am happy to hear you're ok. I followed what you did with the blended winglets closely and with interest, and it's a great shame such a unique aircraft is no longer flying. Regarding brominated resins, I came across this interesting link that talks about some of the restrictions coming in force on brominated additives (it looks like the epoxy systems aren't the focus of the toxicity concern from my brief read of it. http://www.newmoa.org/prevention/chemicalspolicy/Harriman.ppt One thing that I wonder about is whether a brominated resin would still meet strength requirements, no sense in trading one rare failure mechanism for a more likely one, So I think doing a resin switch to brominated epoxy in the engine area would need a bit of an engineering look first to make sure the matrix performance still meets the requirements. Anyone have any familiarity with strength and elasticity of the brominated resins?

There seems to be a bit of misunderstanding here as to what BioDiesel is and isn't. BioDiesel is a fuel for compression ignition engines (i.e. diesel engines), it is therefore a diesel fuel by definition, but that doesn't make it the same as what is commonly known as diesel fuel, so to say "BioDiesel IS Diesel" simply isn't the case, it's chemically different and comes from different feedstocks. Most Biodiesel that is commercially produces is the methyl ester of rapeseed (canola to Canadians) oil. More generically, it is transesterified vegitable oil, and can be made with alcohols other than methanol. Home production of Biodiesel is very possible, but does involve some nasty things (including the above mentioned lye which is caustic, and methanol which causes blindness if absorbed by the body in significant amounts and can be absorbed through skin contact). But it's not accurate to say that it's just veggie oil with some lye and methanol added. It's processed with these things, and the byproducts must be carefully washed out of the fuel. Anyhow, there are significant differences for us as regards our fuel systems. Biodiesel is a sufficiently strong solvent that mixtures greater than B20 in auto use can re-dissolve crud in your fuel tank and drop it into your fuel filter, attack natural rubber and certain other synthetic polymers that diesel won't, and both gels and reaches the CFPP temperature at a higher temperature than regular diesel and much higher than Jet-A(1). I happen to think it's a great fuel, but it's differences from regular diesel or Jet-A need to be fully considered before pouring it into the tank.