Custom DLG

Custom DLG (Full Version)

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j.m. -> Custom DLG (4/26/2008 10:10:52 PM)
hey guys, looking to make my own custom DLG using the vacuum bagging technique. I am going to use some of these for spars: http://www.goodwindskites.com/merch/profile.shtml?index=1055571565_8380&cat=framework.wrappedcarbon&loc=&listpage=1 (the largest ones they sell.) What I need help with is whether I should use virgin 1# white foam and 5.5oz carbon/kevlar cloth, or a stronger foam and lighter fabric? The heavier fabrics can be found pretty cheap, but I am unable to find lighter (~2 oz.) fabric in either carbon or kevlar materials. I know using the heavier fabric will make the plane a little on the heavy side, but I want this plane to be SUPER strong. (that's the reason for the carbon tube spars) so a 12 oz airplane won't be much of a problem for me. I would like to use lighter cloth, but I am unable to fin some. I will be buying cores online, so my choices of foam are rather extensive.

Rusty P -> RE: Custom DLG (4/27/2008 11:39:21 PM)
J.M That could work structurally, but the white foam would have trouble with a high vacuum. A good compromise that many use is the square edge/25psi foam (blue, from DOW) and 1.7 oz. Kevlar. Call up http://sweetcomposites.com and see if you can order some 1.7 oz (120 - 38".) You could also use 2 layers of 1.4 oz glass. That with a doubler on the inner half of the wings should be strong enough. It will cost you weight, but still be less than the carbon cloth. Yeah, your wings will probably turn out heavy, but it will still fly. Besides, everyone's first wings turn out heavy, it's a rule.[)] Let us know how it works out, and see if you can get a pic up when your done, eh? Later

j.m. -> RE: Custom DLG (4/28/2008 3:52:41 PM)
I will not be able to vary the amount of vacuum that i would be using since i will most liikely be using a food saver vacuum pump. I will be usin gone of these since it will cost alot less for me, and as of now i barely ave enough money to buy the foodsaver pump. I have no job right now (i'm 16) but i will have one this summer. I will most likely have to wait till this summer to start this project, but in the mean time i plan on practicing with my own home-cut cores (DOW pink foam) and skinning these with balsa. I am not the best at cutting cores with my home made hotwire bow, so i hope that the balsa will be ale to cover up any small voids in the surface. When i do finally get around to skinning wings with composite fabrics, i plan on using CNC cut cores(who knows, i might make a cnc hot wire cutter too?) because the fabric will show any imperfections in the cut. I have thought about a way to make the wings lighter, and i have come up with the idea of using moderatly heavy (1.5-3oz.) kevlar or carbon cloth on the leading and trailing edges for stiffness and durability, and a single layer of 3/4 oz. glass inbetween the leading and trailing edges. Stiffness for the whole wing will bw provided by the carbon tube spar, and havinh the heavier glass on the ailerons and about 1/2"-1" in front of them will ensure that they are slop-free. The fuse will either be molded, of made using the lost foam technique and vacuum bagging. The tails will most likely not be bagged with 3/4oz glass as is the "standard" for high performance DLG's. I will probably build them much to the configuration of the Bubble Dancer by Mark Drela. (only much, much smaller) Using the lightweight textbook iron on covering (forget what it's called) i beleive i will end up with something that is a little lighter, and much more crash resistant. I know that using a food saver will somewhat limit me in the size of wings that i can bag, but since i will mostly build gliders, i can go up to about a 10" chord, which means i can doo some pretty big wings. The length is limited to about 25'. (yeah, right.) I like the idea of only runnong the pump until all the air is out, and then letting the machine seal off the bag so that I don't need a pump to run for 24 hours straight, or having a regulator that tells the pump to turn on. Much simpler system, near identical results.

j.m. -> RE: Custom DLG (4/29/2008 11:35:14 PM)
bump. AHHH!!!! MODERATORS! DON"T KILL ME!

Rusty P -> RE: Custom DLG (5/5/2008 4:29:52 AM)
Hey, J.M. Sorry about the slow response, been busy... If you know how to scrounge, see if you can dig up an old but still functional refrigerator compressor pump. That should do you fine for your bagging needs unless you go into production. Since you have time, read the Supergee II threads on RCGroups. These are found here: http://www.rcgroups.com/forums/showthread.php?t=246671 http://www.rcgroups.com/forums/showthread.php?t=323802 http://www.rcgroups.com/forums/showthread.php?t=385968 http://www.rcgroups.com/forums/showthread.php?t=545273 http://www.rcgroups.com/forums/showthread.php?t=676909 This has a lot of non relevant discussion, but if you read all that, you will know a whole lot about bagging techniques. In fact, you will learn pretty much all you need to know to do this project. It is a real treasure trove and includes comments on using the compressor pumps for vacuum. For a bag, you can use 1.5 mil drop cloth from the local big box hardware store and some rope caulk weatherstrip from same to make a simple bag on the cheap. I've used that as a bag, and I know someone who build a whole Supergee II using it. It works just fine. You can forget wasting the strong cloth on the trailing edge. They just aren't stressed all that hard. Study, and I mean really study the plans for the Supergee II. They are found here: http://www.charlesriverrc.org/articles/supergee/SuperGeeII.htm Dr. Drela designed this plane for best performance. If you see where he put the reinforcements, that's where they need to be. This design was computer simulated by an expert in the field. He knows his stuff. As a general rule, you can substitute two layers of 1.4 oz. glass for each 1.7 oz layer of Kevlar. The 3/4 oz glass would likely be to weak, and the wing would flex in torsion fairly badly. Use at least one layer of the 1.4 over the whole thing. Then use another layer over the flaperons, and doublers in the middle where the two wings join. The SGII plans show something like this. You don't need to build a Supergee, but the plans will show you much about what these planes need to survive their use. Later

j.m. -> RE: Custom DLG (5/5/2008 11:30:42 AM)
sounds cool! I still think i'm going to use the food saver bags, as they have a small criss cross pattern in them that allows them to be used without breather cloth. This means it will be cheaper than a regular bag if you use a real breather cloth. Where on the fridges are these pumps located? (what i'm asking is can i get one off a fridge in a junk yard) This project will most likely wait for a long time, because as soon as these babies get in stock, i'm getting one: http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6619 And the only thing i really need to be studying right now is schoolwork.[:(][:(][:(]

j.m. -> RE: Custom DLG (5/29/2008 1:27:28 AM)
Alright guys, been drooling looking over the supergee II threads over on rcgroups, and i've kinda jumped into making a dlg head first. I found an old carbon arrow that i stripped all of the clear coating off of, and i'm going to use that for a tailboom. Weight is about 10 grams. I've also started to make some templates to cut out the tail feathers in the supergee II fashion. I am really enthralled about full flying horizontal tails, and i am wondering if there is any other good way to make them using a mount other than the same old carbon v thing i keep seeing. Making one (or buying one AHHH!!!!) won't be much of a possibility for me, so if ther is some way i can make one out of some other material, that would be great. Tails will be made using Home Depot pink foam (little stiffer and slightly heavier than blucor) with the grain parallel to the chord, and 3/4 oz glass biassed perpendicular to this.(many layers, many layers.)(and a couple darts) This will be a rudder/elevator only dlg, so it might look like i have an oversized rudder, but i love touchy controls.(no pics yet, unless you want to look at drawings of templates, but the root chord on the vertical assembly will be 6" and the tips 3" and 4" top and bottom) For the fuse i will try to make a mold of something like a Vandal fuse, making plugs and molds of the top and bottom, rather than left and right halves, due to the very complex shape, and the fact that i wouldn't be able to get them symmetrical any other way. pic of the Vandal DLG: http://www.jonesprototypes.com/DSC09387.jpg Love the look of the fuse, and ther'll be stiffness to boot. Only thing is, the canopy has to go all the way past the wing if you want to remove the wing.

Rusty P -> RE: Custom DLG (6/6/2008 4:29:38 AM)
Hey, J.M. Some good thinking going on here. You're really jumping in and stand to learn a lot. As for the tails, you can get away with one layer of .75 oz glass over most of the tail. You'll want a leading edge layer, and a second layer on the fixed portion. I use a strip of 1.7 oz kevlar along the hinge line as a hinge. I also pull it in the direction of the hinge to make it a bit stiffer (more fibers packed closer together.) It's a very good idea to put in some carbon darts where the control horns go into the surface. As for doing an all flying elevator without a V mount... Actually, v-mounts are pretty simple to make the molds to do. Mark Drela made up some sketches of these molds. So have others. Anyway, if you still want to do this, you can make the fixed portion hollow, and mount a bellcrank in there. The elevator would be two pieces, with a spar joiner running through the axis of rotation, and a drive pin through the bellcrank end. This is how the large thermal duration ships work. If you are near some guys that fly the big molded planes, take a look at them. If not, there are pictures available online. Try http://www.soaringusa.com but make sure you see the prices to cool any glider lust ;-) Oh, as for the vacuum pump, it's the thing at the bottom in the interior that has tubes and a power lead running into it. It's usually a short, pot looking thing, and probably black. Later, -Russ

j.m. -> RE: Custom DLG (6/6/2008 7:51:52 PM)
Thanks for the info on the fridge vacuum pump. Really appreciate it. I have read through ALL of the SGII threads now, and there as a short discussion about using carbon darts and relying on them for stength. THe fact is, all of the force on the tail is centered at the middle of the dart where it is thickest, and can crush the foam. Therefore, it is better to do a +/- 45 degree bias on the tails. Two layers would be super heavy, but would spread the load more evenly. I am not going to haev ailerons for my first composite dlg, so a large rudder is a must. SO, i will have a long nose with the battery all the way forward to make up for this. Probably a polyhedral wing, but i'm not sure yet. I know all about large sailplanes, i just finished a 120" unlimeted class sailplane (scratch build) with my Aerospace III class, and i am making a high start for it right now. I was wondering if there was any way to mount a full flying horizontal tail to the boom without alot of metal. (like none) Maybe a small servo arm jammed up and epoxied into the stab and a balsa thingamajigger to pivot on. (with some carbon thrown in for good luck) A good layup for a hinge is +/- 20 degrees or more. I know exactly what it does. Really stiff in the vertical direction, but not stiff at all in the horizontal direction. On thing i never quite got was how to make the hinge. Do you put the hinge in when you are doing the regular layup and then just trim it with a hacto knife? Or do you cut the rudder off the vertical, bevel it, then glue on the live hinge? I'll probably end up facing my rudder too. Just to make it a tad stiffer, and to hold the skin on.

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