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Sailplane Wing Design Round II

Old 06-03-2012, 03:30 AM
  #51  
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Yeah I don't have any plans to sheet the wing using plywood. I will be sheeting the leading edge top & bottom with balsa though, probably 1/16". As much as I like this super-man strong spar tech I'd still like a good old D-box in there too. The other reasoning for the sheeting is I'd like a clean airfoil up front. Aft of the spar I'm fine with an open structure as the foil is less curvy back there. From the LE to spar though, I don't want that all saggy.
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Old 06-03-2012, 05:57 AM
  #52  
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Originally Posted by soarrich View Post
You'll never break that 8mm rod. I use 1/4" 6061T3, (because I had it), I like the aluminum wing joiners because if you overload them they will bend and stay bent, so you know you over did it. CF will fail catastrophically, the first you'll know about overloading it is when it breaks and you are flying around with 3/4th of a wing. On my Dancing Hippo I used CF tubes for spars so I put the poly in the wing-rod.

BTW, you can fly a sailplane with 3/4th of a wing enough to land safely, been there, done that.
Good points about aluminum Vs carbon fiber wing rods. Now if someone would just invent a "carbuminum" rod we'd be all set :-P

Nice job flying with a 1/4 wing missing. Interestingly, after some trial & error I was sorta able to fly my simulated broken wing glider. Then again that had a fixed position broken wing, the real one was flopping around all over *grin*.

Originally Posted by HO-229 View Post
...It looks as if you’re on the correct path…
Thanks for the failure mode breakdown Dave. Logical as always :-)
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Old 06-04-2012, 05:36 AM
  #53  
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A HUGE THANK YOU to everyone for helping me redesign this wing.
Enough talk though, now its time to build, woohoo!

I spent a few hours tonight working up the new design in my CAD software. Here's a few teaser views...







I'll probably order the CF & wood early this week, can't wait to get started building or should I say re-building :-)
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Old 06-04-2012, 10:02 PM
  #54  
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Check's in the Mail!
I ordered the supplies for the new wing, should have those later this week.

Some of you maybe interested in how much scratch building in wood costs. Here's my shopping list for the new wing...



This order was placed with RCFoam.com. I've dealt with them before & like their level of service & products. There's lots of other online retailers for the this stuff too. Oh & of course don't forget to support your LHS (local hobby shop), I try to buy my parts there when I can.
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Old 06-04-2012, 11:01 PM
  #55  
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Careful when you cut the CF rod, I've hear the CF dust is tough on the lungs, I did mine outside holding my breath.

Are you going to build new tip panels too?
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Old 06-04-2012, 11:58 PM
  #56  
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Now I have an image stuck in my head of you turning blue trying to chop through a big fat CF rod. Seriously though that's good advice about the CF dust. Yes I take precautions when messing with that stuff. I always use a mask (less turning blue that way) & clean up the dust immediately with a damp paper towel.

Yes I'm totally rebuilding the wing including the outer panels. The old ones looked to be in fair shape after the crash but who knows what unseen damage they sustained. Additionally their CF joiner rods cracked during impact. As I'd glued those in, big mistake, that meant major surgery to replace them. Also I don't trust the old design, even if its the outer panels that shoulder less stress, I think its better to just toss the whole thing, start anew & do things right.
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Old 06-05-2012, 12:17 AM
  #57  
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NODD!

Enjoying the thread!

Regards
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Old 06-05-2012, 02:37 AM
  #58  
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Live long and Prosper
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Old 06-11-2012, 08:06 PM
  #59  
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Balsa in a Box
The wood & CF for my new wing arrived today, woohoo!..



This is the second time I've ordered from RCFoam.com. Once again I'm impressed with the packaging & the quality of the wood. The carbon fiber looks real nice too.

Now that I have the parts in hand I can finalize my plans. I wanted to wait until I could take actual real world measurements from the wood & CF. Unlike the first, this wing will be tight & precise. Here's an initial layout for the ribs...



I'm headed off on a fishing trip this week so won't be able to build until later in the week, will post more when I get back.
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Old 07-07-2012, 05:45 AM
  #60  
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Why no progress?
A quick update, its been a few weeks since my building supplies arrived. Unfortunately they're still sitting on my workbench. I've been a tad distracted by a DLG project but that's almost complete so I should be able to get back to the wing shortly.

Oops!
I just noticed, looking at my supplies, that I only ordered four CF spar-caps. This will be a three part wing so I need a total of six, not four, grumble, grumble, grumble. Turns out my over-site might be one of those happy accidents though...

While poking around the Net looking to order another two 12mm x 2mm CF strips I came across some really cool tapered CF. These strips are 12mm wide & start off 1.5mm thick then taper off to 0.5mm over around a meter. So I ordered four figuring I'll use these for my outboard wing sections, tapering off as we approach the wing-tips. I'll use my non tapered CF for the center wing section.

I'm liking this, should save me some weight as surprisingly, 12mm x 2mm x 1m CF does actually weight a fair amount. Using tapered spar-caps should be pretty slick. Now of course I have to wait for them to arrive. I should be able to get going on the center wing though. We like happy accidents.
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Old 07-07-2012, 05:53 AM
  #61  
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Construction Begins!
Enough talk, enough delays, time to get this wing built! Today I started cutting ribs. First I printed them onto 8˝ x 11 sheets then contact cemented them to my wood...



Next I rough cut them on my scroll saw...



Here's the ribs for the wing center section. At this point they don't need to be accurately cut...



Next I head to the belt sander where the shape is refined...



Here's the center wing section rib set. I still need to cut the spar notches & the servo wire holes but its a start...



Feels great to be putting this bird back together. Can't wait to have her flying again. Summer is rolling by fast, I want to get back to enjoying her while its still nice out.
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Old 07-08-2012, 05:17 AM
  #62  
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Using Smelly Socks to Assemble the Wing Center Section
More progress today. I picked up from where I left off yesterday with the ribs. Drilled holes for the servo wires & sanded out the spar-cap notches...



I printed my center section plans on 8˝" x 11" paper then taped them together...



Next I cut the CF spar-caps a little longer than needed. I also cut my 12mm thick shear-webbing making sure it was correctly tapered...



I created a jig for accurately cutting the shear-web into sections...



Here's the full set of shear-webbing for the center wing...



Pinned the lower CF spar-caps to the plans...



Alternating between rib, web, rib, web, rib, I started to assemble the wing...



Before you ask, yes I removed the paper rib template where the shear-webbing glues to the rib...



Ribs & shear-webbing installed...



Next I added the top CF cap-spar then placed our entire collection of dinner knives across them...



Next I added some socks, yes socks...



A piece of MDF board goes on top...



And the cherry on top, a 20 lb dumb-bell weight. I'll leave that to setup overnight. Hopefully no one will need a knife for their midnight snack...

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Old 07-08-2012, 07:17 AM
  #63  
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Im surprised you didnt glue the cat to the MDF. That seems to be alls thats missing . Good luck with the build nodd.
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Old 07-09-2012, 05:48 AM
  #64  
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Here kitty kitty...

The new spar is looking good, feels crazy strong...



In preparation for the Kevlar tow I made tick-marks along the spar so I could keep the wrap neat...



Although there's more wrapping to come I wanted to get the bulk of it done before adding the leading & trailing edges. Having the wing open makes life much easier...



With that done I added the TE strips...



I CA tacked the end ribs in place using angle templates I printed up...



My original wing was a really subtle gull-wing, almost flat, with barely any dihedral. The rather long wing rods & a thin airfoil greatly limited the angles I could use. This time around, using fairly short wing-rods, I'm free to use larger dihedral angles. After playing around on the 'puter I settled on 22° in the center & -9° for the outboard sections...



Although the previous flatter wing was fine, this one should be significantly more stable. As you can see I'm also playing around with winglet designs. I maybe mistaken but this might be the first gull-winged sailplane to feature winglets *shrug* I know I've not seen one before, fun fun. Will have more progress tomorrow.
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Old 07-10-2012, 07:46 AM
  #65  
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No Instructions Required
One of the things I love about building my own designs is the total freedom to screw-up totally, figure out what I did wrong & then get right back in there & build it better.

Before attaching the end ribs I cut another set to be used as the first ribs on the outboard wing-panels. By drilling the wing-rod hole now I'm assured they'll align nicely later on...



Attached the leading edge...



On my last wing I butted the sheeting up against the LE which resulted in plenty of ugly & weak gaps. This time I pre-shaped the LE so that the sheeting will overlap...



I wanted to lock-down the Kevlar wrap so that it couldn't move, fray or whatnot. I considered using CA but that'd take a lot & that stuff isn't cheap. I heard enamel paint works well but the one can I have in my workshop was dried up. Instead I watered down some wood glue & brushed that onto the fibers...



It wicked into the wood nicely & sealed in the Kevlar. I only did this on the sides, I figure the top & bottom fibers will get entombed under the sheeting...



Wing Joint Box
Now things are getting exciting. Time to join the two wing halves.

Here's my chunky 8mm carbon fiber wing-rod. That thing ain't breaking even if an elephant sits on it. To save some epoxy I created hardwood space filling wedges...



To create the wing joint box I added 1/16" basswood shear-webbing to one side only. I eased the sharp edges so when its eventually wrapped it won't chafe the Kevlar...



Goop time! I glued the end ribs together with five minute epoxy & then started to fill the box around the wing-rod with 30 minute epoxy/microballoons goop...



With it about half filled I dropped in my wedges. As they sank the goop rose-up to fill the box to the rim...



With the glue still goopy I capped off the box with another set of 1/16" basswood webs...



Yeap she's starting to look like a wing now, liking the look of that 22° dihedral...



Time to stop for the day, let that setup good & strong over night...


Last edited by Nodd; 07-10-2012 at 08:03 AM.
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Old 07-11-2012, 04:27 AM
  #66  
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Time to work on the outboard wing joiner boxes. Unlike the permanent center joint these will be detachable. Brass tubing will support the CF wing-rod...



Same system as the center joint, the box will be filled with epoxy/microballoon goop. Again I'm using a hardwood wedge to take up some of the space...



I needed a way to keep the epoxy from running into my wing tubes. Then it occurred to me, maybe epoxy in the tube is exactly what I need...



Let these setup for 10 minutes...



Trim the excess goop & I have two nicely capped tubes. I also roughened the brass with some heavy sand-paper to give the goop something to grip...



Installing the tubes...



In goes the goop...



Capped with 1/16" basswood...



Once that was set I wrapped both joints with Kevlar, this time closer wound as I figure this is a high stress area...



Speaking of a high stress area, I thought it'd be a good idea to join the spar-caps in the center using some CF ribbon...



The CF strips were epoxied top & bottom of the main joint. I used packing tape to help keep it in place while the glue dried. A thumb comes in handy too...



Here's the CF strips after the tape (& thumb) was removed. Something tells me my cap strips aren't going to pull apart any time soon...



And just to be sure everything stays together no matter what, more Kevlar wrapping...



So here she is with the completed spar & joinery. I must say I'm quite happy with the way this is looking. Thanks again everyone who offered advice...



Not sure how much I'll get done tomorrow as I'm flying most of the day, then entertaining during the evening. On the plus side though, my fancy tapered CF cap-strips for the outer wing panels are due to arrive tomorrow, fun fun.
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Old 07-11-2012, 04:41 AM
  #67  
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Nodd, what was the brand of balsa that RCfoam has now. I was wondering if they changed balsa brands since they moved to Colorado from Atlanta. Their balsa was first rate.

Jim
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Old 07-11-2012, 05:01 AM
  #68  
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Yeah I'm really impressed with their balsa also. Auszac appears to be the brand...

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Old 07-12-2012, 12:45 AM
  #69  
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Yes, that's the brand they had before. Some of the best wood I have seen. I'll be ordering some more from them.
Thanks,
Jim
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Old 07-14-2012, 05:10 AM
  #70  
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Sheeting
Not much to report today. I have the sheeting done on the center section. Here's how that went...



Unlike my previous fully sheeted center section, this time around only the area ahead of the spar will be sheeted. With the new kryptonite spar I don't see much structural need to slap sheeting all over, should help with the weight too...



I am sheeting the root some however...



To help support the diagonal sheeting I added diagonal ribs...



Sheeted the bottom & made a couple of holes for the servo wires to exit...



Pretty happy with the sheeting...



In other news, my nifty tapered CF spars for the outer wing sections have arrived. I should be able to start cutting ribs & putting those together this weekend.
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Old 07-15-2012, 12:14 AM
  #71  
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Measure four times, cut once.
Time now to put the outer wing panels together. Before I can do that I needed to accurately measure the taper of my new fancy CF spar strips...



Not having a micrometer handy (I need to get one of those), I tried to use a ruler to measure the thickness...



Looks like the thin end is a bit less than one mm. Seeing as I'm going to base the depth of all the rib notches on these measurements, I wanted to be a little more accurate than that, so I used an old trick. Lets measure all four spars at once...



Looks like they total around 3mm...



Divide 3mm by four & we get 0.75mm. So that's my thin end measurement. I did the same for the thicker end...



That's a smidgen over 6mm. So 6.1mm divided by four equals 1.52mm. So I now know, with a fair degree of accuracy, that my spar strips taper from 1.5mm to 0.75mm. Oddly enough that's what the manufacturer said too but if you've ever brought wood at the Home Depot for example, you know to never go by the manufacturer's claims. Best to take real-world measurements.

Anyway I'm going to fire up my CAD software & plot some ribs based on these measurements.
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Old 07-16-2012, 05:37 AM
  #72  
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ATCHOO!
More fun sanding ribs to shape. Warning those with allergies may find the following disturbing...



After a rather dusty couple of hours I have a full set of ribs ready for the outer wing panels...



With the hard part done I'm hoping to get the outer wings together tomorrow.
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Old 07-17-2012, 08:20 AM
  #73  
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Outboard Wing Sections
I printed up a set of plans & started construction by laying the tapered CF spar-caps down...



As with the center wing section, the ribs & shear-webs go down in alternating order...



Done adding ribs & shear-webbing...



Wanting to keep things light out at the tips I split the shear-webbing in the last four bays...



With the CF tapering off to a hair's thickness & hollow shear-webbing these outer panels should be light yet still plenty strong...



That's all for today.
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Old 07-17-2012, 01:32 PM
  #74  
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I can see this wing is isnt goint to lack strength (that's something of an understatement!). How do you expect the weight to compare with the original?

Really nice building by the way.

Steve
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Old 07-17-2012, 02:00 PM
  #75  
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Nodd

What are you using for a building board??
Nice craftsmanship BTW!!!

Regards
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