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Posted by leaktech | Feb 10, 2013 @ 01:19 AM | 1,993 Views
Back at the build lately. Got both wings off the board ready to pot the brass tubes. Next used a power tool to cut the ribs from the spar. That worked. prettygood. Easier than some otber methods I've tried. Used 15 min epoxy to glue the root plywood webs in. The leading edge side of the ribs drooped down so I propped them up while the glue set.
Posted by leaktech | Jul 26, 2012 @ 10:17 PM | 2,781 Views
Made more progress on the SkyBird last few weeks. Have the ribs and most webs installed. Installed the TE sheeting and top spar caps. The root joiner tubes are tacked in and ready for epoxy. Made a nifty drill tool from one of the joiner tubes to remove some balsa so the joiner tube will slip into the ribs. The first 5 ribs have the joiner tube holes cut in but they need a little angle cut into the hole so they will allow the tube to slip in. I cut a end cross and bent the tabs in a little to make a quasi drill. Look at the image so this will make more sense....Continue Reading
Posted by leaktech | Jul 11, 2012 @ 01:47 PM | 2,175 Views
In keeping with my slow style I reviewed the instructions, looked the plans over some more and did more triple checking before I finally glued some sheeting parts together. Next was to glue the bottom spar caps. This wing has two spars next to each other with a plywood web between them. I was careful to wipe up any glue off the sheeting between the spar caps.
Posted by leaktech | Jul 08, 2012 @ 04:47 AM | 2,359 Views
More progress today, did some razor plane and sanding block work on the aft fuse. All the aft top and bottom parts are glued on. Seems pretty stiff, when I twist holding the front and fin post it does not move much.

Recently I've been building my sailplane wings on two building boards at the same time with the poly angle set in the tip panel while building it. I also use .030" steel sheet on top of my ceiling tiles with magnets. This is new technique to me and the jury is still talking in my head weather I like it or not. So far so good, my last wing turned out super straight. I mock up the parts before any glue is used and before that I use a laser to set a straight line to build from. Checked the fit of the parts and found two that needed to be fixed. The inner panel check out good and the tip panel had one issue on the TE parts. This wing has an extended chord on the tip panel and the center TE part needed to be cut down a little to fit the ribs. The ribs are laser cut so they should be spot on. All the other parts were not fitting until I noticed the oversize TE part. One small slice off that part and everything works well now. I did read a thread of a Sky Bird build where the builder had problems because he trusted the plan and parts to be dead on correct. It's better to check out the fit before the glue goes down. Also on the plan is a diagram showing dihedral and polyhedral. I think the diagram is confusing. My solution was to use a protractor and check the plywood poly joiner for the correct angle, it's laser cut and should be spot on. I got 12.4* of poly angle and just raised my tip building board to that angle. Raised the panel 6.0" at the location of the last rib to get 12.4*

No plan on the building board with this building technique. I'm trusting the laser cut ribs to be correct. Everything must be straight, building board, straight edge, 90* squares and magnets, all triple checked before glue.
Posted by leaktech | Jul 07, 2012 @ 02:26 AM | 2,367 Views
Did some work on the Sky Bird fuse today. Top and bottom rear sheeting. Also did a small mock up balance with the motor and battery in there. Seems light in the back with no covering, esc, prop/spinner, and canopy. But there's lots of room to move the battery around and I can cut some of the nose off if needed. Anyway that's good news cuz I don't like adding lead in my models.

Got started on some wing plan and instruction sheet study. I like to lay parts on the plan and make sure I have everything sorted out in my head how all the parts go together. On close inspection I found that the kit builder did not cut the fir spar caps to the correct width chord wise. They're .020"- .025" over size. What will happen is the ribs will get crushed in the spar notch and down the road when I need to install a .060 plywood shear web between two parallel spars it won't fit because .040" of the .060" will be gone. One other problem is the poly joint joiners will not fit correctly because there's a reduction in spar size at that joint so the plywood joiners/shear webs would need to be fudged in. Not a big deal on these issues because wood can always be adjusted but it only took about 30 minutes to sand the inner and outer panel spars to the correct size. It would be a shame to have perfect laser cut ribs and then have several time consuming fixes to do later because the spars are not perfect too. I know it's not much at .020" but it will make life easier later in the build. It's good practice to catch as much as you can before starting a new wing build. It's easy to mess up a wing and hard to undo glue after it sets. Hope I studied the plan well, it's time well spent.
Posted by leaktech | Jul 05, 2012 @ 07:07 PM | 2,389 Views
Got started on a Sky Bird a few months ago. It's a 132" span woody glider that looks like a Bird of Time with a updated selig 3014 airfoil. I only fly E power gliders, and usually solo at my local park. Did some things different from the pure glider side of soaring. This is my 7th woodie sailplane build in the last 4 years. I'm improving the builds but still far from an expert builder and don't want to be an expert either. I think it fun to stray away from the plans and instructions and do something unique. What I have done is not special and most likely been done many times. I don't go into small detail just some direction to allow a Hacker outrunner to fit the fuse, nose extension, light carbon beefup, spruce fin post, and a full flying stabulator to help storage and transportation.
Posted by leaktech | Jun 27, 2012 @ 03:37 PM | 3,954 Views
Best use of carbon fiber is subjective. There is no one best way to use it. In wing construction a spar is often used. One of the best wing spars is a sandwich of carbon top and bottom with some lighter material between the carbon strips that has been glued to the strips. It's like an i beam. The carbon strips are called the caps or cap strips, the middle light material is call the web or shear web. There are a lot of ways to make an i beam spar. Bond any form of straight carbon fibers to foam, balsa, light wood, any exotic you like on the top and bottom and the core material will gain a huge increase in stiffness in the direction of the carbon fibers. In light weight wing construction carbon fiber by itself if not good use of the fibers. To make a light structure a lightweight web must be employed. Sure you can use a solid carbon rod, but the the core material is the carbon matrix mixed with epoxy. That works but unnecessarily heavy for wing construction. Foam and vertical grain balsa are the most common spar web materials used in RC wing construction. A hollow carbon tube is better than a solid rod weight wise but with a tube the web is the walls of the tube so there is no support in the middle of the tube structure. A good reference to review is this site....
http://element6composites.com/technical-cf.asp

Scroll down to the Sandwich Structure to see some of what I use in my wings.
Posted by leaktech | Jun 23, 2012 @ 01:28 AM | 2,838 Views
I finished building a Viking a while back and have been flying it with great success. It thermals easy and has a wide chord so it's easy to see with old eyes. I've built several woodys over the last few years and this one is really pleasing me. It's almost stock from the supplied kit from Skybench.com. My changes are E power, ballist tube, built up flaps, and carbon fiber wing joiner. Saved some weight with the cf joiner but it's still not really a floater, more like a cruiser. The kit wood is not contest grade but very well selected and makes a stout model. I chose the flat bottom airfoil just to see how I would like the slower flying woody. My other woodys have faster more up to date airfoils so the Viking is taking my flying backwards a click or two and I like it. I'm a sport flyer and don't go to many contests these days preferring to fly solo at my local park. The Viking is like flying my Radian except it's a lot bigger and moves a little faster. It's powered with a MVVS outrunner, 60A esc, and 3000 mah lipo. I had to set the esc timing to medium to get rid of a WOT squeal. The climb is respectable about 600' in 30 seconds. I usually don't go that high on the climb out because the thermals are almost always around my local park. Having the flaps is nice because the thermals are strong and everywhere some days and it can be difficult to avoid specking out. I just deploy the flaps and dive a few seconds to get her in good view and go up again. It just seems to stay up there and not loose much until the air gets bad. At which time I'll give a few clicks of down and head over to the mountain and ride some ridge lift from the grass. Anyway it's a great model if you are thinking of a Skybench Viking I say go for it.
Posted by leaktech | Oct 20, 2011 @ 01:28 AM | 3,305 Views
I lost a good Radian fuse and wing set a few weeks ago in a boomer. Decided that was enough push to do this project I've been thinking of for a while. Added one inch of trailing edge balsa to thin it down some and add flaps in the process.
This is not one of those modify your foamy cuz you can, but a solution to my need to get the Radian down to terra firma when loops, spins, dives, won't work.
My flying park has strong thermals all year. One of them a couple weeks ago had me climbing a mountain to retreive the Radian fuse for the electronics. A 2hour hike round trip. At the last moment before it was going past the ridge I did a straight down dive to flutter and snap the wings off to save my electronics. the wing halves were spotted far away from the fuse crash site but too dangerous to hike to for an old man. That's a bummer cuz the wings are likely in fine shape. Like all my builds and mods I like to minimize cost and do things differently but hey it works for me.

I've been flying the flapped Radian for two weeks now and it will as expected dive steeply with flaps deployed without going too fast. Also as expected the landing speed is reduced too. The unexpected plus is penetration seems to be improved. I'm no expert but the thinned TE could the reason. The stock TE is 3/16" thick, the modded TE is 1/16" thick. The improved penetration could all be in my head, but it sure seems like it's better in wind. I don't think the glide is improved from the added 78...Continue Reading
Posted by leaktech | Oct 30, 2010 @ 03:03 AM | 4,642 Views
Been thinking about how to combat my lighter wallet lately and came up with an inexpensive way to make a pretty good glider wing. It's not a pretty, sleek, highperformance molded sailplane wing but it works for me and my present economic state. Want a much larger wing but started this project as proof of concept. I fly electric sailplanes so it does not need the strength of a zoom winch launch job either. Although it may be possible to use some of the ideas here and create a winchable zoom wing with improvements to my techniques. If you do make a wing similar or better than this one please PM me a link. I did maiden this wing today at my local park and was very pleased with the handling. Seemed to go slow or pickup speed and not loose too much height while moving out. I fly a Radian and like the elliptical polyhedral so I did my best to simulate the Radian wing in the larger span....Continue Reading
Posted by leaktech | Jun 13, 2009 @ 08:47 PM | 4,349 Views
I added 12,000 fiber count carbon tow to my Radian today and shot video while doing it. This will add stiffness to any surface with little weight. Carbon tow is cheap too. About $10.00 per 100 feet. Put it on balsa or foam to stiffen. The farther the two surfaces are from each other the better it works. Like a steel "I" beam, if the two surfaces are connected with something that won't compress or release the carbon from the surface it will resist flexing. So in use, this stuff is a lot cheaper to stiffen wings or any surface than buying carbon strips or tubes and much lighter too after you get used to using it. I'm amazed how much weight I can save on some kit carbon. Adding a thick carbon bar to one side of a wing is not very efficient. Carbon tube spars are better than wood spars but you can still do better if your design will allow tall "I" beam type spar capped with strips or tow. Just remember to put your tow over a solid surface like foam or balsa and to keep the carbon lined up over and under like an "I" beam.
Carbon Beef Up On a Parkzone Radian (9 min 37 sec)