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Old Nov 08, 2010, 01:29 PM
yyz
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Originally Posted by G Norsworthy View Post
Mike,

I'll probably assemble the spars in the beds, then bag the sock, but that must wait for the cores.
Good call! I almost screwed the proverbial pooch on that one....
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Old Nov 08, 2010, 01:36 PM
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ok... the hard way....

assume fairly close elliptical planform

A = semi-major axis = 153/2 = 76.5
B = semi-minor axis = 12
wing area = 1/2 ellipse area = (Pi*A*B)/2 = 1442 in sq = 10 ft sq

5kg = 11 lbs = 176 oz = 17.6 oz/ft

sucker is going to be fast. can it thermal at 17.6... hmmmm....


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Weight depends on the day but the intent is to fly at full all the time if we can.
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Old Nov 09, 2010, 12:23 AM
Master of the Wind
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United States, CA, San Jose
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Drew out the tip spars tonight and started cutting material. 3 layers of .014" uni precured at the joint tapering to 1 layer at the tip. The 3 are carried past the proposed servo location since that is where they always break. Not my favorite stuff to work with but another one of those things lurking under the bed that I have been lugging around for what seems like 10 years, looking for a home. May get to lamination by tomorrow.

Big box of end grain balsa showed up today. Kevlar is here, carbon has shipped, foam is at least tentatively ordered, waiting for confirmation. Things are moving.
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Old Nov 12, 2010, 12:10 AM
Master of the Wind
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Tip spar caps done. Joiners are fit to boxes. Carbon cloth is here. Carbon sock is here. Foam at least has something that looks like an order confirmation. HL60 is special order, went for the HL40 which is easier to cut anyway. Foam cuts are drawn out for all surfaces. Next step is to start blocking out foam and make one more joiner to glue in the center section joint.
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Old Nov 14, 2010, 12:26 AM
Master of the Wind
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Made the third joiner, the one that is cut in half, shaped to the dihedral angle, and glued in the center joint never to be seen again. Foam is in. Getting closer on the foam cutter. Need to practice on some DLG tails to get the hang of it.
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Old Nov 14, 2010, 11:32 AM
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Originally Posted by G Norsworthy View Post
...... Need to practice on some DLG tails to get the hang of it......
Dlg tailfeathers are THE most difficult thing to accurately cut. I built a CNC hot wire machine and still have a great deal of difficulty with the tiny stuff. On the other hand if you can cut them,....you can cut anything.

I'd recommend blocking up your root and tip end with short scrap pieces that only have 4" to 6" of span but full chord. Put them in place so that the root and tip are where they would be if you had a full span piece in place. (nothing in the center) Weight them down and cut as if it was a full span piece. Then you can measure the root and tip (to verify correct voltage and wire speed) after the cut without wasting a ton of foam while practicing. The ends of the short blocks closest to the middle will have extra overburn but that's not what you''ll be measuring anyway and it won't be there when you cut a full length piece.
When you're ready to cut a full length piece then you'll need a tiny bit more voltage to keep the wire at the same temp but you'll have a better ballpark guess to start with. Too little voltage or too much wire speed and you'll push the blocks across the table and have problems with wire lag noticeable at the leading and trailing edges. If there's too much voltage there will be excessive overburn and blobs of hardened molten foam scattered around.
For wire, I used 1/32 stainless steel safety wire for years. It's dirt cheap and works well but I'd break a wire every 8 to 10 cores. I've gone to .020 inconel and haven't broken one in a decade of use.

Good Luck !
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Old Nov 14, 2010, 01:30 PM
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Lots to learn going from a Feather Cut to CNC. Initial set up was a little challenging. Stuff like for motor how many phases and degrees per step. Then figuring out what type of lead screw. Metric or Standard and threads per distance.

Took some time to figure out what the software needed or what the descriptions ment. Placed some scraps on the table like TS mention above. The first piece came out looking like a bow tie pasta instead of a partial span stab. Search around the software and found keft option. Changed the keft value until I got a correct thickness part down to .00xmm. Got that six or more tries. Trailing edge is ending up .7 MM instead of tapering to nothing. Got to figure that out. Next will be trying out a tapered planform DLG tail. Making progess anyways!
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Old Nov 14, 2010, 02:35 PM
yyz
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Lots to learn going from a Feather Cut to CNC. Initial set up was a little challenging. Stuff like for motor how many phases and degrees per step. Then figuring out what type of lead screw. Metric or Standard and threads per distance.

Took some time to figure out what the software needed or what the descriptions ment. Placed some scraps on the table like TS mention above. The first piece came out looking like a bow tie pasta instead of a partial span stab. Search around the software and found keft option. Changed the keft value until I got a correct thickness part down to .00xmm. Got that six or more tries. Trailing edge is ending up .7 MM instead of tapering to nothing. Got to figure that out. Next will be trying out a tapered planform DLG tail. Making progess anyways!

Building and setting up your CNC machine would be a great thread and super informative.

Mike
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Old Nov 14, 2010, 06:15 PM
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stab.:....Changed the keft value until I got a correct thickness part down to .00xmm....
My apologies if this is drifting too far off topic, but hopefully it'll be helpful.

You should actually have two kerfs. Imagine cutting an 8" root and a 4" tip as an outer panel. If both are done in one minute then the root is cutting at 8"/min and the tip is cutting at 4"/min. The wire temp is constant thus the overburn (kerf) will be greater at the tip where the wire is going slower. I use GMFC for software and it has two kerf values in the setup to compensate for this. You'll need to figure out how your software deals with different kerfs on tapered panels. The higher the taper the more evident this is.
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Old Nov 14, 2010, 06:37 PM
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Mike not sure if I want to make a thread on CNC foam cutting, but I will post my progress on this project. It helps document the process and seems for later reference. Greg sent me this and it has been helpful. http://tech.groups.yahoo.com/group/CNCFoamcutters/

TS, I got the airfoil thickness but not it the trailing edge. It almost close enough for XC but not for DLG, with some sandpaper or roller to thin it down. If I change the keft I may loose airfoil thickness and get the trailing edge correct. Trading one problem for another. Must be missing something.
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Old Nov 14, 2010, 07:54 PM
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TS, I got the airfoil thickness but not it the trailing edge.....
Try another airfoil from another source. That'll tell you if it's in your software setup or the airfoil data that you have. Some data files don't work so well.
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Old Nov 18, 2010, 12:00 AM
Master of the Wind
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I've not been idle. Mainly drawing out foam cuts and where the spars, servos, RDS go. Here is a sketch of how the T-tail will fit together. Looks like there is plenty of room for the anchors, pushrod, horn, and rudder wiper. Sketch of what the rudder wiper might look like on a bagged part is superimposed in red. Slot in the elevator for horn relief will be bridged ahead with a graphlite stick.
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Old Nov 18, 2010, 06:03 AM
slope'n the Colombian Andes
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Looks good, Greg. Will the top part of the fin be attached to the stabilizer so that you can access the elevator linkage for dis/assembly?

Dieter Mahlein, ShredAir
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Old Nov 18, 2010, 09:16 AM
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The way it is drawn the top part of the fin is end grain balsa and is attached to the fin. I add a few layers of extra carbon cloth in the layup to make a hard shell around the balsa and just a bit below the joint into the foam. I am thinking to hollow it out a bit for access to the pushrod. If it all works out right I can use an L bend at the top of the pushrod and a ball link at the bottom. I can put the pushrod at its upper extent for assembly.
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Old Nov 20, 2010, 01:25 AM
Master of the Wind
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Two nights fighting with the CNC foam cutter using up very expensive time in the garage and I saw where this was headed. I see the potential but not for someone on a tight schedule. The CNC cutter was relegated to the dustbin of history and I made a quick contact with JuzWuz, who went above and beyond what anybody would expect and got me templates in the mail. Tonight we blocked out all the foam and I walked out with the Feathercut. If the Ikea table is built straight I only need to go on a quest for massive weight. If not, I go into work where there is an ultra flat table and plenty of stainless steel junk lying around to keep the corners down. Spent the day looking over Phil's old posts and I think I am ready to cut. Will try a layout on the apartment floor for a quick pic if we get a break in the rain tomorrow. While waiting for the templates I will research the materials needed to make the RDS and order a few remaining odds and ends like mylar.
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