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Old Aug 28, 2006, 04:27 AM
Glider guider
Speedo125's Avatar
United States, FL, Sun City Center
Joined Oct 2005
359 Posts
Question
Kevlar wrap question

My buddy and I are building Paragons for RES/nostalgia. We plan on winch-proofing the spars with carbon caps and kevlar wrap. There is no sheeting, so it seems that something would need to be done to smooth the wrapped spar surfaces for the airflow and for the Monocote to adhere to. Are we missing something simple here? -Thom
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Old Aug 28, 2006, 05:37 AM
Registered User
Punta Gorda, FL
Joined Apr 2002
4,952 Posts
First wrap the kevlar to the two carbon caps to the web. Later finish the spar cap with wood, either hard balsa or spruce or bass. Most of the bending strength in the carbon so don't worry about the wood strength for caps. The jointers are the weak link. So beef up the jointers too. Use 3/16" thick jointers with very hard wood or 1/8" thick aluminum, not plywood. Perhaps the root jointer is then the weak link then.

However, with no sheeting, the wing fails in torsion flutter far before using bending strength. Raise the flutter speed by lower the trailing edge mass and increasing the leading edge mass. Raise the flutter speed by double covering the Monokote for the root panels.

Think about the whole wing structure and many parts working together, not just one weak link improvment.
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Old Aug 28, 2006, 06:48 AM
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John Walter's Avatar
USA, IL, Naperville
Joined Feb 2003
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Kevlar tow source

You can get some very good Kevlar tow here:

http://www.rcgroups.com/forums/showt...&highlight=tow

Tow lies quite flat against the spar cap. Check the photos at the link above.

Full disclosure, I'm Littleflyer's dad.
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Old Aug 28, 2006, 09:22 AM
I'm all about that bass
rdwoebke's Avatar
United States, IN, Indianapolis
Joined Feb 2004
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Quote:
Originally Posted by Ollie

Think about the whole wing structure and many parts working together, not just one weak link improvment.
Just as a note, the original poster mentioned NOS. If he is planning on flying the AMA NOS event, he can't add any sheeting that the plans do not call for. You can do whatever you want to the spar though.

Ryan
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Old Aug 28, 2006, 09:52 AM
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Cambridge, MA USA
Joined May 2001
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Quote:
Originally Posted by Speedo125
My buddy and I are building Paragons for RES/nostalgia. We plan on winch-proofing the spars with carbon caps and kevlar wrap. There is no sheeting, so it seems that something would need to be done to smooth the wrapped spar surfaces for the airflow and for the Monocote to adhere to. Are we missing something simple here?
You can sand or plane down the sparcaps a bit to make room for the carbon.

Note also what Ollie said about flutter.
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Old Aug 28, 2006, 11:44 AM
Glider guider
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United States, FL, Sun City Center
Joined Oct 2005
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Thank you guys. I've been doing a lot of research on RCGroups. I think I'm going to stick with RES and pass on the NOS. I'll beef up the joiners and sheet the LE's to form a D tube and cap the aft portion of the ribs.

I'm ordering some of the kevlar tow for the job. Where are you guys obtaining your carbon? I think I can get some T-6 alum for the joiners.
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Old Aug 28, 2006, 03:03 PM
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Fort Wayne, IN
Joined May 2002
1,694 Posts
Speedo125,

Here is a copy of something I sent Ryan a few months ago. You may find it interesting.



I have got my joiner questions resolved. I used a FG rod and brass tubes in blocks. It will fill the spar area in the first bay and be real strong with ply shear webs and Kevlar tow rap. You can see some pictures of the blocks that I have attached. I still need to trim and fit them but you can get the idea. I decided if the plans, and your build have had no problem with the standard joiner, I'll just do the first bay and make the second bay solid filled and raped for added strength. I am using pre-cured .007 top caps only so that should add a lot of strength also. I will rap most if not all of the center section and a few bays out on the tips.


John
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Old Aug 28, 2006, 03:10 PM
I'm all about that bass
rdwoebke's Avatar
United States, IN, Indianapolis
Joined Feb 2004
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Like John said, I'd probably reccomend switching for something else for the joiners. I built mine with just the plywood "blades" that fit in plywood boxes and they are starting to get a bit loose. Not a huge deal, but could be better.

Ryan
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Old Aug 29, 2006, 11:02 AM
Tailspin
Grand Blanc, Michigan
Joined Feb 2006
436 Posts
I made the "Super Wing" for a NOS Paragon about eight or so years ago (still fly it a lot) and it came out a fair amount heaver than stock (1st Paragon). It will launch on our Wade winches which break molded wings (I know) without fear.

Guess what, it makes no difference, the drag of the plane is so high that the zoom is not much better than a wing with only minor mods and much lighter.

Never had a wing flutter problem but did blow the rudder and fin off once and got lucky and it landed with no damage (I did not land it other than elevator and spoilers).

I would keep it NOS legal as there is no advantage to adding sheeting if you use spruce turbulators and make the spar stiff in torsion as well as bending.

Jack
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