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Old Mar 25, 2011, 06:51 PM
Abundantly deficient.......
CptMike's Avatar
Orange County, CA
Joined May 2004
723 Posts
Build Log
CR Contender Wingeron Build

Okay, I recently received a CR Contender kit from Chip at CR Aircraft. I've been wanting a sleek, speedy 2m with a high aspect ratio for my local hill, Glider Point. I've got aerobatic stuff and a moldie along with others, but this classic by Charlie Richardson, being a twisty wing and having an excellent reputation for speed and carving........well it just had to be done. And I love foam and plywood wing construction for its simplicity, durability, and ease of repair.

I'll be trying to build to Charlie's plans and notes (old school)......ply skins pressed with epoxy, glass cloth and a carbon strip in between. I'll be using a pretty cool wing press in lieu of bagging. Wing tips will be angled also like the original.


Update> Maiden video here





M
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Last edited by CptMike; May 09, 2011 at 07:48 PM.
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Old Mar 25, 2011, 07:10 PM
The Legend continues
CR_Aircraft's Avatar
Carlsbad, Calif
Joined May 2009
530 Posts
Nice to see you getting started Mike,

I've got some stickers for your finished bird, Red over Clear
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Old Mar 25, 2011, 09:12 PM
Impatience is a virtue
MCH27t's Avatar
Denver, Colorado
Joined Nov 2008
686 Posts
Coool! Looking forward to the build
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Old Mar 25, 2011, 09:25 PM
characters welcome!
Mark Wood's Avatar
United States, CA, Bear Valley Springs
Joined Feb 2000
26,500 Posts
This'll be cool! I have a carbon-bagged 2m and I'd enjoy seeing how they go together!

mw
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Old Mar 25, 2011, 10:41 PM
It's not going to build itself
TRISME's Avatar
Aliso Viejo,CA
Joined Aug 2005
6,498 Posts
Nice! Lots of pics please.
Tom
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Old Mar 25, 2011, 10:55 PM
Ask me about VTPR
oldscooler's Avatar
America
Joined Aug 2002
2,223 Posts
Glad your posting Mike, will be a good database when I start mine... E
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Old Mar 26, 2011, 01:17 PM
Fun ain't cheap!
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United States, CA, Santa Barbara
Joined Apr 2003
3,035 Posts
Cool build, I am interested in the full flying rudder system, Are you going to build that in, or go without?
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Old Mar 26, 2011, 04:22 PM
Abundantly deficient.......
CptMike's Avatar
Orange County, CA
Joined May 2004
723 Posts
I am planning on doing the full flying rudder, and maybe making the stab removeable.
I'm leaving an 1/8" margin of ply past the foam trailing edge to allow for the top and bottom skins to meet. Charlie's idea here is to sheet the bottom first, then install the ply spar and wing tube, then sheet the top. This also solves the problem of the trailing edge being tapered on the ends....not allowing them to be taped and folded together for pressing.

The carbon I've got here is .010 thick and going under .018 skins. Wonder if it will press into the foam okay or show up on the airfoil?

M
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Old Mar 28, 2011, 06:13 PM
Abundantly deficient.......
CptMike's Avatar
Orange County, CA
Joined May 2004
723 Posts
So here's the process and the wing press. Thanks go out to Hweeler who built it and is keeping it at my place for now....nice for me. We've build two complete wing sets so far (50" panels) with excellent results. Very straight and true. Again, this is a little different. Per Charlie, I'm only doing the bottom skins first. Carbon is .010 Uni 3/4 wide and I'm using West Systems epoxy, 3/4oz per single skin.

M
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Old Mar 29, 2011, 05:40 PM
The Legend continues
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Carlsbad, Calif
Joined May 2009
530 Posts
How long will you keep it in the press Mike?
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Old Mar 29, 2011, 08:46 PM
Impatience is a virtue
MCH27t's Avatar
Denver, Colorado
Joined Nov 2008
686 Posts
Neat method. Other than being less expensive than a bagging system (perhaps), what do you see as the benefits to this method?
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Old Mar 29, 2011, 10:22 PM
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Roseville, California, United States
Joined Mar 2001
3,098 Posts
Don't let my wife see that press! She'll finally have a case against me keeping the last 10 years of RC Modeler magazine!!
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Old Mar 29, 2011, 10:32 PM
Registered User
United States, CA, Sunnyvale
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Instead of measuring the distance b/w the 2 planks, would/wouldn't a torque wrench used on all the bolts ensure even pressure on all points?
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Old Mar 29, 2011, 10:42 PM
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Carlsbad, Ca
Joined Mar 2007
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Let's see it

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Old Mar 29, 2011, 11:28 PM
Ask me about VTPR
oldscooler's Avatar
America
Joined Aug 2002
2,223 Posts
Quote:
Originally Posted by vhuang168 View Post
Instead of measuring the distance b/w the 2 planks, would/wouldn't a torque wrench used on all the bolts ensure even pressure on all points?
To all, lets think about this. Lets assume "even nut pressure" (no pun intended lol) distributes even "mechanical pressure" down the panel. It in fact does. Pressure X Area = Force. Force is determened by pressure being exerted on a given area (square inches). A tapered wing has a non consistant area from the root to the tip, the area is reducing less toward the tip. Now, lets say we put 2 foot pounds of "nut torque" assuming there isnt differing stud friction between all the studs and we obtain exactly even torque on all studs. Pressure times area means the root being for example 8", one inch of wing length will "resist" 16 foot pounds at 2 foot pounds of torque. You can see where this is going. Resist is the key word here. This is not exact and true numbers. Torque can only be measured in Nm (newton meters). In a nutshell, the area of the wing that has more area per length versus the tip that has less area per length, if we use nut torque as the process factor, the tip-end of the press will crush the cores because it will not have been able to "resist the force" being applied to it until the core gets to a point of equalization to the input nut torque. What you will have is the "top platten' of the press pushing down further towards the tip because of the smaller resisting area.

Another view. Do you realize that say a 400 square inch wing panel at say 2ft pounds of nut-torque has a force of 800 pounds exerting or being resisted by the press? When was the last time you stacked 800 pounds of bricks on your cores in a makeshift pressing on your workbench? I'll bet never because you believed it would crush. 20 or 30 bricks weigh only a couple hundred pounds which is nothing on those cores but it works huh. We did a test with a set of 9.75" x 6.125" x 50" long cores to test the "crush point" of the white EPS cores by using calipers every 1/4 turn on the nuts. As we saw the core begin to crush ever so slightly beyond what we felt was safe, the registered tourque on the nuts was 5-6 foot pounds. That equates to 2000-2500 pounds of resistant force over the whole panel!

So, it was decided it would be better to maintain an even "press gap" between plattens all the way around to first ensure the flattest wing and also to keep from crushing the panel. The average overall torque ended up being 2 ft pounds or 800 pounds of force on those 50" panels which im sure all would agree is plenty of pressing action to have excellent skin adhesion.

E...
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