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Old Sep 15, 2011, 09:25 PM
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Multeric's Avatar
Boca Raton, FL
Joined Apr 2009
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Help!
New airfoil for a Nomad RES

Hello guys,

I am thinking about scratch-building Nomad RES sailplane (i just got the plans). I would like to change the airfoil for one that has more penetration capabilities in windy conditions. Still, I would like it to thermal well.

I was thinking about Clark Y or S3014. How do they compare? Any other suggestions?

Thanks,

Juan
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Old Sep 15, 2011, 09:51 PM
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ErcoupeEd's Avatar
United States, IN, Grabill
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the 3014 airfoil is much better
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Old Sep 16, 2011, 03:17 PM
Spy's sappin' my thermal!
Chris Sutton's Avatar
Seattle, WA
Joined May 2009
137 Posts
You might want to look at the AG34 instead of the 3014. They are very nearly identical as seen here. However, the AG34 will be easier to build accurately since it has no TE camber (flat bottom) and it is specifically designed for woodie planes.

This is from the Allegro-Lite page about the AG3X airfoils:

Quote:
The AG35..38 airfoils on the Allegro-Lite have been specially designed for built-up construction. All parts of the airfoil with open covering are flat by design. This completely eliminates the airfoil modifications due to covering sag and thus avoids the associated performance penalties. Wider than usual rib spacing can also be safely used.

Each airfoil has one flat facet on the bottom, and three flat facets on top.

The intent is to have the bottom sheeting back to at least 30% chord, and the top sheeting back to 45% chord. A top support strip is to be placed at 65% chord. The trailing edge strip forms the remaining facet back to 100% chord.
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Old Sep 16, 2011, 04:51 PM
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Multeric's Avatar
Boca Raton, FL
Joined Apr 2009
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Hello Chris,

At the link you provided, they talk about AG3X system of ribs. Do you think that I would need them for a 100" plane? Will they really make a difference in performance when compared to the AG34 by itself?

Thanks,

Juan

Quote:
Originally Posted by Chris Sutton View Post
You might want to look at the AG34 instead of the 3014. They are very nearly identical as seen here. However, the AG34 will be easier to build accurately since it has no TE camber (flat bottom) and it is specifically designed for woodie planes.

This is from the Allegro-Lite page about the AG3X airfoils:
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Old Sep 16, 2011, 10:48 PM
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Is it really MUCH better? I just looked at the wind tunnel tests that Selig did back in the '80s. (Was it really that far back?). The Clark Y was not that different. Maybe a little more drag when going quite fast, a little less when going slow.

I'm sure either would be fine. However, with that low aspect ratio, if the model is light, I'd think you'd want to go to a fairly fast airfoil.

If you're concerned about making it strong enough, or you want it to be easy to build, go with the Clark Y because it's thicker. If you have confidence in your building, use something thinner.

If the model is light, you might want to provide a place for some ballast to use in windy days.

With computers, it's pretty easy to mix the airfoils. You have to taper them anyway. I suspect the performance advantage is small but real.
Quote:
Originally Posted by ErcoupeEd View Post
the 3014 airfoil is much better
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Old Sep 16, 2011, 10:50 PM
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P.S. If you're not going to sheet the wing, don't worry all that much about the airfoil. People sometimes sand a curve into the bottom front part of the airfoil, and that is said to speed things up a bit.
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Old Sep 19, 2011, 01:06 PM
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Multeric's Avatar
Boca Raton, FL
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I think IŽll give the AG3X a try. AG34, AG35 and AG36.

Thanks!
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Old Sep 22, 2011, 01:02 AM
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granada don's Avatar
Granada Hills Ca.
Joined Nov 2009
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You might look at a Mirage foil it would be correct for your plane's time frame.

G Don
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Old Sep 26, 2011, 02:38 AM
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United States, CA, San Francisco
Joined Dec 2005
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This is my Balsa USA "Breezy" that I just finished restoring. I bought it here on RCG as a wreck a few months ago. BUSA made this kit and the Nomad at the same time. The wings are identical just the fuses are different.

The front of the fuses are similar, the Nomad had a more conventional fuse, the Breezy a Pod-and-Boom configuration.

The wing is covered in Sig Koverall and Dope finished. The fuse is two part automotive paint. Had it's first flight last weekend in Los Bano's. A relaxing flier!

Geppetto
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Old Sep 26, 2011, 06:16 AM
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Beautiful finish 1stGeppetto!!!

Is that tail boom as narrow in width as it looks?
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Old Sep 26, 2011, 11:26 AM
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Multeric's Avatar
Boca Raton, FL
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Great looking plane 1stGeppetto!

Does the Breeze have any penetration issues in 10mph winds?

Thanks,

Juan
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Old Sep 26, 2011, 12:52 PM
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The 'Wack, BC, Canada
Joined Oct 2002
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More than any other feature on a glider the airfoil determines much of the plane's final character. Read up on what folks like about the Allegro Lite and Allegro E-Lite. If it sounds like what you're looking for then using the AG airfoils on your Nomad will make it behave a lot like the Allegro Lite.

Given what they say about how well it penetrates as well as slowing down I'd also consider a little extra time put into the tail airfoils to try to get them looking a bit more like Mark Drela's tail airfoils used on the Allegro Lite. It would be mostly just using a slightly harder wood and maybe slightly wider for the leading and trailing edges and then sanding to shape.
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Old Sep 26, 2011, 01:12 PM
Geppetto
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United States, CA, San Francisco
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Thanks Guy's!

The Boom is about three-eighths of an inch wide and one and a quarter tall. Top and bottom of the Boom are hard balsa and the sides are one-thirty second inch ply.

I haven't weighed it but I did have to add a bit of lead in the nose to balance it. I know it's not the lightest plane I have give the size. Not a "Tank" but no Euro Moldy either.

The first flights were in Slope lift and it didn't seem to have any problem penetrating. Although, I did encounter "Rudder Flutter" that was a bit scary. I thought I was going to rip the tail off of the Boom on the decent portion of the first loop! Good thing my hinges were in solid!

If I had built it from scratch, instead of refurbishing it, I would have made the aerodynamic counter balance of the Rudder an intricate part of the Vertical Stab. There is plenty of Rudder left to control the plane and less chance of fluttering it. I'll probably make this change anyway as I would like to keep the tail connected to the fuse on all flights if possible!

I got into the project because I had seen pictures of them in magazines years ago and liked the looks of them with no idea how they flew. I never saw one at any of the flying sites I visit, nor had I seen one come up on RCG or FeeBay until I saw this one. BUSA stopped kitting them years ago, though they may still sell the plan.

Could a "Nomad" be next for me? I don't know? Could happen!

Keep grinding the Balsa Dust Guy's!

Geppetto
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Old Sep 26, 2011, 08:53 PM
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It is not clear that eliminating the counter balance will help with the flutter. It might make it worse by putting the c.g. of the surface further behind the hinge line. OTOH, the aerodynamics would be better.

If you widened that tailboom or used unidirectional carbon on both sides, I'll bet that rudder flutter will go away. You might not have to widen it all the way back if you extended the taper almost all the way back. It may be that the boom isn't as stiff as it should be in torsion as well. Widening would help here, as would some glass cloth applied with the weave running diagonally. Or, perhaps, 1/64" ply with diagonal grain applied to the sides of the boom?

Also, the stiffer you can make the rudder linkage, the better.
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Old Sep 28, 2011, 01:17 AM
Geppetto
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United States, CA, San Francisco
Joined Dec 2005
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You're right Lincoln. Stiffening the Boom and the linkage would help quite a bit and I'll probably try that before removing the counter balance. I am going to try static balancing the Rudder with some weight to the rear of the leading edge of the Rudder too.

It's going to be a fun riddle to solve. That or It's going to be a straight and level flyer only!

Geppetto
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