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Jun 08, 2021, 08:50 PM
Charles Martin
BavarianCharles's Avatar
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The Aerodynamics of a DLG Unraveled


This article was published in the "new" RC Soaring Digest

https://medium.com/rc-soaring-digest...d-be383532bf29

Good stuff for DLG nerds, like me. Enjoy!

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Jun 08, 2021, 11:26 PM
Registered User
Thanks for posting the link, Charles! Great read. I was a little surprised at the min sink airspeed. It’s probably time for another eye calibration session...
Jun 09, 2021, 06:04 AM
.: Looking for Thermals :.
Ricardo RW's Avatar
Quote:
Originally Posted by BavarianCharles
This article was published in the "new" RC Soaring Digest

https://medium.com/rc-soaring-digest...d-be383532bf29

Good stuff for DLG nerds, like me. Enjoy!

Another nerd here…! Article —of course— on my reading list. Thanks for sharing.
Jun 09, 2021, 09:01 AM
F3B and F3K
RetoF3X's Avatar
Hmm, maybe the authors could have just contacted Tom Siler, who may have given them the polars instead of measuring the airfoils empricially and then modelling them in XFOIL.

Might be interesting though how close the molded NXT comes to the wing Tom designed.

There was some debate how accurate a molded plane can be in the F3B community, and if some optimization of airfoils may get lost by building tolerances (mold not perfectly closed, alignment of mold not 100% perfect, milling accuracy, etc.).

Maybe a chance to check that with the experimental data from the authors?

Reto
Latest blog entry: thoughts on contest flying
Jun 09, 2021, 12:36 PM
Have Fun and Just Fly!
l shems's Avatar
Indeed nice article. Was most amazed by the large Camber for min sink.

But you don't gain much between 3-4 and 8 mm, so....

Have fun and just fly!
Jun 09, 2021, 03:58 PM
I'm not as bad as they say.
Another interesting takeaway is that if you have a 1 m/s tailwind, the best L/D is with 4 or 8 mm camber.
Latest blog entry: AIrcraft I've built.
Jun 09, 2021, 05:33 PM
Have Fun and Just Fly!
l shems's Avatar
Quote:
Originally Posted by mnowell129 View Post
Another interesting takeaway is that if you have a 1 m/s tailwind, the best L/D is with 4 or 8 mm camber.
Totally counterintuitive.

Good to know.

Have fun and just fly!
Jun 10, 2021, 07:24 AM
I'm not as bad as they say.
Very counterintuitive.
Credit to Theo for original graph.
Latest blog entry: AIrcraft I've built.
Jun 10, 2021, 10:53 AM
Have Fun and Just Fly!
l shems's Avatar
Quote:
Originally Posted by mnowell129
Very counterintuitive.
Credit to Theo for original graph.
And with 4 m/s it doesn't make any difference at all.

I still have difficulty reading those graphs with relative airspeed. What happens with headwind? And how would I see that in a graph.

Have fun and just fly!
Jun 10, 2021, 01:39 PM
Duane, LSF IV
Wazmo's Avatar
Quote:
Originally Posted by mnowell129
Very counterintuitive.
Credit to Theo for original graph.
Am I mistaken, or should those lines be drawn from a point on the X-axis where Y=0? They appear to be at Y=-0.2 m/s. Not sure how much that changes the results.
Jun 10, 2021, 02:51 PM
I'm not as bad as they say.
Quote:
Originally Posted by Wazmo
Am I mistaken, or should those lines be drawn from a point on the X-axis where Y=0? They appear to be at Y=-0.2 m/s. Not sure how much that changes the results.
Good catch.
Yep, but I was trying to illustrate the effect not necessarily provide hard numbers.
I find that few pilots know to add camber going downwind.
Last edited by mnowell129; Jun 10, 2021 at 02:57 PM.
Jun 10, 2021, 02:51 PM
I'm not as bad as they say.
Quote:
Originally Posted by l shems
And with 4 m/s it doesn't make any difference at all.

I still have difficulty reading those graphs with relative airspeed. What happens with headwind? And how would I see that in a graph.

Have fun and just fly!
The headwind graph is in the article, but it's trying to show effect of ballast, not camber.

Headwind is a shift the other direction. Shows how camber is not your friend upwind.
Last edited by mnowell129; Jun 10, 2021 at 03:10 PM.
Jun 10, 2021, 03:04 PM
I'm not as bad as they say.
Redrawn with correct axis.
Still shows the same effect.
Have to go to a 4 m/s tailwind to make things more visible.
Last edited by mnowell129; Jun 10, 2021 at 03:12 PM.
Jun 10, 2021, 03:23 PM
Blind Hawk
rdjay's Avatar
Mickey,

Confused I am (in Yoda speak)....

Headwind? Tailwind? Isn't it just airspeed over the wing?

Thanks, Rj
Jun 10, 2021, 03:46 PM
a.k.a. Bob Parks
bbbp's Avatar
Except in turns!


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