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Old Aug 17, 2012, 05:37 PM
Registered User
Cromer,Norfolk, UK
Joined Nov 2006
2,505 Posts
Cool
Discovery within Profili!! section designing.

Hello chaps,

Rather excited by this, and I suspect I'll be doing a lot of it.

I found that if I draw what I think is a nice wing section in MS Paint, and save it as a .tiff, I can import it as a raster into Profili and it'll generate a polar for it and a set of coordinates.

Thats pretty awesome.

I had a fiddle just to see what I could come up with, so here's a comparitive polar with RG15 (just because) for a shape which I drew up.

Its a rubbish wing section (well, it is when inverted anyway) but still, its a fascinating feature of profili, and is amazing for teaching about HOW the shape of a wing section affects its performance.

Heck, I "designed" another wing section, no, I didn't design it, I drew what I thought would work and ran another analysis (sort of thing) am I right in thinking that the MC03 section is showing lower drag than RG15 at higher CL values? So, would that then point to a wing made with that section being quicker in a turn (ie higher CL?)

Apologies for my ignorance and my excitement!

I'm blown away.
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Last edited by MCarlton; Aug 17, 2012 at 05:47 PM.
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Old Aug 17, 2012, 06:08 PM
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United States, CO, Denver
Joined Sep 2005
258 Posts
eyeball impressions

Quote:
Originally Posted by MCarlton View Post
.......am I right in thinking that the MC03 section is showing lower drag than RG15 at higher CL values? So, would that then point to a wing made with that section being quicker in a turn (ie higher CL?)

Apologies for my ignorance and my excitement!

I'm blown away.
I share your excitement for learning how airfoils work and why. Depending on which version of Profili you have, there's a great deal to be learned by taking your favorite section and changing the thickness, then changing the camber and comparing a bunch of modifications to the original airfoil.

In terms of the two graphs that you show, and only looking at them by eye, I see that the MC01 in the first graph is significantly thinner than the RG15 thus would most likely not perform as well at high CL's despite it appearing that it has more camber.

In the second graph the MC03 appears to be of similar thickness to the RG15 but has a lot more camber. That's why it performs better at high angles of attack and high CL's. The consequences are that it performs poorly at low angles of attack or high speeds.

Again with the purchased version of Profili this can be quickly simulated.
Also Xflr5 will do the same and is free but is more difficult to learn to use.

Have Fun

Mike
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Old Aug 17, 2012, 06:18 PM
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Cromer,Norfolk, UK
Joined Nov 2006
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I have the full purchased version of Profili, so it appears I can do rather more with it than I originally thought. The sections I did for this were just "shapes" really, I didn't put any thought into them other than them looking vaguely wing like. I was just impressed that I could draw a wing section by eye, and have a set of polars drawn up for it. Like having a wind tunnel in my computer. Could be a lot of fun.

Matt
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Old Aug 17, 2012, 06:57 PM
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United States, CO, Denver
Joined Sep 2005
258 Posts
Quote:
Originally Posted by MCarlton View Post
I have the full purchased version of Profili, so it appears I can do rather more with it than I originally thought. The sections I did for this were just "shapes" really, I didn't put any thought into them other than them looking vaguely wing like. I was just impressed that I could draw a wing section by eye, and have a set of polars drawn up for it. Like having a wind tunnel in my computer. Could be a lot of fun.

Matt
Go into the "Drawing Polars, Free Criteria" which you can find in the top icons. You'll open up the ability to view 8 different airfoils at once. Try it with the same airfoil 3 or 4 times then go into each and change the thickness or camber and view them...you can modify many criteria and compare quickly. It is possible to overwhelm it and crash the program but it's still amazingly fun and educational.

Mike
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