The Clark Y airfoil…

November 15, 2012 | Radio Controlled Airplanes | By: Mark VandeWettering

I snapped awake at 5:30AM this morning, and couldn’t get back to sleep, so I started a loaf of bread to bake later tonight, and then settled in to thinking about airfoils some more. I had seen references to the “Clark Y” airfoil, but didn’t know how it was defined, so I set out to figure it out. A few minutes of googling revealed a fascinating resource, the UIUC Airfoil Data Site. It has data definitions for literally hundreds of airfoil profiles, including coordinates for the Clark Y. I then dusted off my dim knowledge of gnuplot to draw this (properly scaled) version of the airfoil.

There is a trick to getting gnuplot to work. Here’s the set of commands I used:

set terminal png size 1024,256
set size ratio -1
set ytic .1
set xlabel "Clark Y Airfoil"
plot "clarky.dat" with lines

(You could probably make it look prettier with a bit more work.) The important bit is to set the size ratio: without it gnuplot will change vertical and horizontal scales to fit the data in the window.

Okay, off to make breakfast.

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Comment from Doug Weathers
Time 11/15/2012 at 10:48 am

You are recapitulating the steps we went through for my senior capstone design project, which was a model of a flyback booster (goes up like a rocket, comes down like a glider). NACA airfoil, Kline-Fogleman airfoil, Clark Y. The Clark Y is nice because it has a flat bottom.

My final choice was back to a flat wing, because I was worried about the asymmetrical drag on an airfoil during the ascent phase.

Sadly, we didn’t have time to finish the project before I graduated.

Comment from Mark VandeWettering
Time 11/15/2012 at 12:21 pm

Thanks Doug. You know, it wasn’t clear to me that the Clark actually had a flat bottom. My own tinkering has more modest goals (mostly, just to have fun) but it’s still fun to at least attempt a survey of actual engineering to understand what similarities and differences occur with model airplanes.

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