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.
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.
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.