Quote:
Originally Posted by aerohead
The ideal teardrop form(about 2.7:1 fineness ratio) outside of ground effect has a Cd 0.04.I believe Morelli developed a low drag form of which Aptera borrows from.It was never tested in ground-effect.---- Any lengthening of the ideal teardrop body of revolution exhibits an increase in drag do to skin friction.I believe Cd 0.04 is the limit.Any environmental structure within close proximity will degrade the Cd.
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Good job, guys,
Now we are getting somewhere. My Mark's Handbook indicates minimum drag occurs at L/D = 5 and equals Cd = 0.04 at Re = 6 million. It further suggests that Cd rises at higher Re. But, the data are ancient and I'm not ready to trust them.
There are a number of Wortmann airfoils that reach Cd = 0.006 on chord basis, at around Re = 3 million. These published Wortmann sections are about 18% thick. But, I am pretty sure when I worked on this two years ago that I was able to reach half that value, maybe to 0.002 at higher Reynolds numbers using a commercial airfoil calculator. (Don't remember the name, I've got it here somewhere.)
I'm still hoping to find a recent paper or something that has reviewed the situation for bodies of revolution. My handbook is quoting 1930s data.
Ernie Rogers