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# How to estimate drag of a thick airfoil?

## How to estimate drag of a thick airfoil?

(OP)
Hi guys,

How do I estimate the drag of a well designed deep camber airfoil with a height to length ratio of 1/4.5 with 20% accuracy?
Lift is not important, just need to minimize air resistance

The aspect ratio would be 1/3, not sure if that matters much though

I haven't been able to figure out how to work any of the software :/

Also how would the drag coefficient be affected at varying speeds from 40-200 mph?

In case we end up talking about different shapes, I mean the one labeled "deep camber" in the picture:
http://www.allstar.fiu.edu/aero/images/fig18.gif

### RE: How to estimate drag of a thick airfoil?

What I'd do is figure out the zero lift angle of attack. Then i'd figure out the velocity gradient over the surface. Then I'd use the standard skin friction equations to get an estimate of the drag.

yes Re is important.

Another way of looking at it is that at zero lift it is pretty much the same friction as an ellipse of the same depth/length ratio, so look up the answer for that.

Cheers

Greg Locock

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### RE: How to estimate drag of a thick airfoil?

an aspect ratio of 1/3 certainly matters ... it says (to me) forget 2D drag, this is going to be all 3D drag; which is much harder to estimate.

changing speed from 40mph to 200mph will also certainly affect the results (re Reynolds number).

how/why was the foil shape chosen (a narrow thickness with a pronounced camber, like an engine turbine blade) ?

what does your "length to height ratio" mean ? i mean aspect ratio is span/chord ?

any "good" CFD program should get you what you want, but i'm guessing you don't want to pay for it ?

### RE: How to estimate drag of a thick airfoil?

This airfoil is most certainly a 3-D situation and would call for CFD analysis.

You could consult the book "Fluid Dynamic Drag" by S. Hoerner. It has a lot of drag info on objects with various shapes.

Andries

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