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iron eagel 05-14-2005 07:24 PM

Airfoils
 
I have what may be a simple question. (perhaps) is there a simple answer?

Which causes more drag?
The cord.
The Wingspan/frontal area.
The Thickness of the airfoil (% of cord).
Is there a way to define which is has the greatest effect in regard to lift. all at the same angle of attack.

WS 05-14-2005 07:32 PM

RE: Airfoils
 
The chord x span = area
The greater the chord for a given thickness, the greater the frontal area (and wing area)

I don't think your question is specific to airfoils, but to the whole wing?

Drag is directly proportional to wing area
Wings with higher aspect ratios have less induced drag

Lift increases slightly with thickness (up to a point)
The Lift at any given angle of attack (and the lift/drag ratio) increases with camber (curvature of the mean line), up to a point

The lift slope of all airfoils (lift per degree angle of attack) is practically the same, affected by wing planform and aspect ratio

Wings of rectangular planform have a slightly reduced lift slope
Wings of low aspect ratio have reduced lift slope
Swept wings have reduced lift slope

iron eagel 05-15-2005 12:08 AM

RE: Airfoils
 
Thank you very much for your reply.

I working on a BWB design.

onewasp 05-15-2005 11:09 AM

RE: Airfoils
 
To help with your question just examine the wing for the designs where the lift to drag ratio has been optimized-----sailplanes.

iron eagel 05-15-2005 10:29 PM

RE: Airfoils
 
Thanks very much...


britbrat 05-16-2005 07:51 AM

RE: Airfoils
 

ORIGINAL: WS

The chord x span = area
The greater the chord for a given thickness, the greater the frontal area (and wing area)

For a given thickness, how does increasing the chord increase the frontal area? It will certainly increase the wing area (wetted surface) ------ but frontal area???

Are you referring to a frontal area increase because of exposed under-wing surface at some angle of attack? At zero AOA, for example, I don't see how a change in chord can affect frontal area.

iron eagel 05-16-2005 09:35 AM

RE: Airfoils
 
I was wondering about that myself. It must be a given that the wing in most instance will be flying at some angle of attack.

What I was concerned about in making airfoil selection was how to keep the induced drag low, while creating the maximum lift in a given area.

I want to do the impossible, have a wing with high lift and low drag. lol.

I am planing to have the center of the bwb to be in a high lift region and the tip of the wing be at a low or negative aoa. I hate snap rolls.


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