Chord line, camber line & zero lift line clarification?

[elive]

In this thread, (http://www.rcgroups.com/forums/showthread.php?p=7751486&#post7751486) Phil Barnes talks about the zero lift line of an airfoil.

What is the difference between the chord line, camber line & zero lift line?

Are they the same lines for symmetrical airfoils and/or how different are they for asymmetrical airfoils?

Please let me know...

Regards,

Eric

[Brandano]

the chord line is th line from the leading edge of the airfoil, intended as its foremost portion, tho th trailing edge of th airfoil, and it's always a straight line. The camber line is a curve starting and ending at the same points as the chord, but where each single point is equidistant from both the top and bottom surface. It pretty much shows how the airfoil is curved, and for a symmetric airfoil it's a straight line exactly matching the chord. The zero lift line is really a zero lift angle and not a line as such. An asymmetric profile will produce lift even if its chord is parallel to the airflow, while a symmetric airfoil will require a positive AOA to produce lift. The zero lift angle is the small negative angle that a symmetric.. AN ASIMMETRIC! (sorry, should proofread things better) airfoil will require to produce no lift. This is usually shown on a profile as a line from a point above and in front of the airfoil to the trailing edge of the same, and is only meaningful as a reference angle against the profile chord.

[JetPlaneFlyer]

And to further confuse the issue the zero lift angle for any asymmetric airfoil varies with Re number :(

[slipstick]

The zero lift angle is the small negative angle that a symmetric airfoil will require to produce no lift.
Excellent explanation apart from that small typo.....as you obviously know, it should be "non-symmetrical".

Steve

[elive]

Brandano,

Thanks for the explanation. I understood your meaning even with the typo. :p

Eric

[Mike the Snake]

The chord line is from the center of the LE to the tip of the TE.

The mean camber line is a line drawn that is equidistant from the top and bottom lines.

On a semi-symmetrical foil, this line is not straight-slightly curved, flat bottom foils have even more curved camber lines.

The amount of derivation from the chord line (at it's furthest point i think) in relation to the chord length gives you the camber %. A foil with a camber line that deviates from the chord line say 2mm on a 200mm chord wing would have a 1% camber.

The more the camber, the more lift the foil wants to produce.

I THINK, the zero lift line is the AOA at which the foil creates no lift? Symmetrical would be zero, but a semi-symmetrical foil would need a negative zero lift line I think.

[elive]

The amount of derivation from the chord line (at it's furthest point i think) in relation to the chord length gives you the camber %.


Thanks Mike. That answers another question I wanted to post.

Eric

[BMatthews]

.... I THINK, the zero lift line is the AOA at which the foil creates no lift? Symmetrical would be zero, but a semi-symmetrical foil would need a negative zero lift line I think.

That's exactly right. You can see this in the Foilsim airfoil flying simulator.

JPF, I'm a little confused at your statement. You're saying that a symetrical airfoil produces lift at 0 angle of attack?