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RE: do ailerons provide lift? - 2/7/2013 6:12 PM   
eddieC



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quote:

As you can see from BMatthews post, you can still get lift at negative A0A. 

I suspected as much, from playing with undercambered airfoils. 
Fortunately, mankind has progressed since the Wright Flyer and its ilk. For more conventional, efficient airfoils, I believe my original statements still are true. My bad, thinking we were talking about present day technology. 


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RE: do ailerons provide lift? - 2/7/2013 9:58 PM   
mr_matt



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quote:

ORIGINAL: eddieC
I suspected as much, from playing with undercambered airfoils. 
Fortunately, mankind has progressed since the Wright Flyer and its ilk. For more conventional, efficient airfoils, I believe my original statements still are true. My bad, thinking we were talking about present day technology. 




Positively cambered airfloils can produce lift at negative angles of attack, they don't necessarily have to be undercambered.

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RE: do ailerons provide lift? - 2/7/2013 10:14 PM   
rmh



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Status: offline 		There is no lift at zero or negative angles

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RE: do ailerons provide lift? - 2/7/2013 10:58 PM   
mr_matt



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ORIGINAL: rmh

There is no lift at zero or negative angles



Didn't you see BMatthews curves?


Unless you defined angle of attack to be reference to the zero lift line and not the chord line, you still have lift at negative AoA.



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RE: do ailerons provide lift? - 2/7/2013 11:53 PM   
rmh



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Status: offline 		Yes, I saw that - The definitions of zero lift line and the chord line - are the problem.
You can NOT have lift if the effective AOA is zero or less
The concept of a lifting surface is simple
it is any shape which may develop unequal pressure- Typically higher pressures under the shape - lower pressures above
How efficiently it does this is quite a different matter . The shape may be perfectly flat -and simply forced to hold an angle of attack
OR it may be a flat sheet - curved and forced to move at a given angle of attack
OR it may be a rather involved combination of curves
IF you change the angle it is moving , such that pressure above and below are equal- THAT is a zero lift path draw that line -
it is the zero lift line .

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RE: do ailerons provide lift? - 2/8/2013 12:20 AM   
mr_matt



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"When an airfoil is set to its zero lift AoA, it creates.....wait for it.....zero lift"


I found this on the internets:

quote:

As a wing moves through the air, the wing is inclined to the flight direction at some angle. The angle between the chord line and the flight direction is called the angle of attack and has a large effect on the lift generated by a wing.



And from the same webpage

quote:

Notice on this plot that at zero angle a small amount of lift is generated because of the airfoil shape. If the airfoil had been symmetric, the lift would be zero at zero angle of attack.


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RE: do ailerons provide lift? - 2/8/2013 12:36 AM   
mr_matt



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www.nasa.gov

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RE: do ailerons provide lift? - 2/8/2013 1:48 AM   
rmh



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This is simply an exercize in logic
If No lift is produced was by the moving airfoilthere was no effective angle of attack
stated differently - -there was no effective pressure difference top to bottom
- the wing must be held at some angle to acheive an effective AOA
depending on the shape utilized the appearance of the effective AOA can be misleading . as soon as you throw in"chord line ", things get cloudy
If your idea of the chord line is different than someone elses idea of chord line the AOA will be a different number.
wings ar all about getting effective pressure difference - in the most efficient manner .
How can we as poor model builders know when we have selected the optomized shape?
it's tricky as once yo u change weight - speed and load and speed range- the best shape changes - as does the the necessary shape use to prevent the wing from twisting /bending.
It's all a SWAG- and trying for some "perfect" shape is simply a make work project.

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RE: do ailerons provide lift? - 2/8/2013 4:42 AM   
Lnewqban



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Status: offline 		http://en.wikipedia.org/wiki/Angle_of_attack

http://en.wikipedia.org/wiki/Zero_lift_axis

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RE: do ailerons provide lift? - 2/8/2013 2:11 PM   
rmh



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< Message edited by rmh -- 2/8/2013 7:29 PM >

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