PDA

View Full Version : Flaps and slats



na85
12-22-2008, 01:30 AM
I just heard an argument that didn't make sense to me. Consider a curve describing coefficient of lift vs angle of attack:

http://upload.wikimedia.org/wikipedia/en/4/42/LiftCurve.gif

It was argued that leading-edge slats essentially shift the curve upwards (i.e. allowing more lift at a given AoA), and flaps shift the curve to the left (i.e. causing Clmax occur at a lower AoA).

Here's what gets me. On the graph above if you pull 25 degrees AoA your lift coefficient is about 1.45.

Let's say extending flaps moves the curve left by 5 degrees. What happens if you pull 25 degrees AoA now? Stall? Do flaps really decrease the usable range of AoA for an aircraft?

na85
12-22-2008, 01:30 AM
I just heard an argument that didn't make sense to me. Consider a curve describing coefficient of lift vs angle of attack:

http://upload.wikimedia.org/wikipedia/en/4/42/LiftCurve.gif

It was argued that leading-edge slats essentially shift the curve upwards (i.e. allowing more lift at a given AoA), and flaps shift the curve to the left (i.e. causing Clmax occur at a lower AoA).

Here's what gets me. On the graph above if you pull 25 degrees AoA your lift coefficient is about 1.45.

Let's say extending flaps moves the curve left by 5 degrees. What happens if you pull 25 degrees AoA now? Stall? Do flaps really decrease the usable range of AoA for an aircraft?

Wurkeri
12-22-2008, 03:17 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by na85:
Here's what gets me. On the graph above if you pull 25 degrees AoA your lift coefficient is about 1.45. </div></BLOCKQUOTE>

At 25 deg AoA the wing section or entire wing is allready stalled (I don't know if your graph is about wing section or entire wing).

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by na85:
Let's say extending flaps moves the curve left by 5 degrees. What happens if you pull 25 degrees AoA now? Stall? Do flaps really decrease the usable range of AoA for an aircraft? </div></BLOCKQUOTE>

Yes, it's even more stalled. And yes, flaps (generally) decrease the (reference line based) stall AoA.

From the simhq:

http://www.simhq.com/_air/air_002a.html

http://www.simhq.com/_air/images/air_002a_7.gif