Angle of Attack

[mocfly]

Anyone know what the angle of attack is where the wing produces 0 lift?

 

How did you come up with this angle?

 

[FastEddieB]

On an asymmetrical airfoil, there should be some lift at a 0° angle of attack.

 

So, my thought would be to get zero lift you would have to be at a slightly negative angle of attack.

 

In any case, each airfoil design should somewhere have a graph showing exactly that - there should be one for the airfoil for the CT if you look hard enough.

[FastEddieB]

Here's one example:

 

 

Note that it looks like there's lift at 0°, and you'd have to go to about -3° angle of attack to get zero lift.

[Roger Lee]

Hi Eddie,

 

Isn't the max angle of attack about 17 degrees for most wings?

[FastEddieB]

Hi Eddie,

 

Isn't the max angle of attack about 17 degrees for most wings?

 

I'll dig out "Aerodynamics For Naval Aviators" later and see.

 

I encourage everyone to seek out that dusty tome, available as a free pdf download.

[Roger Lee]

I though that is what I remembered for the old training days.

[Ed Cesnalis]

 

 

What airfoil(s) does FD use?

 

 

cessna 172 is using a naca 2412, ok without flaps, it stalls behind AoA=22deg

[coppercity]

European C180 airfoil.

[Doug G.]

As I understand it most planes AoA for a stall is around 18 degrees. Of course that does not mean there is no lift, and even in the above example the total lift for the wing may be 0 but there will be positive lift on the wing in some places and negative in others, unless, of course it is totally flat and straight. (You can also add some lift for the fuse and the empennage - after that it gets complicated.)

[FastEddieB]

Chris,

 

Were you asking about the critical angle of attack?

 

I assumed you meant zero lift but at a low angle of attack.

 

Anyway, it's not that at the critical angle of attack there's ZERO lift, just that from that point on any further increase in angle of attack causes a decrease in lift.

[mocfly]

Eddie,

I am looking for the angle of attack where the wing stalls.

 

[FastEddieB]

Got it.

 

Please note that "the angle of attack that the wing stalls" is different from the angle of attack that produces zero lift, as in your original question. That's what threw me off.

 

 

Note that at the critical angle of attack, the coefficient of lift is at its maximum, not zero. Beyond that, lift falls off rapidly, but remains non-zero for quite some time.

 

Also note that the only angle of angle of attack that crosses "zero" is to the left of the curve in the above chart. That's the slightly negative angle of attack that truly produces zero lift that I referred to in my initial response.

 

Anyway, if I understand you properly now, every airfoil will have a different critical angle of attack. You should be able to find out your airfoil type and do a Google image search and come up with a graph for your airfoil (which I think someone pointed you to already in this thread).

[Ian]

Does the AoA at which a particular aerofoil stalls vary with airspeed?

[FastEddieB]

Does the AoA at which a particular aerofoil stalls vary with airspeed?

 

No.

 

A wing can be stalled at any airspeed.

 

Again, download "Aerodynamics For Naval Aviators". It will make that crystal clear.

[Ed Cesnalis]

Does the AoA at which a particular aerofoil stalls vary with airspeed?

 

No Critical AOA does not change.

 

Factors that affect the stall:

• Contaminants. Snow, frost, ice and dirt...
  
• Weight Increased weight requires increased lift and an increased angle of attack; therefore the critical angle of attack (stall) will occur at higher airspeeds.
  
• Centre of Gravity. Stalling speed increases as the aircraft C of G moves forward.
  
• Turbulence. Upward vertical gusts abruptly increase the angle of attack beyond the stalling angle, irrespective of airspeed.
  
• Turns. During a turn in level flight, greater lift is required to offset increased load factor; the critical angle of attack is therefore reached at higher airspeeds.
  

[Ed Cesnalis]

No.

 

A wing can be stalled at any airspeed.

 

Again, download "Aerodynamics For Naval Aviators". It will make that crystal clear.

 

That wasn't the question, does it vary, not can it stall

[Jim Meade]

For the FD CTSW, zero lift is at zero AOA.

For many if not most newer airplanes, there is either a stall strip, washout or some other design feature that ensures the wing does not stall across the span at once. It stalls first at the root. We would have some interesting power on stall practice if the wing stalled across the span at the same time.

[FastEddieB]

For the FD CTSW, zero lift is at zero AOA.

 

 

Are you sure?

 

Normally, if I see a wing which is flat on the bottom and curved on the top, I assume some lift at zero angle of attack. That's kind of the reason they're designed that way.

 

That's why my very first thread differentiated symmetrical and asymmetrical airfoils.

 

Not arguing, I'd just like to see the chart for that and envision how and why it could be so.

[Ed Cesnalis]

I couldn't find any data on the airfoil but Eddie makes sense. if Bernoulli's principle has any merit the zero lift angle needs to be negative.

[FastEddieB]

Example:

 

[Jim Meade]

Eddie, I'd show you but I'd have to kill you.

[Doug G.]

Ian, again somewhat of a rookie here, but, as I understand it there is no decoupling of airspeed and AoA. the wing stalls at the same AoA no matter what the airspeed. Getting to that AoA may be more difficult at a higher airspeed - especially if the wings come off first.

[Tom Baker]

Anytime you have air flowing across the wing it is producing lift. The lift may not be enough to support the airplane in flight, but it is lift. The one place where this might not be true is when transitioning from positive lift to negative lift. At some point you would have to pass through zero, but I doubt you could hold it there for long.

[FastEddieB]

Eddie, I'd show you but I'd have to kill you.

 

Then I guess ignorance will have to be bliss!

[Ed Cesnalis]

The critical AOA for most airfoils is 15 degrees. The FD AOI only provides AOA at various flaps and speeds. Yes you can stall at any airspeed, but that simply means the wing gets to 15 degree AOA faster at slower speeds. Obviously changing the airfoil with flaps is a contributing factor.

 

Kinda funny what the AOI says about stalls: 'The stall characteristics in level flight are docile.'

 

 

"Yes you can stall at any airspeed, but that simply means the wing gets to 15 degree AOA faster at slower speeds."

The rate at which my wing gets to critical AOA has to do with the rate, amount and duration of aft stick I employ. To understand how a plane can stall at any speed you need to take the plane out of the landing sequence and give it some altitude so that it is free to achieve unusual attitudes and or explore big sink.

 

 

Flying down the Owens Valley, in the lee of the Sierra you can find yourself in big sink for a 100 miles. I've done the flight in such conditions in my Skyhawk at full available power with the ASI in the green arc but the stall warning is sounding. This has nothing to do with how fast the wing gets close enough to stall for the horn to work it has to do with the fact that the relative wind has a big downward component.

 

"Kinda funny what the AOI says about stalls: 'The stall characteristics in level flight are docile"

 

My CT doesn't want to stall in level flight, it wants to mush, how docile can you get?

 

 

Blue sky microburst anyone?