How does the Angle of Attack affect lift?
21.September, 2009
How does the Angle of Attack affect lift in terms of of the equation F=ma?
F= lift
m= mass of air diverted downwards
a= the change in velocity of the air being diverted downwards
In other words, does increasing the AoA increase the amount of air being diverted down? or does it speed up the vertical velocity of the air?
I know that increasing the AoA results in more lift (until you hit the stall angle), but I don’t understand why.
Skyhawk, I am aware of the "real" lift equation, and the AoA vs. lift coefficient curve, but you’re not really answering my question.
Drewpie,
Yep, your answer is what I’m looking for. You mentioned that increasing the AoA will increase the velocity of airflow on the top of the wing. What I’ve been trying to ask is why this happens. How does tilting a wing increase the velocity of air ontop of a wing?
I think you are really looking for:
Yes increasing AOA increases the velocity on the topside of the airfoil. It does the same thing as increasing the chamber but is less efficient at it.
It does NOT force any air down. You can thinking of it as "sucking a plane upward". There is NO magic column of air pushing the plane up (unless you are talking about the harrier).
And yes you can make a plane fly without any chamber in the wing. Using only angle of attack to create lift. I don’t know if any real planes have been made to fly this way because of the lack of efficiency and control but the IFO you can buy does this little neat trick in a R/C model.
http://www.flyifo.com/htmlpages/tifo.html
21.September, 2009 um 12:40 pm
Whenever you increase the angle-of-attack, you increase the coefficient-of-lift. You trade increased lift for an increase in induced drag.
It is an increase in the camber of the airfoil that results in increased lift.
***EDIT
Not exactly sure what you’re looking for, so I’ll try again:
Hmm. okay.
Yes, it does force more air down and it does increase the velocity of the air.
Think of it this way:
If you had a wing that was flat, it would create no lift.
It would force no air down and would not increace the velocity of the relative wind.
If you increased the camber, slightly, it would produce a little lift. It would force some air down, and increase the velocity of the air.
If you increased it more, it would create more lift. And so on.
You are increasing the effectiveness of the airfoil.
Therefore, it produces more lift. Hence, more downward force, and increased velocity of the relative wind.
References :
21.September, 2009 um 12:47 pm
I think you are really looking for:
Yes increasing AOA increases the velocity on the topside of the airfoil. It does the same thing as increasing the chamber but is less efficient at it.
It does NOT force any air down. You can thinking of it as "sucking a plane upward". There is NO magic column of air pushing the plane up (unless you are talking about the harrier).
And yes you can make a plane fly without any chamber in the wing. Using only angle of attack to create lift. I don’t know if any real planes have been made to fly this way because of the lack of efficiency and control but the IFO you can buy does this little neat trick in a R/C model.
http://www.flyifo.com/htmlpages/tifo.html
References :
Grew up in the 500 building
21.September, 2009 um 1:12 pm
Ok, if you look edge-wise at a wing, it has a bigger portion of the TOP side exposed versus the bottom side when parallel in flight , viewing head-on. If you’re flying level, air will go evenly over the top and bottom sides. If you tilt the wing upwards, then you see more of the underside of the bottom of the wing, and less of the top edge. As more air is trying to go under than over, it increases lift. As less air is trying to move over the top surface, due to less exposure to top surface directly, it has to increase in speed as the pressure/density drops, to stay constant with the laws of physics to try to keep up with the lower wing surface.
References :
21.September, 2009 um 1:21 pm
The angle of attack of a wing directly controls the distribution of pressures acting on the wing. so when you change these pressures you can increse lift, and increasing lift you also increase its oposing force drag.
and when you increase your angle of attack you reach what is called the critical angle of attack, thats the angle that the wing will stall regardless of weight, airspeed, density, temperature. and it happens because the smooth flow over the wing becomes disrupted.
References :
21.September, 2009 um 1:27 pm
Nobody mentioned Bernoulli’s Principle?
Look it up. It is simple and will explain why airplanes can fly, helicopters can lift, and why props are more than just big fans. It is also helpful in other areas of fluid dynamics.
As it applies to airfoils (like wings and props) and as mentioned above; when the flow of air encounters the leading edge of the wing some air will go over the wing and some will go under the wing. The air that goes over the wing must travel a further distance in the same amount of time as the air that went under the wing, due to the shape of the wing. When the fkow of air that went over the wing reaches the trailing esge of the wing it wull reunite with the same air it was seperated from at the leading edge – that is, both the upper and the lower flow have the same amount of time to travel across the upper and lower surfaces and must mett again, at the same time, at the trailing edge of the wing.
In order to travel a greater distance (because of the shape of the wing) in the same amount of time, the upper flow of air must accelerate. When this flow of air accelerates its pressure is reduced (Bernoulli’s Prinicipal). That is to say that the surface pressure below the wing is greater than above the wing, naturally this will make the wing want to "rise", or create lift.
By increasing the AoA you are changing the position of the leading edge of the wing. If you change the AoA (increasing) you are lengthening the upper chord of the airfoil while shortening the lower chord of the airfoil, thus the air has an even greater distance to cover in the same amount of time, thereby increasing lift.
This same principal also explains how flight controls work. Ailerons, flaps, elevator and rudder all work just like the actual wing of the aircraft. They are not used to deflect air in a given direction, but rather change the airflow around the surface to achieve the desired change of velocity.
Thank you, and good night.
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