Predicting lift on an Aerofoil with varying Angles of Attack

In summary, the conversation discusses issues with predicting lift on an aerofoil with respect to angle of attack. The formula for lift and variations of the lift coefficient are mentioned, but none take the angle of attack into account. The experiment aims to find the optimum angle of attack to velocity ratio and a formula to predict lift based on this. The speaker also asks for advice on incorporating stall into the calculations. Various tools and resources are mentioned for generating data on airfoil performance.
  • #1
Tom 77
I am conducting a school based EEI and have found issues in predicting lift on an aerofoil with respect to angle of attack.I understand the formula for lift is L = (1/2) d v2 s CL. I also understand there are many confusing variations to the calculation for the lift coefficient but i am yet to find one that takes the angle of attack into account.

The idea of the experiment is to find the optimum angle of attack to velocity ratio in a wind tunnel acting on a cambered aerofoil and i would like to predict the lift per angle prior to testing, then to reveal the differences and use results for error. Is there a formula i can use to calculate the predicted lift of an Aerofoil which incorporates the angle of attack. I really appreciate any advice or support. Thanks
 
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  • #2
Tom 77 said:
I am conducting a school based EEI and have found issues in predicting lift on an aerofoil with respect to angle of attack.I understand the formula for lift is L = (1/2) d v2 s CL. I also understand there are many confusing variations to the calculation for the lift coefficient but i am yet to find one that takes the angle of attack into account.
https://en.wikipedia.org/wiki/Airfoil#Thin_airfoil_theory
 
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  • #3
Getting a reasonably accurate model is fairly complicated. This is an example library / program that generates data about airfoil performance:

http://web.mit.edu/drela/Public/web/xfoil
 
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FAQ: Predicting lift on an Aerofoil with varying Angles of Attack

1. How does the angle of attack affect lift on an aerofoil?

The angle of attack is the angle between the wing and the relative wind. As the angle of attack increases, the lift on the aerofoil also increases, up to a certain point. This is because at higher angles of attack, the air flowing over the wing is forced to travel a longer distance, creating a lower pressure on the top surface of the wing and a higher pressure on the bottom surface, resulting in lift.

2. What is the maximum angle of attack for an aerofoil?

The maximum angle of attack, also known as the stall angle, varies depending on the design of the aerofoil and the airfoil shape. However, it is typically between 10-20 degrees. Beyond this angle, the airflow over the wing becomes turbulent and the lift begins to decrease.

3. How does the shape of the aerofoil affect lift at different angles of attack?

The shape of the aerofoil, specifically the curvature of the upper surface, plays a significant role in lift generation. A more curved upper surface creates a longer path for the air to travel, resulting in a higher pressure difference and thus, higher lift. This is why many modern aerofoils have a curved upper surface and a flatter lower surface.

4. What other factors besides angle of attack affect lift on an aerofoil?

In addition to angle of attack, factors such as airspeed, air density, and aerofoil design all play a role in determining lift on an aerofoil. Higher airspeed and lower air density result in higher lift, while aerofoils with a high camber (curvature) and thickness tend to generate more lift at lower angles of attack.

5. How is lift calculated for a given aerofoil at a specific angle of attack?

Lift on an aerofoil can be calculated using the lift equation: L = ½ * ρ * V² * S * CL, where ρ is air density, V is airspeed, S is the wing area, and CL is the coefficient of lift. The coefficient of lift is determined experimentally and varies depending on the angle of attack and aerofoil design.

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