When is Lift on an aerofoil proportional to velocity?,

In summary, the speaker conducted a physics experiment where they blew a hairdryer at a makeshift aerofoil at varying distances and wind velocities. They found that the lift was proportional to the velocity, which led them to research the relationship between drag and velocity for laminar flow. They also noted that the trendline on Excel had a gradient of 1 and no constant, and the same was observed on a log graph. However, they expressed doubt about being able to find lift coefficients using the V^2 rule. Another participant suggested that if the Reynolds number is low enough, both drag and lift will be directly proportional to the velocity. However, they doubted that this was the case for the experiment.
  • #1
Andrew__
2
0
Hello,
I was doing my physics coursework, and blew a hairdryer at my makeshift aerofoil across distances of about 10cm and wind velocities of 8-11 m/s, then measured the lift off of a balance. I found they were proportional, exactly (!?), after doing some research I found drag is proportional to velocity for a laminar flow with no turbulence, could this be a similar case but for just very low wind velocities and lift? The gradient of the trendline on excel was *exactly 1 and no constant on the end (through the origin) for speed vs lift, and so was the gradient of a log graph. The reason is I doubt I will be able to find lift coefficients using the V^2 rule, thank you very much in advance?
 
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  • #2
I mean the lift vs speed graph was directly proportional (not a gradient of 1)
 
  • #3
If your Reynolds number is small enough that the flow can be considered creeping flow (aka Stokes flow) then yes, both drag and lift will be directly proportional (or very nearly so) to the velocity. I would doubt your Reynolds number is low enough for that, though.
 

1. What is lift on an aerofoil?

Lift on an aerofoil is the force that acts perpendicular to the direction of motion of the aerofoil. It is the force that enables an aircraft to stay in the air and is generated due to the difference in air pressure on the upper and lower surfaces of the aerofoil.

2. How is lift affected by velocity?

Lift on an aerofoil is directly proportional to the velocity of the air flowing over it. As the velocity increases, the pressure difference between the upper and lower surfaces of the aerofoil increases, resulting in a greater lift force.

3. What is the relationship between lift and airspeed?

The relationship between lift and airspeed is directly proportional. As airspeed increases, the lift force also increases. This is because a higher airspeed results in a greater pressure difference between the upper and lower surfaces of the aerofoil, leading to a higher lift force.

4. Does lift increase indefinitely with increasing velocity?

No, lift does not increase indefinitely with increasing velocity. There is a maximum limit to the amount of lift that can be generated by an aerofoil, known as the critical angle of attack. Beyond this angle, the lift will decrease even with an increase in velocity.

5. How does lift vary with different shapes of aerofoils?

The shape of an aerofoil greatly affects the amount of lift it can generate. A curved or cambered aerofoil will produce more lift compared to a flat aerofoil at the same velocity. Additionally, the angle of attack and the smoothness of the surface also play a role in determining the lift force.

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