How does an inverted aerofoil work?

[threy]

I understand that high velocity will create a region of low pressure and a net upward force will lift up the aerofoil. And does it mean that when the plane is about to board, the aerofoil will be inverted so that the higher pressure will push the plane down? How does inverted aerofoil work as spoilers on racing cars? Which region has low pressure?

 

[rcgldr]

Absent external forces, a parcel of air will accelerate from a higher pressure area to a lower pressure area. As that parcel of air accelerates towards the low pressure area, it's velocity increases and it's pressure decreases in accordance with Bernoulli principle. Maintaining that pressure differential will require some type of external force, which goes beyond Bernoulli.

For a given angle of attack, an aerofoil diverts the relative air flow (air flow relative to the aerofoil). If it diverts the relative air flow downwards, the resulting lift is upwards (and vice versa in the case of wings used on Formula 1 type race cars).

 

[cjl]

A spoiler on a racing car is just an inverted airfoil (and it makes a low pressure region on the bottom surface which helps push the car into the ground for better grip). As for your question about aircraft though, I don't understand what you're trying to say. Specifically, this part:

And does it mean that when the plane is about to board, the aerofoil will be inverted so that the higher pressure will push the plane down?

Ordinary aircraft never invert the airfoil - even as they are landing or taxiing, they are making positive lift and the airfoil is in its normal orientation. They do have a variety of methods to control how much lift they make (spoilers to decrease lift, flaps to increase lift, plus they can change the orientation of the entire aircraft relative to the oncoming flow once they are in flight), but the airfoil itself is never inverted.

 

[rcgldr]

Note the type of "spoiler" used by Nascar type race cars, which is an upwards angled flap at the back of a race car, just reduces lift and/or creates some downforce by deflecting air upwards, but since it's attached directly to the "trunk" of a race car, it doesn't produce a low pressure area below the car. Instead at the front, an air dam and/or "splitter" produce low pressure under the front portion of a race car, and at the back, a "diffuser" is used to maintain low pressure under the rear portion of a car.

Other types of race cars use inverted wings to produce downforce (and also "diffusers"). Indy Race cars also use under body tunneling to further reduce pressure under the car.

 

[PJC01]

I can confirm that the inverted aerofoil, also known as a symmetric airfoil, works by utilizing Bernoulli's principle. This principle states that as the velocity of a fluid (in this case, air) increases, the pressure decreases. This is due to the conservation of energy in a fluid, where the kinetic energy of the fluid increases at the expense of its potential energy. In the case of an aerofoil, the curved shape causes the air to travel a longer distance over the top of the wing compared to the bottom, resulting in a difference in velocity and therefore pressure.

The net upward force, or lift, on the aerofoil is a result of the higher pressure on the bottom of the wing compared to the top. This creates a pressure difference which causes the air to flow from the bottom to the top, creating lift.

In regards to your question about the aerofoil being inverted when a plane is about to land, this is not necessarily the case. Inverted aerofoils are commonly used on racing cars as spoilers, but on airplanes, they are typically used as wing flaps to increase lift and drag during takeoff and landing. The angle of the aerofoil can be adjusted to control the amount of lift and drag, allowing for a controlled landing.

In terms of spoilers on racing cars, inverted aerofoils work by creating a downward force, or negative lift, on the car. This helps to keep the car stable at high speeds and during turns. The low pressure region is still on the top of the aerofoil, but in this case, it is intentionally created to produce a downward force.

In summary, the inverted aerofoil works by utilizing Bernoulli's principle to create lift and control the movement of air around the wing. Its use on airplanes and racing cars differs, but both rely on the same principle to generate the desired effect. The low pressure region is on the top of the aerofoil, and it can be adjusted to produce either lift or negative lift, depending on the application.