# Dynamic behaviour of a rotatable airfoil, at constant and variable flow field

• prezza
In summary: Now that's a blast from the past. More than 35 years ago when I was at school we would take small strips of paper about 3 inches long and 1 inch wide (perhaps a bit less). Fold down the short sides 90 degrees to form vertical surfaces about 1/2 inch tall at each end. They would spin as described. (eg They pitch up and keep pitching up). Sometimes they needed to be given an initial "flip" when launched to set them spinning (eg pull down on the trailing edge as you launch them). They would fly considerable distances if launched from the maths tower building.In summary, the conversation discusses the behavior of a fixed airfoil that can rotate around its axis when subjected to a one-dimensional
prezza

## Homework Statement

While I was learning about drag and lift on airfloils, I imagined a special airfoil which is fixed at a certain elevation and cannot move vertically (y axis) but can be rotated around its axis (z). Let's assume the direction of the flow to be the x axis.
I try to predict the dynamic behaviour of the airfoil after being subjected to a moving fluid. How does the angle of the airfoil change with time when it is subjected to a one dimensional constant velocity flow at x direction.

## Homework Equations

The second question: What is the effect of increasing flow velocity on the angle of airfoil?

## The Attempt at a Solution

In the case of constant velocity flow, I know that the airfoil tries to reach an equilibrium angle. One equilibrium angle can be the one, at which the velocity of the fluid at the top and bottom of the airfoil are equal. So there will be no driving force for rotation. But right after we apply an angle of attack, pressure difference of two sides of the airfoil causes a clockwise rotation. This will continue until stall is occurred. What happens next? Does the airfoil ever reach a steady state or it continues to rotate?

Last edited:
Thanks for the references.

What I mean is not the airfoil in its conventional usage. Just a geometry like an airfoil. and the rotation axis is parallel to its surface. I am not talking about aircrafts at all. Just wondering about the physics of the flow and forces on such a geometry.

Cambered airfoils generate a torque in the downwards pitch direction. If free to rotate, some flat airfoils may end up spinning. I'm not sure if a conventional airfoil would flap back and forth or spin. Do a seb search for spinning wings often used a lawn decorations, which do not fly, as an example.

some flat airfoils may end up spinning

Now that's a blast from the past. More than 35 years ago when I was at school we would take small strips of paper about 3 inches long and 1 inch wide (perhaps a bit less). Fold down the short sides 90 degrees to form vertical surfaces about 1/2 inch tall at each end. They would spin as described. (eg They pitch up and keep pitching up). Sometimes they needed to be given an initial "flip" when launched to set them spinning (eg pull down on the trailing edge as you launch them). They would fly considerable distances if launched from the maths tower building.

#### Attachments

• Untitled.png
1.9 KB · Views: 403
Last edited:

## 1. What is the purpose of studying the dynamic behavior of a rotatable airfoil?

The purpose of studying the dynamic behavior of a rotatable airfoil is to understand how it responds to changes in the flow field, such as varying speeds and angles of attack. This information is important for designing efficient and stable aircraft wings.

## 2. How does the behavior of a rotatable airfoil differ at constant and variable flow fields?

At a constant flow field, the behavior of a rotatable airfoil will be more predictable, with consistent lift and drag forces. However, at a variable flow field, the behavior can be more complex and unpredictable, with changes in lift and drag forces depending on the speed and angle of attack.

## 3. What factors affect the dynamic behavior of a rotatable airfoil?

The dynamic behavior of a rotatable airfoil is affected by various factors, including the shape and size of the airfoil, the speed and angle of attack of the flow field, and the viscosity and density of the air. Other factors such as surface roughness and turbulence also play a role.

## 4. How is the dynamic behavior of a rotatable airfoil measured and analyzed?

The dynamic behavior of a rotatable airfoil can be measured and analyzed using various techniques, such as wind tunnel testing, computational fluid dynamics, and flight testing. These methods allow for the collection of data on lift and drag forces, as well as the visualization of flow patterns around the airfoil.

## 5. How can the knowledge of dynamic behavior of a rotatable airfoil be applied in real-world situations?

The knowledge of dynamic behavior of a rotatable airfoil is crucial in the design and optimization of aircraft wings, as well as other applications such as wind turbines and propellers. It can also be used to improve the performance and stability of existing airfoil designs, leading to more efficient and safer flight. Additionally, understanding the dynamic behavior of airfoils can aid in the development of advanced aircraft control systems.

• Engineering and Comp Sci Homework Help
Replies
31
Views
1K
• Classical Physics
Replies
30
Views
3K
• Classical Physics
Replies
0
Views
135
• Introductory Physics Homework Help
Replies
8
Views
2K
• Aerospace Engineering
Replies
2
Views
1K
• Electromagnetism
Replies
1
Views
864
• Engineering and Comp Sci Homework Help
Replies
4
Views
3K
• Introductory Physics Homework Help
Replies
32
Views
1K
• Mechanical Engineering
Replies
31
Views
2K
• Engineering and Comp Sci Homework Help
Replies
5
Views
9K