Lift and Drag Which frame of reference?

In summary, the equations for Lift and Drag acting on an airplane are defined in either the stability frame or wind frame, depending on how the lift and drag coefficients were calculated. The dynamic pressure, which is used in the equations, is not frame dependent. The reference area is the only factor that matters. The direction of the forces within each frame is determined by a rotation matrix, which differs depending on the frame used. The coefficients are typically obtained from a CFD software.
  • #1
phys_student1
106
0
Lift and Drag...Which frame of reference?

Hi,

When expressing the Lift and Drag acting on an airplane as:

[tex]F_{lift}=qSC_L[/tex]
[tex]F_{drag}=qSC_D[/tex]

where q is the dynamic pressure, S is the wing ref. area, and C's are the lift and drag coefficient.

My question: Some sources, like this one, claim these equations are 'defined' in stability frame {S}, while other claim they are in wind frame {W}. In either case you'll use a rotation matrix to go back to body frame {B}, but this matrix will differ whether going from W->B or S->B, wo which is correct?
 
Engineering news on Phys.org
  • #2
I'm sorry you are not generating any responses at the moment. Is there any additional information you can share with us? Any new findings?
 
  • #3
Not really. I still do not have answer.
 
  • #4
It all depends on how CD and CL were calculated in the first place. The equations themselves are valid in either frame since the dynamic pressure is not frame dependent in the sense that it uses velocity magnitude of the air relative to the body. The only thing that really matters is what reference area was used. The only place the frame would matter is in determining which direction the vector for each force points within each respective frame.
 
  • #5
Well, C_D and C_L are Taylor expanded into many components which are usually obtained from a CFD software, so I am not sure.
 

FAQ: Lift and Drag Which frame of reference?

1. What is the difference between lift and drag in terms of frame of reference?

Lift and drag are aerodynamic forces that act upon an object in motion, such as an airplane. The frame of reference refers to the point from which these forces are measured. In the case of lift, the frame of reference is typically the direction of motion, while for drag, it is usually the opposite direction.

2. How does the frame of reference affect lift and drag?

The frame of reference can greatly impact the magnitude and direction of lift and drag forces. For example, if the frame of reference is perpendicular to the direction of motion, the lift force will be larger than if the frame of reference is parallel to the direction of motion. Similarly, the drag force will be smaller when the frame of reference is perpendicular compared to parallel.

3. Can the frame of reference be changed during flight?

Yes, the frame of reference can change during flight. As an aircraft moves through the air, its orientation and direction may change, causing the frame of reference to shift. This change in frame of reference can have a significant impact on the lift and drag forces acting on the aircraft.

4. How does the shape of an object affect the frame of reference for lift and drag?

The shape of an object can influence the frame of reference for lift and drag. For example, a symmetrical object will have the same frame of reference for lift and drag, while an asymmetrical object will have different frame of references for these forces. Additionally, the shape of an object can affect the distribution of these forces, leading to changes in the overall lift and drag forces.

5. What is the significance of considering frame of reference when studying lift and drag?

The frame of reference is an important factor to consider when studying lift and drag. By understanding how the frame of reference can impact these forces, scientists and engineers can design more efficient and aerodynamic objects, such as airplanes. Additionally, the frame of reference can help explain the complex dynamics of flight and how different factors, such as air pressure and shape, can affect lift and drag.

Similar threads

Simple Machines Revisited + more - making 2.5 ton lift
Replies
2
Views
2K
Ridiculously low drag coefficient from OpenFOAM CFD
Replies
1
Views
2K
How calculate lift/drag using static pressure taps in wind tunnel test?
Replies
9
Views
2K
Moving charges in a moving frame of reference
2
Replies
66
Views
26K
How Does the Jacchia Model Predict Atmospheric Drag for Satellites in LEO?
Replies
0
Views
1K
ABC reference frame synchronous generator modelling in Ltspice
Replies
1
Views
2K
Are vectors independent of reference frames?
Replies
2
Views
2K
I Using reference frames for derivation of Lagrangian
Replies
25
Views
2K
Why does an airplane perform a loop?
Replies
5
Views
5K
Finding the sum and difference of two drag coefficients
Replies
5
Views
1K

Hot Threads

Recent Insights

Back
Top