Hi, first post and started looking at SimScale yesterday.
I’ve designed a model flying wing glider, and before I test it I’d like to know if it will display adverse yaw characteristics. I couldn’t find much info on tutorials for this sort of thing, and wondering if someone can steer me in the right direction,
thanks
Hi there, welcome to the SimScale community! That’s a great question and a very interesting project to start with. Simulating aerodynamic characteristics like adverse yaw is definitely possible in SimScale.
Adverse yaw is the tendency of an aircraft to yaw in the opposite direction of a roll. To analyze this, you need to calculate the aerodynamic forces and moments acting on your glider, specifically the yawing moment.
Here’s a general approach you can take using a CFD simulation:
1. Simulation Setup
You’ll need to place your glider geometry inside a virtual wind tunnel. This is done by creating an “External flow volume” around your CAD model. The goal is to simulate airflow over the wing and calculate the resulting forces.
For the simulation itself, you can start with an Incompressible analysis. The step-by-step forum tutorial on an Aerodynamic Study of a Model Plane is an excellent resource that walks you through the entire process, from creating the mesh to setting up boundary conditions and the simulation run. While it focuses on lift and drag, the fundamental workflow is exactly what you need.
2. Calculating the Yawing Moment
This is the key step for your analysis. You need to tell SimScale to calculate the aerodynamic moments. You can do this by adding a Forces and moments result control.
This is where you define the parameters to calculate the coefficients. The SimScale knowledge base has a great article on how to set this up: How To Analyze Pitch, Lift, and Drag Coefficients.
To measure yaw, you will need to adapt the settings from that article. For example, if your glider flies along the X-axis and the wings are along the Y-axis:
Center of Rotation**: This should be the center of gravity of your glider.
Drag Direction**: This would be along the direction of flight (e.g., X-axis).
Lift Direction**: This would be perpendicular to the flight direction (e.g., Z-axis).
Pitch Axis: The article uses this for the pitching moment. For your case, to measure the **yawing moment, you would set this to the vertical axis (e.g., Y-axis). The moment calculated around this axis will be your yawing moment.
3. Simulating Conditions for Adverse Yaw
To properly test for adverse yaw, you would need to simulate the condition that causes it: a roll induced by aileron deflection.
The most direct way to do this is to edit your CAD model to roll in any way you would like to simulate it. For example, rotate the glider along its fuselage. Then, run the simulation with this modified geometry. By analyzing the yawing moment coefficient from the “Forces and Moments” result control, you can determine if the yaw is in the opposite direction of the intended roll.
Starting with a simpler analysis, like running the simulation with a small angle of sideslip (by giving the inlet velocity components in two directions), can also give you valuable insights into the directional stability of your glider.
Give these resources a look, and don’t hesitate to ask further questions as you progress.
Thank you for the detailed explanation. I have step 1 done, I’ll have to read and digest step 2 & 3 and see how I go. Cheers.