# Force Balance in Wind Tunnel

I am considering a model wing inside a wind tunnel supported from underneath from its center of mass. Two load cells can be used, when properly oriented, to measure the lift force and the drag force. How can two load cells be arranged to also measure the pitching moment and specifically the constant aerodynamic moment I discussed in other threads?

Thank you!

• So you want to measure two orthogonal forces - this requires two sensors already. There is no degree of freedom left to measure pitching moment, too. It will be best to do two identical runs and measure one first and the other in the second run. Jan 29, 2019 at 21:34
• Yes, i have two load cells and I am learning how to use them. One for lift and one for drag (orthogonal to lift). trying to see what arrangement (separate experiment) I need to put the two load cells to measure the aerodynamic pitching moment. I will only place the wing model (not the fuselage) in the test area. Jan 30, 2019 at 13:37

I had imagined simply mounting your lift and drag sensors on a simple (HO gauge model railroad) track for a DIY homebuilt wind tunnel.

Pitching moments for your wing could be done as a separate experiment. Your could pivot on your aerodynamic center (as an axle) and measure pitching torque moments with the load cell attached to the end of the fuselage. Once these moments are established, you can then design the H stab based on area and distance from your wing. Ideally, the H stab will keep your pitching moments zero through all angles of attack (including stall), leaving pitch control to the pilot (with the elevator).

Similar study can be done with you center of pressure (center of all lifts), once you establish it in your planform design.