A typical educational wind tunnel need only measure the lift and drag forces and be able to
control the angle of attack of the mounted model. This paper presents a simple design for the
balance apparatus to measure lift and drag. Two load cells are used in the apparatus, one to
measure the vertical force (lift) and one to measure the horizontal force (drag). This can be used
for aerodynamics studies of airplane and airfoil models, as well as ground vehicles such as trucks
and cars. If desired, a third load cell can be added to enable measurements of the pitching
moment. A linear actuator is used to change the angle of attack of plane and airfoil models. The
actuator is mounted inside the force balance apparatus, using a parallel four-bar linkage so that
the angle of attack is linearly related to the actuator position. The linear actuator can be
controlled by a computer, and the lift, drag, and angle of attack data recorded on the same
computer. This design is simple and easy to fabricate, can be added to an old wind tunnel in need
of an upgrade or replacement or included as part of a new wind tunnel built from scratch.
Complete details of the design including engineering drawings are included in the paper. The
design is also low cost compared to commercial wind tunnel balances and gives sufficient
accuracy for educational and some research purposes. A counterweight is used to mechanically
zero the force readout. The new load balance has been tested and found accurate. It has sufficient
precision to perform a sting drag measurement as well. A quick-connect mechanism is used for
mounting and removing models.