Download Figure 1: Pro E image of base mount; final design. ... parts: yellow = load cells; green=rotating piece An Affordable Testing Device

An Affordable Testing Device
To Measure Lift On Prototyped Airfoils
Figure 1: Pro E image of base mount; final design. Key
parts: yellow = load cells; green=rotating piece
Figure 2: Final Device: airfoil is on top. Load cells are center
with cable come out of them
Rebecca Baker
Summary:
This project addresses the need for an affordable testing device to test the lift
properties of prototyped airfoils on a small scale. Currently, labs that own wind tunnels,
especially large wind tunnels, rent out the use of the wind tunnels for tests. This can be
too expensive for those whose projects are small and on a tight budget. A cheaper way to
test simple airfoils accurately and efficiently is needed. The wind tunnels being
addressed in this project are small, with a cross section of approximately 21in by 20in.
The principle requirements are low cost, measure lift and drag, hold the airfoil
steady, reusable, and fits into the wind tunnel. The most important requirement was to
measure lift and drag on the airfoil. The final products must be able to give a readout that
can be converted into the forces of lift and drag on the airfoil. Another important
requirement was to be able to reuse the device for a different airfoil or shape. These
requirements guided the design process.
Multiple concepts were drafted using the above requirements. This first aspect
considered was the manner in which the airfoil would be held. The two main options
were holding the airfoil from the bottom or holding it from the sides. Three concept
designs were generated for both of these options. The major component that ended up
driving the final design was the manner in which the forces were measured. In the
concept design phase several options were looked at using strain gages, while the final
design needed to incorporate two load cells, which were decided upon based on
availability.
The final design has one strut coming up from a base plate to attach to the airfoil.
Within the strut the load cells are arranged in order to contain the vertical and horizontal
forces in one load cell for each of the forces. The airfoil was created in ProE using data
points for a NACA 23015 sized airfoil. This size was chosen because it is a common
lower speed airfoil, and values for the lift and drag coefficients are readily available.
Also the final design allows the angle of attack to be adjusted from -15o to 25o. This will
make the device more useful for different tests. The physical part was created in the 3D
prototyping machine, and attached to the mounting part of the device with a bolt. Finally
the whole device was secured to the bottom of the testing section using bolts going
through slots in the bottom. This kept the whole device securely fastened and kept it
from moving in the wind tunnel.
Final testing showed that the device does give a voltage readout for lift on the
airfoil. This voltage readout can be converted into force pounds using the calibration
number on the load cell. The expected forces were higher than the results of the tests,
which could be contributed to several factors including the downwash forces created by
the air movement around the ends of the airfoil. The lift did increase as the angle of
attack increased as expected. The drag forces were too small to measure straight from the
load cell output, and an amplifier might allow the drag force to be measured. Overall the
device gave a voltage output that can be converted into a lift force. It can be moved into
and out of the wind tunnel. The device is completely reusable. The airfoil can be
detached to accommodate a different shape. The final product meets the major design
requirements.