The Dynamic Airfoil Testing Apparatus

Student Team: Deep Singh, Gustavo Carvalho Grade Mancini, Karishma Chavda, Carter Bell, Anahita Yazdi Faculty Mentor: Professor Steven A. Velinsky, Jean-Jacques Chattot

Project Sponsor: Robert Edwards (Advanced Modeling Aeronautics Team Captain)

ACKNOWLEDGEMENTS

We would like to thank Professor Steven Velinksy, Professor Jean-Jacques Chattot, Professor Stephen Robinson, Professor Michael Hill, Professor Bruce White, Mitchell Olson, Scott Block, Rachael Larson, Robert Edwards, AMAT and Arm Control Team (ACT) for their knowledge and support throughout this project.

MATERIALS LIST PARTS

RESULTS

Department of Mechanical and Aerospace Engineering. College of Engineering. University of California, Davis

FINAL DESIGN - TEST STAND

Strain Gauge

Amplifying Circuit

Arduino A/D

Converter MATLAB Excel

The three graphs here represent Cd and CL data obtained while testing in the ABLWT. Data was collected using angles of attack between -5˚ and 15˚. Based on this data, the stall angle of attack was found to be between 9˚ and 12˚. This data is representative of the double element airfoil section (seen in Figure 5), which the AMAT team supplied.

INTRODUCTION

The UC Davis Advanced Modeling Aeronautics Team (AMAT) needed a dynamic

airfoil test apparatus to experimentally determine CL and CD, the coefficients of lift

and drag for their airfoil. There was no way for the team to experimentally confirm

their theoretical values prior to competition. This test apparatus is intended to be

an integral tool for AMAT to use for future airfoil designs. This project will also help

provide test data of the aerodynamic properties of a given airfoil, to supplement

AMAT’s design report. Our team designed and built a test stand to be used in the

Atmospheric Boundary-Layer Wind Tunnel (ABLWT).

DESIGN CRITERIA

The test stand must: • Measure the lift and drag forces on the airfoil. • Allow for a variable angle of attack. • Collect data while airflow passes over test section. • Be a modular test apparatus that can be used with a variety of airfoil sizes and

designs. • Be simple to use and easy to modify. • Minimize airflow disturbance due to test stand. • Remain within the given $400 budget.

FINAL DESIGN - DATA AQUISTION

Figure 1: A flow chart showing the data acquisition system.

Figure 2: The force experienced by the airfoil is measured as a voltage change in the strain gauges. This voltage difference is amplified by the circuit and converted

The Spar attachment is designed for maximum resolution in angle of attack variation. The slots cut in the PVC allow the hose clamps to secure set angles of attack through contact friction against the spar.

The Center Upright Member fits through a 6-inch diameter, preexisting, hole in the floor of the ABLWT. This member is bolted to the Upper Cross Member, which is free to rotate in Front Side Parallelogram Members. An inelastic cable connects the cantilever beam assembly to the bottom of the Center Upright Member. There are two connection points in this member which correspond to different stand angles, β (12˚ and 22˚).

Part Price Parts Price

Nuts/Bolts $22.24 PVC $4.99

Cable/Crimps $0.71 Hose Clamps $8.99

Bearings $73.12 Strain Gauges $29.20

Aluminum Flat bar $64.23 Op Amps $6.70

Aluminum Rod $11.11 Resistors $2.68

Aluminum Angle $39.89 Zener Diode *Donated

Steel Flat bar $6.20 Potentiometer *Donated

Particle Board $14.74 Arduino $49.95

TESTING

into a force in MATLAB. The force measurements are then exported to Excel and decoupled into lift and drag. Then they are used to calculate the corresponding coefficients. The zener diode was used as a safety measure protect Arduino from receiving more than the maximum of 5V.

The total price of materials was $334.75. The addition of tax and shipping costs still kept the total expense below the $400 limit. Aluminum flat bar was used for all parallelogram members as well as the Center Upright Member. Aluminum rod was used for the Upper and Lower Cross Members. The circular cross section of this rod minimized air flow disturbance as compared to a rectangular cross section. Steel was used instead of aluminum for the cantilever beam because it has a more favorable elastic properties. The Spar attachments were made from PVC because of its flexibility and durability. These are important properties for a component that is to be clamped repeatedly. All members were machined in the student Engineering and Fabrication Lab.

Figure 3.

Figure 4.

Figure 5.

Figure 3 shows group members Gustavo and Deep adjusting β between trials. The mount, during active testing, appears in Figure 4. Finally, Figure 5 displays the double element airfoil used during testing as well as the Top Parallelogram Members with the Spar Attachments.

The figure to the left illustrates the flow velocity and disturbances inside the tunnel. The orange points indicates laminar uniform flow (about 4-5 m/s at 1250 RPM or 157-196 inches per second) which is the ideal operating conditions of the ABLWT. The figure shows how the stand, without the airfoil, influences the flow inside the tunnel.