Aerodynamic Performance of a Model Aircraft: The DC-6B

The DC-6B model set-up on the aerodynamic force balance is displayed below.

Figure 1. Mounted DC-6B model. A) DC-6B model inside low-speed wind tunnel test section with an external aerodynamic balance. B) DC-6B Model mounted on the balance by three articulated points. There is also a yaw angle control motor, pitch control motor and an electronic level to calibrate the pitch angle.

Figure 2. Low speed wind tunnel control panel. The pitch angle and the yaw angle can be electronically controlled from the panel during the tests with the wind tunnel running.

1. Calibration of set-up

1. Lock the external balance on the wind tunnel control panel.
2. Install the struts on the aerodynamic balance as illustrated in Figure 1. The struts are bolted to the balance.
3. Set the yaw angle to zero by adjusting the knob on the yaw motor, and set the pitch angle to zero using the pitch motor. The pitch angle should be calibrated using an electronic level. The measurements are first made at different angles with only the struts in place, and no model airplane. This enables the effects of the struts from the airplane to be subtracted.
4. Turn on the computer and external balance force acquisition system. It is necessary to turn on the system at least 30 min prior testing.
5. Open the measurement control software.
6. Record the room pressure and temperature. Make sure to correct the barometric pressure using the local temperature and local gravity.
7. Check if the test section and wind tunnel are free from debris and loosen parts, then close the test section doors.
8. Unlock the external balance and set the wind tunnel speed to zero.
9. Turn on the wind tunnel and wind tunnel cooling system.
10. Record the balance forces and moments.
11. Set the dynamic pressure to 7 inches H₂O, and record the balance forces and moments.
12. Use the yaw control to set the yaw angle to 5°. Adjust the dynamic pressure to 7 inches H₂O if necessary.
13. Record the balance forces and moments. Change yaw angle to 10°. Adjust the dynamic pressure to 7 inches H₂O if necessary.
14. Record the balance forces and moments.
15. Turn off the wind tunnel and lock the external balance.
16. Install the DC-6B model with the tail on.
17. Calibrate the angle of attack and pitch indicator. Calibrate the pitch angle prior to the test using an electronic level.
18. Unlock the external balance.
19. Set the angle of attack by pressing the nose up or down on the control panel Figure 2. Angles of attack for testing α = -6°, -4°, -2°, 0°, 2°, 4°, 6°, 8°, 10°.
20. Record the balance forces and moments.
21. Repeat steps 1.19 to 1.20, incrementally increasing the angle of attack until all the test points are complete.
22. Return the angle of attack, α, to zero and set yaw angle. Yaw angles for testing β = 0°, 5°, 10°.
23. Record the balance forces and moments.
24. Repeat steps 1.22 to 1.23 incrementally increasing the yaw angle until all the test points are complete.
25. Lock the external balance and remove the tail from the DC-6B model. Install the tail cone, and repeat steps 1.19 to 1.24.
26. When all data has been collected, turn off the wind tunnel cooling system, lock the external balance, and turn off the wind tunnel.

2. Testing at non-zero wind speeds

1. Check if the test section and wind tunnel are free from debris and loosen parts and then close the test section doors.
2. Set pitch angle to zero.
3. Unlock the external balance.
4. Set the wind tunnel speed dial to zero and turn on the wind tunnel and wind cooling system.
5. Record the balance forces and moments.
6. Set dynamic pressure to 7 inches H₂O.
7. Set angle of attack, starting with α = -6°. Angles of attack for testing α = -6°, -4°, -2°, 0°, 2°, 4°, 6°, 8°, 10°.
8. Adjust dynamic pressure to 7 inches H2O if necessary, and record the balance forces and moments.
9. Repeat steps 2.7 - 2.8 incrementally increasing the angle of attack until all the test points are executed.
10. Return the angle of attack to zero and set the yaw angle. The following yaw angles should be tested β = 0°, 5°, 10°.
11. Adjust dynamic pressure to 7 inches H2O if necessary, and record the balance forces and moments.
12. Repeat steps 2.10 - 2.11 incrementally increasing the yaw angle until all test points are executed.
13. Slowly decrease the airspeed to zero, then lock the external balance.
14. Remove the DC-6B model tail cone and install the complete tail.
15. Repeat steps 2.7 to 2.12.
16. When all data has been collected, turn off the wind tunnel cooling system, lock the external balance, and turn off the wind tunnel.