Wind Tunnel Tests

The Tests

The wind tunnel tests were conducted in the subsonic wind tunnel at the facilities of the Council for Scientific and Industrial Research (CSIR), in Pretoria, South Africa during April and May of 2005. Think of the CSIR as a sort of South African mini NASA. The CSIR wind tunnel personnel were very enthusiastic about the testing program and very professional in their approach.

The test model was in the tunnel for approximately two weeks accompanied by Flight Sciences folks. All testing was accomplished at a tunnel speed of 120 meters per second (approximately 230 knots) except for a series of runs at progressively lower speeds accomplished in order to estimate the effects of Reynolds Number on the test data. Following the usual tunnel calibration runs, lift, drag, side-force, pitching moment, yawing moment and rolling moment data were obtained. These parameters were measured through a large range of angles of attack and angles of yaw. Measurements were made for two different canard configurations, at various flap settings and at various elevator settings. In addition, the flow over the model was visualized using tufts and a sublimating material.

The Significant Results

As with all testing, some results were very good and some results were not so good. That’s why you’ve got to test. In our case, at least five useful, significant results were obtained as a result of the wind tunnel tests.

Very Good Results

1. The very low drag characteristics of Phoenix were confirmed.

2. Very good correlation was obtained between the wind tunnel results and the analytical results which we had accomplished prior to the tests (important result for subsequent fixes).

Not So Good Results

1. The aircraft lift curve slope was shown to be lower than predicted with stall occurring at a lower angle of attack than predicted.

2. At the Aft Center of Gravity location, static longitudinal (pitching) stability was shown to be weaker than desired.  

3. Directional stability was shown to be acceptable up to a sideslip angle of 10 degrees but too weak from 10 degrees to 15 degrees.

Aerodynamic Fixes

As a result of the wind tunnel tests the following modifications were made to the tested design in order to correct the undesirable results:

1. The airfoils used on the wing and canard were changed.  

2. The location of the wing on the fuselage was modified slightly.

3. The location of the canard on the fuselage was modified and the canard size was increased.

4. The airfoils used on the vertical tails and ventral fins were changed to slightly thicker sections with a larger leading edge radius.

GALLERY (Click to enlarge)

Figure 1 - Getting Ready	Figure 2 - Mike and Brad Working	Figure 3 - The Tunnel
Figure 4 - Testing	Figure 5 - Testing	Figure 6 - Testing
Figure 7 - Tufts	Figure 8 - Flow Visualization	Figure 9 - Waiting for Results