Tracking the Vortex
By Mina Cappuccio
September 3, 1999
We switched over to the mid-mount canard since my last journal. We ran with the mid-mount canard. We were mostly running stability and control data runs. That means we ran Alpha sweeps at a constant Side Slip angle for different canard angles and side slip angle sweeps at a constant alpha for different canard angles. This was done with different canard elevators. We tested with the vertical tail on and off and with the horizontal tail on and off. We did a bunch of rudder effectiveness runs where we had to change the rudder on the tail to different angles. This test was to check if the rudder was affected by a vortex caused by the mid-mount canard.
We finished running with the mid-mount canard on Friday, and we were hoping to start the smoke visualization, but the equipment wasn't ready. Saturday we did three or four more runs with the mid-mount canard, and then we switched over to the high-mount canard. We finished up some of our runs, and then we were ready to do the smoke visualization.
Meanwhile, Monday and Tuesday, the smoke Vis cameras and laser system was being fine tuned. On Tuesday, we finally did the laser smoke screen visualization. They turned on their system. We did a few test runs. We were able to trace the vortex, but it was hard to see because the lenses on the cameras lacked zoom capability. So we had to come down and replace the lenses. Then we had a lot of trouble with backscatter, or too much light. When you run the laser system you shut off all the lights, and we painted the model black so that we wouldn't get any reflection off the model. Having the cameras on the same side of the tunnel as the laser didn't work. Because of the angles of the cameras and the way the laser was pointing there was too much light scatter. You couldn't see anything but light. This required that the cameras be moved to the other side. They mounted the cameras high so that they would still look down on the side of the model that was painted black. That helped, but the fuselage was creating a shadow on part of the wing. Finally, we got it to work so that we could trace the vortices.
We saw two vortices that were coming off the leading edge of the wing and going underneath the surface of the wing at low angles of attack. When we pitched the model up to a higher angle of attack the vortices went over the wing. The third vortex we saw was the one that came off the canard tip. That was really hard to do. One problem was the angle of the camera relative to the laser beam, and the other problem was the white walls of the wind tunnel. There was so much reflection of the laser beam light off the white walls and into the camera.
The smoke is special, it has tiny molecules. What we really see is the core, or the void, of the vortex. When we looked at the television monitor where the camera signal is coming in, what we saw were these black dots. The black dots indicated the void of the vortex, and we had to use the zoom lenses on the cameras to find them. Sure enough those black dots were the void of the vortices. You could track it by moving the laser light sheet. You could see where the vortex started and how it progressed downstream. The vortices coming off the wings were beautiful, you could see very large holes, but the one that was coming off the canard had a very small hole. So we changed the lens on the camera to get more zoom capability and then we went back in and ran again. We traced it from the canard and traced it off the canard. You could see the void starting, and then you could follow it over the wing surface and by the vertical tail. This was the predicted result.
Then we were told that the last day of our test was next Friday. We thought we had reserved the tunnel until the middle of next week. We started getting nervous because the smoke visualization was taking time. Mike Elsey from Boeing was getting nervous because we needed to complete the force data runs. So we only got one flow visualization run in and that was it. That was disappointing.
Yesterday, we met with the managers to determine when the actual last day of the test would be. The argument was over the definition of occupancy. I took the total hours and divided it into shift weeks. They were using log hours. We compromised on Tuesday, September 14, 1999.
We have a few more runs on the high-mount canard, and then we'll have a few more runs with the mid-mount canard. We hope to wrap up with some TE flap studies on some of the optimized LE flaps tested at the beginning of the test.