Finishing some of the Test Objectives
By Mina Cappuccio
August 25, 1999
We finished up the variable camber leading and trailing edge flap study. We came up with the optimum settings for the inboard and outboard leading and trailing edge flaps.
The results were rather interesting. The Variable Camber flaps were supposed to yield better results than the plain flaps. We only ended up testing two variable camber outboard leading edge deflections. The first and highest deflection we tested ended up being the best one. When we tested the second flap, which was less deflection, it didn't give better performance so we didn't bother testing the rest. We built a bunch of leading edge flap deflections, but we only tested two.
On the inboard leading edge deflection flap study the variable camber flaps didn't work. They didn't produce a higher performance; the aerodynamic results were not better. We had to use the plain leading edge flaps on the inboard wing. We ended up using a combination of plain flaps on the inboard wing and variable camber on the outboard wing.
Then we tested the high mount canards. It took a shift and a half, twelve hours, to install them and get them working and ready to run. It didn't take long to install the canards, but it took a long time to calibrate them. We kept finding errors in the installation. The way the canard works is as follows: There is a motor that drives a ball screw, which moves and pivots the canards. This causes a signal to the LVDT, which stands for linear variable displacement translation. This instrument consists of a rod connected to the motor and the canard. When the rod moves it sends a voltage back to the computer, and that voltage reading gets translated by the data system to counts which is then converted to an angle.
This is actually a complex geometry problem. The angle for the high mount canard is a three-dimensional angle so we have to think about a corner of a box. To measure the angle, the designers made a mechanism to measure the height. There are tooling balls on the canards. There is a flat surface on the fuselage, which has a bracket on it at 90 degrees. Attached to the bracket is a height gauge measuring system. As you rotate the canard the tooling balls move to different places in space, and the gauge is calibrated to show a height measurement related to the canard angles. The computers translate all this to angles.
We ran on Saturday. We moved the canard to find out how the airplane trimmed. Every time we move the canard to a different angle our pitching moment changes. We were trying to find the optimum angle for the canard so that the pitching moment was zero or so that the airplane was trimmed. This means the nose isn't going up and it isn't going down, it's stable. When you take off, you have to make sure that your horizontal tails and your canards are at the right angle so that you don't flip over or so that the airplane is trim or the pitching moments are zero. We found the optimum angles for the canards.
When we were moving the canard angles, the limit switch inside the nose stopped the canard and got stuck and jammed. We had to adjust this. Then it worked fine. We also did some more oil flow runs.
Then we tested the sealed slat flaps. We tested these and came up with the optimum angles. It turned out that the sealed slates worked better than the plain and variable camber flaps. This was as expected. One of the reasons we tested the variable camber leading edge flaps was because we were hoping the variable camber leading edge flaps would give us good performance because they are easier to manufacture and to use on an airplane. The sealed slats are harder to manufacture and harder work mechanically on the airplane. They are costly.
We have to make trade-offs. In this case you have to trade off performance for cost. We try to make things faster, better, and cheaper. Usually you can't get all three. You can make things faster and better, or better and cheaper, or you can do faster and cheaper, but it's not better.
We have finished with the oil flows. We are now finished with two of the three objectives for the test. We can move onto meeting the third objective which is related to testing the mid- and high-mount canards. We are now testing the mid-mount canard.
Meanwhile, I am looking forward to starting a water aerobics class. I buy season tickets to the San Jose Sharks games. My preseason tickets arrived this past weekend. My bowling league starts up next week with a meeting and bowling the following week. This is how I release the tension of wind tunnel tests.