Three Weeks to Go

December 29, 1997

Preparations for my Supersonic Transport Wind Tunnel Test are alive and well. You'd think things might slow down a bit with the holidays coming. No way!

We just found out that our internal balance doesn't work the way we thought it did! The internal balance fits inside the model and is held in place by struts that mount to the wind tunnel floor. This balance, in turn, holds on to the model and measures all of the forces acting on it, like Lift and Drag. By the way, these forces, like Lift and Drag, are what I will sometimes call "loads." This is a brand new balance that was built to handle the high loads this model will generate in our tunnel. It turns out that the electrical signals coming out of the balance are arranged differently than we thought, so we have to redo the wiring that takes the signals to the computer where they are recorded.

We also have to change the way the computer software interprets those signals once they arrive at the computer. Late-breaking changes like this always add a lot of excitement and stress to test preparations. We have electronics and software experts on our team that are going to work over parts of the holiday to fix this problem. We had planned to move our model and new balance next week into a special preparation area where we have plans to check out the health of the balance. Hopefully, our team will have the balance ready so we can stay on schedule!

That's not all! In my weekly telephone conferences with Boeing, Lockheed, and Langley Research Center, we all decided to add some stuff to this test. On a test like this, we usually want to get a picture of the airflow on the model. We do this with a number of methods which I'll introduce to you later. But this week we decided to add another method, called oil flow pictures, to this test, which means we added some more runs to our run schedule. Oil flow is where we put drops of colorful oil on the wing, run the tunnel, and then take a picture of where all the drops flowed to. We get really neat pictures which show us how the air goes around the model. But then we have to stop the tunnel and clean off the model before we can get the next picture. This is slow work and really has a big impact on the run schedule.

On another front, some members of the team wanted to add more instruments to our model. We already measure pressures and aerodynamic loads, but they wanted to add a device which actually measures the loads on just part of our model - in this case the wing tip. We would have to add special devices to the model, run wires to get the signal from them to the computer, and modify our software to interpret the signals. We decided ... No! Sometimes we have to decide we cannot accommodate something new this late in the game.

We also found out we were missing some accelerometers. These go in the model and measure the tilt angle of the model (called the angle of attack.) It seems everyone thought everyone else was going to provide these. So now we are scrambling to find some and install them in the model.

From the above stories, you can get the idea that preparing for a test like this takes a lot of communication, debate, and decision making. When a miscommunication happens (and they always do) the test team has to really work hard to make things work, like with the balance. The goal is to have good communications, and that's why we have so many meetings to talk about how things are going. Sometimes this is the hard part of testing, and sometimes the fun part!

This pictures shows me standing near some of the parts we are going to test on the wings. Most of these are the flaps that we will test on the front and back of the wings. Our run schedule includes testing lots of these to try to produce lots of Lift without having too much Drag.