The First Few days of the 40- by 80-Foot Wind Tunnel Calibration

by Stephen Jaeger

Monday Morning, June 1st, 1998

 Today is the first day of our wind-off calibration for the new 40- by 80-Foot Wind Tunnel Test Section. For the last two years, NASA has spent $25 million to renovate the test section. They peeled away the shell of the wind tunnel and lined it with four feet of sound-absorbing fiberglass wedges. Then they covered the fiberglass with a floor made of metal sheets with small holes to allow the sound to pass through into the fiberglass. This week we are going to bounce sound waves off the floor of the tunnel. We can measure the resulting echo and determine how well the lining absorbs sound.

7:40 AM: I arrive at work, make coffee and read my E-mail. I respond to some messages regarding the AIAA (American Institute of Aeronautics and Astronautics.) I am the local newsletter editor. We are trying to coordinate advertising for an upcoming public meeting on the International Space Station.

8:30 AM: I talk to Ron and Mike, the wind tunnel mechanics about lifting in the JLG. The JLG, or cherry picker, is a vehicle with a basket on the end of a boom. An operator can lift themselves up to 45 feet. Since the wind tunnel is 40 feet high inside, we need the JLG to reach up to the ceiling panels so that we can test them. Like the mechanics, Julie and I are certified to run the JLG. Mike said they could lift it in as soon as they find planks to cover the floor.

9:00 AM: I crawl through the balance house below the test section with Julie to look for instrumentation power. We need clean instrumentation power to run our acquisition system. Sometimes, using power right out of the wall can affect our results. I also sent off a quick E-mail to the group to remind them to be careful in the test section. The test section floor is very fragile. Moving heavy equipment and dropping tools on the floor can damage it very easily.

10:00 AM: While waiting for the mechanics, I take some time out to work on my performance evaluation for the past year. My company computes my yearly raise based on my work performance.

10:30 AM: I return to the test section to see what's going on.

11:30 AM: I consult with a student, Jessica about putting fiberglass foam in the dodecahedron to deaden reflections. The dodecahedron is a 12 sided speaker box designed to produce the same noise in every direction. Jessica rotated the box on a turntable with noise fed through the speakers and measured the change in the sound as it rotated past the microphone. Jessica is helping us out by calibrating the speakers we will use for the calibration.

12:30 PM: I went for a run and lifted weights. I ate a salad for lunch.

1:30 PM: Paul, Jessica and I go over the dodecahedron calibration data.

2:30 PM: I showed Julie how to use an end mill to cut a slot in a bracket she needs to mount some power supplies. The end mill is like a drill except the bit can cut slots instead of holes. I review Paul's data log.

3:00 PM: I found the instrument power outlets and I ran an extension cord to it. Then Ron and Mike lift in the JLG.

4:00 PM: I work on some miscellaneous errands.

4:30 PM: Paul and Julie come by to discuss the status of the test so far. I venture up to the test section to check on the progress and to see if there is something more interesting to do than just sit at my computer.

4:45 PM: Tested JLG in test section. Found hard hats. Discussed progress with Paul. Wrote list of things to do for tomorrow. E-mailed list of things to do for mechanics.

6:00 PM: Worked on performance evaluation and went home.

Tuesday Morning, June 2nd, 1998

8:00 AM: Made coffee and read E-mail.

8:45 AM: Went up to the test section to see what kind of trouble I could get into. The mechanics were lifting in the Arc.

9:00 AM: Julie and I went looking for harnesses for the JLG.

9:30 AM: Paul and I positioned the Arc over the first floor panel called F1. I began the laborious process of making fiberglass and cloth pillows to wrap around the Arc to reduce possible reflections.

10:30 AM: I tried starting the JLG but I ran the battery down. (Whoops.) Mike started recharging the battery.

11:30 AM: Went to lunch for Chinese food with friends from the branch. Went to vote. I have voted in almost every election since I was 18.

1:00 PM: Did some paperwork.

1:30 PM: I successfully started the JLG and maneuvered it around the test section and up to the ceiling to make sure I can reach all of the panels that we want to test. I try not to look down too much because it's a long drop. Rob, another engineer, has set up his device in the test section to test it. I think it will work very well.

2:00 PM: Julie has been having trouble with our test setup. The electrical power we are using appears to be interfering with our measurements. I located a portable transformer downstairs. It weighs about 180 pounds so I use a hand truck to haul it up to the test section. It works a bit better but we found if we just crank the speaker louder.

3:30 PM: Paul and I position the Arc over the floor panel and Julie begins taking some data.

5:00 PM: I do some paperwork.

8:00 PM: I found out my dad has gone to the hospital with a possible stroke, so I flew to Idaho for a week to help out. He's still in critical condition, but we're hopeful. Fortunately, I have good friends and co-workers who can cover for me during this busy time.

Tuesday Morning, June 9th, 1998

10:00 AM: After flying back from Idaho this morning, I turned on the computer and was greeted with 56 E-mail messages. Things back up when you're gone. No time to read them now.

10:30 AM: I boogie up to the test section. Julie and Paul have completed the "local" acoustic testing. I have been told the "Rob Rig" (or the calibration pole), Rob designed has worked very well, and I am glad I'll get a chance to see it work.

11:00 AM: I try out the Rob Rig on the JLG. It works very well.

2:00 PM: There is a mandate from the Federal government to document our activities for the national archives. Some time in the future, say in the year 2050, an historian may want to look back in the past and try to figure out what we we're doing here. To make their job easier, we make an effort to document our tests with notes, files and photographs. Therefore, I have called a photographer over to the test section to take photos of our equipment.

3:30 till midnight: The wind Tunnel Mechanic, Ron and I are the only ones left tonight. We spent most of the time moving equipment out of the test section and wrapping our microphone stands with fiberglass and cloth. We are getting ready to do pulse reflection measurements in the test section.

Wednesday Morning, June 10th, 1998

12:30 PM: I slept in. I was working till midnight last night so it seems fair.

1:00 PM - 6:00 PM: Ron, Paul, Chris and I ran microphone cables through the test section down to the control room for three microphones. The microphones are mounted 15 feet in the air on commercial microphone stands. They surround a 12-foot tower at the center of the test section. On the tower I have mounted a yachting cannon. The yachting cannon fires a 10-gauge shotgun blank. We want to record the blast of the cannon and the reflections off of the walls and ceilings.

Meanwhile, Julie has prepared software that we will use to "capture" or record the noise. Because the blast of the cannon is so fast, our instruments must be "triggered" by the sound itself so that we can record the signal.

7:00 PM: Well, no one seems to be here except Ron and I, so it seems like a good time to fire the cannon. We called NASA security first to make sure no one gets alarmed by the loud noise. I set up the analyzer to capture a cannon blast. I put on some earmuffs to protect my hearing and I discharge the cannon by pulling on a rope hanging down from the tower. The cannon immediately emits a large cloud of smoke and debris. The wind tunnel responds with a few echoes of its own from the test section out to the vane sets and beyond. I DO like this job.