GM Wind Tunnel and Brochure

Great shot of the fan nosecone.

One of the highlights of working at GM Design was the opportunity to work in the GM wind tunnel (General Motors Research Aerodynamic Laboratory). Photos just don’t do the shear scale of the place justice. It was completely incredible. On several occasions I was able to walk around the entire tunnel and I was always overwhelmed rounding the corner (slipping between the turning vanes located at the corners of the loop) and seeing the fan with its nose cone, the huge blades, and on the other side, its long, tapered nacelle.

The form transitions inside the tunnel at that scale and in an unforgiving material like concrete were totally amazing. Then there were the echos—it took all of the constraint I had not to create echos for my own amusement. The place had a unique smell. And a unique sound. It generated a deep rumbling sound like the the Star Trek Enterprise on impulse power. It was like science fiction or something.

As you approached the test area, the concrete rolled up very steeply. The test area with its bright metal surface plate was well lit, but the adjacent tunnels were not, so the test area faded quickly into darkness intensifying the mysterious effect. The control room had a launch control, military feel to it. Outside of the test area were stairs that led to the level above which was all open. Huge. There were glass windows in up there so you could look down on the model.

This shot is fairly representative of the feel of the tunnel.

Testing Sessions

There was a lot of waiting during testing. Engineers had a list of things they needed to test, and it took time to prepare the model and run the tests. Once the air was up to speed, they would go through different procedures to gather the data they were after. Sometimes the model would be angled into the wind and that took more time. Once the session was ended, it took time for the wind to die down enough that you could enter the test area to make changes. You were allowed to enter the test area before the wind completely stopped. The moving air felt more like a flow of water because, I suppose, it was incredibly uniform without any gusts that occur naturally.

A test session could easily last 30 minutes or more. When the engineers would complete their tests, they would set us loose to try things. There might be some things that studio management would want to try, but not always. A designer and modeler would make changes to the clay and the testing process would start over again. So you usually had an opportunity to try stuff to see what worked. The wind tunnel staff was very adamant about not having anything fly off the model and potentially damaging the blades. If something flew off, we’d have to go find it.

A couple of things I remember being told about the tunnel. The fans were made from laminated spruce with metal capped balsa tips. There wasn’t much space between the ends of the blades and the adjacent circular wall section, so a pieces of flying debris could easily damage the blades. The balsa tips were designed to be repaired more easily than the blades themselves. The blades were made from wood because of strength and durability. The test area was capable of 160 mph. It was necked down I think to 3:1 or 4:1 creating a venturi to speed up the air. The reason for this was to keep the air speed relatively low at the fan so the tip speed of the blades would remain sub-sonic. Cool.

There are four rotating pads that have two more rotating pads contained in them that attach to the story-high balance under the floor. Kind of reminds me of Ezekiel’s wheel within a wheel. This is to be able to accommodate different tracks and wheelbases. I never witnessed smoke being used during a test.

Bill Mitchell and aerodynamics

When the wind tunnel was first used, the first clay models to be tested were pretty far along in the design process. They were taken to the wind tunnel to see if there was anything to be done to knock off a few points of drag. Like rounding off a grill molding with an 1/8-inch radius—something that would decrease drag but would not show. There were cooling flow tests made on some models, so there was experimentation with air dams under the front valance. That sort of thing. But nothing radical. Before the GM wind tunnel opened in 1980, Bill Mitchell had made it very clear that cars were designed in the studios, not the wind tunnel. When he was shown a car (I think it was the Pininfarina Studio CNR*) that was aerodynamically designed to lower drag, he said, “Too bad aero had to go that way.” Meaning that was not any sort of look GM is going to have on its cars.

Designers are always looking for something new, however. The first experiences with the tunnel had limited effects on styling. But over time what was learned in the tunnel would start to influence styling trends for all-new car designs. So cars became more aerodynamic because the look became trendy, not so much because some feature was proven to work aerodynamically. What looked aerodynamic might actually create drag and lift. Like spoilers and ground effects treatments. You couldn’t assume something would work just because it looked like it should work.

As the benefits of testing became more appreciated, the tunnel models became more sophisticated. Instead of dragging the studio clay model to the tunnel, a second full-size clay model would be built specifically for testing. It might have a mocked-up suspension, drivetrain, and engine made from wood. A radiator equipped with potentiometers measured airflow, so grill designs could be tested to reduce airflow in the hopes of reducing drag (to the minimum that would still cool the engine). Usually testing revealed the opposite—insufficient flow. (In fact, there was less opportunity for air getting around a front-wheel-drive transverse engine then a longitudinally oriented rear wheel drive engine. That meant that airflow needed to be increased for cooling—the exact opposite of the trend to minimize or eliminate grills). Models sometimes had an interior of sorts that started at the belt line. It would have plexiglass windows and be lined with pillowed foam. A-pillar and outside rearview mirror designs could be tested for wind noise.

*Pininfarina Studio CNR—“Compasso d’Oro Award 1979 for this Ideal Aerodynamic Shape, outcome of a theoretical experimental research project promoted by the National Research Italian Council. The outstanding drag coefficient (CD=0,20) allowed to achieve a substantial reduction in fuel consumption.”

The turning vanes are visible in the background.

Motor service hatch, stairs, and man with lantern.

Wind Tunnel Stories

I remember going over to the wind tunnel to witness the tunnel testing of the 1983 Riviera Indy Pace Car. The convertible had the top down, four dummies in the car (I mean crash dummies, not idiots), and two yellow flags attached at an angle to the rear bumper. When they brought the air up to speed, that Riv was flying, the dummies were shaking, and the flags shredding. It was floating in the wind with just enough lift to make it a bad airplane, bound to earth only by the shear weight of the thing and the limits of its suspension travel. Didn’t look very stable to me. I was glad I didn’t have to ride in it at the track. If memory serves me correctly, I think they told me that it registered the highest drag of any car tested to date.

There was a story floating around that the Cadillac Bustle-back Seville had a very high drag coefficient when wind tunnel tested. Just for the heck of it they turned the car around backwards and it tested a lot better. However, the Seville came out before the GM tunnel was operational. George Camp doesn’t think the story is true, and Wayne Kady doesn’t remember the car being tested, unless Cadillac division tested it themselves. So it’s probably not a true story. Does make you wonder, though.

The 1983 Buick Riviera Pace Car. All four Buick Pace Cars are in the Alfred P. Sloan Museum.

Before the GM Wind Tunnel was constructed, scale models would be shipped to a tunnel in California (maybe CalTech, I don’t remember). The black dots are from ink put on the model and the trails trace airflow on the surface. Back in those days GM could afford Polaroid film.

Tech Center Architectural Weirdness

By the way, the Tech Center had several very interesting architectural oddities. There was a stairway to adjacent to Buick One Studio that went from the basement up to the second floor. I used to run up and down the stairway occasionally to get some exercise (and to get warm. I was perpetually cold in the studios in the winter). The stairway extended one flight of stairs above the second floor to a landing. There was a locked door there that wasn’t locked one day. On the other side of that door was a walkway that ran latterly down the length of the building lined by electrical conduit, HVAC ducting, and other mechanicals. You could see from one end of the building to the other and look down on the ceilings of the studios.

The weirdest place I was ever in was between the ceiling and the roof of the styling dome. On the north end of the building there was a door that accessed a flight of very steep, narrow stairs. I was at the dome to help set up a show or something and happened to walk to that end of the building. The door was open and I just sort of walked up the stairs. In the space between the ceiling and the roof was a series of metal walkways with metal stairs between them. Above your head was a concave roof, and below you was a convex ceiling. I don’t remember exactly how much space there was between them, but I think it might have been about eight feet. The walkways led to the apex of the ceiling where lights could be directed to light up models. In the movie The Rocketeer there is a scene towards the end of the movie where a struggle is taking place inside of the German airship. The structure of the airship is clearly seen with its catwalks and curved framework. Those scenes reminded me of what the area between the ceiling and roof of the styling dome looked like.

Lastly, the Tech Center buildings are interconnected with tunnels. Some are large enough to take a model through. For example, to get a model to the styling dome the model would be taken to the basement of the styling building using one of three freight elevators. Then it would be taken through a large tunnel that led to another freight elevator at the east end of the dome, and finally up to auditorium floor level. There was another fairly large tunnel to the east that connected to the basement of an engineering building. But there were smaller tunnels as well, perhaps about only eight feet wide. There was one that led north to the west of the main lake. It had a locked door. I wonder where that one went. Weird.

Wind Tunnel Brochure

The Gallery is comprised of pages from the Wind Tunnel brochure. The brochure is available in PDF format. Right click on this link to save the file to your hard drive.