fan650

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.

 

Fan-distant650

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.

 

wind tunnel web

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.”

 

Fan-straight650

The turning vanes are visible in the background.

 


 

Fan-hatch650

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.

 

1983RivieraPaceCar650

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

 

SplitWindowAero650

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.

6 Comments
  1. Wayne Barratt

    That’s a great insite into the workings of the GM wind tunnel, Gary. I have been trying to find information about the wind tunnel at GM for over a year as I have been told by Jim Lutz that my ex. GM 1985 Chevrolet Cavalier Race Car actually spent some time in that very tunnel whilst the GM Performance Division tweaked the aerodynamic setup of that car.
    Wayne

  2. This was in response to an email I received about designs becoming more aerodynamic because of CAFE minimums.

    Cars got more aero because the look got trendy, not to meet CAFE numbers. Designers got an idea of what kinds of forms and intersections worked aerodynamically, so that influenced their designs. Perhaps the look could be justified because of drag reduction, but if what worked aerodynamically didn’t look good, it didn’t see the light of day. Believe me.

    Engineering fiefdoms might beat the CAFE drums but nobody at Styling cared unless it catered to their own interests.

    Spoilers, ground effects, and air dams look aerodynamic, but most probably create lift and drag. When I was there I never remember a car going back to the wind tunnel to see if a air dam was effective. Costs too much and takes too much time to do that.

    Design (styling, really) is not a scientific process. When I was there decisions were based on a formula, V=S x O. Validity equaled salary times opinion. Now decisions are based on costs, clinics, and fear. It seems nowadays when something innovative comes out of GM, where they seemed to let the young designers have their way, then the outcome is just plain goofy. Like the new Camaro. Looks to me like a 3D cartoon with too few polygons.

    They changed the name of the place from Styling Staff to GM Design Staff and then to GM Design Center. But it is still styling.

    Under Earl and Mitchell Styling ruled the corporation. GM Corporate put Rybicki in charge ahead of Jordan to keep Chuck from being VP so long. During Rybicki and Jordan, Design Staff started to lose its domineering influence. That might not be necessarily a bad thing, but then the bean counters and fortune tellers ran the place. They gave us the Aztec. Now the government owns GM.

  3. Dr. Richard M. Andres

    I am pleased to see the pictures of the GM tunnel. I did most of the design of the airpath, fan and counter rotation vanes, etc. while under the employ of Sverdrup & Parcel. I worked closely with Kent and Gino at GM. It was my first concrete tunnel and the heater/cooler was deemed necessary. Seeing the fan picture on the cover of Science Illustrated was great.

    Dr. Richard Andres

  4. Ron Will

    I remember one time when a model with a very sharp vertical grill design came back from the tunnel with very poor ratings (probably a Cadillac). The recomendations were to soften the radius for the top edges of the grill. Bill Mitchell reviewed the results and said, “I don’t know which direction the wind is going, but we’re not going that way.” That was the end of the recomendation.

  5. Ron Will

    During the mid 1970’s I was interested in building a 3 wheel car. The profile shape was akin to a wing. I was worried that at speed it would lift off the ground and try to fly. Corvette designer, Randy Wittine, did a lot of tunnel work at the time. He talked to the engineers who ran the tunnel and we figured out a way to get my model in the tunnel for testing. This was in the small tunnel at the North end of the Tech Center, before the new big south tunnel was built. Each GM tunnel project was budgeted a certain amount of tunnel time. They often did not use up the full project time. They said to keep my model handy for one of these times and they would slip my model in to use up the rest of the time. The engineers were also very interested in running a new shape in the tunnel other than the standard boxy sedan. They even built a special cross bar for the tunnel to hold my single rear wheel. I built a 3/8 scale model and kept it in an old Cadillac hearse at the Tech Center. In June of 1975 the word came. “Get your model over here fast. We can run your model.” It was great fun. We did ink drop tests and smoke tests with full instrumentation of Cd and lift. As it turns out, we put a small wing on the back and ducted the air for the radiators thru the bottom and out the back. This removed any danger of lift and thats the way we built the full size car. (Ron’s 3-Wheel Phantom will be the subject of a future post—Gary)

  6. Tom

    I have a GM Tech Center made and tested 3/8 clear plastic wind tunnel model of the 1986 corvette pace car convertible frame. It was vacumformed off of 3/8 scale wood models. Every section is just like the full size car. Up until the mid 80’s, there was a building on the south side of 12 mile, that was full of wood and clay 3/8 scale model cars from the 50’s to the 70’s.

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