Wednesday, January 27, 2016

Visiting the ARC Wind Tunnel

Today was a fun day - the Auto Research Center (ARC) hosted their "Bike Fitter Appreciation Day" at their wind tunnel in Indianapolis.  Wind tunnel testing for cyclists is a relatively new adventure for them, and they had this event to help spread the word.  I am really grateful to have this opportunity, and it was a really cool experience.  A big "thank you" to Tim Jennings and the rest of the ARC crew for inviting us.  Being a cycling nerd and a motorsports dork, I totally geeked out.

Getting Brent's bike ready for his run.
The black table is specifically installed for cycling tests.
The event started at 8:00 AM.  I was the first one there and the only guest there for about an hour before another fitter showed up.  So, I had a lot of time to talk to the staff, hang out in the tunnel, and ask annoying questions about every detail of the tunnel.  They showed me how they configure and calibrate everything.  Another fitter, Brent Emery from Milwaukee, was scheduled for 9:00 AM.  After some time getting his bike set up, we got to watch him do a run.  Brent happens to have won a silver medal in the team pursuit in the 1984 Summer Olympics.

The wind tunnel is pretty cool.  It was originally designed for racing and automotive purposes.  When not configured for bikes, they can test 1/2 scale cars and 1/4 scale semis with a rolling floor.  For cycling, they go 30 mph, but for race cars, up to 118 mph.  It uses a 451 HP electric motor, and to quote one of the technicians, they're "responsible for most of the blackouts in the immediate area."

For cycling purposes, the wind tunnel is set up with the black table, as shown in the pictures.  The rolling floor is not used, and the tunnel is calibrated with the table in place, so that is basically "zero."  The table is equipped with 6-axis sensors to measure several parameters.  For cycling purposes, we're mostly concerned about the following terms:

Drag - The force opposite the motion of an object.  We tend to think of this as a bad thing, and a bike/rider's drag is expressed as CdA - the drag area.  We can also think of this as how many watts we need to go forward.  A big person will require more wattage than a small person to overcome their larger CdA.  The ARC wind tunnel is accurate to within .25 watts.  The main objective of wind tunnel time is to find ways to reduce our CdA so we can go faster with the same power output.

Yaw - The angle at which the wind hits the cyclist.  Zero degrees of yaw is wind coming straight on.  This is what you would experience riding on a completely windless day.  Most cyclists don't get perfectly windless conditions, and it is common to experience 15+ degrees of yaw at normal riding speeds.  The drag on a bike and rider will vary based on the yaw angle.  The ARC table can emulate up to 30 degrees of yaw.

The ARC table has two mounts that replace the skewers, and rollers to spin the tires.  They will typically spin the tires during a test, and usually discourage riders from pedaling because the body movement makes it difficult to get consistent measurements.

A peek inside the control room.
Tim also gave me a tour of most of rest of the ARC facility, although the doors to the 7-post shaker rig and their drivetrain dyno were closed, meaning something secret was going on in there.  I did get to see the inner workings of the tunnel itself including the motor, cooling for the actual floor of the tunnel (the downforce of race cars will create a lot of heat on the rolling belt and the supporting structure and instrumentation), and the stuff to control humidity.

I also got to see their rapid prototyping room.  They have three 3D printers, and they actually had a few interesting parts looking around, mostly parts used to mount a race car or semi model and control it in the tunnel.  The race car models are mounted to a device called a "sting", which hangs down from above the tunnel.  The sting includes instrumentation and motor controls to allow them to do stuff like emulate braking or turning to see how those changes in angles affect the aerodynamics - downforce, drag, etc.

This was really a great experience, and it's nice to have such a facility nearby.  Wind tunnel time is not cheap, but if it is something you are interested in, drop me a note at and we can see about doing a session.  In the meantime, you can learn more about ARC here:

Thank you again to Tim and the rest of the crew at ARC for a great learning experience!

1 comment:

  1. Nice meeting you there. Nice facility and a great crew.