wind tunnel bike data plotting

email hidden said:

In Chris Lieto's blog leading up to the Hawaii Ironman I saw his post
"My Ride"
http://lietokonadiaries.blogspot.com/2007/10/my-ride.html

Including an interesting chart from a wind tunnel:
http://bp2.blogger.com/_XYseXu0kC4k/RwpKEPnC54I/AAAAAAAAAEA/0YYOYm7qegI/s1600-h/yaw.006.jpg

My question is what's that plotted on the horizontal axis?

Dear AF,

The yaw is the angle at which the wind strikes the bike and rider
(rider-on), with 0 degrees being head on, followed by 5, 10, 15, and
20 degrees to the side.

The graph reveals how annoyingly tricky aerodynamics can be.

For the two upper bikes, drag rises as we expect because the
silhouettes of the bikes are getting larger as they turn sideways, so
there's more effective frontal area.

But the lower two bikes behave differently. Their wind drag actually
drops with a little side wind and ends up the same as head on as the
wind swings out to 20 degrees--something sneaky is going on with the
turbulence of the air flow around the wheels and frame.

Cheers,

Carl Fogel

Quoted message said:

In Chris Lieto's blog leading up to the Hawaii Ironman I saw his post
"My Ride"
http://lietokonadiaries.blogspot.com/2007/10/my-ride.html

Including an interesting chart from a wind tunnel:
http://bp2.blogger.com/_XYseXu0kC4k/RwpKEPnC54I/AAAAAAAAAEA/0YYOYm7qegI/s1600-h/yaw.006.jpg

My question is what's that plotted on the horizontal axis?

In Aerodynamics, the Yaw Angle is the angle between the direction of the
motion of an object and the wind direction. For example, if the rider
is facing directly into the wind, the Yaw Angle is zero.

HTH

RF

RF said:

Quoted message said:

In Chris Lieto's blog leading up to the Hawaii Ironman I saw his post
"My Ride"
http://lietokonadiaries.blogspot.com/2007/10/my-ride.html

Quoted message said:

Including an interesting chart from a wind tunnel:
http://bp2.blogger.com/_XYseXu0kC4k/RwpKEPnC54I/AAAAAAAAAEA/0YYOYm7qe...

Quoted message said:

My question is what's that plotted on the horizontal axis?

In Aerodynamics, the Yaw Angle is the angle between the direction of the
motion of an object and the wind direction. For example, if the rider
is facing directly into the wind, the Yaw Angle is zero.

HTH

RF

Thnaks Carl and RF.

How could the Scott Plasma TT bike (it *looks* really aero!) rank so
close to the 2006 Trek Madone road bike (doesn't really look that
aero)? Is the Madone that good? Is the Scott that bad? Do you feel
sorry for David Millar? ;-)

Plasma: http://www.scottusa.com/category/71/plasma
Madone: http://www.trekbikes.com/us/en/bikes/2006/archive/madone55

Quoted message said:

On Tue, 09 Oct 2007 16:57:57 -0700, "[email hidden]"

Quoted message said:

In Chris Lieto's blog leading up to the Hawaii Ironman I saw his post
"My Ride"
http://lietokonadiaries.blogspot.com/2007/10/my-ride.html

Quoted message said:

Including an interesting chart from a wind tunnel:
http://bp2.blogger.com/_XYseXu0kC4k/RwpKEPnC54I/AAAAAAAAAEA/0YYOYm7qe...

Quoted message said:

My question is what's that plotted on the horizontal axis?

Dear AF,

The yaw is the angle at which the wind strikes the bike and rider
(rider-on), with 0 degrees being head on, followed by 5, 10, 15, and
20 degrees to the side.

The graph reveals how annoyingly tricky aerodynamics can be.

For the two upper bikes, drag rises as we expect because the
silhouettes of the bikes are getting larger as they turn sideways, so
there's more effective frontal area.

But the lower two bikes behave differently. Their wind drag actually
drops with a little side wind and ends up the same as head on as the
wind swings out to 20 degrees--something sneaky is going on with the
turbulence of the air flow around the wheels and frame.

Cheers,

Carl Fogel

It has nothing to do with frontal area. Increasing yaw angle induces
flow separation and vortex shedding off of the downwind edges of the
rider/bike bits. It's the same phenomenon that causes an airplane to
stall out if the angle of attack is too high. Proper airfoil shaped
tubing can go to a higher yaw angle before shedding. The idea of
getting oblique airflow to generate forward thrust is hardly sneaky.
It's been making sailboats go for a couple thousand years now.