Good question, I was just using the default CdA vs yaw values that BBS picks for you once you enter a 0 degree CdA value.
So just now I referred to the thread where Damon Rinard indicated how to correct for drag force at yaw as measured in the tunnel, and used data from the Zabriskie-dummy on a P4
If I am doing this right (damon can maybe check me?) then the cda reduction at yaw in my test cases was less pronounced than zabriskie on a p4. It seems like the adjustment is so small you can mostly ignore it, even.
edit: (the cda conversion there is just approximated using the 50g drag = .005 CdA rule of thumb)
Define how those CdA vs yaw numbers were derived... and also define how they are being used to determine drag force in modeling programs.
For instance, when they yaw the table 10deg they don't increase the tunnel speed to simulate a crosswind... they leave that the same. The apparent rider speed actually *drops* in that case. When you are riding on the road and you have a crosswind, the wind hitting your body is greater than when there is no wind.
So is the CdA value based on the tunnel speed and measured in-line drag force, or do they calculate the apparent rider speed and base it on that? I'm guessing they don't do any calculation, which is why the dropoff in CdA with yaw is so large.
I do believe that many people can experience a slight benefit from a pure crosswind, but it's a lot less than those tunnel numbers would indicate.
Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter
So just now I referred to the thread where Damon Rinard indicated how to correct for drag force at yaw as measured in the tunnel, and used data from the Zabriskie-dummy on a P4
If I am doing this right (damon can maybe check me?) then the cda reduction at yaw in my test cases was less pronounced than zabriskie on a p4. It seems like the adjustment is so small you can mostly ignore it, even.
edit: (the cda conversion there is just approximated using the 50g drag = .005 CdA rule of thumb)
rruff wrote:
As we know from various wind tunnel results, drag can be a good deal less at medium and high yaw than at zero yaw. Define how those CdA vs yaw numbers were derived... and also define how they are being used to determine drag force in modeling programs.
For instance, when they yaw the table 10deg they don't increase the tunnel speed to simulate a crosswind... they leave that the same. The apparent rider speed actually *drops* in that case. When you are riding on the road and you have a crosswind, the wind hitting your body is greater than when there is no wind.
So is the CdA value based on the tunnel speed and measured in-line drag force, or do they calculate the apparent rider speed and base it on that? I'm guessing they don't do any calculation, which is why the dropoff in CdA with yaw is so large.
I do believe that many people can experience a slight benefit from a pure crosswind, but it's a lot less than those tunnel numbers would indicate.
Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter