kileyay wrote:
I think you're really going to be disappointed by the final product, even if I release all the 'raw' data I have available -- that which was given to me on a thumb drive from A2. Maybe I can get more, which I have asked for, without success thus far, but I think you are possible the only person who is going to be upset by what I put out -- at least, the only person this upset. Here's the data in the rawest form I have for the baseline run. I'm sorry you're so outraged. FFS man...give me a break. The intent is not to obfuscate -- it's to make it accessible to people who don't have your quantitative sophistication...which is to say, almost everyone. Talk about out of touch.
I'm happy to take your suggestions, input, and help. But not if you're going to be borderline abusive.
I finally had some time to look into this.
First, the data seems to be corrected for beta-square. I stand corrected.
The reported data is packaged weirdly. I
assume the measured data sits in the 'RAW' and 'Q' columns.
Other observations: RAW grams is scaled with dynamic pressure 'Q' (pounds/square-feet) and translated to square-feet-CxA in wind coordinates. The CxA values are then transformed to bike/body coordinates using the YAW angle. Finally the CdA in m^2 and drag&watts at 24mph is calculated.
Rant: full grown engineers chose grams, feet, inches, miles and water head as "units". FFS. I
assume the YAW data is entered, not measured. Would be nice to know more about how the YAW of the wind vs the body is dealt with. As I see it, there are eight (8!) sources of errors here: wind flow vs tunnel geometry vs load cell vs platform rotation vs rotation measurement vs wheel struts vs wheel hubs vs fork/frame vs rider position. Yikes!
Five of those eight are 'static' and can (should!) be under control by the tunnel operator. But the wheel hubs, frame and rider position are all individual to the test specimen and affected by the test procedure.
Basically, I'm positive that the wheels, fork/frame and rider are NOT perfectly aligned with the wind flow at the indicated YAW=0deg. Question is how to 'tare' the YAW after every change. We're taking millimeters here that generate significant 'noise' in YAW.
My suggestion to deal with the varying-between-runs CdA-vs-YAW phenomenon is to make use of the measured YAW "torque" and adjust the YAW 'tare' to get a neutral left-right curve. Clear, huh?
There is a Raw Side F and a RAW Side R and my guess is that the measured
total side force and YAW torque is dissolved in a front-wheel and a rear-wheel side force. If you (from the yaw sweep) find the YAW offset that produces left-right-symmetric 'torque-per-YAW', chances are that the between-runs CdA graphs will line up a lot better.
What say RChung et al?