

 From:
Cleophas Jackson/AA/USEPA/US
 To:
Byron Bunker/AA/USEPA/US@EPA
 Date:
07/05/2011 02:55 PM
 Subject:
Fw: Six Degree Yaw Information



Cleophas Jackson
U.S. EPA - OTAQ
Assistant Division Director
Compliance and Innovative Strategies Division
2000 Traverwood Drive
Ann Arbor, MI 48105
(734) 214-4824
(734) 214-4051 FAX
----- Forwarded by Cleophas Jackson/AA/USEPA/US on 07/05/2011 02:55 PM -----

 From:
"Rick Mihelic" <Rick.Mihelic@PACCAR.com>
 To:
Arvon Mitcham/AA/USEPA/US@EPA
 Cc:
Cleophas Jackson/AA/USEPA/US@EPA
 Date:
07/05/2011 02:30 PM
 Subject:
Six Degree Yaw Information



During our meeting 6/30, I committed to provide you with data on yaw averaging methodology in support of EMA's position that using a simple average of Cd's for +/- 6 degree yaw cases was sufficient to evaluate whether a modified vehicle was performing sufficiently better in yaw than the zero degree yaw case would indicate.    
 
The EPA requirement reviewed last week that yaw averaging would need to include data from -12 degrees to 12 degrees in 3 degree increments is extremely costly with respect to CFD analyses.  This request would drive each vehicle to need nine discrete CFD analyses to comply with the requirement, when three would suffice in EMA's recommendation (-6, 0 and +6).     Analysis run costs would be three times greater for conducting this volume of analyses for very limited improvement in data quality.     While the labor need to prepare cases and review results would increase as well although some of this might be automated.    
 
In terms of physical testing, I believe this +/-12 degree range is also challenging for major wind tunnels like NRC, ARC or UWAL, due to throat size and blockage issues, so the issue is not unique to CFD.
 
I referred to this information in my May and June visits to your facility and have added other detail.
 
If you have questions, please contact me.   
 
The data is proprietary and not for publication.  
 
 
Thank you for the opportunity to provide this.
 
Rick Mihelic
Manager Vehicle Performance & Engineering Analysis 
Peterbilt Motors Company
3200 Airport Road, Denton, Texas 76207
940-566-7694
rick.mihelic@paccar.com

**attachment included: **
 
 

