Quote:
Originally Posted by RobertSmalls
What do you make of my grille block, in terms of its contribution to Cd: Insight grille block
I will probably also block most of the are to the driver's side of the license plate, leaving <10inē of cooling air inlet low in the bumper, and ducted to the front wheel wells.
I see in the other thread you translated the above percentages into Cd figures:
Code:
zero------ Cd 0.488
10 %----- Cd 0.375
20 %----- Cd 0.299
30 %----- Cd 0.240
40 %----- Cd 0.194
50 %----- Cd 0.162
60 %----- Cd 0.135
70 %----- Cd 0.125
80 %----- Cd 0.118
90 %----- Cd 0.118
100 %---- Cd 0.115
It is interesting to compare your table to this one:
Specifically the half-sphere (approximating a 0% chop) and streamlined half-body (which has Cd=0.09 with zero ground clearance and no features).
Like the EV1 and the UFE-III, the Insight's rear glass doesn't exactly follow the template. I believe a 35-40% chop is a better approximation of the Insight's shape. That would place it around a Cd of 0.21, i.e. a 0.04 Cd reduction from aeromods other than the tail, and the potential for 0.10 Cd reduction from a complete boat-tail.
My tail extension will be cantilevered, not towed, and its underside will depart from that of the template to allow good clearance angles. This departure occupies 17% of the tail extension's area, in rear projection, which could not result in a drag penalty of more than 0.017 Cd.
It looks like I'm on track to build a car with a Cd of 0.13-0.15! I will be impressed if I achieve a figure in that range. |
Robert,if the grille block isn't cooking anything under the hood then I guess you're good to go.
Since the hybrids have expensive MOSFET and IGFET power transistors requiring cooling,I'm at a loss for recommendations with these advanced powertrains.
With respect to the drag reduction contribution from the block, crude logic might suggest that if you've cut airflow by 50%,then maybe that load has been halved.Just a SWAG.
Don Sherman got 0.4 mpg @ 70 mph with complete block to Pinto.2.0 mpg when airdam was added,then after cutting some block away for minimum cooling,gain came in at 1.4 mpg @ 70 mph.
With respect to the tail,I see no reason why you couldn't achieve your 0.13-0.15 numbers.