Cd asked me to ask these questions at El Mirage last weekend during the SCTA land speed racing event. I had planned photos and questions, but then a camera problem, a minor car problem, and my daughter's limited patience with 100+ F temperatures limited my time in the pits. (She likes the place, and asked to come back to camp during cooler months.)
Quote:
Originally Posted by Cd
... why it is that everyone concentrates on the front of the car, versus the rear of the car ? ... Boat tails are as rare as the do-do bird. From what i have read, it may have something to do with the rules. can you please ask ? ... And just for the nerds like me, please ask if the car you are photographing has been tested for a Cd figure ? ...
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I'll report on two conversations that turned to aero. My best conversation was with the crew members of this car:
These guys are from a company in Arizona that sells tuning kits (Megasquirt). I was attracted to the car because it presented lots of "aero features" for a roadster such as the radius of the nose, the low side skirts, a diffuser, and a flat low spoiler:
We only got to speak about the rear spoiler. I had seen the car run earlier (when my camera was still busted) and had watched how the dust the car kicked up nonetheless remained low to the ground, not rising above the plane of the spoiler. He said he had seen video showing that too. But asked what the Cd was or if it had been tested, how they had determined the position and shape? He said they had not tested the design in a tunnel or anything. He had really just "sight-guessed." He said they were considering extending the side plates of the spoiler forward to the axle. He mentioned that the roadsters at the event all generate a huge wake, and that's totally true. It is amazing how many roadster teams do nothing with that area. One even seemed to be running with the rumble seat lid wide open in the wind. The wake on that one seemed colossal.
I missed my second chance to photograph the car racing when I was trying to mend part of my own airdam with a too-short strip of zip-tie. Grrr!
I spoke with another owner, later. This car was a late-model green Corvette outfitted for the race and no longer a street-legal vehicle. He and his wife and another woman seemed to be the whole team. The car pulled up to the observation area after a run and we struck up a conversation.
Importantly, the woman who had been driving reported that at top speed or thereabouts the car experienced a little shudder or something and she thought it might slide (if I understood correctly).
I asked about the front air dam, and he said he "I hope it helps" ... it was low down to about an inch off the ground and in the design/style of a Chevy Volt airdam (no photos my camera was busted). I asked about the rake and wondered if the low airdam might undermine the rake, and he said he thought both would help with drag. I wondered aloud if the airdam would undermine the rake's effect on lift. (Privately, I was wondering if lift might have been the source of his driver's experience of seeming loss of traction or something.) He didn't seem to know/agree that rake was for reducing lift. He thought it was to reduce drag by achieving a better angle along the rear window and trunk lid. I agreed it probably would. I am not sure of my thinking.
Is rake about reducing lift by creating a vacuum under the rear portions of the car? Is it drag reduction? Both?
My daughter lost her patience with the heat, so I cut my losses and split so as not to spoil her from another visit in cooler months. This is her third LSR event with me (Bonneville 9/2012 & El Mirage 11/2013). She likes the place. An EM meet-up in the cooler months, like November, would be awesome.
Anyway, the upshot of these two conversations (not a scientific sample, haha!) was that aero was not all that thoroughly researched, though clearly the teams are thinking about it.
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