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Old 02-25-2011, 09:04 AM   #135 (permalink)
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Originally Posted by NeilBlanchard View Post
Hmmm, I missed that part of the discussion, I guess. It is odd to think that the air is "bumped" out of the way and has a spring affect? One would think that a given volume moves out of the way a given distance, and then moves back.

There must be a repelling force between the molecules in the air that is acting as a spring. So, it is not just the static volume of air that gets displaced, but rather the speed and shape of the front that has a lot to do with it.

So, then the shape of the front does have an indirect affect on drag -- blunt front ends "punch" the air harder, and may *improve* the air flow on the trailing side, by creating higher pressure? But at high(er) speeds, this leading pressure wave becomes critical, and the front must be pointy to split the air, rather than "punch" it?
Neil, I was satisfied about the relative less importance of front shape when I started hauling a (small) motorcycle across the front of my truck. My Scamp 19' fifth wheel camper is not ideal aero-wise but it has generous radius and is slightly tapered and therefore does better wake management than square boxy trailers as evidence by MPG numbers from both camps. I was worrried MPGs would take a big "hit" with the bike on front but it didn't hurt bad at all as it turned out. I was pleasantly surprised and relieved as I found this setup the safest and most comforting way to haul the bike along with the trailer (which trumps fuel economy actually).

It's anecdotal but I don't think irrelevant field data.
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