Postby Graham.Fountain » 05 Jan 2014 11:22
<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Despite the wedge shape (at least on the Coupe) you get huge amount of lift.<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
The air flowing over the car has further to travel than that underneath, so it's moving faster (relative to the car), and, according to Bernoulli, there is lower pressure above. Hence, as with an airfoil section, there will be lift even though the car has a wedge shape.
However, it's hard to explain how the front air dam creates a partial vacuum underneath, and thus reduces lift, by air speeds. This is partly why I prefer the Newtonian explanation, which, unlike the simple application of Bernoulli's law, explains how a wing gives lift when flying upside down.
The important question is, do you necessarily increase drag if you counter that aerodynamic lift by adding stuff to the bodywork?
Also, now that I'm more sober, I can give a better estimate for how much power to do 201 and 218 mph: If rolling resistance and aerodynamic drag were equal at 50 mph, which won't be exactly correct, but should be about right, then the power required at 109 mph would be (109/50) squared times the power needed to overcome rolling resistance at 50, plus (109/50) cubed times the power needed to overcome aerodynamic forces at 50 mph, which sum to, allowing for BLs inaccuracies, 105 hp:
POWER@50*(109/50)*(109/50) /2+ POWER@50*(109/50)*(109/50)*(109/50))/2 = POWER@109 = 105 hp.
POWER@50 = 105*2/((1+ (109/50))*(109/50)*(109/50) ) hp.
POWER@50 = 13.9 hp.
And:
POWER@201 = POWER@50*(201/50)*(201/50) /2+ POWER@50*(201/50)*(201/50)*(201/50)/2 hp.
POWER@201 =563.8 hp.
Which sounds more nearly like "well in excess of 500" than 658.4.
And:
POWER@218 = POWER@50*(218/50)*(218/50) /2+ POWER@50*(218/50)*(218/50)*(218/50)/2 hp.
POWER@218 = 707.9 hp.
So:
POWER@218/POWER@109 = 6.74.
That is, when allowing that the rolling losses are equal to aerodynamic ones at 50 mph, it really only takes 6.74 times as much power to go twice as fast as 109 mph, not 8 times as much. Still, 8 times wasn't that bad first approximation when having drink taken.
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