Quote:
Originally Posted by Christ
But this would screw with volumetric efficiency, since the engine would have to work harder to draw in the air it needs. So you're still trading efficiency.
Looking at this from both sides, I'm thinking that it's more like a novelty aero-experiment than something viable for right now.
Dave has openly stated that the gains are there to be had, and said that an aero shape was not a valid opponent to this "design"... yet just stated that the achieved Cd of the capsule, which can only be achieved with help, is still higher than the airfoil.
By the way guys, the vacuum needs to occur in the concave area for this to work... that would mean there would have to be a pressure vent somewhere else... like at the tip of the tail cone.
Saying that you're re-issuing drag to another area is a false statement.
The efficiency loss comes from the necessity to drive a vacuum pump to keep the boundary layer attached at the concave region. The idea that the flow slows down so dramatically to stay attached there is what causes the pressure to rise in that area compared to other areas.
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Yes its the efficiency being lost in the pumping, I don't think either of us disagree. What Wink and I are suggesting is that the pumping is going to be exactly equal to the amount of force you create.
Effectively what has to happen is some air(to be vacuumed close to the surface like this) has to be accelerated to the speed of the car. If I am going to pull it inside the car in
any way its at least got to be moving the same speed, otherwise its going to hit the bodywork and be driven off. Another way to do this same thing would be to have a spoiler out from the edge just a little and angled down not up. It will force the air along this curve but its going to come at huge drag costs.
Also I'm not so convinced its going to do it anyway, at least not as a high pressure area. I'm sticking with the rule of thumb that the inverse(air traveling
inside pipe with the exact specifications and air being vacuumed out instead of in) generates high pressure and this can only generate low pressure.
well. . .I take that back. If. . .IF the pump is pulling harder than the relative motion of the object and fluid it would become a high pressure spot. . . but then its like your pulling the car backwards in the form of the suction you are creating not to mention the enormous losses you are suffering to MAKING that suction.