Quote:
Originally Posted by cbergeron
I just don't think lowering the car makes it more fuel efficient. A vacuum is created beneath the vehicle which I think creates drag. Formula F1 race cars are low to the ground so they can turn at high speed because this vacuum keeps the car on the ground.
I know it's accepted in theory but that doesn't mean it's correct. I firmly believe that raising the car up with thinner wheels provides a better Cd (with a smooth underbelly that is).
I have a feeling it's part of the reason that the Aptera achieves higher than 200 MPG.
I'm not trying pick a fight, I'm just trying to get everyone thinking.  |
In a partial vacuum, there is by definition less air, which in turn means less air dragging on the car.
Interference drag, on the other hand, results when two bodies are too close to each other, such that the flow around one interferes with the flow around the other, with total drag being more than the sum of that from the respective parts. This phenom. became especially apparent with the development of the DC-3 transport plane in the 1930s. A streamlined fuselage had drag X, and a streamlined wing had drag Y, so arithmetically, X + Y should have meant total drag Z. Turned out, total drag was ~63% more than the sum of the individual fuse and wing. Wing fillets reduced the interference drag somewhat. Studies similarly showed that external stores (i.e., bombs) hanging off airplane wings should not be too close to the wing, but rather ~.4 diameter removed from it, to give the air sufficient space to flow past. HPV guys should take this into account, as many HPV streamliners may be running too close to the pavement.
Moral of the story: Lowering the car sandwiches dynamic air between it and the pavement. Could be, interference drag is at work when the gap is too small. Form drag happens when the gap is too large.
Look for the sweet spot.