Aerodynamics acording to Myth Busters!

In article ,
"Bill Daniels" bildan@comcast-dot-net wrote:

You guys haven't mentioned the biggie - roof racks. Removing the cross bars
from my Grand Cherokee added 2MPG. Glider pilots look at roof racks and see
open air brakes. I can't believe the number of vehicles I see in Denver
with ski racks in July.

Then, of course, you can park the truck. I understand that trucks have very
low drag when parked.

If the vehicle has a MPG computer, you can see what speed does to MPG. At
65, my Jeep gets 19MPG. At 55, it gets 24MPG. At 45, it gets 36MPG. If
you do the numbers, saving two minutes by driving fast costs big time.
Those are REALLY expensive minutes - more than the rental on some airplanes.


Real world case; let's use your figures for simplicity's sake:

I want to drive from Vancouver to Kelowna. A little check with Google
Maps tells us that that's a distance of...

....393 kilometers, or about 245 miles.

At 65, that takes me about 3 hours, 45 minutes and I use about 13
gallons of gas.

At 55, it takes 4 hours, 30 minutes and I use about 10 gallons of gas.

Even at Canadian gas prices, those 10 litres of fuel cost me only about
$11.50. Is that really too much to pay to save 45 minutes of my precious
time? 25 cents a minute seem pretty cheap to me.




Bill Daniels


"Morgans" wrote in message
...

"Ernest Christley" wrote

I've seen SUV's with what looks like reverse scoops that could have to
catch the air passing over the top of the vehicle and blow it down the
back. Counterintuitive until you realize that attached flow offers less
drag.

That scoop helps drag, but more importantly, it prevents carbon monoxide
from entering in the back window when it is open and driving at highway
speeds.

When a chopped off SUV has the window open, that low pressure area in the
back gathers up the exhaust, and the swirling motion of the vortex allows
some to enter in though the open window. Not good. The scoop supplies
fresh air flowing down from the top, and keeps the bad air down lower than
the open window.

They have been doing that since the 60's, on old station wagons, before
they cared about mileage and aerodynamics.
--
Jim in NC

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling four feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect if you
sit in the bottom of that cupboard."