James,
From the information I have read and been told by college professors, the
teardrop is one of the most efficient shapes known. If you think about how
it is formed.--Liquid water drawn by gravity assumes the teardrop shape on
it's own. The nose of the drop is rounded but somewhat blunt. Why? Because
it's fairly easy to push a rounded shape thru the air. The air see's no need
to shape it like a needle. The aft part of the raindrop is drawn back to a
point by the partial vacuum created by the air trying to rejoin itself
behind the rain drop. As they say, "It is easier to push something into the
air than to get it out of the air." You want the body to fill the void until
the air is comfortable rejoining itself without detaching from the cars
skin.
I don't want to start the 6 or 7 degree wrangle again, but all the current
books I have read and the NACA paper describing plotting NACA flush surface
inlets, refer to 7 degrees. That's what I go by.
Lift would be determined primarily by the side profile of the vehicle. You
do not want it to look like a wing from the side. Even though it's harder to
load and unload, do not sweep the back up the vehicle up behind the rear
tires. It creates a low pressure area there which picks up the inevitable
salt dust and turns it into a big rooster tail. That action requires
horsepower and slows you down. We absolutely proved that on our first liner.
Anything you use to influence the air to keep the car on the ground will
use horsepower and slow you down. (i.e., spoilers, horizontal wings, etc.)
The vertical fin to insure the stability of the car in a straight line is
the only compromise I will make. I put about 2" of rake in the car so I have
some positive pressure on the front of the car to keep the nose down.
I have come up with a slightly compliant front end for this year with
micro switches on the front axle and led's in the cockpit to see if I
develop any lift in the front end at speed.
One of my books says," with a given nose shape and a given tail shape,
adding additional length only increases skin friction drag".
Everything we do requires some compromises.
I believe in the "KISS" philosophy and it has worked for me. Keep the shape
of the car simple. This is not a beauty contest. Only Glen's clocks matter.
Everytime you FORCE the air to change direction, you use horsepower and slow
down. Once aerodynamic drag exceeds available traction, adding more power
will not make you go faster.
Flat bottom cars have a few supporters. If you remember Roger Lessman's
liner of ten or so years ago, it had a flat bottom with side skirts and no
rake to it. I have part of his car hanging in my workshop. I picked it up
from the dumpster after the car blew over backwards approaching 300 MPH.
They allow no option but flight if they pitch up for any reason and air gets
under them. Each year when I return from the salt, I take the belly pans off
my car, stand them up and take a picture of them so I can see what the salt
trails from the four wheels are doing under the car. Mine come straight back
from the tires until they dissipate.
I also believe that we have a responsibility to have enough ground
clearance to allow us to exit the course at any point and not block access
to the guys waiting in line. I'm old fashioned.
I have been rambling like crazy and I am pure amateur at this. Take my
words for what they are worth to you.
Howard Nafzger
/// unsubscribe/change address requests to majordomo@autox.team.net or try
/// http://www.team.net/mailman/listinfo
/// Archives at http://www.team.net/archive/land-speed
/// what is needed. It isn't that difficult, folks.
|