Mike,
The following is based on my experience and observation at speeds up to
320 mph.
Above that -- I don't know anything.
Keith and Dave have the best answer. CFD works best during initial
design when you already
have, in the computer, the exact digital representation of the object.
As Dave said, if that isn't
perfect, it's worse than useless. The more complex the shape, the harder
it is to predict it's
behavior. That's why all stock bodied cars running over 200 mph make me
nervous.
With a Streamliner or Lakester I see it as a problem that can be worked
with. There are
forces trying to make the car pitch, roll and yaw when it's going in a
straight line. The
first thing to do is make absolutely sure that no mater what happens,
the car won't yaw.
The only thing I know that will accomplish this is a vertical fin. It
doesn't need to be
airfoil shape but it does need to be very, very strong. A flat plate has
the advantage
over an airfoil because when it's pushing laterally a lot of drag is
generated.
Ask Ed Tradup or Rick Yacoucci about vertical fins.
Tire stagger, of course, must be minimized even if you have an open
differential.
I have seen no evidence that roll is a problem when the car is going
straight.
You need to get some kind of information that will allow you to make a
judgment
about how much force, up or down, is being placed on the front wheels.
There are
many ways to do this but the only way that is as good as a load cell is
a load cell.
As I said, K & D have the very best answer.
The driver can be an good source of information. If the driver talks
about the car's stability
like Rick has or Howard, when he said he was glad it had a six speed
transmission
because it would be boring to drive otherwise, you should have a
acceptable setup.
If the car doesn't settle down feel stable to the driver above about 200
mph -- fix it.
As speed increases can change very, very quickly. Airflow around some
part of
the car can be 100% laminar at 303 mph and 99% turbulent at 313.
You're on the right track Mike. Keep asking questions,
Bryan
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