[Land-speed] Bloodhound

[John Burk]

Mayf
Found the ac by hanging a wooden model from various points and blew air at
it . As far as I know aerodynamic center and center of pressure are
synonymous . The wing drag adds to stability and reduces acceleration a lot
less . Equivalent tail ballast would have eliminated directional stability .
Unless lift is a problem ballast hurts by reducing acceleration while the
car is power limited . For high hp cars that are always traction limited
ballast helps by reduces aero drag as a % of thrust leaving more for
acceleration . LSR is drag racing , acceleration = speed . Front slip , I
think is like under steer in a corner , front lateral slip ends as soon as
the throttle closes , rear later slip doesn't . The nose touches when it
tips 5 deg and I'm not worried about it digging in but staying down could
have been a problem without the wings were added . Old Joe Devine finally
gave up on the 6 ft long nose panels and Joe Timney finished them . I agree
, I like aluminum . I over-optimistically entered this year but it'll be
finish for next year . Thanks for the questions .
John



> John, you say the true ac is 7 inches behind the cg. May I ask how you
> determined the ac?  Why did you choose to add drag to the rear of the car?
> Weight seems to be better in that acceleration of the car is not generally
> an issue. And if I think about the ring and pinion in the car then the
> pinion is always trying to ride up the ring gear and that causes down
> force all by itself.   With regards to the ac ( I am assuming that you are
> talking about the center of pressure), During a run with full traction to
> the wheels then control authority is vested in the friction forces
> steering the car. Aero forces play a small role unil the car looses
> traction and then the wind forces help it weather vane. IMHO,  and that is
> worth not much these days.  I am always concerned when the drive wheels
> are asked to do more than they generally do, especially on a front driver
> with high performance. The tire/surface interaction is being asked to
> provide forward drive traction as well as steering forces and the budget
> for each of these needs to be carefully determined.  One fo the items I
> was wondering about is what happens if the rear tips up a tad. How high
> does it have to go before the nose digs  in? That's a ride I wouldn't want
> to have, lol.  Some of the cars I see have virtually no clearance with the
> surface.  Just some odd thoughts from a quick look and most likely al have
> already been addressed. As I said, very innovative for sure and it will be
> interesting to see it run. When is the launch event? Oh, the coach work
> looks beautiful! Hand forming aluminum is an art and I know nothing about
> it except it looks great.  I can barely use a rattle can to paint with..
>
> Nice job on the car and the mechanical installations.
>
> mayf