would this suggest that the center of moment moves forward with
increasing air speed due to the flat nose of most roadsters? Therefore
you might want the greatest cross section at the rear to keep the center
of moment aft as speed increases?
Dave Dahlgren
Vaughn Rockney wrote:
>
> The way I learned this in Physics class is that for stability of flight, the
> center of gravity needs to be ahead of the center of moment, and the further
> it is, the more stable the flight. The center of moment is the point around
> which the object tends to rotate. Think of it at as the mounting point of a
> wind vane, where a sideways wind causes no movement of the vane. You can
> move the center of moment rearward by adding vertical fins to the rear of
> the car. You can move the center of gravity forward by adding weight to the
> front of the car. The most stable shape is an arrow. Heavy weight in the
> nose, fins on the tail. Try to shoot an arrow backwards, and it will always
> spin and fly with the tip forward.
> This physics flies directly in the face of common practice at Bonneville,
> where guys put a huge amount of weight in the rear of the car "to make it
> stable", so there must be more to it. Nonetheless I'm baffled when I see
> guys trying to cure spin with more weight in the back, but there are times
> when it seems to work. Perhaps with all the weight in the back, the
> improvement in traction causes the rear wheels become like rear fins in the
> salt, and at the same time, there is not enough weight back there to cause
> the center of gravity to be behind the center of moment. I do know some
> guys have it figured out and some haven't, and I'm one of the latter.
> ----- Original Message -----
> From: Keith Turk <kturk@ala.net>
> To: <land-speed@autox.team.net>
> Sent: Wednesday, June 16, 1999 8:23 AM
> Subject: Center of Pressure and Gravity
>
> > The Term Center of pressure refers to the Point at which all aerodynamic
> > forces take place on an airfoil... It Moves with changes in speed as there
> > is a change in aerodynamic Properties of air flow over the car....
> >
> > Someone started to talk about Center of Gravity and the two types of Roll
> > charatarisics.... Static and Dynamic...in relation to CG...
> >
> > Picture a standard Kitchen chair.. if you balance it on two legs so that
> it
> > stays upright... the center of Gravity is dead over the point at which it
> > is being Balanced.. if you tilt it fore or aft... it will fall over.. as a
> > result of the Center of Gravity being placed outside the point at which it
> > is balanced... this is called Static Rollover
> >
> > On a Car you have four wheels and a very Low CG to get the weight outside
> > of the point it is being balanced on is really tough to do.... Right up
> > till you consider the second kind of Rollover which is Dynamic... and it
> > has to do with the Rolling Moments being aided by the dynamics of weight
> > being shifted as the car spins.... Picture our chair again only this time
> > take the front Legs and place them closer to the floor and give it a
> > shove.. the weight is forward of the pivot point but the inertia of the
> > shove and stored energy in the mass will cause the chair to go over
> > backwards if pushed hard enough... that is dynamic Rollover..
> >
> > To relate this to a Car... think about the Long Slides Tom was talking
> > about and then think about what happens when a wheel digs into the salt...
> > causing the car to start to pivot about that Point.... Kinda like our back
> > chair legs... if the shove is hard enough the car will start to roll ....
> >
> > If your not confused enough let me know.. I can be really confusing....
> > Keith Turk
> > Austin Healey 100 / Bugeye / Box Sprite / Bonneville Land Speed Racer
> > Camaro ( D Gas Altered )
> >
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