Actually it's more of a case of Horsepower vs. Traction (or downforce) vs.
Acceleration. For our example lets say you have 1000 hp, and your car weighs
3000 lbs. At 200 mph you find that for this particular vehicle, you have
some serious problems applying that power to the slippery salt surface.
There are 3 solutions to this problem.
1. Build a wing or spoiler that will generate downforce on the rear
of the vehicle to improve traction. The advantage is that the faster you go,
the more downforce you get, and the car remains light so it can accelerate
quickly. The tradeoff is that with this downforce, wind drag is also
generated. If you are using a spoiler (attached to the trunk), you are also
creating a larger pocket of turbulent air (vacuum) behind the car. The
bigger the pocket, the bigger the vacuum or wind drag on the vehicle. With a
wing these losses are less since turbulence is minimized.
2. Add more ballast to the car. The problem being that until your
engine gets into it's peak power range, the ballast is forcing your car to
accelerate at a slower pace. Although Bonneville is a long course, when you
are dealing with higher speeds, and chasing records, every mph counts, and
taking an extra 1/2 mile to get the heavier car up to speed translates into
1/2 mile of acceleration lost ( I'm assuming that the car is still
accelerating - very slowly- as it goes through the timing lights) and may
cost a mph or two. This is not really a consideration if the car tops itself
out at mile 3 and won't go any faster no matter how long you stay on it. The
advantage here is no increased wind drag.
3. Run tires that are wider than the conventional Land Speed Tires-
such as the 8.00x8.20x15 NASCAR Super Speedway tires. The problem is that
although you increase traction provided you already have enough weight, you
increase you rolling resistance, and as a result, slow the car.
So what's the solution? depends on the car, aerodynamics, weight,
horsepower, gearing and it's basically a trial and error session for each
vehicle. Each of these approaches have worked for different competitors, so
it's tough to say. For a guy like Al Teague, who's still picking up speed
through the back of mile 5, ballast is a bigger issue than a guy with a
small block that's wrung out at mile 2 and is just holding on to make it
through the traps.
Darrell Ferguson
BLACK RADON ENGINEERING
DARRELL FERGUSON
CELLULARONE
EAST BAY FIELD OPERATIONS
(415) 298-9000
(510) 703-6970
> -----Original Message-----
> From: John Beckett [SMTP:johnbeck@blueridge.cc.nc.us]
> Sent: Wednesday, June 09, 1999 12:43 PM
> To: Keith Turk; land-speed@autox.team.net
> Subject: Re: Horsepower and Wings
>
> I think that your on the right track with your thinking. The problem
> is at
> what point (speed) do you loose traction and spin out. And the surface
> that
> your running on is a big factor in that equation as well as the
> aerodynamic
> qualities of the vehicle your running.
>
> At what point is the traction worth more to you than the drag it
> creats?
> Another words your going to have to take it out to the salt and test for
> yourself. And be prepaired.
>
> JB
>
>
>
>
> At 01:26 PM 6/9/99 -0500, Keith Turk wrote:
> >I was talking with Darrell off line here a bit ago and a thought came to
> my
> >mind.....
> >
> >I am dead set against running a wing on my car if I can get away with
> it...
> >(based on stability at speed)
> >
> >anykind of aerodynamic tool which Produces downforce also produces
> drag...
> >and to move drag takes HP...
> >
> >I heard a comment here a couple of weeks ago about us having more HP then
> >the traction allows... is this the case out there for most of you?
> >
> >Keith Turk
> >Austin Healey 100, Bugeye, Box sprites, Bonneville Camaro ( Land Speed
> >Racer)
> >
>
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