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...............................................-- Rambling Thoughts on --

....................................................-- Land Speed Racing --...............

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The “Four Big Factors” (Aero Drag, HP, Weight (Center of Gravity/Center of Pressure), Gears):

Aero Drag, HP, Weight, and Gears (transmission & rear gearing) all have to be taken into
consideration to be successful on the salt. You don't have to take them into consideration, but
they will still be effecting your efforts to go fast. Let's take a look at them one by one.

Aero Drag (Drag Force):

First let me start with a quote from my friend Rex Schimmer that he made on landracing.com:

“At your cars maximum aero speed much more horse power is going to over come aero drag than
accelerate the car. Look at the cars that run in the 350+ area, they are accelerating maybe 20 mph
in the last mile, do the math how much HP does it take to accelerate a 4-5000 LB car 20 mph in a
mile as compared to how much HP does it take to over come the aero drag! Not even a contest.”

I think that statement sums it up nicely by pointing out that our main enemy in LSR is not weight,
which is the case in most motor sports, but it is “aero drag”.

Aero Drag, the drag force on a car, at a given speed is (Drag = A X Cd X V Squared / 410)
where A is the frontal area of the car, Cd is the coefficient of drag and V is the vehicle speed
(MPH) and is squared in the equation.

If you are running in a special construction class like streamliner or lakester you want to do
everything you can do to minimize the frontal area of your car. Think of the frontal area as not
being the front of the car necessarily, but a cross-section of the car at it's widest point looking at
the car from the front. In some classes like “competition coupe” you can chop the top to a point
and also look for the narrowest car you can find. In some of the classes you are stuck with just
looking for the smallest, as viewed from the front car you can find.

The next factor in the equation is Cd, coefficient of drag. In essence this is how “slippery” is the
car. Does the design of the car produce good aerodynamic flow of the air over the car with
minimum turbulence with the air staying attached to the car. If you have say a 1934 Ford Sedan
and a 1994 Ford Taurus with the same frontal area which one do you think would have the lower
Cd. OK we all get the point. Here are some typical drag coefficients I got from the March 2006
edition of HOT ROD:

Flat plate ............................................... 1.15
Indy car ................................................. 0.75
“Bad” production sedan ....................... 0.50
“Average” production sedan ................ 0.43
“Good” production sedan ..................... 0.35
Late ‘80s C4 Corvette .......................... 0.32
NASCAR Cup superspeedway car ...... 0.30
Perfect sphere ....................................... 0.15
LSR streamliner .................................... 0.11
Airfoil ...................................................... 0.05

Note: You can find the Cd for many cars on the site found ( HERE )

Looking at the Cd's above you can immediately see the advantage the streamliner has over our ‘34 Ford Sedan and again you can see that the class you decide to run in will either give you great freedom
in lowering the Cd (Special Construction) or will severely limit you in the effect you can have on the Cd (Production).

One really important point here to remember though is that the Area and the Cd are equal in this equation. Cutting the area in half will have the same effect as cutting the Cd in half. Pick a car
that gets you the smallest frontal area and the best Cd first and then work on both as much as the
rules will allow. Your favorite car might not be the best car to work with, so if you pick it you
will all ready be behind in the game of going fast.

My links page, found ( HERE ), will give you reference sources for aerodynamic related sites and books under the “Aerodynamics Related Sites” section. If you are building a streamliner or lakester these are must reads and they will help anyone else also to differing degrees.

In the equation we are using (Drag = A X Cd X V Squared / 410) we can see that since the velocity is squared then as the speed doubles the drag goes up by 4 times what it was. Another reason it is hard to go fast.

As we go along here I'm going to take these formulas and apply them to a car and see how that works out. Not to bore you, but because I'm familiar with it and have data on it I'll use Hooley's Stude as an example.

Using the above formula and guessing his frontal area is around 20.2 square feet and again guessing that the Stude has a Cd around .30 and using a speed of 220 MPH (he ran about 219 the first year) we get a Drag Force of 715. Now lets see what HP is required at that drag force and speed.

...........[ You can download a spread sheet for the above formula ( HERE ) ]

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