Vehicle Drag Vs Down Force

[examorph]

I am planning on designing/building a race car with the use of an aluminium frame and sheet metal to enter in a small contest, I am having trouble deciding how I should build the body, I read about aerodynamics and found that it is important to have a low Drag Coefficient so that there is very little air resistance but after I continued reading I found that formula one cars do the opposite there drag coefficient is the same as an average van but they have a lot of down force, so I got confused, should I be concentrating on drag or down force?

Just some extra information if needed: The race car weights very little, can be picked up with one hand. It is ran by a small electric motor and can reach speeds WELL OVER 50mph.

 

[thruthefence]

This detail proves the "No Free Lunch" axiom. It's called induced drag, you are using the excess horsepower of the car to force the moving air to do "work". In this case, stick the car down to the pavement so it can corner faster.

 

[examorph]

Done some more research on better sources than I used in the past and found that down force is only really important if going at very high speeds for example 100mph+, I also noticed that the drag coefficient is not as important unless you are going at high speeds also, this is what I have read online please correct me if I am wrong.

So now what has confused me is...what should my design be for the car? what am I aiming for (less drag)?

I am confused, please someone clear things up for me.

 

[MikeHalloran]

Before you go any farther, buy the rule book for the class in which you intend to race. That will guide you in the direction in which you need to go, and it will be much quicker than us guessing about what you are trying to do.


Mike Halloran
Pembroke Pines, FL, USA

 

[rb1957]

down force is important for cornering.

like above, understand the class of car you're racing. what are the class limits on design? what are the tracks like ? what do successfull cars look like ? analyze the tracks ... where will you get the most bang for your buck ? cornering or straight line speed ? i suspect the key to success is being able to (quickly) optimise your car for different tracks.

oh, and have a really good driver !

 

[KENAT]

Ditto RB1957, down force is to improve turning.

If you're familiar with the classic friction force equation you should be able to deduce why.

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[WildMTMan]

Before retiring I had built several cars, trucks and boats. Something I learned very early was the need for proper aerodynamics in every performance situation, whether high speed or low speed, there is always an advantage proper design. When I want to build a vehicle, I usually build a small scale replica, throw it in a wind tunnel.

A wind tunnel doesn't have to be expensive either. I've had very accurate modeling with a plastic tube or barrel with the ends cut off, a 24-36" fan, a kicthen scale, thread or yarn, some plastic wrap, and box tape. Most of its obvious, but the kitchen scale is place below the wind tunnel with a cut-out in the tube sitting on the platten, and the tape and plastic wrap, aused to seal the bottom and keep wind flow accurate and cinform whether you have rise or down-force...

Once you have the aerodynamics, then you work on the fine tuning of weight distribution. Determine you chassis dynamics, whether you need high polar moment like a road race car, or low polar moment like a drag racer.

Then more fine tuning on bearings, brakes, transmission working pressures, under-hood drag, etc to free up speed. Then you keep tuning till you've wrung every single ounce of speed at every tracks elevation and climates, and you have built a real racer...

 

[GregLocock]

For our solar car we built a 1/5 model, mounted it on a sheet of plywood, and fitted that to the top of a car. Lots of little manometer tubes gave us the pressure readings which worked surprisingly well.

Cheers

Greg Locock


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