Making a more efficient, aerodynamic soapbox gravity race car

[freebeard]

On something this size It would be fun to take your eggcrate form, wrap it with fiberglass cloth stapled down, inflate it with a shop vac, and spray resin onto it. Then squeegee resin out under Mylar plastic to get a smooth surface.

[freebeard]

On something this size it might be fun to make the eggcrate form, wrap it with fiberglass cloth stapled down, inflate it with a shopvac, and spray it with resin. Squeegee resin out under Mylar plastic to get a finish surface.

[bizzybody]

Something that will help is to get rid of the big sun visor on your helmet and add a full face shield. Lots of drag catching the wind in your open face hole and under the visor.

For more inspiration, Google Barrett Jackson gravity racers. In 2007 Barrett Jackson auctioned sixteen or seventeen gravity racers made by Aston Martin, Bentley, BMW, General Motors, Nissan, Chrysler, Volkswagen, Audi, Mazda, Porsche and Pininfarina and others. (I searched for a full gallery but every article I found had at most one picture of one of them.)

This may be one of them. http://twwhlspls.com/wp-content/uplo...gravity_04.jpg I wonder if stiletto heels on the driver would be more aerodynamic?

[coverturtle]

Just a few thoughts for orengomotors:

The 170kg car will accelerate just as fast as the 70kg car, so I'm glad you are considering additional weights.

Inertial advantage should be kept in the design. The overall weight of the car does not matter so much as the distribution of the weight. Set the center of gravity as far to the rear as can be safe and if the rules allow, make your extra weights (and driver body mass!) movable from raised to lower to ground level over the course of the race. For toy racers, this strategy is very effective but since the altitude change for your courses is so great, the overall effect may be mimimal.

The spinning weight of the wheels, of course, should be kept to a minimum.

With most of the weight at the rear, the rear wheels should have the greater air pressure and front wheels should have just enough air pressure to minimize tire flexing friction and the minimum weight distribution to maintain safe steering. Check weight distributions with the driver seated with helmet, etc.

Are wheel covers necessary if the wheels are enclosed within the body? If not, reduce rotational inertia.

I noticed that the red racer you posted had the driver sitting up at the rear of the car, which put the most mass at the rear.

Very good aerodynamic coaching from aerohead, freebeard and others! Please let us see some photos of the final racer.

[Frank]

You do want to keep the center-of-gravity ahead of the center-of-pressure though. Not as important at low speeds but at 80-90 km/h it may be significant.

[ChazInMT]

Originally Posted by Frank

You do want to keep the center-of-gravity ahead of the center-of-pressure though. Not as important at low speeds but at 80-90 km/h it may be significant.

So this is rocket science?

[orengomotors]

Originally Posted by renault_megane_dci

The part from your shoulders should be that little smaller than your helmet and shoulders in order to only fill the wake.

The next step would be to try and lower your position as much as possible.

Also if you could reduce rear track in order to have the wheels covered that would help aero but it probably is a compromise with handling.
I suggest more distance between front and rear.
Are there tight turns in your races ?
If not, a longer wheel-base should not be an issue.

my suspension has an adjustable wheel-base, so i can change it with no modifications if i need it. but why do you want to do this?

[orengomotors]

Originally Posted by aerohead

Are you going to make a male mold (plug) ?,then make a female mold from it ,and then layup your shell in the mold?
If so,once your body bulkheads are established,heavy wire can be used to span the gaps between bulkheads,onto which expanded metal lath can be attached.Then a cement based molding plaster can be applied onto the lath and built up and smoothed to create your plug.
After the plaster is cured it can be sealed with shellac,coated with polyvinyl alcohol mold release agent,and three coats of carnauba wax,before a plaster splash (mold) is created over the plug.
The splash is tooling epoxy followed by birdnests of plaster-soaked hemp fiber built up about 25mm thickness to create the female mold from which you'll make your shell.

yes! exactly.
good idea, i will follow your advice

[freebeard]

How many pieces would you make for the female mold?

The Myers Max was often compared to a bathtub because the body was a single tub with a filler piece for the hood. Here's the evolution, from Old Red to the new Kickout SS.



The most successful fiberglass body ever. (maybe Corvette excepted)

What a fun project though you can do anything in fiberglass. The Fiat_Turbina for instance, or the Volhart-Sagitta scaled to 2/3-3/4 with the wheel/cabin proportion altered. A single-seater Shranx with little 4" headlights.

[renault_megane_dci]

Originally Posted by orengomotors

my suspension has an adjustable wheel-base, so i can change it with no modifications if i need it. but why do you want to do this?

Efficient aero shape asks for the rear to be narrower than the front.

If the rear wheels are enclosed in the body leaving only a flat panel, it's even better.

But still, if there is handling performance required, you don't want your vehicle to have a triangular shape wheel base.
I might be wrong but I feel if you have a narrower rear track, some handling performance can be found back with a longer wheel base.

What's the good angle for the sides, 20° ?