Making a more efficient, aerodynamic soapbox gravity race car

[Xist]

Originally Posted by aerohead

You're gaining on it!
*Letting air go under the body is a no-no,so dropping the nose down to ground level would be a good move.Here's 'Kamm's' pumpkin seed body at top,notice how he did the nose
For the rear underside,for lowest drag,about a 2.5-degree up-slope angle has been found to be best.Here's Jaray's pumpkin seed of 1922.Really good pressure recovery (1st diffuser on Earth).

Orengo, are there any bumps on the track, or reason you would think you might need the 10° angle?

Aerohead, Ye Olde Template has the 2.5° angle, but you added 16.3° and 10.5° wheel fairings? Is there benefit to having it like that instead of:

[freebeard]

The 10° is from the ground, not the bottom of the vehicle. Why not both?

[orengomotors]

Originally Posted by renault_megane_dci

I love this thread so far !

Could you describe a typical race like how many bends and their variety so we could get a good idea of the compromise between speed and handling ( for instance a narrower rear track should help speed through aero at the expense of stability) ?

I am already thinking spring brakes to get energy back after the braking

hi!
well there are races with a lot of corners and others very straight.
last race:


spring brakes are a very goood idea!!

[orengomotors]

Orengo, are there any bumps on the track, or reason you would think you might need the 10° angle?

well it's only a recommendation, not a rule.
the 10º is from the bottom because it the departure angle, it's used to express the maximum ramp angle that the car can exit without scratching.

[aerohead]

Originally Posted by Xist

Orengo, are there any bumps on the track, or reason you would think you might need the 10° angle?

Aerohead, Ye Olde Template has the 2.5° angle, but you added 16.3° and 10.5° wheel fairings? Is there benefit to having it like that instead of:

The fairings respect Approach,Breakover,and Ramp, SAE practices for clearance standards for road clearance.
Nothing on the Template should ever experience a ground strike.

[aerohead]

Originally Posted by freebeard

The 10° is from the ground, not the bottom of the vehicle. Why not both?

It's just a convention that was adopted long ago to make things easy for designers.

[euromodder]

I wouldn't mess with wheel fairings or fenders - enclose everything instead.

Vehicle's too short to do proper fairings
You'd still have the suspension parts exposed or need large fairings to cover them
You'd get interference drag between the fairings and body
It's a lot of work to fabricate.

Use the width to make a good underbody design that shields the wheels as much as possible,
diffuser on the rear
streamlined fairing aft of the rider's helmet


Why do you use round-section (motorcycle style) tyres instead of flat/squared section tyres (car-like) - to cope with the camber ?

Seems like a lot of negative camber on the wheels - does it understeer with so little weight up front ?
Maybe more contact area on square-section front tires might do the same ?

Or you could further increase the negative camber further and use dual compound motorcycle / scooter tires with better gripping rubber on their sides
Sort of this

[nimblemotors]

That lay-down position is what you want. If the rules allow it you could lay down completely flat and use a camera to see where you are going.
Do the rules require four wheels?

Originally Posted by orengomotors

well, the actual gravity racer record is hold by an American guy:

https://youtu.be/Q1ndyA0UW2w
https://youtu.be/olF1WM7TMLM

the record is 84.4 mph!!

[orengomotors]

Originally Posted by euromodder

I wouldn't mess with wheel fairings or fenders - enclose everything instead.

Vehicle's too short to do proper fairings
You'd still have the suspension parts exposed or need large fairings to cover them
You'd get interference drag between the fairings and body
It's a lot of work to fabricate.

Use the width to make a good underbody design that shields the wheels as much as possible,
diffuser on the rear
streamlined fairing aft of the rider's helmet


Why do you use round-section (motorcycle style) tyres instead of flat/squared section tyres (car-like) - to cope with the camber ?

Seems like a lot of negative camber on the wheels - does it understeer with so little weight up front ?
Maybe more contact area on square-section front tires might do the same ?

Or you could further increase the negative camber further and use dual compound motorcycle / scooter tires with better gripping rubber on their sides
Sort of this

Hi,
Yes, doing wheel fairings has to be a massive amount of work. i had been trying to do fiberglass parts these days and it's not so easy as it seems.
Maybe i will do the fairings for the next seasson.
the suspension parts that are exposed, i was thinking to do something like this to cover the wishbones:
https://youtu.be/karr67ZYho4 what do you think? it seem to be a fast effective metod.

we use round section tires to have small amounts of rolling resistance, even with massive camber. yes, it understeers at low speeds, but having the center of gravity at the rear give us more potential energy at the top of the track.

this car of your foto is an awesome car! lots of engineering behind him, very interesting, if someone wants to read about it read the book equations of motion.
Another interesting article is this formula sae with the same concept:
http://www.zonagravedad.com/images/C...n_Dynamics.pdf

What do you think about doing a body shape like the one of this car?

[orengomotors]

Originally Posted by nimblemotors

That lay-down position is what you want. If the rules allow it you could lay down completely flat and use a camera to see where you are going.
Do the rules require four wheels?

hi,
I'm working on cleaning up the steering system, that now is blocking a 30cm space, that can be used to lay me down more.
Yes, there are 3 and 4 wheels categories.