Making a more efficient, aerodynamic soapbox gravity race car

[freebeard]

Originally Posted by OP

Yes, there are 3 and 4 wheels categories.

A reverse tricycle would be most conformant. An adjustable wheel-base is not the same as adjustable track. A rearward weight bias is at odds with a narrow rear track. For a solution look to the new Ford GT40, with [semi-]separate pontoons for the rear wheels. Or Luigi Colani:



Edit: It had been a while since I opened the 3D modeller, so I took a crack at this. It took about 2 1/2 hours.



FWIW, there are three primitive shapes—a superelliptic forebody, a 'conning tower' or wingtip shape for the driver position and an airfoil shape for the rear wheels. It would probably need open wheelwells based on the dimensional rules, and a lot of merging and filleting would be possible.

[orengomotors]

hi,
I have not yet had time to start with the body, I will wait for off season to make the body.
I've been working on other aspects, such as rolling resistance, I changed tires to a set of Mitas Super B5 with 6 ply.
I did an experiment that i'm going to post here, on how inflating the wheels a bar more than I normally use, it gives me a final 2kph more in a very short distance.

A video from last race:

https://www.youtube.com/watch?v=6-xiM1T1iLc

[aerohead]

The course looks dangerous,especially in town.Barricades would be nice to keep onlookers off the course.Around the trees would be good too!
You're hitting 50 kph with around Cd 0.90.If the new body cuts that in half or better,you're going to have some serious velocity and fully exposed to some serious fixed obstacles.
I'd recommend as much crumple zone as you can fit within the shell.
She looked very stable.Thanks for sharing.

[darcane]

Cool video! Thanks for sharing.

A few questions/comments:

• You have a lot more traffic to deal with than I was expecting. Is this typical for your racing?
• Even without bodywork, you appear to be one of the fastest cars on the track. I only spotted one car that passed you, but you later passed him.
• You have lots of corners where you lose quite a bit of speed. My guess is that maintaining speed through corners will be just as important as reducing drag. Are you limited by traction here? Or maybe confidence?
• How do you get the telemetry data? Is that Dashware?

[ChazInMT]

That's about the most fun I've ever seen here on em!!!! Thanks for sharing!!!

[euromodder]

Originally Posted by orengomotors

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.

Don't make wings - use a symmetrical design instead.
Wings can add downforce, but if you want downforce in the corners, they'll also add drag all the way down unless you make them movable

In order to use downforce up front, you need to attach the wings rather solidly which requires a heavier structure otherwise the foam will bend or rotate on the struts.

Even 30cm of this kind of wing will give a fair bit of lift @ 50 kph
It'll work on model airplanes because they are light and the lift will move the entire model rather than break the wing.
On a heavy kart, downforce will break the wing if it's not strong enough or move it when not well fixed.

we use round section tires to have small amounts of rolling resistance, even with massive camber.

Tyres seem to be a very much outdated design offering less than optimal lateral grip and stability
There's just about nothing between the thread blocks to keep them stable and the pattern will make them follow ridges in the road .

I'd think you may be better off with something like this



Reifenwerk Heidenau


What size are they ?
8" by 4" wide (size I got from the googling mitas super B5) ?
If so, that seems to be limiting the choice a lot .


Dual compound scooter or motorcycle tyres could offer a lot of grip on their sides.
Front compound is softer as it doesn't have to lay down power, but the harder part of the rear tyre is narrower - so you'd need to take into account the camber to see if you'd really be running on the softest compound of the front tyres.



Cool video

That 3 wheeler was passing you in the hairpins where I'd think you could go faster
Three-wheeler seems to have bigger wheels, is that right ?

But your kart is faster
With a shell, it'll go faster still (aero + a bit extra weight) so it needs to turn better as well.

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

The driver is laying down - so it's very low.
That kind of design won't work with your upright seating position
You'd still stick out like a sore thumb

ChazinMT's design is more suited for what you've got, but enclose the rear wheels as well ; and make the headrest fairing narrower or round off the front some more.

[Frank Lee]

Round section tires generally have worse r.r. than flat. Unless you need all that camber you might be better off with flat section tires. This would be a good thing to test.

[orengomotors]

Originally Posted by aerohead

The course looks dangerous,especially in town.Barricades would be nice to keep onlookers off the course.Around the trees would be good too!
You're hitting 50 kph with around Cd 0.90.If the new body cuts that in half or better,you're going to have some serious velocity and fully exposed to some serious fixed obstacles.
I'd recommend as much crumple zone as you can fit within the shell.
She looked very stable.Thanks for sharing.

Hi Aerohead,
Yes, the course was dangerous because this wasn't a race, it was like a carnival parade of the towns fest, and is meant by low speed vehicles, but in the soapbox racing barricades are used extensively.

[orengomotors]

Originally Posted by darcane

Cool video! Thanks for sharing.

A few questions/comments:

• You have a lot more traffic to deal with than I was expecting. Is this typical for your racing?
• Even without bodywork, you appear to be one of the fastest cars on the track. I only spotted one car that passed you, but you later passed him.
• You have lots of corners where you lose quite a bit of speed. My guess is that maintaining speed through corners will be just as important as reducing drag. Are you limited by traction here? Or maybe confidence?
• How do you get the telemetry data? Is that Dashware?

-well, this wasn't a race actually but it depends, in some races, you descend one by one, and on others you descend every interval of time, (10 sec).
-this speed was lost because this course was very flat.
-Yes! you're right, is dashware, i like it, very simple and useful.

[iamnotahippee]

So i don't really have any aero comments, but i would like to point out that that is totally AWESOME! It is a good thing they don't do that around where i live because i don't think i could stay away.
One question i have though...what about the possibility of a windscreen in front of the driver's position? With some lexan a nice aero shape could be had, and then keep his head from being a flat surface for the wind to strike.