You´ve read about this you say, than you know that it´s easy to lose the effect and bottom out, right Just to point that out in case you´re building something
The group-C cars have some of the best underbodies as far as I know, and I´m pretty sure that the perfect underbody is close to one of them... Check them out, if you haven´t allready... We´ll se what the aero guys have to say on this one, I´m quite interested in this myself
The perfect underbody will be one of the group C cars, take a look at them, their diffusers were increddibly big and almost came out at the end as an arrow shape, so the top bodywork and the bottom of the diffuser hit each other. If you combine technology of now and those underbodys you can create the best underbody. Off course those Group C cars had ground effect, those cars were probably faster then the LMP1 Cars from now.
That made me think about the brabham which sucked the air away under the car. You can do that but it is high advanced and alot harder than a underbody with an huge diffuser
wesley123 wrote:That made me think about the brabham which sucked the air away under the car. You can do that but it is high advanced and alot harder than a underbody with an huge diffuser
I disagree its probably easier to design than a perfect passive system
big fan + skirts = downforce. also its not speed sensitive so you always have the same amount of down force
wesley123 wrote:That made me think about the brabham which sucked the air away under the car. You can do that but it is high advanced and alot harder than a underbody with an huge diffuser
I disagree its probably easier to design than a perfect passive system
big fan + skirts = downforce. also its not speed sensitive so you always have the same amount of down force
that is true, but do you know how a thing like that gets made? And maybe he hasnt got enough resources to build a thing like that? I dont know for what it is but i think it is too advanced, if you make an error in the design or it stops working then all the downforce will be gone.
Actually, I would think the brute force approach of a f**king big fan would give you ground effect without doing any under-car aero design work. Remember the early wings they were sticking on were pretty much big planks on long sticks. The benefits would kick in with finesse of the finer details once everyone took it on. Same deal as just whacking in a bigger engine or a swatting greater turbo/supercharger to get more power rather than lightweight agility with aero. Think the brabham was a '79 (?) and the fan was crank driven allegedly for cooling, but no-one believed that for very long. Ground-effect first done by JPS Lotus?
Active system has a problem of that performance of fan would depend on engine speed if fan is driven by engine. You probably can make electrical engine with a buffer battery or some transmission system, however that complicates design.
I think skirts are easier to do and more consistent. One thing to watch out is getting aero balance right, can't remember where I read this but inverted underwing profile has center of aero load at about 20% of its chord and that makes car oversteery.
First of all, i have to "reveal" what i am planning to do.
My goal is to creat a perfect underbody for a 65` Mustang Fastback for
open road/track/hillclimb racing.
So I am really considering building an active system.
But anyone of you guys out there has some nice underbody foto shots of an active system or even a good passive one with skirts and Bernoulli/Venturi-tunnel system?
It would be cool if you can show us the car in different ways, by this we can see what is possible and telling what you can do wand what your budget is will be fine too, so then we can tell you exactly what your options are.
What series are you planning on running that allows active aero, or sealed skirts, etc?
And again, there is no such thing as perfect in motorsport.
You will get into very dangerous territory very quickly if you're talkin massive downforce underbodies, passive or active. There's a reason why they're banned most everywhere. Something fails or breaks, lose a massive amount of grip very quickly.
I'd say put super hardened steel (4130, 4340... something Rc50+) half-rounds in a broad grid on the underbody work. Maybe 0.500 to 0.750" radius. Something where if you start bottoming the car you have a chance of keeping the air flowing so you don't lose all grip, and can get back to the pits and up your springrates. Bump rubbers would probably also be a good idea.
Are your suspension, wheel bearings, etc all stout enough to handle double to triple the originally designed loads?
As for skirts, I'd have them spring loaded and rolling on tiny casters, or rollers, or again something hardened. Something to keep them forced down onto the ground.
The other item is, you're going to need some other aero element on your car to be able to adjust balance. Likely this will have to be something at the front of the car. On a coupe, like a Mustang, generally this would be a splitter. However, to get a splitter to really work you're going to have to run super low front RH, which is going to choke the underbody venturi.
Front splitter and rear wing would probably be a good way to go here.. relegate underbody work to maybe a small rear diffuser and smooth otherwise to mitigate drag.
Grip is a four letter word. All opinions are my own and not those of current or previous employers.
A passive system would need a goodish amount of speed to generate gobs of downforce.
If you create a smooth underbody what happens with engine cooling?
Would you not get more performance by investing your effort and money in reducing weight and optimising the suspension & brakes? Then worry about getting downforce later?
Surely the main thing you need is for the car to be balanced and drivable?
Just to point that out in case you´re building something 
