Im interested to know the ideas behind downforce and how it aids in performance on cars.

Im led to believe that the lower the pressure under the car and the higher pressure above the car results in downforce.

What kind of systems make this acheivable?
Wings will cause downforce obviously, but how much does the flat smooth floorplan aid in this process ?

What speeds does the smooth underside come into its own and aid in grip/downforce?

30mph+
80mph+
120mph+

Hope any one can help or offer there knowledge in this HUGE topic.

 

You got another idea in your head Luke. Lol

 

Hello mate long time no hear.. How ae you?

Im always thinking of something new and stupid

 

venturi on the back + a flat floor will give down force on the rear i believe. something to do with speeding the airflow along the bottom of the car i think.

 

Here you go mate

http://en.wikipedia.org/wiki/Ground_effect_in_cars

Most of it is based on Bernoulli's Principle on compressible flows

Which is also here

http://en.wikipedia.org/wiki/Bernoulli%27s_principle


Like you said - The basic idea is to create an area of low pressure underneath the car, so that the higher pressure above the car will apply a downward force

 

if you look at saloon car racers from the seventies (batmobile bmws, zakspeed fords etc) when they experimented with these things, or the pikes peak racers, you will see that they have huge appendages (ooh er missus) on to generate meaningful downforce. that tells me that the basic shape of a saloon car is not suited to generating downforce.

as for your first question, the idea behind downforce is to effectively add more weight to the tyres to make them grip better, without adding mass that makes braking and acceleration worse (ignoring the fact that to generate downforce will probably increase the drag so your high speed acceleration will suffer).

 

search up "ground effects"
using front splitters rear diffusers and undercarrage tunnels iirc just look in old formula 1 history theres LOADS on it and how it works!

basic principle is to let as little air as possible through under the front bumper. keep the maximum amount of air under the car and not let it escape out the sideskirts. and directing the flow out from under the car, as high as possible (on the longest possible trajectory) into the flow of the air which is passing over the car. in the most efficient manner
thus creating downforce with little drag .

 

Similar to how an aircraft wing works, flat on the bottom, and curved on top, so the air moving over the top has to flow faster, thus creating a lower pressure, so the wing tries to fill the gap as it were, thus creating lift. Downforcs is exactly the same principle, just the other way up

 

In simple terms, more air traveling over the car = good for downforce
Less air traveling under the car = Good for downforce

 

I'm not sure that statement is correct.

 

Me neither Doug, something's not right there!

 

Maybe I'm wrong, but seems logic to me.

 

the smoother the bottom the less chances there are or vorticies being formed which will cause different effects on the cars aerodynamics

you want the air flow to be as smooth as possible and any holes will generate different pressure spots, which, in turn, will lead to drag

yuo want the top of the car to be the one creating the drag as this equates to downforce and pushes the car down

creating downforce "underneath" the car will mean lift, which is bad

 

nonsense dojj.

kverna, congratulations. you've just posted a picture of a car acting like a plane's wing and giving lift, the opposite of downforce

 

The idea is to create lower pressure under the car than above it.

 

Dojj, crap!

 

As I understand it with regard the topside of the car the air flowing over the car gives both down force and uplift.

When the air flows over the bonnet it acts as a lift and upon arriving at the front screen will then cause both drag and down force as it interrupts and causes higher pressure.

When past this and on the roof of the car a huge uplift is created and further more when travelling over the rear screen/boot areas.
Thus when travailing at higher speeds the back of the car goes light due to the air literally lifting the car from its footings.

The underside im yet to understand with regard to splitters channelling and rear diffusers.

 

The Curved Top Of A Wing Means Air Has To Flow Faster, This Creates Lower Pressure Effectively Suckin The Wing Upwards. In Reverse A Flat Bottom Offers Less Resistance To The Air Thus Meaning It Can Flow Faster Creating Lower Pressure And Pushing The Car On To The Road

 

If The Back Of The Car Underneath Slopes Upwards Then, The Volume Of Space Increases, But As The Volume Of Air Entering Doesnt Change The Pressure Drops,

 

Joffy, just for you

http://www.say-it-in-english.com/BasicEnglish8.html

you're saying that the curved surface makes the air travel faster which creates lower pressure - correct. you then say that a flat underneath will give faster air - that's nonsense as the air has the shortest distance to travel across a flat surface so it travels slower

 

No I Said The Flat Surface Gives Less Resistance To The Air Which Lets It Flow Faster, The Raise At The Back Gives The Space Under The Car More Volume With The Same Amount Of Air Going In Gives Less Pressure??

 

but what is going to make it flow faster?

 

Less Resistance?? Its Not The Speed Its The Space Underneath The Car Compared With The Volume Of Air Entering It, If The Surface Is Angled Upwards Then The Volume Of Space Has To Increase And The Mass Of Air Stays The Same, If The Mass Stays The Same And The Volume Increases Then The Pressure Has To Be Lower??

 

sorry mate, not being funny but i can't process the information in your posts. the capital letters makes my brain think everything is a new sentence and i just can't string it all together

 

good point, ive just read it and its confused me, fuck knows why its done that, bare with me

 

less resistance?? its not the speed its the space underneath the car compared with the volume of air entering it, if the surface is angled upwards then the volume of space has to increase and as the mass of air stays the same, if the mass stays the same and the volume increases then the pressure has to be lower??

 

try that lol

 

Joffy - Your caps key is working overtime there...

 

right, i get you now you're explaining how a rear diffuser works

 

tell me about it, bloody caps lock, FuCkIn ThInG

 

my nephew has 2 degrees in fluid dynamics, has won several awards for his designs and curently earns a 6 figure salary doing stuff he does with his degree, and that's what he's "basicly" described it as being

obviously i won't be able to post up 6 years of his studys any more than i could expand on what he was on about, or perhaps i am misquoting him in some small way, but he explained that you need to keep the smooth bits smooth as possible and design the turbulence to do what it needs to do away from the object you are trying to areo

if i can tempt him on here to explain then i will attempt to do so, but i don't think he'll be intrested

 

i agree with what your saying but not the effect it will have on the body in question, if the smooth bits are extra smooth and the rough bits create turbulence then the speed difference between them will be greater, if you refer this back to the diagram above, this means the car/plane will have a greater aerodynamic influence, but ot say you need the top of the car to 'create drag' is wrong. every moving thing unless in a vacumn 'creates drag'. but that is one thing that designers and engineers will try to lower as whatever the body it will always slow you down and not neccessarily give you any advantage ie downforce

 

also, if he already had a degree in fluid mechanics, why would he want another??

 

why 2 degrees in the same thing? makes no sense to study the same thing twice did he not understand it first or 2nd time? i also have a degree in mechanical engineering with much fluid dynamics study. whoop de doo

maybe you should convince him to post, as it must be getting lost in translation between the two of you as he must know his stuff on the subject and it would be of interest to a lot of people on here

 

my brother had a 3rd degree in burns but i aint boasting

 

Im sorry but that is

 

had to be said, if i didnt someone would lol

 

Interesting reading though i will look through a few links later and i have also looked breifly into the designs behind Lotus cars on this subject.

Home work for tonight me thinks.

 

Afpmsl!! My sides hurt laughing at that!

 

This book :

http://www.amazon.co.uk/Competition-.../dp/1844252302

Is very good and interesting - if you are a nerd like me

Faster airflow = pressure drop = downforce or lift dependant on position : Think carb venturi and where the petrol goes in.

Get a piece of A4 paper and hold it in front of your mouth parralel to the ground. blow hard over the top and the paper will rise : faster air flow = pressure drop = lift (or down force in reverse).

A (aero) wing is longer on the upside then the down, the air goes quicker over that side giving pressue drop / lift. Trouble is the airflow needs to rejoin without separation and there is allways a ballancing act with drag