Generating more downforce
- Thread starter GTdan
- Start date
Fatman
Member +
I've done quite a bit of research into the field, originally for my Glanza and now more likely to get applied to an EP82. To achieve a reasonable increase in downforce you need to do two things: reduce the amount of air getting under the car and make life easier for the air that does make it in there.
To explain why picture an airplane wing. On the top we have a largely smooth flat area, air flows quickly over this with very little restriction. On the bottom of the airfoil we have a gentle curve. This offers a bit of a ‘restriction’ to the airflow and it effectively goes the long way round. Because of this difference in speeds a difference in pressure is created. Low pressure on the top, due to the unimpeded flow and high pressure on the bottom. Naturally this wants to be equalized, creating the lift effect.
A car is very similar. It has a largely ‘flat’ area on the bottom and the ‘long way round’ on the top. The lift effect is created in reverse, resulting in downforce. Our goal is to increase this effect, whilst hopefully not putting anything more in the way of the airflow (increasing parasitic drag). To achieve this we want to reduce the quantity of air flowing under the car (thus increasing the amount over the top) and make the journey under the car as smooth as possible, thus increasing its speed relative to the flow on the top of the car.
In general terms lower = better when it comes to generating meaningful downforce, unfortunately by dropping the car lower you can actually induce unwanted compromises in geometry that will reduce your effective cornering speed, despite having more mechanical grip. A compromise needs to be struck between ride height and using other aerodynamic devices such as splitters/undertrays etc. Some of these devices include:
Front lips. Not just a showpiece, a lip on your front bumper increases air deflection away and over the car.
Sideskirts. These ‘seal’ in the air that’s under the car, encouraging it to flow to the rear rather than leaking out the sides. Keeping that high speed flow across the length of the car increases the net downforce.
Splitters. A splitter is effectively a large flat aerodynamic device that extends from the front extremities of your bumper through to usually about the firewall area. As well as effectively lowering your car this large flat uninterrupted area has no impedement to flow like your stock engine bay that it's covering up.
Diffusers. Effectively creating an easy means for air trapped under the car to escape, it encourages high speed flow.
Undertrays. Going one step further than a front Splitter, this smooths out the remainder of the floorpan of your car, making sure the air has an uninterrupted flow from front to rear.
Canards. These by themselves do not produce much appreciable downforce. Primarily these are used to finetune the direction of air over the wheel wells or airflow whilst turning. Can look cool though.
To explain why picture an airplane wing. On the top we have a largely smooth flat area, air flows quickly over this with very little restriction. On the bottom of the airfoil we have a gentle curve. This offers a bit of a ‘restriction’ to the airflow and it effectively goes the long way round. Because of this difference in speeds a difference in pressure is created. Low pressure on the top, due to the unimpeded flow and high pressure on the bottom. Naturally this wants to be equalized, creating the lift effect.
A car is very similar. It has a largely ‘flat’ area on the bottom and the ‘long way round’ on the top. The lift effect is created in reverse, resulting in downforce. Our goal is to increase this effect, whilst hopefully not putting anything more in the way of the airflow (increasing parasitic drag). To achieve this we want to reduce the quantity of air flowing under the car (thus increasing the amount over the top) and make the journey under the car as smooth as possible, thus increasing its speed relative to the flow on the top of the car.
In general terms lower = better when it comes to generating meaningful downforce, unfortunately by dropping the car lower you can actually induce unwanted compromises in geometry that will reduce your effective cornering speed, despite having more mechanical grip. A compromise needs to be struck between ride height and using other aerodynamic devices such as splitters/undertrays etc. Some of these devices include:
Front lips. Not just a showpiece, a lip on your front bumper increases air deflection away and over the car.
Sideskirts. These ‘seal’ in the air that’s under the car, encouraging it to flow to the rear rather than leaking out the sides. Keeping that high speed flow across the length of the car increases the net downforce.
Splitters. A splitter is effectively a large flat aerodynamic device that extends from the front extremities of your bumper through to usually about the firewall area. As well as effectively lowering your car this large flat uninterrupted area has no impedement to flow like your stock engine bay that it's covering up.
Diffusers. Effectively creating an easy means for air trapped under the car to escape, it encourages high speed flow.
Undertrays. Going one step further than a front Splitter, this smooths out the remainder of the floorpan of your car, making sure the air has an uninterrupted flow from front to rear.
Canards. These by themselves do not produce much appreciable downforce. Primarily these are used to finetune the direction of air over the wheel wells or airflow whilst turning. Can look cool though.
Last edited:
Streetech
Member +
Do you want to edit that again mate so the information is correct?
@Dan
I looked into this when i was bored doing my dissertation, I already had the front of my car modeled on the computer so it was a simple case of adding the required mods after a couple of calculations and running the flow simulation. I didnt bother saving the results as it didnt help me at the time.
I will have another go and see what I can come up as I am interested in this for the mk1.
Fatman
Member +
Do you want to point out what's incorrect and I'll be happy to edit accordingly...
Aga
Member +
the canards dont generate downforce like a wing does. that means , they dont push the bumpers down. their work is to make the air travelling alongside the sides of the car turbulent, in order to prevent it from sliding underneath the car, thus reducing the downforce generated by the air travelling underneath the car. Thats why, canards have to be used with sideskirts, and preety low at that (like tom's). most of the downforce is generated by making the air underneath the car travel in a different speed as the air travelling above (faster or slower? fucking bernulli, i dont remember!
) , thus generating vacuum, creating the downforce.since you're chasing downforce i suggest the following.
front spoiler with undertray.
a bonnet with reverse vents on top
a tom's (or worse) rear wing
toms's sideskirts
a tom's bumper wouldnt hurt, you could use 2 of the vents for brake cooling and plug the rest.
front fenders with holes to relieve the pressure buildup on the wheelwell
cut open holes on the rear bumper for the above reason
and you will have to do the same on the inner arches , plastic and otherwise
as for a rear diffuser, with that huge hole where the rear axle is, theres gonna be a huge amount of fabrication to get this closed up...so unless you re building a time attack car, i`d leave it. you can cut some vents on the rear bumper though, to relieve pressure there too.
Streetech
Member +
Swap them round.
The flat area on a plane wing is at the bottom for the slow moving air. The rounded/curved section is on the top making the air travel faster causing Low pressure and Lift.
Obviously, just turn that upside down and you get downforce.
HorwathBence
Member +
Well... i have had a litle accident on the Hungaroring last year... and after that i ve made some initial calculations using Finite Element Method... i am studying mech engineering... And come out that there is a huge lifting force on the back of the car... but it is so complex, and i ve just used a primitive modell derived from 3 images... i started to gather information about it... i dig a lot...
Now i need to scann the original car, then analise it... than make some virtual changes... and then analyse it again and again...
Many of my consultant said, that flows around the car are so complex, that every detail counts... so correct results are hard to make... but trends can be found...
I mean, that if i scan the bodywork, than i ll have the problem with the enginebay... the radiators... a simple flow analisys is not as difficult, and can be done by som boundary options... but what about the flow through the rads, and where ll hey go...
Now i need to scann the original car, then analise it... than make some virtual changes... and then analyse it again and again...
Many of my consultant said, that flows around the car are so complex, that every detail counts... so correct results are hard to make... but trends can be found...
I mean, that if i scan the bodywork, than i ll have the problem with the enginebay... the radiators... a simple flow analisys is not as difficult, and can be done by som boundary options... but what about the flow through the rads, and where ll hey go...
HorwathBence
Member +
there are some fist roles... u can find it in som literature like "aerodynamics of road vehicles..."
Basiquely they are like thet under the car there are huge friction, via that there are slower flow than above it, wich results a greater upforce. U can make the underbody flat, but be carefull with the exhaust, couse most composit fyber are extremely flamable, and can take heat about 100°c... and u should let the air somewhere from the enginebay, some through the hud, some through the undertray (???)... The front undertray can generate huge amount of df, as the rear diffuser... but if the flow separates from the too steep diffuser it worths nothing.
The spliter moves the point of flow spliting downvards cousing les air under the bottom of the car, wich means less friction and loses under it... but more air abowe and more lift....
U can generate a vortex vith fins (not direct df) on the side of the car, blocking the air getting under the car.. oh i forget... faster flow, less pressure, under the car relative "vacuum" meand downforce...
and tehre are some more... but i am a bit long.. think so..
sorry
Basiquely they are like thet under the car there are huge friction, via that there are slower flow than above it, wich results a greater upforce. U can make the underbody flat, but be carefull with the exhaust, couse most composit fyber are extremely flamable, and can take heat about 100°c... and u should let the air somewhere from the enginebay, some through the hud, some through the undertray (???)... The front undertray can generate huge amount of df, as the rear diffuser... but if the flow separates from the too steep diffuser it worths nothing.
The spliter moves the point of flow spliting downvards cousing les air under the bottom of the car, wich means less friction and loses under it... but more air abowe and more lift....
U can generate a vortex vith fins (not direct df) on the side of the car, blocking the air getting under the car.. oh i forget... faster flow, less pressure, under the car relative "vacuum" meand downforce...
and tehre are some more... but i am a bit long.. think so..
sorry
350ep70gr
Member +
HorwathBence
Member +
If i have some time i ll work on it, than try to make sthg of it...
for fun here are some images... they do not mean anything, as u can see they are brutal modells, and extreme wings... ( the maximum syze the fia let on a 24h car)
just for the laugh
for fun here are some images... they do not mean anything, as u can see they are brutal modells, and extreme wings... ( the maximum syze the fia let on a 24h car)
just for the laugh