generating front down force 2

[torque2me]

currently building rear wheel drive classic mini 240bhp
has tendencey to lift at greater speeds. my qestion is this

as i want to keep the exterior of the shell original how can i create downforce through the front grill ie in what was the engine compartment, dont want external spoilers etc
any ideas ?

 

[safetydan]

Are you using the car to go racing, or do you just like to drive fast? There might be a few different ways to create the downforce, but really the amounts you would be generating would be very very low without body modifications (less than 100 pounds at 100 mph). Also, when you are talking about lifting at high speeds, what kind of speed are you talking 100mph+?

 

[GregLocock]

240 brake should take him to well over 100 mph, so this does make some sense.

Basically you need to arrange for the air under the front axle to expand. So, fit a front spoiler to reduce the amount of air coming in, side skirts to prevent leakage, and then a shaped floor to the old engine bay to expand the incoming air efficiently.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[torque2me]

thanks guys
it is 100mph + when on circuit i will be cornering at these speeds hence my concern

abit more infill, i know im being a bit fussy but it really is important to keep the original external lines of the car as i am dual building ie it will be road leagal but all road going bits will simply click off to reduce weight for racing.

the front end is carbon fibre etc with rad and fuel tank etc under the bonnett. ive thought that doing a flat floor pan with rear diffuser would be a subtle as i can get.

question does the diffuser only give more rear grip?
therfore increasing my problem ?
question are you suggesting that i resrict air through fron grill and perhaps vent out through bonnet in which case does exit hole have to be bigger that entry hole?

 

[GregLocock]

I'm a bit unhappy with the way I expressed the previous post.

Starting from the back of the car the diffuser is used to decelerate the air underneath the car back to the free stream velocity. As such it will create maximum downforce where the slot is narrowest, and none at the very back.

Moving forward along the car, if the velocity stays high then the downforce stays high. So you want to keep the narrow slot.

At the front of the car we have to encourage the air to accelerate to a high speed, and feed it into the slot. Having an enormous frontal area for the 'intake' won't help - that's the funnel analogy and it does not work (hold a funnel out the car window, wide bit to the front. What speed is the air coming out the spout?).








Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[safetydan]

When you say the car is lifting at higher speeds, are you referring to the front or the rear of the car? Seeing you don't want to the change the external looks of the car, there are going to be several problems with generating aerodynamic downforce. This is only to maintain higher levels of grip when cornering, but produces large amounts of drag at higher speeds. You have to look at where you want your trade offs. Because you do not want to add anything to exterior of the car (wings, spoilers) there are not many options for increasing your grip through aerodynamic means. A better solution would be to increase the mechanical grip of your car while cornering. When you referred to the car lifting at higher speeds, I'm thinking you are experiencing oversteer (loose) on your rear tires. Basically you want to transfer more weight to the rear of the car, either by putting softer springs in the rear or putting stiffer springs on the front, or a hundred other things. Read a couple of good race engineering books and you'll figure it out. I know this doesn't exactly answer your question, but really your levels of downforce are limited because of retaining the "Stock" look of the car.