Wide-track front end and aero info.

[ottocycle]

Hello all,

It is cold damp winter day in Washington and I have been pondering ideas for my "steam-punk seven" project. It is all academic at this stage but as I think about the bits I have and how I can string them together a couple of questions have come to mind that I would like to get some answers to from those more qualified than I.

 

I know some of you have converted their cars to a "wide-track" front end. How do you like the conversion? I can appreciate the advantages it would have as far as camber control is concerned, particularly with wide modern tires, but unless the upright or chassis pick up points are also changed, lengthening the stock wishbones would throw off the factory designed roll center. Does it matter or am I missing something?

 

As we all deal with aero issues on our cars I am interested in reducing high speed front end lift. I read the thread about aero, diffusers etc. and agree with IAN7 that it is hard to make a brick aerodynamic but it is important to try to minimize the front end lift. I am thinking of enclosing the bottom of my car and ducting the radiator over the hood like the CSR's. I then thought about the possibilities of ducting that hot air under the car towards a tail diffuser. Without skirts would the air be accelerated enough to make a difference or would it cause additional lift? Any ideas?

 

Thanks,

 

Dermot.

Fury/Hayabusa.

[Croc]

As we all deal with aero issues on our cars I am interested in reducing high speed front end lift. I read the thread about aero, diffusers etc. and agree with IAN7 that it is hard to make a brick aerodynamic but it is important to try to minimize the front end lift. I am thinking of enclosing the bottom of my car and ducting the radiator over the hood like the CSR's. I then thought about the possibilities of ducting that hot air under the car towards a tail diffuser. Without skirts would the air be accelerated enough to make a difference or would it cause additional lift? Any ideas?

 

Hi Dermot,

To check my memory I went digging through my library of motor racing books to confirm some facts. In the early 1980s Formula 1 took a ground effects approach of running cars very low, on very stiff suspension with “skirts” around the perimeter of the central chassis tub (including the side pods/sponsons). This gave an area of low pressure that would act as additional downforce on the car improving cornering.

 

The problem with this approach was maintaining the enclosure of the low pressure area so that it remained effective downforce. So the Formula 1 cars had to run very hard springs to maintain the “contact patch” during regular track conditions such as cornering or bumps on a straight. If the air escaped then the downforce was lost – potentially perilous if it was being used in a cornering manouveur. A side note is that I read an interview with Alan Jones and he said these types of car were hard on the driver as all forces were transmitted direct to the driver without absorption by the car.

 

What you are thinking of is a variation on this – channeling air under the car to a diffuser to force a negative air pressure zone. Another analogy is that you are trying to produce a NACA ducting effect but in large scale.

Sounds great in theory but how do you keep the air from escaping out the sides? Well, Formula 1 used skirts but they were only effective if they hung right to the surface of the road. Even a hovercraft only functions with positive life if its skirts rub the surface. NACA ducts only work because they can channel the air.

 

While I am not an engineer (and hopefully someone more techie than me will be along to respond shortly) but I cannot see how you make this work in practice on a car that may be used on roads. A track only car could readily take advantage of this but a road car that has to deal with bumps, humps, kerbs, speed humps, etc?

 

Still, the worst case that could happen is that you do not channel the air under the car, there is some level of leakage but still when the residual (after losses out the side) air flowing to the rear of the car meets the diffuser, some of that will flow upwards to create the negative pressure and add downforce. Even if it does not the car is smoother underneath so evacuates air with less resistance. Given the number of performance cars that have this feature and I have to assume they are wind tunnel tested then there is still a benefit from doing this. It may not be as much as you are hoping for.

 

So hopefully someone now comes along to challenge my layperson logic on this!

Sorry but I am clueless on answering your suspension question!

 

Cheers

[ottocycle]

Thanks Mike,

 

I appreciate and agree with your comments. I "know enough to be dangerous" and have a modest library to help me along. What I did not explain clearly is this. I know that one cannot get aerodynamic efficiency and viable down-force from a seven, I was thinking of ways to reduce the lift. We have all felt it at the track at speed, for example at NJMP at the end of the pit straight as one goes over the rise the car gets light. For want of a better term I would call it a "gravity damper" as the vector powering us up the rise and air bubble under the front of the car cause it to ride on a cushion of uncertainty as the front end is unloaded and goes into full droop. If my car was faster it would "yump" as our Scandinavian friends would say. Mike D's "snowplow" has helped to minimize this and from what I understand Caterham went to a lot of trouble with your CSR to minimize this characteristic.

On my Fury I get a build up of air under the hood that lightens the front end over 100 mph. I am thinking of ways to minimize this buildup of air and by isolating the underhood area from the intake air it cannot lift the car. That is why your car and the recent Shelby roadster (I cannot remember its full name) have the separate duct for the radiator. I was wondering if there might be any benefit to venting that hot radiator air under the car rather than over (I know it sounds counterintuitive) but having thought about it further without skirts and a wing profile under the car I do not see it having any benefits. (The easier path of logic here is, of course, if it worked everyone would do it. QED.)

I am hoping my next car will be lighter so I am paying more attention to lift.

See you at NJMP in the Spring.

 

Cheers-

 

Dermot.

[danilo]

Perhaps time for a Reality Check?

Find the Blatchat forum and then search within it for Aero..

You might discover that what you want will Not be accomplished by what you think... and be surprised by what has been shown to work.