Properties of a Downforce Fan

[marcush.]

Doing a project for a road rally car and I'm planning to use a fan like the Brabham BT46B. I want to use a separate engine (at a constant speed) for this but I have no idea how powerful it needs to be to produce about as much DF as an F1 car (the goal). Assuming I use the best fan blade angle possible.

Can anyone help me on this as it is a bit above me?

for the safety of the driver i would encourage you to go with giant wings instead.

Giant wings can break as well. I cannot see the logic.

as for the drag : you will easily add the same drag by adding a wing to the car -1200mm wide and 100mm high -so what?
Friction of the seal rubbing the ground -maybe a bit of an issue very hard to quantify at this point .sure the sealsystem is a little challenge but something doable ,surely easier than gearing up to produce wings for your car.
The concept has the advantage of producing potentially a lot of downforce at low speeds .so the increase in grip in tight bends should be staggering .
The wing theme can work at low speeds as well but then you face the compromise of huge drag as the speed goes up.
As a tradeoff rules permitting the fan could be a good direction.

[munudeges]

I'd love to hear how this works out if you do it. Somehow I have a hard time believing that it will work well enough at the speeds you'll be operating at but it's possible you might be able to perfect some kind of effect out of it. There's at least some figures on the thread to get you started.

Crazy engineering ideas are a part of motorsport.

[machin]

I'm keen to see how you get on with this.... Could you start out with a cheap working car and modify it, just to test the concept?

3: In the unlikely event you did produce some meaningful downforce, it would just compress your springs and not push the tyres into the road.

Chris, are you forgetting Newton's Third law?

[xxChrisxx]

I'm keen to see how you get on with this.... Could you start out with a cheap working car and modify it, just to test the concept?

3: In the unlikely event you did produce some meaningful downforce, it would just compress your springs and not push the tyres into the road.

Chris, are you forgetting Newton's Third law?

Of course not, but sadly a car driving down a bumpy road isn't a textbook case that can be solved using a free body diagram.

So what you would expect is an increase in grip, but would acutally end up with the springs compressing to solid (or breaking) and the wheels to bounce off the road at every single bump.

Yuo are right, it was very poorly worded, so to revise the wording: It would not increase road holding.

[xpensive]

Wow, our new teacher has spoken, how's trix behind that lectern anyway, you often give classes in ground-effects?

[mep]

Why is everybody annoyed when I point out some safety concerns?
I am normally not very much into safety when we talk about on track actions but the cars should be build in a safe way.
Also I separate very strict between nice designs and crude ones.
Giving a floor a aerodynamic shape is a nice one putting a fan is a crude one in my mind.

[xxChrisxx]

Also I separate very strict between nice designs and crude ones.
Giving a floor a aerodynamic shape is a nice one putting a fan is a crude one in my mind.

I am a big proponent of the KISS principle.

If he already had a car with a fully sculpted floor, I can see that using a fan a la Chaparral 2J being a logical step.


It's like the people I see spending spend silly money and take extreme care making minute changes to suspension geometry 'to gain a few tenths', yet buy crap tyres.

It's an arse about face way of doing things.

[mep]

I don't really get what you want to say with this in regards to my previous comment. Maybe you don't really understand why I consider a fan a bad design.

[marcush.]

Why is everybody annoyed when I point out some safety concerns?
I am normally not very much into safety when we talk about on track actions but the cars should be build in a safe way.
Also I separate very strict between nice designs and crude ones.
Giving a floor a aerodynamic shape is a nice one putting a fan is a crude one in my mind.

Mep ,no offence there but a fan is not a crude device.Actually MrMurray had a engine bay fan mounted in the famous F1 to suck off the boundary layer of the reflexcurve shaped difusser in the series car ...so theres a lot you can do without ending in a motorsaw massacre.
The Chapparal blower car and Gordons BT46 in Anderstorp did carve themselves into my brain as much as the Lotus 79.

[xpensive]

I have to say that I find all these negative, "von oben" and almost patronizing, attitudes on this thread depressing.

If MIKEY! has the guts and green to move along with this, may the force be with him I say!

Keep me posted on your progress and don't hesitate to PM me if you need more help with the calcs and fan selection!

[machin]

It's like the people I see spending spend silly money and take extreme care making minute changes to suspension geometry 'to gain a few tenths', yet buy crap tyres.

Indeed, and what Mikey is doing is trying something which potentially may give a big step increase in car performance -he's following your rule I quote above -concentrate on the things which give you the biggest increase in performance.

Going back to your earlier comment regarding compression of springs etc; do you agree that the very high downforce Pikes Peak Rally cars are faster with or without downforce, despite the effect on compression of the springs? Well this is effectively no different except the method by which the downforce is generated. If the problem of sealing the underfloor can be overcome then why would the downforce be any detrimental on this car than it is on Pikes Peak Car?

[xxChrisxx]

Indeed, and what Mikey is doing is trying something which potentially may give a big step increase in car performance -he's following your rule I quote above -concentrate on the things which give you the biggest increase in performance.

That's just bollocks. The rule is to apply a bit of common sense and get a solid performing car before sticking 'go faster' --- on it wihtout a moments thought to acutally what it's doing to the car.

HEY I KNOW! Top fuel dragsters use nitromethane, they produce a lot of power. So he should put nitomethane in his tank instead of petrol. What would happen then?

Going back to your earlier comment regarding compression of springs etc; do you agree that the very high downforce Pikes Peak Rally cars are faster with or without downforce, despite the effect on compression of the springs? Well this is effectively no different except the method by which the downforce is generated. If the problem of sealing the underfloor can be overcome then why would the downforce be any detrimental on this car than it is on Pikes Peak Car?

Pikes peak cars have flat/sculpted bottoms, huge splitters and diveplanes. The collosal wings are either bolted directly to strengthened struts, bypassing the springs altogether. Or have spring/damper rates specifically designed to take the aero loads. They also have 1000BHP to overcome the drag.

Basically they were designed to do the job, everything the proposed car isn't.

You can't take the chassis/suspension/runninggear/whatever of a road car, bolt a --- huge fan on it to give 'f1 levels of downforce' and expect it to work. The whole concept is just silly.

If he were proposing designing and building a car from scratch, with specifically designed suspension and underbody to acommodate underbody aero and a fan, then there really isn't any reason why it wouldn't work.

But he's not, he's trying to be Heath Robinson.

[machin]

I think he realises he can't take a standard Fiat 500 and "stick a fan on it" and expect to beat everybody!

It sounds to me like he's building from scratch... using suitable parts he can lay his hands on....

If you can advise the guy on spring rates (etc, etc) that ARE suitable, that would be way more constructive than just saying it won't work... in fact you've kind of changed your tune now...:-

If he were proposing designing and building a car from scratch, with specifically designed suspension and underbody to acommodate underbody aero and a fan, then there really isn't any reason why it wouldn't work.

This forum would be way better if people came up with solutions rather than just shooting down other people's plans... Xpensive has started the ball rolling helping out with the fan specs.. what else can we all help with?

[HampusA]

Doing a project for a road rally car and I'm planning to use a fan like the Brabham BT46B. I want to use a separate engine (at a constant speed) for this but I have no idea how powerful it needs to be to produce about as much DF as an F1 car (the goal). Assuming I use the best fan blade angle possible.

Can anyone help me on this as it is a bit above me?

for the safety of the driver i would encourage you to go with giant wings instead.

Giant wings can break as well. I cannot see the logic.

as for the drag : you will easily add the same drag by adding a wing to the car -1200mm wide and 100mm high -so what?
Friction of the seal rubbing the ground -maybe a bit of an issue very hard to quantify at this point .sure the sealsystem is a little challenge but something doable ,surely easier than gearing up to produce wings for your car.
The concept has the advantage of producing potentially a lot of downforce at low speeds .so the increase in grip in tight bends should be staggering .
The wing theme can work at low speeds as well but then you face the compromise of huge drag as the speed goes up.
As a tradeoff rules permitting the fan could be a good direction.

Hmm let me think here....

Putting on solid wings that won´t break by the themselves or setting up a big fan under the car together with skirts and everything else that goes with it?

Wings work all the time, even if your in the air.

Fans work only when you are touching the ground. Thus it´s a hell of alot safer for normal roads to be using bigger wings because no matter what happens, they will produce downforce.

A fan will produce downforce up to that point you hit a bump or theres a drop in the road.

[machin]

Wings work all the time, even if your in the air.

Unless the car is going slow/stopped, or sideways, in which cases they give you nothing.....

A fan on the other hand produces downforce in both these situations, although as you say:

Fans work only when you are touching the ground

So the problem we need to solve is making sure the "skirt" provides a good enough seal.... Anyone willing to have a go at suggesting a solution, rather than just pointing out the problems?