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It's old school F1, but still F1, so I'm not sure where to put this post. My question is this:
I know the Brabham bt46b and 2J Chapparell fan car was primarily aimed at increasing mid-low speed cornering, I just don't know what speeds this would be. Does anyone have an estimation or information, or simply want to take an educated guess as to what speeds the fan car would be most effective and what speeds it would drop off?
Thanks for your interest.
Compulsory fan car image, just for the love of the design:
Downforce relying on a fan is an active one which is much better, obviously, than a passive one. Brabham's , as SectorOne said, was linked with the engine's rpm, which is not ideal.
Ideally, you would want an independantly powered fan with max rotation speed even with the car stand still. That way, you would have all downforce, provided from it, throughout all the car's speed range. If you add other things like wings on the bodywork, you will add further downforce as the speed increases, which is the typical situation, obviously.
The benefit of a fan is evident because let's say, with it's downforce, you get your car to corner at 5 or 6Gs. But that will happen regardless of the speed, so you will take very tight corners at quite high speed(nowadays they corner between 1.5 and 2Gs on the low speed corners 60-120kmh)
For curiosity, if you could get a good seal on the underbody and fitted powerful enough fans to create an almost vacuum in there, you would get almost the atmospheric pressure acting on the floor's area. For reference, let's say the current width of the floor(1,4m) over a length of 1,8m which would give an area of 2,52m^2. As standard atmospheric pressure is equal to 101325Pa, you would get 56742 lbs of downforce with a complete vacuum underneath the car. That would provide huge G figures in cornering(42Gs over a 600kg car) but maybe getting even close to complete vacuum might be very difficult, if not impossible, in practical terms.
I remember reading somewhere brabham fan car would squat on its suspension during standstill when they were revving and warming it up on the grid. Must have been some pretty powerful suction going on.
Artur Craft wrote:Downforce relying on a fan is an active one which is much better, obviously, than a passive one. Brabham's , as SectorOne said, was linked with the engine's rpm, which is not ideal.
Ideally, you would want an independantly powered fan with max rotation speed even with the car stand still. That way, you would have all downforce, provided from it, throughout all the car's speed range. If you add other things like wings on the bodywork, you will add further downforce as the speed increases, which is the typical situation, obviously.
The benefit of a fan is evident because let's say, with it's downforce, you get your car to corner at 5 or 6Gs. But that will happen regardless of the speed, so you will take very tight corners at quite high speed(nowadays they corner between 1.5 and 2Gs on the low speed corners 60-120kmh)
For curiosity, if you could get a good seal on the underbody and fitted powerful enough fans to create an almost vacuum in there, you would get almost the atmospheric pressure acting on the floor's area. For reference, let's say the current width of the floor(1,4m) over a length of 1,8m which would give an area of 2,52m^2. As standard atmospheric pressure is equal to 101325Pa, you would get 56742 lbs of downforce with a complete vacuum underneath the car. That would provide huge G figures in cornering(42Gs over a 600kg car) but maybe getting even close to complete vacuum might be very difficult, if not impossible, in practical terms.
Thank you all.
My plan was to separate engine rpm from downforce fan. These figures are very interesting. I have a car that has an area available for downforce which is 2m x 2m almost exactly. I can build a seal with the ground like the Lotus 79-80 did, this will be very easy to do over the space (even the front and rear is not too difficult). I know the seal wont be complete whilst it drives over undulating surfaces, but Im hoping to add enough downforce to corner fast at low speeds (~4G @ 60-kmph) my car weighs ~500kgs with me in it. Im just not sure on the calculations.
The biggest unknown is the leakage rate under the skirt and the overall power vs fan rpm vs volume flow rate vs pressure drop characteristic. There was another thread on fan cars within the last year, it may be worth searching.
Once you can guess what pressure differential you can get then the downforce is easy, and if you know enough about your tires then working out the latacc is easy.
