Sucker Car

[Def]

The E30 ground clearance is too much to have the underbody flow to create usable downforce.Until someone builds relatively flat floor that is a few inches from the ground,but I cant think of what rate springs will be needed in that case.
I have an intention to install my radiator in the spare tire well,tilt 45 degree front.Sucking air from underneath and exhausting between the taillights.It should help with the drag at least.

You don't gain much in ground effect until you're talking. fractions of an inch. Its still a large area to make downforce with.


There's a ton of downforce to be had with a little work on the underbody.

[bawareca]

You don't gain much in ground effect until you're talking. fractions of an inch. Its still a large area to make downforce with.


There's a ton of downforce to be had with a little work on the underbody.

Exactly my point.In my opinion,sucking air for the radiator underneath and exhausting it behind the car will be more beneficial for reducing the low pressure behind the car,than it will harm the negligible downforce that can be created under E30.Also,if there is a chance for the underflow to stall, side deflectors can be used to force more air under the car to accelerate the flow.But I really doubt that could be the case.

[Def]

Exactly my point.In my opinion,sucking air for the radiator underneath and exhausting it behind the car will be more beneficial for reducing the low pressure behind the car,than it will harm the negligible downforce that can be created under E30.Also,if there is a chance for the underflow to stall, side deflectors can be used to force more air under the car to accelerate the flow.But I really doubt that could be the case.

Do you have any formal/informal background into aerodynamics?

I'm not really sure where you're going here, but you're making all sorts of stuff up as you're going along...


A small fan on the other side of a dense heat exchanger isn't going to "suck" the static pressure below what you're getting with a slightly raked flat underbody. It takes energy out of the flow to force it through a heat exchanger, and the reason most well designed ducts increase in area is to raise the static pressure of the air and slow the incoming flow.

So I stand by my original statement, best to let the underbody airflow do its thing and pick up airflow somewhere else, preferably somewhere that allows you to use that higher pressure duct to make downforce (i.e. on a sidepod mounted radiator with a side entry a 'sideskirt splitter').

[bawareca]

I am not expert in any way.I dont care about the fan.If the radiator is ducted and sealed on the both sides(like a "tube between the underbody and rear panel),there will be a huge pressure difference between the both sides,which will "suck" and force the flow thru the radiator.

[Def]

I am not expert in any way.I dont care about the fan.If the radiator is ducted and sealed on the both sides(like a "tube between the underbody and rear panel),there will be a huge pressure difference between the both sides,which will "suck" and force the flow thru the radiator.

The static pressure drop to move a reasonable amount of air through a heat exchanger is exceedingly high compared to most pressures around a car. Hence why most radiator stagnate the freestream air to get enough static pressure differential.


The radiator drawing from underneath the car will increase the static area over a very large area underneath the car.


If it was such a "free lunch" and the radiators were so free flowing, you could feed them with relatively small submerged vents on each side of the car. With experimentation you'd find that's not the case, and you'd probably need somewhat draggy ducts just to build up enough static pressure on the radiators to get a good deal of flow through them.

[bawareca]

I will just stick with what the BMW Motorsports did,I fully trust their design

[Def]

Is that their only radiator ducting, or is that for an auxillary cooler like diff/trans?

[bawareca]

That is a very good question.I always thought those are the water radiators,but looks like they are the tranny and diff coolers.

[Def]

That'd work fine for a diff/trans cooler since you'd be using just the fan suction for flow. Doesn't look like near enough flow area for a radiator that's not stagnating the free stream air.


I still don't think it'd do any favors to your downforce, especially with the sharp inlet angle on those coolers (possibly caused by packaging constraints). The flow is definitely separated leading into the ducting.

[bawareca]

I was thinking more of a drag reduction than of a downforce.But a straight duct thru the trunk with no restriction inside may work.

[Def]

I was thinking more of a drag reduction than of a downforce.But a straight duct thru the trunk with no restriction inside may work.

I'm not sure the work that would go into moving the air up and through the ducts would be much less than the static pressure reduction on the rear of the car (if that's what you're getting at).

It's really tough to beat a smooth underbody with a big diffuser to expand and slow down the flow for efficiency, and you create a deceptively large amount of drag trying to channel flow around different places.

[bawareca]

I hear you,but it is so much easy to make some ducting than to make a flat floor It is in my list for near future to do a flat floor from the rear seats back.But the real benefit with such a huge clearance car would be a complete flat floor that hangs a few inches from the body.Dreams.....