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Anyone have Aero questions?


@NineLivesJohnny
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When you use the term "lift" does it always mean lifting the vehicle or does it sometimes mean airplane wing lift, which in the case of an upside down wing would mean downforce? I've seen the term "lift" used in context with you and other manufactures and it would sometimes seem to mean downforce.

 

If you compare wings of different widths (with the same cord), do the downforce/drag ratios stay pretty much the same? Comparing say a 55" to a 70" width.

 

I'm trying to calc what a 55" wing would do compared to 70", would it be accurate if you reduced the downforce number the same as the percentage of width difference?

 

Does a rear diffuser work with no undertray?

 

Does the general rule of a splitter, that it should go back to at least the front axle line, apply to a rear diffuser, that it should go forward at least to the rear axle center line?

 

Would an undertray work if it had a longitudinal gap in the center? Say a big gap for engine trans exhaust diff. So it would be like 1/3 of car width on each side and a 1/3 width gap in the center. These things are already running hot and closing it off would cause heating problems.

 

Trying to quantify the drag number in the charts that is given in pounds. Is this like pulling the car backwards with that many pounds of force?

 

Any thoughts ideas on the aero on this car? It's not my car but similar to what I want to build.

z32.jpg

Edited by Dimsun Racing
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On 3/2/2021 at 7:43 PM, Bandit said:

ot popped for using brake duct fans for downforce. Those guys are looking for the tiniest advantage so while it may not be noticeable, it may be measurable.

 

Teams across the board were doing this, huge 60+ amp 3" fans blowing air from an undesirable area out to a more desirable area. 3" fans are typically "brake fans" but were often installed in other areas. 

 

Keep in mind these fans were generally used to induce more flow in a direction that it would already go, or to create a high pressure zone to limit flow into an undesirable area. The amount of power required to move the air in a direction it does not want to go, because of a big pressure differential, can be many multiples bigger. 

 

For example if you take a hood and cut hood vents in the right spot, you will get a downforce gain with no motor being used. If you add a small fan to help pull more air out through that opening, you might get a small gain.

 

If you try to use that small fan to blow the underhood air out a hole cut in the front airdam, past the high pressure airstream of the car, the fan might actually lack enough power to even stop the air from flowing into the duct (let alone even push a single molecule out the airdam hole). With enough HP you could make this work.......

 

Fans to help flow, much easier than fans to MAKE flow.....

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When w were running in the NCATS series we had an incident at Mosport that resulted in an engine bay fire and had to get a local shop to repair the car (eastern race) in time for the Toronto Indy weekend. Checked out the repairs, warmed up the car and went out for practice.

 

The driver reported that the electrical went out and he had smelled something at the same time. The car was towed in, found a couple blown fuses, checked for shorted wiring, replaced the fuses with paired circuit breakers of the same amperage and tried again. No dice; same problem, car quit on the main straight. Practice was ending so took a chance and bypassed the circuit breakers. Same result but this time with melted wires.

 

We had a couple of hours before qualifying so we could check things more carefully. Found out the other shop had wired the rad fan backwards during the repairs. Fixed that, rewired the dash as we were waiting for our turn to qualify. I had a very nervous driver as I worked upside down in the car to do the wiring while in the line-up and getting pushed forward. As we reached the front of the line, I did the final connections and climbed out of the car in time for him to get in and head out for the session. No more problems that season or the next three.

 

The reason: the rad fan was being pushed backward by the air flow through the rad at speed and acted like a generator. 

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  • 4 weeks later...
On 3/2/2021 at 5:45 PM, Bandit said:

Out of curiosity, any idea what the CFM flow created by fans would be required to make measurable downforce?

 

Say a guy was to lay his radiator flat, parallel with the ground, integrated into the splitter, and run a 8000 cfm rad fan on it. Noticeable gain or not likely?

 

Off to see if the cfm rating of Jim Hall's fan is stated anywhere...

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The more the better I would think. I asked the guys to do some CFD testing with brake fans, to see if cheap fans would have a noticeable difference. then covid hit and we became super busy.  

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On 3/11/2021 at 2:11 AM, Dimsun Racing said:

When you use the term "lift" does it always mean lifting the vehicle or does it sometimes mean airplane wing lift, which in the case of an upside down wing would mean downforce? I've seen the term "lift" used in context with you and other manufactures and it would sometimes seem to mean downforce.

 

If you compare wings of different widths (with the same cord), do the downforce/drag ratios stay pretty much the same? Comparing say a 55" to a 70" width.

 

I'm trying to calc what a 55" wing would do compared to 70", would it be accurate if you reduced the downforce number the same as the percentage of width difference?

 

Does a rear diffuser work with no undertray?

 

Does the general rule of a splitter, that it should go back to at least the front axle line, apply to a rear diffuser, that it should go forward at least to the rear axle center line?

 

Would an undertray work if it had a longitudinal gap in the center? Say a big gap for engine trans exhaust diff. So it would be like 1/3 of car width on each side and a 1/3 width gap in the center. These things are already running hot and closing it off would cause heating problems.

 

Trying to quantify the drag number in the charts that is given in pounds. Is this like pulling the car backwards with that many pounds of force?

 

Any thoughts ideas on the aero on this car? It's not my car but similar to what I want to build.

z32.jpg

That depends really. 
we where testing diffusors quite alot of diffusor set ups and it all depends on what's up stream. 

 

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