NACA ducts in sport car flat floor

[Belatti]

Hi, what do you think about creating vacum in a sport cars flat floor using a couple of Naca ducts connected to the center of the rear brake rotors?

Has any of the aero guys from the forum have figures about the air flow that a 280mm brake rotor can suck at, lets say, 200rpm ?

Additional brake rotor data:
diameter 280mm
thickness 25,4mm
air gap 14mm
ventilation 14 vanes
inside diameter 190mm
flange thickness 6mm

Its the Brembo 09.5890.10/20

[Jersey Tom]

Not quite following you.. could you elaborate?

[tok-tokkie]

A NACA duct is an air inlet (to oil cooler for example) which does not cause turbulence in the other air flowing on past it on the outside. So I don't understand where a NACA duct fits into your proposal.
However using a ventilated brake disk as a centrifugal fan impeller is a novel idea. I think the problem will be with the small volume. Volume is proportional to the RPM, proportional to the Diameter ^3 & directly proportional to the vane width.

[ISLAMATRON]

great idea... I might try to incorperate that into my weekend racer

[Belatti]

A NACA duct is an air inlet (to oil cooler for example) which does not cause turbulence in the other air flowing on past it on the outside. So I don't understand where a NACA duct fits into your proposal..

It would suck some air that passes down the car helping to reduce pressure or reducing air impact before the rear wheel, without disturbing airflow to the diffuser.

However using a ventilated brake disk as a centrifugal fan impeller is a novel idea.

The ventilated brake disc its a kind of centrifugal fan, thats the way it cools.

I think the problem will be with the small volume. Volume is proportional to the RPM, proportional to the Diameter ^3 & directly proportional to the vane width.

Yeah, but considering the caliper, the rim, the hub and the air hose I wander if its worth it...

[DaveKillens]

It's a novel concept, and if the regulations allow, worth pursuing.

I have two doncerns however. First off, dust and grit from the road surface would be sucked into the brake ducting system, and possibly add to a lot of contamination of the brake disk and possibly the pads. Secondly, mass airflow would be in direct relationship with rear wheel rotation speed. Where you really need massive downforce is on slower, tight corners, and since the rear wheels would not be spinning at maximum revolutions, downforce is not as high as desired.

[Belatti]

Where you really need massive downforce is on slower, tight corners, and since the rear wheels would not be spinning at maximum revolutions, downforce is not as high as desired.

Yeah, but the same happends with ´conventional´ wings: they ´give´ massive downforce at 300kph but not that massive at 80kph...

Plus, the curves of this ´kind´of fan is not known for the things I mentioned above, so we dont know its efficiency with more or less rpm...

[marcello]

forgive my ignorance, but I thought that creating a vacuum underneath the floor by using turbines and such required sideskirts around the floor perimeter to seal the vacuum. Given the current regulations on minimum ground clearence, that would certainly not be legal. Furthermore, I thought the whole reason why the Brabham BT46B was banned was because it violated regulations regarding movable aerodynamic parts...

[Jersey Tom]

Still have no idea what this concept is. Using vaned rotors to suck air out from underneath the car?

[marcush.]

just an idea:
why not use this very concept to redirect airflow with raising speed ?
this way around you could possibly reduce downforce at highest speeds or tweek the position of centre of pressure with speed ....giving possibly new roads or opportunities in car setup ...

[Belatti]

forgive my ignorance, but I thought that creating a vacuum underneath the floor by using turbines and such required sideskirts around the floor perimeter to seal the vacuum. Given the current regulations on minimum ground clearence, that would certainly not be legal. Furthermore, I thought the whole reason why the Brabham BT46B was banned was because it violated regulations regarding movable aerodynamic parts...

Forget about F1 rules. This is "another racing series". I will quote myself

Hi, what do you think about creating vacum in a sport cars flat floor using a couple of Naca ducts connected to the center of the rear brake rotors?

The rules states 40mm ground clearence min and its not a novel concept, I have seen the naca ducts in the floor of cars that are 10 years old.

Still have no idea what this concept is. Using vaned rotors to suck air out from underneath the car?

Yeah, are we writing that bad?

just an idea:
why not use this very concept to redirect airflow with raising speed ?
this way around you could possibly reduce downforce at highest speeds or tweek the position of centre of pressure with speed ....giving possibly new roads or opportunities in car setup ...

Nice, but I´ll let that for more advanced series. I dont have a windtunnel, I dont have a CFD model, I dont even have a CFD software and I dont know how to use it, yet. The series is really a low budget one and testing time is shorter than short. Here developments come from the intuitive department

[RH1300S]

Neat idea.

Would you put it another way?

Why not say that you need to get air to the rotors for cooling and why not take it from an area of unwanted high pressure?

Another thought - is it more beneficial to create low pressure by using the discs or is it better to find an area of high pressure to feed the discs so that they cool properly? Will your brakes stay cool enough? My understanding of vented discs was that they needed a good feed of high pressure air (not that you couldn't find that under the car!) and the vanes dispersed the air between the disc faces.

At the end of the day - even if you don't exactly suck the car to the floor (which you probably won't!) - then you can at least relieve an area of high pressure under the car.

[xpensive]

Quite obviously, somebody needs to draft some ball-park numbers to get a feel for what we are talking about here.

If the vehicle is moving by 50 m/s (180 km/h or 112 mph), with a ground clearance of 0.2 m and a whidth of 1.8,
an air-flow of 18 m^3/sec(38 000 cfm) is passing by underneath it.

This has to be compared with the evacuating capacity of the discs, of which I have very little idea, but if you figure the radial air-speed the same as the peripheral speed of two 320 mm dia, 20 mm thick discs on 600 mm wheels you get a
total of 1.2 m^3 per second passing through the brakes.

Something like that, thoughts anyone?

[Belatti]

Why not say that you need to get air to the rotors for cooling and why not take it from an area of unwanted high pressure?

Because that is what the majority does in sportcars like LMP3 or alikes.

Another thought - is it more beneficial to create low pressure by using the discs or is it better to find an area of high pressure to feed the discs so that they cool properly? Will your brakes stay cool enough?

Yeah, they will stay cool. They stay cool even without ventilation in a 35c day. The whole system was not working properly but it will since Im planning different discs, calipers, pads compounds and brake pumps. Then they will need cooling -but not too much- for a very light car with little downforce that wont let braking at more than 1.8G.

[RH1300S]

Do the discs actually 'pump' air?

Could you rig up something so that you could attach a flexible duct to the inside of the disc (just have the free end somewhere you can feel/measure any flow) - I'm sure you could make up a box in cardboard to seal off the driveshaft etc as you would have to if you made the thing properly. Have the car wheels off the ground and run it in gear to a decent roadspeed? If it's pumping anything surely you could measure/feel the flow into the duct.