Aerodynamics Question - Calling all racers...

[fastx19]

Hi.

On our current race car, the shroud behind the radiator has been removed and as such has left a rather large opening into the trunk. Well, people have suggested I should create some type of duct system to get the air out of the trunk(boot) or it could create a lifting effect at higher speeds.

I will be running this car frequently above 100mph.

So, my question is around the shape of the duct. I was going to follow a standard Dallara mod and duct it out near the front of the car.

However, my dad was over and suggested I make it longer and vent out near the window instead.

See the following pic

What are your thoughts? I could see how the longer vent would allow some potential of tuning the down force..

Eric Armstrong

 

[indigoth]

most that I have seen cut holes in the trunk hood and the air moving through the radiator goes over the trunk and over the windshield. from what I understand, tho, that's an illegal mod for racing. an opening into the wheel wells was also discussed which is supposed to be a legal mod. it doesn't increase the downforce on the front end, but it does tend to reduce the front-end-lift effect of the stock configuration.

jim

 

[fastx19]

Rules...

Are for sissies!

Actually, we are going to run in Amod which allows for almost anything. This car is being built primarily for hill climbs only.

An occasional Autocross or Open track day, but those will be for fun, not points.

Eric

 

[bill]

aerodynamics

aerodynamics of the standard car are pretty good to start with but in order to do improvements witch involve new ideas so to speak you need access to a wind tunnel you might end up hurting them instead of making them better. a inch can affect them i would stick to the dallara ones they have or at least i hope they have a wind tunnel also cross winds can be a issue to. aerodynamics are not a easy one to alter on the x1/9 some stuff is a no brainer like tailgate on a truck or keeping the roof on the x1/9 but this is a tough one. just my:2c:

 

[DougESmith]

What about this

I have always wonders about using the original shape of the front and trunck to creat ducting that turns the nose into an upside down airfoil creating down force. You could maybe even hide winglets inside the ducting for more down force.

 

[AngeloX19]

Take this as an opinion, but most of it comes from an aerodynamicist who designed aircraft before going on to work and design bodywork for Daytona Prototypes and other racers. I followed his suggestions. First make sure the duct is sealed so air cannot escape under the car. Having the opening closer to the nose versus further back increased the pressure differential and helps with through flow. A radius on the exit helps with flow as well. As does a narrowing duct on exit. I'm not sure about a curved duct. Here's a pic of what my friend made. Maybe try googling vented hood pics?

 

[bikesandcars]

Most racers have a fuel cell / fuel pump and re-located brake reservoirs in the trunk area.

Every racer conversion I've seen (including our lemons car) has cut and bent the original radiator baffle backwards to vent the radiator upwards (as in that pic above) and create a relatively tight compartment (shrunken trunk) for the fuel cell. conveniently, the hood is braced so that it allows 2 cutouts to be made in the sheet metal for the venting without having to compromise hood strength.

I've always thought about adding a 1 inch high metal strip before the exit on the hood to create a little more vacuum, but there was plenty of cooling without it.

We also fitted a front splitter that runs under the radiator and forward to force air up through the radiator and out. It probably promotes a little downforce, but it's mainly there to enhance cooling.

I think with a big hole and no exit it create's useless drag. creating a vent behind the radiator will reduce this drag. To create downforce you would need to lower the car and put a splitter on to force air that would normally go under the car to go over the car.

To really get aggressive you could make a sheet metal ramp from below the radiator to the firewall, and remove the hood