Aerodynamics Resource Thread

[Rakuny]

hmm, well I can see that it is attached to the fuel tank guard, but it looks flat to me in the picture.

is there a small angle there as well?

[Erron Spalsbury]

There is. It's only a few degrees if you measure it from the car, but with the cars rake, it's about 7.

[J. Fast]

It's a shame this thread didn't go any further. Would anyone be interested in posting up their home-brewed examples and reasoning for aspects of design/effectiveness
What do you guys think about using Alumilite or Dibond sheets for splitter/diffuser making?
Our gas tank is very much in the way as far as having a diffuser goes, would it be better to have a little less angle and be able to extend the diffuser a bit more past the ending of the gas tank?

As it relates to our cars and is quite helpful here's some stills I took from my PRM racecar video subscription on U-Tube and ninja edited... You can just stare at them... stare some more... and stare some more. That's what I did. Then I went and bought some material and built some shit. I don't have all the pics loaded ATM but you'll get the point.





Now, to answer your question regarding utilizing Alumalite... I used Econopanel (alumalite is the same thing) for my entire under tray. I selected it because it's lightweight, rigid, durable, and a good way to go if you're in the trial and error phase of setting up your aero. It's relatively inexpensive and quite easy to manipulate also.






As for my undertray. I've 1 1/14" stand-offs secured to the bottom of the cab of my cars which allows me to affix econopanel to.



This is underpanel sheet





My input on your question regarding rear diffuser angles? When I first started researching and reading about aero several years ago at 3stech I was caught up on ideal aerodynamic angles, geometry, and so forth. I came to discover you really can't be dead set on them. What we're really looking for is effective airflow management and maintaining pressure/airflow separation under the vehicle. Be critical of the entrance and exit regions at the under tray and ensure air moving in the laminar flow direction remains uninterrupted. The biggest hindrance to the effectiveness of the under tray are not the entrance and exit angles (unless they're too extreme), typically its lateral wind shear and tire scatter. Therefore, IMO, what's most important over the entrance and exit angles of the splitter and rear diffuser is the presence of end fences. The end fences provide separation and block airflow/pressures not in equilibrium, or traveling in the laminar direction of flow, from interfering with the airflow from the entrance to exit at the under the body.

Worry less about the angles at the splitter and diffusers entrance and exit (somewhere between 1 degree and 10 is great and generally wont stall) and spend more time on pressure region separation from the sides and tires. You will get the greatest net gains for downforce and drag reduction if you focus more on those two things.

The entrance to exit transition at the underbody should be smooth and free from voids and gaps. Those two things create space for low pressure to migrate to because it's the path of least resistance. They break up the laminar flow column and cause stalling.

Flat bottom, no voids, smooth transition from entrance -> to under tray -> to exit for introduction of air to underbody and onto the rear diffuser. Use end fences to block flow from outside airstream. End fences... to work effectively for tire scatter need to extend to at least where the rims meet the tires. The end fence should at minimum extend verticall into the underbody to the same finish plane of the rim/tire bead.

Hate to say it because I myself don't post some stuff because of it but... as it applys to aero, when you don't have a wind tunnel... Take something that's working and tested for someone else on your exact same car and PLAIGARIZE!