mazdeuce - Seth said:
In reply to sleepyhead :
A rear diffuser and semi/completely flat bottom is part of the plan, long term. As I understand it, the advantage to a diffuser is that it's basicaly "free" as far as drag is concerned. The down side is that it's not very tunable without building several of them and testing. So you build one and you get what you get and balance that with other aero on the car. Reading says that the effectiveness goes WAY up with a flat bottom, but a flat bottom is a bunch of work and means that the air that's currently exiting behind the motor and out the bottom of the car needs to go somewhere else. There are BIG chunks of frame rail aft of the wheels to the fire wall, it's not like an Insight, so it's going to take some thinking and testing. The good news is that low power means low heat relatively speaking.
So it's gong to need a wing at some point for tunability, but a diffuser should mean less wing and less drag. Right now I need to get alignment and brakes where they need to be and see how time is progressing. Actually, right now I need to go work on the kitchen.
yeah, a diffuser is generally "free" from a drag perspective... since you're essentially* giving the air from under the car a "more ideal" path to meet up with the air coming from the top of the car. It's very analogous/similar to the rear upper surface of a wing.
*cars are highly 3-dimensional objects from an aerodynamic perspective... so it's not that simple
you could tune it if you mounted the front edge in a way that it was supported but still allowed to... bend (?) so that you could have adjustable length mounts for the rear top side so that you can adjust the angle. The tricky part is sealing the edges of the "flat" part with the vertical sides.
if you're limited to a front splitter, and a rear diffuser... with "OEM" in the middle... you could probably make the rear diffuser more effective by loading up the rear edge of the front splitter with VG's to help the the flow "jump" the disturbed middle section and re-attach on the diffuser. I'll see if I can dig up the drag of a cylinder vs. a cylinder with a plate behind it... it's kinda similar.
mazdeuce - Seth said:
In reply to sleepyhead :
that the air that's currently exiting behind the motor and out the bottom of the car needs to go somewhere else. There are BIG chunks of frame rail aft of the wheels to the fire wall, it's not like an Insight, so it's going to take some thinking and testing. The good news is that low power means low heat relatively speaking.
One thing to keep in mind is that you're kind of confusing two things together. The main contributor to "air in the engine bay that needs to get out" is really the radiator... and the fact that the front end around it allows a lot air to seep around the radiator and into the engine bay. Now, the exhaust and block certainly does heat up the air... and blocking off the engine bay will require more cooling... and/or wrapping the exhaust back to behind the passenger cabin. But some of this could be mitigated by more strictly controlling the radiator flow... which generally would also help generate more front downforce, since you'd be ideally directing the radiator's exit flow upward.
will it need a wing eventually? sure... I mean, even the Nissan GT-R LM Nissmo had a rear wing. After all, a rear wing can actually help produce more front downforce be creating a higher low pressure at the back end of the car which helps draw more air over the front splitter.
it's all a system
