[Richard O'Clery]

Good aero stuff guys.

In addition, you can exit some radiator hot air out of the front wheel wells/arches if you have too much for good reattachment over the windscreen, but may have to be careful about increasing drag at the sides through flow separation around the car. Not much of a problem with a road car if the sides of the car are draggy anyway (ie big wheel arches, mirrors, vents etc) in the quest for a really cool looking machine. Minimising side drag (for want of a better expression) lead to the really ugly slab sided sports racing cars of the 80s and 90s.

In principal, a flat undertray should be included with as big a rear diffuser as possible, noting the gearbox will take up a fair amount of room at the back. But, if we find we are limited with the amount of front downforce available because any more makes too much drag, we will need to tune down the rear diffuser/spoiler. One way to keep good (fairly) smooth airflow under the car, reduce the downforce of the diffuser, and add cooling air to blow the engine bay is to use inverted NACA ducts near the transition from the flat floor to the diffuser (ie behind the seats). Everything comes at a cost though, because the extra air going out of the rear mesh will add drag by interfering with the reattachment of the air between the diffuser and our (well designed) spoiler, unless it is carefully vented and accelerated to smoothly join the airflow at the upper surface. Like suspension, in practice aero will always be a compromise. Particularly on a road car.

You can also use some of the air coming in under the front of the car by sloping part of the undertray up at the front across a proportion of the width of the car. This increases front downforce, but the air has to be managed as it makes its way towards the diffuser. You can use its own increased pressure to vent some out of the sideskirts with vanes or vortex generators... To complex for our budget? Maybe, but you can get the basics without a wind tunnel by using transducers to measure the relative movement of the shock absorbers as speed increases to work out approximate front and rear lift ratios, and then play around with aero ideas until the balance is good. Too much drag? Make more power! (sorry).

Howard, I will concede 2400lbs (1090kgs) until I finish my car as Australian Design Rules compliant and have it on the weighbridge. Unfortunately, I do have a sneaking suspicion your weight estimate will be pretty close to the fact once the climate control, power windows and comfy interior are added...