OK, I'm out of pocket for part of the circuit hire and a video camera that
fell of the back off the ute at 40mph, but the results were interesting.
To get a baseline look at the airflow over both our cars (a '97 SX and a '95
MR-2 Turbo) an R-33 GT-R, R-32 GT-S and a (domestic) '96 Ford Falcon XR-6.
1. Rent a race circuit. You could do this on a public road, but the
police will probably take a dim view. We used a circuit about two hours
from Sydney that is only used these days for club racing. The main straight
is about 800 metres long.
2. Load a utility with a small petrol generator (to power the smoke
machine) a stage-type smoke machine with a long boom and nozzle (made from
conduit and garden hose). A smoke operator and someone to hold a video
camera (more on that later)
3. Drive the car under test and the utility on the main straight and
record the flow by locating the smoke at various parts of the car. High
speed is not required to achieve this. The highest we saw was about 80Km/h
(45mph). The video camera is used to record this.
Unfortunately, the video camera was dropped from the vehicle at about
70Km/h... Trust me, there are lots of pieces in those things :) However,
we continued to observe and found the following:
1. The S14 seems to have a very clean shape. The flow of the smoke
tracks nicely, but parts about halfway down the back window. There's a
"dead" area below this, so I'd conclude the rear spoiler was never
aero-tested, since it doesn't seem to do anything at all. We'd need to get
it a fair amount higher and probably increase the angle of attack. The
car's "wake" is also very low and quite small. The front spoiler seems to
also have no real effect.
2. The MR-2 is not as clean, with the flow parting at the top of the rear
window. We'd need an enormous wing at the back to to get it up into the
airflow. However, the front spoiler does a lot to deflect air away from the
underside of the car. The little "lip" on the front spoiler is quite
effective. It's wake is very pronounced, possibly because of where the
airflow parts company.
3. The GT-S was somewhere between the two previous cars. Phil's car had
the "Silvia" style rear wing rather than that more overt "GT-R" style.
However, the front spoiler does a very efficient job of diverting air. It's
mirrors generated the biggest turbulence of all the cars we tested.
4. The GT-R flows air in a very similar fashion to the S14, but it's
higher (and adjustable) wing does have a visible effect. I would guess that
the engineers simply raised it until it started having an effect they could
measure. The rear wake was changed a fair amount by changing the angle of
attack of the wing (as you'd expect). The front spoiler was also effective.
5. The Falcon was the biggest car of the lot, but also suprisingly clean
(which probably accounts for it's low wind noise inside). Interestingly,
the "little" wing on the boot (no higher than an S14) was actually IN the
air stream. The is probably because the high boot angle on the car.
Finally, take it easy on the smoke mix. The oil used is a pig to get off
the car if you use too much of it.
All in all a very interesting day. I just wish I had some images left to
show for it.