Porsche Aero
How come you criticize the 911's brakelight
for separating the flow at the top of the rear windscreen, and then later in the
same article conclude that the beetle would be improved by having a tiny spoiler
to cause separation at exactly the same location? It seems to me that Porsche
used their brake light to do exactly the aero mods that were needed.
Patrick McAuliffe
Australia
The Porsche needs airflow to the rear
intercooler inlet.
LPG Oxy Welding
Your article on
oxy/acetylene welding was excellent as usual, but I thought I'd suggest an
alternative that I have been using for years - oxy/LPG. Oxy/acetylene can be a
dangerous system to uses as you mentioned, especially if no anti-flashback
devices are fitted (and for home/casual use they remain expensive).
I
rent just the oxy bottle (so saving the cost of acetylene and the bottle rental,
which is high for casual users) and use standard 4 kg or 9 kg LPG gas bottles -
with my BBQ bottle always available too if I run low and LPG is available 24x7
in most places.
Easier to light, safer to use and the temperature
difference is bugger all for most applications - and an advantage when using on
thinner materials. Oxy/LPG is plenty good enough for cutting jobs too I have cut
through large RSJ beams and 16mm steel plate with little effort, nearly as fast
as with acetylene and with less distortion.
To use LPG you have to get a
new nozzle for your cutting head (at around $40-50) and sometimes an adapter for
the bottle so the regulator screws on correctly. The standard oxy/acetylene
regulators work fine as do the standard flame nozzles. I have been using my CIG
Comet 3 system for more than 15 years doing all sorts of work and have had no
problems.
Steve Blume
Australia
Aero Testing
I was wondering if you
guys could do some wool tuft testing on a car that has no spoiler and then again
on the same car but with a spoiler. or if you guys can show a car that has an
aggressive looking body kit and wool tuft test that car and then do the same car
stock just to see if it really does affect the aero performance. i just think
itll be cool to see. :D
Steve Dogg
Canada
We haven’t done this in AutoSpeed but we did
exactly what you suggested for a previous magazine. After the kit had been
fitted it looked better in the wool tufting but a professional motorsport driver
could tell no difference on the track. Fuel economy? We don’t know.
Vortex Generator Inventor Comments
I just read your road test article on Airtab
VGs. My compliments on your work and photos! It was an unusually good article. I
am the original inventor of Airtabs (originally called Wheeler VGs or Wishbone
VGs in various NASA WT reports) and sold the rights to some good friends I met
while lecturing at U.S. Navy Test PilotSchool, who then formed Airtab back in
the early 1990's. Prior to that, I had over 600 hours of wind tunnel occupancy
hours working with them and can add some comments you might find
interesting.
I have a couple of comments:
1) The slight
"outward-pointing position" of the lower outboard tufts on the rear window of
the Prius probably does not indicate ordinary flow separation. It is more
likely the case that the tufts are positioned along the edge of a large
rotational flow caused when the side flow is pulled inboard as it exits the
slanted C-pillar (due to the low static pressure on the rear window). Ordinarily
a large, slow-turning vortex is formed there and it will be particularly strong
if attached flow is created over the entire rear window. If the lower corner
tuft fluttered wildly, then the flow is separated. If it merely angles
sharply outboard as shown in the photos, then it is being swept there by
the slow-rotating C- pillar "vortex".
2) I consulted to GM on their
Aero 2002 and used my VGs along it's trailing edge just like you used them on
your Insight, and we achieved the lowest "unpowered" Cd I know of on a driveable
automobile. (I say "unpowered" because the Ford Probe-5 recorded a lower figure,
but only with high-powered fans located in the trunk that sucked air in from the
rear quarter panels then blew it out the rear. As far as I'm concerned, that
doesn't count, because if enough power is supplied to the fans, the Probe-5
could record zero aero drag or even positive thrust!)
Regardless of that,
to be honest, the gain on GM's Aeros 2002 was miniscule because of the small
base area. Similarly, the Honda Insight is not a suitable vehicle to test the
base pressure drag alleviation capabilities of the VGs. The base area of such
cars is so small the parasitic drag of the devices will approximate the drag
reduction achieved. This application for VGs should be tested on a
hatchback or van where the base area is a very large fraction of the car's
frontal area. Then you should see some nice results. (If you Email me at my home
I can provide some very convincing wind tunnel data proving Airtabs can reduce
base pressure drag from both Lockheed Georgia WT on a full size 1982 Honda
hatchback and 1984 McDonnell Douglas, where we spent a month evaluating them on
a truncated external fuel tank for the F-15.)
Gary Wheeler
United States
|