Playing around with fans and blowers and yarn and such, I found that a long piece of thread inside the blowing end (reverse) of a shop vac gives somewhat of an idea on aerodynamic shapes around the car.
The thread can't be too long.... 3-4 feet or so... and there is some turbulance from the vac... but pointing the contraption at things like the mirror or the cowl gives an idea of what is going on there.
BTW, I did this a week or so ago and was not too sure of the hood result.... it seemed the airflow was center out quite a bit. But today I saw the same thing on the freeway with yarn taped to the hood.
Simple... not too precise... but when you see that thread sucked right into the cowl or that nice taper around the mirror followed by the nasty turbulance right behind it.... I think it provides some cheap and easy insight.
If, for some crazy reason, you want to try to smooth out the airstream some, you can bundle together soda straws and blow the air through them. That should give you a less turbulent stream of air. But, it may cut down on the flow too much.
I have a leaf blower here that I have thought about using to do the same thing you did with the shopvac. I am glad to hear that it seems to work.
Did you use a thin piece of thread or a piece of yarn?
Hey leaf blower great idea I have one of those too and it is variable so you can test at different wind speeds. We used to have a big squirrel cage blower that put out 60 mph wind in a 2 square foot duct that would work pretty good too - could do the entire front end at a lower speed maybe 20mph by the time it was spread out.
HAH! no!.. like geared to a wheel... Although the guy with the skateboarding speed record at bonneville (????) used a pulse-jet...
I'm building a powered skateboard to end them all... every powered skateboard up to this point has been bogus. I'm thinking less "powered skateboard," more "stand-up motorcycle." Fully suspended, with mechanically articulated steering. Another topic entirely, just... explaining.