Photographing Tuft Testing - interference from camera truck?

[brucepick]

I lined up a buddy at work to drive his van alongside my Civic to shoot tuft tests of the Kamm roof extension.

Will the van interfere with the air flow and mess up the tuft testing?

[There's a thread for project at http://ecomodder.com/forum/showthrea...upe-18906.html, so I'd like to limit this discussion to tuft testing please.]

[ecomodded]

That looks like it is going to work well it retains a clear view out the window as well, that is important.

I have never tuft tested so not speaking from personal knowledge but i did find a video that may put your concerns to rest.
http://www.youtube.com/watch?feature...&v=4dx1vWLM6A8

[Cd]

I know nothing of aerodynamics , but when I did my tuft testing, I had the chase car at a normal distance and passed me as my car was driving in the other lane.
There was no interference drag that I could see.

http://ecomodder.com/forum/showthrea...ack-21527.html

No other traffic was present at the time of my test ( perhaps one or two that passed by in the left lane .
)

Of course no interference drag will be present from the tailing vehicle, and I would guess the only time you have to worry about the interference drag is as the chase vehicle approaches the front fender of the car being tested.

[Cd]

BTW, speeds in the above test were approximately 40 mph, and the chase vehicle was a Saturn coupe.

If you haven't done the test yet, I'd like to suggest adding tufts at the C pillar and trailing on down to the edge of the trunk/boot.

Of course a visible color of yarn is preferred. When I did my test, I found that using super small diameter line ( "string "? ) seemed to give better results than actual yarn, since the yarn has " hairs" which stick to one another and cause drag from the yarn itself .

I used line that was perhaps 1/ 16 " or smaller, and no longer than 3 1/2 " - 4 "

Any longer and the line gets flutter which skews the results.

( I tested several colors for visibility as well as different lengths and materials - yarn and line.

[aerohead]

In wind tunnel testing it is recommended that the vehicles frontal area be no more than 5% of the tunnels test section cross-section to minimize 'wall' effects.
Also,when a vehicle is next to you,a venturi is formed between the two vehicles,accelerating the air to a lower pressure and higher velocity which could impact your results.
I would recommend as large a clearance as legally possible and still maintain your 'shot.'
Gran Prix drivers can sense a change in handling characteristics of the car when structures are within 30-feet.