Re: 98 Passat Wagon - Helicopter mode

[Josh Pinkert <flush@us.net>]

At 04:30 PM 5/20/98 -0400, Don Hoefer wrote:
>
>John,
>
>> Has anyone else discovered the problem with the new Passat
>> Wagon's design?  If you have the sunroof open all the way
>> with the windows closed, and drive anywhere near 50MPH,
>> the air pressure pulses rapidly popping your ears HARD and
>> it sounds like a helicopter.
>> 
>> Do any of the Audi's have this problem?
>
>Oh yes.  Think of an organ pipe.  A long tube with a hole in it.
>It will resonate at it's natural frequency.  The bigger the pipe
>the lower the frequency.  Cars are pretty big.  My Coupe must do
>three or four hertz.  To stop the pipe from vibrating, drill a hole
>in it to set up canceling resonances, or open a window in the car.
>
>Don Hoefer
>'82 Coupe
>
>Massachusetts, USA
>

No problems on my A4q.  It's pretty silent at speed.

The problem is truly the resonance.  But I think the resonating piece is
the roof panel itself.  They're usually a little flexy and not very well
re-inforced.  With the sunroof open, try grabbing the edge of the roof  and
see how much it flexes.  If this were stiffer, it'd resonate at a higher
pitch...

 
--        
Josh Pinkert 
flush@us.net 
'98 A4q 2.8 
'72 911T 
--