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Re: OT Physics Problem



On 4 Feb 2003, at 11:36, Bob Schmidt wrote:

> While mobiling over the weekend, I developed light rime ice at the leading 
> edge of my Hustler and commercial AM/FM antenna.  This appeared to set up 
> an oscillation in both antennas that was at right angles to the direction 
> of travel.  This does not occur without the ice build up.
> 
> Since we have many physics oriented folks on the list, I thought someone 
> might know why this occurs.
> 
> Thanks
> 
> Bob, WA9JDR

My OT explanation

Ice forming is not equal or even over the surface on the antenna as the wind flow hit the antenna these 
surface difference deflect the air flow unnevenly causing the antenna to move a bit on a side and a bit on 
the other side perpendicular to the vehicule motion. This start an oscillation like a pendullum reduce the 
speed the oscillation lenght will reduce increasing the speed the oscillation will increased.

You will see the same oscillations in dense fog this time it is the fine water mist who are responsible for 
the oscillation because they are not hitting the antenna evenly on the surface.

You will not see this phenomenon in a snow storm snow cristal are to heavy and they are only crashing 
on the antenna bending it backwards. Air flow alone is well distributed and will only bend the antenna 
backwards due to air resistance and pressure developped on the antenna.

These oscillations swing the antennas so strongly that i remember reducing my speed afraid of damaging 
the antennas. But i guess car engineers figure out the whole affair and calculate and design the antenna 
to be unbreakable...


Luc Leblanc VE2DWE (AMSAT 33583)
Coordonnateur AMSAT pour le Québec
Quebec AMSAT coordinator
SITES WEB:http://www.sorel-tracy.qc.ca/~luclebla/
          http://www.qsl.net/ve2dwe/
C.P.341
Sorel-Tracy QC.
Canada
J3P 5N6


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