REFLECTOR: Pitot static problem

[Laurence Coen]

BlankI have a Kolsman, shark fin pitot static probe on the nose of my plane. 
I have determined that the static port is not usable in this configuration. 
Apparently the pressure wave extends enough ahead of the nose to cause a 
static error of approximately 0.25 psi at cruse. This in turn drops the 
airspeed indication some 30 to 40 knts and lowers the altitude by over 500 
feet.  My first attempt at a fix was to install a safety wire "bump" ahead 
of the static port.  This reduced the altitude error to about 150 feet but 
created a new problem.  My IAS for went from 60 knts to 70 knts for Vso. 
This means that my true speed is 10 knts slower that the IAS.  A feller 
could get hurt that way.  After looking at a number of pictures of 
installations of this type of probe it became evident that it needs to be 
mounted on about a 3 foot boom.  Not what I wanted to do.  I installed a 
static port beneath the pilot side door.  Now both air speed and altimeter 
are behaving as they should.

Larry Coen
N136LC
SE/RG Franklin/IVO

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