Guys, I am astonished to hear anyone advocating a protruding static port and especially for the purpose of sticking out of the boundary layer.   I worked on the critical altimetry for reduced vertical separation minimums at Boeing in the mid-90s and on air data systems at General Dynamics (now Lockheed).  On every airplane and missile design I've ever worked on, the only reason to make a static port anything other than perfectly flush was to insert a correction if the static port was located in a place where the local pressure was different from ambient pressure.  Projecting anything with an edge or corner out of the boundary layer was guaranteed to produce local separation and vortices with unpredictable and probably inconsistent effects on the measured pressure.   On Boeings, we even went to great lengths to measure and minimize skin waviness for 10 feet ahead of the static ports.

The static pressure gradient across the boundary layer is generally accepted to be negligible.  A protruding static port will probably measure pressure that's a little lower than the local static pressure, which is acceptable only if the port is located in an area with higher than ambient pressure.   Perhaps Paul's RV ports were located in such an area.

Lancair tech support (whoever it was who answered the phone in 2008) told me to make them flush.  I presume that the port  position that they identified on the Legacy is where the local Cp is zero, i.e., ambient pressure.  At any rate, my flush ports seem to work fine.  If you have a Garmin, a good test is to fly a closed course and see if the deduced wind value is consistent on all headings.  If it is, then a number of things (magnetometer alignment, pitot pressure, static pressure, and OAT) are working correctly. Charley Brown
Legacy #299  200 hr


On Jan 21, 2013, at 7:06 PM, Paul Besing wrote:

Yes, it has to protrude out about 3/16" on average.  I had this exact problem with my RV.  I decided I wanted a nice flush look and my airspeed were very inaccurate until it was discovered that they needed to come out of the boundary layer. --
Paul Besing
"Flying releases the mind from the tyranny of petty things"



On Jan 22, 2013, at 1:25 AM, Dan Ballin <dballin@gmail.com> wrote:

Needs to protrude a little for paint/body work and then there is an
argument to have them stick out slight more to get out of the boundary
layer.  Others can comment on that, but I would recommend using the
Evo static ports.  KCI part number KA0075.  Way nicer and have a
standard NPT thread so easier to install and you can install it after
paint.

Dan
N386DM LEG2



On Mon, Jan 21, 2013 at 11:47 AM, Jeffrey W. Skiba <jskiba@icosa.net> wrote:

on page Chapter 24 REV. 0/02-15-02 of the Legacy RG construction manual,
gives directions for the static ports, however it does not state if they
should be flush with the skin or slightly protrude ? if they need to stick
out Is there a max and a min suggested ?



Thanks

Jeff.

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