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Date: Mon, 21 Jan 2013 22:42:29 -0500
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Subject: Re: [LML] Re: the Legacy RG Static ports
From: Charles Brown <browncc1@verizon.net>
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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. =20

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.=20

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.=20


--
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.
>=20
> Dan
> N386DM LEG2
>=20
>=20
>=20
> 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 ?
>>=20
>>=20
>>=20
>> Thanks
>>=20
>> Jeff.
>>=20
>>=20
> <Screen Shot 2013-01-21 at 11.57.56 AM.png>--
> For archives and unsub =
http://mail.lancaironline.net:81/lists/lml/List.html


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