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Date: Mon, 20 Aug 2012 18:44:42 -0400
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From: Sky2high@aol.com
Subject: Re: [LML] Re: Question about TAS Error (and Winds Calculation) based on OAT (...
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Tim,
 
Yeah, get it accurate because there's even more to it than that.   Sometime 
before the Phase I flight testing was completed and every two years  
thereafter the FARs require testing of the static system, the sensitive  altimeter 
and the pressure altitude encoder used currently for transponder Mode  C 
replies.  However, while that ensures the integrity and accuracy against  test 
data, there is no in-flight check on the accuracy of the static port and  
system for vertically locating the aircraft.  
 
Some of this will be interesting with NEXGEN (ADS-B) since the  precision 
WAAS GPS will provide data for locating the flight on the "globe"  model used 
by all the other aircraft in your traffic 30 NM hockey  puck and as 
broadcast on ADS-B Out.  Of course, if flying below 10,000 you  may be relying on 
some other guy's crummy Mode C approximation of his  altitude.   True Speed 
will also be taken care by the GPS data for  your "force" vector.  (Eerie, 
eh?)  Oh, that's right, the wing only  cares about accurate indicated airspeed 
to hold everything up........
 
Uh, I'd get the static fixed so it was right.  Maybe fly level with  
someone's certificated craft in formation and compare (altimeter error  adjusted 
by each guy's logbook entries).
 
Grayhawk 
 
 
In a message dated 8/20/2012 1:03:49 P.M. Central Daylight Time,  
Tim@myrv10.com writes:

Exactly...and so would be wind display and things that rely
on  getting an accurate TAS.  That's why I actually change ports
to get  the error low.  I don't know that without a lot of work
a person can  guarantee static port accuracy down to the 0-1kt
range, especially when it  changes with cruise speed, but I
think it's very worthwhile to try to  minimize the error.  As
Grayhawk says, if it is static error, it could  mean altitude
is off by a long ways too.

There are ways to do things  like build up little dams in front
of or behind the static port, to test  what effects you can
have and make it read accurately.  The first step  though
would be a good leak test.  Once you know the system is  tight,
and you make sure your OAT probe is accurate and all the  puzzle
pieces have been inspected, it isn't too big of a problem to
just  troubleshoot port location error. It does take a few test
flights, but this  is what I see as our responsibility as homebuilt
pilots...to make sure we  can match quality and standards to
certified levels.  What I find is  that if you do the
diligence on your systems, it will pay in rewards of  everything
working well and being accurate.

Tim


On  8/20/2012 7:07 AM, Sky2high@aol.com wrote:
> If your static port is off,  so is your indicated altitude - by a
> lot.................
>  Grayhawk
> In a message dated 8/19/2012 1:19:03 P.M. Central Daylight  Time,
> Tim@myrv10.com writes:
>
>     Could  it be static error...maybe port location, or other?  Mine  was
>     off by 8 kts (reading low). A rework of the  port to a domed one and
>     my error is now 2kts  low.  But, depending on your particular port
>      issue if any, yours could be reading high.
>      Tim

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<DIV>Tim,</DIV>
<DIV>&nbsp;</DIV>
<DIV>Yeah, get it accurate because&nbsp;there's even more to it than that.&=
nbsp;=20
Sometime before the Phase I flight testing was completed and every two year=
s=20
thereafter the FARs require testing of the static system, the sensitive=20
altimeter and the pressure altitude encoder used currently for transponder =
Mode=20
C replies.&nbsp; However, while that ensures the integrity and accuracy aga=
inst=20
test data, there is no in-flight check on the accuracy of the static port a=
nd=20
system for vertically locating the aircraft.&nbsp; </DIV>
<DIV>&nbsp;</DIV>
<DIV>Some of this will be interesting with NEXGEN (ADS-B) since&nbsp;the=20
precision WAAS GPS will provide data for locating the flight on the "globe"=
=20
model used by all&nbsp;the other&nbsp;aircraft in your traffic 30 NM&nbsp;h=
ockey=20
puck and as broadcast on ADS-B Out.&nbsp; Of course, if flying below 10,000=
 you=20
may be relying on some other guy's crummy Mode C approximation of his=20
altitude.&nbsp;&nbsp; True Speed will also be taken care by the GPS data fo=
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your "force" vector.&nbsp; (Eerie, eh?)&nbsp; Oh, that's right, the wing on=
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cares about accurate&nbsp;indicated airspeed to hold everything up........<=
/DIV>
<DIV>&nbsp;</DIV>
<DIV>Uh, I'd get the static fixed so it was right.&nbsp; Maybe fly level wi=
th=20
someone's certificated craft&nbsp;in formation and compare (altimeter error=
=20
adjusted by each guy's logbook entries).</DIV>
<DIV>&nbsp;</DIV>
<DIV>Grayhawk&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>
<DIV>In a message dated 8/20/2012 1:03:49 P.M. Central Daylight Time,=20
Tim@myrv10.com writes:</DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: blue 2px solid; PADDING-LEFT: 5px; MARGIN-LEFT: 5px">=
<FONT=20
  style=3D"BACKGROUND-COLOR: transparent" color=3D#000000 size=3D2=20
  face=3DArial>Exactly...and so would be wind display and things that rely<=
BR>on=20
  getting an accurate TAS.&nbsp; That's why I actually change ports<BR>to g=
et=20
  the error low.&nbsp; I don't know that without a lot of work<BR>a person =
can=20
  guarantee static port accuracy down to the 0-1kt<BR>range, especially whe=
n it=20
  changes with cruise speed, but I<BR>think it's very worthwhile to try to=
=20
  minimize the error.&nbsp; As<BR>Grayhawk says, if it is static error, it =
could=20
  mean altitude<BR>is off by a long ways too.<BR><BR>There are ways to do t=
hings=20
  like build up little dams in front<BR>of or behind the static port, to te=
st=20
  what effects you can<BR>have and make it read accurately.&nbsp; The first=
 step=20
  though<BR>would be a good leak test.&nbsp; Once you know the system is=20
  tight,<BR>and you make sure your OAT probe is accurate and all the=20
  puzzle<BR>pieces have been inspected, it isn't too big of a problem to<BR=
>just=20
  troubleshoot port location error. It does take a few test<BR>flights, but=
 this=20
  is what I see as our responsibility as homebuilt<BR>pilots...to make sure=
 we=20
  can match quality and standards to<BR>certified levels.&nbsp; What I find=
 is=20
  that if you do the<BR>diligence on your systems, it will pay in rewards o=
f=20
  everything<BR>working well and being accurate.<BR><BR>Tim<BR><BR><BR>On=
=20
  8/20/2012 7:07 AM, Sky2high@aol.com wrote:<BR>&gt; If your static port is=
 off,=20
  so is your indicated altitude - by a<BR>&gt; lot.................<BR>&gt;=
=20
  Grayhawk<BR>&gt; In a message dated 8/19/2012 1:19:03 P.M. Central Daylig=
ht=20
  Time,<BR>&gt; Tim@myrv10.com writes:<BR>&gt;<BR>&gt;&nbsp; &nbsp;&nbsp; C=
ould=20
  it be static error...maybe port location, or other?&nbsp; Mine=20
  was<BR>&gt;&nbsp; &nbsp;&nbsp; off by 8 kts (reading low). A rework of th=
e=20
  port to a domed one and<BR>&gt;&nbsp; &nbsp;&nbsp; my error is now 2kts=
=20
  low.&nbsp; But, depending on your particular port<BR>&gt;&nbsp; &nbsp;&nb=
sp;=20
  issue if any, yours could be reading high.<BR>&gt;&nbsp; &nbsp;&nbsp;=20
  Tim<BR><BR>--<BR>For archives and unsub=20
  http://mail.lancaironline.net:81/lists/lml/List.html<BR></FONT></BLOCKQUO=
TE></DIV></FONT></BODY></HTML>
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