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Date: Tue, 06 Apr 2010 17:39:16 -0400
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Subject: Re: [LML] fixes for S-TEC 50 alt hold
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Keith,
 
I have had an S-TEC 50 installed and "operating" since 1997 in my 320. 
 
1. I also had to reverse the pitch operation because the servo was mounted  
on the right side of the elevator push rod tunnel and the servo/push rod  
connector was aft of the servo.  STEC standard is  different.  Before 
reversing things, first test of altitude hold  was in the air (ignorance is bliss) 
and the more altitude that was lost, the  more down elevator was commanded 
(it thought it was commanding up). Oh  well......... 
 
2. Before I relocated the static port to the Lancair recommended position,  
I also had problems with altitude hold.  That was primarily because of  
static pressure fluctuations and the solution was to vent the transducer to the 
 cabin.  Note that there will be slight altitude changes the cabin air  
vents and or the cabin heat valve conditions are altered.  If you  had such a 
problem connected to the static port, your altimeter and  airspeed should 
have been erratic also.
 
3. RG 58 coax is well known to be an RF leaker.  If your GPS antenna  
connections were bad, you may want to examine the comm antenna connections  also. 
 Another way may be to move or reroute the STEC harness or  the antenna 
leads (although that may cause other problems such as all  temperature 
indications going awry).  Many sensitive wires have grounded  shields - remember 
that a shield should be grounded only at one end to avoid  ground loops.  If an 
antenna shield ground is bad, there is no  shield.  Testing wires on the 
ground is one thing, but remember the first  rule when considering whether 
something will work in flight - the effect of  constant vibration.
 
Scott Krueger
 
 
In a message dated 4/6/2010 6:59:39 A.M. Central Daylight Time,  
keith.smith@gmail.com writes:

The  altitude hold function on my LNC2 never worked since the day I bought 
the  airplane (coming up on 12 months ago).  I'll leave out all of the 
things  we tried to fix it that had no effect, and limit it to the relevant steps 
that  actually had a positive change.  Note, the alt hold is now working 
very  well (with one caveat, which I'll note at the end).  The purpose of  
posting this is to have it in the archive, in case anyone else runs into  
similar issues with their AP in the future.

- trim indicators (ie, add  up trim, add down trim) were reversed
- pitch servo was reversed
-  pressure transducer (pin 16) was apparently wired with someone counting 
the  pins from the wrong part of the connector, so no static port data was 
reaching  the AP

All of those things were fixed, resulting in an altitude hold  that almost 
worked perfectly. It was a good 1/2 - 1 second 'behind' the  airplane.  

The final fix was to disconnect the static line from  the pressure 
transducer, venting it to the cabin.  For an STEC-50, which  only has altitude hold 
(doesn't have the ability to maintain a specified  altitude), this was a 
great solution.

Now it works like a  champ!

The only hitch now is that when I transmit on radio, the alt  hold (and hdg 
hold for that matter, but it's less noticeable) functions are  
significantly disrupted.  My guess is that the transmission from the com  radio is 
hurting the signal from the pressure transducer back to the AP. I am  going to 
research the possibility of adding some shielding to that  cable.

Keith


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<DIV>Keith,</DIV>
<DIV>&nbsp;</DIV>
<DIV>I have had an S-TEC 50 installed and "operating" since 1997 in my 320=
.=20
</DIV>
<DIV>&nbsp;</DIV>
<DIV>1. I also had to reverse the pitch operation because the servo was mo=
unted=20
on the right side of the elevator push rod tunnel and the servo/push rod=
=20
connector was aft of the servo.&nbsp; STEC standard is=20
different.&nbsp;&nbsp;Before reversing things,&nbsp;first test of altitude=
 hold=20
was in the air (ignorance is bliss) and the more altitude that was lost,=
 the=20
more down elevator was commanded (it thought it was commanding up).&nbsp;O=
h=20
well.........&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>2. Before I relocated the static port to the Lancair recommended posi=
tion,=20
I also had problems with altitude hold.&nbsp; That was primarily because=
 of=20
static pressure fluctuations and the solution was to vent the transducer=
 to the=20
cabin.&nbsp; Note that there will be slight altitude changes&nbsp;the cabi=
n air=20
vents and or the cabin heat valve&nbsp;conditions are&nbsp;altered.&nbsp;=
 If you=20
had such a&nbsp;problem connected to the static port, your altimeter and=
=20
airspeed should have been erratic also.</DIV>
<DIV>&nbsp;</DIV>
<DIV>3. RG 58 coax is well known to be an RF leaker.&nbsp; If your GPS ant=
enna=20
connections were bad, you may want to examine the comm antenna connections=
=20
also.&nbsp; Another way may be to move or reroute the STEC harness or=20
the&nbsp;antenna leads&nbsp;(although that may cause other problems such=
 as all=20
temperature indications going awry).&nbsp; Many sensitive wires have groun=
ded=20
shields - remember that a shield should be grounded only at one end to avo=
id=20
ground loops.&nbsp; If an antenna shield ground is bad, there is no=20
shield.&nbsp; Testing wires on the ground is one thing, but remember the=
 first=20
rule when considering whether something will work in flight - the effect=
 of=20
constant vibration.</DIV>
<DIV>&nbsp;</DIV>
<DIV>Scott Krueger</DIV>
<DIV>&nbsp;</DIV>
<DIV>
<DIV>In a message dated 4/6/2010 6:59:39 A.M. Central Daylight Time,=20
keith.smith@gmail.com writes:</DIV>
<BLOCKQUOTE  style=3D"BORDER-LEFT: blue 2px solid; PADDING-LEFT: 5px; MARG=
IN-LEFT: 5px"><FONT    style=3D"BACKGROUND-COLOR: transparent" color=3D#00=
0000 size=3D2 face=3DArial>The=20
  altitude hold function on my LNC2 never worked since the day I bought th=
e=20
  airplane (coming up on 12 months ago).&nbsp; I'll leave out all of the=
 things=20
  we tried to fix it that had no effect, and limit it to the relevant step=
s that=20
  actually had a positive change.&nbsp; Note, the alt hold is now working=
 very=20
  well (with one caveat, which I'll note at the end).&nbsp; The purpose of=
=20
  posting this is to have it in the archive, in case anyone else runs into=
=20
  similar issues with their AP in the future.<BR><BR>- trim indicators (ie=
, add=20
  up trim, add down trim) were reversed<BR>- pitch servo was reversed<BR>-=
=20
  pressure transducer (pin 16) was apparently wired with someone counting=
 the=20
  pins from the wrong part of the connector, so no static port data was re=
aching=20
  the AP<BR><BR>All of those things were fixed, resulting in an altitude=
 hold=20
  that almost worked perfectly. It was a good 1/2 - 1 second 'behind' the=
=20
  airplane.&nbsp; <BR><BR>The final fix was to disconnect the static line=
 from=20
  the pressure transducer, venting it to the cabin.&nbsp; For an STEC-50,=
 which=20
  only has altitude hold (doesn't have the ability to maintain a specified=
=20
  altitude), this was a great solution.<BR><BR>Now it works like a=20
  champ!<BR><BR>The only hitch now is that when I transmit on radio, the=
 alt=20
  hold (and hdg hold for that matter, but it's less noticeable) functions=
 are=20
  significantly disrupted.&nbsp; My guess is that the transmission from th=
e com=20
  radio is hurting the signal from the pressure transducer back to the AP.=
 I am=20
  going to research the possibility of adding some shielding to that=20
  cable.<BR><BR>Keith<BR></FONT></BLOCKQUOTE></DIV></FONT></BODY></HTML>

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