X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 19 Oct 2008 06:20:12 -0400 Message-ID: X-Original-Return-Path: Received: from imo-d22.mx.aol.com ([205.188.144.208] verified) by logan.com (CommuniGate Pro SMTP 5.2.8) with ESMTP id 3218392 for lml@lancaironline.net; Sat, 18 Oct 2008 08:45:16 -0400 Received: from VTAILJEFF@aol.com by imo-d22.mx.aol.com (mail_out_v39.1.) id q.be8.3dd3e563 (48552) for ; Sat, 18 Oct 2008 08:45:11 -0400 (EDT) From: VTAILJEFF@aol.com X-Original-Message-ID: X-Original-Date: Sat, 18 Oct 2008 08:45:34 EDT Subject: Re: [LML] Re: S-Tec Autopilot Problems X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1224333934" X-Mailer: Unknown sub 34 X-Spam-Flag:NO -------------------------------1224333934 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en Another failure mode of the STEC system (and IMHO has resulted in a fatal =20 accident) is a loss of ground signal to the TC that results in the AP contin= uing=20 to "operate" without any attitude reference. This results in a slow turn=20 left or right depending on if you are 28 v dc or 14 v dc system. If you onl= y=20 have a single attitude indicator and a TC in your cockpit and are IMC you c= an=20 have a heck of a time sorting our what has failed. OBTW the TC has a terrib= le=20 history of stuck flag failures. The FAA issued an SAIB on this two years ag= o=20 but so far STEC has kept this under the wraps. =20 Jeff =20 =20 In a message dated 10/17/2008 8:04:21 P.M. Central Daylight Time, =20 Sky2high@aol.com writes: Wayne and John, =20 My many years of experience with the S-Tec 50 as reflected in a file that i= s=20 over 1.5" thick, provides these observations: =20 1. The pitch board (regardless of version) is a dangerous, but interesting,= =20 device: a. One type of pitch board failure results in the TC tach test pin to=20 always "true" even if the TC has failed or is electrically off. A possible= =20 preflight Pilot checklist test should be to pull the TC circuit breaker and= =20 reset the AP. If it becomes operational (green ready light), the board is=20= bad. =20 Note, S-Tec test procedures will not detect this failure. If the AP is use= d=20 during this failed condition whilst in flight, the resulting death spiral i= s =20 interesting and demonstrates the usefulness of an AP disconnect switch. =20 b. I know nothing about static lag, but a bad static hookup can be=20 avoided by leaving the sensor open to the cockpit pressure (if the cabin is= not=20 pressurized). Since altitude hold is used in stable cruise flight, it is=20 responsive to the consistent cabin pressure, merely changing no more than 5= 0 feet=20 when the cabin air vents are opened or closed (thus demonstrating lack of=20 "lag"). =20 c. In my thick file is a page describing 34 different component=20 configurations on the pitch board for modifying pitch sensitivity. That is= ,=20 simultaneous modifications to 7 or eight components, not just a single resi= stance. =20 2. The S-Tec 50 occupies 3 valuable 3" holes in the panel (TC, DG and AP =20 Brain). =20 3. The TC gyro is tilted (as they are in all TCs) and turbulence results in= =20 AP turns - sometimes as much as 5 degrees off the course. =20 4. GPSS (ARINC Roll Steering) requires the addition of another box. =20 Otherwise, the thing tracks the necessary 430W over-the-ground course line=20 like a pig after a truffle. Too much work to switch to something else now. =20 =20 Scott Krueger AKA Grayhawk Lancair N92EX IO320 SB 89/96 Aurora, IL (KARR) Pilot not TSO'd, Certificated score only > 70%. =20 =20 In a message dated 10/17/2008 1:26:25 A.M. Central Daylight Time, =20 aflyer@lazy8.net writes: =20 One thing I do know about the S-Tec autopilot is that the pitch algorithms=20 are extremely sensitive to any lag or delay in the static system. On certif= ied=20 installations the =E2=80=9Cbrain box=E2=80=9D is required to be mounted ve= ry close (3 =20 feet or less) to the static ports, and the autopilot must have its own stat= ic=20 ports, and not share them with any other instrument. Also not allowed are t= he=20 little bottles that are supposed to catch moisture in the tubing.=20 Pitch oscillations are the main symptoms of too much static lag.=20 John Huft=20 RV spy=20 =20 From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Wayn= e=20 Bailey Sent: Sunday, October 12, 2008 6:49 PM To: lml@lancaironline.net Subject: [LML] Blue Mountain Avionics Autopilot =20 Small tail 360 with Stec50 autopilot. =20 =20 AP works OK to maintaining heading - but pitch enters oscillations=20 eventually becoming so severe requires disconnection of AP after about 30 -= 40 =20 seconds. Incredibly there is no 'gain' adjustment in the pitch axis of th= e STEC=20 50. I have read about replacing resistor on board to modify gain - but a=20 little uncomfortable with this option. No slop in the linkage. =20 Have not dug into the servos yet - but hoping there is a way to mechanicall= y=20 reduce the 'gain' by extending the servo attachment point radially outward=20 on bellcrank - or ?? =20 Alternatively thinking about installing BMA EFIS Gen 4 system with new serv= o=20 actuators. Anyone have any experience with BMA gen 4 EFIS on a close=20 coupled LNC2? I do know there is gain on both axis. =20 Thanks again for the help. =20 Wayne =20 =20 ____________________________________ New MapQuest Local shows what's happening at your destination. Dining, =20 Movies, Events, News & more. _Try it out! _=20 (http://pr.atwola.com/promoclk/100000075x1211031713x1200669822/aol?redir=3Dh= ttp://local.mapquest.com/?ncid=3Demlcntnew00 000002)=20 **************New MapQuest Local shows what's happening at your destination.= =20 Dining, Movies, Events, News & more. Try it out=20 (http://local.mapquest.com/?ncid=3Demlcntnew00000002) -------------------------------1224333934 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en
Another failure mode of the STEC system (and IMHO has resulted in a fat= al=20 accident) is a loss of ground signal to the TC that results in the AP contin= uing=20 to "operate" without any attitude reference. This results in a slow turn lef= t or=20 right depending on if you are 28 v dc or 14 v dc system. If you only have a=20 single attitude indicator and a TC in your cockpit and are IMC you can have=20= a=20 heck of a time sorting our what has failed. OBTW the TC has a terrible histo= ry=20 of stuck flag failures. The FAA issued an SAIB on this two years ago but so=20= far=20 STEC has kept this under the wraps.
 
Jeff
 
In a message dated 10/17/2008 8:04:21 P.M. Central Daylight Time,=20 Sky2high@aol.com writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>
Wayne and John,
 
My many years of experience with the S-Tec 50 as reflected in a file=20= that=20 is over 1.5" thick, provides these observations:
 
1. The pitch board (regardless of version) is a dangerous, but=20 interesting, device:
    a. One type of pitch board failure results in= the=20 TC tach test pin to always "true" even if the TC has failed or is=20 electrically off.  A possible preflight Pilot checklist test sho= uld=20 be to pull the TC circuit breaker and reset the AP.  If it becomes=20 operational (green ready light), the board is bad.  Note, S-Tec test=20 procedures will not detect this failure.  If the AP is used duri= ng=20 this failed condition whilst in flight, the resulting death spiral is= =20 interesting and demonstrates the usefulness of an AP disconnect=20 switch.
 
    b. I know nothing about static lag, but a bad= =20 static hookup can be avoided by leaving the sensor open to the cockpit=20 pressure (if the cabin is not pressurized).  Since altitude hold is u= sed=20 in stable cruise flight, it is responsive to the consistent cabin pressure= ,=20 merely changing no more than 50 feet when the cabin air vents are opened o= r=20 closed (thus demonstrating lack of "lag").
 
    c. In my thick file is a page describing 34=20 different component configurations on the pitch board for modifying pitch=20 sensitivity.  That is, simultaneous modifications to 7 or eight=20 components, not just a single resistance.
 
2. The S-Tec 50 occupies 3 valuable 3" holes in the panel (TC, DG and= AP=20 Brain).
 
3. The TC gyro is tilted (as they are in all TCs) and turbulence= =20 results in AP turns - sometimes as much as 5 degrees off the course.
 
4. GPSS (ARINC Roll Steering) requires the addition of another box.
 
Otherwise, the thing tracks the necessary 430W over-the-ground=20 course line like a pig after a truffle.  Too much work to switch to=20 something else now.
 
Scott=20 Krueger AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL=20 (KARR)

Pilot not TSO'd, Certificated score only >=20 70%.
 
In a message dated 10/17/2008 1:26:25 A.M. Central Daylight Time,=20 aflyer@lazy8.net writes:

One=20 thing I do know about the S-Tec autopilot is that the pitch algorithms a= re=20 extremely sensitive to any lag or delay in the static system. On certifi= ed=20 installations the =E2=80=9Cbrain box=E2=80=9D  is required to be mo= unted very close (3=20 feet or less) to the static ports, and the autopilot must have its own=20 static ports, and not share them with any other instrument. Also not all= owed=20 are the little bottles that are supposed to catch moisture in the=20 tubing.

 Pitch=20 oscillations are the main symptoms of too much static=20 lag.

 John=20 Huft

RV=20 spy

 

From: Lancair M= ailing=20 List [mailto:lml@lancaironline.net] On Behalf Of Wayne=20 Bailey
Sent: Sunday, October 12, 2008 6:49 PM
To:=20 lml@lancaironline.net
Subject: [LML] Blue Mountain Avionics=20 Autopilot

 

Small tail 360 with Stec50 autopilot. =20

 AP works OK to maintaining heading= - but=20 pitch enters oscillations eventually becoming so severe=20 requires disconnection of AP after about 30 - 40=20 seconds.   Incredibly there is no 'gain' adjustment in t= he=20 pitch axis of the STEC 50.  I have read about replacing resis= tor=20 on board to modify gain - but a little uncomfortable wit= h=20 this option.  No slop in the linkage.

 Have not dug into the servos yet - but=20 hoping there is a way to mechanically reduce the 'g= ain'=20 by extending the servo attachment point radially outward on bellcr= ank=20 - or ??

 Alternatively thinking about installing= BMA=20 EFIS Gen 4 system with new servo actuators.  Anyone have any=20 experience with BMA gen 4 EFIS on a close coupled LNC2? I do=20= know=20 there is gain on both axis.

 Thanks again for the=20 help.


Wayne

 

&nbs= p;

 






New MapQuest Local shows what's happening at your destinati= on. Dining, Movies, Events, News & more. Try it out!
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