Return-Path: Sender: (Marvin Kaye) To: lml@lancaironline.net Date: Fri, 12 Dec 2003 15:50:15 -0500 Message-ID: X-Original-Return-Path: Received: from imo-r05.mx.aol.com ([152.163.225.101] verified) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 2888135 for lml@lancaironline.net; Fri, 12 Dec 2003 14:02:28 -0500 Received: from Sky2high@aol.com by imo-r05.mx.aol.com (mail_out_v36_r1.1.) id q.1ca.15f2320f (4410) for ; Fri, 12 Dec 2003 14:02:19 -0500 (EST) From: Sky2high@aol.com X-Original-Message-ID: <1ca.15f2320f.2d0b6abb@aol.com> X-Original-Date: Fri, 12 Dec 2003 14:02:19 EST Subject: Further to S-Tec AutoPilots - A Maintainence Suggestion X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1071255739" X-Mailer: Thailand for Windows sub 280 -------------------------------1071255739 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit I utilize a S-Tec 50 with their heading gyro and driven by a Garmin 430 plus GPSS. My 320 has about 600 hours, most of the time (400 hours) is from cross-country flights and most of that time is with the A/P engaged. I have frequently complained about how the use of the tilted "rate" gyro in the turn coordinator translates turbulence into turns - big turns. I want to retract "big." Last year in the Kittyhawk to OSH race, I wanted to utilize GPSS and the A/P to manage the most efficient flight line (for race purposes). Of course, flying low at midday usually results in turbulence and those flight legs were no disappointment in jostling that surely took an inch off my height after each flight. I had to discontinue the use of the A/P because moderate turbulence (light chop to ATPs) led to some deviations that were as great as 12 degrees with very poor recovery to the course line. The A/P had never been this bad although its' usual use is at higher altitudes and in smoother air. Later, I consulted with the local avionics shop and they suggested that carbon buildup on the armature/brushes makes the servo motor not very responsive. They made two suggestions: 1) Remove the servo motor and clean it or, second best was; 2) Run the motor at 40 VDC for 5 or 10 minutes on a yearly basis to clean up some of the carbon. I had them perform #2 because, for me, removal of the servo motor from the wing is no simple task. Test flights indicated a significant improvement in that "big" deviations had become less big - more like 4 or 5 degrees, still not the best. Recently, during a cold and miserable day, I pulled the servo and removed the black plastic enclosure (one screw on the back), secured the wee springs holding the brushes in place, took out the two screws that hold the bearing/brush block in place and, using q-tips dipped in alcohol, cleaned the brushes and the armature of quite a bit of carbon. Reassembly included securing the two screw heads and their lock washers with a touch of Locktite. The following test flights were much more satisfying in that turbulence would only produce a 1 degree (or so) deviation. So..... If you are experiencing sloppy course tracking during turbulence (under "perfect" GPSS guidance), consider cleaning the servo motor. Report back if you find improvement. This suggestion is meant for those whose A/P has been in service for some time and performance has degraded even though the best possible GPS signals are being used. Scott Krueger Sky2high@aol.com II-P N92EX IO320 Aurora, IL (KARR) PS- Maybe I'll pull the pitch servo from the elevator tunnel, do the same and take pix. Ugh, Yuck..... PPS- Gary, note that I said "servo motor," succumbing to your ceaseless crusade to fix the language, "one word at a time." "...as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns - the ones we don't know we don't know." D. Rumsfeld -------------------------------1071255739 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
I utilize a S-Tec 50 with their heading gyro and driven by a Garmin 430= =20 plus GPSS. My 320 has about 600 hours, most of the time (400 hours) is=20= from=20 cross-country flights and most of that time is with the A/P engaged.
 
I have frequently complained about how the use of the tilted "rate" gyr= o in=20 the turn coordinator translates turbulence into turns - big turns. I wa= nt=20 to retract "big."
 
Last year in the Kittyhawk to OSH race, I wanted to utilize GPSS and th= e=20 A/P to manage the most efficient flight line (for race purposes).  Of=20 course, flying low at midday usually results in turbulence and those flight=20= legs=20 were no disappointment in jostling that surely took an inch off my height af= ter=20 each flight.  I had to discontinue the use of the A/P because moderate=20 turbulence (light chop to ATPs) led to some deviations that were as gre= at=20 as 12 degrees with very poor recovery to the course line. The A/P had never=20= been=20 this bad although its' usual use is at higher altitudes and in smoother=20 air.
 
Later, I consulted with the local avionics shop and they suggested that= =20 carbon buildup on the armature/brushes makes the servo motor not very=20 responsive.  They made two suggestions: 1) Remove the servo motor and c= lean=20 it or, second best was; 2) Run the motor at 40 VDC for 5 or 10 minutes on a=20 yearly basis to clean up some of the carbon.  I had them perform #2=20 because, for me, removal of the servo motor from the wing is no simple=20 task.  Test flights indicated a significant improvement in that "big"=20 deviations had become less big - more like 4 or 5 degrees, still not the=20 best.
 
Recently, during a cold and miserable day, I pulled the servo and remov= ed=20 the black plastic enclosure (one screw on the back), secured the wee springs= =20 holding the brushes in place, took out the two screws that hold the=20 bearing/brush block in place and, using q-tips dipped in alcohol, cleaned th= e=20 brushes and the armature of quite a bit of carbon. Reassembly included secur= ing=20 the two screw heads and their lock washers with a touch of Locktite. The=20 following test flights were much more satisfying in that turbulence would on= ly=20 produce a 1 degree (or so) deviation.
 
So.....
 
If you are experiencing sloppy course tracking during turbulence (under= =20 "perfect" GPSS guidance), consider cleaning the servo motor.  Report ba= ck=20 if you find improvement.  This suggestion is meant for those whose A/P=20= has=20 been in service for some time and performance has degraded even though the b= est=20 possible GPS signals are being used.
 
Scott=20 Krueger
Sky2high@aol.com
II-P N92EX IO320 Aurora, IL (KARR)
 
PS- Maybe=20 I'll pull the pitch servo from the elevator tunnel, do the same and take pix= .=20 Ugh, Yuck.....
 
PPS- Gary,=20 note that I said "servo motor," succumbing to your ceaseless crusade to fix=20= the=20 language, "one word at a time."


"...as we know, there are known knowns; there are things we kno= w we=20 know. We also know there are known unknowns; that is to say we know there ar= e=20 some things we do not know. But there are also unknown unknowns - the ones w= e=20 don't know we don't know." D. Rumsfeld
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