X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 1 [X] Return-Path: Sender: To: lml Date: Thu, 07 Dec 2006 18:51:43 -0500 Message-ID: X-Original-Return-Path: Received: from imo-d20.mx.aol.com ([205.188.139.136] verified) by logan.com (CommuniGate Pro SMTP 5.1.3) with ESMTP id 1652324 for lml@lancaironline.net; Thu, 07 Dec 2006 18:48:44 -0500 Received-SPF: pass receiver=logan.com; client-ip=205.188.139.136; envelope-from=Sky2high@aol.com Received: from Sky2high@aol.com by imo-d20.mx.aol.com (mail_out_v38_r7.6.) id o.cf3.3fef9cd (30740); Thu, 7 Dec 2006 18:48:01 -0500 (EST) From: Sky2high@aol.com X-Original-Message-ID: X-Original-Date: Thu, 7 Dec 2006 18:47:58 EST Subject: Re: [LML] Re: High Ignition Advance Problem X-Original-To: bakercdb@gmail.com, lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1165535278" X-Mailer: 9.0 Security Edition for Windows sub 5330 X-Spam-Flag: NO -------------------------------1165535278 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Clark, Yep, she's broke! It will be very informative to know why the unit failed so as to permanently operate at the max advance. Most of my high power operations, >2450 RPM, >24" MAP, <6000 Palt) result in an advance between 21 to 25 DBTDC. Lower power, 2480 RPM, 19-20" MAP, >8000 Palt, result in 28-29 DBTDC. I only see the 30's during idle or taxi (very low power since I don't like "low" power). If the RPM sensor failed so as to always report RPM less than 400, the timing would probably have been set to 0 DBTDC (engine start conditions). If the MAP sensor sent near 0" indications, I could imagine the timing going to max advance. This would be different than selecting the "ignore the MAP" jumper. Also, it would have been interesting to see what would have happened if you had selected the fixed 25 degree setting. Note, removing the MAP "vacuum" tube cannot eliminate timing adjustments based on the MAP sensor since it would see 29" (or so) on the ground and less ambient atmospheric pressure as one climbed. Just like there was no effect from ram air on the induction system running at WOT. There must be a jumper or switch setting that would allow you to operate independent of MAP sensing. Consider this relationship (assuming 8:1 CR) - At takeoff power, 2700 RPM and 29" MAP, 25 DBTDC may allow the combustion event to deliver max pressure at the optimum piston position (perhaps even better at some timing less than 25). At highly reduced power, say 1200 RPM and 10" MAP (fast taxi), at 25 DBTDC the peak pressure may occur long after the best piston position, thus is inefficient(so what, efficiency at idle is not a priority objective). If the timing is advanced, the peak pressure is advanced to the better piston position or the fuel can be reduced to deliver the same pressure at the same piston position. This is also true at high altitudes - even at 2500 RPM, the MAP (NA engine) may only be 16-18" (low power) and timing advance may deliver the same power (pressure) with less fuel or more power with the same fuel as with the standard mistimed combustion event (i.e. fixed at 25 DBTDC). Of course, there are other benefits of electronic ignitions (see any automobile). Scott PS: Knowledge is power (especially the timing info). In a message dated 12/7/2006 3:12:26 P.M. Central Standard Time, bakercdb@gmail.com writes: Interesting about the observations on your LSE system. Just to expand a little: * I was getting considerably different readings between the two units. * The suspect unit was at ~39degrees at 1,000 to 1,500 rpm (I couldn't take any more prop blast while holding the timing light), while the other unit remained near 25 degrees. * Maximum advance should have been limited to 34 degrees as I had the low advance curve jumper installed (not the 39 shown on the suspect unit). * Pulling the vacuum advance connection is supposed to remove any advance due to manifold pressure. Pulling the tube made no difference to the suspect unit (the other unit was already at minimum advance). However, I am not familiar with the exact dynamics between RPM, MP, and timing. Finally, as more substantive evidence, I manually retarded the suspect unit by 15 degrees (ie, set the timing while at 15degrees ATDC, not TDC as is usual procedure. A test flight showed the temps back to normal. I have not yet received the manufacturer's findings. Regards Clark On 12/7/06, _Sky2high@aol.com_ (mailto:Sky2high@aol.com) <_Sky2high@aol.com_ (mailto:Sky2high@aol.com) > wrote: In a message dated 12/7/2006 1:06:47 P.M. Central Standard Time, _bakercdb@gmail.com_ (mailto:bakercdb@gmail.com) writes: On the 2nd leg of a long cross country trip, I noticed that CHTs were running noticeably higher than usual on climb out. After leveling off at 6,500msl, CHTs were uniformly running approximately 40+ degrees higher than normal. Upon landing, the problem was eventually traced to one of my PMag ignitions that, was going to full advance at idle (39degrees). This was a failure mode of electronic ignitions that I hadn't considered before. Given the engine seemed to be running fine otherwise, I didn't try switching off one ignition in flight, which likely would have pinpointed the problem. Clark, Low MAP and low RPM are exactly the low power combination that encourages electronic ignitions to fully advance the timing. Indeed, the P-Mag may be broken (always delivering max advance), but a significant advance at idle is not a good failure indication. I regularly see 34-35 DBTDC at low RPM (idle or close to idle) and my base timing is 20 DBTDC because of a CR greater than 8.7 (equivalent to your 39 DBTDC unless your jumpers also are set for a base timing of 20 DBTDC). Perhaps the P-Mag goes to a large advance because the MAP sensor is always indicating low pressure. What happens if you set the jumpers to use RPM only for the timing? You shouldn't get much advance for operation above 2500 RPM. I have to assume the RPM sensor is working for the P-Mag to operate at all. PS: You may have experienced the kind of condition that led me to the conclusion that I must have a display of the in flight timing for any ignition that changes the timing. Scott Krueger AKA Grayhawk . -------------------------------1165535278 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Clark,
 
Yep, she's broke!
 
It will be very informative to know why the unit failed so as to=20 permanently operate at the max advance. 
 
Most of my high power operations, >2450 RPM, >24" MAP, <6000 P= alt)=20 result in an advance between 21 to 25 DBTDC.  Lower power, 2480 RPM, 19= -20"=20 MAP, >8000 Palt, result in 28-29 DBTDC.  I only see the 30's during=20= idle=20 or taxi (very low power since I don't like "low" power).
 
If the RPM sensor failed so as to always report RPM less than= =20 400, the timing would probably have been set to 0 DBTDC (engine start=20 conditions).  If the MAP sensor sent near 0" indications, I could=20 imagine the timing going to max advance.  This would be different=20 than selecting the "ignore the MAP" jumper.  Also, it would have b= een=20 interesting to see what would have happened if you had selected the fixed 25= =20 degree setting.
 
Note, removing the MAP "vacuum" tube cannot eliminate timing adjustment= s=20 based on the MAP sensor since it would see 29" (or so) on the ground an= d=20 less ambient atmospheric pressure as one climbed.  Just like there was=20= no=20 effect from ram air on the induction system running at WOT.  There must= be=20 a jumper or switch setting that would allow you to operate independent of MA= P=20 sensing.
 
Consider this relationship (assuming 8:1 CR) -  At takeoff po= wer,=20 2700 RPM and 29" MAP, 25 DBTDC may allow the combustion event to delive= r=20 max pressure at the optimum piston position (perhaps even better at som= e=20 timing less than 25).  At highly reduced power, say 1200 RPM and 1= 0"=20 MAP (fast taxi), at 25 DBTDC the peak pressure may occur long after the best= =20 piston position, thus is inefficient(so what, efficiency at idle is not a=20 priority objective).  If the timing is advanced, the peak pressure is=20 advanced to the better piston position or the fuel can be reduced to deliver= the=20 same pressure at the same piston position.  This is also true at high=20 altitudes - even at 2500 RPM, the MAP (NA engine) may only be 16-18" (l= ow=20 power) and timing advance may deliver the same power (pressure) with less fu= el=20 or more power with the same fuel as with the standard mistimed combusti= on=20 event (i.e. fixed at 25 DBTDC).
 
Of course, there are other benefits of electronic ignitions (see any=20 automobile).
 
Scott
 
PS: Knowledge is power (especially the timing info).
 
 
In a message dated 12/7/2006 3:12:26 P.M. Central Standard Time,=20 bakercdb@gmail.com writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>
Interesting about the observations on your LSE system. 
 
Just to expand a little:
* I was getting considerably different readings between the two=20 units. 
* The suspect unit was at ~39degrees at 1,000 to 1,500 rpm (I couldn'= t=20 take any more prop blast while holding the timing light), while the other=20= unit=20 remained near 25 degrees. 
* Maximum advance should have been limited to 34 degrees as I had the= low=20 advance curve jumper installed (not the 39 shown on the suspect unit).
* Pulling the vacuum advance connection is supposed to remove any adv= ance=20 due to manifold pressure.  Pulling the tube made no difference to the= =20 suspect unit (the other unit was already at minimum advance).  Howeve= r, I=20 am not familiar with the exact dynamics between RPM, MP, and timing.
 
Finally, as more substantive evidence, I manually retarded the suspec= t=20 unit by 15 degrees (ie, set the timing while at 15degrees ATDC, not&n= bsp;=20 TDC as is usual procedure.  A test flight showed the temps back to=20 normal.  I have not yet received the manufacturer's findings.
 
 
Regards
Clark
 
On 12/7/06, Sky2high@aol.com <Sky2high@aol.com> wrote:=20
In a message dated 12/7/2006 1:06:47 P.M. Central Standard Time, bakercdb@gmail.com=20 writes:
On the 2nd leg of a long cross country trip, I noticed that CHTs=20= were=20 running noticeably higher than usual on climb out.  After levelin= g=20 off at 6,500msl, CHTs were uniformly running approximately 40+ degrees= =20 higher than normal.  Upon landing, the problem was eventually tra= ced=20 to one of my PMag ignitions that, was going to full advance at idle=20 (39degrees). This was a failure mode of electronic ignitions that= I=20 hadn't considered before.  Given the engine seemed to be running=20= fine=20 otherwise, I didn't try switching off one ignition in flight, which li= kely=20 would have pinpointed the problem.
Clark,
 
Low MAP and low RPM are exactly the low power combination that= =20 encourages electronic ignitions to fully advance the timing.  Indee= d,=20 the P-Mag may be broken (always delivering max advance), but a=20 significant advance at idle is not a good failure indication. = I=20 regularly see 34-35 DBTDC at low RPM (idle or close to idle) and my base= =20 timing is 20 DBTDC because of a CR greater than 8.7 (equivalent to your=20= 39=20 DBTDC unless your jumpers also are set for a base timing of 20 DBTDC).
 
Perhaps the P-Mag goes to a large advance because th= e=20 MAP sensor is always indicating low pressure.  What happens if= you=20 set the jumpers to use RPM only for the timing?  You shouldn't get=20= much=20 advance for operation above 2500 RPM.  I have to assume the RPM sen= sor=20 is working for the P-Mag to operate at all.
 
PS:  You may have experienced the kind of condition that=20= led=20 me to the conclusion that I must have a display of the in flight ti= ming=20 for any ignition that changes the timing.
 
Scott Krueger AKA=20 Grayhawk
.

 
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