X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 23 Oct 2005 13:23:57 -0400 Message-ID: X-Original-Return-Path: Received: from imo-d20.mx.aol.com ([205.188.139.136] verified) by logan.com (CommuniGate Pro SMTP 5.0c6) with ESMTP id 780823 for lml@lancaironline.net; Sun, 23 Oct 2005 12:49:29 -0400 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_r6.3.) id q.46.7446177b (57293) for ; Sun, 23 Oct 2005 12:48:42 -0400 (EDT) From: Sky2high@aol.com X-Original-Message-ID: <46.7446177b.308d18e9@aol.com> X-Original-Date: Sun, 23 Oct 2005 12:48:41 EDT Subject: Advanced Ignition Timing and EIs on normally aspirated engines. X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1130086121" X-Mailer: 9.0 Security Edition for Windows sub 5009 X-Spam-Flag: NO -------------------------------1130086121 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Jonathan, Thanks for the additional information - I wrote this before reading your piece. In a message dated 10/19/2005 8:52:31 A.M. Central Standard Time, walter@advancedpilot.com writes: If the claim is that altering timing with electronic ignition will increase HP, then I have a problem with that. I have a neat little chart out of Taylor which shows HP change related to timing changes and it is underwhelming how much change is NOT seen as timing is altered. Walter, et al, Darn, I still don't have a copy of Taylor Vol 1. Because of that I don't know what other variables were being controlled. Oh well, see below: First, some terms we can all agree on. After starting, an aircraft engine runs with the spark occurring some Degrees (D) Before Top Dead Center (BTDC). Before the piston reaches its' highest travel in the cylinder. This allows for the time it takes to finish the compression stroke, burn the fuel and reach some maximum high cylinder pressure some degrees after top dead center (ATDC), during which the most work can be done by the piston over a certain range of rotational degrees in the down (expansion) stroke. Many aircraft engines are timed to fire the plug 25 degrees BTDC - not an arbitrary number, but one that is a compromise providing good operation over a range of mixtures, RPMs and compression ratios including its corollary - altitude air pressure - if the timing is fixed, as in magnetos. Thus, 25 DBTDC is useful over a broad range of power settings. At 2500 RPM, the engine is rotating 15,000 degrees per second and, at 25 DBTDC that is merely 1.67 milliseconds BTDC. Generally, advancing the spark means earlier or greater than 25 DBTDC and retarding the spark would mean later or less than 25 DBTDC. In examining many computer adjusted spark timing schemes, 2400-2600 RPM and 21" - 24" MAP generally yield about 25 DBTDC for engines with a compression ratio (CR) below 8.6:1. Higher CRs suggest a reduction in the base spark advancement regime (retard or later than 25 DBTDC), as do very high power settings so that the optimal cylinder pressure is reached at the right time. Likewise, low power settings suggest advancing the spark for the same purpose. Lower power settings are frequently reached by flying at higher altitudes (say above 8000 MSL and Wide Open Throttle or WOT), where even high CRs can't completely compensate for lower ambient pressures. Note that induction pressures are maintained by engines equipped with superchargers or turbochargers and have low CRs. So, in discussing only normal aspirated engines: Do timing changes increase HP? One might additionally ask, relative to what? Not more than the laboratory engine can deliver (all other things being equal), but adjusting the timing to deliver the best, non destructive cylinder pressure can have a beneficial effect on performance. The aircraft engine cam may be timed (valve timing) to deliver max torque at 2500 RPM, but HP is also related to RPM. Where: HP = (Torque x RPM)/5252 Thus, HP rises as RPM increases to some practical limit. Thrust is another story. Do timing changes provide more efficient fuel consumption? At low power settings, (more importantly, high altitudes Wide Open Throttle), spark advance can better utilize fuel burned in the cylinder. Thus, higher CHTs, Lower EGTs and lower fuel burn for the same or more power (again, trying to reach optimal cylinder pressure). EIs, used in cars for many years, provide additional benefits because of consistent, high energy sparks to plugs with exotic metals and larger gaps that are more effective at always lighting the fire. Consider the many EI systems available or being developed for aircraft engines that do indeed alter the spark timing - PRISM, P-MAGs, LASAR, ElectroAir, EPIC, TCM FADEC, etc. Gross spark mistiming of any engine can lead to its destruction - too early or late can result in extreme cylinder pressures at the wrong time. It also depends on the engine since some large displacement engines are "sensitive" because they got that way by boring and stroking a lesser capacity cylinder, thus weakening its structure. BTW, without going into the circumstances, my original IO 320 ran for 20 hours on magnetos with less than optimal timing - when finally measured, it was 34 DBTDC. Yes, it ran hot and rough, rationalized as symptoms of a new engine. There was no evidence that the engine was damaged. Scott Krueger AKA Grayhawk Lancair N92EX IO320 SB 89/96 Aurora, IL (KARR) -------------------------------1130086121 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Jonathan, Thanks for the additional information - I wrote this before=20 reading your piece.
In a message dated 10/19/2005 8:52:31 A.M. Central Standard Time,=20 walter@advancedpilot.com writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>If the=20 claim is that altering timing with electronic ignition will
increase H= P,=20 then I have a problem with that.  I have a neat little
chart out=20= of=20 Taylor which shows HP change related to timing changes and
it is=20 underwhelming how much change is NOT seen as timing is=20 altered.
Walter, et al,
 
Darn, I still don't have a copy of Taylor Vol 1.  Because of that=20= I=20 don't know what other variables were being controlled. Oh well, see below:
 
First, some terms we can all agree on.  After starting, an aircraf= t=20 engine runs with the spark occurring some Degrees (D) Before Top Dead=20 Center (BTDC).  Before the piston reaches its' highest travel in the=20 cylinder.  This allows for the time it takes to finish the compression=20 stroke, burn the fuel and reach some maximum high cylinder=20 pressure some degrees after top dead center (ATDC), during which the mo= st=20 work can be done by the piston over a certain range of rotational degre= es=20 in the down (expansion) stroke.  Many aircraft engines are timed t= o=20 fire the plug 25 degrees BTDC - not an arbitrary number, but one that is a=20 compromise providing good operation over a range of mixtures, RPMs and=20 compression ratios including its corollary - altitude air pressure - if the=20 timing is fixed, as in magnetos.  Thus, 25 DBTDC is useful over a broad= =20 range of power settings.  At 2500 RPM, the engine is rotating 15,000=20 degrees per second and, at 25 DBTDC that is merely 1.67=20 milliseconds BTDC.  Generally, advancing the spark means earlier o= r=20 greater than 25 DBTDC and retarding the spark would mean later or less=20= than=20 25 DBTDC. 
 
In examining many computer adjusted spark timing schemes, 2400-2600 RPM= and=20 21" - 24" MAP generally yield about 25 DBTDC for engines with a compres= sion=20 ratio (CR) below 8.6:1.  Higher CRs suggest a reduction in the base=20 spark advancement regime (retard or later than 25 DBTDC), as do ve= ry=20 high power settings so that the optimal cylinder pressure is reached at the=20 right time.  Likewise, low power settings suggest advancing the spark f= or=20 the same purpose.  Lower power settings are frequently reached by flyin= g at=20 higher altitudes (say above 8000 MSL and Wide Open Throttle or WOT), where e= ven=20 high CRs can't completely compensate for lower ambient pressures. = =20 Note that induction pressures are maintained by engines equipped with=20 superchargers or turbochargers and have low CRs. So, in=20 discussing only normal aspirated engines:
 
Do timing changes increase HP?
 
One might additionally ask, relative to what? Not more than the laborat= ory=20 engine can deliver (all other things being equal), but adjusting the timing=20= to=20 deliver the best, non destructive cylinder pressure can have a beneficial ef= fect=20 on performance.  The aircraft engine cam may be timed (valve=20 timing) to deliver max torque at 2500 RPM, but HP is also related to=20 RPM. Where:   
HP =3D (Torque x RPM)/5252
Thus, HP rises as RPM increases to some practical limit. Thrust is anot= her=20 story.
 
Do timing changes provide more efficient fuel consumption?
 
At low power settings, (more importantly, high altitudes Wide Open=20 Throttle), spark advance can better utilize fuel burned in the=20 cylinder.  Thus, higher CHTs, Lower EGTs and lower fuel burn for the sa= me=20 or more power (again, trying to reach optimal cylinder pressure).
 
EIs, used in cars for many years, provide additional benefits because o= f=20 consistent, high energy sparks to plugs with exotic metals and larger gaps t= hat=20 are more effective at always lighting the fire.  Consider the many EI=20 systems available or being developed for aircraft engines that do indeed alt= er=20 the spark timing - PRISM, P-MAGs, LASAR, ElectroAir, EPIC, TCM FADEC,=20 etc.
 
Gross spark mistiming of any engine can lead to its destruction - too e= arly=20 or late can result in extreme cylinder pressures at the wrong time.  It= =20 also depends on the engine since some large displacement engines are "sensit= ive"=20 because they got that way by boring and stroking a lesser capacity cylinder,= =20 thus weakening its structure.
 
BTW, without going into the circumstances, my original IO 320 ran for 2= 0=20 hours on magnetos with less than optimal timing - when finally measured= , it=20 was 34 DBTDC.  Yes, it ran hot and rough, rationalized as=20 symptoms of a new engine.  There was no evidence that the engine was=20 damaged. =20
 
Scott Krueger=20 AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL=20 (KARR)



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