X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 12 Mar 2009 19:30:04 -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 5.2.13) with ESMTP id 3545389 for lml@lancaironline.net; Thu, 12 Mar 2009 13:39:29 -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_v39.1.) id q.c71.4291781a (39329) for ; Thu, 12 Mar 2009 13:38:45 -0400 (EDT) From: Sky2high@aol.com X-Original-Message-ID: X-Original-Date: Thu, 12 Mar 2009 13:38:54 EDT Subject: Re: [LML] Re: LOP vs ROP Climb: Time and Fuel Burn (LIVP) X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1236879534" X-Mailer: AOL 9.1 sub 5003 X-Spam-Flag:NO -------------------------------1236879534 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Chuck, I wonder what the article said about "timing". The burn time can be related to octane, compression ratio, mixture and certainly rpm among others. In a fixed ignition timing model, those factors certainly affect when max cylinder pressure is reached whether it is good or bad. Obviously, variable ignition timing, if available, can also affect when the peak pressure is reached. Interesting. Scott Krueger In a message dated 3/12/2009 10:07:28 A.M. Central Daylight Time, cjensen@dts9000.com writes: A year or two ago, Aviation Consumer wrote an interesting article on MP v RPM and what was the best tradeoff between friction and cylinder pressures. The consensus, as best these things can be known, what it was better to operate the RPM at a higher level, than low. The friction loss associated with the higher RPM was offset by the reduced peak pressures such that the wear and tear on the engine is less at 24 x 25 than 24 x 24 and certainly better than 25 x 23. So, if you are going to reduce power, between MP or RPM, it is better to reduce MP since higher RPM keeps PP lower, at least that was their general conclusion, supported by engine shop experience. Thanks, Chuck Jensen Diversified Technologies 2680 Westcott Blvd Knoxville, TN 37931 Phn: 865-539-9000 x100 Cell: 865-406-9001 Fax: 865-539-9001 cjensen@dts9000.com -----Original Message----- From: Lancair Mailing List [mailto:lml@lancaironline.net]On Behalf Of Colyn Case at earthlink Sent: Thursday, March 12, 2009 10:31 AM To: lml@lancaironline.net Subject: [LML] Re: LOP vs ROP Climb: Time and Fuel Burn (LIVP) Jeff, that's interesting. I wonder why you get those high temps. I wonder what is different in our engine setups. my CHT's are steady @380 in the max/max condition @140knots. It's been tested to 20,000 in that config. CHT's get better than that with less power or more speed. I have exhaust tunnel extensions which seem to make a huge difference for cooling. also have ceramic coated exhaust. I don't know how much of a factor that is. Some will say that 2700rpm is a bad idea because of higher friction losses. On the other hand the flame front always moves at the same speed so if the crank is turning faster your theta pp (angle after top dead center where peak pressure occurs) is bigger and the peak pressure is less. .....which seems good for everything. the pulse on the crank is not as concentrated, the CHT's are lower. assuming everything else is setup right. Colyn **************A Good Credit Score is 700 or Above. See yours in just 2 easy steps! (http://pr.atwola.com/promoclk/100126575x1219671244x1201345076/aol?redir=http:%2F%2Fwww.freecreditreport.com%2Fpm%2Fdefault.aspx%3Fsc%3D668072%26hmpgID %3D62%26bcd%3DfebemailfooterNO62) -------------------------------1236879534 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Chuck,
 
I wonder what the article said about "timing".  The burn time can=20= be=20 related to octane, compression ratio, mixture and certainly rpm among=20 others.  In a fixed ignition timing model, those factors certainly affe= ct=20 when max cylinder pressure is reached whether it is good or bad. =20 Obviously, variable ignition timing, if available, can also affect when the=20= peak=20 pressure is reached.
 
Interesting.
 
Scott Krueger
 
In a message dated 3/12/2009 10:07:28 A.M. Central Daylight Time,=20 cjensen@dts9000.com writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>
A=20 year or two ago, Aviation Consumer wrote an interesting article on MP= v=20 RPM and what was the best tradeoff between friction and cylinder=20 pressures.  The consensus, as best these things can be known, what it= was=20 better to operate the RPM at a higher level, than low.  The friction=20= loss=20 associated with the higher RPM was offset by the reduced peak pressures su= ch=20 that the wear and tear on the engine is less at 24 x 25 than 24 x 24 and=20 certainly better than 25 x 23.  
 
So,=20 if you are going to reduce power, between MP or RPM, it is better to=20 reduce MP since higher RPM keeps PP lower, at least that was their general= =20 conclusion, supported by engine shop experience.

Thanks,
Chuck Jensen

Diversified=20 Technologies
2680=20 Westcott Blvd
Knoxville, TN  37931
Phn:    865-539-9000 x100=20
Cell:   = =20 865-406-9001
Fax:     865-539-9001
cjensen@dts9000.com

-----Original Message-----
From: Lancair Mailing List= =20 [mailto:lml@lancaironline.net]On Behalf Of Colyn Case at=20 earthlink
Sent: Thursday, March 12, 2009 10:31 AM
To:=20 lml@lancaironline.net
Subject: [LML] Re: LOP vs ROP Climb: Tim= e=20 and Fuel Burn (LIVP)

Jeff,
that's interesting.  I wonder why=20= you get=20 those high temps.
I wonder what is different in our engin= e=20 setups.
my CHT's are steady @380 in the max/max= =20 condition @140knots.
It's been tested to 20,000 in that=20 config.
CHT's get better than that  with l= ess=20 power or more speed.
I have exhaust tunnel extensions which=20= seem to=20 make a huge difference for cooling.
also have ceramic coated exhaust. = I don't=20 know how much of a factor that is.
 
Some will say that 2700rpm is a bad ide= a=20 because of higher friction losses.
On the other hand the flame front alway= s moves=20 at the same speed so if the
crank is turning faster your theta pp (= angle=20 after top dead center where peak pressure occurs) is bigger
and the peak pressure is less.  ..= ...which=20 seems good for everything.  the pulse on the crank
is not as concentrated, the CHT's are=20 lower.  assuming everything else is setup right.
 
Colyn

A Good Credit Score is 700 or Above. See yours in just 2 easy steps!<= /BODY> -------------------------------1236879534--