Return-Path: Sender: "Marvin Kaye" To: lml@lancaironline.net Date: Tue, 22 Mar 2005 12:10:38 -0500 Message-ID: X-Original-Return-Path: Received: from imo-m28.mx.aol.com ([64.12.137.9] verified) by logan.com (CommuniGate Pro SMTP 4.3c3) with ESMTP id 815494 for lml@lancaironline.net; Tue, 22 Mar 2005 10:50:31 -0500 Received-SPF: pass receiver=logan.com; client-ip=64.12.137.9; envelope-from=REHBINC@aol.com Received: from REHBINC@aol.com by imo-m28.mx.aol.com (mail_out_v37_r3.8.) id q.1c9.24f3ca9d (3310) for ; Tue, 22 Mar 2005 10:49:41 -0500 (EST) From: REHBINC@aol.com X-Original-Message-ID: <1c9.24f3ca9d.2f719895@aol.com> X-Original-Date: Tue, 22 Mar 2005 10:49:41 EST Subject: Re: [LML] Re: superchargers X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1111506581" X-Mailer: 9.0 for Windows sub 5116 -------------------------------1111506581 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit George, I have compressor maps for lots of aircraft centrifugal compressors - - and only one of them gets to 80% at any point on the map. It is unlikely that the fixed rpm ratio version of that unit would operate at that optimum efficiency for more than a small portion of its operating life. You've got me there. I don't have any maps for "aircraft compressors". I do however have many for general applications and it is not uncommon for them to peak in the upper 80s to 90% efficiency. I only assume that aircraft would use equipment with similar efficiency. Why wouldn't an aircraft compressor operate at or near its optimum efficiency nearly all of its life? Airplanes are routinely flown at roughly the same altitudes and power settings for the majority of there lives. >> 4) To get the air temperature back down to tolerable (detonation margins) ranges requires an intercooler All sorts of engines run without intercoolers, without damage. Detonation is a function of temperature AND pressure in the cylinder at, or near, full compression, not the temperature in the intake. Besides, if you are flying up high, where an add on system makes sence, the air starts out colder so it isn't all that much warmer than it would have been at ground level. The principle reason for adding an intercooler is the same as for adding a supercharger, to make the intake air denser and increase the mass flow through the engine. << Well, after reading that, I am sort of beginning to wonder that NACA never knew what it was doing. NACA was part of the government. Enough said The primary reason in an aircraft to use an intercooler is not to gain more charge density. It is a LOT easier to do that with the compressor. By your own words, a compressor saps power from the engine. An intercooler ups the load on the compressor slightly, but the result is more efficient than jacking up the compressor ratio. The primary reason is to provide adequate detonation margins at higher power settings. If you think that one of the primary component causes of detonation is NOT the temperature of the induction air - - - then I would suggest that you take another look at the hard data. I never said it wasn't one component. But there is a lot more to it than just that. What is important is the combination of factors in the combustion chamber. If all you want to do is get away from detonation, cut the compression ratio by a quarter point. If you want to make more power, ad an intercooler. I have been teaching this precise subject matter on Saturday mornings every other month for the last 34 months. I studied the subject at the graduate level for nearly that long. In addition to teaching the subject, I have measured the results, directly, on the test stand on a TIO-540J2BD engine - - with and without an intercooler. George, I spent 5 years playing around with race cars and yet I know full well that there is absolutely no way I could ever catch up to the hands on experience you already have with piston engines. I respect that. By and large, I have agreed with the vast majority of your statements on this forum over the past few years and even picked up a detail or two that I didn't know before. Thanks. However, when you make the blanket statement that a mechanically driven supercharger will result in a slower airplane, we have to part company. Neither thermodynamics nor history support such a stand. On the contrary, both show that well matched components will result in improved performance. That is not to say that it couldn't be done even better with a turbine driven supercharger or some other system. Rob -------------------------------1111506581 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
George,
  I have compressor maps for lots of airc= raft centrifugal compressors - - and
only one of them gets to 80% at any=20= point on the map.
 
  It is unlikely that the fixed rpm rat= io version of that unit would operate
at
that optimum efficiency for=20= more than a small portion of its operating life.
You've got me there. I don't have any maps for "aircraft compressors".=20= I do however have many for general applications and it is not uncommon for t= hem to peak in the upper 80s to 90% efficiency. I only assume that aircraft=20= would use equipment with similar efficiency.
 
Why wouldn't an aircraft compressor operate at or near its optimum effi= ciency nearly all of its life? Airplanes are routinely flown at roughly the=20= same altitudes and power settings for the majority of there lives.
 

 
  >>  4) =20=      To get the air temperature back down to tolerable (deton= ation
  margins) ranges requires an intercooler All sorts of engines= run without
intercoolers, without damage. Detonation is a function of te= mperature AND
pressure in the cylinder at, or near, full compression, not= the temperature in
the intake. Besides, if you are flying up high, where= an add on system makes
sence, the air starts out colder so it isn't all=20= that much warmer than it
would have been at ground level.
 
&= nbsp; The principle reason for adding an intercooler is the same as for addi= ng a
supercharger, to make the intake air denser and increase the mass fl= ow through
the engine. <<
  
  Well, after re= ading that,  I am sort of beginning to wonder that  NACA
never=
knew what it was doing.
NACA was part of the government. Enough said

 
  The primary reason in an= aircraft to use an intercooler is not to gain more
charge density. = It is a LOT easier to do that with the compressor.
By your own words, a compressor saps power from the engine. An intercoo= ler ups the load on the compressor slightly, but the result is more efficien= t than jacking up the compressor ratio.

 
  The primary reason is to= provide adequate detonation margins at higher power
settings.
 =20=
  If you think that one of the primary component causes of detonati= on is NOT
the temperature of the induction air - - -   then&nbs= p; I would suggest that you
take another look at the hard data.
I never said it wasn't one component. But there is a lot more to it tha= n just that. What is important is the combination of factors in the combusti= on chamber. If all you want to do is get away from detonation, cut the compr= ession ratio by a quarter point. If you want to make more power, ad an inter= cooler.

 
  I  have been teachi= ng this precise subject matter on Saturday mornings every
other month for= the last  34 months.  
I studied the subject at the graduate level for nearly that long.
 

 
  In addition to teaching=20= the subject,  I have measured the results, directly,
  on the t= est stand on a TIO-540J2BD engine - - with and without an
intercooler.
George, I spent 5 years playing around with race cars and yet I know fu= ll well that there is absolutely no way I could ever catch up to the hands o= n experience you already have with piston engines. I respect that. By and la= rge, I have agreed with the vast majority of your statements on this forum o= ver the past few years and even picked up a detail or two that I didn't know= before. Thanks.
 
However, when you make the blanket statement that a mechanically driven= supercharger will result in a slower airplane, we have to part company. Nei= ther thermodynamics nor history support such a stand. On the contrary, both=20= show that well matched components will result in improved performance. That=20= is not to say that it couldn't be done even better with a turbine driven sup= ercharger or some other system.
 
Rob
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