Return-Path: Sender: "Marvin Kaye" To: lml@lancaironline.net Date: Thu, 24 Mar 2005 16:36:10 -0500 Message-ID: X-Original-Return-Path: Received: from imo-d23.mx.aol.com ([205.188.139.137] verified) by logan.com (CommuniGate Pro SMTP 4.3c3) with ESMTP id 819253 for lml@lancaironline.net; Thu, 24 Mar 2005 16:30:45 -0500 Received-SPF: pass receiver=logan.com; client-ip=205.188.139.137; envelope-from=REHBINC@aol.com Received: from REHBINC@aol.com by imo-d23.mx.aol.com (mail_out_v37_r5.33.) id q.15b.4d9c6f08 (3924) for ; Thu, 24 Mar 2005 16:29:57 -0500 (EST) From: REHBINC@aol.com X-Original-Message-ID: <15b.4d9c6f08.2f748b55@aol.com> X-Original-Date: Thu, 24 Mar 2005 16:29:57 EST Subject: Re: [LML] Re: superchargers X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1111699797" X-Mailer: 9.0 for Windows sub 5116 -------------------------------1111699797 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en George: Airplanes, unlike cars, operate from a baseline 30=E2=80=9D Hg ambient at=20= sea level=20 - - to a baseline ambient of only 12-13=E2=80=9D Hg , with pressure ratio= s varying=20 from 1.2 up to 2.8 to 3.0. Thus, at constant RPM, the compressor would spend most of its life well of= f=20 of any =E2=80=9Coptimum=E2=80=9D pre-determined design point. =20 The variable speed turbo-supercharger compressor helps to mitigate this=20 problem to a substantial degree. =20 Actually, I think it is quite a bit easier to make a mechanicly driven=20 centrifugal compressor system work efficiently in an airplane than in a car.= Power=20 demand, and engine speed are much more consistant in an airplane and even=20 cruise altitudes are fairly predictable, where most operation takes place an= d=20 economy is most important. (reffering to typical Detroit/Tokyo/Whichita mode= ls,=20 not racing applications here)=20 In an airplane, you simply turn it on when you climb through a given altitud= e=20 and shut it off when you descend through the same level. In a car, low engin= e=20 speed would decimate the boost from a mechanically driven centrifugal=20 compressor. Assuming the engine is already operating at or near the engine=E2=80=99s =20 detonation limited maximum BMEP - - (many aircraft engines are) - - then i= n order to=20 improve the detonation margin, without reducing power (reduction in CR goes=20 the wrong direction on the power and the efficiency issues) or in order to=20 increase the BMEP - - and remain free of detonation, one will have to do o= ne or=20 more of the following: =20 1) Reduce the CHTs;=20 2) Increase the fuel octane; 3) Reduce the induction air temperature.=20 Add to this list: 4) Increase engine speed; 5) Reduce major combustion chamber radius; 6) Reduce/Alter combustion chamber turbulence; 7) Alter combustion chamber wall angles to reduce infrared and=20 shockwave energy reflected into areas of instabillity. 8) Relocate spark plug(s) Reductions in IAT from the intercooler will buy one LARGE improvements in=20 the detonation limited BMEP (ie, more horsepower becomes usefully available= ). That sounds a lot like something I said earlier. Your'e starting to agree=20 with me. =20 >>However, when you make the blanket statement that a mechanically driven=20 supercharger will result in a slower airplane, we have to part company.< -------------------------------1111699797 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en

George:

Airplanes, unlik= e cars, operate from a baseline 30=E2=80=9D Hg ambient at sea level -=20= - to a baseline ambient of only 12-13=E2=80=9D Hg , with p= ressure ratios varying from 1.2 up to 2.8 to 3.0.

Thus, at constant RPM,= the compressor would spend most of its life well off of a= ny =E2=80=9Coptimum=E2=80=9D pre-determined design point.

The variable speed tur= bo-supercharger compressor helps to mitigate this problem to a substantial d= egree.

=

Actually, I think it is quite a bit easier to make a mechanicly driven=20= centrifugal compressor system work efficiently in an airplane than in a= car. Power demand, and engine speed are much more consistant in an ai= rplane and even cruise altitudes are fairly predictable, where most ope= ration takes place and economy is most important. (reffering to typical Detr= oit/Tokyo/Whichita models, not racing applications here)

In an airplane, you simply turn it on when you climb through a given al= titude and shut it off when you descend through the same level. In a car, lo= w engine speed would decimate the boost from a mechanically driven centrifug= al compressor.

Assuming the engine is already op= erating at or near the engine=E2=80=99s detonation limited = maximum BMEP - - (many aircraft engines are) - - then in order to imp= rove the detonation margin, without reducing power (reduction in CR goes the= wrong direction on the power and the efficiency issues) or in order t= o increase the BMEP - - and remain free of detonation, one will=20= have to do one or more of the following:

1)       Reduce the CHTs; <= /SPAN>

2)       Increase the fuel octane;

3)       Reduce the induction air temp= erature.

Add to this list:

4)&N>Increase the fuel octane;

3) Reduce the induction air temp= erature.

Add to this list:

4) Increase eng= ine speed;

5) Reduce major= combustion chamber radius;

6) Reduce/Alter= combustion chamber turbulence;

7) Alter combus= tion chamber wall angles to reduce infrared and shockwave energy r= eflected into areas of instabillity.

8) Relocat= e spark plug(s)

Reductions in=20= IAT from the intercooler will buy one LARGE improvements in the =20= detonation limited BMEP (ie, more horsepower becomes usefully available).

That sounds a lot like something I said earlier. Your'e starting to agr= ee with me.

>>= However, when you make the blanket statement that a mechanically driven=20= supercharger will result in a slower airplane, we have to part company.<<<= /SPAN>

I didn=E2=80=99t say t= hat. I said the data I had seen revealed that one particular aircraft=20= using one particular configuration of belt driven compressor ended up, based= on actual test, going no faster with the belt driven compressor than=20= it did without.

I felt that was what you were implying by making the statement. I see W= alter came to the opposite conclusion. If I am mistaken, then I appologize.=20= I did not mean to put words in your mouth.

It's ironic that in the beginning my intent was to steer this thread&nb= sp;away from an argument between personalities and back toward a discussion=20= of the merits and fundamentals. I seem to have had the opposite effect on th= e argumentative part.

I am still curious to know what boost Rick runs on his otherwise&n= bsp;stock engine at Reno.

Rob

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