Return-Path: Sender: (Marvin Kaye) To: lml@lancaironline.net Date: Tue, 21 Oct 2003 17:18:46 -0400 Message-ID: X-Original-Return-Path: Received: from imo-r01.mx.aol.com ([152.163.225.97] verified) by logan.com (CommuniGate Pro SMTP 4.1.5) with ESMTP id 2645653 for lml@lancaironline.net; Tue, 21 Oct 2003 16:10:37 -0400 Received: from Epijk@aol.com by imo-r01.mx.aol.com (mail_out_v36_r1.1.) id q.14b.25a5fd6a (4012) for ; Tue, 21 Oct 2003 16:09:03 -0400 (EDT) From: Epijk@aol.com X-Original-Message-ID: <14b.25a5fd6a.2cc6ec5f@aol.com> X-Original-Date: Tue, 21 Oct 2003 16:09:03 EDT Subject: Re: [LML] Horsepower Calculation X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_14b.25a5fd6a.2cc6ec5f_boundary" X-Mailer: 7.0 for Windows sub 10708 --part1_14b.25a5fd6a.2cc6ec5f_boundary Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable I am very curious as to which "industry" was the source of this alleged=20 "standard" : "....industry standard (verifable in any STC POH) is:=20 (RPM/2700)*(MAP/29)=3DHP..."=20 The SAE standard equation for HP is: HP (measured) =3D Torque x RPM / 5252. That standard has been adopted by practically every industry I can think of.= =20 The "standard" HP which manufacturers advertise is generally accepted as the= =20 power produced at atmospheric conditions of 29.92 in. hg. barometric pressur= e,=20 59=B0F atmospheric pressure, and a specified relative humidity.=20 There are other "standard" atmospheric conditions used by some car=20 manufacturers (and by Lycoming) to achieve higher advertised power levels. T= here is also=20 an accepted methodology for correcting a measurement taken at some other se= t=20 of atmospheric conditions back to the standard. The alleged "industry standard" equation (quoted above) looks as if it might= =20 be an attempt to calculate a power output at known conditions based on the=20 known (actually, advertised) max engine power.=20 If that is the case, then the equation should look like this: calculated-HP =3D rated HP * (actual-RPM / Rating-RPM) * (actual-MAP /=20 rating-MAP) The quoted "2700" figure only applies to engines rated at 2700. If you had a= =20 Lyc rated at 290 HP at 2575 RPM on 29.5" MAP, operating at 2300 RPM on 25"=20 MAP, then the APPROXIMATE power (from that equation) would be 219 HP. BTW, that equation produces only an APPROXIMATION, because it is well-known=20 that power is not linear with MAP, but for normally aspirated engines, it=20 approximates linear between about 20" and 29" MAP, and can vary significantl= y with=20 the reduced backpressure experienced at altitude.=20 If you doubt that, just examine the equations and curves which Lycoming=20 publishes to determine HP from known operating conditions. Hope that helps. Jack Kane --part1_14b.25a5fd6a.2cc6ec5f_boundary Content-Type: text/html; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable I am very curious as to w= hich "industry" was the source of this alleged "standard" :

"....industry standard (verifable in any STC POH) is: (R= PM/2700)*(MAP/29)=3DHP..." <= BR>
The SAE standard equation for HP is:

HP (measured) =3D Torque x RPM / 5252.

That standard has been adopted by practically every industry I can think of.= The "standard" HP which manufacturers advertise is generally accepted= as the power produced at atmospheric conditions of 29.92 in. hg. barometric= pressure, 59=B0F atmospheric pressure, and a specified relative humidity. <= BR>
There are other "standard" atmospheric conditions used by some car manufactu= rers (and by Lycoming) to achieve higher advertised power levels. There is a= lso an accepted methodology for correcting a measurement taken at some= other set of atmospheric conditions back to the standard.

The alleged "industry standard" equation (quoted above) looks as if it mi= ght be an attempt to calculate a power output at known conditions based=20= on the known (actually, advertised) max engine power.

If that is the case, then the equation should look like this:

calculated-HP =3D rated HP * (actual-RPM / Rating-RPM) * (actual-MAP / ratin= g-MAP)

The quoted "2700" figure only applies to engines rated at 2700. If you had a= Lyc rated at 290 HP at 2575 RPM on 29.5" MAP, operating at 2300 RPM on 25"=20= MAP, then the APPROXIMATE power (from that equation) would be 219 HP.

BTW, that equation produces only an APPROXIMATION, because it is well-known=20= that power is not linear with MAP, but for normally aspirated engines, it approximates linear between about 20" and 29" MAP, and can vary=20= significantly with the reduced backpressure experienced at altitude.

If you doubt that, just examine the equations and curves which Lycoming publ= ishes to determine HP from known operating conditions.

Hope that helps.
Jack Kane --part1_14b.25a5fd6a.2cc6ec5f_boundary--