Return-Path: Sender: "Marvin Kaye" To: lml@lancaironline.net Date: Wed, 22 Dec 2004 14:33:31 -0500 Message-ID: X-Original-Return-Path: Received: from imo-m22.mx.aol.com ([64.12.137.3] verified) by logan.com (CommuniGate Pro SMTP 4.2.5) with ESMTP id 577078 for lml@lancaironline.net; Wed, 22 Dec 2004 14:21:45 -0500 Received-SPF: pass receiver=logan.com; client-ip=64.12.137.3; envelope-from=Sky2high@aol.com Received: from Sky2high@aol.com by imo-m22.mx.aol.com (mail_out_v37_r3.8.) id q.90.53a38f42 (4238) for ; Wed, 22 Dec 2004 14:21:10 -0500 (EST) From: Sky2high@aol.com X-Original-Message-ID: <90.53a38f42.2efb2326@aol.com> X-Original-Date: Wed, 22 Dec 2004 14:21:10 EST Subject: Re: [LML] Re: airspeed vs. power X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1103743270" X-Mailer: 9.0 Security Edition for Windows sub 5000 -------------------------------1103743270 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit In a message dated 12/22/2004 12:00:16 P.M. Central Standard Time, REHBINC@aol.com writes: My calculator gives slightly different results: I get a change in air speed of 1.58% rather than 1.95%. I think you may have used IAS rather than TAS. Also, correcting for OAT and MAP gives 1.60% predicted change in air speed If you are going to correct for accessory losses, then you should probably also be correcting for the throttling loss. This power is the throttle depression (inHg), 1" in this case, multiplied by RPM x displacement (in^3)x volumetric efficiency(VE) divided by 122150 to get horsepower. I would guess that VE for a naturally aspirated engine is about .92, somebody out there may know the real value for a specific engine. VE will also change slightly with RPM. Rob, What correction for OAT (should be TAT) and MAP? What about the correction to induction air temp after it passes thru the hot oil sump? Throttle depression? I am measuring MAP (Manifold Absolute Pressure) in the manifold, after the throttle. MAP at wide open throttle (WOT) is without (theoretically) any induction system vacuum. Assuming instrument accuracy and assuming we could actually measure the true ambient pressure we could also measure the Ram air rise. I think the only measure of "power" would be delivered thrust. I would tie my tail to a fish scale attached to a SUV but something's different when the prop is screwing thru the air. I guess the only way to do these things is side by side until I pull ahead! All other things being equal! Scott Krueger AKA Grayhawk N92EX IO320 Aurora, IL (KARR) -------------------------------1103743270 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable

In a message dated 12/22/2004 12:00:16 P.M. Central Standard Time,=20 REHBINC@aol.com writes:

<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>

My calculator gives slightly different results:

I get a change in air speed of 1.58% rather than 1.95%. I think you m= ay=20 have used IAS rather than TAS.

Also, correcting for OAT and MAP gives 1.60% predicted change in air=20 speed

If you are going to correct for accessory losses, then you should=20 probably also be correcting for the throttling loss. This power is th= e=20 throttle depression (inHg), 1" in this case, multiplied by RPM x displacem= ent=20 (in^3)x volumetric efficiency(VE) divided by 122150 to get horsepower. I w= ould=20 guess that VE for a naturally aspirated engine is about .92, somebody out=20 there may know the real value for a specific engine. VE will also change=20 slightly with RPM.

Rob,

What correction for OAT (should be TAT) and MAP? What about the=20 correction to induction air temp after it passes thru the hot oil sump?

Throttle depression? I am measuring MAP (Manifold Absolute Pressu= re)=20 in the manifold, after the throttle. MAP at wide open throttle (WOT) i= s=20 without (theoretically) any induction system vacuum. Assuming instrume= nt=20 accuracy and assuming we could actually measure the true ambient pressu= re=20 we could also measure the Ram air rise. I think the only measure=20= of=20 "power" would be delivered thrust. I would tie my tail to a fish scale= =20 attached to a SUV but something's different when the prop is screwing thru t= he=20 air.

I guess the only way to do these things is side by side until I pull=20 ahead! All other things being equal!=20

Scott Krueger=20 AKA Grayhawk
N92EX IO320 Aurora, IL=20 (KARR)

-------------------------------1103743270--