X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 09 Apr 2006 23:29:42 -0400 Message-ID: X-Original-Return-Path: Received: from imo-m17.mx.aol.com ([64.12.138.207] verified) by logan.com (CommuniGate Pro SMTP 5.0.9) with ESMTP id 1063552 for lml@lancaironline.net; Sun, 09 Apr 2006 21:31:28 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.138.207; envelope-from=Sky2high@aol.com Received: from Sky2high@aol.com by imo-m17.mx.aol.com (mail_out_v38_r7.3.) id q.316.2611e18 (2168) for ; Sun, 9 Apr 2006 21:30:44 -0400 (EDT) From: Sky2high@aol.com X-Original-Message-ID: <316.2611e18.316b0f44@aol.com> X-Original-Date: Sun, 9 Apr 2006 21:30:44 EDT Subject: Re: [LML] fixed-pitch prop X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1144632644" X-Mailer: 9.0 Security Edition for Windows sub 2340 X-Spam-Flag: NO -------------------------------1144632644 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit In a message dated 4/8/2006 11:42:19 P.M. Central Daylight Time, elippse@sbcglobal.net writes: Actually, Scotty, I do have a fixed-pitch prop. But my prop has very little drag; I have to use a lot of braking to bring it to a stop (on the ground, of course!). And this with an idle rpm of 680! I'm sure you, with all your knowledge of things aerodynamic, have a copy of "Aerodynamics For Naval Aviators". Look on page 149 where it compares wind-milling vs stopped drag vs pitch. It turns out that a prop with 23 deg. to 60 deg. pitch has less drag wind-milling than stopped. My effective pitch, from VMPH X 1056 / rpm, usually computes to 76". That works out to 27 deg at the 75% radius of a 63" diameter prop. That, along with the minimal area of my prop beyond 12" radius, is the reason it has so little drag. 'True, even though my 235 has a best L/D of 15:1 at 110 mph IAS, it probably won't get that with the engine off. One of these days I'll have to shut off the engine, at altitude, and see if the prop will even wind-mill, and what kind of glide I do get! Paul, Numerical mumbo jumbo won't get you where you want to go if things get quiet...... Try to get the engine at idle power and see what your sink rate is at best glide - Use this as your best case for the engine out, prop rotating sink rate. It's fine that you want to rely on the Navy - That means if the engine seized (no oil, a common failure problem) your sink rate is even worse. Don't quote the false 15:1 rate (where ever you read that in an ad), go find out what it is and scare yourself into reality! Report back here on the LML for others to learn. Note: Do any experimentation over an airport. Scott Krueger AKA Grayhawk LNC2 N92EX IO 320 SB 89/96 PS Your prop may have very little drag when powering your craft, but you have no idea what it is when it is turning the engine.... or not.... -------------------------------1144632644 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
In a message dated 4/8/2006 11:42:19 P.M. Central Daylight Time,=20 elippse@sbcglobal.net writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>Actually, Scotty, I do have a fixed-pitch prop.  But my=20= prop=20 has very little drag; I have to use a lot of braking to bring it to a stop= (on=20 the ground, of course!). And this with an idle rpm of 680! I'm sure you, w= ith=20 all your knowledge of things aerodynamic, have a copy of "Aerodynamics=20 For Naval Aviators". Look on page 149 where it compares wind-milling=20= vs=20 stopped drag vs pitch. It turns out that a prop with 23 deg. to=20= 60=20 deg. pitch has less drag wind-milling than stopped. My effective pitc= h,=20 from VMPH X 1056 / rpm, usually compu= tes to=20 76". That works out to 27 deg at the 75% radius of a 63" diameter prop. Th= at,=20 along with the minimal area of my prop beyond 12" radius, is the reason it= has=20 so little drag. 'True, even though my 235 has a best L/D of 15:1 at 1= 10=20 mph IAS, it probably won't get that with the engine off. One of these days= =20 I'll have to shut off the engine, at altitude, and see if the prop wi= ll=20 even wind-mill, and what kind of glide I do=20 get!
Paul,
 
Numerical mumbo jumbo won't get you where you want to go if things get=20 quiet......  Try to get the engine at idle power and see what= =20 your sink rate is at best glide - Use this as your best case for the en= gine=20 out, prop rotating sink rate.  It's fine that you want to rely on the N= avy=20 - That means if the engine seized (no oil, a common failure proble= m)=20 your sink rate is even worse.  Don't quote the false 15:1 rate (where e= ver=20 you read that in an ad), go find out what it is and scare yourself into=20 reality!  Report back here on the LML for others to learn. 
 
Note: Do any experimentation over an airport.
 
 
Scott Krueger=20 AKA Grayhawk
LNC2 N92EX IO 320 SB 89/96
 
PS Your prop=20 may have very little drag when powering your craft, but you have no idea wha= t it=20 is when it is turning the engine.... or not....


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