Return-Path: Received: from [24.25.9.100] (HELO ms-smtp-01-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.2b8) with ESMTP id 335756 for flyrotary@lancaironline.net; Tue, 27 Jul 2004 10:56:34 -0400 Received-SPF: error receiver=logan.com; client-ip=24.25.9.100; envelope-from=eanderson@carolina.rr.com Received: from EDWARD (cpe-069-132-183-211.carolina.rr.com [69.132.183.211]) by ms-smtp-01-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id i6REu1Pg027555 for ; Tue, 27 Jul 2004 10:56:02 -0400 (EDT) Message-ID: <000c01c473e9$d9c5a740$2402a8c0@EDWARD> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Prop Speeds Date: Tue, 27 Jul 2004 10:56:08 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0009_01C473C8.527ACED0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1409 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0009_01C473C8.527ACED0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MessageNo, I think you are correct, Al The "corkscrew" calculation will almost always under-estimate the = speed capability of a decent propeller as it only considers the "Screw = Pitch" (which is a notoriously flaky and difficult parameter for an = amateur to determine accurately in the first place). What that approach = fails to consider is that the propeller, of course, is an airfoil and = the blades produce lift similar to a wing. This lift vector, of course, = is complex due to the prop rotation, but it is generally perpendicular = (more or less) to the surface of the blade. This results in more "pull" = on the blade of the propeller and results in more thrust and forward = movement per revolution than just calculating the distance the "screw = effect" would pull your aircraft along. Therefore, you airspeed will = generally be higher than the "corkscrew" calculations alone would = indicate. That, at least is my understanding of the why you go faster = than the "corkscrew" calculation would indicate. Ed Ed Anderson RV-6A N494BW Rotary Powered Matthews, NC ----- Original Message -----=20 From: Al Gietzen=20 To: Rotary motors in aircraft=20 Sent: Tuesday, July 27, 2004 9:30 AM Subject: [FlyRotary] Re: Prop Speeds Subject: [FlyRotary] Prop Speeds Wow, that is 2935 RPM at the prop with a prop tip speed of just under = 900 FPS. I am still too shy to run mine that fast, although I could = easily get there. Interestingly, the calculations say the max corkscrew = speed of that prop at that RPM is only 197mph. He could pick up a = little for being really clean, and maybe some more depending on how they = calculate prop pitch. The pitch is a measure of the angle of the chord of the blade; or = sometimes the flat on the RAF airfoil; it doesn't measure the "lift" of = the airfoil. So it seems to me quite possible to go faster than the = "corkscrew" speed of the prop. But then I could be wrong . . . Al ------=_NextPart_000_0009_01C473C8.527ACED0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message
No, I think you are correct, = Al
 
    The "corkscrew" = calculation will=20 almost always under-estimate the speed capability of a decent propeller = as it=20 only considers the "Screw Pitch" (which is a notoriously flaky and = difficult=20 parameter for an amateur to determine accurately in the first = place). =20 What that approach fails to consider is that the propeller, of = course,=20 is an airfoil and the blades produce lift similar to a wing.  This = lift=20 vector, of course, is complex due to the prop rotation,  but = it is=20 generally perpendicular (more or less) to the surface of the = blade.  This=20 results in more "pull" on the blade of the propeller and results in more = thrust=20 and forward movement per revolution than just calculating the distance = the=20 "screw effect" would pull your aircraft along.  Therefore, you = airspeed=20 will generally be higher than the "corkscrew" calculations alone would=20 indicate.  That, at least is my understanding of the why you = go faster=20 than the "corkscrew" calculation would indicate.
 
Ed
 
Ed Anderson
RV-6A N494BW Rotary=20 Powered
Matthews, NC
----- Original Message -----
From:=20 Al = Gietzen=20
Sent: Tuesday, July 27, 2004 = 9:30=20 AM
Subject: [FlyRotary] Re: Prop=20 Speeds

 

Subject:=20 [FlyRotary] Prop Speeds

 

Wow, that is 2935 RPM = at the prop=20 with a prop tip speed of just under 900 FPS.  I am still too shy = to run=20 mine that fast, although I could easily get there.  = Interestingly, the=20 calculations say the max corkscrew speed of that prop at that RPM is = only=20 197mph.  He could pick up a little for being really clean, and = maybe some=20 more depending on how they calculate prop = pitch.

 

The pitch = is a=20 measure of the angle of the chord of the blade; or sometimes the flat = on the=20 RAF airfoil; it doesn=92t measure the =93lift=94 of the airfoil.  = So it seems=20 to me quite possible to go faster than the =93corkscrew=94 speed of = the=20 prop.  But then I could be wrong . . .

 

Al

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