X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from imr-da01.mx.aol.com ([205.188.105.143] verified) by logan.com (CommuniGate Pro SMTP 5.3.8) with ESMTP id 4439903 for flyrotary@lancaironline.net; Sun, 22 Aug 2010 11:29:58 -0400 Received-SPF: pass receiver=logan.com; client-ip=205.188.105.143; envelope-from=Lehanover@aol.com Received: from imo-da03.mx.aol.com (imo-da03.mx.aol.com [205.188.169.201]) by imr-da01.mx.aol.com (8.14.1/8.14.1) with ESMTP id o7MFTKKj028185 for ; Sun, 22 Aug 2010 11:29:20 -0400 Received: from Lehanover@aol.com by imo-da03.mx.aol.com (mail_out_v42.9.) id q.ee1.3e434d (43958) for ; Sun, 22 Aug 2010 11:29:16 -0400 (EDT) Received: from magic-d20.mail.aol.com (magic-d20.mail.aol.com [172.19.155.136]) by cia-dd01.mx.aol.com (v129.4) with ESMTP id MAILCIADD017-abb64c71424c1b5; Sun, 22 Aug 2010 11:29:16 -0400 From: Lehanover@aol.com Message-ID: <3536a.31a351e0.39a29c4c@aol.com> Date: Sun, 22 Aug 2010 11:29:16 EDT Subject: Re: [FlyRotary] Re: Prop orientation with TDC To: flyrotary@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_3536a.31a351e0.39a29c4c_boundary" X-Mailer: AOL 9.0 VR sub 5204 X-AOL-IP: 173.88.9.178 X-Spam-Flag:NO X-AOL-SENDER: Lehanover@aol.com --part1_3536a.31a351e0.39a29c4c_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit In a message dated 8/22/2010 10:28:20 A.M. Eastern Standard Time, blake.lewis@gmail.com writes: On Sat, Aug 21, 2010 at 7:34 AM, Jeff Whaley wrote: > What is the Rotaries best prop orientation at the prop flange relative to TDC? > The Lycomings are typically entering the compression stroke at 11-10 o'clock and 5-4 o'clock. > The 13B goes through 3 compression strokes per e-shaft revolution - does this predicate a 3-bladed prop is the ideal match? > Jeff The orientation idea comes from the older 4 cylinder airplane engines that had to be hand started. So the position of the blade made a difference in that the person starting the engine needed a good body position to start out. It was also a good idea, because in the event of an engine stoppage, that very same position had the prop near horizontal, and that kept a blade from digging in on landing. In the rotary powered craft, the engine will be at TDC twice per crank shaft rotation (for a two rotor) so, 2 times the reduction ratio tells you how many times it gets to TDC per propeller revolution. 3 times for a 3 rotor, and 4 times for a 4 rotor. A 2 rotor with a 2.78:1 reduction unit will see TDC 2 X 2.78 = 5.56 or about every 65 degrees of prop rotation. This suggests that hand propping might be more difficult because of the mechanical disadvantage of the reduction unit, and should the engine fire, the length of time available to remove your hand might be very short, should the very next rotor face fire as well. Lynn E. Hanover --part1_3536a.31a351e0.39a29c4c_boundary Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
In a message dated 8/22/2010 10:28:20 A.M. Eastern Standard Time,=20 blake.lewis@gmail.com writes:
On Sat,=20 Aug 21, 2010 at 7:34 AM, Jeff Whaley <jwhaley@datacast.com>=20 wrote:
> What is the Rotaries best prop orientation at the prop fl= ange=20 relative to TDC?
> The Lycomings are typically entering the compre= ssion=20 stroke at 11-10 o'clock and 5-4 o'clock.
> The 13B goes through 3= =20 compression strokes per e-shaft revolution - does this predicate a 3-bla= ded=20 prop is the ideal match?
> Jeff
The orientation idea comes from the older 4 cylinder airplane engines= that=20 had to be hand started. So the position of the blade made a difference in= that=20 the person starting the engine needed a good body position to start out.= It was=20 also a good idea, because in the event of an engine stoppage, that very sa= me=20 position had the prop near horizontal, and that kept a blade from digging= in on=20 landing.
 
In the rotary powered craft, the engine will be at TDC twice per cran= k=20 shaft rotation (for a two rotor) so, 2 times the reduction ratio tells you= how=20 many times it gets to TDC per propeller revolution. 3 times for a 3 rotor,= and 4=20 times for a 4 rotor.
 
A 2 rotor with a 2.78:1 reduction unit will see TDC 2 X 2.78 =3D 5.56= or=20 about every 65 degrees of prop rotation. 
 
This suggests that hand propping might be more difficult because of= the=20 mechanical disadvantage of the reduction unit, and should the engine fire,= the=20 length of time available to remove your hand might be very short, should= the=20 very next rotor face fire as well.
 
Lynn E. Hanover 
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