X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 2 [X] Return-Path: Received: from imf20aec.mail.bellsouth.net ([205.152.59.68] verified) by logan.com (CommuniGate Pro SMTP 5.1.8) with ESMTP id 1986470 for flyrotary@lancaironline.net; Sun, 15 Apr 2007 10:02:28 -0400 Received-SPF: none receiver=logan.com; client-ip=205.152.59.68; envelope-from=rusty@radrotary.com Received: from ibm64aec.bellsouth.net ([65.6.194.9]) by imf20aec.mail.bellsouth.net with ESMTP id <20070415140136.QXTO13958.imf20aec.mail.bellsouth.net@ibm64aec.bellsouth.net> for ; Sun, 15 Apr 2007 10:01:36 -0400 Received: from rd ([65.6.194.9]) by ibm64aec.bellsouth.net with ESMTP id <20070415140134.QUMV23107.ibm64aec.bellsouth.net@rd> for ; Sun, 15 Apr 2007 10:01:34 -0400 From: "Russell Duffy" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: single rotor testing Date: Sun, 15 Apr 2007 09:01:34 -0500 Message-ID: <000001c77f66$93f076b0$6e01a8c0@rd> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C77F3C.AB1A6EB0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6822 Importance: Normal Thread-Index: Acd/C9IfRQX6iINWReuX84nYT1+upgAWGFZw In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C77F3C.AB1A6EB0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Maybe the low idle problem is related to the mixture problem. Hi Bob, =20 The low speed problem is known as "torque reversals" and would also = effect single piston engines I believe. =20 =20 As I understand it, the rotor fires, and accelerates the engine forward. Once the thrust from the exhaust is over, it has to coast around part of = the revolution to get back to where it can fire again. While coasting, the compression for the next cycle hits, and the engine starts decelerating, only to suddenly accelerate again when it fires the next time. This = torque reversal is what causes the shake. =20 =20 As you add more rotors (or cylinders), then you get to a point where acceleration is being generated by one rotor, while another is trying to decelerate from compression. Since the firing pulse is so much greater = than the compression force, the net result is that you always have forward torque. =20 =20 The only way you can smooth out a single rotor at low rpm would be to = have a heavy flywheel. The inertia from the flywheel would help you "coast" through the compression stroke, and significantly reduce the = deceleration. The downside is obvious for aircraft applications.=20 =20 Cheers, Rusty =20 ------=_NextPart_000_0001_01C77F3C.AB1A6EB0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Message

Maybe the low idle problem is related to the mixture=20 problem.

Hi=20 Bob,
 
The low = speed problem is=20 known as "torque reversals" and would also effect single piston = engines I=20 believe. 
 
As I = understand it, the=20 rotor fires, and accelerates the engine forward.  Once the thrust = from the=20 exhaust is over, it has to coast around part of the revolution to get = back to=20 where it can fire again.  While coasting, the = compression for the=20 next cycle hits, and the engine starts decelerating, only to suddenly = accelerate=20 again when it fires the next time.  This torque reversal = is what=20 causes the shake.  
 
As you = add=20 more rotors (or cylinders), then you get to a point = where acceleration=20 is being generated by one rotor, while another is trying to decelerate = from=20 compression.  Since the firing pulse is so much greater = than the=20 compression force, the net result is that you always have=20 forward torque.  
 
The only = way you can=20 smooth out a single rotor at low rpm would be to have a heavy = flywheel. =20 The inertia from the flywheel would help you "coast" through the = compression=20 stroke, and significantly reduce the deceleration.  The = downside is=20 obvious for aircraft applications. 
 
Cheers,
Rusty=20   


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