Return-Path: Received: from imo-d03.mx.aol.com ([205.188.157.35] verified) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 2945900 for flyrotary@lancaironline.net; Fri, 23 Jan 2004 14:24:38 -0500 Received: from Lehanover@aol.com by imo-d03.mx.aol.com (mail_out_v36_r4.12.) id q.155.2bfe16b4 (3996) for ; Fri, 23 Jan 2004 14:24:24 -0500 (EST) From: Lehanover@aol.com Message-ID: <155.2bfe16b4.2d42cee8@aol.com> Date: Fri, 23 Jan 2004 14:24:24 EST Subject: Re: [FlyRotary] FW: [VAF Mailing List] Engine Choice To: flyrotary@lancaironline.net MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: AOL 5.0 for Windows sub 138 In a message dated 1/22/2004 9:23:51 PM Central Standard Time, gregory_fuess@yahoo.com writes: << Forgive me for beating a dead horse about torsionals. I have been reading another list for (VAF and RV-7) ~2 years, and have anxiously anticipated installing a 13B, and now instead a Renesis engine, in my soon-to-start RV-7. Now, I am hearing things that cause me to question my ability to make a sound decision in this regard, as this is the first discussion of torsionals is the first I have heard. I am beginning to question my ability to follow through on what I had taken to be the best alternative engine choice. Let me swat that horse a few times. I repeat. This is not a factor. Only a near solid connection makes any of this a problem and there isn't one in the Ford based reduction system. The pieces have enough slop to null out nearly all of the offending impulses. There are no reversals in a rotary, while there are substantial reversals in a piston engine. If you are looking for an engine that can pitch half of a propeller blade, buy a flat 4 cylinder (real) airplane engine. The spring coupling used on the Ross set up, or the plastic coupling used by Tracy's design provide more than enough of a disconnect to eliminate these impulses as a hazard to the propeller, or the gear train and drop the remaining offensive pulsations to the idle speed of the engine. I believe everything your engineer friend said. It all sounds accurate to me. However, there is an endearing quality in people that requires them to reinvent the wheel every so often. Many competent people have been forced to cure a failure mode in a torsionally resonant system. Any system that uses a drive shaft to drive a propeller with a piston engine, or anything else, would have to face down such problems. So Molt Taylor and Jim Bede and many others in the automobile, trucking, and farm equipment industry have had to cure this problem. Molt Taylor used a coupler filled with steel shot to disconnect the engine from the drive system. Jim Bede used soft rubber donut joints in the drive line to null resonant impulses from a very shaky cycle engine. There are mountains of material available on how this problem has been overcome. It is a very destructive phenomena and a wise man thinks through each application to determine if there is a possibility that he has designed in a fault that may show up some day to bite him. There are not just two basic ways to defeat the problem, but three. The most obvious method is used by Mazda in the automobiles. A heavy flywheel. Just that simple. We are not interested in anything heavy in air plane use so that leaves only a tight system that uses the gearbox and prop as the flywheel to absorb the impulses, Or, the loose, or soft system that isolates the engine from the gear box as in a spring system or a plastic or rubber isolation system. The tight system requires great rigidity and close fitting, rather wide gear assemblies. As has been proven, very expensive. Very heavy. The loose system requires only a small amount of compliance to drop the offending RPM close to the idle speed of the engine. The plates that mount the plastic isolation discs or springs provide a measure of flywheel effect and the problem is solved. Great rigidity is not required. The teeth in the gear train can be small, and as a result lighter and cheaper., in fact, the gear train is available at any Ford dealer, so the very conservative could change the gear set every 500 or 1,000 hours if it makes you feel more comfortable. This system cannot transmit high amplitude resonance to the propeller, so a wide range of propellers can be used. Here are two links you may like to review. The second link has to do with the development of the BD-5 drive train. http://home.earthlink.net/~rotaryeng/ACRE.html http://www.prime-mover.org/Engines/Torsional/contact1/contact1.html Lynn E. Hanover