Hi Jeff The actual gyroscopic load total doesn't alter because the prop mass/diameter/speed doesn't change with distance. However, changing its arm (extension) would alter its distribution along the crank with the bearing acting as a pivot and could well move it into the same journal as one where harmonics are focussed as well. The total moments either side of the pivot must equal zero.
John The Martindale Family 29 Jane Circuit Toormina NSW 2452 Australia ph: 61 2 66 584767 email: johnja...@optusnet.com.au ----- Original Message ----- From: "Jeff Scott" <jscott.pi...@juno.com> To: <kr...@mylist.net> Sent: Wednesday, June 22, 2005 12:54 AM Subject: Re: KR> Detonation as crank failure cause? > > Detonation can certainly cause some bearing damage, but it would have to be quite severe and continuous to break a crank. I've torn down an engine subjected to severe and constant detonation (mistimed ignition timing due to a slipped harmonic balancer in a boat). It looked like someone had worked over the tops of the pistons with a ball peen hammer. The rod bearing damage was minimal, any damage to the mains was undecernable, and the crankshaft journals were all still within specs, although no longer perfectly round. Had it continued to run as it was, it would have pounded out the rod bearings and damaged the crank by flattening or otherwise trashing the rod journals first. > > Perhaps it's time to take into account the gyroscopic loads imposed by the spinning prop. The prop makes a great gyroscope out in front of the plane. Any change in direction is resisted by the gyroscopic effect of the prop and that load is transmitted as a bending moment to the prop hub. In the Corvair, there is only one small bearing in the front of the case taking that load. That bearing get's used like a fulcrum with second main countering the gyroscopic load from the prop. That works pretty well when you transmit that load through a solid shaft like aircraft engines and even the VW to some degree. However, in a Corvair, you are transmitting that load through the front two rod throws. The 90 degree break across the throw right next to the bearing journal indicates to me that the crank was being flexed with that type of load just as if you had bent it back and forth until it broke. The further you move the prop out from that bearing, the more it magnifies that load. That doesn't mean that the Corvair is a bad or dangerous engine. Only that you have to be mindful of it's design limitations and place the prop as close to the front bearing as possible to keep the gyroscopic loads transmitted to the crankshaft to a minimum. Also perfectly tracked and balanced, as well as light weight props would be in order. > > Ok, here's the disclaimer. I am a mechanic, not an engineer, so take my analysis with a grain of salt. It is also not my intention to throw rocks at anyone's plane or engine choice. My interest here lies strictly in the safety of my friends. > > -Jeff Scott > > > > -- "Mark Jones" <mjo...@muellersales.com> wrote: > No one has mentioned anything about detonation of the engine as a factor in crank failure. Detonation causes undue stresses on a crank by creating a hammer like force generated from the piston through the rods to the crank. This hammer-like shock wave being imposed on the crank causes severe overloading. Detonation can destroy an engine very quickly. How many of the crank failure engines actually were subjected to detonation. The only one who has confessed to having detonation was Mark Langford and his was a brief period on departure per his post of June 10th. Just something else to think about. > > Mark Jones (N886MJ) > Wales, WI > Visit my web site: http://mywebpage.netscape.com/n886mj > Email: flyk...@wi.rr.com > > _______________________________________ > Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp > to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > please see other KRnet info at http://www.krnet.org/info.html > > > _______________________________________ > Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp > to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > please see other KRnet info at http://www.krnet.org/info.html
