3M Engines

[GREEN, DOUG]

The goal is to resolve the impulses from the firing stroke into pure
rotation for the circular rubber in the mount to damp.

Ensuring the center of mass is at the center of rotation will minimize
translation effects, reducing leverage of mass above the centerline,
leaving mostly rotation. 

Trying shims of different thickness, and measuring aileron servo current
consumption...may see a trend...

may extrapolate the results to indicate how much to lower the engine

eg mount the engine on the wrong side of the engine mounting lugs, to
the other side of the beams...effectively lowering the engine by the
thickness of the beams of the mount. (But don't fly, test vibration
only)

If the constraint of a nose ring is removed, it then becomes possible to
mount the engine at different heights (on eg Pastomount). 

Could it be possible to make further improvements to the performance of
the Hyde type mount?

Doug

wgalligan wrote:
> 
> I dont think is so much a question of the center of mass as it is the center of rotation.  It is logical that the mass is above the c/l of rotation in a std piston engine.  If as in a previous post, you raise the engine above the centerline, then there is a new leverage point acting on the c/l of the mounts rotational axis, not a good idea.
> The closest thing I have seen in having the mass centraly located in a model engine is in either the Wankel or the new RCV type engines.  The whole point of the soft mount is to isolate the impulses from the firing stroke not contain the mass of the engine.  Did I say that right?
> 
> Wayne
> 
> > Eric,
> >
> > The Hyde mount design intent was to have the center of mass of the
> > engine and the center of rotation at the same point.
> >
> > Do we really know the center of mass of these newer engines?
> >
> > Does the center of effective mass change when the header/coupler/pipe is
> > attached?
> >
> > An experiment:
> >
> > Install metal shims of various thicknesses between the Hyde mount beams
> > and the engine mounting lugs to shift the center of effective mass of
> > the engine/header/coupler/pipe
> >
> > Measure aileron servo current consumption
> >
> > It may be possible to optimize the performance combination of mount and
> > the engine/header/coupler/pipe.
> >
> > Doug
> >
> >
> > > "Henderson,Eric" wrote:
> > >
> > > There is a time when a 2-c idles so low that it "bounces" as much as a
> > > 4-c at idle. Basically it is missing a beat so that it is firing at
> > > the same frequency as a slow running 4-c. At around 2000-2500 rpm they
> > > both smooth out.
> > >
> > > I have extensive time on 1.40, and now 1.60, 2-cycles that lets me
> > > compare them with the big YS 4-c's and how they run and shake a plane.
> > > I have run both engine types with and without nose rings.
> > >
> > > My goal was to get a plane that is shaken and "punished" the least!
> > > (Not ignoring sound issues BTW). I have observed that the best set-up
> > > is a non-nose ring Hydemount. All nose-rings add to airframe
> > > vibration. They provide poor isolation and have to be set with no side
> > > pressures to be iso-effective.
> > >
> > > All my nose ring installations cause aileron-buzz at certain - read
> > > most used in flight - rpm settings. This just kills the digital
> > > aileron servo!
> > >
> > > The 4-c is the worst culprit by far. The DZ is a shaker and this may
> > > be why the fuel foams and causes dead stick's at low rpms. The L is
> > > smoother but the more nitro you use the more "bang" and thus the more
> > > energy to dissipate.
> > >
> > > The smoothest set-up, by far, is a 2-c with no-nose ring. There
> > > appears to be no problem with the engine and prop torquing/twisting.
> > > The newer planes have room for a bigger hockey-puck-rear-plate. Planes
> > > with FG cowls are much easier to install without Herculean engineering
> > > of a nose ring support.
> > >
> > > I have put 4 and 2-cycles in the same airframe on the same mounts and
> > > same range of props and I have seen a distinctly better isolation when
> > > the 2-c is installed. The current batch of Webra 1,45, OS 1.40 RX and
> > > FI users can probably tell us what they are seeing.
> > >
> > > The "Mintor-men" will soon be reporting as well - right guys?
> > >
> > > From a noise point of view my Hydeout with an L, is quieter that my
> > > Temptation with an OS 1.60, that is quieter than my Hydeout with a
> > > DZ.... Not by much however...
> > >
> > > Regards,
> > >
> > > E.
> > >
> > >
> >
> > =====================================
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> >
> 
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