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Date: Wed, 04 Apr 2012 16:08:27 -0400
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From: Gary Casey <casey.gary@yahoo.com>
Reply-To: Gary Casey <casey.gary@yahoo.com>
Subject: Re: engine movement
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Just some observations on the "engine movement" issue. =A0As I was building=
 I did some analysis of the engine mount system and compared it to that use=
d in the Lycoming engines. =A0I suppose the idea behind the so-called dynaf=
ocal mounts is that the stiff orientation (in the axial direction) of the m=
ounts are all directed, or focused, to a single point. =A0The "soft" orient=
ation of a mount is in the lateral direction. =A0The net result is that the=
 engine can move freely (well, more freely) in any direction as long as the=
 point that is in the focus of the mounts doesn't move. =A0Imagine the moun=
ts being just greased plates so you could swivel it all around. =A0Problem =
is that in the Continental system the focal point is well BEHIND the CG of =
the engine/prop assembly. =A0So the weight of the engine will easily pull t=
he nose down. =A0The Lycoming configuration (for the 6 cylinder engine - I =
don't know about the 4's) the focal point is either at the CG or the prop
 flange depending on which of the two mounting systems are used. =A0And the=
 Lycoming mounts are spread widely apart compared to the Continentals. =A0A=
nother secondary issue is that as best I can tell the Continental mounts ar=
e focused (incorrectly) on the crank centerline instead of the CG, which is=
 lower. =A0But I don't know whether or not that contributes to the problem.=
 I don't know of a solution short of changing the orientation of the mounts=
. =A0The engine CG is essentially over the front mount, so it should be poi=
nted more or less vertical in the side view and the rear mount angle more f=
orward. =A0I would be tempted to even point the front mount truly vertical,=
 compromising the focus, but giving it more stiffness in the vertical direc=
tion. =A0So how about reverting to the old non-focused mount in the front a=
nd leaving the rear alone. =A0I'll bet the sag would be less, although perc=
eived vibration might be more. =A0Just some random thoughts from a would-be
 engineer.=0AGary Casey=0A=0AOn Apr 2, 2012, at 1:59 PM, Paul Miller wrote:=
=0A=0AThis photo demonstrates how much the engine pulls down (and also to t=
he left) relative to the cowl during normal operation in the Legacy.=A0 Thi=
s was from a photo shoot at normal power.=A0 At rest, the spinner is flush =
with the cowl so I estimate at least an inch drop.=A0 This corresponds to w=
hat I'm finding with interference on the lower cowl but it is at least an i=
nch away when I remove the cowl for inspection.=A0 My plan is to shim up th=
e mount at the front two isolators.=A0 These are relatively new Berry mount=
s, no shims installed. All of the hard hits I previously had on the upper c=
owl are now removed.=A0 I use a white primer between flights inside the upp=
er cowl to provide witness marks and the most recent flights have shown no =
interference.=A0 However, I still get interference during flight at cruise =
RPMs that I am starting to identify on the lower cowl.=A0 Hopefully, those =
are the last.=A0 Tight cowling + twisting engines =3D lot of work.=0A=0APau=
l=0A
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<html><body><div style=3D"color:#000; background-color:#fff; font-family:bo=
okman old style, new york, times, serif;font-size:12pt"><div>Just some obse=
rvations on the "engine movement" issue. &nbsp;As I was building I did some=
 analysis of the engine mount system and compared it to that used in the Ly=
coming engines. &nbsp;I suppose the idea behind the so-called dynafocal mou=
nts is that the stiff orientation (in the axial direction) of the mounts ar=
e all directed, or focused, to a single point. &nbsp;The "soft" orientation=
 of a mount is in the lateral direction. &nbsp;The net result is that the e=
ngine can move freely (well, more freely) in any direction as long as the p=
oint that is in the focus of the mounts doesn't move. &nbsp;Imagine the mou=
nts being just greased plates so you could swivel it all around. &nbsp;Prob=
lem is that in the Continental system the focal point is well BEHIND the CG=
 of the engine/prop assembly. &nbsp;So the weight of the engine will
 easily pull the nose down. &nbsp;The Lycoming configuration (for the 6 cyl=
inder engine - I don't know about the 4's) the focal point is either at the=
 CG or the prop flange depending on which of the two mounting systems are u=
sed. &nbsp;And the Lycoming mounts are spread widely apart compared to the =
Continentals. &nbsp;Another secondary issue is that as best I can tell the =
Continental mounts are focused (incorrectly) on the crank centerline instea=
d of the CG, which is lower. &nbsp;But I don't know whether or not that con=
tributes to the problem. I don't know of a solution short of changing the o=
rientation of the mounts. &nbsp;The engine CG is essentially over the front=
 mount, so it should be pointed more or less vertical in the side view and =
the rear mount angle more forward. &nbsp;I would be tempted to even point t=
he front mount truly vertical, compromising the focus, but giving it more s=
tiffness in the vertical direction. &nbsp;So how about reverting to
 the old non-focused mount in the front and leaving the rear alone. &nbsp;I=
'll bet the sag would be less, although perceived vibration might be more. =
&nbsp;Just some random thoughts from a would-be engineer.</div><div>Gary Ca=
sey</div><div><br></div><div><span class=3D"Apple-style-span" style=3D"colo=
r: rgb(69, 69, 69); font-family: arial, helvetica, sans-serif; font-size: 1=
3px; ">On Apr 2, 2012, at 1:59 PM, Paul Miller wrote:<br><br>This photo dem=
onstrates how much the engine pulls down (and also to the left) relative to=
 the cowl during normal operation in the Legacy.&nbsp; This was from a phot=
o shoot at normal power.&nbsp; At rest, the spinner is flush with the cowl =
so I estimate at least an inch drop.&nbsp; This corresponds to what I'm fin=
ding with interference on the lower cowl but it is at least an inch away wh=
en I remove the cowl for inspection.&nbsp; My plan is to shim up the mount =
at the front two isolators.&nbsp; These are relatively new Berry mounts,
 no shims installed. All of the hard hits I previously had on the upper cow=
l are now removed.&nbsp; I use a white primer between flights inside the up=
per cowl to provide witness marks and the most recent flights have shown no=
 interference.&nbsp; However, I still get interference during flight at cru=
ise RPMs that I am starting to identify on the lower cowl.&nbsp; Hopefully,=
 those are the last.&nbsp; Tight cowling + twisting engines =3D lot of work=
.<br><br>Paul</span><br></div>  </div></body></html>
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