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Date: Sun, 05 Jul 2009 22:28:38 -0400
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From: Chris Zavatson <chris_zavatson@yahoo.com>
Subject: Re: [LML] Re: Now for something completely different
In-Reply-To: <list-3745710@logan.com>
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Paul,=0AI check all of the following at least annually.=0AInternal leaks:=
=0AInternal leaks are checked by removing the nose gear fork.=A0 The hollow=
 interior should remain dry.=A0 If the tiny O-rings of the guide key begin =
leaking, hydraulic fluid will start filling the hollow interior of the tube=
.=A0 There may be no exterior signs of a problem.=A0 The tube will just kee=
p filling until the shimmy damper starts pulling in air.=A0=0AFluid Level:=
=0AThis can be check by depressurizing and fully collapsing the strut.=A0 R=
emove the valve and using a syringe check to see how much fluid is needed t=
o bring the level back up the valve opening.=A0 Fluid will be lost in norma=
l operation, even if it is only a very small amount.=A0 Since shimmy is so =
catastrophic it is important to know the rate at which fluid is leaving the=
 system.=A0 If the level ever gets to low the damper will not work.=A0 The =
idea is to catch leaks and low fluid levels before they can produce a shimm=
y event.=A0 It is sort of like checking engine oil.=A0 We are all familiar =
with our engine's oil burn rate, but we still check the oil level during pr=
e-flight.=A0 We=A0want to catch any sudden change.=0ADamping Force:=0AThis =
is a little more challenging if the self centering feature is installed.=A0=
 It requires=A0two flat and smooth metal plates with grease between them.=
=A0 With the tow bar attached the strut should be rotated through its full=
=A0range of travel.=A0=A0I am not aware of any values for=A0damping ever ha=
ving been published, but experience with newly overhauled struts will give =
an indication of the proper resistance.=A0=A0It is very difficult to turn t=
he strut by hand just grabbing onto the wheel.=A0=A0 In addition to overall=
 resistance, it is important to feel for any dead spots.=A0 This indicates =
either worn parts or air in the damper.=A0 Newly overhauled units need to b=
e cycled back and forth=A0a lot to remove all the air - on the order of 20-=
30 cycles.=0AEven with=A0all the oil removed you wouldn't=A0see much of any=
 change in strut extension.=A0 Temperature=A0has a much=A0greater effect on=
 strut extension than fluid level.=0Ahope this helps,=0AChris=0A=0AChris Za=
vatson=0AN91CZ=0A360std=0Awww.N91CZ.com=A0=A0=A0=0A=0A=0A=0A      
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<html><head><style type=3D"text/css"><!-- DIV {margin:0px;} --></style></he=
ad><body><div style=3D"font-family:arial, helvetica, sans-serif;font-size:1=
0pt"><DIV>Paul,</DIV>=0A<DIV>I check all of the following at least annually=
.</DIV>=0A<DIV>Internal leaks:</DIV>=0A<DIV>Internal leaks are checked by r=
emoving the nose gear fork.&nbsp; The hollow interior should remain dry.&nb=
sp; If the tiny O-rings of the guide key begin leaking, hydraulic fluid wil=
l start filling the hollow interior of the tube.&nbsp; There may be no exte=
rior signs of a problem.&nbsp; The tube will just keep filling until the sh=
immy damper starts pulling in air.&nbsp;</DIV>=0A<DIV>Fluid Level:</DIV>=0A=
<DIV>This can be check by depressurizing and fully collapsing the strut.&nb=
sp; Remove the valve and using a syringe check to see how much fluid is nee=
ded to bring the level back up the valve opening.&nbsp; Fluid will be lost =
in normal operation, even if it is only a very small amount.&nbsp; Since sh=
immy is so catastrophic it is important to know the rate at which fluid is =
leaving the system.&nbsp; If the level ever gets to low the damper will not=
 work.&nbsp; The idea is to catch leaks and low fluid levels before they ca=
n produce a shimmy event.&nbsp; It is sort of like checking engine oil.&nbs=
p; We are all familiar with our engine's oil burn rate, but we still check =
the oil level during pre-flight.&nbsp; We&nbsp;want to catch any sudden cha=
nge.</DIV>=0A<DIV>Damping Force:</DIV>=0A<DIV>This is a little more challen=
ging if the self centering feature is installed.&nbsp; It requires&nbsp;two=
 flat and smooth metal plates with grease between them.&nbsp; With the tow =
bar attached the strut should be rotated through its full&nbsp;range of tra=
vel.&nbsp;&nbsp;I am not aware of any values for&nbsp;damping ever having b=
een published, but experience with newly overhauled struts will give an ind=
ication of the proper resistance.&nbsp;&nbsp;It is very difficult to turn t=
he strut by hand just grabbing onto the wheel.&nbsp;&nbsp; In addition to o=
verall resistance, it is important to feel for any dead spots.&nbsp; This i=
ndicates either worn parts or air in the damper.&nbsp; Newly overhauled uni=
ts need to be cycled back and forth&nbsp;a lot to remove all the air - on t=
he order of 20-30 cycles.</DIV>=0A<DIV>Even with&nbsp;all the oil removed y=
ou wouldn't&nbsp;see much of any change in strut extension.&nbsp; Temperatu=
re&nbsp;has a much&nbsp;greater effect on strut extension than fluid level.=
</DIV>=0A<DIV>hope this helps,</DIV>=0A<DIV>Chris</DIV>=0A<DIV>&nbsp;</DIV>=
=0A<DIV>Chris Zavatson</DIV>=0A<DIV>N91CZ</DIV>=0A<DIV>360std</DIV>=0A<DIV>=
<A href=3D"http://www.n91cz.com/">www.N91CZ.com</A>&nbsp;&nbsp;&nbsp;<BR></=
DIV></div><br>=0A=0A=0A=0A      </body></html>
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