Rust removal?

On Feb 27, 1:12*pm, wrote:
On Feb 26, 5:32*am, JJ Sinclair wrote:





Hey JJ - any reason to be concerned about the tightness of the fit of
the pins in the bushings? *I'd think you wouldn't want a shimmy in
flight. Is there any risk of that?

Andy

Some will experience what is known as the "clunk". That is the sound
you may hear when rolling into a thermal. It is the fuselage sliding
in the lift fittings and going "clunk". If you hear this you need at
least a 20 thousands shim on one aft lift fitting, determine which one
by measuring from the TE probe on the fin with a steel tape to a
common point on each wing, say the aileron cut-out. Don't be surprised
to find your prize possession is off by close to an inch! This will
tell you where to epoxy the shim onto one of the aft lift fittings.
Some will find their lift fittings are too tight which makes getting
the wing onto the lift fittings a chore. Clean the fittings and scrub
them with magic-marker, then put it together again. Then remove the
wing and observe the magic-marked pins. The shinny spots show the
interference fit areas. My ship showed a problem on the front end of
the forward lift fitting and the back end of the aft lift fitting. It
took months of working these areas down with emery cloth every time I
flew to finally get the wing to slide on easily. Believe me you don't
remove much steel with sandpaper!
JJ

I guess I was wondering what happens if, due to sanding, the lift pins
end up smaller in diameter than the bushings. Then it seems to me that
no matter how much you shim you could end up with a clunker since the
distance between opposing lift fittings is fixed by the main pins so
you can't really push the wings further to get the (usually tapered)
lift pins to snugly engage with the bushings all the way around the
circumference.

If I recall correctly my 1980-vintage LS-4 was put together such that
you could pull straight up on the trailing edge of the wing right near
the root and feel the lift pin "clunk" from resting on the bottom of
the bushing to the top. It was only a fraction of an inch, but you
could feel it. The glider was a mix of wings and fuse from two
different S/Ns so this could also just be rigging rather than wear,
but it's what raised the question in my mind.

9B- Hide quoted text -

- Show quoted text -

The point under discussion is how to remove corrosion from a slightly
rusted lift fitting. I just measured (with a micrometer) a rusted rear
lift pin on a G-102 left wing and locked the micrometer at this
reading. I then polished the lift fitting to bright steel using medium
grade emery cloth. The locked micrometer went back on the lift fitting
with the same force it took to remove it when rusted. There was no
measurable difference between the rusted reading and the bright steel
reading, meaning the amount of steel removed by the above process
could not be detected. I ask again; How much steel do you think you
can remove by scrubbung off light rust with sandpaper? To me this is
nothing more than common sense!
JJ

On Feb 28, 9:25*am, wrote:
On Feb 27, 1:12*pm, wrote:





On Feb 26, 5:32*am, JJ Sinclair wrote:

Hey JJ - any reason to be concerned about the tightness of the fit of
the pins in the bushings? *I'd think you wouldn't want a shimmy in
flight. Is there any risk of that?

Andy

Some will experience what is known as the "clunk". That is the sound
you may hear when rolling into a thermal. It is the fuselage sliding
in the lift fittings and going "clunk". If you hear this you need at
least a 20 thousands shim on one aft lift fitting, determine which one
by measuring from the TE probe on the fin with a steel tape to a
common point on each wing, say the aileron cut-out. Don't be surprised
to find your prize possession is off by close to an inch! This will
tell you where to epoxy the shim onto one of the aft lift fittings.
Some will find their lift fittings are too tight which makes getting
the wing onto the lift fittings a chore. Clean the fittings and scrub
them with magic-marker, then put it together again. Then remove the
wing and observe the magic-marked pins. The shinny spots show the
interference fit areas. My ship showed a problem on the front end of
the forward lift fitting and the back end of the aft lift fitting. It
took months of working these areas down with emery cloth every time I
flew to finally get the wing to slide on easily. Believe me you don't
remove much steel with sandpaper!
JJ

I guess I was wondering what happens if, due to sanding, the lift pins
end up smaller in diameter than the bushings. Then it seems to me that
no matter how much you shim you could end up with a clunker since the
distance between opposing lift fittings is fixed by the main pins so
you can't really push the wings further to get the (usually tapered)
lift pins to snugly engage with the bushings all the way around the
circumference.

If I recall correctly my 1980-vintage LS-4 was put together such that
you could pull straight up on the trailing edge of the wing right near
the root and feel the lift pin "clunk" from resting on the bottom of
the bushing to the top. It was only a fraction of an inch, but you
could feel it. The glider was a mix of wings and fuse from two
different S/Ns so this could also just be rigging rather than wear,
but it's what raised the question in my mind.

9B- Hide quoted text -

- Show quoted text -

The point under discussion is how to remove corrosion from a slightly
rusted lift fitting. I just measured (with a micrometer) a rusted rear
lift pin on a G-102 left wing and locked the micrometer at this
reading. I then polished the lift fitting to bright steel using medium
grade emery cloth. The locked micrometer went back on the lift fitting
with the same force it took to remove it when rusted. There was no
measurable difference between the rusted reading and the bright steel
reading, meaning the amount of steel removed by the above process
could not be detected. I ask again; How much steel do you think you
can remove by scrubbung off light rust with sandpaper? To me this is
nothing more than common sense!
JJ- Hide quoted text -

- Show quoted text -

I have spent hours taking off 1 thousandth of an inch from an oversize
pin.
JJ is absolutely right. You can't go wrong by sanding off the surface
corrosion to bright and then protecting it.
That said- if you see pitting, that is another matter.
And NEVER be tempted to save a little time time by picking up a file.
32 years doin' it.
UH

On Feb 28, 12:48*pm, wrote:
On Feb 28, 9:25*am, wrote:



On Feb 27, 1:12*pm, wrote:

On Feb 26, 5:32*am, JJ Sinclair wrote:

Hey JJ - any reason to be concerned about the tightness of the fit of
the pins in the bushings? *I'd think you wouldn't want a shimmy in
flight. Is there any risk of that?

Andy

Some will experience what is known as the "clunk". That is the sound
you may hear when rolling into a thermal. It is the fuselage sliding
in the lift fittings and going "clunk". If you hear this you need at
least a 20 thousands shim on one aft lift fitting, determine which one
by measuring from the TE probe on the fin with a steel tape to a
common point on each wing, say the aileron cut-out. Don't be surprised
to find your prize possession is off by close to an inch! This will
tell you where to epoxy the shim onto one of the aft lift fittings.
Some will find their lift fittings are too tight which makes getting
the wing onto the lift fittings a chore. Clean the fittings and scrub
them with magic-marker, then put it together again. Then remove the
wing and observe the magic-marked pins. The shinny spots show the
interference fit areas. My ship showed a problem on the front end of
the forward lift fitting and the back end of the aft lift fitting. It
took months of working these areas down with emery cloth every time I
flew to finally get the wing to slide on easily. Believe me you don't
remove much steel with sandpaper!
JJ

I guess I was wondering what happens if, due to sanding, the lift pins
end up smaller in diameter than the bushings. Then it seems to me that
no matter how much you shim you could end up with a clunker since the
distance between opposing lift fittings is fixed by the main pins so
you can't really push the wings further to get the (usually tapered)
lift pins to snugly engage with the bushings all the way around the
circumference.

If I recall correctly my 1980-vintage LS-4 was put together such that
you could pull straight up on the trailing edge of the wing right near
the root and feel the lift pin "clunk" from resting on the bottom of
the bushing to the top. It was only a fraction of an inch, but you
could feel it. The glider was a mix of wings and fuse from two
different S/Ns so this could also just be rigging rather than wear,
but it's what raised the question in my mind.

9B- Hide quoted text -

- Show quoted text -

The point under discussion is how to remove corrosion from a slightly
rusted lift fitting. I just measured (with a micrometer) a rusted rear
lift pin on a G-102 left wing and locked the micrometer at this
reading. I then polished the lift fitting to bright steel using medium
grade emery cloth. The locked micrometer went back on the lift fitting
with the same force it took to remove it when rusted. There was no
measurable difference between the rusted reading and the bright steel
reading, meaning the amount of steel removed by the above process
could not be detected. I ask again; How much steel do you think you
can remove by scrubbung off light rust with sandpaper? To me this is
nothing more than common sense!
JJ- Hide quoted text -

- Show quoted text -

I have spent hours taking off 1 thousandth of an inch from an oversize
pin.
JJ is absolutely right. You can't go wrong by sanding off the surface
corrosion to bright and then protecting it.
That said- if you see pitting, that is another matter.
And NEVER be tempted to save a little time time by picking up a file.
32 years doin' it.
UH

That's a good enough answer for me. Get some 40 grit and go to
town. ;-)