[rebel-builders] Moose: Elevator trim (crush tube)...was: Ray Allen Servo
Posted: Sun Feb 19, 2012 5:29 pm
Not necessary to butt it up to the ends. The failure mode is bending in
the middle and there is very little tendancy to bend near the ends. The
original rod is plenty strong enough if it is short or straight. We need
to stop it from bending and failing at the bend in what is commonly
known as buckling of a column.
For anybody not familiar, this is the same reason a high slender antenna
tower will have guy wires at several heights. Each attachment stabilizes
the column so that it can't start to bend (buckle) or oscillate at that
attachment point (node).
Yes a longer horn reduces forces on the rod and reduces sensitivity of
the trim control. I use the outer hole on my horn.
Failure can also be bending in the middle due to buckling vibration and
fatigue rather than one time overload.
Ken
craig wrote:
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the middle and there is very little tendancy to bend near the ends. The
original rod is plenty strong enough if it is short or straight. We need
to stop it from bending and failing at the bend in what is commonly
known as buckling of a column.
For anybody not familiar, this is the same reason a high slender antenna
tower will have guy wires at several heights. Each attachment stabilizes
the column so that it can't start to bend (buckle) or oscillate at that
attachment point (node).
Yes a longer horn reduces forces on the rod and reduces sensitivity of
the trim control. I use the outer hole on my horn.
Failure can also be bending in the middle due to buckling vibration and
fatigue rather than one time overload.
Ken
craig wrote:
Yes, I'm familiar with the engineering aspect of columns and
tension/compression. It sounds like the mounting method is to place the
tube over the rod and fill it with Pro Seal. If I'm understanding this
right, I'm not sure the end result is a true column since it's not really
being loaded at either end. I guess if you can but it up against both ends
of the rod tightly that'd help.
Another suggestion might be to mount the rod further away from the trim
section on the horn gaining some leverage that way. CW
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