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Scott--
The portion of your recent post on the pressure spike topic (which
I have highlighted in red, below) has my head spinning. The reason
is that I have spent the last two weeks re-rigging my hydraulic
cylinders because I did it wrong the first time around. I had
previously rigged the cylinders to keep pressure on the system when
the gear was retracted, and had the cylinders bottom out
just after the gear was down as you implied they should. According
to Pg. 292 of the plans, the way I did it was exactly backwards, and
that scheme seems to have actually bent one my cylinder attach
bolts. If you go to Pg. 292 of the Builder's
Manual Ch. 11 , it emphasizes that the cylinders must bottom
out internally (or against the supplied aluminum spools) when the
gear is retracted. But paragraph 6 goes on to state: "The
gear down side, due to reduced geometry, does not require that the
system be bottomed out." That's why I posed my original question
about going to 800 PSI rather than 500 PSI.
So I've rigged my cylinders per the instructions on Pg. 292:
Cylinders bottomed out against the spool pieces when the gear is
retracted, but NOT bottomed out when the shaft is extended
and the gear is down. Therefore I have low-side pressure pushing on
the over-center link when the gear is down. Is this wrong? Would it
even be possible to rig the cylinders so they are bottomed out both
with the gear up and the gear down?
I note that the plans describe the original placement of the main
gear cylinders back on Pg. 168 in Chapter 5, but the details of
their action and adjustment comes 124 pages later in Chapter 11.
It's almost like Lance added a page due to some confusion on this
issue. (I know I'm confused.)
Help!
--John
At least for LNC2's the down actuators are to assist
gravity and the nose gear gas spring in order to extend the
gear. The infamous rat-trap springs on the main gear are to
merely lock the over center. Thus, not much hydro pressure is
needed to extend the mains and nose even at 122 Kts (max
extension speed).
When the gear is extended the actuators under pressure are
merely used to keep the over center links locked (kinda like a
backup system). The actuator down stops must be set to keep
hydro pressure off of the links. "Why?" You might ask. Well,
examine the geometry - the force triangle is from the pivot to
the link to the link-spar attach point and back to the pivot
along the spar. If enough hydro force is applied to the
actuator, the rod may become bent or the now excessive force
present at the link-spar connection can delaminate it from the
spar. Hard landings with some side loads have caused failure
there and that is why a service bulletin recommends putting a
reinforcing plate between the link-spar attach point and the
upper spar.
Yes, excessive
pressure without proper down stop rigging can cause
problems.
Scott Krueger
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