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
In a message dated 5/27/2014 7:11:00 A.M. Central Daylight Time,
snopercod@comporium.net writes:
Chris--
Since the low-side pressure is
pushing on the over-center links with the gear down, have you considered
whether upping the pressure from 500 to 800 will bend anything down
there?
Best--
--John
On 5/18/2014 6:00 AM, Lancair
Mailing List wrote:
Sent: Thursday, May 15, 2014 7:33
AM
Subject: Hydraulic Pressure Spike
Video
...
I have my low side pressure switch set to 800 psi which has proven to be
high enough to avoid any gear hesitations and/or extension
failures.