REFLECTOR: Hydraulic system pressure

[John Dibble]

When I was fitting a new nose cylinder, I opened the dump valve when I 
wanted to retract the gear by hand to check clearances.  Sometimes I 
would forget to open the dump valve.  In that case I could still push 
the linkage to under center, but I could not budge the wheel when I 
tried to pull it up, so I don't see how it can retract, even when under 
center, if the valve is closed.  The next time I have the canard off, 
I'll bleed off the pressure, push the linkage under center and see if I 
can push enough to compress the shock spring and see what happens.  I'll 
be surprised if it retracts.

On 9/5/2013 6:28 PM, Don Johnston wrote:
> I would be willing to bet that if removed the hydraulic pressure from 
> the system and had a slightly worn gas strut, that in a dozen landings 
> or so you would get enough bounce in the system to have the nose gear 
> come back off overcenter enough to have an uncommanded retraction.
>
> But I'm not going to be the one to test that theory.  ;-)
>
>
>
> On Thursday, September 5, 2013, Scott Baker wrote:
>
>     On 9/5/2013 4:25 PM, John Dibble wrote:
>
>         On 9/5/2013 3:08 PM, Scott Baker wrote:
>
>             Hello John,
>             The recommended gear DOWN hydraulic pressure of 550psi is
>             already significantly lower than the recommended gear UP
>             pressure (something in the neighborhood of 1150psi).
>             While true, the main landing gear does not benefit from
>             hydraulic pressure when in the gear DOWN and LOCKED
>             position - the nose gear linkage is aided by hydraulic
>             pressure to keep it in the over-center (Down/Locked) position.
>             Somewhere in the Reflector archives is a video focusing on
>             the nose gear mono shock at the moment of landing.  When
>             the nose wheel touches the runway, the top of the nose
>             strut wants to move rearward - and in fact, it does move a
>             small distance, which is counteracted by the mono-shock.
>              Without the benefit of hydraulic pressure to help keep
>             the nose gear linkage in the over-center position, the
>             nose gear could easily collapse at the nose wheel touches
>             down.
>
>         I respectfully disagree.  With the linkage in over center
>         position, rearward strut motion will try to push the linkage
>         even more over center, but the cylinder won't allow that
>         because it's extended as far as it can go.
>
>         John
>
>
>     Theory and reality sometimes do not match.
>     When considering "What gear-down hydraulic pressure is the best?"
>     ... Since the hydraulic system is already in place - and since the
>     factory recommended 550psi is a really low pressure for hydraulic
>     systems that does not cause undue stress on hydraulic seals (and
>     is proven to work) - why not err on the side of what works?
>     Fixing an abraded nose section following a nose gear collapse is a
>     major inconvenience.  Why invite trouble?
>     Best,
>     Scott B.
>
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