REFLECTOR: Hydraulic system pressure

[jerry at jlbent.com]

I guess this raises a question about the dump valve and gear down saftey.
If the nose gear needs the pressure to maintain the lock, then we should be
aware of an increased probability of nose gear collapse when using the dump
valve.


Jerry Brainard
Jerry at JLBEnt.com


   	-------Original Message-------
From: Scott Baker <scottb33333 at gmail.com>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Subject: Re: REFLECTOR: Hydraulic system pressure
Sent: Sep 05 '13 3:56pm

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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