REFLECTOR: Hydraulic system pressure

[Don Johnston]

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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