REFLECTOR: Hydraulic system pressure

[Scott Baker]

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.