REFLECTOR: Video of NOSE GEAR DOOR DO-HICKEY

Dave Black dvblack at comcast.net
Sun Jun 5 14:41:10 CDT 2005


Tom,

> 1. Why does the retracted nose wheel bounce in turbulence? The hydraulic
> fluid in the lines is incompressible and should hold everything firm. 

The hydraulic lines can stretch (balloon) a little, and could allow for a
little bouncing in turbulence. But it's equally logical that the gear and
linkages should flex at least a little in turbulence. 
 
> 2. If bouncing nose gear can not be eliminated, wouldn't the sequencing
> valve in the current design be triggered as much as the mechanical link
> systems, in terms of slamming the doors open & closed in turbulence?

The sequence valve MIGHT be triggered during extreme turbulence, but it should
make little or no difference to the doors. That's because the hydraulic
pressure has not been reversed, as it would have to be to push the nose gear
and doors down. 

Also, don't forget that the hydraulic pump turns off once the gear is
retracted. If hydraulic pressure drops low enough that the gear can bounce in
turbulence, it'll turn on momentarily and pull the gear back up. Test this by
momentarily opening the Dump Valve. 

The sequence valve simply determines whether main line hydraulic pressure is
applied to the nose door actuator or not. IF the gear were to move down far
enough to close the Sequence Valve, the nose door actuator would still stay
right where it was, because the hydraulic pressure on the whole system
(including the nose door actuator) would not have changed and still be high. 

The whole concept of Nose Doors slamming comes about because of the incredible
amount of physical force required to activate the Sequence Valve once it's in
a pressurized system. The Factory location for this valve has poor leverage,
such that the gear has insufficient torque to depress the valve, and simply
"bounces" off of it. Until the Main Gear retracts, and the hydraulic pressure
skyrockets. At that time, the valve is finally depressed and the doors slam
due to the extreme pressure.

The one disadvantage I see to the all-mechanical Nose Door Actuator is that
any flexing or bouncing in the Nose Gear would directly translate to slight
movement in the Nose Doors. I believe this can be overcome by the addition of
an overcenter spring to the doors, or by another method to take up any
mechanical "play."
 

Dave Black
Shortwing RG


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