REFLECTOR: Nose gear Hydraulic Band-Aid

[Dave Black]

Steve,

> My nose gear doors slam close and Scott Swing said some people
> are using an in line regulator to slow them down.  Any help
> would be appreciated.

The nose gear slamming problem has been with us since the advent of the RG.

Here's why:

When a single hydraulic pump operates multiple actuators, it'll first run the
actuator which requires the lowest hydraulic pressure. That's why the Nose
Gear comes up before the Mains. But the Nose Doors require even less hydraulic
pressure to operate than the Nose Gear. If there were no Sequence Valve, the
Nose Doors would close first, then the Nose Gear would come up. 

But the Sequence Valve requires a great deal of mechanical force to open it.
Much more force than the retracting Nose Gear can supply. So the Nose Gear
'bounces' off the Sequence Valve when the gear is 99% retracted. This 'bounce'
opens the Sequence Valve momentarily, causing the Doors to close slightly. But
at this point, both Nose Gear and Nose Doors halt -- leaving Nose Doors open
and Nose Gear slightly extended. 

When the hydraulic pressure builds a bit more, the Main Gear begins
retracting. Once the Main Gear is up, the hydraulic pressure increases again.
At this point, there is finally enough hydraulic pressure on the Nose Gear
actuator to force the Sequence Valve open. Once the Valve opens, the now
extremely high hydraulic pressure causes the very lightweight Nose Doors to
SLAM shut. 

>From lowest hydraulic pressure to highest, the retraction cycle looks like this:
1) Nose Gear retracts
2) Nose Gear 'bounces' off Sequence Valve and stops
3) Main Gear retracts
4) Nose Gear opens Sequence Valve and Doors slam shut
5) High-pressure cutoff switch operates.

If you wish to confirm this, try manually pulling up the Nose Gear after the
'bounce' at #2. The Nose Doors will close. In this test, you are providing the
additional force necessary to open the Sequence Valve. 


The "trick" to eliminating Nose Door slamming is to relocate the Sequence Valve
near to a linkage pivot point, where more leverage is available to push the
Valve open. If the Sequence Valve is relocated 2 inches from a Nose Gear pivot
point, the gear retraction cycle looks like this:

1) Nose Gear retracts
2) Sequence Valve opens and Nose Doors close silently and completely
3) Main Gear retracts
4) High-pressure cutoff switch operates.


So, you can fix the slamming by relocating the Sequence Valve or 'Band-Aid' it
by installing a Flow Restrictor. The Band-Aid is simpler, but the fix is more satisfying.


Dave Black
Shortwing RG