Cargo Door Snubber

[Spookyload]

Need some help in understanding how the cargo door snubber actuator works. Anyone out there in the know? Thanks

[NATOPS1]

Think of it like a shock absorber.... only this \"shock absorber\" works like this….instead of compressing air to reduce shock it allows hydraulic fluid to flow (at a set rate) between the “damping side†and the “replenishing sideâ€. This set rate prevents the door form lowering at excessive rates.

(With no hydraulic pressure used to close the door) As the door is released from the uplock the weight of the door will cause a pressure increase inside the snubber. This pressure increase will displace a check valve that will allow the “pressure†(hydraulic fluid) to bleed off (flow to the other side) at a specific rate and slow the speed of the door.

[Wombat]

The snubber is SUPPOSED to dampen the door as it releases from the uplock so there is no sudden drop with a subsequent shock load to the tuning fork and surrounding structure on the door. It never seems to work that way.

If the system works as per theory, when you select "DOOR CLOSE", the door raises to take the weight off the uplock, the uplock releases, the door is then powered down.

The laws of physics seems to ensure the area of the door cylinder piston causes a faster response than the lock cylinder and usually loads the uplock latch before it releases. The door then drops several inches before the damper and door cylinder hydraulics slows it down.

The policy the RAAF used when the H was introduced was to select "DOOR OPEN", pull the manual release then let the switch go and let the door close under it's own weight. Obviously in-flight that isn't practical.

Bob D, you might notice in one of the DVD's I sent that it shows a RAAF loadie using the manual release when closing the door.

Wombat

[NATOPS1]

USMC and Navy do the same... Door open, Manual release, allow weight to drop the door....

[Spectre623]

That was (is) standard practice for the AF also. You would get yelled at if you just went to Door Close or just pulled the EMER release handle. Bill

[bbuech]

The cargo door actuating systems incorporate an independent hydraulic snubber to prevent the door from being rapidly driven from the uplock during closing. The snubber is located forward of the cargo door actuator. Hydraulic fluid MIL-H-5606 or MIL-H-83282 is used in the snubber.

The snubber assembly consists of two main sections; a damping chamber and a reservoir chamber. Snubbing is provided by the damping chamber while the reservoir chamber replenishes the damping chamber.

The damping chamber consists of an actuating piston and cylinder. A check valve and an orifice are incorporated in the head of the piston. When the cargo door is opened, hydraulic fluid flows through the check valve and orifice to the rod side of the damping chamber. Closing the cargo door causes the check valve to close so that fluid flow is restricted to the piston head side of the damping chamber through the orfice. This action snubs the closing of the cargo door.

The reservoir chamber consist of a spring-loaded type of accumulator which replenishes the damping chamber. A servicing indicator rod is attached to the piston in the reservoir chamber.

The rod is color coded; green for normal operation, blue for proper service, and yellow for servicing requirement.

A servicing data plate is located on the snubber for proper servicing procedures. A servicing unit with a hand pump or equivalent must be used to service the snubber. The servicing pressure must not exceed 150 PSI. When the yellow marker on the indicator rod is partially hidden by the end cap with the cylinder rod fully extended and the temperature is above 40 degee F, the snubber should be serviced. The snubber is properly serviced when the blue ring on the indicator rod protrudes 1/8 inch maximum beyond the cap with the cylinder rod fully extended. A filler port with an incorporated check valve is provided on the reservoir chamber.

Edited January 9, 2009 by bbuech