Main gear/Nose gear Hydraulic Actuators:

 

                                    Nose/

-------------------------------      Main    Door

Piston Diameter (In)......  1 1/8    5/8

Down Piston Area (Sq In)  .99     .307            

Pushrod Diameter (In).....   3/8     5/16

Pushrod Side Area (Sq In) .88     .230

Down Force (550 psi,Lbs). 545     169

Up Force (1100 psi,Lbs)... 968     253    

Up side Volume (Cu in)*...   7        .92

Dn Side Volume(Cu in)*...   7.9    1.23

 

*Assumes that the main gear actuators move 8 inches, the nose 7 inches and the door actuators about 4 inches.

 

Using the old small reservoir and filling it "full" while the gear was down meant that, upon retraction, the reservoir had to hold approximately 3.3 cubic inches more hydraulic fluid.  No wonder hydraulic fluid would be expelled from the reservoir breather hole!  No wonder the newer pumps have a much larger reservoir.

 

Note that each gear is held up by 968 pounds of force and each door held closed by 253 pounds.  Of course, this is against physical stops (steel tubes on the door actuator shafts).  The retraction forces must overcome the 100 pound nose gear gas spring and the springs on the door actuators.  Besides tucking everything away nicely, these forces are useful to prevent sagging during hi-G maneuvers.  Remember that the pressure switches have a "dead band" where there will be some reduction in pressure before the pump is kicked on to restore the pressure limit - that means less holding force at the lower pressure.  Remember also that the gear doors don't close until the sequence valves are opened and there can be some wear on the valve actuator and contact area so that the valve may not open completely - check annually or every 200 retractions.

 

On the down side (no pun intended), over center links are held in place by 545 pounds of force and the doors held open by 169 pounds.  The door pistons reach the end of the cylinders for the physical stop.  The gear actuators should also, otherwise there will be 545 pounds against the links rather than just a snugness to keep the links from coming open.  Who knows what happens after things warm up and expand if the pistons are not against the cylinder stop?  Better it be against a stop rather than increasing the force on the links (bending things, delaminating things.....).

 

Thanks to Mike Renaith for piquing my interest.