Main gear/Nose gear Hydraulic Actuators:

= ; &nb= sp; =20 Nose/

------------------------------- =20 Main Door

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

Down Piston Area (Sq In) .99 =20 .307 =

Pushrod Diameter (In)..... 3/8 =20 5/16

Pushrod Side Area (Sq In) .88 .230

Down Force (550 psi,Lbs). 545 169

Up Force (1100 psi,Lbs)... 968 =20 253

Up side Volume (Cu in)*... =20 7 .92

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

*Assumes that the main gear actuators move 8 inches, the nose 7 inches=20= and=20 the door actuators about 4 inches.

Using the old small reservoir and filling it "full" while the gear= was=20 down meant that, upon retraction, the reservoir had to hold approximately 3.= 3=20 cubic inches more hydraulic fluid. No wonder hydraulic fluid woul= d be=20 expelled from the reservoir breather hole! No wonder the newer pumps h= ave=20 a much larger reservoir.

Note that each gear is held up by 968 pounds of force and each doo= r=20 held closed by 253 pounds. Of course, this is against physical st= ops=20 (steel tubes on the door actuator shafts). The retraction forces must=20 overcome the 100 pound nose gear gas spring and the springs on the door=20 actuators. Besides tucking everything away nicely, these forces are us= eful=20 to prevent sagging during hi-G maneuvers. Remember that the press= ure=20 switches have a "dead band" where there will be some reduction in=20 pressure before the pump is kicked on to restore the pressure limit - t= hat=20 means less holding force at the lower pressure. Remember also that the= =20 gear doors don't close until the sequence valves are opened and there can be= =20 some wear on the valve actuator and contact area so that the valve may not o= pen=20 completely - check annually or every 200 retractions.

On the down side (no pun intended), over center links are held in place= by=20 545 pounds of force and the doors held open by 169 pounds. The door=20 pistons reach the end of the cylinders for the physical stop. The gear= =20 actuators should also, otherwise there will be 545 pounds against the links=20 rather than just a snugness to keep the links from coming open.&nb= sp;=20 Who knows what happens after things warm up and expand if the pistons are no= t=20 against the cylinder stop? Better it be against a stop rather than=20 increasing the force on the links (bending things, delaminating=20 things.....).

Thanks to Mike Renaith for piquing my interest.

Scott Krueger=20 AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL (KARR)

Fai= r=20 and Balanced Opinions at No Charge!
Metaphysical Monologues taken at your= own=20 Risk.