Service and Repair Manual

AN 01-25CN-2

PARAGRAPH 6

  e. Test the relief valve as follows: install a test gage on the forward side of the auxiliary hand pump. Tighten down the hand pump relief valve for 2000 p.s.i. and pump up the system with the auxiliary hand pump. Place the landing gear control handle in neutral and the flap control handle in the "UP" position. Test the flap relief valve for 1500 psi. Repeat this test with the landing gear control handle in neutral and the flap control in the "DOWN" position. Repeat with the flap control handle in the neutral position and the landing gear in both the "UP" and "DOWN" position. Test the landing gear relief valve for 1500 p.s.i.

  4. To disassemble the auxiliary hand pump relief valve, disconnect the hydraulic lines and remove the valve from the airplane.

  Loosen the lock nut and turn out the set screw. The gasket will be removed with the set screw. The spring and plunger will now drop out of the valve body.

  5. To assemble the auxiliary hand pump valve, clean the valve thoroughly in alcohol and blow out with compressed air if available. Then proceed as follows:

    a. Be sure that the needle point on the plunger has not been damaged in any way.

    b. Drop the plunger and spring into the valve body and screw the set screw with gasket and lock nut into the valve body.

    c. Set the relief valve to by-pass at 1500 p.s.i. and install the valve in the airplane.

  (h) LANDING GEAR RETRACTING STRUTS.

  1. The retracting struts (Drawing 87-31-505) each have a stroke of 11-1/16 inches. Both struts are equipped with two sets of hydraulically operated locks, which are operated by the over-travel of an internal sliding pawl. The locks consist of two sets of radial segments retained in square broached holes in the pis. ton, which are positively cammed into and out of their locked positions.

  2. Figure 100 shows a section through the upper half of the retracting strut with the piston and

pawl at the left or forward end (landing gear down), and a section through the lower half with the piston and pawl to the right (landing gear up).

3. Considering the upper half with the landing gear down, oil pressure in the aft end of the cyclinder holds the piston "B" and pawl "E" forward. Locks "D" which are retained in the piston, are held out, preventing the piston from moving aft. When retraction of the gear takes place, pressure at the aft end of the cylinder is relieved and pressure at the forward end is built up, forcing the pawl "E" aft with respect to the piston and cylinder until locks "D" are released. The pressure then forces the piston aft, the locks being moved inward by the beveled shoulder of the cylinder wall.

4. At the other end of the stroke, the piston is finally stopped by the bearing "K". The pawl continues to move aft, forcing the locks "D" out into the recess in the cylinder, thereby locking the landing gear in the "up" position. 5. At the beginning of this retracting stroke, as soon as the pawl leaves the forward end of the cylinder, the 3/16-inch diameter pin "I" is free to move aft. Oil pressure forces the 3/8-inch diameter pin "J" forward, rotating the rocker "F", which operates a bell crank to close the warning horn switch. (i) TAIL GEAR RETRACTING STRUT (See Fig. 101)_The principle of operation is the same for this strut as that described above for the landing gear retracting strut, except that no provision is made for locking the tail gear in the "UP" position. However, a lock is provided for the "DOWN" position. This lock is not connected to the landing gear lock warning system. A compression spring "G", holds the actuator "L" in the locked down position in case the hydraulic locking pressure should be reduced by leakage. The tail wheel is held in the "'UP" position merely by hydraulic pressure on the piston. (j) WING FLAP ACTUATING STRUTThis strut consists of a simple hydraulic cylinder and piston located as described in this Section. (2) FILLING AND BLEEDING THE HYDRAULIC SYSTEM. (a) The airplane should be supported on jacks or cradles so that the landing gear and wing flaps can be operated. (b) Fill the system through the reserve tank in the fuselage with fluid in accordance with Air Force Spec. 3586. Fill the tank to the base of the cap opening, with the landing gear down and the flaps