SD3-60 AIRCRAFT MAINTENANCE MANUAL

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1 AMM MAXARET UNITS - DESCRIPTION & OPERATION 1. Description A. General The Maxaret anti-skid unit permits application of maximum normal braking effort under all conditions without incurring wheel skid. A unit and an associated modulator is installed inside each main wheel axle. Refer to , pb201. The direction of rotation of the left and right Maxaret units (Pt. No.AC and AC respectively) is indicated by an arrow engraved on the unit nameplates. B. Unit Refer to Figure 1. A thrust rod actuated valve arrangement, contained in a valve block, is controlled by a flywheel which is sensitive to angular deceleration consistent with an approaching skid. A flange on the input shaft is held in a spring clutch mechanism carrying three planet gears which mesh with a sun gear keyed to a main shaft. The main shaft engages a drive ring which imparts drive to the flywheel via a drive spring. C. Installation Refer to Figure 2. An external sealing ring is fitted to the associated modulator and the modulator is secured to the valve block end of the Maxaret unit with three screws and washers. The Maxaret and modulator assembly is located in the main wheel axle by two keys on the Maxaret unit case and the assembly is secured in the axle by a retaining nut. A crank assembly, located in the drive cover assembly, engages the Maxaret splined input shaft and the drive cover assembly is secured to the main wheel with three bolts. Page 1

2 Section through Maxaret Unit Figure 1 Page 2

3 Maxaret Installation Figure 2 Page 3

4 2. Operation NOTE: Figure 3 is a diagramatic representation of the unit, showing the relative positions of the components during normal brake application. Figure 4 illustrates the principle of valve actuation as a result of sudden deceleration consistent with an approaching skid on the landing wheel. The input shaft, through the medium of the clutch mechanism, gear train and main shaft, drives the drive ring. The drive spring, which grips the drive ring, imparts a drive to the flywheel. Refer to Figure 3. During normal brake application, the thrust bearings lie in the base of the cam face formed on the drive ring and the valve thrust rod is clear of the valve stem. The valve is closed and pressure is maintained in the brake supply line. Page 4

5 Functional Diagram Figure 3 Page 5

6 Refer to Figure 4. When conditions cause the landing wheel and, consequently, the shaft to decelerate suddenly, the drive ring and flywheel overrun the shaft. The overrun of the drive ring is limited to 120 by the engagement of the segmental bosses on the shaft with internal keys on the drive ring, after which the flywheel overruns the drive ring. The overrun of the flywheel, relative to the drive ring, is permitted by its tendency to expand the drive spring which releases the grip of the spring coils encompassing the drive ring. This change in the angular relationship of shaft to drive ring causes the two thrust bearings to ride up the cam face and move the valve thrust rod, against the thrust rod spring and torsion spring loading, to open the valve. When a wheel bounces clear of the ground during brake application, the input shaft will stop and, after initial clutch slip, the main shaft will also stop. The consequent inertia load of the flywheel moves the valve mechanism to 'brake off' and the drive spring retains sufficient frictional contact with the drive ring to maintain the valve mechanism in this attitude for several seconds. Page 6

7 Functional Diagram Figure 4 Page 7

8 AMM MAXARET UNITS - MAINTENANCE PRACTICES 1. Removal/Installation A. Remove a maxaret unit (1) Off load main system pressure and emergency brake pressure. Refer to , pb301. (2) Deflate reservoir. (3) Break the locking wire and disconnect the three flexible hoses at top of landing gear beam, and B.P. flexible hose on shuttle valve. Blank off connections. (4) Free the three flexible hoses from their attachment fairlead at the lower end of the landing gear beam. (5) Remove three screws from main wheel and remove drive cover assembly, withdrawing spline shaft from maxaret unit. (6) Remove split pin, nut, washer and locking bolt from slotted wheelnut. (7) Remove retaining nut from inside main axle. (8) Withdraw maxaret and modulator and associated piping from inside main axle. (9) Break locking wire and remove three screws and washers from the valve block end of maxaret to disconnect it from the modulator. B. Install a maxaret unit (1) Carry out procedures referenced at (a) and (b) below to connect maxaret to modulator unit. (a) Select correct maxaret unit AC for right hand AC for left hand. (b) Assemble maxaret to modulator using three screws and washers, torque load to 21 lb.ins, then wire lock. (2) Feed the flexible hoses through the main wheel axle and install maxaret and modulator assembly. Locate maxaret in the two grooves in the main wheel axle. (3) Fit retaining nut to inside of main wheel axle and torque load to lb.ft. NOTE: Shimming Pt.No.SD should be introduced behind the retaining nut to align locking bolt holes. Page 201

9 (4) Fit locking bolt, washer and nut to slotted wheelnut. Torque load to lb.ins., and install new split pin Pt.No.MS After installation slightly flatten head of split pin. NOTE: Ensure that slotted wheelnut is not disturbed. (5) Fit drive cover assembly ensuring that spline shaft engages with serrations in maxaret unit. Wire-lock screws. (6) Identify and re-connect the three flexible hoses at top of landing gear beam, and B.P. flexible hose on shuttle valve. Torque tighten and wire-lock. Refer to , pb1. (7) Fit three flexible hoses to fairlead at the lower end of landing gear beam. (8) Bleed the brakes and then carry out brake function test. Refer to , pb201. Page 202

10 Maxaret Unit - Removal/Installation Figure 201 Page 203

SD3-60 AIRCRAFT MAINTENANCE MANUAL

SD3-60 AIRCRAFT MAINTENANCE MANUAL AMM 39.0.0.0PLATE BRAKES - DESCRIPTION & OPERATION 1. Description A. General Refer to Figure 1. This multi-piston type brake plate incorporates a heat pack comprising jigsaw type segmented rotor assemblies