SD3-60 AIRCRAFT MAINTENANCE MANUAL - DESCRIPTION & OPERATION

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Norman Singleton
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1 SD3-60 AIRCRAFT MAINTENANCE MANUAL z PAMM STEERING - DESCRIPTION & OPERATION 1. Description The nosewheel is operationally steerable through a radius of 55 degrees on either side of the aircraft centre line by means of a hydraulically operated rack and pinion mounted on the shock absorber unit. The input lever is directly signalled by a steering handle and cable circuit and employs main hydraulic pressure as the power medium. Pressure is made available via a solenoid-operated selector valve controlled by an ON/OFF switch on panel 7P. The switch is subject to the overriding authority of the weight switch relay within the right equipment bay (station 74) and can only be effectively switched ON when the aircraft is on the ground. Centring cams, located within the nose gear shock absorber, engage to 'centre' the nose wheel when the weight of the aircraft is relieved from the shock absorber. The centring cams are effective within a 30 degree radius on either side of the aircraft centre line. When the aircraft is on the ground (shock absorber compressed) the cams disengage thus permitting the nose wheel to be steered throughout the operating range. Full castoring of the nose wheel (180 degrees) to facilitate towing is afforded by the 'auto-maticdisengage' design principle of the steering rack and pinion which occurs at 55 degrees either side of the aircraft centre line. A. Detail Refer to Figure 1. Mechanical aspects of the steering control system are shown. The control handle is attached to the inboard end of an input spindle, housed within a control box within the flight compartment left sidewall. The control box input and output spindles incorporate sprockets and are joined by a short endless chain. NOTE: Slack in the chain is eliminated by an adjustable rider sprocket assembly. The signalling cable circuit is routed between a pulley on the control box output spindle and a pulley/lever assembly on the nose gear pintle axis. An adjustable link on the pulley/lever attaches to a servo valve operating lever on the steering valve differential box. The operating lever has limited movement on each side of the null position. The steering valve differential box schedules hydraulic pressure to the rack and pinion steering cylinders in response to servo valve operating lever movement. The rack gearing meshes with a steering cuff which rotates around the bottom of the shock absorber body and controls the wheel fork turning radius through a connecting link. Page 1

2 z SD3-60 AIRCRAFT MAINTENANCE MANUAL Steering Controls Figure 1 Page 2

3 SD3-60 AIRCRAFT MAINTENANCE MANUAL z Hydraulic Operation Figure 2 Page 3

4 z SD3-60 AIRCRAFT MAINTENANCE MANUAL 2. Operation Refer to Figure 1. Refer to Figure 2. The steering system is operational when all of the following conditions are met:- A. main hydraulic system pressure is available. B. weight switch relay GCI is de-energised (aircraft on ground). Refer to , pb1. C. circuit breaker No.34 (panel 1D) is closed - energising the 28V dc left essential services busbar. D. the steering selector switch (panel 7P) is selected ON. In these conditions, movement of the control handle will displace the steering valve spool from its null position, admitting hydraulic pressure to the steering cylinder appropriate to the input signal. The opposite steering cylinder will be vented to the system return lines as the rack moves, transmitting the steering motion to the steering cuff, connecting link and wheel fork. A springbiased follow-up linkage which operates along the steering rack cam face monitors the turning radius and correspondingly moves the servo valve spool towards the null position, thus cancelling the input signal when the required turning radius has been reached. Steering control is 'lost' when the steering cuff disengages from the rack (55 degrees) followed by the closure of the hydraulic power shut-off valve (57 degrees) causing the nose wheel to become free-castoring until it returns to the steering range. Castoring during application of asymmetric engine power or towing (within the steering range) is assured by two pressure relief valves which vent hydraulic fluid from one side of the steering cylinder to the other as the rack is driven by the steering cuff. When the aircraft becomes airborne, the weight switch relay (controlled by weight switches on the main gear, left and right) is energised. This isolates the power supply to the selector valve thus interconnecting the valves delivery and return ports. The rack and steering cuff will then be driven to the 'wheel centring' position prior to gear retraction due to engagement of centring cams as the now unloaded shock absorber fully extends. Cable tensioners, situated between the turnbuckles and steering control box, act as compensators to take up cable slackness caused by the radial movement of nose landing gear on retraction. Page 4

5 SD3-60 AIRCRAFT MAINTENANCE MANUAL z AMM NOSEWHEEL STEERING - MAINTENANCE PRACTICES 1. Servicing A. Lubrication Routine lubrication data. Refer to , pb301. B. Prime and bleed the steering system. Special tools and equipment:- Hydraulic power rig : T Turntable (two metal sheets sandwiched together with grease). NOTE: The steering system self-primes during the following procedure. (1) Refer to , pb201. Jack nose of aircraft until wheel is clear of ground. (2) Place turntable under the nosewheel. (3) Disengage the centering cams by lowering the aircraft onto the turntable until the visible parallel length of the shock absorber piston has closed to a maximum of five inches. (4) Check that hydraulic fluid CONTENTS gauge (panel 7P) reads within the green sector. (5) Provide electrical power, close C/B No. 34 (panel 1D) and select NOSEWHEEL STEERING control switch ON. (6) Connect hydraulic power rig to the GROUND TEST (PRESSURE and RETURN) connectors on the hydraulic servicing panel. (7) Start rig and raise SYSTEM pressure (panel 7P) to approximately 500 psi. WARNING: DO NOT INPUT STEERING COMMANDS DURING STEP (B) WHICH FOLLOWS. (THIS STEP REQUIRES A MAINTENANCE OPERATOR TO BE WITHIN THE NOSEWHEEL BAY). (8) Slacken pressure inlet connection on the steering control valve on upper right side of nosegear until air-free fluid is emitted (the connection is the forward outboard of four). Tighten the connection and clean up spillage. (9) Prime and bleed the steering control valve and steering actuator as follows:- (a) Adjust power rig flow rate to 2.0 ± 0.25 gal/min and raise SYSTEM pressure (panel 7P) to psi. (b) Move steering control handle from central position to full LEFT and full RIGHT in turn until steering response is smooth (all air expelled to return lines). Page 201

6 z SD3-60 AIRCRAFT MAINTENANCE MANUAL (c) Stop the rig. (d) Top up and bleed the reservoir. Refer to , pb301. NOTE: The reservoir should be re-bled following the next complete day of operation. (10) Test the steering system - refer to para 2.B.(5) thru (12). 2. Adjustment/Test Special tools and equipment Hydraulic power rig : T Turntable (two metal sheets,sandwiched together with grease). Tensiometer : T Rigging Pins:- S1 : S2 : S3 : S4 : T T T T A. Rig the steering controls Refer to Figure 201. NOTE: This procedure assumes that steering valve and differential box settings have not been disturbed. (1) Open circuit breaker No. 34 on distribution panel 1D. (2) Refer to , pb201. Jack nose of aircraft until wheel is clear of ground. NOTE: Check that nose wheel 'centers' as aircraft load is relieved from shock absorber. (3) With reference to details A and C insert rigging pins S1 and S2. (4) With reference to detail B insert rigging pins S3 and S4 to maintain settings. (5) Arrange cables as shown in main view. (6) Equally adjust the turnbuckles to provide cable tensioning appropriate to ambient temperature. Refer to , pb1. Fit turnbuckle locking clips. (7) Adjust rider sprocket positioning nut (detail A) to take up slack in control box chain. Wirelock the adjustment nut. Page 202

7 SD3-60 AIRCRAFT MAINTENANCE MANUAL z (8) Connect adjustable link to pulley and steering valve levers. Tighten locknut and wirelock. (9) Remove all four rigging pins. (10) Test the steering system (para B). B. Test the steering system (1) Refer to , pb201. Jack nose of aircraft until wheel is clear of ground. (2) Position turntable under nosewheel and lower aircraft until centering cams are disengaged (visible parallel length of shock abosorber piston not in access of 5 inches). (3) Refer to , pb301. Provide electrical power. (4) Connect hydraulic power rig to the GROUND TEST (PRESSURE and RETURN) connectors on the hydraulic servicing panel. (5) Start rig, adjust flow rate to 2.0 ± 0.25 gal/min and raise SYSTEM pressure (panel 7P) to psi. (6) Close C/B No. 34 on distribution panel 1D and set NOSE WHEEL STEERING control switch (panel 7P) to ON. (7) Move steering control handle from central position to full LEFT and full RIGHT in turn, checking:- NOTE: On nose gears incorporating Dowty Rotol Service Bulletin No SD, after powering to either full LEFT or full RIGHT the steering section of the nose gear will require a small manual rotation back towards its central position in order to open the SOV and permit powered steering again. (a) that the nose wheel moves in correct sense. (b) that the maximum steering angle in each direction is nominally 55 degrees. (c) that the time for movement between extremes of travel is between 5 and 10 seconds. (8) Recheck operating times (7) (c) over four further cycles. (9) Select NOSE WHEEL STEERING switch to OFF and check wheel does not respond to steering control handle input i.e. selector valve is functional. Refer to , pb1. (10) Stop and disconnect hydraulic rig. (11) Raise aircraft nose, remove turntable from below nose wheel and fully lower aircraft. (12) Switch off electrical power if no longer required on aircraft. Page 203

8 z SD3-60 AIRCRAFT MAINTENANCE MANUAL Steering Controls - Rigging Figure 201 Page 204

SD3-60 AIRCRAFT MAINTENANCE MANUAL & RETRACTION - DESCRIPTION & OPERATION

SD3-60 AIRCRAFT MAINTENANCE MANUAL & RETRACTION - DESCRIPTION & OPERATION AMM 17.0.0.0EXTENSION & RETRACTION - DESCRIPTION & OPERATION 1. Description A. General The landing gear is extended and retracted by the operation of a hydraulic actuator at each of the main and nose gear