Catapult Type H, Mark 8

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Catapult Type H, Mark 8, NAVAER 51-15HA-502, 1956, describes the hydraulic catapult installed in the Essex class carriers. This online version was created from a poor quality black and white photocopy. If you have access to a better original, please contact us.

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NAVAER 51-15HA-502

TABLE OF CONTENTS

Section	Page
I INTRODUCTION	1
1-1 Purpose	1
1-5 Responsibility	1
1-10 Scope	1
1-12 Section I - Introduction	1
1-13 Section II - General Description	1
1-14 Section III - Detailed Description	1
1-15 Section IV - Operation of the Catapult	1
1-16 Section V - Maintenance	1
1-17 Section VI - Malfunctions	2
1-18 Section VII- Pressure Indicator Cards	2
II GENERAL DESCRIPTION	3
2-1 Purpose	3
2-3 Specifications	3
2-5 Catapult Capacity	3
2-6 Shuttle Travel	3
2-7 Engine	3
2-8 Construction and Function	3
2-10 The Power Plant	3
2-16 The Engine	4
2-21 The Drive System	4
2-26 The Control System	4
2-28 Catapult Operation	6
2-29 Launching Operation	6
2-31 Supplementary Information	11
III DETAILED DESCRIPTION	12
3-1 Launching System	12
3-3 Launching Accumulator and Manifold	12
3-7 Piston Valve	12
3-14 Four-Way Valve	14
3-18 Firing Operating Valve	14
3-27 Elbow Check Valve	17
3-33 Cylinder and Ram	17
3-38 Crosshead	19
3-40 Fixed Sheaves	19
3-42 Bridle Tensioner	19
3-46 Cable Whip Dampers	19
3-50 Cable Equalizer	23
3-53 Cable Tensioner	23
3-57 Runaway Shot Preventer	23
3-67 Shuttle	29
3-69 Cables	29
3-71 Holdback and Release Units	29

Section	Page
3-75 Launching Bridles or Pendants	29
3-78 Arresting System	32
3-80 Constant Pressure Valve	32
3-87 Air Trap Cylinder	34
3-90 Retracting Accumulator	34
3-94 Retracting Valve	35
3-97 Bypass Valve and Mechanical Controls	35
3-103 Hydraulic Stops	39
3-105 Operating Valves	39
3-107 Pressure Indicators	39
3-109 Four-Way Valve	39
3-111 Power Plant and Signal System	41
3-112 Pumps	41
3-117 Pump Motors and Controllers	41
3-118 Pressure Regulators	41
3-120 Drain Pump	43
3-122 Deck Edge Control Box	43
3-124 Firing Control Panel	43
3-126 Retracting Control Panel	43
3-128 Signal System - Launching Cycle	47
3-130 Signal System - Retracting Cycle	47
3-132 Signal System - Suspension Cycle	49
3-135 Electric Speedometer	50
IV OPERATION OF THE CATAPULT	51
4-1 Launching Preparation	51
4-2 Procedure	51
4-3 Catapult Operation	52
4-4 General	52
4-5 Sequence of Operations	52
4-6 General	52
4-7 Launching Operating Procedures	52
4-8 Retracting Operating Procedure	53
4-9 Signals Recommended	54
4-10 "No Load" Launchings	54
4-11 General	54
4-14 "No Load" Launching Signals	54
4-15 Supplementary Operating Notes	54
4-28 Securing the Catapult	55
4-29 Procedure	55
V MAINTENANCE	57
5-1 General	57
5-3 Preventive Maintenance	57
5-7 Preventive Maintenance Schedules	57
5-8 Daily Schedule	57
5-9 Weekly Schedule	59
5-10 Semimonthly Schedule	59

TABLE OF CONTENTS (CONTINUED)

Section	Page
5-11 Monthly Schedule	60
5-12 Completion of 1500 Launchings	60
5-13 Quarterly Schedule	60
5-14 Semiannual Schedule	60
5-15 Catapult Not in Regular Use	60
5-16 Lubrication Schedules	61
5-17 Corrective Maintenance	61
5-20 General Corrective Maintenance Procedures	61
5-21 Packings	61
5-22 O-Ring Packings - Running and Static Seals	61
5-23 Repeated Failure of O-Rings	61
5-24 V-Ring Packing-Synthetic Rubber	61
5-25 Copper Gaskets	63
5-26 Wipers - Felt and Metallic	63
5-27 Cleaning and Inspection of Packed Joints	63
5-28 Wire Rope	63
5-29 Care and Handling of Wire Rope Cable	63
5-31 Seizing	63
5-35 Inspection of Wire Rope	64
5-37 Lubrication of Wire Rope	64
5-38 Semiannual Inspection of Cable Terminals	64
5-39 Pouring of Cable Terminals	65
5-40 Care and Use of Pyrometer	65
5-41 Tempilstiks	65
5-42 Pouring Procedures for Catapult Terminals	65
5-43 Preparation of the Wire Rope	65
5-44 Preparation of Terminal for Pouring of Zinc	67
5-45 Preparation and Pouring of Zinc	68
5-46 Finishing the Terminal	69
5-47 Inspecting the Terminal	69
5-48 Use and Care of Gasoline Blowtorch	69
5-49 Installation of Cables	70
5-50 Testing of Terminals	70
5-51 Compensating for Cable Stretch	71
5-53 Pumps	72
5-54 Checking Capacity of Power Plant Pumps	72

Section	Page
5-55 General Maintenance of Catapult Pumps	72
5-56 Venting Pumps and Cleaning Pump Section Lines	72
5-57 Electrical Components	72
5-59 Solenoid Valve Maintenance	72
5-60 Pulling Out Crosshead	73
5-62 Checking Slot Alignment in Bypass Valve	73
5-64 Leaking High-Pressure Shutoff Valves	74
5-66 Bridles and Pendants	74
5-68 Liquid Level Gages	74
5-70 Detailed Corrective Maintenance Procedures	74
5-71 Piston Valve	74
5-72 Fluid Leakage at Valve Securing Stem	74
5-73 Leakage between Cover and Large Head	74
5-74 Fluid Leakage between Large Head and Body of Piston Valve	74
5-75 Fluid Leakage between Small Head and Adapter	75
5-76 Fluid Leakage between Adapter and Body	75
5-77 Fluid Leakage between Flange of Piston Valve and Manifold	75
5-78 Fluid Leakage between Engine Cylinder Elbow and Piston Valve	76
5-79 Binding	76
5-80 Air Trap Cylinder	77
5-81 Disassembly of Air Trap Cylinder	77
5-82 Fluid Leakage between Flange and Cylinder at Piston End of Cylinder	77
5-83 Fluid Leakage from Weep Holes at End of Rod	77
5-84 Fluid Leakage between Bracket and Cylinder	77
5-85 Fluid Leakage between Air Trap Cylinder and Clapper Valve or between Clapper Valve and Elbow Check Valve	77
5-86 Clapper Valve	78
5-87 Binding	78
5-88 Elbow Check Valve	78

iii

TABLE OF CONTENTS (CONTINUED)

Section	Page
5-89 Leakage at Actuating Rod	78
5-90 Leakage of Interior Packings	78
5-91 Binding or Sticking	78
5-92 Replacement of Switch (DO Aux Switch)	79
5-93 Four-Way Valve	79
5-94 Fluid Leakage	79
5-95 Binding	79
5-96 Firing Operating Valve	79
5-97 Air Leakage	79
5-98 Fluid Leakage	79
5-99 Sluggish Operation or Nonoperation	79
5-100 Engine Cylinder and Engine Cylinder Elbow	80
5-101 Fluid Leakage	80
5-102 Engine Cylinder and Ram	80
5-103 Fluid Leakage	80
5-104 Ram and Brake Cylinder	81
5-105 Fluid Leakage	81
5-106 Braking Cylinder and Spacer	81
5-107 Fluid Leakage	81
5-108 Braking Cylinder Spacer and Bypass Valve	81
5-109 Fluid Leakage	81
5-110 Hydraulic Stops	81
5-111 Fluid Leakage	81
5-112 Binding	81
5-113 Retracting Valve	81
5-114 Fluid Leakage between Bypass Valve and Stem End of Retracting Valve	81
5-115 Fluid Leakage at Ports of Retracting Valve	81
5-116 Interior Fluid Leakage of Retracting Valve	81
5-117 Fluid Leakage between Flange and Body of Valve	82
5-118 Disassembly for Replacement of Interior Packings of Retracting Valve and of Connection to Bypass Valve Body	82
5-119 Binding of Valve or Stem Failure	82
5-120 Bypass Valve	82
5-121 Fluid Leakage between Gland and Body of Valve	82
5-122 Fluid Leakage between Plug Shaft and Gland Nut	82

Section	Page
5-123 Leakage from Bypass Valve to Gravity Tank	83
5-124 Constant Pressure Valve	83
5-125 Air Leakage	83
5-126 Fluid Leakage	83
5-127 Fluid Leakage between Dome Cover and Body	83
5-128 Fluid Leakage at Flange to 4-inch Line to Air Trap Cylinder	83
5-129 Fluid Leakage Down Past Dome Piston	84
5-130 Fluid Leakage at Plugs or Vents	84
5-131 Fluid Leakage between Lower Spindle and Retainer or between Retainer and Retainer Housing	84
5-132 Fluid Leakage between Retainer Housing and Body	84
5-133 Fluid Leakage at Seat	84
5-134 Fluid Leakage between Seat and Body	84
5-135 Fluid Leakage between Constant Pressure Valve and Bypass Valve Body	84
5-136 Fluid Leakage between Constant Pressure Valve and Elbow of Line to Retracting Gravity Tank	84
5-137 Disassembly for Leak at Flange of 4-inch Line to Air Trap Cylinder	84
5-138 Disassembly for Leakage between Dome Cover and Dome Body	84
5-139 Complete Disassembly of Constant Pressure Valve	84
5-140 Damping Cylinder	86
5-141 Air Leakage at Ports	86
5-142 Air Leakage at Plug	86
5-143 Air Leakage at Piston	86
5-144 Binding	86
5-145 Sluggish Operation	86
5-146 Cable Tensioner	86
5-147 Air Leakage	86
5-148 Fluid Leakage between Head and Tank	86
5-149 Fluid Leakage between Head and Cylinder	87

TABLE OF CONTENTS (CONTINUED)

Section	Page
5-150 Fluid Leakage at Sheave End of Cylinder	87
5-151 Testing and Replacement of Fluid	87
5-152 Replacement of Slippers	87
5-153 Replacement of Crosshead Sheave	88
5-154 Binding of Ram	88
5-155 Sticking Clapper Valve	88
5-156 Cable Whip Dampers	88
5-157 Air Leakage	88
5-158 Fluid Leakage between Dome and Flange of Cylinder	88
5-159 Fluid Leak from Crosshead End of Cylinder	88
5-160 Fluid Leakage at Coupling End of Cylinder	88
5-161 Checking Alignment to Eliminate Scoring at Ram	89
5-162 Testing and Replacement of Fluid	89
5-163 Replacement of Slippers and Crosshead	90
5-164 Replacement of Cable Equalizer Sheave	90
5-165 Replacement of Cable Equalizer Slippers	90
5-166 Shuttle	90
5-167 Replacement of Slippers and Wipers	90
5-168 Replacement of Hook	91
5-169 Retrieving Sheaves	91
5-170 Replacement	91
5-171 Towing Sheaves	91
5-172 Replacement	91
5-173 Engine Crosshead	91
5-174 Replacement of Slippers	91
5-175 Runaway Shot Preventer	92
5-176 Oil Leakage at Runaway Shot Preventer Valve	92
5-177 Oil Leakage from Runaway Shot Preventer Cylinder	92
5-178 Runaway Shot Preventer Valve - Checking and Adjusting	93

Section	Page
VI MALFUNCTIONS	93
6-1 General	93
6-3 Preparation for Launching	93
6-4 General	93
6-5 Pump Difficulties	93
6-6 Excessive Pump Noise	93
6-10 Pressure Indicator Difficulties	93
6-11 Loss of Accumulator Charge	93
6-15 Stuck Piston Valve Securing Stem	94
6-16 Pre-launching	94
6-17 General	94
6-18 First Ready	94
6-21 Bridle Tensioning	95
6-22 Final Ready	95
6-23 Firing	95
6-25 Firing Operating Valve	95
6-26 Cold Shot	95
6-29 Runaway Shot	96
6-31 Slow Shot	96
6-34 Normal Airplane Launching	96
6-39 Late Cutoff	97
6-40 No Cutoff	97
6-41 Brake Stroke	97
6-42 General	97
6-43 Excessive Tow Cable Whip	97
6-44 Erratic Rebound	97
6-45 Early Brake Stroke	97
6-46 Excessive Brake Penetration or Pressure	97
6-52 Retraction	98
6-53 General	98
6-54 Catapult Does Not Retract	98
6-55 Slow Start of Retraction	98
6-57 Slow Retraction	99
6-60 Yellow Light Does Not Come On	99
6-61 Loss of Retracting Accumulator Pressure	99
6-63 Bypass Valve Does Not Open	99
VII PRESSURE INDICATOR CARDS	100
7-1 General	100

TABLE OF ILLUSTRATIONS

Figure	Page
1-1 Type H Mark 8 Catapult	vi
2-1 Type H Mark 8 Catapult Engine	5
2-2 Hydraulic Diagram - Standby Position	7
2-3 Hydraulic Diagram - Firing Position	8
2-4 Hydraulic Diagram - Braking Position	9
2-5 Hydraulic Diagram - Retracting Position	10
3-1 Piston Valve, Elbow, and Elbow Check Valve	13
3-2 Four-Way Valve	15
3-3 Firing Operating Valve	16
3-4 Cylinder and Ram	18
3-5 Crosshead	20
3-6 Bridle Tensioner	21
3-7 Cable Whip Damper	22
3-8 Cable Equalizer	24
3-9 Cable Tensioner	25
3-10 Runaway Shot Preventer	26
3-11 Runaway Shot Preventer Valve	27
3-12 Shuttle	30
3-13 Holdback and Release Unit - "D" Ring Type	31
3-14 Holdback and Release Unit - Tension Bar Type	31
3-15 Constant Pressure Valve	33
3-16 Air Trap Cylinder	34
3-17 Retracting Valve	36
3-18 Bypass Valve and Mechanical Controls	37
3-19 Hydraulic Stops	38
3-20 Operating Valve	39
3-21 Pressure Indicator	40
3-22 Power Plant and Signal System - Electrical	42
3-23 Deck Edge Control Box	44
3-24 Firing Control Panel	45
3-25 Retracting Control Panel	46

Figure	Page
3-26 Signal System - Schematic Diagram	48
5-1 Lubrication Chart	62
5-2 Locating the Seizing	66
5-3 Unlaying the Strands	66
5-4 Brooming-Out the Wires	66
5-5 Degreasing with Solvent	67
5-6 Dipping in Acid	67
5-7 Neutralizing with Soda	67
5-8 Washing with Water	68
5-9 Cleaning the Terminal	68
5-10 Placing the Terminal	68
5-11 Applying Asbestos Paste	69
5-12 Wrapping Asbestos Paste	69
5-13 Wrapping Top with Asbestos	69
5-14 Heating the Terminal	70
5-15 Measuring Temperature of Zinc	70
5-16 Pouring the Zinc	70
5-17 Sawing Off the "Hot-Top"	71
5-18 Inspecting Face of Terminal	71
5-19 Inspecting Bottom of Terminal	71
7-1 Normal Indicator Cards	101
7-2 Indicator Cards Showing Early Brake Stroke	102
7-3 Indicator Cards for "No Load" Shots	103
7-4 Indicator Cards - Excessive Initial Engine Cylinder Pressure	104
7-5 Indicator Cards Runaway Shot	104
7-6 Indicator Cards Slow Shots	105
7-7 Indicator Cards - Early and Late Cutoff	106
7-8 Brake Stroke - Various Launching Conditions	107
7-9 Indicator Cards - Brake Malfunctions	108
7-10 Indicator Cards - Brake Malfunctions	109

Figure 1-1. Type H Mark 8 Catapult

SECTION I
INTRODUCTION

1-1. PURPOSE

1-2. This handbook provides all necessary information for the operation and maintenance of the Type H, Mark 8 Catapult.

1-3. The handbook is issued as a basic Handbook of Instructions to effect the safest and most efficient operation of the H8 Catapult. The operative function of the parts of the catapult and a description of the parts both by text and illustrations is included with the operation and maintenance instructions.

1-4. This handbook also contains a treatment of the possible malfunctions of the engine with instructions for the correction or prevention of these known malfunctions.

1.5. RESPONSIBILITY

1-6. Commanding Officers and others charged with the proper operation of catapults and for the safety of personnel and material involved are advised that all launchings shall be made under the direct supervision of an officer qualified for this work having an intimate knowledge of the catapult, this handbook, and all applicable Bureau of Aeronautics Technical Orders, Bulletins and Changes. He need not be a naval aviator.

1-7. The catapult officer shall be charged with the proper inspection of the catapult and with the observance of all safety precautions. He shall have authority to hold up a launching at any time, if some adverse condition should arise. He shall be required to sign the checkoff list, prior to the first launching of any launching operation, certifying that he has checked the various items listed by personal observation.

1-8. The Commanding Officers of vessels or stations operating catapults shall cause a catapult log to be kept in which shall be recorded all data regarding launchings, and overhaul or repair to the catapult. This log need not be submitted to the Bureau, but will be maintained as a record from which such information as requested may be supplied. Any unusual condition arising in the operation of a catapult shall be made the subject of an FUR report to the Bureau of Aeronautics.

1-9. The signed checkoff lists shall be kept as part of the catapult records.

1-10. SCOPE.

1-11. This handbook has been divided into six distinct sections, as follows:

1-12. SECTION I - INTRODUCTION. This section introduces the handbook, its purpose, objectives, and scope. It points out, briefly, the responsibilities of personnel in charge of or assigned to catapult operation.

1-13. SECTION II - GENERAL DESCRIPTION. This section presents the purpose and specifications of the Type H, Mark 8 Catapult and an overall picture of the construction and functioning of the engine.

1-14. SECTION III - DETAILED DESCRIPTION. This section gives a detailed description, with sectioned illustrations, of each component part of the entire catapult installation. It will also present a detailed explanation of the function and operation of these component parts. The section is divided into three distinct groups according to function, namely: The Launching System, the Arresting System, and the Power Plant and Signal System.

1-15. SECTION IV - OPERATION OF THE CATAPULT. In this section is given all the requirements necessary to bring the catapult from the "Secured" condition to the "Ready" condition. It includes all the operations and procedures necessary to fulfill the requirements of the checkoff list. This section also presents the general requirements for engine settings and the general procedures for launching as regards deck handling of the aircraft to be launched. It gives the detailed procedures for operating the catapult including the individual actions of the catapult crew and the system of signals between the members of the crew, the catapult officer and the pilot. Procedures for securing the catapult, for "no load" launchings and supplementary safety precautions are also included in this section.

1-16. SECTION V - MAINTENANCE. This section contains the detailed requirements and the detailed procedures for inspection and maintenance of the

catapult. It is divided into two sub-sections; namely, Preventive Maintenance which details the periodic lubrication, inspection, and test proceedings and Corrective Maintenance which details the correct procedures for replacement of worn or defective parts of the catapult.

1-17. SECTION VI - MALFUNCTIONS. This section contains a treatment of the common malfunctions that

would prevent the efficient or safe operation of the engine. Causes of each malfunction are presented with the recommended remedial actions.

1-18. SECTION VII -PRESSURE INDICATOR CARDS. This section gives examples of normal and abnormal indicator cards and describes the method of interpretation. The typical cards given are correlated with Section VI as regards the malfunctions indicated.

SECTION II
GENERAL DESCRIPTION

2-1. PURPOSE.

2-2. The Type H, Mark 8 Catapult is a hydropneumatic, flush deck type catapult designed for launching an airplane from the flight deck of an aircraft carrier.

2-3. SPECIFICATIONS.

2-4. The H8 catapult's general characteristics are as follows:

2-5. CATAPULT CAPACITY.

Maximum Shuttle End Speed 105 knots

Maximum Load (dead weight) at 105 Knots End Speed 15,500 lb.

Maximum Launching Accumulator Operating Pressure 3,500 psi

Average Acceleration (power run, 105 knots) 3.25 G's.

Maximum Acceleration (power run, 105 knots) 4.6 G's.

Firing Cycle 33 sec.

Time of Power Stroke (105 knots) 1.69 sec.

Time of Retracting 12 sec.

2-6. SHUTTLE TRAVEL.

Launching Stroke 150 ft.

Brake Stroke (maximum) 40 ft.

Overtravel 8 ft.

Total Stroke (maximum) 198 ft.

2-7. ENGINE.

Reeving Ratio 10 to 1

Power Stroke 15 ft.

Brake Stroke (maximum) 4 ft.

Total Stroke (maximum) 19 ft.

2-8. CONSTRUCTION AND FUNCTION.

2-9. The H8 Catapult will be considered to be composed of the following four main groups:
a. The Power Plant
b. The Engine
c. The Drive System
d. The Control System

2-10. THE POWER PLANT. The power plant consists essentially of nine electrically driven pump units and two air-fluid accumulators. Seven pump units and one accumulator system supply the launching power and the remaining two pump units, with the other accumulator, supply the power to retract the engine to battery position. Each pump unit consists of a hydraulic pump, driven by an electric motor connected directly by means of a flexible coupling. The pump and motor are mounted on a common bedplate. The units are provided with the controls necessary to run the pumps individually or collectively to build up and maintain the desired accumulator pressures. The fluid pressure developed by the pumps compresses the air charge present in the accumulators. This compressed air acts as an expanding power source, while the nonflammable hydraulic fluid is used as the working medium. The pumps run continuously during operations and are gravity fed from overhead fluid storage tanks. Automatic regulation of the pump delivery rate by the pressure regulators maintains the desired accumulator pressure.

2-11. The function of the gravity tanks is to provide a head of fluid for the system. The level in the gravity tanks varies as fluid is taken into or returned from the system, but at no time are the gravity tanks ever completely full or completely empty. The air space above the fluid in the gravity tanks allows room for air trapped in the fluid to escape. The gravity tanks are provided with liquid level gages and with air vents which must be kept open.

2-12. A sump tank is installed in the launching system. Its function is to provide additional storage space for fluid received from the launching gravity tank to be delivered to the accumulator by the pumps. Further release of trapped air will occur within the sump tank; therefore, the tank is provided with a vent line that joins to the vent of the launching gravity tank. The gravity tanks and sump tank are furnished under the cognizance of the Bureau of Ships.

2-13. The launching accumulator system consists of five high-pressure, cylindrical, steel vessels containing an initial charge of compressed air. The largest

vessel, the accumulator, receives the hydraulic fluid from the pumps which further compresses the air to the required launching pressure. The other four vessels, the air flasks, are interconnected to the accumulator at the top so that the air can pass freely from one vessel to another, thus maintaining uniform pressure on the fluid stored in the accumulator. The fluid from the pumps is delivered to the accumulator via a manifold which also acts as a passageway for the launching power fluid to the piston valve.

2-14. The retracting accumulator system consists of the single air-fluid accumulator with a manifold connected to the retracting valve.

2-15. Both accumulator systems contain blowoff valves for exhausting air in the accumulators, and blowdown valves for lowering the liquid level. In addition, accumulator pressure gages and liquid level gages are furnished.

2-16. THE ENGINE. The engine, figure 2-1, consists mainly of three concentric cylinders, the inner and outer ones fixed, with the middle one moving. The outer main engine cylinder is anchored to one end of the catapult supporting structure and extends through it. The ram or central cylinder slides within the main engine cylinder and over the inner third cylinder, the braking cylinder, which is anchored to the opposite end of the catapult structure. The ram carries the crosshead which consists of a frame with four axles. Upon these axles are mounted the movable sheaves of the towing cables and the movable sheaves of the retrieving cables.

2-17. The power end of the main engine cylinder is open to an elbow leading down to the piston valve and up to the elbow check valve. The elbow check valve controls the flow of fluid from the main engine cylinder to the launching gravity tank. The power end of the ram is completely closed so that the launching fluid in the main cylinder (surrounding the ram) is separated from the retracting fluid within the ram. The braking cylinder is open at both ends to provide passage for that portion of the retracting fluid contained within the ram. The anchored end of the braking cylinder is open to the rotary bypass valve which bypasses the retracting fluid to the retracting gravity tank during launching or shuts off the flow during braking and retracting. The bypass valve is closed at the beginning of the brake stroke by the operation of the mechanical linkage actuated by a cam on the crosshead.

1-18. The piston valve is a pilot-operated, differential piston valve which controls the admission of the fluid from the launching accumulator to the main cylinder. It is open only during the power stroke of a

launching. During standby it is kept closed by the launching accumulator pressure and seals the fluid in the launching accumulator.

2-19. The constant pressure valve located near the rotary bypass valve is a loaded check valve with a limited lift; its purpose is to restrain the flow of the fluid from the brake cylinder to the retracting gravity tank during the brake stroke, thus causing brake pressure to be developed.

2-20. The retracting valve is a pilot-operated, poppet valve which controls the flow of fluid from the retracting accumulator to the braking cylinder returning the engine to battery position.

2-21. THE DRIVE SYSTEM. The drive system comprises the cable equalizer, two cable whip dampers, the cables, guide sheaves with suitable supporting structures, the shuttle, and the cable tensioner. The function of the drive system is to transmit the motion and power developed by the engine within the ship's structure to the shuttle on the flight deck.

2-22. Two nests, containing five freely rotating sheaves each, are mounted on axles supported by the same structure holding the main engine cylinder. These fixed sheaves with their opposite, movable, sheaves on the crosshead form the towing sheave system to increase the motion of the shuttle with respect to the crosshead. A similar arrangement of sheaves is fixed on the structure supporting the other end of the engine and work in conjunction with the ocher nest of movable sheaves on the crosshead to form the retrieving sheave system.

2-23. The cable equalizer is a mechanism provided to support the anchor end of the towing cables and to permit equalization of tension in the cables. It also provides a lengthwise adjustment of the position of the shuttle on the deck to take up the permanent stretch of the towing cables.

2-24. The cable whip dampers are provided to take up the slack and reduce the whip in the towing cables when the retrieving cables are stretched by the brake stroke.

2-25. The function of the cable tensioner is to remove the slack from the cable system and to maintain tension in the cables at all times. It also acts as a shock absorbing anchor for the retrieving cables during the beginning of the brake stroke when the catapult inertia load is imposed on the retrieving cables.

2-26. THE CONTROL SYSTEM. The control system is comprised of the devices necessary to control the

Figure 2-1. Type H Mark 8 Catapult Engine

various operations of the catapult and auxiliary mechanisms, prior to, during, and after operations. The signal system is instrumental in the transmission of signals between the catapult compartment and the flight deck. A supplementary telephone system is also provided. This communication circuit is neither provided by nor under the cognizance of the Bureau of Aeronautics.

2-27. The operation of the catapult is controlled from three control panels; namely, the deck edge control panel located at the flight deck edge, and the retracting and firing control panels located in the catapult compartment. The deck edge control panel contains lights and control buttons, and is positioned to give the controls operator an unobstructed view of the take-. off area and the airplane. The compartment panels contain lights, control buttons, gages, valves, and pressure regulators which control the operation of the catapult.

2-28. CATAPULT OPERATION. Refer to figures 2-2 to 2-5. A general description of the operating cycle of the H8 Catapult follows: Hydraulic fluid is pumped from the sump tank into the launching accumulator where it is stored against the cushion of high pressure air contained in the upper part of the launching accumulator and its four air flasks. A plane is attached to the catapult by a looped cable (pendant) from the catapult shuttle aft to the airplane tow hooks and by a holdback from the airplane holdback hook aft to the catapult holdback cleats. The bridle and holdback are tensioned by application of pressure from the bridle tensioner pump to the bridle tensioning jacks. During this time the elbow check valve is open to provide "makeup" fluid from launching gravity tank to the main engine cylinder for the resulting small displacement. When the "FIRE" button on the deck edge control box is depressed, the catapult firing circuit is energized and the launching is begun.

a. The fluid stored in the launching accumulator under a predetermined pressure flows through the opened piston valve into the elbow, past the metering plug into the main engine cylinder starting the catapult launching stroke by forcing the ram through the cylinder. The crosshead, attached to the ram, is moved and the power of the engine is transmitted by the crosshead, through the cables and sheaves of the drive system, to the shuttle, which tows the attached plane forward.

b. During the launching stroke the bypass valve is open to the retracting gravity tank permitting the retracting fluid in the inner ram chamber to flow back to the retracting gravity tank. Near the end of the launching stroke a crosshead cam depresses a cutoff roller assembly which mechanically overcomes the hydraulic lock on the firing operating valve, through

cutoff linkage, and returns it to standby. Return of the firing operating valve to standby gents the piston valve allowing the piston valve poppet to seat thus closing the piston valve and cutting off the pressure to the main engine cylinder. The elbow check valve opens at this drop of pressure to permit return of the fluid on retraction and to keep the engine cylinder filled during the brake stroke.

c. Upon the completion of the launching stroke, the crosshead cam actuates the mechanical controls which close the bypass valve to start the brake stroke. When the retracting fluid can no longer flow through the closed bypass valve, it is forced through the constant pressure valve under considerable back pressure which is built up in the braking cylinder in resisting the momentum of the ram, the attached engine components, the drive system and shuttle, and the system is thus brought to rest.

d. In the event of a runaway shot, which results in an excessive acceleration of the catapult, an elevated hydraulic pressure will develop in the runaway shot preventer cylinder which will actuate the runaway shot preventer valve. The runaway shot preventer valve, through the cutoff linkage, will return the firing operating valve to the "standby" position which will cut off the launching pressure. The runaway shot preventer thus provides an emergency means of early cutoff of launching pressure to prevent damage to the catapult which would result from excessive end speed.

e. To bring the system to battery position, the retracting valve is opened and the fluid from the retracting accumulator flows back under pressure through the braking cylinder into the ram. The pressure required during retracting is less than the pressure required to open the constant pressure valve hence the ram is pushed back to its original battery position. During the retracting stroke the bypass valve is held in the closed position, by the action of the damping cylinder actuated by the "RETRACT" button, and will not open until the "RETRACT" button is released after the crosshead reaches battery position. The elbow check valve is kept open by retracting accumulator pressure, allowing the fluid in the launching end of the cylinder to flow back into the launching gravity tank.

2-29. LAUNCHING OPERATION. The force developed by the catapult engine is transmitted through the drive system to the shuttle and thence to the airplane by means of a wire rope bridle or pendant attached to the shuttle. This bridle is placed over the airplane's towing hooks.

2-30. In operation, the plane is placed behind the shuttle which is in the battery, or ready, position. The launching pendant or bridle is attached and the tail of the plane anchored to the deck by means of a

Figure 2-2. Hydraulic Diagram - Standby Position

Figure 2-3. Hydraulic Diagram - Firing Position

Figure 2-4. Hydraulic Diagram - Braking Position

Figure 2-5. Hydraulic Diagram - Retracting Position

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holdback and release device having a breakable link of predetermined strength. The slack in the holdback and bridle is removed by the bridle tensioner which also adds some tension to the towing system. The link in the holdback, which is a ring or bar, is sufficiently strong to withstand the initial bridle or pendant tension, the static thrust of the airplane engine, plus a safety margin. When the catapult is fired, the towing force ruptures the holdback link and the plane is towed forward and launched. At the end of the shuttle power run, the bridle is shed automatically from the airplane towing hooks. 2-31. SUPPLEMENTARY INFORMATION.		2-32. An assembly parts list, NavAer 51-15HA-504 listing the assemblies and their component parts with the number of each required for particular installation on individual vessel's is supplied. The Catalog of Navy Material, Aviation Supply Office, Catalog Section. Class 90, Section 9004, provides an illustrated part list containing an assembly index and assembly breakdown table to be used in requisitioning replacement for expended or defective items. An allowance list NavAer 00-35QD-10 itemizes the catapult spare parts and tools for each catapult. A complete set of spare parts is furnished with each catapult when it installed. Copies of allowance lists are obtained from Aeronautical Publication Supply Points as listed it Aeronautic Publication Index NavAer 00-500.

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