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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Richard Pekelney


Classification changed to Unclassified
By authority of Chief of the Bureau of Aeronautics
NAVAER 51-15HA-502
Bureau of Aeronautics Authenticator

NAVAER 51-15HA-502
Operation and Maintenance
DATED 15 MAY 1952
1 OCTOBER 1956

NAVAER 51-15HA-502



Section Page
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
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
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
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
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



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



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



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
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
7-1 General 100



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
Figure 1-1. Type H Mark 8 Catapult




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.


1-6. 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.





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.


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


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.


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.



2-9. 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
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 2-2. Hydraulic Diagram - Standby Position

Figure 2-3. Hydraulic Diagram - Firing Position
Figure 2-3. Hydraulic Diagram - Firing Position

Figure 2-4. Hydraulic Diagram - Braking Position
Figure 2-4. Hydraulic Diagram - Braking Position

Figure 2-5. Hydraulic Diagram - Retracting Position
Figure 2-5. Hydraulic Diagram - Retracting Position

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.


  2-32. 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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