Catapult Type H, Mark 8


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 Handbook Operation and Maintenance Instructions CATAPULT TYPE H, MARK 8 THIS PUBLICATION SUPERSEDES NAVAER 51-15HA-502 DATED 15 MAY 1952 PUBLISHED UNDER AUTHORITY OF THE SECRETARY OF THE AIR FORCE AND THE CHIEF OF THE BUREAU OF AERONAUTICS 1 OCTOBER 1956



1-1 Purpose1
1-5 Responsibility1
1-10 Scope1
  1-12 Section I – Introduction1
  1-13 Section II – General Description1
  1-14 Section III – Detailed Description1
  1-15 Section IV – Operation of the Catapult1
  1-16 Section V – Maintenance1
  1-17 Section VI – Malfunctions2
  1-18 Section VII- Pressure Indicator Cards2
2-1 Purpose3
2-3 Specifications3
  2-5 Catapult Capacity3
  2-6 Shuttle Travel3
  2-7 Engine3
2-8 Construction and Function3
  2-10 The Power Plant3
  2-16 The Engine4
  2-21 The Drive System4
  2-26 The Control System4
  2-28 Catapult Operation6
  2-29 Launching Operation6
2-31 Supplementary Information11
3-1 Launching System12
  3-3 Launching Accumulator and Manifold12
  3-7 Piston Valve12
  3-14 Four-Way Valve14
  3-18 Firing Operating Valve14
  3-27 Elbow Check Valve17
  3-33 Cylinder and Ram17
  3-38 Crosshead19
  3-40 Fixed Sheaves19
  3-42 Bridle Tensioner19
  3-46 Cable Whip Dampers19
  3-50 Cable Equalizer23
  3-53 Cable Tensioner23
  3-57 Runaway Shot Preventer23
  3-67 Shuttle29
  3-69 Cables29
  3-71 Holdback and Release Units29
3-75 Launching Bridles or Pendants29
  3-78 Arresting System32
  3-80 Constant Pressure Valve32
  3-87 Air Trap Cylinder34
  3-90 Retracting Accumulator34
  3-94 Retracting Valve35
  3-97 Bypass Valve and Mechanical Controls35
  3-103 Hydraulic Stops39
  3-105 Operating Valves39
  3-107 Pressure Indicators39
  3-109 Four-Way Valve39
3-111 Power Plant and Signal System41
  3-112 Pumps41
  3-117 Pump Motors and Controllers41
  3-118 Pressure Regulators41
  3-120 Drain Pump43
  3-122 Deck Edge Control Box43
  3-124 Firing Control Panel43
  3-126 Retracting Control Panel43
  3-128 Signal System – Launching Cycle47
  3-130 Signal System – Retracting Cycle47
  3-132 Signal System – Suspension Cycle49
  3-135 Electric Speedometer50
4-1 Launching Preparation51
  4-2 Procedure51
4-3 Catapult Operation52
  4-4 General52
  4-5 Sequence of Operations52
  4-6 General52
  4-7 Launching Operating Procedures52
  4-8 Retracting Operating Procedure53
  4-9 Signals Recommended54
  4-10 “No Load” Launchings54
    4-11 General54
    4-14 “No Load” Launching Signals54
4-15 Supplementary Operating Notes54
4-28 Securing the Catapult55
  4-29 Procedure55
5-1 General57
5-3 Preventive Maintenance57
  5-7 Preventive Maintenance Schedules57
    5-8 Daily Schedule57
    5-9 Weekly Schedule59
    5-10 Semimonthly Schedule59


  5-11 Monthly Schedule60
  5-12 Completion of 1500 Launchings60
  5-13 Quarterly Schedule60
  5-14 Semiannual Schedule60
  5-15 Catapult Not in Regular Use60
  5-16 Lubrication Schedules61
5-17 Corrective Maintenance61
5-20 General Corrective Maintenance Procedures61
5-21 Packings61
  5-22 O-Ring Packings – Running and Static Seals61
  5-23 Repeated Failure of O-Rings61
  5-24 V-Ring Packing-Synthetic Rubber61
  5-25 Copper Gaskets63
  5-26 Wipers – Felt and Metallic63
  5-27 Cleaning and Inspection of Packed Joints63
5-28 Wire Rope63
  5-29 Care and Handling of Wire Rope Cable63
  5-31 Seizing63
  5-35 Inspection of Wire Rope64
  5-37 Lubrication of Wire Rope64
  5-38 Semiannual Inspection of Cable Terminals64
  5-39 Pouring of Cable Terminals65
  5-40 Care and Use of Pyrometer65
  5-41 Tempilstiks65
  5-42 Pouring Procedures for Catapult Terminals65
  5-43 Preparation of the Wire Rope65
  5-44 Preparation of Terminal for Pouring of Zinc67
  5-45 Preparation and Pouring of Zinc68
  5-46 Finishing the Terminal69
  5-47 Inspecting the Terminal69
  5-48 Use and Care of Gasoline Blowtorch69
  5-49 Installation of Cables70
  5-50 Testing of Terminals70
5-51 Compensating for Cable Stretch71
5-53 Pumps72
  5-54 Checking Capacity of Power Plant Pumps72
  5-55 General Maintenance of Catapult Pumps72
  5-56 Venting Pumps and Cleaning Pump Section Lines72
5-57 Electrical Components72
5-59 Solenoid Valve Maintenance72
5-60 Pulling Out Crosshead73
5-62 Checking Slot Alignment in Bypass Valve73
5-64 Leaking High-Pressure Shutoff Valves74
5-66 Bridles and Pendants74
5-68 Liquid Level Gages74
5-70 Detailed Corrective Maintenance Procedures74
5-71 Piston Valve74
  5-72 Fluid Leakage at Valve Securing Stem74
  5-73 Leakage between Cover and Large Head74
  5-74 Fluid Leakage between Large Head and Body of Piston Valve74
  5-75 Fluid Leakage between Small Head and Adapter75
  5-76 Fluid Leakage between Adapter and Body75
  5-77 Fluid Leakage between Flange of Piston Valve and Manifold75
  5-78 Fluid Leakage between Engine Cylinder Elbow and Piston Valve76
5-79 Binding76
5-80 Air Trap Cylinder77
5-81 Disassembly of Air Trap Cylinder77
5-82 Fluid Leakage between Flange and Cylinder at Piston End of Cylinder77
5-83 Fluid Leakage from Weep Holes at End of Rod77
5-84 Fluid Leakage between Bracket and Cylinder77
5-85 Fluid Leakage between Air Trap Cylinder and Clapper Valve or between Clapper Valve and Elbow Check Valve77
5-86 Clapper Valve78
  5-87 Binding78
5-88 Elbow Check Valve78


5-89 Leakage at Actuating Rod78
  5-90 Leakage of Interior Packings78
  5-91 Binding or Sticking78
  5-92 Replacement of Switch (DO Aux Switch)79
5-93 Four-Way Valve79
  5-94 Fluid Leakage79
  5-95 Binding79
5-96 Firing Operating Valve79
  5-97 Air Leakage79
  5-98 Fluid Leakage79
  5-99 Sluggish Operation or Nonoperation79
5-100 Engine Cylinder and Engine Cylinder Elbow80
  5-101 Fluid Leakage80
5-102 Engine Cylinder and Ram80
  5-103 Fluid Leakage80
5-104 Ram and Brake Cylinder81
  5-105 Fluid Leakage81
5-106 Braking Cylinder and Spacer81
  5-107 Fluid Leakage81
5-108 Braking Cylinder Spacer and Bypass Valve81
  5-109 Fluid Leakage81
5-110 Hydraulic Stops81
  5-111 Fluid Leakage81
  5-112 Binding81
5-113 Retracting Valve81
  5-114 Fluid Leakage between Bypass Valve and Stem End of Retracting Valve81
  5-115 Fluid Leakage at Ports of Retracting Valve81
  5-116 Interior Fluid Leakage of Retracting Valve81
  5-117 Fluid Leakage between Flange and Body of Valve82
  5-118 Disassembly for Replacement of Interior Packings of Retracting Valve and of Connection to Bypass Valve Body82
  5-119 Binding of Valve or Stem Failure82
5-120 Bypass Valve82
  5-121 Fluid Leakage between Gland and Body of Valve82
  5-122 Fluid Leakage between Plug Shaft and Gland Nut82
  5-123 Leakage from Bypass Valve to Gravity Tank83
5-124 Constant Pressure Valve83
  5-125 Air Leakage83
  5-126 Fluid Leakage83
  5-127 Fluid Leakage between Dome Cover and Body83
  5-128 Fluid Leakage at Flange to 4-inch Line to Air Trap Cylinder83
  5-129 Fluid Leakage Down Past Dome Piston84
  5-130 Fluid Leakage at Plugs or Vents84
  5-131 Fluid Leakage between Lower Spindle and Retainer or between Retainer and Retainer Housing84
  5-132 Fluid Leakage between Retainer Housing and Body84
  5-133 Fluid Leakage at Seat84
  5-134 Fluid Leakage between Seat and Body84
  5-135 Fluid Leakage between Constant Pressure Valve and Bypass Valve Body84
  5-136 Fluid Leakage between Constant Pressure Valve and Elbow of Line to Retracting Gravity Tank84
  5-137 Disassembly for Leak at Flange of 4-inch Line to Air Trap Cylinder84
  5-138 Disassembly for Leakage between Dome Cover and Dome Body84
  5-139 Complete Disassembly of Constant Pressure Valve84
5-140 Damping Cylinder86
  5-141 Air Leakage at Ports86
  5-142 Air Leakage at Plug86
  5-143 Air Leakage at Piston86
  5-144 Binding86
  5-145 Sluggish Operation86
5-146 Cable Tensioner86
  5-147 Air Leakage86
  5-148 Fluid Leakage between Head and Tank86
  5-149 Fluid Leakage between Head and Cylinder87


  5-150 Fluid Leakage at Sheave End of Cylinder87
  5-151 Testing and Replacement of Fluid87
  5-152 Replacement of Slippers87
  5-153 Replacement of Crosshead Sheave88
  5-154 Binding of Ram88
  5-155 Sticking Clapper Valve88
5-156 Cable Whip Dampers88
  5-157 Air Leakage88
  5-158 Fluid Leakage between Dome and Flange of Cylinder88
  5-159 Fluid Leak from Crosshead End of Cylinder88
  5-160 Fluid Leakage at Coupling End of Cylinder88
  5-161 Checking Alignment to Eliminate Scoring at Ram89
  5-162 Testing and Replacement of Fluid89
  5-163 Replacement of Slippers and Crosshead90
  5-164 Replacement of Cable Equalizer Sheave90
  5-165 Replacement of Cable Equalizer Slippers90
5-166 Shuttle90
  5-167 Replacement of Slippers and Wipers90
  5-168 Replacement of Hook91
5-169 Retrieving Sheaves91
  5-170 Replacement91
5-171 Towing Sheaves91
  5-172 Replacement91
5-173 Engine Crosshead91
  5-174 Replacement of Slippers91
5-175 Runaway Shot Preventer92
  5-176 Oil Leakage at Runaway Shot Preventer Valve92
  5-177 Oil Leakage from Runaway Shot Preventer Cylinder92
  5-178 Runaway Shot Preventer Valve – Checking and Adjusting93
6-1 General93
6-3 Preparation for Launching93
  6-4 General93
  6-5 Pump Difficulties93
  6-6 Excessive Pump Noise93
  6-10 Pressure Indicator Difficulties93
  6-11 Loss of Accumulator Charge93
  6-15 Stuck Piston Valve Securing Stem94
6-16 Pre-launching94
  6-17 General94
  6-18 First Ready94
  6-21 Bridle Tensioning95
  6-22 Final Ready95
  6-23 Firing95
  6-25 Firing Operating Valve95
  6-26 Cold Shot95
  6-29 Runaway Shot96
  6-31 Slow Shot96
  6-34 Normal Airplane Launching96
  6-39 Late Cutoff97
  6-40 No Cutoff97
6-41 Brake Stroke97
  6-42 General97
  6-43 Excessive Tow Cable Whip97
  6-44 Erratic Rebound97
  6-45 Early Brake Stroke97
  6-46 Excessive Brake Penetration or Pressure97
6-52 Retraction98
  6-53 General98
  6-54 Catapult Does Not Retract98
  6-55 Slow Start of Retraction98
  6-57 Slow Retraction99
  6-60 Yellow Light Does Not Come On99
  6-61 Loss of Retracting Accumulator Pressure99
  6-63 Bypass Valve Does Not Open99
7-1 General100


1-1 Type H Mark 8 Catapultvi
2-1 Type H Mark 8 Catapult Engine5
2-2 Hydraulic Diagram – Standby Position7
2-3 Hydraulic Diagram – Firing Position8
2-4 Hydraulic Diagram – Braking Position9
2-5 Hydraulic Diagram – Retracting Position10
3-1 Piston Valve, Elbow, and Elbow Check Valve13
3-2 Four-Way Valve15
3-3 Firing Operating Valve16
3-4 Cylinder and Ram18
3-5 Crosshead20
3-6 Bridle Tensioner21
3-7 Cable Whip Damper22
3-8 Cable Equalizer24
3-9 Cable Tensioner25
3-10 Runaway Shot Preventer26
3-11 Runaway Shot Preventer Valve27
3-12 Shuttle30
3-13 Holdback and Release Unit – “D” Ring Type31
3-14 Holdback and Release Unit – Tension Bar Type31
3-15 Constant Pressure Valve33
3-16 Air Trap Cylinder34
3-17 Retracting Valve36
3-18 Bypass Valve and Mechanical Controls37
3-19 Hydraulic Stops38
3-20 Operating Valve39
3-21 Pressure Indicator40
3-22 Power Plant and Signal System – Electrical42
3-23 Deck Edge Control Box44
3-24 Firing Control Panel45
3-25 Retracting Control Panel46
3-26 Signal System – Schematic Diagram48
5-1 Lubrication Chart62
5-2 Locating the Seizing66
5-3 Unlaying the Strands66
5-4 Brooming-Out the Wires66
5-5 Degreasing with Solvent67
5-6 Dipping in Acid67
5-7 Neutralizing with Soda67
5-8 Washing with Water68
5-9 Cleaning the Terminal68
5-10 Placing the Terminal68
5-11 Applying Asbestos Paste69
5-12 Wrapping Asbestos Paste69
5-13 Wrapping Top with Asbestos69
5-14 Heating the Terminal70
5-15 Measuring Temperature of Zinc70
5-16 Pouring the Zinc70
5-17 Sawing Off the “Hot-Top”71
5-18 Inspecting Face of Terminal71
5-19 Inspecting Bottom of Terminal71
7-1 Normal Indicator Cards101
7-2 Indicator Cards Showing Early Brake Stroke102
7-3 Indicator Cards for “No Load” Shots103
7-4 Indicator Cards – Excessive Initial Engine Cylinder Pressure104
7-5 Indicator Cards Runaway Shot104
7-6 Indicator Cards Slow Shots105
7-7 Indicator Cards – Early and Late Cutoff106
7-8 Brake Stroke – Various Launching Conditions107
7-9 Indicator Cards – Brake Malfunctions108
7-10 Indicator Cards – Brake Malfunctions109


Figure 1-1. Type H Mark 8 Catapult
Figure 1-1. Type H Mark 8 Catapult


1-1. PURPOSE1-2. 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 thatwould 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.


2-1. 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.


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


Maximum Shuttle End Speed105 knots
Maximum Load (dead weight) at 105 Knots End Speed15,500 lb.
Maximum Launching Accumulator Operating Pressure3,500 psi
Average Acceleration (power run, 105 knots)3.25 G’s.
Maximum Acceleration (power run, 105 knots)4.6 G’s.
Firing Cycle33 sec.
Time of Power Stroke (105 knots)1.69 sec.
Time of Retracting12 sec.



Launching Stroke150 ft.
Brake Stroke (maximum)40 ft.
Overtravel8 ft.
Total Stroke (maximum)198 ft.


2-7. ENGINE.

Reeving Ratio10 to 1
Power Stroke15 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
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.2-31. 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.