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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|NAVAER 51-15HA-502TABLE OF CONTENTS|
|TABLE OF CONTENTS (CONTINUED)|
|TABLE OF CONTENTS (CONTINUED)|
|TABLE OF CONTENTS (CONTINUED)|
|TABLE OF ILLUSTRATIONS|
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 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.|
|2-1. 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:
2-5. CATAPULT CAPACITY.
2-6. SHUTTLE TRAVEL.
2-8. CONSTRUCTION AND FUNCTION.2-9. The H8 Catapult will be considered to be composed of the following four main groups:
|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
|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.|