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.  These thru holes are currently used as the keyway for the choke ring wrench.  This wrench is used to remove the choke ring when its design life, based on the aforementioned wear, expires.  Specifically, the wrench is used to unscrew the threaded outer diameter of the choke ring from the mating threads on the water brake cylinder.  However, while these thru holes are an effective attachment point for the choke ring wrench, they also create geometric stress concentrations.  As a result, the choke ring occasionally cracks across the thru holes.

When cracking of the choke ring occurs, the integrity of the water brake is compromised because the braking pressure is no longer maintained at the designed level.  Therefore a cracked choke ring must be replaced before the catapult can be operated again.  Due to thread interference caused by the crack, the choke ring cannot be removed using the choke ring wrench.  As a result, the task of removing a cracked choke ring is currently a labor intensive process.

  Text Box: The choke ring is the inner most cylinder mated to the forward end of the water chamber.  The choke ring has a variable inner diameter, with its minimal diameter being slightly greater than that of the spear.  As the spear engages the water vortex, it is the tight fit of the choke ring that creates the water pressure used for braking.  The annulus ring and jet ring are mated to the forward end of the choke ring.  Together, these two cylinders create an outward conical exit for the displaced water.  The choke ring is made of Nickel Aluminum Bronze, a softer and less durable material than that of the spear.  This durability disparity is intentional, with the choke ring being the sacrificial component.  As a result, the inner surface of the choke ring wears over time.  Around the inner surface there are twelve thru holes, 5/16 inch in diameter, located along the middle diameter of the choke ring.  These thru holes are currently used as the keyway for the choke ring wrench.  This wrench is used to remove the choke ring when its design life, based on the aforementioned wear, expires.  Specifically, the wrench is used to unscrew the threaded outer diameter of the choke ring from the mating threads on the water brake cylinder.  However, while these thru holes are an effective attachment point for the choke ring wrench, they also create geometric stress concentrations.  As a result, the choke ring occasionally cracks across the thru holes. When cracking of the choke ring occurs, the integrity of the water brake is compromised because the braking pressure is no longer maintained at the designed level.  Therefore a cracked choke ring must be replaced before the catapult can be operated again.  Due to thread interference caused by the crack, the choke ring cannot be removed using the choke ring wrench.  As a result, the task of removing a cracked choke ring is currently a labor intensive process. Text Box: The United States Navy uses steam powered catapults to launch aircraft from the deck of aircraft carriers.  When operated, these catapults are accelerated from approximately 0 to 160 knots in under two seconds.  The guiding track for the pistons is approximately 300 feet long.  As a piston approaches the end of the track, the aircraft disconnects from the catapult.  After the aircraft releases from the catapult system, the piston is brought to a sudden stop by a water brake. The water brake is an integral part of the catapult system.  It is precisely the non-destructive nature of the water brake that allows each fired catapult to be retracted and reused for future launches.  The details of the water brake are as follows.  The catapult is connected to a large metal spear located beneath the surface of the deck.  It is this spear that engages the water brake by plunging into a series of aligned horizontal cylinders.  In order of engagement, the spear passes through the striker ring, annulus ring, choke ring, and finally the water brake cylinder.    Within the rear water brake cylinder, a water vortex is maintained such that no water flows into the forward cylinders.  [i] Lew Clayton: Engineer, Catapult Structures, Naval Air Warfare Center Aircraft Division.