A cartridge for storing pipe lengths on a horizontal directional drill that allows easy loading and unloading of pipes from the cartridge while it is attached to the drill. Longitudinal support members and towers at each end of the cartridge provide structural support to the cartridge and maintain the pipe lengths within the cartridge. The sides of the cartridge are open and unobstructed. Loading and unloading of pipes can, therefore, be done through the sides of the cartridge.

FIELD OF THE INVENTION 
     The present invention relates generally to horizontal directional drill machines. It relates particularly to a stakedown assembly for a horizontal directional drill machine. 
     BACKGROUND OF THE INVENTION 
     A horizontal directional drill machine is a common and well-known machine for installing pipes beneath the ground and generally parallel to the surface. These machines are used in many different applications and are available in a wide range of sizes. Typical applications where a horizontal directional drill machine might be used include the installation of fiber optic cables, electrical cables, gas lines, water systems, or sewer systems. Horizontal directional drill machines are commonly rated in terms of pull-back capacity. Some machines for smaller applications have as little as five thousand pounds of pull-back capacity. Other machines are available with a pull-back capacity of as much as one million pounds. 
     One alternative to a horizontal directional drill machine is the traditional trencher machine. A trencher machine simply digs a trench into the ground, and after (for example) pipe is laid down in the bottom of the trench, the trench is filled and the pipe is buried. The advantage of a horizontal directional drill machine over a trenching machine is that a pipe can be buried in the ground over long distances without digging a trench. Thus, a horizontal directional drill is particularly desirable when a trench would be difficult or too costly to dig. For example, a horizontal directional drill machine finds particularly advantageous application for installing pipes under roadways, where destruction of the road is expensive and inconvenient to travelers, or under a waterway like a river, where trenching would be impossible. 
     A unique aspect of a horizontal directional drill machine is the special drill head that is attached to the front end of a pipe to be laid. The drill head has an angled shape which allows the operator to change the direction of the pipe after it has entered the ground. Direction changes are achieved by stopping the pipe and drill head rotation and orienting the drill head at a desired angle. Then, by pushing on the drill pipe without rotating it, the drill head and attached pipe will veer in the desired direction. Thus, by effecting directional changes to pipe travel, a pipe might enter the ground at an angle, travel horizontally over a long distance, and exit the ground at another angle. This ability to change the direction of pipe travel also allows the operator to steer the pipe around underground obstacles like boulders. 
     A completely drilled pipe length is made up of an assembly of shorter pipe lengths that are attached to each other end to end. As the pipe is drilled through the ground successive pipe lengths are attached to the preceding pipe assembly to provide additional length. The additional pipe lengths are stored on the drill in a cartridge, and the bottom pipes in the cartridge are successively attached to the preceding pipe assembly with the aid of a loader. Typically, the cartridge is detachable from the drill body to allow the cartridge to be fully loaded with pipes away from the drill, but this feature is not a necessity for operation of the drill. 
     Frequently, a need arises during operation of the drill to access the stored pipe lengths in the cartridge while the cartridge is still attached to the drill body. This can occur when a pipe assembly is nearly fully drilled, but a small number of pipe lengths are still required for completion. Instead of detaching the cartridge and attaching a new cartridge fully loaded with new pipe lengths, it is often more convenient to individually load the additional pipe lengths required into the already attached, but empty, cartridge. Additionally, equipment problems can occasionally occur with the drill so that the stored pipes have to be removed one by one from the cartridge while it is still attached to the drill. This situation might arise if the loader assembly fails and the bottom pipe becomes jammed. 
     Although cartridge and pipe sizes vary widely depending on the size of the drill, the cartridge is commonly between two and three feet deep from its top to the bottom, and the pipes can weigh about seventy-five pounds each. Prior art cartridges support the pipe lengths between side walls that extend longitudinally along the cartridge. These cartridges are loaded and unloaded from the top of the cartridge. Loading and unloading heavy pipes through the top of the cartridge can be difficult and can cause back injuries. Depending on whether the operator is loading or unloading, he must also lower the pipe down into the bottom or lift the pipe up from the bottom of the cartridge through the entire depth of about two to three feet. It is therefore desirable to have a cartridge that would allow easier loading and unloading of the pipes while the cartridge is attached to the drill. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved pipe cartridge for a horizontal, directional drill. 
     It is another object to provide a cartridge which allows pipes to be loaded and unloaded from the sides of the cartridge, instead of from the top. 
     According to the invention, the cartridge includes longitudinal support members that extend along a lower part of the cartridge. Each end of the cartridge comprises a tower including side plates, an end plate, and dividing plates. The side plates restrain side-to-side movement of the pipes. The end plates restrain end-to-end movement of the pipes, while the dividing plates extend vertically within the cartridge to separate the pipes into columns. The sides of the cartridge are open between the towers. Pipes can, therefore, be loaded into the cartridge by angling one end of the pipe into the cartridge from the side and lifting the other end up over a tower. To unload a pipe, the procedure is simply reversed. 
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     The invention, including its construction and method of operation, is illustrated more or less diagrammatically in the drawings, in which: 
     FIG. 1 is a side elevational view of a horizontal directional drill, showing the drill in its operating mode with the cartridge fully loaded with pipes; 
     FIG. 2 is a side elevational view of a horizontal directional drill, showing the drill in its operating mode with the cartridge empty and an operator loading a new pipe into the cartridge; and 
     FIG. 3 is a perspective view of one end of the cartridge, with the cartridge about half full of pipes. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and particularly to FIG. 1, a horizontal directional drill machine is shown generally at  10 . The drill  10  includes a frame  12  supported by driven tracks  14  for moving the drill machine  10  from place to place. 
     The drill machine  10  includes a longitudinally elongated boom  16  pivotally mounted on the front end of the frame  12 , as at  17 . A conventional pipe drill assembly  18  is mounted on the boom  16 , extending coextensively therewith. The drill assembly  18  is designed to drill a series of pipe sections P 1 , P 2 , P 3 , et seq., into the ground, in sequence. 
     In the operating mode of the drill machine  10 , the boom  16  is pivoted upward away from the frame  12  so that pipe section P 1  extends from the drill assembly  18  and intersects the ground at an angle. A special drill head (not shown) is attached to the front end of the first drill pipe section P 1 . In order to drill the pipe section P 1  into the ground and make any desired directional changes in its path, a variety of push, pull, and rotational forces are applied to the pipe section P 1  by the drill assembly  18 . The manner in which the drill assembly  18  applies these forces to the drill pipe section P 1  are not described, but are well known to those skilled in the art. 
     As the first pipe section P 1  is drilled into the ground, new pipe sections P 2 , P 3 , et seq., are successively attached to the rear end of the preceding pipe sections. A cartridge  22  of pipe sections P 2 , P 3 , et seq. is provided on the boom  16  for storing these additional pipe sections, and a semi-automatic or fully automatic loader (not shown) may be provided for attaching them to the preceding pipe sections. 
     Turning now to FIGS. 2 and 3, according to the invention the cartridge  22  includes a front end tower  30  and a rear end tower  31 . Connecting the two towers  30  and  31  are longitudinal support members  32  which extend along a lower part of the cartridge  22  on the outer sides. 
     The towers  30  and  31  each include side plates  34  which extend a short distance longitudinally of the cartridge  22 . The side plates  34  extend up to define the top  23  of the cartridge  22 . End plates  36  extend between the side plates  34  and, also, up to the top  23  of the cartridge  22 . 
     A series of dividing plates  38  are provided for separating the columns of pipes. The dividing plates  38  are attached to the end plates  36 . Each extends up to the top  23  of the cartridge  22  between the end plates  36 . 
     The top  46  of the cartridge  22  is open between the side plates  34  and the end plates  36 . The open top  46  permits reloading the cartridge  22  with new pipes P when the cartridge  22  is detached from the drill  10 . Removable pins  48  are installed through the tower side plates  34  and prevent the pipes P from inadvertently coming out of the cartridge  22  through the open top  46 . 
     It has been discovered that the support structure of the towers  30  and the longitudinal support members  32  make cross bars or walls extending along the sides of the cartridge  22  unnecessary. Therefore, as can be readily appreciated from the drawings, the sides of the cartridge  22  are open. 
     Referring specifically to FIG. 2, the ease with which pipe lengths P can be loaded and unloaded through the open sides of the cartridge  22  is readily apparent. To load a new pipe length P into the cartridge  22 , the front end of the pipe length is angled into the interior of the cartridge  22  through the open top  40 . The pipe length P is aligned with the desired column by placing one end of the pipe length against the end plate  36  between two dividing plates  38  or a dividing plate  38  and a side plate  34 . Then, the other end of the pipe length is lifted up and over the nearest side plate  34 . Finally, the other end is lowered through the top  46  (with pin  48  removed) down into the bottom of the cartridge  22  between the two dividing plates  38  or a dividing plate  38  and a side plate  34 . To remove a pipe length P from the cartridge  22 , the process is reversed. 
     While the pipe lengths are in the cartridge  22 , they sometimes drip water, sludge or debris which then carry. A plurality of drain holes  37  are provided in the end plates  36  to allow it to escape. 
     While a preferred embodiment of the invention has been described, it should be understood that the invention is not so limited, and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.