This invention relates to mechanically actuated catapults for propelling projectiles. Mechanical devices for use in weaponry have continued to be of interest despite the great preponderance of guns and combustible powders. The archer's bow for example is widely used for target shooting and the taking of game. The projecting of missiles comparable in size and weight to a bullet has been accomplished over the centuries by the use of catapults and slings of various kinds. The most common of the present day devices employ two pieces of elastic tubing joined together by a shot holding pouch. The free ends of the tubing are attached to two legs of a Y-shaped structure. The third leg serves as a grip. This design of long standing makes inefficient use of the energy which is stored in the elastic. In the application of the weapon the elastic is stretched from a limp condition; a portion of the available reach of the user is thus wasted in taking up the slack in the elastic. When the pouch is released to discharge the sling, the elastic first contracts to the point of slackness. This amount of drive does not represent the optimum which could be obtained from the system. Further motion of the pouch and the release of the shot must come as a result of momentum.
In an archery bow, by contrast, the string is always taut. The full arm span of the archer is thus utilized. An additional advantage of the archer's bow over the sling is in the coupling between the driving element and the missile. In the sling the position of the pellet in the pouch is somewhat indeterminate. During release of the pouch the position of the latter which imparts force to the pellet varies from shot to shot. On a bow string, on the other hand, the point of drive is well defined. When the string reaches and passes its original position, it begins to decelerate and thus separates cleanly from the arrow. At this point the arrow has reached its maximum velocity.
The archer's bow does however have a major problem. The driving force comes from the relatively heavy flat springs which are its limbs. These possess considerable inertia and must therefore be made with considerable stiffness to achieve their purpose. To achieve arrow velocities of 200 or 300 feet per second, it is necessary to use bows having draws of 30 to 50 pounds.
Elastic materials for mechanical weaponry can be evaluated and compared by considering the force per unit density required to deflect a standard sized specimen of the material a unit distance. The lower the density, the less of the stored energy need be dissipated in accelerating the spring itself. When considered from this standpoint, rubber and elastomers in general are more efficient than fiberglass or metal springs.
From the standpoint of minimizing user effort it is desirable to employ long elastic elements so that the operating force can be applied gradually. It is difficult however to maintain compactness when long elastic members are used.
A few attempts have been made in the prior art to combine the archer's bow and the sling. Some bows for example have used double strings which incorporated a shot holding pouch. Catapults have also been devised for projecting arrows. U.S. Pat. No. 3,967,017 teaches a construction which is rifle-like in form, contains a stretched elastic band and launches an arrow. To date there has been no catapult which is compact and efficient.
The present invention overcomes many of the shortcomings of previous bows, catapults and combinations thereof. It is an objective of the present invention to provide, in a catapult, means for maintaining an elastic member in tension continuously so as to utilize to a greater extent the energy stored during drawback.
It is a second objective of the present invention to provide in a catapult means for folding a tensed elastic member several times so as to permit the use of relativel long elastic cords in a compact weapon.
The means for achieving these and other objectives will be described in the appended drawings, specifications and claims.