US3822884A - Shot propelling arrow - Google Patents

Referring now to FIG. I, a shot arrow 11 is shown nocked on a

bowstring

12 of a

standard bow

14. It can be seen that the shot arrow 11 of this invention is fired from the

bow

14 in substantially the same manner as a standard arrow.

The shot arrow 11 is best described with reference to FIG. 2 and hasa

tubular shaft

15 which has an open

forward end portion

15a and a

rear end portion

15b to which a

nock

16 is attached by any suitable means. A

seal

17, preferably molded of a suitable plastic, is mounted at the

rear end portion

15b of the

shaft

15 to prevent the passage of air therethrough and may have a forwardly extending obturating rim 17a. A

compression chamber

18 is defined in the

shaft

15 between the

seal

17 and a

piston

19 which is preferably molded of a suitable plastic such as high density polyethylene and is slidably mounted in the

shaft

15. The

piston

19 preferably has av rearwardly extending obturating

rim

19a which enhances the air-sealing ability of the

piston

19; the piston may also have a concave

forward end portion

19b shaped to accommodate a

shot particle

20 and a threaded opening to facilitate adjustment of the

piston

19 in a manner which will subsequently be further described. A plurality of

metallic shot particles

20 are fitted into the

shaft

15 forwardly of the

piston

19. The

shot particles

20 are preferably spherical steel projectiles having a diameter only slightly less than the inner diameter of the

shaft

15 so that they form a single line of projectiles within the shaft. This arrangement prevents any jamming which might occur were significantly smaller particles used. The shot arrow 1 l is preferably constructed to propel roughly 15 to 30 projectiles, the number depending upon the energy required per projectile. A modern bow can transfer about 20 ft. lb. to an arrow so if, for example, 1 ft. lb. per projectile were required, about 20 shot particles would be used.

Operation of the shot arrow of this invention will now be described. The shot arrow 11, loaded with a plurality of

shot particles

20, is fired from a conventional bow 14 (FIG. 1) in a manner substantially the same as for the firing of a conventional arrow. The shot arrow 11 is nocked on the

bowstring

12, and the bowstring is drawn back from its rest position to the full draw position illustrated in FIG. 1. When the

bowstring

12 is released, the limbs of the

bow

14, through the bowstring l2, exert a force accelerating the shot arrow 11 in a manner well known to those skilled in the art.

Referring now to FIG. 2, while the

shaft

15 is being accelerated by the bowstring, the

shot particles

20 and, accordingly, the

piston

19 remain substantially fixed in position relative to the

bow

14 due to inertia so that the

seal

17 is effectively accelerated toward the

piston

19. This action compresses the air which is trapped in the

compression chamber

18 by the sealing action of the obturating rims 17a and 190. As th speed of the

shaft

15 increases, the pressure of this trapped air increases and applies a forwardly directed force to the

piston

19 as shown by the

arrow

24 in FIG. 2. This force causes forward acceleration of the

piston

19 and shot 20, which acceleration is, however, at a much slower rate than that of the shaft.

As the

seal

17 approaches the

piston

19, the volume of the trapped air decreases further, thereby increasing its pressure. When the

seal

17 very closely approaches the

piston

19, the pressure increases at a much greater rate reaching anextremely high value, on the order of 10,000 psi, when the seal and piston come roughly within one-quarter inch of each other. This high pressure produces a corresponding high force on the

piston

19, sufficient to overcome the inertia of the shot particles, thus accelerating the piston and shot

particles

20 until the speed of the shot particles equals the speed of the

shaft

15. This is the point of maximum pressure of the trapped air in the

compression chamber

18.

The equal and opposite forces applied by the trapped air to the

piston

19 and seal 17 now further accelerate the

shot particles

20 and slow the

shaft

15. If we assume the total mas of the

shot particles

20 to be equal to the mass of the shot arrow 11 and neglect the effects of friction, the hereinabove described operation of the shot arrow 11 will cause the

shot particles

20 to leave the

shaft

15 and be propelled toward the target while the

shaft

15 and

piston

19, having transferred all forward kinetic energy to the shot, lose all forward velocity and fall to the ground.

Although the

piston

19 is initially forwardly propelled with the

shot particles

20, the pressure in the

compression chamber

18 decreases below ambient as the piston moves forward of its initial position so that, before it can leave the

shaft

15, the pressure in front of the piston is sufficiently higher than the pressure in the compression chamber to push the piston back toward its original position. Only a small pressure differential is necessary because the piston is very light, and the tendency of the piston to leave the shaft is partially overcome by friction. It should be noted, however, that some leakage of air, either into or out of the

compression chamber

18, may occur. Although this leakage would not be sufficient to allow the

piston

19 to leave the

shaft

15, it may cause the final position of the piston to be noticeably different from its position before the arrow 11 was fired. This may be corrected before a new load of

shot particles

20 is loaded into the

shaft

15 in a manner to be subsequently described herein with reference to FIG. 5.

The separation of the

shot

20 from the

shaft

15 physically appears as caused by an elastic collision between the

shaft

15 and shot 20, the trapped air serving as a transfer medium whereby substantially all the energy applied to the

shaft

15 by the

bow

14 is transferred to the shot. If the shot arrow 11 is constructed so that the collision occurs at the moment the

nock

16 leaves the

bowstring

12, it can be seen that substantially all of the energy of the bow will be transferred to the arrow and used to propel the

shot particles

20 to their target. Thus, by using the shot arrow of this invention, maximum transfer of the bows energy to the shot can be effected while the arrows shaft is made to fall near the archers feet for easy retrieval.

It should be noted that certain factors can cause slight deviations from the optimum operating conditions hereinabove described. For example, frictional interaction between the inner surface of the

shaft

15 and the

piston

19 and shot

particles

20 results in greater initial acceleration of the shot than would be produced by compression chamber pressure alone. This frictional interaction also prevents a complete transfer of energy so that some residual energy is retained by the shaft after the

shot particles

20 have been expelled. However, it has been found that this only causes the shaft to travel a short distance (generally less than 10 ft.) before the shaft falls to the ground.

The adiabatic compression of the trapped air during the collision causes the temperature of the air to increase greatly. Were a small quantity of oil, or some other combustible material, inadvertently introduced in the shaft and subjected to this temperature, this high compressive temperature could result in a small explosion which, while insufficient to damage the arrow, could tend to propel the

shaft

15 rearwardly after the impact. Therefore, it is advantageous to construct the shot arrow 11 so that the collision" and maximum air temperature occur shortly before the

nock

16 leaves the

bowstring

12.

This may be accomplished by elongating the rear seal so that it is constructed substantially in the form illustrated as sea] 117 of'FIG. 3. It should be readily apparent that since the point of collision between the piston and rear seal occurs when their velocities become equal, the point of collision is dependent upon the pressure buildup in the

compression chamber

18 and thus related to the length of the chamber. Accordingly, if the forward end portion of the

seal

117 is extended forwardly to decrease the length of the

compression chamber

18, the pressure increase, and accordingly the acceleration of the

piston

19, will occur at a greater rate so that the collision will occur at an earlier point in the flight of the shot arrow 11. By controlling the length of the

seal

117, the point of collision can be controlled so that it occurs at any desired point. In this manner, the occurrence of the collision before the nock leaves the

bowstring

12 can be assured so'that,

should diesel ignition of any combustibles in the

shaft

15 occur, the resultant explosion will only serve to increase the energy imparted to the shot particles and not likely present a hazard to the archer.

Another embodiment of the seal is illustrated in FIG. 4 and designated as

seal

217. The point of collision of the arrow 11 can be controlled through the use of the

seal

217 without any adjustment of the length of the seal. Only its position need be altered. When the

seal

217 is secured in place by a suitable epoxy-type adhesive, the forward and rear obturating rims 2l7a'and 2171;, respectively, maintain the integrity of the air seals so that the

seal

217 performs a function substantially identical to the

seal

117. It should be noted that due to the size of the

seal

117 of FIG. 3, its use significantly increases the mass of the shot arrow 11 while no such increase is produced by use of the

seal

217. Clearly, the embodiment of the seal described would depend upon the mass which must be added to the

shaft

15 to match the weight of the shot propelling arrow 11 to that of the

shot

20 for optimum performance of the shot arrow as previously described. For example, if *30 projectiles were to be fired, a more massive arrow would preferably be used and, accordingly, a heavier sealing means such as the

seal

117 of FIG. 3 is desirable. If 15 projectiles are fired, a lighter arrow and, possibly, the

seal

217 would be required. Additionally, other sealing means may be used without departing from the spirit and scope of this invention.

As previously indicated, when the shot arrow 11 is fired, some air may leakpast the

piston

19, either into or out of the

compression chamber

18, so that the final position of the

piston

19 is altered. To preserve the operating characteristics of the arrow, itis thus necessary to move the

piston

19 to its former rest position so that the

compression chamber

18 will be of proper length. For this purpose, an adjusting means such as an adjusting

rod

21 shown in FIG. 5 may be used. The adjusting

rod

21 may be of any desired length sufficient to extend through the open

forward end portion

15a of the

shaft

15 and has a threaded

end portion

21a for attachment to the threaded

opening

190 of the

piston

19.

It should be readily apparent that after attachment of the adjusting

rod

21 to the

piston

19, the rod may be moved slowly to relocate the piston. This slow motion of the

piston

19 will permit air to flow around it as will be readily understood by those skilled in the art.

The final location of the

piston

19 may be accurately determined by the use of calibration marks 21b, one or more of which would be preferably positioned on the adjusting

rod

21. Alignment of a suitable calibration mark 21b with the

forward end portion

15a of the

shaft

15 would show that the

piston

19 was properly positioned.

It it is desired to retain the

shot particles

20 in the

shaft

15 for an extended time period prior to shooting the shot arrow 11 or if there is a possibility that the shot may fall out of the

shaft

15 before or during firing, a suitable shot retaining means should be used.

FIG. 3 illustrates a

retainer

22 which may be molded of rubber or other suitable material and is shaped to have an inwardly directed

circumferential lip

22a. The

retainer

22 is fitted onto the

shaft

15 with the

circumferential lip

22a positioned against, and extending inwardly of, the

forward end portion

15a of the shaft. The

circumferential lip

22a should be dimensioned to loosely hold the most forwardly positioned

shot particle

20 within the

shaft

15 while the shot arrow 11 is at rest but to readily release the

shot particles

20 with a minimum loss of energy of the particles when the arrow is fired. The

retainer

22 serves the additional function of protecting the forward end portion of the

shaft

15 against damage when the shot arrow 11 falls to the ground and helping to prevent dirt, grass or other debris from entering the

shaft

15. If desired, the

lip

22a may be segmented or cover only a portion of the periphery of the opening so that energy loss is minimized. The

lip

22a need only hold the

shot particles

20 against being inadvertently allowed to fall from the open

forward end portion

15a of the

shaft

15.

FIG. 4 illustrates an alternate shot retaining means in the form of a knock-

off closure

24 which is preferably fitted over the

forward end portion

15a of the shaft and is detached therefrom by the most forwardly directed shot

particle

20 when the arrow is fired.

It should be understood that components of the shot arrow 11 may be further modified if desired. For example, a rear seal may be used wherein two generally frusto-conical members are threaded together to expand a tubular plastic sleeve into tightly fitting, sealing relationship within the

shaft

15. Such a rear seal would function in a manner similar to the

rear seal

217 of FIG. 4 and, additionally, could be moved within the shaft for removal or repositioning by loosening the threaded members. Although the shot-arrow 11 has been described in conjunction with discrete, spherical

steel shot particles

20, it should be understood that other projectiles, including elongated projectiles, shot particles which are connected in one or more long chains, or projectiles having a cylindrical or other desired shape may be used without departing from the spirit and scope of this invention. The

shot particles

20 may be formed of any desired material having sifficient hardness to withstand the large magnitude forces produced when the shot propelling arrow 11 is fired without significant deformation which would detract from the effectiveness of the arrow.