Method and apparatus for managing recoil of electromagnetic guns

A power supply generating a reaction torque generally simultaneously with its power output is utilized to supply power to fire the railgun. The power supply and the railgun are cooperatively mounted together such that the reaction torque of the power supply upon discharge counteracts the recoil force of the railgun, thereby transferring lateral forces through the compulsator to a position in the power supply which is removed from the position of the coupling between the railgun and the power supply.

BACKGROUND OF THE INVENTION 
The present invention relates generally to electromagnetic railguns, and 
more specifically relates to methods and apparatus for managing recoil of 
electromagnetic railguns, which methods and apparatus are particularly 
advantageous when the railgun is on a platform or is carried on a vehicle. 
Gun recoil is a well known phenomena associated with projectile-firing 
mechanisms of all types. Although usually thought of in connection with 
gas pressure, or thermodynamic, guns, the recoil phenomenon is present in 
electromagnetic guns, i.e., railguns. The force which propels the 
projectile down the barrel of the gun also causes the gun to recoil in an 
opposite direction. Recoil is a significant problem with large 
high-powered guns mounted on vehicles, such as trucks or armored carriers. 
The guns are typically mounted as high as possible on the vehicle to 
facilitate access and "vision" of the gun. The axis of the gun (i.e., the 
barrel), is therefore typically significantly above the center of gravity 
of the vehicle or other platform. Accordingly, recoil of the gun will 
typically manifest itself as an overturning moment on the vehicle. In many 
cases, this overturning moment places a limit on the size or power of the 
gun which may be mounted on a particular vehicle. 
Several techniques have been proposed for attempting to manage recoil. For 
example, U.S. Pat. No. 4,527,457, issued July 9, 1985 to Fikse, discloses 
an embodiment of a railgun wherein a mechanicam is provided in the railgun 
to generate a reaction force which is substantially equivalent to, but in 
the opposite direction of, the recoil force. Fikse suggests the use of a 
second pair of generally parallel conductors, which are responsive to the 
same current utilized to fire the projectile from the railgun. This second 
pair of conductors is utilized to accelerate a recoil mass in a closed 
system to generate the reaction force. Fikse also suggests the use of an 
exhaust jet having an expansion chamber and a nozzle whereby the hot gases 
associated with the forming of the plasma which accelerates the projectile 
down the railgun will pass through the nozzle to generate the reaction 
force. As will be readily recognized, the proposals of Fikse are extremely 
inefficient in that they require a dramatic energy increase in the system 
to compensate for the railgun recoil. 
Other proposed systems for managing railgun recoil have included varying 
the conformity of the rails of the railgun itself in an attempt to 
redistribute the recoil direction. However, such proposed techniques have 
imposed substantial limitations on the performance of the railgun. 
Accordingly, the present invention provides a new method and apparatus for 
managing recoil in electromagnetic railguns by utilizing a power source 
for firing the railgun which is cooperatively coupled to the railgun and 
which is adapted to generate a force similar to, and opposing, the railgun 
recoil force. Such coupling arrangement redistributes the recoil force to 
lower the overturning moment of the assembly. 
SUMMARY OF THE INVENTION 
The present invention includes the cooperative use of a railgun and a power 
supply for that railgun, which power supply, at the time of discharge, 
exhibits a reaction torque in the stator. In a preferred embodiment, the 
power supply will be a compensated pulsed alternator power supply, also 
known as a "compulsator". Also in a preferred embodiment, the railgun is 
rigidly secured to the stator of the power source such that at the time 
the railgun is actuated, and both the projectile force and the recoil 
force are generated, the reaction torque will be generated in the power 
supply stator, and will effectively transfer the recoil force through the 
diameter of the power supply. This transfer reduces the overturning moment 
on any platform upon which the power supply and railgun are mounted.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to the drawings in more detail, and particularly to FIG. 1, 
therein is schematically depicted an electromagnetic railgun 10 
cooperatively coupled to a compulsator power supply 12, in accordance with 
the present invention. Railgun 10 can be of any type known to the art, 
such as, for example, a parallel rail railgun or a coaxial railgun. 
Compulsator power supply 12 will preferably be a device constructed in 
accordance with U.S. Pat. No. 4,200,831 issued Apr. 29, 1980 to Weldon, et 
al. The disclosure of U.S. Pat. No. 4,200,831 is hereby incorporated 
herein by reference. 
Briefly, compulsator 12 is an alternator specially adapted to produce short 
duration, high power pulses of electrical power. The rotor of the 
compulsator is driven by an appropriate device for the particular 
application in question, such as, for example, a gas turbine. Once the 
compulsator rotor is driven to design speed, an external switch is closed 
at the appropriate time to produce a half sinusoidal pulse, or a fraction 
thereof, to provide the desired output current to the railgun. As will be 
apparent from the discussion to follow, although compulsators have been 
proposed for use which have two rotors rotating in opposite directions, so 
as to minimize the reaction torque at the time of discharge, such designs 
would not be optimal for use with the present invention. 
At the time the power is extracted from compulsator 12, the mechanical 
power extracted from the rotor is equal to the electrical power generated, 
i.e.: 
EQU T.omega.=VI, 
where; 
T=torque; 
.omega.=angular velocity; 
V=generated (open circuit) voltage; and 
I=the output current of the compulsator. 
For a single rotor compulsator, at the time the power is extracted from the 
rotor, the torque (T) is applied to the compulsator stator as a reaction 
torque which manifests itself as a reaction force at the periphery of the 
compulsator stator. The extracted electrical current (I) is delivered to 
the railgun and is the source of the force on the projectile: 
EQU F=1/2 L'I.sup.2 
where 
F=the force on the railgun projectile; and 
L'=the inductance gradient of the railgun. 
Therefore, discounting losses in the system, the compulsator output power 
matches the railgun input power (the power to the projectile). 
Additionally, again discounting losses in the system, such as friction 
losses, the recoil force of the railgun will be proportional to the input 
power of the railgun. Accordingly, the recoil force of the railgun will be 
generally proportional to the reaction torque on the compulsator stator. 
Accordingly, even allowing for losses in the system, a functional relation 
exists between the projectile force, the recoil force, and the reaction 
torque and reaction force of the compulsator. 
Referring now also to FIG. 2, by solidly mounting railgun 10 to an upper 
portion of stator 14 of compulsator 12, the recoil of railgun 10 can be 
effectively transferred through the diameter 16 of compulsator stator 14 
to a plane 18 intersecting the lower extreme of compulsator stator 14, or 
another member securely affixed thereto, by allowing it to react against 
the discharge torque of the compulsator. 
The physical construction of railgun 10 and of compulsator 12 (and 
particularly of compulsator stator 14), as well as the physical coupling 
of the two, may be accomplished in accordance with conventional principles 
of mechanical engineering. Clearly, however, compulsator stator 14 will be 
designed to withstand the impinging forces of the compulsator reaction 
torque and the railgun recoil. Similarly, coupling 20 between railgun 10 
and stator 14 will be adapted to withstand the above forces without 
damage. 
Referring now also to FIG. 3, therein is schematically depicted a vehicle 
22, such as a truck, with a compulsator 12 and a railgun 10 attached 
thereto in accordance with the present invention. Railgun 10 and 
compulsator 12 are mounted on the bed 24 of truck 22. In accordance with 
the preferred design considerations set forth earlier herein, railgun 10 
is located in a relatively high position for access and for gun "vision". 
Yet, as can be seen from a comparison of FIG. 2 and FIG. 3, the lateral 
force representing the overturning moment is transferred through 
compulsator 12 to plane 18 located beneath the center of gravity 26 of 
truck 22. 
As can be seen from FIG. 3, the force propelling the projectile out of 
railgun 10, along line 28, generates an opposite recoil force along line 
30. Railgun 10 is appropriately mounted to compulsator 12 relative to the 
rotation of compulsator 12 such that at the time electrical current is 
withdrawn from compulsator 12 and applied to railgun 10, thereby 
generating the projectile force and the recoil force, the reaction force 
32 on compulsator stator 14 (in the opposite direction of the rotor 
rotation) proximate the axis of railgun 10 is directed in the direction of 
projectile force along line 28. As will be recognized by those skilled in 
the art, the reaction force 32 on compulsator stator 14 is a rotational 
moment around the compulsator rotor. Accordingly, 180 degrees from a 
reaction force vector along the barrel of railgun 10, (along line 30) is a 
reaction force vector in the opposite direction along plane 18. However, 
as noted above, the opposite reaction force vector along plane 18 is 
situated beneath center of gravity 26 of truck 22. 
Those skilled in the art will recognize that many modifications and 
variations may be made in the techniques and structures described and 
illustrated herein without departing from the spirit and scope of the 
present invention. Accordingly, it should be readily understood that the 
foregoing description and drawings are illustrative only and are not to be 
considered as limitations upon the present invention.