US2407844A

US2407844A - Bomb fuse

Info

Publication number: US2407844A
Application number: US602795A
Authority: US
Inventors: Ernest C Moriarty
Original assignee: Individual
Current assignee: Individual
Priority date: 1932-04-02
Filing date: 1932-04-02
Publication date: 1946-09-17
Anticipated expiration: 1963-09-17

Description

Sept. 17, 1946. E. c. MoRlARTY BOMB FUSE Fild April 2, 19:52

4 Sheets-Sheet 1 dtorrceg *Sept 17, 1946. E M0R|ARTY 2,407,844

BOMB FUSE Filed April 2, 1932 4 Sheets-Sheet 2 Sept. 17, 1946. E. c. MoRlARTY BOMB FUSE Filed April 2, 1932 4 Sheets-Sheet 3 Sepi 17, 1946- E. c. MoRlARTY l 2,407,844

BOMB FUSE Filed April 2, 1932 b4 Sheets-sheet 4 573 @JL M dfarmey Patented Sept. 17, 1946 SITES. TENT OFFKC BOMB FUSE Ernest C. Moriarty, Washington, D. C.

Application April 2, 1932, Serial No. 602,795

10 claims. 1

This invcntion relates to bomb fuses and more particularly to fuses for bombs launched from aircraft.

The objects of this invention are:

First, to provide a bomb fuse that is simple in construction and is made of few parts;

Second, to provide a bomb fuse Whose ring mechanism may be removed from the body of the fuse in either the armed or unarmed condition, Without removing the body of the fuse from the bomb, and when so removed, all parts of the firing mechanism are self-contained and visible, and the mechanism may be operated by hand;

Third, to provide a bomb fuse that has no loose part-s that might be lost and whose firing mechanism, Which includes the initiating explosive train, may be stoWed separately from the body, Which may contain a booster charge;

Fourth, to provide a bomb fuse that may be armed or unarmed by hand Without removing any part from the fuse or the fuse from the bomb, and Without the use of tools or spare parts. Also, fuses having been armed accidentally may be returned to the unarmed condition Without the use of tools;

Fifth, to provide a fuse that can be readily checked as to completeness of assembly of its parts. their condition and ability to function;

Sixth, to provide a bomb fuse that has great resistance to firing When in the unarmed condition;

Seventh, to provide a bomb fuse that is more certain to fire by utilizing a plurality of initiating explosive trains;

Eighth, to provide means for obtaining various delays in arming of the fuse to suit the conditions under Which the bomb is to be launched;

Ninth, to provide a. bomb fuse that, if accidentally armed While being carried by an aircraft at high speed, will be automatically unarmed When the speed of the aircraft is vreduced below a predetermined air speed;

Tenth, to provide a bomb fuse in Which the friction caused by the mass of the parts is decreased as a function of the angle of inclination of the axis of the fuse With the horizontal;

Eleventh, to provide a bomb fuse that is relatively inexpensive to manufacture and assemble.

With the above and other objects in view, this invention consists in the arrangement and construction of parts as Will be hereinafter more fully described.

A bomb fuse usually consists of a firing mechanism that is designed to initiate the exp-losion The large number of such fail-ures has resulted in the practise, especially in the larger size of bombs, of using two fuses in each bomb, one in the nose and one in Vthe tail of the bomb. Failure of a bomb fuse to function as intended may be due to defective elements in the detonating or ignition train, a defective booster, or the defects in the firing mechanism, Which may be due to defects in design or to the condition of the mechanism.

A bomb fuse is usually attached to'a bomb in an unarmed condition and remains so set until the bomb is launched on its flight. In its unarmed condition a resistance is interposed to prevent the firing of the explosive train leading to the main charge of the bomb, this resistance being sufiicient to prevent an accidental explosion or even permitting a heavy impact such as that caused by dropping the bomb on a hard surface from any altitude less than that Which Will cause the explosion of the main charge of the bomb Without fuse action. Until a bomb is launched, its fuse usually is constrained from arming by a Wire or other suitable means. When launching a bomb, the' constraining Wire is removed and the fuse arms. As bombs are sometimes accidentally dropped While the aircraft is taking off and also because it is safer to use fuses that do not arm until the bombs have cleared the aircraft from Which they are launched, a delay in arming, after the constraining device is removed, is desirable,

A bomb fuse is in the armed condition When the resistance to firing is such that the fuse Will function to explode the bomb when it impacts on an object or at the end of a time interval.

The resistance to firing in the unarmed condition' is usually obtained by the physical strength of the parts of the mechanism, but it may be increased by a discontinuity in the firing train of' the fuse. Such a discontinuity is usually referred 'to as detonator out of line, and is accomplished by anl arrangement Where the initi'ating explosive train is out of line With the fir- -i-ng pin and the lead to the booster and main explosive charge of the bomb When the fuse is unarmed. For a given initiating train of explosives there is a minimum distance that must separate it from the other explosives in order to insure that its accidental firing will not cause the detonation of the other explosives in the bomb, the factor of safety increasing as the minimum distance is exceeded.

Bomb fuse; are usually armed by the action of air on a propeller, the time required to actuate the propeller giving the desired delay. The size of a bomb fuse propeller is limited by the clearance in the bomb racks. etc., and hence, the internal work due to friction, springs, etc., that is, to be overcome by the torque of the propeller is also limited.

This invention is based in part on the above consideration, and is applicable to bomb fuses of the usual type of both nose and tail fuses, but is not limited thereto.

The mechanism of my invention is simple in construction and contains but comparatively few parts. This is desirable. as it lessens the liability of malfunctioning due to the omission of parts or the use of defective parts during the assembling of the fuse. The mechanism may be assembled in two units; the fuse body, with or without a booster, and the firing mechanism: The firing mechanism may be removed from the fuse body with the fuse in either the unarmed or armed condition, without removing the body of the fuse from the bomb, and when so removed, all parts of the mechanism are self-contained and visible and the mechanism may be operated by hand. There are no loose parts that might be lost. Also, the firing mechanism which includes the initiating explosive train may be sto-wed separate from the body of the fuse which may oontain a weaker charge, a separate stowage of detonators being usually considered a safer practise. The fuses may be armed or unarmed by hand without removing any part from the fuse or the fuse from the bomb and without the use of tools or snare parts. Fuses that have been armed accidentally may be returned to the armed condition without the use of tools. The ready means of checking the completness of the assembling of the parts of the fuse, their condition, and their ability to function, lessens the liability of malfunctioning of the fuses when the bombs are launched.

The resistance to firing when the fuses are in the unarmed condition is accomplished by both physical strength of the parts of the mechanism and by the initiating ex'olosive trains being out of line with the firing pin and the lead to the booster charge. The construction and operation of the detonator holders is such that the detonator may be separated from the booster lead by three or four times the distance usually found in bomb fuses. In case of severe impact, a drop on a hard surface from a high altitude, resulting in crushing the parts of the fuse, an additional safeguard is provided consistingr of means for sealing the lead to the booster. and thus increasing the resistance to firing in excess of that due to the distance which separates the initiating explosive train from the lead to the lbooster charge.

The construction of the detonator holder is such that two o-r more initiating explosive trains may be mounted therein, and the fuse set to fire either one, as may be desired, or all may be fired simultaneously. The liability of malfunctioning due to a defective element in either train is thereby reduced.

The delay in arming is accomplished by the action of an air operated propeller, the shaft of which looks the mechanism in the unarmed po- ILO sition and retains it in this position until the end of the delay. This is desirable as the resistance to firing is not lessened progressively during the arrning delay, the other parts of the fuse remaining in their unarmed position until the end of the delay, Means are provided for obtaining any length of delay that may be desired. In the case of dive bombing, where bombs may be launched from a plane traveling in a nearly vertical, vertical or beyond the vertical (plane on its back) direction, and where the velocity of the plane is practically equal to its terminal velocity, all bomb fuses of the usual design arm too quickly. To meet this condition, when there is a slow separation of the bomb and the plane (both falling practically in a vertical direction) means are provided for obtaining a suitable delay by a relatively large number of turns of a slow-revolving propeller having a steep pitch or the equivalent thereto.

In case a fuse should be accidentally armed when a bombl is carried by an aircraft traveling at a high speed, means are provided for unarming the fuse when the speed of the aircraft is reduced :below a given air speed. This is desirable in case the aircraft is to land with bombs attached to it.

In the arming mechanisms of bomb fuses it is the usual practise to mount the propellers so that they turn parts of the mechanisms on a screw thread, Due to the small torque developed by the propellers, generally a fractional part of an inch-pound at an air speed of miles per hour, either the diameter of the screw threads or the mass of the revolving parts must be relatively small. Bombs are generally carried in a position practically parallel to the longitudinal axis of the aircraft, and are launched from this position. At low air speeds when the aircraft is traveling in a, direction which is substantially horizontal, the torque, due to friction that must be overcome in order to turn a part of the fuse on a screw thread is practically proportional to the mass of the part and there is little if any change in the torque when the axis of the bomb is inclined to the horizontal. At high air speeds there may be a thrust on the part due to the action of the air, especially if the part is exposed to the air and the fuse is designed to operate at a low terminal velocity. The difficulty experienced in turning parts of a fuse on a screw thread by the action of an air propeller is Well known to those Skilled in the art, and their use in .bomb fuses has been limited. In order to overcome the difliculty of turning parts of considerable mass, I have devised means whereby the torque due to the friction caused by the mass of the parts is decreased as a function of the angle of inclination of the axis of the fuse with the horizontal, so that these parts may be operated by propellers of the usual size.

This invention may be best understood by reference to the accompanying drawings, in which:

Fig. 1 shows a fuse assembled in the nose of a bomb;

Fig. 2 shows a fuse asseinbled in the tail of a bomb;

Fig. 3 is a cross-section of the fuse in Fig. l showing the propeller after it reaches the limit of its longitudinal travel and again after it has rotated the striker somewhat;

Fig. 4 is a cross-section of the fuse on line fl-ll of Fig. 3;

Fig. 5 is a cross-section of the fuse on line 5-5 of Fig. 3;

Fig. 6 is a cross-section of the fuse on line 6-6 of Fig. 3;

Fig. 7 is a cross-section of the fuse on line 7-7 of Fig. 3;

Fig. 8 is a cross-section of Fig. 7 at 8-8;

Fig. 9 is a cross-section of the fuse on line 9--9 of Fig. 3;

Fig. 10 is a cross-section of the fuse on line li-l of Fig. 3;

Fig. 11 is a cross-section of the body of the fuse with the ring mechanism removed;

Fig. 12 is a plan view of the fuse body;

Fig. 13 is a cross-section of the firing mechanism removed from the body of the fuse;

Fig. 14 is a view of the firing mechanism from below;

Fig. 15 shows the fuse body 'in one piece;

Fig. 16 is a plan view of the fuse body in one piece;

Figs. 17 and 18 show the detonator holder with and without a pivot, respectively;

Fig. 19 is a view of the detonator holder from below;

Fig. 20 is a cross-section of a portion of the fuse through vent, firing pin, detonator and booster lead;

Fig. 21 shows a detent for holding the fuse in the armed position;

Fig. 22 is an elevation of the detonator holder showing the cam slot;

Fig. 23 shows how the fuse may be armed in three different positions;

Fig. 24 shows the detonator holder with three detonators;

Fig. 25 shows vthe firing pin holder with two ring pins;

Fig. 26 shows the detonator holder with two detonators;

Fig. 27 shows the firing pin holder with a skirt around the top;

Fig. 28 is a plan view of Fig. 27;

Fig. 29 is a diagram of the propeller having two vanes;

Fig. 30 shows a design with auxiliary vanes on the striker;

Fig. 31 shows a propeller with vanes set at two angles;

Figs. 32 and 33 show a spring that may be used for arming or unarming; I

Fig. 34 shows a looking pin for the fuse without a propeller;

Fig. 35 shows a striker with rollers to reduce the friction.

Similar numerals refer throughout the several views.

Reference numeral 59, Fig. 1, represents the body of a bomb, 3! the main explosive charge of a bomb, and 32 is a part of the booster charge assembled in an adapter 33. Reference numeral 35 represents the body of the fuse, 36 a striker, 57 a propeller, 38 an arming wire that passes through a hole in 35 and through one vane of 37, it being retained in position by a clip 39. Propeller 37 is secured to shaft 40 by nuts lil. The

to similar vparts axis of shaft is not coincident with the axis r of the body of the fuse. Thumb screw 42 holds the firing mechanism in the fuse body 35.

In Fig. 2, 133 is the cone of the tail to which the vanesI 44 are attached. The body of the fuse is extended rearward and this extension, together with nut 45, serves as a means for holding the cone in place on the bomb. The base of the cone 43 is secured to the bomb 35 by studs 135, so that opening 4? is opposite thumb nut yllii. rE'he -cap 48 covers the opening in the extension of the fuse 6 body. It does not rotate with the propeller shaft but with the striker to which it is attached. The clearance between the extension and cap must permit sufiicient longitudinal movement of the striker relative to the fuse body for the fuse to function.

In Fig. 3, @9 is the remainder of the booster charge assembled in the fuse body and held in place by a thin disk 50. Detonator holder 5| is pivoted on a small bearing surface in the body of the fuse by pivot 52 and has a cylindrical stem 53 which projects through firing pin holder 54 and is secured to striker 33 by a pin 55 that is shearable on impact. Firing pin holder 54 carries the ring pin, as will be described later, and is held in place -fby thumb nut 42. By unscrewing thumb nut 42, the entire firing mechanism can be lifted out of the body of the fuse. The propeller shaft di) is threaded throughout its entire length with the exception of the portion 56 which stops the rotation of the shaft when it reaches bearing 57 which is internally threaded to cooperate with the threads on shaft 40, and the 'propeller then turns the striker 36 and detonator holder 5| to the armed position. Detonator holder 51 has a small bearing surface 58 touching the firing pin holder 54. The real importance of this will be explained later. The upper part of the fuse body 55 may be formed from a separate piece and forced onto the body 55 as shown. Vent assures the easy passage of stem 53 into cavity 6! by allowing the enclosed air to escape readily.

Fig. 4 is a cross-section of the fuse at Fig. 3. This shows how pin secures stem 53 to the cylindrical portion of striker 35. Three projections 62 extend from the top of the body of the fuse and have intervening spaces. The height of these projections must be slightly greater than the full movement required of the striker relative to the body of the fuse in operation. Shaf-t ed passes through a slot that is partly in the striker and partly in the fuse body and thus prevents rotation of the former relative to the latter until the shaft is withdrawn during the arming of the fuse.

Fig. 5 is a cross-section of the fuse at 5--5, Fig. 3. This shows three projections 53 that extend from the lower` side of the striker 35, which has intervening spaces. In the unarmed condition of the fuse the projections 53 are in alignmerit with the projections 62, thereby preventing longitudinal movement of the striker relative to the fuse body.

Fig. 6 is a cross-section of the fuse at 'e`-5, Fig. 3, but which is reduced from the dimensions of that figure. This shows the position of the detonator 64 in the detonator holder in the unarmed condition. This is shown in cross-section in Fig. 20.

Fig. 7 is a cross-section of the fuse at l Fig. 3, showing a vent hole 55 that in the unarmed condition of the bomb is directly over the detonator or initiating explosive train. This vent is for the escape of gas in case the detonator should be fired accidentally when the fuse is unarmed. There is enough clearance around shaft fiil and striker 35 for this gas to readily escape to the atmosphere. Piece 55 is the firing pin whose position, as well as the location of the vent in firing pin holder 5=t, is shown more clearly in Figs. 8 and 20. This pin is located at the same radius from the axis of the fuse as the vent and diametrically opposite it, so that the detonator, which is under the vent when rotated. through Will be under the firing pin.

The method of supporting the firing pin by a small shearable pin is shown in Fig. 20. The end of thumb screw 42 enters a cavity in firing pin holder 54 and holds it secure in relation to the body of the fuse as the striker and detonator holder rotate during the arming of the fuse.

Fig. 8 shows a portion of a cross-section of the fuse at 8-8, Fig. '7. The firing pin does not extend below the lower side, but does extend above the upper side of ring pin holder 54 and to within a short distance from the cylindrical projection of striker 36. This, during operation, allows the firing pin sufiicient movement relative to the bearing 54 to insure explosion of the detonator.

Fig. 9 is a cross-section of the fuse at 9-6;

Fig. 3, but which is reduced from the dimensions of that gure. This shows the position of the lead '61 from the cavity of the fuse body to part of the booster charge 49. This lead 61 is in line with the firing pin as is shown in Fig. 20.

Fig. 10 is a cross-section of the fuse at ifl-lfl, Fig. 3. This shows the method of obtaining an exact rotation of 180 of the striker and detonator relative to the body of the fuse. Stop 68 is shown in the unarmed condition resting against one of the projections 62. During the arming operation, stop 66 passes through arcuate slot 66 and comes to rest in cavity 16. Means for maintaining the stop in this cavity while the armed condition prevails, will be described later.

Fig. ll is a cross-section of the body of the fuse with the firing mechanism removed. Two of the projeotions 62 are shown here and the arcuate slot 69. Also, that part of the slot 86 contained in the fuse body, into which shaft 69 fits, is seen at the left of the cavity which hormally holds the ring mechanism.

Fig. 13 shows the firing mechanism removed from the body of the fuse. and cavity 'il are in front of the plane of the section as shown in Figs. '7 and 9 respectively. The cavity 1.2 receives the end of thumb screw 42.

Fig. 15 shows a fuse body of one piece, that is, part 59 is made integral with the body of the fuse instead of Sepa-rate as shown in Fig. 3.

Figs. 17 and 13 show detonator holders with and without pivot 52.

Fig. 20 is a cross-section of a portion of the fuse through the vent, firing pin, detonator and booster lead. This shows the location of vent 65 over the detonator 64 and firing pin 66 over cavity 16 in the unarmed condition. She-arable pin '53 supports the firing pin until the striker shears it on impact. The lead 61, to part of the booster charge, is shown in line with the firing pin. Detonator 613 and lead 6? are retained in place by soft metal containers. Soft metal gasket M is for the purpose of sealing lead 61 in case the bomb is accidentally dropped Without arming. If the impact is sufiicient to shear

projections

62 and 63, Fig. 3, the striker will move longitudinally relative to the fuse body and impinges upon firing pin 56, shearing supporting pin '23, moving the firing pin into cavity 'H and forcing the detonator holder against gasket 'a'li whereby the lead 61 to the booster charge is effectively sealed. It will thus be seen that there is a very high resistance to firing the main charge of the bomb by an impact on the striker when the fuse is in the unarmed condition. In fact, it will stand any impact short of that sufiicient to fire the main charge without fuse action.

Fig. 21 shows a detent that, after the arming operation, will hold the fuse looked in the armed The firing pin 66 position until the bomb strikes its objective. The plunger 15 projects into cam slot 19 due to the action of spring 16. Thumb nut 18 is for the purpose of withdrawing the plunger from the cam slot in case it is desired to unarm the fuse by hand. Spring 15 acts on bushing 11 and a shoulder on plunger 15. The plunger does not bear against the surface of the cam slot and therefore offers no initial moment, due to friction, that opposes the turning of the detonator holder in the fuse body. Such reduction of friction is important, as will be explained more fully later. However, during the arming operation, the cam slot has a large mechanical advantage in compressing spring 16, and when the slot is opposite the plunger, the compressed spring will force the plunger into the slot and lock the fuse in the armed condition. It will be seen that this gives an 180 movement of the detonator holder relative to the fuse body so that the firing pin, detonator and booster lead will be in line. The detent may also be applied to the cylindrical projection of the striker and have the same action. Also, more than one detent may be used when the fuse is designed to be red with the detonator holder in several different positions, as will be further explained later on.

Fig. 22 shows an elevation of a detonator holder showing the cam slot 19.

Fig. 23 shows a slight change in design over that shown in Fig. 10 whereby the fuse may be armed in three diiferent positions. Slots 69 are cut in two of the projections 62 and cavity'16 in the third one. The fuse may be armed by stop 68, coming to rest against either of stop pins 8| or cavity 16. The stop pins 8| may be inserted or removed, as necessary. The amount of rotation of the firing mechanism relative to the fuse body until the stop strikes the first stop pin is 60, the second stop pin 180 and the cavity 300.

This fuse has been shown with three

projections

62, 63 on the body and the striker, but it is evident that a fuse could be constructed with one or two or more projections. If one projection on each part is used, the arming requires a rotation through an angle of 180', more or less, depending upon .the angles subtended by the projections. If two projections are used on each part, there will be two positions, one and one 270 from the unarmed position, in which it. may be arranged to have the fuse armed.

Fig. 24 shows the detonator holder with three detonators so located that one will be under the firing pin after a rotation of the firing mechanism relative to the fuse body of 60, 180 or 300 respectively. Each detonator consists of a percussion cap, a delay pellet and a detonating element. The delay pellets have different time delays so that a selection may be made of a delay suitable to the particular use to which the bomb is to be put.

Fig. 25 shows a firing pin holder 54 with two firing pins 66 and two vents 65 which in the unarmed position are over the two detonators shown in Fig. 26. Such an arrangement is desirable in order to decrease the probability of failures.

Fig. 26 shows a detonator holder with two detonators 64. In the unarmed condition the cavities 1| are under the respective firing pins 66 of Fig. 25, but a rotation of 180 of .the detonator holder relative to the fuse body will place the detonators under the respective firing pins of Fig. 25, so that on impact both detonators will be red simultaneously.

Fig. 27 shows a firing pin holder 54 with a skirt 82. Such an arrangement makes it possible to set the fuse deeper into the bomb with the striker projecting from the bomb by as small a distance as may be desired. The skirt is engaged by thumb screw 42 of Fig. 3 which, as is apparent, must be outside the bomb. The cylindrical portion of the striker Fig. 13 is designed to project into the skirt of the firing pin holder to a point near the firing pin, in the unarmed condition, and to move sufficiently far into the skirt to strike the firing pin and explode the fuse on impact.

The distance that the striker of a nose fuse projects beyond the body of the fuse is largely determined by the angle from the vertical that it is desired to have the striker impinge upon a horizontal surface, the angle increasing as the projection of the striker from the body of the bomb is increased.

Fig. 29 shows a diagram of a propeller having two vanes. If F represents the resultant force acting on each vane, the torque about an axis perpendicular to the plane of the figure and passing through its center will be 2TF, r being the radius from the center of .the gure to the center of pressure of each vane. The torque about an axis parallel to the above-mentioned axis but separated from it by a distance a: will be (r-x)F+(r+x)F=2rF. Hence, it follows that the torque about any axis parallel to the first mentioned axis will be 2rF.

Referring to Fig. 3, when the stop 56 of the propeller shaft reaches bearing 51, the torque of the propeller tends to turn the striker and detonator holder about the axis of the fuse body. While .the propeller is turning, it stores up momentum and the moment of this momentum about .the axis of shaft 120 will be the same as that about the axis of the fuse. This can be readily proved by replacing the force in diagram of Fig. 29 by momentum.

Fig. 30 shows a modification in arming propellers that is desirable sometimes. Here auxiliary vanes 83 have been secured to the head of the striker. With this design propeller shaft Lif) may or may not have the stop 56 as shown in Fig. 8. If the stop is omitted, the propeller screws the shaft out of the fuse and together they fall away from it in space. The striker is then rotated to the armed position by means of vanes 83. If the stop 58 is used, the striker is rotated by the combinedaction of the two propellers.

One of the major problems in designing fuses for bombs to be launched from aircraft is the reduction of the internal friction of the fuse parts that must be overcome by the action of the propeller. In the present fuse, when the axis of the fuse is horizontal, the reaction, due to mass of the striker on the body of the fuse, acts on the cylindrical projection of the striker which extends into the fuse body. The radius of the projection of the striker is relatively large and offers a correspondingly large torque due to friction to be overcome by the action of the propeller. After the bomb has been launched, the axis of the bomb and fuse turn towards the vertical. The reaction due to the mass of the striker has two components, one acting on the projection of the striker and one on the small saring surface 53 of Fig. 3 which is supported by firing pin holder 543. When the fuse is Vertical, the entire mass of the striker and detonator holder is supported by bearing 58. This bearing may be made as small as desired so that the torque necessary to turn striker and detonator holder on this bearing when the fuse is Vertical will be less than the torque exerted by-the propeller. Transferring the reaction due to the mass of the parts to be turned from a bearing of large diameter to a bearing of small diameter when the axis of the fuse is inclined, results in a reduction of the moment due to friction, and the reduction increases as the angle that the axis of the fuse makes with the horizontal increases.

When the fuse is used as a tail fuse, the reaction due to the mass of the striker and detonator holder is on the pivot 52 of Fig. 3, the action of this pivot being similar to the small bearing 58 in the case of a nose fuse.

When the terminal velocity of the striker of a nose fuse isl considerably less than the terminal velocity of the bomb as a unit, the pivot 52 of Fig. 3 may be used to take the end thrust of the striker due to the action of the air. When the terminal velocity of the striker is higher than that of the bomb, the pivot 52 may be omitted as the striker will always tend to fall out of the bomb When its axis approaches the vertical.

In order to overcome the reaction of the shaft 49, Fig. 3, on bearing 51 and the body of the fuse, a propeller having a maximum torque at zero velocity of rotation is needed. Such propellers arm the fuse too quickly. The propeller shown in Fig. 31 has been arranged to overcome this fault. V When an air propeller with flat vanes is revolved by the action of the air, the resultant direction of the air stream on the vanes changes so that the angle of incidence is reduced. If the load on the propeller is small, the angle of incidence at the extreme radius of the vanes may be zero or less. In the latter case, the outward portion of the vanes acts as an air brake and the torque of this portion is negative. When the torque due to the load on the propeller and the negative torque equals the positive torque of the inner portion of the vanes, the corresponding velocity of rotation of the propeller will be the maximum for that particular velocity and condition of the air.

In view of the above, vanes 84 of Fig. 31 are set to give the maximum torque at zero velocity of rotation and vanes 85 are set normal to the air stream and hence give zero torque at zero velocity o f rotation of the propeller. But as the propeller turns, vanes 85 exert a negative torque with the result that the maximum speed of the propeller under any given conditions is equivalent to that of a propeller having a very steep pitch. Propellers made in this manner are very easy to adjust. The proper size and shape of the positive vanes may be calculated and tested for torque in a wind tunnel separately from vane 85, and when assembled in a propeller with vanes 85, the time for any number of revolutions may be arrived at by adjusting the angle or size of the vanes 85, the time being shortened if they are inclined slightly so as to exert a positive torque or being increased if they are inclined slightly in the opposite direction. The two sets of vanes may be on one propeller or each set or combination thereof may be contained in separate propellers mounted on one propeller shaft.

The operation of the propeller shafts is not limited to any particular type of propeller, as any type giving sufficient torque and the desired delay may be used. The propeller shafts may be shorter than those shown if the bombs are to be launched at low air speeds, but the' length must be suificient to engage the body of the fuse. With any given length of propeller'shaft, a preliminary adjustment may be made so that the portion entering the fuse is such as to give any desired delay less than the maximum delay that may be obtained for a given air speed and condition of the air.

Figs. 32 and 33 show a further modification of the fuse. The spring 86 is mounted on the core 81, one end of the spring being attached to piece 88 which is soldered or otherwise secured to the core and, also, attached to the body of the fuse by pin 89. The other end of the spring is attached to a slider 98 which has a projection 95 that may be turned up or down. When turned up and inserted in a cavity in the striker, the spring will be compressed by rotation of the striker relative to the body of the fuse. The movement of the slider is limited to 180 by the stop 93 which is formed by an increase in diameter of the core. As shown, the spring opposes the action of the propeller to arm the fuse. The force exerted by the spring may be adjusted so that the fuse will not arm until a given air speed is' exceeded, and if the fuse is accidentally armed when the carrying plane goes into a steep dive, where its air speed is high, it will unarm when the plane assumes normal flight and the air speed of the fuse is reduced below that for which the spring is adjusted. It is evident that the spring may be so arranged that it is elongated during arming by contracting returns the fuse to the unarmed condition.

A spring may be designed to be in a compressed condition when the fuse is unarmed so that the force it exerts will assist in arming the fuse. Again, it may be designed to exert sufficient force to arm the fuse without the action of a propeller, in which case the fuse may be locked in the unarmed position by means of a pin 94, Fig. 34, which passes through the striker and a projection 95 on the body of the fuse, the pin being withdrawn by an arming wire 38 attached thereto. The spring without a propeller gives a very quick arming arrangement, which may, if desired, have an initiating explosive train with a delay sufiiciently long to allow the aircraft to reach a safe distance before the bomb explodes.

In case it is desired to have a fuse that arms very quickly when dropped from an aircraft traveling at a Very high speed at a low altitude, the moment due to the friction of the striker may be reduced by substituting

rollers

95 and 91, Fig. 35, for the projections 63 of Fig. 13. The view of Fig. 35 is from below the striker. The rollers are supported by bearings 98 attached to the striker.

The rollers engage the inner surface of 59, Fig. 3, rolling thereon when the fuse arms. Rollers 96 do not touch the cylindrical portion of the striker and rollers 97 do not touch each other.

It is evident that these rollers may be used in lieu of the projections 53 of Fig. in any of the combinations of parts thatl have been previously described.

The fuse may be designed to arm by a right or left-hand rotation of the striker. When the direction of rotation is selected, the threads on the base of the fuse should be such that the torque of the propellers does not tend to unscrew the fuse from the bomb.

It willV be understood that the above description and accompanying drawings comprehend only the general and preferred embodiments of my invention, and that various changes in the construction, proportion and arrangement of 12 parts may be made within the scope of the appended claims without sacrificing any of the advantages of this invention.

I claim:

1. A bomb fuse comprising a fuse body having first projections with intervening spaces thereon and provided with a cavity therein, a striker having second projections with intervening spaces thereon, a firing pin holder, a detonator holder, the three latter parts having a common axis with said cavity, said firing pin holder being secured in the body of the f-use by means of a detent operated from without the body of the fuse, said detonator holder being at the bottom of the cavity and having a stem passing through the firing pin holder and attached at the mouth of a cavity in said striker by a shearable connection, said striker being mounted in the fuse body so that it may rotate between stops, said first and second projections being in alignment in the unarmed condition and being opposite corresponding spaces in the armed condition, a firing pin, a detonator, a lead to an explosive charge, the latter three elements being out of line when the fuse is unarmed and being in line when the fuse is armed, a shaft for preventing rotation of the striker and detonator holder relative to the fuse body when the fuse is unarmed and providing a delay during arming, and a propeller for arm- 1 ing said fuse.

2. A bomb fuse comprising a fuse body having first projections With intervening spaces thereon and provided with a cavity therein, a striker having second projections with intervening spaces thereon, a firing pin holder, a detonator holder, the three latter parts having a common axis with said cavity, said firing pin holder being secured in the body of the fuse by means of a detent operated from without the 'body of the fuse, said detonator holder being at the bottom of the cavity and having a stem passing through the firing pin holder and attached at the mouth of a cavity in said striker by a shearable connection, said striker being mounted in the fuse body so that it may rotate between stops, said rst and second projections being in alignment in the unarmed condition and being opposite corresponding spaces in the armed condition, a firing pin, a detonator, a lead to an explosive charge,

I" the latter three elements being out of line when the fuse is unarmed and being in line When the fuse is armed, a shaft for preventing rotation of the striker and detonator holder relative to the fuse body when the fuse is unarmed and provid- 3 ing a delay during arming, a rst propeller for removing said shaft from the fuse, and a second propeller attached to the striker for rotating the striker and detonator holder relative to the fuse body to the armed position.

3. A bomb fuse comprising a fuse body having first projeotions with intervening spaces thereon and provided with a cavity therein, a striker having second projections with intervening spaces thereon, a firing pin holder, a detonator holder,

the three latter parts having a common axis with said cavity, said firing pin holder being secured in the body of the fuse by means of a detent operatedV from without the body of the fuse, said detonator holder being at the bottom of the cavity and'having a stem passing through the firing pin holder and attached at the mouth of a cavity in said striker by a shearable connection, said striker being mounted in the fuse body so that it may rotate between stops, said first and second projections being in alignment in the unarmed condition and being opposite corresponding spaces in the armed condition, a firing pin, a detonator, a lead to an explosive charge, the latter three elements being out of line When the fuse is unarmed and being in line when the fuse is armed, a shaft for preventing rotation of the striker and detonator holder relative to the fuse body When the fuse is unarmed and providing a delay during arming, a propeller for arming said fuse, and a spring for unarming said fuse at a predetermined air speed in case it is accidentally armed.

4. A bomb fuse comprising a ifuse body having first projections With intervening spaces thereon and provided With a cavity therein, a striker having second projections With intervening spaces thereon, a ring pin holder, a detonator holder, the three latter parts having a common axis With said cavity, said ring pin holder being secured in the body of the fuse by means of a detent operated from Without the body of the fuse, said detonator holder being at the bottom of the cavity and having a stem passing through the ring pin holder and attached at the mouth of a cavity in said striker by a shearable connection, said strikei` being mounted in the fuse body so that it may rotate between stops, said first and second projections being in alignment in the unarmed condition and being opposite corresponding spaces in the armed condition, a firing pin, a detonator, a lead to an explosive charge, the latter three elements being out of line When the fuse is unarmed and in line When the fuse is armed, a pin for preventing rotation of the striker and detonator holder relative to the fuse body before launching, a spring to arm said fuse after launching, and a detent to maintain the fuse in the armed position.

5. A bomb fuse comprising a fuse body having first projections thereon With intervening Spaces, a striker rotatably mounted in said fuse body and having second projections thereon with intervening spaces, said second projections consisting of rollers that roll on an inside surface of a part of the fuse body and support the mass of the striker When the axis of the fuse is horizontal, said first and second projections being in alignment When the fuse is unarmed, and means for rotating said striker relative to said fuse body When the fuse is 14 being armed, whereby said first and second projections are opposite corresponding Spaces permitting longitudinal motion of said striker relative to said fuse body.

6. A bom-b fuse comprising a fuse body having first projections thereon With intervening spaces, a striker rotatably mounted in said fuse body and having second projections thereon With intervening spaces, said first and second projections being in alignment When the fuse is unarmed, and means for rotating said striker relative to said fuse body When the fuse is being armed, Whereby said first and second projections are opposite corresponding spaces permitting longitudinal motion of said striker relative to said fuse body.

7. A bomb fuse comprising a striker, a detonator holder and means comprising a common axis about Which said striker and detonator holder turns While the fuse is being armed.

8. A bomb fuse comprising a. detonator holder, a plurality of detonators contained in said holder, a firing pin, a lead to an explosive charge, said detonators being out of line With said firing pin and said lead to the explosive charge when the fuse is unarmed, and air pressure actuataible means for rotating said detonator holder relative to and until a preselected detonator is in alignment With said firing pin and lead to the `explosive charge.

9. A bomb fuse comprising a fuse body having first projections With intervening spaces thereon, a striker having second projections with intervening spaces thereon, said first and second projections being in alignment When the fuse is unanmed but being opposite corresponding intervening spaces When the fuse is armed.

10. A bomb fuse comprising firing mechanism movable from an unarmed position to an armed position and vice Versa, propeller means actuatable by air pressure to move said mechanism to the armed position, and means energized by said movement to the armed position effective to return said mechanism to the unarmed position When the torque exerted by said propeller becomes less than a predetermined value.

ERNEST C. MORIARTY.