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M103 nose fuze , USA , WW2

pzgr40

Well-Known Member
Premium Member
Cutaway model of a ‘Nose bomb fuze M103’ nose fuze (pict.01) as used in the U.S series AN-M100 aircraft bombs. This nose fuze is the most used nose bomb fuze in U.S. aircraft bombs in WW.2, used into the Kerean conflict as wel as in the Vietnam war, where it was phased out.

Description and functioning of the fuze:
Upon release of the bomb the safety wire is withdrawn from the propeller (1) of the fuze and starts rotating in the air stream. The propeller -is connected to and- drives a small gear wheel in the centre line of the nosecap (3) that drives two planetary gearwheels left and right of the centre gearwheel. These two gearwheels have a excentric shaft at the botton which stand in line and are placed in two holes of a gearwheel placed over these shafts. When rotating this gearwheel makes an excentric rotating movement. The teeth of this gearwheel fall into the inner teeth of a brass flange (2). The brass flange is connected to the nosecap (3) with two radial screws that fall in a groove (4) on the outer circumference of the brass disc, locking the brass disc to the nosecap in longitudal direction, but allowing the brass disc to –radially- rotate in the nosecap. A threaded rod (5) is connected to the base of the brass flange (2), screwed into the hammer piece (6) of the firing pin. As this threaded rod is unscrewed from the hammer piece by the propeller driving the toothgear, The nosecap (3) starts rising.

Picture.05;
To prevent the nosecap from rotating compared to the fuze body (8 ), two longitudal steel strips (7) are placed on the inside of the nosecap which fall in two slots machined in the circumference of the hammer (6) piece of the firing pin.

Between the hammer piece (6) and the upper flange of the fuze body (8 ), thirteen steel safety cilinders (9) are placed which prevent the hammer piece from moving downward. Two of these cilinders are connected by means of a leaf spring (10), bend around the stem of the hammer piece. The rest of the cilinders fills up the space between the two spring tensioned cilinders and around the stem of the hammer piece. At the moment the nosecap (3) has risen far enough (about 220 revolutions of the propeller) the cilinders are swept out by the cilinders connected to the leaf spring. The fuze is now partly armed.

To the base of the hammer piece (6) two firing pins are attached; the long needle shaped centre line firing pin (11) for direct action, and the short round shaped firing pin (12) for the delay action (0,1 second).
Three radial pins protrude from the flange of the fuze body; the first one (not visibele in the pictures ) is a shear wire that keeps the hammer piece in forward position untill the moment of impact. The second one (14) is a guidance pin that enshures the small firing pin (12) will hit the firing cap (15) of the delay element (13). The third pin is the springloaded delay selector (16) pin; in the inward position (Pict 04, left) it activates the 0,1 sec delay action, retracted (pict.04, right) it switches off the delay.

At the base of the fuze body a slot is machined which houses the safety slider (Pict.06) with the firing cap. In the slider, three holes are drilled in line, the left one housing the firing cap, the middle and right holes are blind holes to allow the centre line firing pin to move down unimpeded if the delay firing pin (12) is used. The slider is moved by means of two horizontal springs in the slider if released. In the top of the slider a step (18 ) is machined, this to allow for safe-delay-direct action selection. In the front of the slider a two step recess (19) is machined, in which a spring loaded pin (20) falls if the slider moves from safe to delay or direct action. This pin allows the slider to move in one direction only.

In the fuze body a long steel pin (22) swaged to a springloaded brass bushing (21) is placed in the longitudal direction.

This pin can be found in three positions:
*Completely down (as in picture 02), preventing the safety slider from moving into one of both armed positions (direct or delay). The flange of the brass bushing (21) is shouldered under the threaded rod (5) of the nosecap (3) and can only move upward if the nosecap is unscrewed.
*Partly upward: the delay selector is placed in the delay position (pict.04, left, pin inward) allowing the pin to rise only untill it is stopped by the selector pin. The steel pin (22) will rise until the step in the safety slider (18 ) arrests the slider from moving further. The firing cap (17) is placed in line with the delay element (13) and the firing cap of the delay element (15).
*Fully upward: the delay selector is placed in the non delay position (pict.04, right, pin pulled out), allowing the pin (22) to move upward all the way together with the threaded rod (5). The safety slider is not stopped and moves all the way to the other side, placing the firing cap (17) of the slider below the centre line firing pin (11) for the non delay functioning.

Upon impact, the hammer piece (6) with the two firing pins moves downward; when the delay ignition (15-13) is chosen and activated, the firing pin in the centre line (11) moves into a blind hole in the safety slider. If the direct action is chosen, the centreline firing pin (11), as well as the delay firing pin (12) activate the firing caps, but as the direct fuze is much faster than the delay fuze, it will function before the delay fuze has functioned.

Below the safety slider a brass disc (23) is placed housing two detonators (blue and green), which are ignited by the firing cap (17) in the safety slider and ignite the main booster (24).

Regards, D.J.H
 

Attachments

  • Pict.01 - AN-M103 nose fuze.jpg
    Pict.01 - AN-M103 nose fuze.jpg
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  • Pict.02 - AN-M103 nose fuze direct action fuze.jpg
    Pict.02 - AN-M103 nose fuze direct action fuze.jpg
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  • Pict.03 - AN-M103 nose fuze direct delayed action.jpg
    Pict.03 - AN-M103 nose fuze direct delayed action.jpg
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  • Pict.04 - AN-M103 nose fuze delay selector.jpg
    Pict.04 - AN-M103 nose fuze delay selector.jpg
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  • Pict.05 - AN-M103 nose cap and safety cilinders.jpg
    Pict.05 - AN-M103 nose cap and safety cilinders.jpg
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  • Pict.06 - AN-M103 safety slider.jpg
    Pict.06 - AN-M103 safety slider.jpg
    29.8 KB · Views: 48
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