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M904E2/E3/E4 MECHANICAL IMPACT NOSE FUZE
Table 1-1.LDGP and Fire Bomb Cook-Off Times

Aviation Ordinanceman 1 - Aviation theories and other practices
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The fuze may be configured for a number of preselected arming and functioning delays needed by a mission. There are nine arming delays from 2 to 18 seconds in 2-second increments, and any combination of six functioning delays from instantaneous to 250 milliseconds (0.250 seconds) may be selected. An internal governor, driven by the permanently mounted arming vane, allows relatively constant arming times at release speeds ranging from 170 to over 525 knots. Functioning times are determined by the installation of an M9 delay element. Anyone of six delay elements may be installed. Each delay element is identified by the functioning delay time stamped on the element body—NONDELAY (instantaneous), 0.01, 0.025, 0.05, 0.1, or 0.25 second. Physical Description The M904 (series) fuze contains approximately 1 1/2 ounces of tetryl in the booster, which is located at the base of the fuze body. The entire fuze weighs about 2 1/3 pounds and is 9 1/4 inches long. The M904E4 is a thermally protected fuze. It is especially designed for use with the thermally protected Mk 80 (series) general-purpose bombs and the thermally protected M148E1 adapter booster. This significantly increases the cook-off time (table 1-1) of the bombs subjected to intense heat or flame. ARMING DELAY TIMES.— Arming delay times are inscribed into the face of the forward nose retaining ring. A white indexing line is scribed on the knurled delay setting knob below the arming vane. The white indexing line must be matched to one of the indicated arming times to select the desired arming delay. To select the required arming delay time, depress the setting index locking pin and rotate the knurled arming delay setting knob until the white indexing line is aligned with the desired arming delay time stamped on the nose retaining ring. The 2- and 4-second arming times are for use with retarded weapons, and are only set by removing the stop screw located next to the setting index locking pin. Never try to reinstall the stop screw when either of these two settings are used. The stop screw may be reinstalled at any delay setting of 6 seconds or more. IDENTIFICATION OF ARMED FUZES.— There are three conditions of the M904 fuze—safe, partially armed, and fully armed. You can verify the fuze conditions by looking through the two observation windows in the fuze body (fig. 1-1). To check the fuze condition, hold the fuze vertically and look through the windows perpendicular to the fuze body. Look at REVIEW NUMBER 1 ANSWERS TO QUESTIONS Q1. THROUGH Q8. Al. A2. A3. A4. AS. A6. A7. A8. A fuze controls bomb detonation. The time or number of vane revolutions needed for the firing train to align after a bomb is released is the arming time. The time required for a fuze to detonate after impact or a preset time is known as the functioning time. The distance along the trajectory that a bomb travels from the releasing aircraft in an unarmed condition is known as the safe air travel (SAF). The two basic classes offices are electrical and mechanical. The force used to initiate the mechanical fuze is like the hammer and primer used to fire a rifle. A mechanical force drives a striker into a sensitive detonator. An electrical impulse initiates an electrical fuze. The three special safety features incorporated into fuzes are detonator safe, shear safe, and delay arming features. 1-4







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