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
bodyNONDELAY (instantaneous), 0.01, 0.025, 0.05,
0.1, or 0.25 second.
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
IDENTIFICATION OF ARMED FUZES.
There are three conditions of the M904 fuzesafe,
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.
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.