Aviation Ordnanceman 3,2,&1

CHAPTER 1 - BOMBS, FUZES, AND ASSOCIATED COMPONENTS

Bombs must be manufactured to withstand reasonable heat and be insensitive to the shock of ordinary handling. They must also be capable of being dropped from an aircraft in a safe condition when in-flight emergencies occur.

Bomb detonation is controlled by the action of a fuze. A fuze is a device that causes the detonation of an explosive charge at the proper time after certain conditions are met. A bomb fuze is a mechanical or an electrical device. It has the sensitive explosive elements (the primer and detonator) and the necessary mechanical/electrical action to detonate the main burster charge. The primer is fired by a mechanical action or an electrical impulse, which causes the detonator to explode. The primer-detonator explosion is relayed to the main charge by a booster charge. This completes the explosive train.

FUZE TERMINOLOGY AND BASIC FUZE THEORY

LEARNING OBJECTIVE: Describe the operation of mechanical and electrical fuzes. Identify special safety features that are inherent in bomb fuzes.

This chapter will introduce you to some of the common terms and acronyms associated with fuzes used in the Navy. Basic fuze theory, general classes of fuzes, and the various types of fuzes are also discussed in this chapter.

FUZE TERMINOLOGY

Some of the most common fuze terms that you should know are defined as follows:

^{Arming time.} The amount of time or vane revolutions needed for the firing train to be aligned after the bomb is released, or from time of release until the bomb is fully armed. It is also known as safe separation time (SST).

Delay. When the functioning time of a fuze is longer than 0.0005 second.

External evidence of arming (EEA). A means by which a fuze is physically determined to be in a safe or armed condition.

Functioning time. The time required for a fuze to detonate after impact or a preset time.

Instantaneous. When the functioning time of a fuze is 0.0003 second or less.

Nondelay. When the functioning time of a fuze is 0.0003 to 0.0005 second.

Proximity (VT). The action that causes a fuze to detonate before impact when any substantial object is detected at a predetermined distance from the fuze.

Safe air travel (SAT). The distance along the trajectory that a bomb travels from the releasing aircraft in an unarmed condition.

BASIC FUZE THEORY

Fuzes are normally divided into two general classes-mechanical and electrical. These classes only refer to the primary operating principles. They maybe subdivided by their method of functioning or by the action that initiates the explosive train-impact, mechanical time, proximity, hydrostatic, or long delay. Another classification is their position in the bomb-nose, tail, side, or multipositioned. Mechanical and electrical fuzes are discussed in the following text.

Mechanical Fuzes

In its simplest form, a mechanical fuze is like the hammer and primer used to fire a rifle or pistol. A mechanical force (in this case, the bomb impacting the target) drives a striker into a sensitive detonator. The detonator ignites a train of explosives, eventually firing the main or filler charge. A mechanical bomb fuze is more complicated than the simple hammer and primer. For safe, effective operation, any fuze (mechanical or electrical) must have the following design features:

It must remain safe in stowage, while it is handled in normal movement, and during loading and downloading evolutions.

It must remain safe while being carried aboard the aircraft.

It must remain safe until the bomb is released and is well clear of the delivery aircraft (arming delay or safe separation period).

Depending upon the type of target, the fuze may be required to delay the detonation of the bomb after impact for a preset time (functioning delay). Functioning delay may vary from a few milliseconds to many hours.

It should not detonate the bomb if the bomb is accidentally released or if the bomb is jettisoned in a safe condition from the aircraft.

To provide these qualities, a number of design features are used. Most features are common to all types of fuzes.

Electrical Fuzes

Electrical fuzes have many characteristics of mechanical fuzes. They differ in fuze initiation. An electrical impulse is used to initiate the electrical fuze rather than the mechanical action of arming vane rotation.

An electrical pulse from the delivery aircraft charges capacitors in the fuze as the bomb is released from the aircraft. Arming and functioning delays are produced by a series of resistor/capacitor networks in the fuze. The functioning delay is electromechanically initiated, with the necessary circuits closed by means of shock-sensitive switches.

The electric bomb fuze remains safe until it is energized by the electrical charging system carried in the aircraft. Because of the interlocks provided in the release equipment, electrical charging can occur only after the bomb is released from the rack or shackle and has begun its separation from the aircraft; however, it is still connected electrical y to the aircraft's bomb arming unit. At this time, the fuze receives an energizing charge required for selection of the desired arming and impact times.