This document discusses the design considerations for aircraft armament control systems and global positioning systems (GPS). It covers the requirements for a stores management system (SMS) to safely manage and control weapons. Key components discussed include power supplies, a master armament safety switch in the cockpit, suspension and release equipment, and GPS integration. Safety and availability are primary drivers in the redundant, fail-safe system design.

1. Chapter 2
Aero weapons
ARMAMENT CONTROL
&
GLOBAL POSITIONING SYSTEMS
DESIGN ISSUES

2. INTRODUCTION
 The control of weapons by an aircraft requires several subsystems to interact
such that the weapons can be safely released and then guide to their target.
 The overriding principle for the control of a weapon must be such that the
safety of the crew and the aircraft is not compromised.
 When considering safety and certification, it is essential that an aircraft only
releases a weapon when intended.
 This would appear to be an obvious requirement, but it is the primary driver in
the design of the Armament Control System.
 Central to achieving compliance with this requirement is the SMS( Stores
Management system ).
 The SMS manages the weapon load-out and controls the safe arming, release,
jettison and operation of any store loaded on the aircraft, including the
generation of high-integrity data messages required by the weapon to ensure
its safe operation.
 This chapter will explore the design considerations for an SMS and its
associated components and outline common system architectures that are
found in a modern Armament Control System

3. INTRODUCTION
 In designing a safe and available SMS, there is the need to consider how aircrew
training will be undertaken.
 Once a weapon has been integrated with an aircraft, it can be very expensive to
undertake aircrew training solely by firing real weapons against targets on a
weapons range.
 To overcome this expense, various forms of training systems have been developed.
This chapter will review the training aids that are designed into the aircraft system
and discuss the system implications of each.
 Although safe control of weapons is essential, the weapons also have to be
released such that they have the best opportunity of hitting the target.
 Therefore, navigation accuracy is an important factor. The emphasis placed on the
employment of GPS in guided weapon systems has enabled the continued potency
of legacy aircraft and defined the baseline capability for new platforms.
 The integration of such weapons brings with it special problems for the aircraft
systems integrator.
 This chapter will also outline the basic operation of the GPS and discuss a number
of aircraft system design issues that need to be considered when integrating such
weapons.

4. Stores Management System Design
 The safe arming, release, jettison and operation of stores are paramount in
a weapons integration programme.
 This means that special attention must be given to the parts of the aircraft
system which are involved in these functions. Within an Armament Control
System, this is primarily the SMS.
 The SMS is responsible for compiling and managing the stores inventory.
Many smart weapons have the ability to tell the aircraft what type of
weapon they are, potentially simplifying the logistics of preparing an
aircraft for a mission by enabling the aircraft to automatically identify
exactly what is loaded on each station.
 In addition to keeping the crew informed of the status and availability of
weapons, this data may be required by the aircraft’s Flight Control System
to alter performance parameters.
 Also as stores are released, it may be important for continued controlled
flight that the distribution of heavy stores is controlled such that their
release does not impose an unstable condition on the aircraft (e.g. many
heavy stores present on one wing with very few loaded on the other).

5. Stores Management System Design
 By knowing which stores are loaded on which stations, the SMS is able to ensure
that only stations carrying weapons are included in any weapon release sequences
whilst providing facilities for the safe (unarmed) jettison of stores if required, for
example, under emergency conditions (e.g. an engine flameout on take-off, when
the mass of the aircraft may need to be quickly reduced).
 The SMS will also control the priming of weapons prior to release in addition to
ensuring that during a release sequence, safe intervals are maintained between
individual releases.
 All these demands make a modern SMS a complex subsystem. Multi-channel
systems that are designed to maintain integrity and availability are common.
 Such systems employ high integrity software and are generally designed to be
immune to electromagnetic interference to ensure the system remains safe at all
times when in its operational environment.
 However, the total system involved in the management and deployment of
weapons will also consist of a number of other components such as dedicated
power supplies, cockpit switches, wiring and store carriage and release systems.
 Together, all these components make up the platform’s Armament Control System.

6. SMS Design Requirements
 Whilst there are a number of weapons integration requirements partitioned to the
SMS, the primary consideration is safety.
 Whilst it is relatively easy to design a fail-safe system, ask any pilot what would be their
biggest concern having battled through a range of air defences to get to the target and
it would be the inability to release the weapons.
 Therefore, a real SMS will have the added complexity needed to ensure that the system
is available to use when required.
 These two primary requirements (safety and availability) provide an apparent
contradiction which the SMS designer must overcome in the system design.
 In the United Kingdom, these basic requirements are captured by DEF STAN 00-
970(Design and Airworthiness Requirements for Service Aircraft) as follows:
1. The armament system shall be such that no single fault or failure shall adversely affect
the safety or operation of the system.
2. The armament system shall be such that a single fault or failure shall neither:
(i) Prevent release or jettison of the store(s) when required.
(ii) Result in inadvertent or un commanded release or jettison of the store(s).
(iii) Prevent the weapon being released live and in the correct condition when required.
(iv) Result in the arming of a weapon before release.
(v) Prevent the weapon being made safe after having been selected live.

7. SMS Design Requirements

8. SMS Design Requirements
 Figure 4.1 depicts a system implementation which satisfies the safety and
availability requirements.
 The figure shows a simple weapon loaded to a carriage system ( Suspension and
Release Equipment – S&RE) which has two inputs, either of which can initiate the
release mechanism.
 Therefore, to control the S&RE, this system implementation has two channels: A
and B. The system is powered by two separate power supplies (also A and B), and
these are further subdivided into Logic Supplies (used to power the SMS
electronics) and Fire Supplies (used by the SMS to initiate the release of the
weapon).
 The SMS release circuits are also duplicated and have separate inputs from a
double pole changeover switch.
 Tracing the circuit through, it can be seen that each release circuit controls its own
channel’s upper Fire Supply switch (this could be a relay which provides an air-gap
in the firing chain for greater integrity or a semiconductor switch) and the other
channel’s lower Fire Supply switch.
 Therefore, if the Release Button is operated, then under failure-free conditions,
both channels will energise the Fire Supply switches and the S&RE will be initiated
by both channels

9. SMS Design Requirements
 Also shown in the diagram are the Built-in Test (BIT) circuits A and B.
 These will be monitoring the Release Circuits for correct operation, and should a
failure be detected in say channel A, then the BIT A circuit will detect this and
switch over control of the channel
 A upper Fire Supply switch to channel B. Channel B now has full authority to fire a
single channel of the S&RE to release the weapon.

10. Other System Components
 A real Armament Control System will require not only the SMS but a number of
other
 components which, when connected together, provide a complete and safe system.
The key items are:
(i) Armament power supplies
(ii) A Master Armament Safety Switch (MASS)
(iii) Cockpit controls (e.g. Late Arm, Weapon Release/Trigger and Jettison
switches)
(iv) S&RE.
Armament Power Supplies
 Modern armament systems are electrically powered. They are identified to help
support the fundamental requirements of safety and availability.
 For example, under emergency operating conditions, there may be a need to
jettison stores. This drives both a platform safety requirement (to be able to
release stores in an emergency) and the availability requirement that even under a
single failure condition, the system will still operate.
 Dual power supplies are therefore required, and as noted earlier, these are usually
subdivided into Logic and Fire Supplies

11. Other System Components
 It is normal practice to provide the channel A and B supplies from separate bus bars
and to route these through the aircraft whilst maintaining segregation wherever
possible.
 This will provide a measure of fault-tolerance particularly if the aircraft sustains battle
damage.
Master Armament Safety Switch
 The MASS is a power isolation switch located in the aircraft cockpit. Provision of the
switch is primarily a requirement to ensure the safety of ground personnel when an
aircraft is armed.
 Originally, the switch was used only to isolate the Fire Supplies, but current
requirements dictate that a three-position switch is used so that the SMS Logic Supplies
can also be isolated.
 The three positions of the switch in order of rotation are Safe (when all system power
supplies are isolated), Standby (when system Logic Supplies are switched on but Fire
Supplies remain isolated) and Live (when both Logic and Fire Supplies are energised).
 Power supplies to armament systems are required to be tolerant of high transient loads
(e.g. providing the currents required to fire S&RE pyrotechnic cartridges when releasing
a weapon).
 Therefore, the MASS does not usually carry the full current used by the armament
system but, instead, switches the supplies to the coils of contactors (Armament Safety
Break Contactors).
 It is not uncommon for such contactors to have a continuous current rating of greater
than 100 A. The contactors are used to route the Fire Supplies to separate distribution
bus bars that are reserved for the safety-involved armament supplies.

12. Other System Components
 As noted earlier, the MASS is primarily a ground personnel safety aid. Therefore, it
is essential that ground personnel know the state of the switch.
 Legacy aircraft have a mechanical flag used to indicate the position of the MASS,
which is visible from a distance. Modern aircraft use indicator lights mounted
external to the cockpit which can be viewed from a distance under all lighting
conditions.
Cockpit Controls
 Executive control of the armament system is always vested with the aircrew, and
this is achieved by a number of switches and controls located in the cockpit. We
have already discussed the MASS, but the other switches are Late Arm, Weapon
Release/the Trigger and Emergency and Selective Jettison buttons.
 The Late Arm switch (on aircraft in the United States, this is known as Master Arm,
not to be confused with the function of the MASS), is usually a guarded toggle
switch. Late Arm provides a key function in the integrity chain of the armament
system, being the last ‘enable’
 in the overall Fire Supply switching sequence, and would normally only be switched
to the live position just prior to weapons release. To initiate a weapon release, the
aircrew will use the Weapon Release Button or the Trigger (for forward-fired
munitions).

13. Other System Components
 Both these controls will usually be located on the pilot’s control column and may
also be guarded to avoid inadvertent operation.
 The Weapon Release Button is usually the final sanction to the system that the
weapon package can be released from the aircraft.
 However, the timing of the release and the order in which weapons are released
are controlled by the SMS, possibly with precise inputs from the Weapon Aiming
Computer to ensure an accurate delivery of ordnance on target.
 The Weapon Release Button is, in reality, a commit button which enables the
system to accurately deliver ordnance
 The Emergency (clear all stations) and Selective Jettison (clear crew-selected
stations) buttons are used to initiate stores jettison sequences when required.
 The crew must also have weapon selection and status information displayed, so
that full
 end-to-end control of the system can be maintained. On legacy systems, there
could be dedicated control panels which provide the aircrew with the ability to
select weapons into attack packages and to set key parameters such as modes, fuze
settings and release intervals.
 On modern aircraft with glass cockpits, then the weapon parameter selections
would be achieved via one of the aircraft’s Multi-function Displays. During an
attack, key timing cues could also be displayed on the pilot’s Head-up Display

14. Other System Components
Suspension and Release Equipment
 S&RE are used to attach the weapon to the aircraft. For Air-to-Ground weapons
and other stores, there is a need to employ standard mechanical interfaces, which
within NATO are a ‘hook and eye’ attachment.
 The eye or bale lugs are screwed into the store, and the aircraft mounted rack
contains hooks to grab the bale lugs. Sway braces which tighten against the store
are employed to reduce lateral movement of the store during captive flight.
 Various types of S&RE are available. Some are gas operated, employing pyrotechnic
cartridges that produce high pressure hot gas to open the mechanism and to
charge pistons which push the store away from the aircraft at release.
 Others, particularly on systems where the speed of the aircraft at store release is
relatively low or where the store is light-weight, contain an electromagnetic
solenoid to operate the mechanism, with the store separating under the influence
of gravity.
 Whilst the electromagnetic release unit requires low maintenance, the pyrotechnic
cartridges used in a hot gas system produce corrosive residue which brings with it
maintenance penalties.
 For this reason, cold gas systems have been developed. Such systems use
compressed gas (usually purified air), either held in a local accumulator in each
rack or in a central accumulator feeding all the racks on the aircraft.

15. Other System Components

16. Other System Components

17. Other System Components

18. An Introduction to the GPS
 When releasing bombs at medium altitude, there is often cloud covering the target. Rules of
Engagement may dictate that the release of Laser-Guided Bombs (LGBs) may be prohibited
in such conditions.
 The use of a ‘fire-and-forget’ GPS-guided weapon eliminates the need to see the target prior
to launch. Also collateral damage considerations are paramount, particularly in
peacekeeping missions.
 Again, a GPS-guided weapon coupled with a low-cost inertial navigation system can greatly
improve accuracy and therefore reduce the potential for collateral damage.
 GPS is a space-based radio-navigation system that was originally developed by the United
States as a military force enhancement system.
 The system works by measuring the difference between the time of reception (as defined by
the receiver’s clock) of a ranging signal ( transmitted by the satellites) and the time of
transmission contained within the satellite’s navigation data (as defined by the satellite’s
clock) multiplied by the speed of light.
 This is known as the pseudo range. The original GPS supported two standards of service, but
these are now being enhanced with a third service specific for an enhanced military
capability.
 These services are:
- The Standard Positioning Service (SPS) that is designed to provide a less than military
accuracy positioning service for civilian uses.
- The Precise Positioning Service (PPS) that is available primarily to the United States
and its allies as a more accurate system.
- The new M-Code service that delivers improved security and accuracy.
- The GPS consists of three parts. These are the satellites, the GPS receiver and a
ground-based Control Segment.