Vehicle Integration Between Carl-Gustaf M4 and Trackfire

Vehicle Integration between Carl-Gustaf M4 and Trackfire

RWS

A concept study on mechanical solutions

Fordonsintegrering mellan Carl-Gustaf M4 och Trackfire RWS En konceptstudie på mekaniska lösningar

Isabelle Dietmann

Faculty of Health, Science and Technology Degree Project for Master of Science in Engineering, Mechanical Engineering 30 hp Supervisor: Anders Gåård Examiner: Jens Bergström 2020-07-04

Abstract

Saab Dynamics is a division of Swedish company Saab AB, offering solutions, products, and services for military defence. Included in the Saab Dynamics portfolio is the Carl-Gustaf recoilless rifle; a man-portable, reusable, anti-tank weapon system. Another Saab produced system is the Trackfire Remote Weapon Station; a remotely operated weapon and sensor system, purposed for use on all types of military platforms. Armoured vehicles used by the Swedish Armed Forces are sometimes equipped with remote weapon stations that aim to provide the vehicle crew with protection, by allowing them to operate the weapons from inside the vehicle. These weapon stations can integrate a selection of different weapons, but there are currently no systems in operation that allow integration of the Carl-Gustaf system.

This project was initiated based on a request from the Life Guards, for an integrating system between the Carl-Gustaf M4 and a remote weapon station. The project was conducted at Saab Dynamics, Karlskoga, in cooperation with Karlstad University, and aimed to generate suggestions of vehicle integration between the Carl-Gustaf M4 and a remote weapon station. The project was performed as a product development process, using a systematic method for construction and design to develop concept solutions of an integrating system between Carl- Gustaf M4 barrels, and the Trackfire RWS.

The report includes a literature study, performed during a feasibility study, on the three systems: Carl-Gustaf weapon system, remote weapon stations, and wheeled armoured vehicles. Recoil principles and interior ballistics of recoilless rifles are further explained and applied to the study. The feasibility study resulted in a specification of requirements, which was used as a foundation for the concept development.

Concepts of solutions were generated and eliminated using a brainstorming session, a morphological matrix, elimination matrices, and decision matrices. One concept was chosen as the final concept solution; a concept comprised of a construction that enables integration of four Carl-Gustaf M4 barrels on the Trackfire RWS, while dampening the recoil that comes from firing a gun. The construction was modelled and analysed using 3D design and engineering platform 3DExperience. Analyses revealed a strong construction that withstands forces arising when a weapon is operated, yet further analyses on how the construction would manage subjection to long-term vehicle vibration and weapon operation are required. Construction dimension optimisations are encouraged, as well as further development of construction details. Recommendations and suggestions on how to proceed with the system integration are provided as a final part of the report.

Sammanfattning

Saab Dynamics är en division i svenska företaget Saab AB, som erbjuder lösningar, produkter och tjänster för militärt försvar. Inkluderat i Saab Dynamics porfolio finns granatgevär Carl- Gustaf; ett bärbart, återanvändbart pansarvärnsvapen. Ett annat Saab-producerat system är Trackfire Remote Weapon Station; ett fjärrstyrt vapen- och sensorsystem, ämnat för användning på alla typer av militärplattformar. Pansarfordon som används av Försvarsmakten är ibland utrustade med fjärrstyrda vapenstationer som skyddar fordonsbesättningen genom att låta dem manövrera vapnen inifrån fordonet. Dessa vapenstationer kan integrera ett urval av olika vapen, men för närvarande finns det inget system i drift som tillåter integrering av Carl-Gustaf systemet.

Detta projekt initierades baserat på en begäran från Livgardet, om ett integrerande system mellan Carl-Gustaf M4 och en fjärrstyrd vapenstation. Projektet utfördes på Saab Dynamics Karlskoga, i samarbete med Karlstads universitet, och syftade till att generera förslag på fordonsintegrering mellan Carl-Gustaf M4 och en fjärrstyrd vapenstation. Projektet utfördes som en produktutvecklingsprocess, och använde en systematisk metod för konstruktion och design för att utveckla konceptlösningar för ett integrerande system mellan Carl-Gustaf M4 eldrör och Trackfire RWS.

Rapporten inkluderar en litteraturstudie, som utfördes under en förstudie, om de tre systemen: Carl-Gustaf granatgevär, fjärrstyrda vapenstationer och hjuldrivna pansarfordon. Rekylprinciper och inre ballistik hos granatgevär förklaras vidare och appliceras i studien. Förstudien resulterade i en kravspecifikation, som användes som grund för konceptutvecklingen.

Konceptlösningar genererades och eliminerades genom användning av en brainstorming session, en morfologisk matris, elimineringsmatriser och beslutsmatriser. Ett koncept valdes ut som den slutliga lösningen; ett koncept bestående av en konstruktion som möjliggör integrering av fyra Carl-Gustaf M4 eldrör på Trackfire RWS, samtidigt som den dämpar rekylen som uppstår vid skjutning av ett eldrör. Konstruktionen modellerades och analyserades i 3D-design- och teknikplattformen 3DExperience. Analyser avslöjade en stark konstruktion som motstår de krafter som uppstår vid användning av ett granatgevär, dock är fortsatta analyser av hur konstruktionen skulle klara att utsättas för fordonsvibrationer och gevärsanvändning under en längre period nödvändiga. Optimering av konstruktionsdimensioner uppmuntras, så som fortsatt utveckling av konstruktionsdetaljer. Rekommendationer och förslag på hur arbetet med systemintegrationen kan fortsättas presenteras i slutet av rapporten.

Acknowledgements

I would like to express my deepest and sincerest gratitude towards my supervisor at Saab Dynamics, Elin Wallberg, for her constant support and encouragement. Special thanks to Urban Bruzén, for providing me with the opportunity of conducting this project, and for much needed guidance and feedback throughout the process. Thanks to Mats Lundkvist at the Life Guards, and Nils-Ola Svensson at Saab Järfälla, for organising interesting and rewarding visits, and providing essential information whenever needed. Tomas Pettersson and Linus Olsson; thank you so much for always answering my questions and for putting your own time aside to help me. Additionally, I would like to direct my gratitude towards my supervisor at Karlstad University, Anders Gåård, as well as the following people at Saab Dynamics who contributed with their expertise, and made this project an invaluable experience: Petri Hiltunen, Chamoun Malki, Jonas Björnsson, Martin Persson, Magnus Samuelsson, Burton Stopek, and Emanuel Hällgren.

Isabelle Dietmann 2020-07-04, Karlstad

Table of Contents

Abbreviations and Symbols ...... 1

1 Introduction ...... 2

1.1 Background ...... 2 1.1.1 Saab AB and Saab Dynamics ...... 2 1.1.2 Carl-Gustaf weapon system ...... 3 1.1.3 Remote weapon station (RWS) ...... 3 1.1.4 Armoured vehicle ...... 4 1.2 Project definition ...... 5 1.2.1 Goals and purposes ...... 5 1.2.2 Delimitations ...... 6

2 Theory ...... 7

2.1 Standard principles and equations ...... 7 2.2 Recoilless rifles ...... 7 2.2.1 Definitions and principles ...... 7 2.2.2 Carl-Gustaf weapon system ...... 9 2.3 Wheeled armoured vehicle (WAV) ...... 10 2.4 Trackfire RWS ...... 11 2.5 Current gun recoil systems ...... 12 2.5.1 Springs ...... 12 2.6 Product development ...... 13 2.6.1 Systematic method for construction and design ...... 13 2.6.2 Product development ...... 14

3 Method ...... 17

3.1 Feasibility study ...... 17 3.1.1 Project start ...... 17 3.1.2 Research ...... 17 3.1.3 Specification of requirements ...... 17 3.2 Concept generating ...... 18 3.2.1 Brainstorming ...... 18 3.2.2 Morphological matrix ...... 18 3.3 Concept selection ...... 18 3.3.1 Evaluation ...... 18 3.3.2 Elimination ...... 19 3.3.3 Concept selection ...... 19 3.4 Product layout and detail construction ...... 20 3.4.1 Delimitations ...... 20 3.4.2 Product layout ...... 20

3.4.3 Material selection ...... 20 3.4.4 Detail construction ...... 20 3.5 Analyses ...... 21 3.5.1 Finite Element Analysis ...... 21 3.5.2 System balance ...... 21 3.6 SoR follow-up ...... 21

4 Results ...... 22

4.1 Feasibility study ...... 22 4.1.1 Project start ...... 22 4.1.2 Research ...... 22 4.1.3 Specification of requirements ...... 22 4.2 Concept generating ...... 24 4.2.1 Brainstorming ...... 24 4.2.2 Morphological matrix ...... 24 4.3 Concept selection ...... 27 4.3.1 Evaluation ...... 27 4.3.2 Elimination ...... 27 4.3.3 Concept selection ...... 30 4.4 Product layout and detail Construction ...... 32 4.4.1 Delimitations ...... 32 4.4.2 Product layout ...... 32 4.4.3 Material selection ...... 35 4.4.4 Recoil dampening ...... 37 4.4.5 Manufacturing ...... 38 4.4.6 Assembly ...... 38 4.4.7 Summary ...... 39 4.5 Analyses ...... 41 4.5.1 Finite Element Analysis ...... 41 4.5.2 System balance ...... 44 4.6 SoR follow-up ...... 48

5 Discussion ...... 49

5.1 Method ...... 49 5.1.1 Concept generating...... 49 5.2 Results ...... 49 5.2.1 Concept selection ...... 49 5.2.2 Material selection ...... 50 5.2.3 Finite Element Analysis ...... 50 5.2.4 System balance ...... 50 5.3 System integration ...... 50

6 Future Work ...... 52

6.1 What is left to do ...... 52

6.1.1 Product layout and detail construction ...... 52 6.1.2 Analyses ...... 52 6.1.3 System integration ...... 52 6.2 Suggestions ...... 53 6.2.1 Detail construction ...... 53

7 Conclusions ...... 55

References ...... 56

Appendices ...... i

Appendix 1 – Gantt-Chart ...... ii Appendix 2 – Evaluation Matrix ...... iii Appendix 3 – List of requirements ...... iv Appendix 4 – Concept selection ...... vii Appendix 5 – Concept sketches ...... xiii Appendix 6 – FEA results ...... xxix

Abbreviations and Symbols

Symbols Abbreviations

A Sectional area CAD Computer Aided Design a Acceleration CG M4 Carl-Gustaf M4

E Young’s modulus CoG Centre of Gravity e Energy DU Director’s Unit

F Force FEA Finite Element Analysis

Ft Tangential force FoS Factor of Safety

KIC Fracture toughness PW Primary Weapon k Spring constant PWI Primary Weapon Interface m Mass PWC Primary Weapon Cradle

P Pressure SAF Swedish Armed Forces p Momentum SBD Saab Dynamics

R Outer radius SoR Specification of Requirements r Inner radius SWI Secondary Weapon Interface t Time WAV Wheeled Armoured Vehicle

V Volume v Velocity

α Angular acceleration

휌 Density

σvM Von Mises Stress

σy Yield strength

1 Introduction

This chapter introduces Saab AB and its areas of business, and provides descriptions of the three systems Carl-Gustaf weapon system, remote weapon stations, and armoured vehicles, and defines goals and purposes of the project.

1.1 Background

1.1.1 Saab AB and Saab Dynamics

1.1.1.1 The history of Saab AB

Saab AB is a Swedish company offering solutions, products, and services for military defence and civil security to the global market.

Svenska Aeroplan AB, later to be known as SAAB, was founded in 1937, with registered offices in Trollhättan, Sweden [1,2]. The company was founded on a request from the Swedish government of a domestic defence industry. In 1944 Saab entered the civil aircraft market, and two years later the Saab 92 was introduced as the first Saab car, which set the style for Saab cars for the next 30 years. In 1948 the Saab J29 Tunnan jet fighter flew for the first time; the first Western European fighter with a swept wing, which possessed both speed and agility ahead of its time. 1948 was also the year of the first order of the Carl-Gustaf recoilless rifle system. Aircraft Saab 32 Lansen, Sweden’s first weapons system, flew for the first time in 1952; an event that is considered the mark of Saab’s entry into the electronic age. In 1965 Saab acquired its current name: Saab AB. In 1967 Saab entered the missile business, and in 1968 they acquired the light-aircraft manufacturer Malmö Flygindustri AB (MFI). The year after that, Saab merged with lorry, bus, and heavy-duty diesel engine manufacturer Scania-Vabis AB, which lead to a new company name; Saab-Scania AB. In 1990, General Motors came in as part-owners of Saab, leading to the formation of Saab Automobile, which separated the car manufacturing from other activities at Saab-Scania. The Saab-Scania merger ended, and vehicle operations were separated into Saab and Scania. In 2000, Saab acquired defence group Celsius AB, gathering flight, flight electronics, and robot manufacturing within Saab. In 2014, Saab acquired ThyssenKrupp Marine Systems AB, formerly known as Kockums.

The Saab Group currently consists of six areas of business: Aeronautics, Dynamics, Surveillance, Support and Services, Industrial Products and Services, and Kockums [3]. In 2018, Saab had over 17 000 employees, and sales of over 33 000 MSEK.

1.1.1.2 Saab Dynamics

Saab Dynamics (SBD) specialises in the defence industry, and offers products such as combat weapons, missile systems, torpedoes, unmanned underwater vehicles, training systems, and advanced camouflage systems for armed forces. The division has its main offices in Karlskoga and Linköping, Sweden, and had 2 252 people in their employment in 2018, and a turnover of 5 319 MSEK.

1.1.2 Carl-Gustaf weapon system

Included in the SBD portfolio are ground combat weapons NLAW, AT4, Bill 2 and Carl-Gustaf [4]. The Carl-Gustaf recoilless rifle is a man-portable reusable anti-tank weapon system that can be used with a wide range of ammunition including HE, HEAT, anti-structure, smoke, and illumination [5].

The first model of the Carl-Gustaf was produced in 1948 and was given the name Carl-Gustaf M1. In 1964, the new lighter and shorter Carl-Gustaf M2 was introduced. This model weighed 14.2 kg and had a length of 1 130 mm. The third model, M3, was presented in 1991 with a weight of 10 kg and a length of 1 065 mm.

The newest model in the series was introduced in 2014 and was named Carl-Gustaf M4, hereon referred to as the CG M4, the gun, the barrel, or the weapon (see figure 1) [6]. The weight and length had then been reduced to less than 7 kg and 1000 mm, respectively. Other new features included compatibility with intelligent sight systems, improved ergonomics, and a doubled service life from 500 to 1000 firing rounds. Also, the CG M4 can be carried while loaded, which enables the gunners to reduce the action time. The Carl-Gustaf system can be operated by a two- man team consisting of a gunner and an assistant gunner. The CG M4 is also compatible with programmable ammunition.

Figure 1. The Carl-Gustaf M4 weapon system [7].

1.1.3 Remote weapon station (RWS)

An RWS is a remotely operated weaponised system, purposed for mounting on different types of military vehicles [8]. Using an RWS provides a gunner with protection by allowing him or her to operate the weapon system from inside the vehicle.

1.1.3.1 Trackfire RWS

The Trackfire RWS is a family of fully stabilised remotely operated weapon and sensor systems, and is a part of Saab’s portfolio of fire control products, along with the Universal Tank and Anti- Aircraft Sight (UTAAS) for Combat Vehicle 90. The Trackfire RWS, hereon called the Trackfire, is designed for use on all types of military platforms such as vehicles, vessels, and static

emplacements [9-11]. A wide range of machine guns, automatic grenade launchers, and lightweight medium calibre cannons can be integrated with the Trackfire, see figure 2. However, there is currently no system in operation that allows integration of the Carl-Gustaf system. All Trackfire operations can be performed from below armour or deck to ensure the safety of the crew.

Figure 2. The Trackfire RWS [10].

1.1.3.2 Protector Nordic RWS

The Protector Nordic, produced by Norwegian company Kongsberg Defence and Security, is currently used on military vehicle Patria 360 in the Swedish Armed Forces (SAF). The Protector Nordic is an RWS designed for small and medium calibre weapons and can be used both on land and sea in extreme environmental conditions [12].

1.1.4 Armoured vehicle

Armoured Vehicles are military vehicles that are fitted with armour plating providing protection against bullets and projectiles [13]. Armoured vehicles are divided into two distinct groups: tracked and wheeled.

1.1.4.1 Patria XA-360 AMV

The Patria XA-360 AMV is an eight-wheeled armoured modular vehicle with a cruising speed of 90 km/h, produced by Finnish defence company Patria Land Systems Oy [14]. Patria has been used by the SAF since 2013. It possesses high levels of technology, and can accommodate a total number of 11 crew members, including a driver, a gunner, and a commander. The vehicle has a weight of 28 000-30 000 kg, length of 8.76 m, width of 3.44 m, and height of 3.49 m.

1.1.4.2 RG-32 Galten

RG-32 Galten, simply known as ‘Galten’, is a four-wheel drive mine-resistant Light Armoured Vehicle produced by BAE Land Systems OMC South Africa, and has been used by the SAF since 2006 [15]. The vehicle is able to climb an uphill slope of 60%, climb 35 cm high steps, and wade through 80 cm deep water. Galten is mainly purposed for troop transport and can carry a maximum of 1000 kg. It is 5.32 m long, 2.80 m high and 2.21 m wide.

1.2 Project definition

A range of weapons can be integrated with the Trackfire and Protector Nordic, but as stated above, the Carl-Gustaf system cannot. The most recent model, the CG M4, is of particular interest for integration since previous models are considered too heavy weighted. The RWS is in this case purposed for mounting on an armoured vehicle, such as the Patria 360 or Galten, where the gunner would be able to fire the CG M4s from inside the vehicle, protected from the enemy.

There are several factors to take into consideration in order to enable integration of CG M4 on an RWS. The system must, for instance, manage vibrations from the vehicle, and withstand recoil that comes from firing the CG M4. There is limited space, and various restrictions regarding both safety and functionality that apply both on and around the RWS, and all these factors complicate the integration.

Previous work regarding this issue includes a project conducted at SBD Karlskoga and Karlstad University in 2018, where a concept of integration between the CG M4 and the Trackfire was developed and analysed [16]. This concept included a fixed solution with a carrying capacity of three CG M4 barrels. The present study was initiated as ‘round 2’, to examine the possibility of other ways of vehicle integration between the CG M4 and the RWSs.

The project is based on a request that emerged between SBD and their partners at the Life Guards, SAF. The project will investigate new possibilities of integration of the two systems CG M4 and an RWS, where wishes and requirements that were defined in the previous study will be revised, and possibly altered or eliminated.

1.2.1 Goals and purposes

The project objective is to generate suggestions of vehicle integration between the CG M4 weapon system and an RWS. The project is a concept study that aims to develop construction solutions of functional and user-friendly vehicle integration between the CG M4 and the RWS.

The goal of the project is to present one or a few concepts of integration between the RWS and the CG M4 systems. One concept is to be presented as the final suggestion of vehicle integration, and is to be analysed regarding its abilities to withstand forces that arise from operating the system.

1.2.2 Delimitations

• The project will use the Trackfire RWS as the reference RWS for the integration, meaning assumptions, dimensions, limitations, and other factors used during the project are based on the Trackfire configuration. • The project will focus on mechanical solutions for the integration, and will not develop any software or electronic components that may be necessary to produce a fully working integrating system. If the solution requires systems of this kind, this is specified in chapter 6. • The project will not include any cost evaluations or consider any economic aspects.

2 Theory

This chapter includes information obtained during the feasibility study. It explains mechanisms present during operation of the Trackfire, Carl-Gustaf M4, and Patria 360.

For confidentiality reasons, exact details and numbers concerning design and functionality of Carl- Gustaf and the Trackfire are purposely excluded from this report.

2.1 Standard principles and equations

Cross sectional area of hollow cylinder 퐴 = 휋(푅2 − 푟2) (1)

∑푖 푚푖푟푖 Centre of gravity 푟푔 = (2) ∑푖 푚푖

푚 Density 휌 = (3) 푉

σ Factor of safety (FoS) against plastic deformation 푛 = 푦 (4) σ푚푎푥

Newton’s second law 퐹 = 푚푎 (5)

퐹 Pressure 푃 = (6) 퐴

Tangential acceleration of rotating body 푎 = 훼푟 (7)

Newton’s third law: Newton’s third law is the law of Action and Reaction, which states that when two particles interact, the force on one particle is equal and opposite to the force on the other [17, 18].

2.2 Recoilless rifles

2.2.1 Definitions and principles

Guns can be divided into four distinct categories: a ‘true’ gun, a howitzer, a mortar, and a recoilless rifle [19]. With this follows: all recoilless rifles are recoilless guns, but not all recoilless guns are recoilless rifles.

Ballistics is the science concerning firing, flight behaviour, and impact effect of ammunition. Interior, intermediate, exterior, and terminal ballistics are the four main phases of ballistics. To understand the dynamic behaviour of a firing recoilless rifle, one needs to look inside the gun, and study the interior ballistics. Interior ballistics describes what happens inside the gun, from the moment the gunner pulls the trigger until the moment the projectile exits the barrel; a category including ignition of the propellant, burning of the propellant in the chamber, pressurisation of the chamber, initial projectile motion, interior barrel dynamics of the projectile, and tube dynamics during firing. The study of interior ballistics is what provides information on how to calculate pressures and projectile velocity inside a gun barrel [20, 21].

A conventional recoilless rifle consists of a combustion chamber, a barrel, and a nozzle, in accordance with figure 3. The barrel is hollow with internal, usually spiral, rifling, to provide spin stabilisation to the ammunition as it exits the barrel [22]. At the breach of the rifle there is a nozzle, which is used to release the recoiling gases.

Figure 3. Typical cross section of a recoilless rifle.

As the gunner pulls the trigger of the weapon, the propellant ignites and gas pressure builds up inside the cartridge, which accelerates the projectile [23, 24]. The initial barrel pressure depends on the following:

• The amount of burned propellant. This can be described as the rate at which a propellant burns as a function of gas pressure, the amount of burning propellant surface, and density of the solid propellant. • The amount of propellant gas that has been discharged through the nozzle; this is determined by the pressure in the rifle, the geometry of the weapon and the temperature of the propellant gas. • The volume behind the projectile. The propellant gas expands into this volume. • The temperature of the propellant gas. Gas temperature is a function of the type of propellant used, the effects of gas expansion, and conduction of heat through the rifle walls.

The recoiling system of a recoilless rifle builds on the Recoilless Principle, derived from the Momentum Theorem of particles. The theorem explains how the rate of change in momentum of a system, as a function of time, is equal to all external forces acting on the system in accordance with equation 8 [25].

(푚 푣 −푚 푣 ) 퐹 = 1 1 0 0 = 푝̇ (8) ∆푡

In extension, the theorem explains why a gun will travel in the opposite direction of a launched projectile; an event known as the gun recoil. If the gun is to experience no recoil, it also follows that the forces directed forward need to be balanced by the forces directed rearward. Early versions of recoilless rifles derived the Recoilless Principle by launching two charges in opposite directions; a method that proved to be both dangerous and impractical.

Current recoilless rifles use the rear nozzle to vent the propellant gases so that the recoil force is countered, meaning that the forces directed rearward become equal to the ones forcing the projectile forward [26]. The combustion chamber is typically dimensionally larger than the ammunition cartridge. The projectile is fitted into the rifled barrel, and the cartridge base is

supported by a breach block, while the rest of the cartridge is suspended inside the chamber area, not touching the chamber walls (see figure 3) [27]. As the propellant charge ignites and the gases start to expand, they first fill the cartridge case and then continue to expand into the chamber. The pressure drives the projectile forward, and the gases counterbalance the recoil as they are released through vents in the breach block. This way, the system does not absorb the recoiling force, making it ‘recoilless’. By reducing the recoil, these rifles can be used when there is not enough mass to counteract the recoil forces of a projectile firing, and the firepower can be maximised without compromising the mobility of the soldiers.

2.2.2 Carl-Gustaf weapon system

The nozzle in the Carl-Gustaf system is a cone called the Venturi. The Carl-Gustaf ammunition essentially consists of a cartridge containing a projectile and a propellant substance. The Carl- Gustaf system differs from the conventional recoilless rifle in the way that the venting system is built into the cartridge, using a thin plastic plate as cartridge base. The projectile is still fitted into the internal rifling, but the cartridge case is supported by the chamber walls and the outer ring of the Venturi. As the projectile is pushed forward by the gas pressure, the plastic blowout shatters, and the gases are vented through the Venturi. Accordingly, there are no venting systems built into the Carl-Gustaf weapons. When loading the gun, the Venturi is opened, and the cartridge is inserted from the back and fitted into the barrel rifling. The Venturi is closed, securing the cartridge. The total weight of a CG M4 loaded with a projectile is approximated to 10 kg [24, 28].

Although the CG M4 is called recoilless, there is significant gun recoil present as the weapon is fired. Because of the plastic plate at the cartridge base, as illustrated by figure 4, the internal pressure releases the projectile from the cartridge, pushing it forward inside the barrel, causing an accelerating rearward movement of the gun. As a result of the high pressure, the thin back plate shatters. The propellant gases are now released through the Venturi at the rear of the barrel, exerting a force on the Venturi walls, which causes the gun to accelerate in the forward direction. The gases released through the Venturi produce a back blast that is dangerous to anyone standing behind it. The size and exact behaviour of the recoil depends on the type of ammunition used, but the rearward recoil is typically almost twice the size of the forward recoil

[24, 29]. For any type of ammunition, there is a maximum allowed recoil energy, emax. For some types of ammunition, the weapon will experience a slight anticlockwise rotation, caused by an angular acceleration, αmax. Also, as the CG M4 barrel is pressurised during firing, it can experience a small expansion in diameter.

(a)

(b)

(c)

Figure 4. The firing principle of a Carl-Gustaf weapon system. a) The cartridge has been inserted and the propellant is ignited. b) Pressure builds up, the projectile is pushed forward inside the barrel, and the gun recoils backward. c) The cartridge base shatters, gas pressure is released through the Venturi, and the gun recoils forward.

2.3 Wheeled armoured vehicle (WAV)

The performance of a WAV is generally judged by the firing power, meaning that firing accuracy and mobility of the weapon is of utmost importance [13]. As a projectile moves inside a gun barrel during firing, it interacts with the barrel, causing vibrational movements of the gun [30]. The motion of the projectile inside the barrel depends partially on the gun/projectile stiffness, the clearance between the projectile and the barrel, the projectile velocity, and the barrel centreline curvature. The projectile motion, as well as vibrations arising from motion of the vehicle, makes up the two dynamic events that cause vibration of a gun barrel mounted on a vehicle. Figure 5 shows a typical WAV, consisting of a vehicle body, a gun turret, tyres, and mechanical suspension units. The recoil shock that arises from firing the gun, as well as the vibrations arising from the vehicle being driven on rough terrain, causes unstable oscillation of the vehicle body. The oscillation, in turn, affects the firing accuracy.

Figure 5. Wheeled armoured vehicle.

2.4 Trackfire RWS

Weapon control systems are mainly composed of a fire control system and a gun control system. By using sensors to collect ballistic data, the fire control system decides which conditions and motions of the gun that will provide the highest first shot hit probability. The gun control system uses azimuth and elevation drivers, as well as stabilisation algorithms, to implement the gun.

The Trackfire system includes an operator’s console and a sensor module [9]. The operator’s console consists of a fire control panel, control handles, and a gunner’s display. The sensor module is a self-contained sub-system providing CCD TV, infra-red, and laser range finder channels for the operator. The Trackfire Stabilised Independent Line of Sight (SILOS) uses a sensor module that is decoupled from the weapon axes and independently stabilised, enabling the operator to maintain line of sight with the target. This feature significantly reduces target acquisition times, which allows for execution of complex engagement sequences involving repetitive target lasing.

The Trackfire Director Unit (DU) is a main unit located externally on the host platform, and is defined as a gyro stabilised pan/tilt weapon and sensor platform [31]. The DU sub-systems include an azimuth drive assembly, which allows the DU to infinitely rotate 360°, and an indirect elevation drive assembly with an operating range from -23˚ to +55˚. Furthermore, there are two weapon interfaces included in the DU: the Primary Weapon Interface (PWI) positioned in the centre top area of the Trackfire, and the Secondary Weapon Interface (SWI) positioned on the right hand side of the Trackfire (see figure 6). The Primary Weapon Cradle Sub-assembly (PWC) provides the mechanical mounting interface for the primary weapon (PW) and the PWI.

Figure 6. The Trackfire RWS sub-systems explained.

If recoil from the integrated weapons was to be transmitted directly into the DU, this recoil would, consequently, be transmitted into the DU and the host platform mounting surface. To reduce gunfire recoil, the weapon interfaces use a recoil buffer designed to reduce gunfire recoil into the DU. As the weapon is fired, the recoil is transmitted into the PWI that mitigates the recoiling forces transmitted into the DU.

2.5 Current gun recoil systems

The dynamics of a gun recoil system can be described by a mechanical model including a recoiling mass, a spring, and a damper [32]. The equation of motion is given by (9).

.. . 푚푥 + 퐶푥 + 퐾푥 = 0 (9)

Where C is the damping coefficient and K is the spring stiffness.

2.5.1 Springs

The static relationship of a force exerted by a spring on a body is defined by (10) [17, 18].

퐹 = −푘푥 (10)

Where x is the spring deformation.

The work exerted on a body by a spring is defined by (11).

2 푥2 1 2 2 푈1−2 = ∫ 퐹 ⅆ푟 = − ∫ 푘푥 ⅆ푥 = 푘(푥1 − 푥2 ) (11) 1 푥1 2

If the spring is deformed from a relaxed state, i.e. x1=0, (11) can be transformed into (12).

1 𝑒 = 푘푥2 (12) spring 2

2.6 Product development

Modern product development includes three main processes: Market, Construction and Design, and Manufacturing. These processes can be performed using a variety of methods and approaches [33]. There are methods of synthesis, which aim to present ways to describe what is to be achieved during the design and construction phase, and how this is achieved. The work can be iterative, meaning the work is performed by repeating rounds of analyses and validation, or it can be sequential, where each project phase is completed before the next begins [34]. This chapter aims to describe methods of product development relevant to this thesis.

2.6.1 Systematic method for construction and design

A systematic approach to solving a problem can be conducted using three steps; define the problem, investigate the problem, and solve the problem [33]. Furthermore, there are different methods to succeed with each of these three steps.

2.6.1.1 Define the problem

By defining the problem, one seeks to clarify the nature of it. Three main activities are implemented, and the result of these activities is used to define a specification of requirements (SoR) that aims to specify exactly what results the project is expected to deliver:

• Formulate the problem by clarifying what the problem is in as simple terms as possible. • Establish the level of the problem by determining an appropriate starting point for how the problem is to be treated. Higher levels will increase workloads, but also offer possibilities of finding many, and more radical solutions. • Fractionate and delimit the problem.

2.6.1.2 Investigate the problem

Investigating the problem deepens the knowledge on the subject: its background, its current status, and its expected future status. The objective of the investigation is to provide a complete list of requirements to implement in the product solution.

• Divide the problem into sub-problems. • Analyse the problem and suggest possible solution criteria. • Specify the problem by establishing project limitations, and by formulating criteria and their circumstantial status.

2.6.1.3 Solve the problem

The most common way to divide the solution process for construction and design is by implementing the following phases:

• Product specification • Concept generation • Concept selection • Product layout and detail construction • Manufacturing adaption

The following section describes the product development process in detail.

2.6.2 Product development

The construction and design part of the product development process is when the actual product solution is created, and this process includes the following activities [33]:

• Feasibility study - Analyse the problem - Collect and study background material - Define a requirement specification • Product specification - Define goals and purposes of the project • Concept generating - Develop concepts based on defined requirements • Concept selection - Evaluation of concept solutions - Choose concept • Product layout and detail construction

2.6.2.1 Feasibility study

The feasibility study is meant to broaden the overall knowledge of the subject to be investigated. It is to investigate possible technical solutions and conditions to ensure that resources are not sent off in the wrong direction. This initial phase of the construction and design process is meant to provide enough knowledge to enable the construction of an SoR, which seeks to list all customer demands and wishes, and to rank their relevance regarding the expected outcome.

2.6.2.2 Concept generating

During the phase called concept generating, the creative work is supported by different methods and a systematic workflow. The objective is to generate as many ideas as possible, so that all possible solutions can be explored before a few selected ideas are chosen for further investigation. The process is based on the requirements specified during the Product Specification phase.

One possible choice of process method is the ‘Idea method’, where focus is directed towards the strength of each individual idea, rather than clusters of ideas [35]. The input is a bunch of quantitative ideas produced as an initial step of the concept generating phase. A selection of these ideas is chosen for further evaluation. People present during this process are asked to choose their favourite ideas.

Concept generating can be performed using a variety of methods, where brainstorming is the overall dominating method used to generate new ideas. A brainstorming session aims to produce as many ideas as possible; a process where quantity surmounts quality, and no criticism is allowed. The participants are meant to inspire each other to develop new ideas as new perspectives are introduced by the other attendees.

2.6.2.2.1 Morphological matrix One method to categorise ideas developed during the brainstorming session is to combine the solutions by using a morphological matrix. The complete function of a system can normally be divided into sub-functions. The morphological matrix provides each sub-function with corresponding sub-solutions, so that complete solutions can be created by combining these sub- solutions.

2.6.2.3 Concept selection

When evaluating the solutions developed during the concept generating phase, each concept is to be analysed in respect to the SoR. Each concept is to be provided with a value that represents its qualities in comparison to the specified requirements. The final chosen concept is meant to be the one possessing the highest value.

The selection process includes the following activities:

• Eliminate alternatives that do not satisfy the requirements defined in the SoR • Screen the concepts through a decision matrix (Known as Pugh’s method) • Score the concepts by weighing the criteria (Known as Kesselring’s method)

2.6.2.3.1 Elimination An elimination matrix is a useful tool when deciding which concepts to eliminate from the process. The elimination matrix is meant to evaluate whether the concepts meet the following criteria:

• The concept solves the main issue • The concept fulfils all defined requirements • The concept can be realised • The concept is within the budget • The concept is advantageous through environmental, safety, and ergonomic perspectives • The concept suits the company business profile

If the concepts do not meet these criteria, they are eliminated.

2.6.2.3.2 Selection When choosing the final concept, one may use a decision matrix. The decision matrix compares the different concepts to each other. The criteria to be satisfied in this case consist of the wishes defined in the SoR, along with requirements that are of particular importance.

2.6.2.3.3 Product layout and detail construction The chosen concept solution is now to be developed into a functional product. Activities to go through are e.g. CAD-modelling, make drawings, specify technical parameters, etc. A new construction detail, i.e. a construction that cannot be plagiarised or copied from a previous solution, needs to be defined regarding its:

• layout and architectural build • shapes, dimensions, and colours • choice of material

3 Method

Present chapter states the events and methods used throughout the project process. The project was performed as a product development process, using a systematic and sequential work process.

3.1 Feasibility study

3.1.1 Project start

A project plan, including a Gantt-Chart, was constructed at the beginning of the project, and was used throughout the process to ensure the project progression. The project goals, objectives, and challenges were defined.

3.1.2 Research

3.1.2.1 Literature

Background research on the Trackfire and the CG M4 provided a clearer image of the final product desired by the customer. Academic literature was studied to deepen the knowledge on to the subject relevant areas.

3.1.2.2 Visits

A visit to the customers at the Life Guards was made; a visit that provided the opportunity of making physical observations of Patria 360, Protector Nordic, and the CG M4. The requirement list could on this occasion be revised and, later, updated. Another visit was made, this time to the Saab AB offices in Järfälla. This visit offered additional information on the Trackfire: its abilities and limits. Both trips provided new information that would be taken into consideration while defining the SoR.

3.1.3 Specification of requirements

The previously conducted study on vehicle integration between the two systems CG M4 and the Trackfire could be used to draft a first version of a requirement list. Feedback provided from the Life Guards regarding this previous study was used to add to the list.

All listed requirements and wishes were arranged in a criteria matrix where each requirement and wish was given a weight from 1-5 based on its importance to the requested product.

The first finished version of the SoR was reviewed and approved by supervisors at SBD.

3.2 Concept generating

3.2.1 Brainstorming

A number of individuals at SBD were gathered for a brainstorming session. To ensure that all attendees had a clear view of the project scope, they were handed a list of system requirements prior to the session. The session had one main objective: to come up with concept suggestions of vehicle integration between CG M4 and the Trackfire. This focus was divided into sub-questions: what will the construction look like, how are the weapons attached to the construction, and how is flexibility of the system ensured?

3.2.2 Morphological matrix

All ideas were documented and, later, organised and categorised in a morphological matrix. The matrix intended to present solutions to each sub-question brought up during the brainstorming session.

The morphological matrix generated sub-systems that were divided into two groups: concepts concerning construction position and layout, as well as concepts concerning how the weapons would be attached, and how the gun recoil would be handled.

All concepts regarding model and positioning of the guns were, in theory, meant to be compatible with those concerning concepts of recoil and attachment. The different sub-solutions could then be combined, and result in complete concept solutions. Combinations that were considered not feasible were immediately eliminated, while the concepts that were deemed good enough to evaluate further were given designations and specified in more detail.

3.3 Concept selection

3.3.1 Evaluation

All concepts were tried in evaluation matrices; one matrix for concepts concerning model and positioning, and one matrix for concepts concerning recoil and attachment. The evaluation matrix aimed to compare each concept with each requirement, to see if they were satisfied. Some requirements were only applicable for concepts regarding one of the two groups. Requirements regarding environmental aspects, impact tests, and ESD, were not included in the matrices, since these were not considered at this stage of the development process. An additional requirement was introduced to the matrix concerning concepts of model and positioning: E1 – The concept can be combined with at least one of the concepts for recoil and attachment. If a concept met a requirement, the corresponding cell was given the colour green. Red was used for requirements not fulfilled, and yellow was used when there were uncertainties to whether the requirement was fulfilled or not.

3.3.2 Elimination

3.3.2.1 Elimination matrix

The same principle as for the Evaluation matrix was applied for the elimination matrix; the two groups of concepts were tried in two different matrices, where each concept had to answer to the following questions:

• Does the concept solve the main issue? • Does the concept fulfil all specified requirements? • Is the concept realisable? • Is the concept advantageous regarding safety and ergonomic aspects? • Does the concept suit the company business profile?

Each concept answered each question with a yes, no, or a question mark; the question mark stating that more information on the concept was required. Concepts that did not satisfy the specified criteria of the evaluation matrix were immediately eliminated. Concepts that answered every question with a ‘yes’ were kept to continue the process.

3.3.2.2 Concept ranking

The remaining concepts were shown to a number of five individuals at SBD. These individuals were then asked to rank their three top choices from each of the two groups. The concepts were discussed at length, to see if some concepts could be combined and/or developed further.

During the elimination process, a lot of new concepts regarding recoil and attachment were developed, all based on- or inspired by the most popular concepts of the concept ranking. The concepts were developed to such an extent that they were given new designations, and were chosen to continue the process as ‘round 2’, leaving the previous concepts belonging to ‘round 1’. Thus, it was the concepts belonging to ‘round 2’ that were later tried in the decision matrix.

Concepts for positioning of the weapons did not include too many construction details, but rather focused on where the weapons were to be positioned in relation to each other and the Trackfire.

3.3.3 Concept selection

The final remaining sub-concepts were evaluated in two decision matrices. This time, the requirements were weighted based on their considered importance. The concept corresponding to the highest total score was chosen as the final concept solution of each respective group.

The highest scored concept for model and positioning, and the highest scored concept for recoil and attachment, were combined to form three full concepts. No matrices were necessary to make the final decision between these three. One concept was chosen as the final concept solution.

3.4 Product layout and detail construction

3.4.1 Delimitations

Delimitations on how the development process was to proceed were established; which parts were to be further developed and analysed, and which parts were to be put aside for future work.

3.4.2 Product layout

As a final concept had been established, approximate shapes and dimensions were determined. The construction was modelled in CAD-program 3DExperience CATIA.

3.4.3 Material selection

The most important material properties were defined, so that suitable materials could be selected for the construction.

When selecting a suitable material for the construction, two important parameters were considered above all others: maximised material stiffness and minimised system mass. As one of the requirements defined in the SoR is that each sub-system must not exceed the weight of 20 kg, this set the limit for material density according to equation 3. Furthermore, the construction must withstand long-term subjection to vibration and recoil forces, and thus needs to exhibit a certain level of fracture resistance. Metals possess high levels of fracture toughness, and viewing of tables showing the fracture toughness of materials commonly used for high strength applications, lead to further material restrictions.

Material database CES EduPack 2019 was used to screen different choices of material. The following stages were implemented:

• Step 1, limit the list of materials by using restrictions based on defined requirements and desired properties. • Step 2, find the most suitable materials using a chart to minimise the mass and maximise the stiffness.

Materials found in the selection chart were compared with lists of materials commonly used for constructions at SBD. A combination of information gathered from the selection chart, and from experienced engineers at SBD, lead to the choice standing between four materials. These materials were compared regarding their price and properties. Once a material was chosen, the CAD-model was assigned the corresponding material properties.

3.4.4 Detail construction

Springs to dampen the recoil were determined using equation 10 and 12. Details on ways of manufacturing and assembling the construction were established.

3.5 Analyses

3.5.1 Finite Element Analysis

To verify that the construction was strong enough to withstand the forces arising during the firing recoil, the CAD-model was analysed using 3DExperience FEA-program SIMULIA.

The recoil force was simulated as a contact pressure in accordance with equation 6. Since the forward recoil is not as powerful as the rearward recoil, the simulations were only performed with analyses on the rearward recoil, along with analyses on the rotational recoil. A Factor of Safety (FoS) of 1.5 was set as the minimum FoS required to ensure no plastic deformation of the construction occurs when a shot is fired.

3.5.2 System balance

When the construction is mounted on the Trackfire, it will add weight and height to the Trackfire that was not considered when the Trackfire was originally designed. To relieve the engine of unnecessary work, and thereby decrease engine efficiency that would otherwise be required to keep the construction in position, a counter mass can be used to balance the construction so that the total centre of gravity (CoG) aligns with the elevation axis.

The total weight of one loaded CG M4 barrel is approximated to 10 kg, meaning four fully loaded weapons would have a total weight of 40 kg. However, if one barrel is fired, the system will become unbalanced, and the total CoG will deviate from the origin. Thus, before determining the exact weight of the counter mass, analyses on the CoG deviation from the origin were performed during different loading conditions. An approximate counter mass was first established, using equation 2, where ri is the distance to the CoG of each individual part. The mass was then modelled and optimised in 3DExperience CATIA. 3DExperience was further used to analyse the CoG deviation.

3.6 SoR follow-up

As a final follow-up of the chosen concept, the developed and analysed construction was tried against the requirements previously defined in the SoR. Yellow criteria were defined as wishes and requirements possibly fulfilled; further analyses might prove that they are. Red criteria were defined as wishes and requirements not yet fulfilled, though if the concept and construction is given further attention, they may become fulfilled.

4 Results

This chapter presents all results obtained during the project process.

4.1 Feasibility study

4.1.1 Project start

The Gantt-Chart constructed to ensure the project progression is available in appendix 1.

4.1.2 Research

4.1.2.1 Visit to the Life Guards

The visit to the Life Guards provided information on what the customer expected from the requested product, and also provided the chance of physical investigation of the systems currently in use. The customer clarified that the weapons intended for the integration are only meant for firing from the Trackfire, and are not meant to be demounted for manual use. Firing should be controlled by the gunner from below deck, using technology compatible with the Trackfire firing system. This means that certain fittings and brackets normally attached to the CG M4 while used by foot soldiers, will not be necessary if the barrels are only fired from the Trackfire.

4.1.2.2 Visit to Saab AB, Järfälla

The visit to Saab AB, Järfälla, provided information on the Trackfire, as well as limitations and possibilities for the integration. The visit led to a decision in limiting the interface of the integration to the same interface currently used for the PWI. This way, the interface would maintain its current design, and the function of integrating CG M4 barrels is simply added to the construction. Alternatives eliminated were:

• Replacing the SWI with a new system to integrate the CG M4. This would allow the Trackfire to use the primary weaponry and the CG M4 simultaneously. The biggest drawback, however, is that the allowed weight of the system would be limited to 40 kg. Since the customer was asking for a system with a carrying capacity of four CG M4 barrels, this alternative would not allow that. • Keeping the Primary and Secondary Weapon Interfaces as they are, and adding an integrating system for the CG M4 to the Trackfire. This would likely be a very complex construction which would require changes being made to the Trackfire construction. It would also affect the performance of the Trackfire systems due to added weight and balancing issues.

4.1.3 Specification of requirements

The first reviewed and approved version of the requirement list can be found in appendix 3. The Criteria matrix enclosed in the SoR can be seen in table 1.

Table 1. Criteria matrix

The criteria matrix of table 1 shows that it is essential that the construction can integrate at least one CG M4 barrel, but the customer would strongly prefer four barrels. The system must withstand recoil and vibrational forces, and the weapons must be positioned so that no personnel or equipment are hurt or damaged as the system is fired.

4.2 Concept generating

4.2.1 Brainstorming

The brainstorming session resulted in a variety of ideas, though all attendees agreed that each integrated weapon should be provided with its own recoil dampening mechanism, rather than one recoil buffer used to dampen the whole system. Therefore, all ideas that did not include recoil dampening for each barrel were immediately eliminated.

4.2.2 Morphological matrix

The ideas brought forward from the brainstorming session are shown in the morphological matrix in table 2.

Table 2. Morphological matrix

All concept ideas extracted from the Morphological matrix are colour coded and described in short below. Sketches to illustrate the concepts are attached in appendix 5.

4.2.2.1 Model and position

Integration of 1 barrel

C1.1: Integrate 1 barrel by attaching it in the current interface. The barrel can be loaded while attached.

Integration of 2 barrels

C2.1: Integrate 2 barrels by placing one in the interface and the other on a table above. The barrels will have to be drawn out to enable loading.

C2.2: Integrate 2 barrels by placing one in the interface and the other in a drawer above. The barrels will have to be drawn out to enable loading.

C2.3: Integrate 2 barrels by placing them next to each other on a table. If placed some distance apart, the barrels can be loaded while attached.

Integration of 3 barrels

C3.1: Integrate 3 barrels by placing one barrel in the interface, two on top in a fence. If placed some distance apart, the barrels can be loaded while attached.

C3.2: Integrate 3 barrels by placing one barrel in the interface, two on top in drawers. The barrels will have to be drawn out to enable loading.

C3.3: Integrate 3 barrels by placing one barrel in the interface, two on top on a table. If placed some distance apart, the barrels can be loaded while attached.

C3.4: Integrate 3 barrels by stacking them on top of each other in drawers. The barrels will have to be drawn out to enable loading.

C3.5: Integrate 3 barrels by placing them all next to each other on a table. The barrels will have to be drawn out to enable loading.

Integration of 4 barrels

C4.1: Integrate 4 barrels by placing one in the interface, three on top like in a fireplace. The barrels will have to be drawn out to enable loading.

C4.2: Integrate 4 barrels by placing one in the interface, three on top like on a boat. The barrels can be loaded while attached.

C4.3: Integrate 4 barrels by placing one in the interface, three on top like on a staircase. The barrels will have to be drawn out to enable loading.

C4.4: Integrate 4 barrels by placing one in the interface, three on top on a table. The barrels will have to be drawn out to enable loading.

C4.5: Integrate 4 barrels by placing one in the interface, two on top, one on top of that, in a fence. The barrels can be loaded while attached.

C4.6: Integrate 4 barrels by placing one in the interface, two on top, one on top of that, in drawers. The barrels will have to be drawn out to enable loading.

C4.7: Integrate 4 barrels by placing two next to each other, and two next to each other above the first two, like in an oven. If placed some distance apart, the barrels can be loaded while attached.

C4.8: Integrate 4 barrels by placing two next to each other, and two next to each other above the first two, like in an oven. The barrels will have to be drawn out to enable loading.

C4.9: Integrate 4 barrels by placing them in a wheel. The barrels will have to be drawn out to enable loading.

C4.10: Integrate 4 barrels by placing them like a flower. The barrels can be loaded while attached.

4.2.2.2 Recoil and attachment

A1: Use existing pic.rail; clamp or click/insert into fitting to force the barrel to stay in position. Combine with rubber clamp to dampen recoil.

A2: Use a claw or clamping screws to keep the barrel in position. Combine with rubber clamp to dampen recoil.

A3: Use existing pic.rail; insert into fitting provided with springs for recoil dampening and positioning. Combine with a clamp or claw for additional barrel stability.

A4: Attach wire dampeners to the barrel for positioning.

A6: Insert rifle into a sleeve that acts as a stop mechanism. Provide the stops with springs to dampen the recoil and for positioning.

A7: Attach barrel to a swing that swings back and forth when the barrel is fired. Attach barrel by using clamps to keep the barrel in position.

A8: Attach new brackets to the barrel to enable an attachment that allows rotation. Mount on rods provided with springs for recoil dampening and positioning.

A9: Attach new brackets to the barrel to enable a ‘clicking’ stop mechanism. Mount on rods provided with springs for recoil dampening and positioning.

A10: Use clamp/claw/clamping screws to attach the barrel to a construction mounted on rods provided with springs for recoil dampening.

4.3 Concept selection

A detailed description of the concept selection process, as well as sketches of all developed concept ideas, can be found in appendix 4 and 5.

4.3.1 Evaluation

The evaluation matrices revealed that five concepts did not meet the specified requirements: C4.9, C4.10, A1, A2, and A10.

The evaluation matrices can be found in appendix 2.

4.3.2 Elimination

4.3.2.1 Elimination matrix

The Elimination matrices are shown in table 3 and 4.

Table 3. Elimination matrix for concepts concerning model and positioning

Table 4. Elimination matrix for concepts concerning recoil and attachment

Table 3 shows that six concepts regarding model and positioning were eliminated: four due to uncertainties regarding their capability of maintaining a stable system, and two because they did not fulfil requirements specified in the evaluation matrix. Table 4 eliminates four concepts for recoil and attachment, all except one because of inabilities to satisfy specified requirements.

4.3.2.2 Concept ranking

The results obtained from the concept ranking are shown in table 5.

Table 5. Results from concept ranking for concepts concerning model and positioning Individual Concept Total 1 2 3 4 5 C1.1 0 C2.1 3 3 C2.2 0 C2.3 0 C3.2 0 C3.3 2 2 C3.5 0 C4.1 1 1 C4.2 2 2 C4.3 1 1 C4.4 3 1 2 3 1 10 C4.7 0 C4.8 1 3 3 2 2 11

Table 6. Results from concept ranking for concepts concerning recoil and attachment Individual Concept Total 1 2 3 4 5 A3 2 1 3 A4 2 2 4 A5 1 3 3 3 3 13 A6 2 2 4 A8 1 1 2 A9 3 1 4

Table 5 shows that two concepts; concept C4.4 and C4.8 were the clear favourites, and thus only these two were chosen to continue the process.

Table 6 shows that concept A5 was the most popular concept regarding recoil and attachment. A4, A6, and A9, all received four points each. These four concepts inspired the development of concepts A11-A17.

4.3.2.3 Concept descriptions, round 2

The following concepts of recoil and attachment were all based on, or inspired by, concepts A4, A5, A6, and A9.

A11: New brackets are attached to the barrel. The brackets have two pockets: one provided with rubber lining, and one with limited space. A lever or locking mechanism is inserted into the rubber lined pocket, designed to dampen the rotational recoil. Another lever in inserted into the other pocket, designed to dampen the axial recoil.

A12: The barrel is attached to a block by existing Picatinny rail. The block is mounted on a rod provided with springs to dampen the axial recoil. The block is free to rotate around the rod but the barrel is attached to a wire dampener that will ensure rotational flexibility of the barrel, while keeping it in position.

A13: The barrel is attached to a block by existing Picatinny rail. The block is mounted on a rod provided with springs to dampen the axial recoil. The block is free to rotate around the rod but the barrel rests on a structure with bearings to keep the barrel in its position.

A14: The barrel is attached to a block by existing Picatinny rail. The block is mounted on a rod provided with springs to dampen the axial recoil. The block is free to rotate around the rod but the barrel rests in a rubber clamp.

A15: New brackets are attached to the barrel. The brackets rest in an attachment allowing for rotational sliding of the two surfaces against each other. The attachment is mounted on a block which rests on two rods provided with springs to dampen the axial recoil.

A16: New brackets are attached to the barrel. The brackets rest in an attachment allowing for rotational sliding of the two surfaces against each other. The attachment is mounted directly on a rod provided with springs to dampen the axial recoil. A wire dampener is attached at the bottom of the barrel to ensure that the barrel reverts to its original rotational position.

A17: New brackets are attached to the barrel. The brackets are attached to a rod provided with springs to dampen the axial recoil. The brackets are fixed and will not allow for any rotation of the barrel.

4.3.3 Concept selection

The two decision matrices are shown in table 7 and 8.

Table 7. Decision matrix concerning concepts of model and positioning Concepts Criterion Weight C4.4 C4.8 R10 Minimum maintenance 2 4 3 R19 Easy loading of barrels 3 2 2 W1 Integration of 4 barrels 3 5 5 W2 Splinter guards 1 4 4 W3 Protection from tree branches 2 4 4 W4 Minimum changes on the Trackfire and barrels 3 5 5 W5 No loose tools 1 3 3 W6 Barrels comfortable to carry manually 1 5 5 Stable construction 3 3 4 Result 73 74

Table 8. Decision matrix concerning concepts of recoil and attachment Concepts Criterion Weight A11 A12 A13 A14 A15 A16 A17 R6 1 barrel fireable without affecting the others 3 5 5 5 5 5 5 5 R12 No damage of system components while fired 3 5 3 2 3 5 5 5 R10 Minimum maintenance 2 2 2 2 3 2 2 4 W4 Minimum changes on Trackfire and barrels 3 2 5 5 5 2 2 2 W5 No loose tools 1 3 5 5 5 3 3 5 W8 Barrels revert to original axial position 3 5 5 5 4 5 5 5 W8 Barrels revert to original rotational position 1 5 4 5 4 4 4 5 Stable system 3 5 2 3 4 5 5 5 Result 78 73 74 78 77 77 84

Table 7 and 8 show that concept C4.8 and A17 were the most suitable concepts according to the decision matrices. The three full concepts, F1-F3, formed from these two selected sub-concepts, are described as follows:

F1: Four barrels are attached, using the stacking principle of concept C4.8. The barrels are provided with customised brackets attached to blocks mounted on rods positioned diagonally over the box opening. The rods are provided with springs to dampen the axial recoil.

F2: Four barrels are attached, using the stacking principle of concept C4.8. The barrels are provided with customised brackets attached to blocks mounted on rods positioned over and under the barrels. The rods are provided with springs to dampen the axial recoil. The upper barrels are positioned further ahead than the lower barrels to allow for loading of the barrels without detaching them.

F3: Four barrels are attached, using the stacking principle of concept C4.8. The barrels are provided with customised brackets attached to blocks mounted on rods positioned diagonally over the box opening. The rods are provided with springs to dampen the axial recoil.

No matrices were necessary to make the final decision between these three concepts; F2 was based on the idea of placing the two upper barrels slightly further out than the two lower barrels, to simplify the ammunition loading process. However, the back blast from the barrels would not allow this. Due to the limited amount of space allowed for the integration, the rods were placed on a diagonal line over the barrels, rather than on each side. The spacing issue was also why concept F3 was eliminated. Concept F1 was chosen as the final concept solution. A detailed concept description follows.

4.3.3.1 Final concept

Four barrels are attached, using the stacking principle of the ‘oven’, see appendix 5. The construction consists of four ‘boxes’, hereon called containers, each meant to hold one barrel. These containers are attached back-to-back, and bottom-to-bottom. This is to ensure that the weight of each subsystem is kept to a minimum, and to make disassembling of the subsystems as simple as possible. The construction of the four containers is mounted on a baseplate that is attached instead of the PWI on the Trackfire. The baseplate is also meant to hold a counter mass required to keep the centre of gravity at the centre of the elevation axis. The barrels are provided with customised brackets designed to withstand forces that are transferred during firing of the barrel. These brackets are attached to blocks mounted on rods. The rods are provided with springs to dampen the firing recoil. The blocks are free to rotate around the rod axes, allowing for some rotational flexibility, although this concept mainly focuses on preventing rotation of the barrels, meaning that the new brackets need to exhibit a certain level of strength.

4.3.3.1.1 Working titles A first sketch of the chosen concept is presented in figure 7. From here on forth, the solution and its sub-systems are referred to by the following terms:

Construction The construction of the four containers and their sub-assemblies in its entirety.

Container The construction is made up of four containers. Each container is a type of box or pocket used to hold sub-assemblies of four ears, two rods, four springs, and two blocks. The container and sub-assemblies are meant to hold one barrel each.

Base plate The base plate works as the mounting interface between the Trackfire and the construction.

Blocks The blocks are mounted on the rods. They work as the link between the rods and the brackets.

Brackets The customised brackets attached to the barrel. The brackets function as the link between the blocks and the barrels.

Ears The ears are mounted on the containers. The rods are held in place by the ears.

Rods The rods are suspended between the ears, and hold the blocks and the springs.

Figure 7. An early sketch of the chosen concept solution.

4.4 Product layout and detail Construction

4.4.1 Delimitations

Continued work is focused on layout, functionality, and structural strength of the containers and rods. Blocks and brackets will not be developed or analysed further. Suggestions of construction will follow in chapter 6.

4.4.2 Product layout

Construction dimensions were estimated in accordance with figure 8. The dashed circle represents the barrel.

c = 50 mm t = 20 mm b = 400 mm d = 20 mm

L1 = 200 mm

L2 = 120 mm H = 180 mm r = 10 mm

Figure 8. Container dimensions.

Figure 9 shows the finished CAD-model of the construction. Each container, including ears and rods, was made of the exact same design to simplify the manufacturing process. M10 hex bolts secured with locknuts were used to assemble the containers, and dowel pins were used to secure the horizontal parts of the containers.

(a)

(b)

Figure 9. (a) The finished CAD-model of the construction. (b) The construction holding four CG M4 barrels.

The new brackets were attached on each side of the barrel, positioned according to figure 10. This allowed for two possible positions of the barrel. When the Venturi is closed, the bracket on the same side as the Venturi handle is to be attached to the upper block of the container, see figure 11. Instructions for this operation can easily be given with a sign, or similar, printed on the blocks and brackets. Positioning the barrels this way ensures that the Venturi stays open during the ammunition loading process, i.e. it does not cause unnecessary irritation by closing in the operator’s face. Also, the brackets will not hinder attachment of the handle normally used to carry the CG M4. As comfortable carrying was desired (see list of requirements, appendix 3), this offers the option of using this handle for manual carrying.

Figure 10. Position of new brackets on the CG M4 barrel.

Figure 11. The construction holding all four barrels, shown from behind.

4.4.3 Material selection

4.4.3.1 Containers

3 Volume of one container: 푏푡(퐿1 + 퐻 + 퐿2) = 0.0040 m

푚 20 The maximum limit for material density (1): 휌 = = = 5000 kg/m3 푉 0.004

The material selection was performed using the following steps:

Step 1, limit the list of materials by:

• Only presenting metals • Only presenting materials with a density of less than 5000 kg/m3 • Demanding a fracture toughness of at least 20 MPa m1/2 • Demanding excellent freshwater durability • Demanding excellent UV radiation durability

Step 2, find the most suitable materials by plotting the inverted Young’s modulus against the density.

The most suitable materials, with the highest possible stiffness and lowest possible density, are found along the black curve in the selection chart of figure 12. Grey areas in the chart represent materials that do not satisfy the demands defined in step 1 of the selection process. According to the selection chart, the most suitable material is a beryllium-aluminium alloy.

Figure 12. Selection chart, showing the most suitable materials for the containers.

Aluminium 6082 T6 and aluminium 7075 T6 are two versions of aluminium commonly used at SBD, that are also present in the selection chart. The four final materials are presented in table 9.

Table 9. A selection of average properties of the four materials beryllium-aluminium, aluminium 6082, and aluminium 7075 Material Properties Be-Al Ti-SiC Al 6082 Al 7075 E (GPa) 205 245 72 73 σy (MPa) 216 1000 260 445 Price (SEK/kg) 4060 22900 21 43 ρ (kg/m3) 2160 3930 2700 2800 KIC (MPa m1/2) 15 34 33 27 Durability Service temperature range (°C) (-273)-330 (-273)-505 (-273)-140 (-273)-90 Fresh water Excellent Excellent Excellent Excellent Salt water Excellent Excellent Acceptable Acceptable UV radiation Excellent Excellent Excellent Excellent Weldabiliy Good x Good Unsuitable

Table 9 shows that the beryllium alloy is approximately 100-200 times more expensive than Al 6082 and 7075, and the titanium alloy is 540-1100 times more expensive. Although a price limit was never set for this project, these materials were deemed too expensive. Due to its weldability, Al 6082 T6 (EN AW 6082) was finally chosen over Al 7075.

4.4.3.2 Rods

When selecting a material for the rods, three parameters were prioritised: high strength, high stiffness, and good corrosion resistance. Lists of commonly used stainless steels were reviewed, and the choice fell on a duplex stainless steel: EN 1.4460. The steel exhibits excellent corrosion

resistance and is commonly used for propeller shafts, pump shafts, and piston rods, possessing the following average properties:

E = 200 GPa 휌 = 7.8 kg/m3

σy = 500 MPa

KIC = 100 MPa m1/2

4.4.4 Recoil dampening

4.4.4.1 Axial recoil

Combining equations 10 and 12 gives the following relationship:

1 𝑒 = 퐹 푥 (13) spring 2 spring

The maximum allowed energy to be released during a backward recoil of a CG M4 barrel is emax. If a spring is to dampen this recoil, it needs to be able to absorb the same amount of energy. Since each barrel is mounted on two bars, both provided with springs, each spring needs to be 푒 able to absorb at least 푚푎푥. When choosing springs for the construction, they therefore need to 2 fulfil the following requirement:

1 푒 𝑒 = 퐹 푥 = 푚푎푥 (14) spring,min 2 spring,min 2

Where espring,min is the minimum amount of energy that the spring needs to absorb, Fspring,min is the minimum spring force, and x is the spring compression.

The spring force Fspring is the force exerted by the spring on the block. Applying Newton’s third law regarding action and reaction, the force exerted by the spring on the block is equal to the force exerted on the ear. The spring chosen to dampen the backward recoil in the construction in this project was a tool spring (article no 5356 Lesjöfors), with properties according to table 10.

Table 10. Spring properties Outer diameter Axis diameter Unstretched length Spring constant

A B L0 k 40 mm 20 mm 51 mm 350 N/mm

Applying the condition of equation 14, inserting into equation 10 and 13:

2푒 푥 = √ spring,min (15) 푘

푘푥 = 퐹

As the barrel recoils, the spring will exert a maximum force, F, on the ears, and experience a maximum deflection of x mm1.

1 Values used and obtained during this calculation are excluded for confidentiality reasons.

4.4.5 Manufacturing

The containers are to be cut and bent from 20 mm thick sheets of aluminium 6082 T6. The ears are separately cut from the same aluminium sheet, and a hole of diameter 20 mm is drilled through each ear. The rods are to be made from existing stainless steel rods of diameter 20 mm. The ears are welded onto the containers.

Two clearance holes are drilled through each wall of the container, symmetrically placed so that the holes align with the ones on another container when they are assembled.

4.4.6 Assembly

The brackets need to be attached by the producer of the CG M4, and the ears need to be welded onto the containers by the manufacturer of the construction. All other construction parts can be assembled by the buyer.

The base plate is screwed into position on the RWS.

The containers all have the exact same design, and are assembled in a way that allows for integration of either two or four barrels. Two containers are to be attached back-to-back to each other. The first container is positioned with the short side to the base plate and screwed into position. The other container is placed with the same side facing downwards, and back-to-back with the other container. If only two integrated barrels are desired, the container construction is finished. If four barrels are desired, these are assembled on top of the first set, but with the longer sides facing down. See figure 13 for a full process description.

Since all screw holes are clearance holes, dowel pins can be used to secure the horizontal parts of the containers.

The rods have diameters that fit the holes of the ears. One end of a rod is threaded through one of the ears, and then as the rod is further pushed through the hole, the spring, block, and spring, in that particular order, are successively threaded onto the rod. The other end of the rod is threaded through the other ear, and finally both rod ends are secured with screws.

Figure 13. The assembly process of the containers.

4.4.7 Summary

Established component details are summarised in table 11.

Table 11. Summary of components detail construction Component Assembly Material Manufacturing Article 20mm Screwed to the Base plate Aluminium 6082 T6 Cut from sheet EN6082 Trackfire Tibnor Screwed to other 20mm Cut and bent from Containers containers and base Aluminium 6082 T6 EN6082 sheet plate Tibnor 20mm Welded onto Ears Aluminium 6082 T6 Cut from sheet EN6082 containers Tibnor Threaded through Ø20 ears and clamped Stainless rod Rods Stainless steel 10 088 Cut from rod by screw at each EN1.4305 end Tibnor Blocks Threaded onto rods x x x Brackets Glued to barrels x x x Tool spring Springs Threaded onto rods x x 5356 Lesjöfors

When material properties are applied to the construction parts:

• One container, including ears and rods, obtains a total weight of 14 kg. • The base plate obtains a weight of 6 kg. • One loaded gun weighs approximately 10 kg.

The construction obtains a weight of 102 kg, not including screws, blocks, or springs, when carrying four loaded weapons.

4.5 Analyses

4.5.1 Finite Element Analysis

The four containers were connected to each other by sliding contact and bolt connection. The rods were tied to the ears by bonded contact, not allowing any rotation. The bottom surfaces, i.e. the two surfaces that are supposed to face the bottom plate, were restrained with a clamping condition, allowing no movement in any direction. The global mesh size was set to 34 mm, using tetrahedral elements (see figure 14).

Figure 14. The simulation mesh.

4.5.1.1 Axial recoil

The pressure applied to the ears exposed to the backward recoil was calculated combining equations 1, 6, and 10.

퐹 푘푥 푃 = = (16) 퐴 휋(푅2−푟2)

Where R and r are the outer and inner radius, respectively, of the dampening springs that make contact with the ears (see table 10): 퐴 퐵 푅 = and 푟 = 2 2

Figure 15. FEA-structural simulation showing the location of global maximum stress after rearward recoil.

The simulations revealed that the maximum stress in the construction, as it experiences recoil on the back ears of the top right container, appeared on the lower back ear of the lower left container (see figure 15). The highest stresses appeared in the regions where the ears are attached to the containers, so to ensure maximum strength, the weld needs to be strong with no sharp corners. The edge fillets of this construction were given radii of 3 mm, and nowhere in the construction did the highest von Mises Stress exceed the Yield Strength of the material. The maximum displacement reached a value of 0.6 mm.

4.5.1.2 Rotational recoil

Equations (5) and (7) give:

퐹푡 = 푚푟𝑖푓푙푒훼푟𝑖푓푙푒푟 (17)

퐹 Since there are two rods to absorb the rotational recoil, the force exerted on each rod was 푡. 2

The simulations revealed the highest stress levels to be located in the rods, reaching a value of 240 MPa, see figure 16. The maximum displacement reached a value of 1.8 mm.

Figure 16. FEA-structural simulation showing the location of global maximum stress after rotational recoil.

4.5.1.3 Combined axial and rotational recoil

The two loading cases were applied simultaneously to simulate a full weapon recoil.

Figure 17. FEA-structural simulation showing the location of global maximum stress after full weapon recoil.

The simulations showed that the highest stress levels were found in the rods, reaching a value of 269 MPa, see figure 17. The maximum displacements reached a maximum value of 2.0 mm.

4.5.1.4 Summary

The results of the simulations are summarised in table 12. Additional figures showing stresses and displacements from the FEA-simulations are presented in appendix 6.

Table 12. Maximum values of von Mises stresses and displacements Recoil σvM,max (MPa) Δmax (mm) Only axial 88.30 0.555 Only rotational 240.39 1.828 Combined rotational and axial 269.31 1.978

Table 12 shows the maximum stress levels in the material, as well as construction displacements, obtained from the simulations. The highest stresses appeared when a full recoil including both backward axial, and anticlockwise rotational, was simulated. The highest stresses in this case appeared in the rods near the lower ears. Since σvM,max < σy, no plastic deformation occurred.

The axial recoil alone caused the highest stress levels to appear in the weld between the ears and the containers. The FoS (equation 4) became:

σ푦,푐표푛푡푎푖푛푒푟 260 푛1 = = = 2.95 σ푚푎푥 88

The combined rotational and axial recoil, as well as the rotational recoil alone, caused the highest stress levels to appear in the rods. The FoS became:

σ푦,푟표푑푠 500 푛2 = = = 1.86 σ푚푎푥 269

Since ni > 1.5, the construction was deemed strong enough to withstand the recoil forces of a fired CG M4 barrel.

4.5.2 System balance

4.5.2.1 Centre of gravity

The analysis was performed from a 2-dimensional perspective, see figure 11b. Four loaded guns would have a total weight of 40 kg, symmetrically distributed around the vertical centre axis. Thus, the construction CoG lies exactly in the construction centre.

To perform the analysis, the construction was first simplified to consist of rectangular blocks, while carrying barrels represented by hollow cylinders. The counter mass was modelled as a rectangular block suspended from the construction bottom, so that the elevation axis (i.e. the z- axis of figure 18) ran through the interface between the counter mass and the construction.

(a)

(b) Figure 18. (a) A simplified 3D-sketch of the construction. (b) A cross section of the simplified construction showing the counter mass dimensions and the distance to the construction CoG (rc)

and the distance to the counter mass CoG (rm).

The aim was to statically balance the construction, so that the total centre of gravity was placed in the centre of the elevation axis, i.e. at the intersection of the y- and z-axis of figure 18.

The counter mass was given dimensions 퐿 푚 × 푡푚 × ℎ푚 (see figure 18b).

Using (2) to place the total CoG at the origin (rg = 0):

푚푚푟푚+푚푐푟푐 푟푔 = = 0 => 푚푚 푚푐+푚푚

푚푚 푚푚 = = 휌푚 푉푚 퐿푚푡푚ℎ푚

The density acquired was used to find a suitable material to use for the counter mass 2. The counter mass modelled in 3DExperience was assigned material properties of tool steel, chromium alloy (AISI H19): 휌 ≈ 8000 kg/m3.

The construction CAD-model was simplified to consist of the four containers, ears, and rods. The barrels were represented by hollow cylinders centred in each container, and the ammunition was represented by solid cylinders centred in the barrels (see figure 19).

(a) (b) Figure 19. CAD-models of the simplified construction and counter mass (a) as it would look if mounted on the Trackfire, no barrels loaded, (b) with all barrels loaded.

The CAD-model was used to keep the CoG at the centre of the elevation axis, while optimising the counter mass dimensions.

2 Values used and obtained during this calculation are excluded for confidentiality reasons.

4.5.2.2 Centre of gravity deviation

The solid cylinders representing the CG M4 ammunition were systematically removed so that the CoG could be measured at different loading conditions.

Table 13 shows that when no barrels are loaded, the deviation from the origin is almost 11 mm. This deviation was considered small enough to neglect, i.e. the counter mass can be sized to balance a fully loaded system.

Table 13. CoG at different loading conditions Barrels loaded Δy (mm) Δz (mm) All (ref) 0 0 None 10.7 0 C3, C43 2.6 0 C1, C2 7.9 0 C1, C4 5.2 0

3 Designations according to figure 17.

4.6 SoR follow-up

Table 14 compares each criterion with the developed construction.

Table 14. Each criterion tried against the final concept solution

Table 14 shows that the construction needs further development and analysing before some criteria can be satisfied.

5 Discussion

This chapter offers perspectives on the report by arguing and discussing the project process and the project results.

5.1 Method

5.1.1 Concept generating

Many of the requirements defined in the SoR were not satisfied or fully analysed before the final concept was chosen. Because this project was performed over a limited period of time, and many requirements demanded knowledge of construction details that were not yet developed during the concept generating phase, these requirements were temporarily overlooked. These specific requirements also complicated the process of eliminating early concepts, since most concepts required more specific construction details to be able to answer to the requirements. Consequently, many concepts were eliminated because they seemed not to fulfil specific requirements, meaning there is a chance some of these concepts would have been just as realisable as the final concept chosen. With this said, the process was continuously followed by supervisors and colleagues at SBD, and the final concept was generally deemed the most suitable solution.

Some of the requirements were later fulfilled during the construction phases, for instance during the material selection phase, where requirements regarding UV-radiation and water durability were satisfied. If the project is to be resumed on a later occasion, the list of requirements needs to be considered before and while the system is developed further.

5.2 Results

5.2.1 Concept selection

5.2.1.1 Interface

As the project started there were no requirements defined regarding where on the RWS the integrating system was to be positioned. Once the decision on using the PWI was made, the objective was to allow use of both the weapons currently used, as well as the new integrating CG M4 system, by quick assembly and disassembly of the different systems. To be able to do this, the PWC would have to remain mounted, or else the demounting process would quickly become more complicated.

If the PWC currently used on the Trackfire is kept mounted on the Trackfire at the same time as the CG M4 integrating construction, this cradle will act as a counter mass. The exact weight and dimensions of the cradle were not defined in this report, and these need to be considered while deciding the weight and dimensions of an additional counter mass. The report presents a method to decide these parameters, but the final counter mass presented in this report is only an approximation, and also indirectly includes the weight and dimensions of the PWC.

If the PWC was to be removed, however, new possibilities regarding the CG M4 construction emerge. A suggestion is to integrate the developed construction so that the construction centre of gravity aligns with the elevation axis. This will relieve the Trackfire of unnecessary weight by counter masses, and thus offer a more stable system. This will require optimisation of construction dimensions, since the construction does not fit into the space where the PWC is currently housed.

The issue thus lies in the conflict between choosing a more stable, lightweight system, or a quick mounting-demounting process.

5.2.2 Material selection

The material chosen for the construction was aluminium 6082 T6, mainly because of its low material density while still being sufficiently stiff. However, system stiffness is of great importance to an RWS, so an alternative to aluminium could be using a steel material. Since steel is considerably denser than aluminium, the system dimensions would have to be reduced to ensure that the requirement of 20 kg maximum sub-system weight is still fulfilled. If the construction is deemed stable enough, using steel could be advantageous, since a reduction in system dimensions could reduce the system height and width, and thus allow for more integrating space if the PWC, hypothetically, was to be removed.

5.2.3 Finite Element Analysis

The results of the FEA showed that the highest stress level in the construction, when subjected to recoil, meets the safety factor by a margin. Based on these results, optimisations on construction dimensions are possible, which might enable further volume and weight reduction. However, analyses were only made on the construction with regards to it experiencing one recoil, while being rigidly clamped to the base plate. In real life, the situation will be different, as vibrations, and rough terrain and weather, will influence the stability of the construction.

5.2.4 System balance

An important aspect to consider when adding elements to the Trackfire is, as previously discussed, the system stability. The final construction presented in this report adds considerable height and weight to the system, and said height and weight was not considered when the Trackfire was originally designed. To ensure that the system remains stable, a way to counter the added weight by using a counter mass was presented, but the system will, regardless, be affected by all the added equipment. Full analyses on the Trackfire behaviour while carrying the construction and the counter mass are required to provide a full understanding on the effect of the added integrating system.

5.3 System integration

One important fact to keep in mind is that there are several factors to consider before a Carl- Gustaf weapon can be integrated on an RWS. A system to allow firing of the guns from inside the vehicles needs to be developed. Also, the ammunition used today is not designed to lie inside a

barrel for a longer period of time, while simultaneously being subjected to shock and vibration resulting from vehicle movement. It is also essential that no dust or dirt enter the barrels while they are being driven through rough terrain; a problem that can be solved by using protective shoot-through lids. These lids will, naturally, have to be replaced after a shot has been fired, possibly adding to the list of equipment and duties that the crew must deal with. This section is thus meant to emphasise that the construction may solve the mechanical part of integrating a CG M4 weapon, but there are many other issues to address before a complete CG M4 system integration can be performed.

6 Future Work

This chapter states activities that require further attention, and gives suggestions on possible construction details and how to proceed with the project if desired.

6.1 What is left to do

6.1.1 Product layout and detail construction

• Develop locking mechanism between blocks and brackets • Determine dimensions of brackets • Material selection for blocks and brackets • Optimise construction dimensions • Further develop a suitable construction to use as a counter mass • Develop protective casings for the springs • Develop protection to protect the barrels from rough terrain and weather • Make drawings of the construction and define tolerances

6.1.2 Analyses

• Perform shot analyses on the weapon while attached to the construction to ensure there are no unexpected surprises, e.g. the Venturi opens. • Analyse the Trackfire performance once the construction is assembled and mounted. • Analyse what happens to the construction over time - What happens to the construction after e.g. 100 shots have been fired? - What happens to the construction if shots are fired from one container more often than the others? - What happens to the construction after it has been subjected to e.g. 100 days of vehicle vibration? - What happens to the construction after 100 shots have been fired, and after subjection to 100 days of vehicle vibration while driven in hard wind and rain?

6.1.3 System integration

As discussed in chapter 5.3, there are many other circumstantial aspects to consider before a CG M4 weapon can be integrated on the Trackfire. A full system SoR, including required electronics, software, and other details necessary to enable a full CG M4 system integration, needs to be defined.

6.2 Suggestions

6.2.1 Detail construction

6.2.1.1 Locking mechanism

The blocks are designed to function as locking mechanisms that are compatible with the brackets on the barrels. There is a button on each bracket that can be pushed inwards in the direction of the barrel wall. The barrel is attached by the buttons being threaded through the tracks on the sides of the blocks. As the button reaches the deeper pocket in the block, it ‘clicks’, and secures the barrel. Using an unlocking mechanism that causes both buttons to retreat at the same time, the barrel can now either be pulled backwards into the long tracks of the blocks, or be detached. The backward-function is how the barrels are loaded while still attached. See figure 20 for a full process description.

Figure 20. The principle of the locking mechanism.

6.2.1.2 Protection of construction

Use a sheet of a durable material to cover the construction. The empty screw holes offer a suitable interface for attachment (see figure 21).

Figure 21. Protective cover using the empty screw holes as interface.

6.2.1.3 Integration

Optimise construction dimensions so that the construction obtains the same width as the current PWC. Remove the current PWC and attach the construction so that its centre of gravity aligns with the elevation axis.

7 Conclusions

This chapter summarises the report and concludes the results.

The project aimed to result in concept solutions for vehicle integration between Carl-Gustaf M4 and a remote weapon station, and was only to investigate mechanical solutions for the integration. Conclusively, the project goal was fulfilled; different concepts of solution for integration between Carl-Gustaf M4 and Trackfire RWS were explored and developed, and a final concept solution was presented, developed, and analysed.

The solution is constituted by a construction of four containers with a recoil dampening system consisting of springs, where each container holds one barrel. A focus on minimising material density and maximising material stiffness lead to a decision in using aluminium 6082 T6 for manufacturing of the containers. Analyses revealed that the construction is strong enough to withstand weapon recoil. The construction centre of gravity deviation, when carrying a counter mass to balance the construction around the elevation axis, was explored for different loading conditions. The maximum deviation obtained a value of 11 mm; a number small enough to neglect.

The concept satisfies defined requirements to a certain extent; the construction integrates CG M4 barrels on the Trackfire RWS, and is a flexible system that allows the user to choose between installing either two or four barrels. The integration utilises the same interface as the current PWI, allowing the SWI to be used as usual. All included sub-systems are easily assembled and mounted on the Trackfire.

The construction needs further attention before it can be viewed as a finished product, and to ensure remaining requirements are fulfilled. Construction dimension optimisations are recommended, and continued detail construction is necessary to complete the product. Further structural analyses need to be performed, to provide a full understanding of how the system would behave in a real life situation, and over a longer period of time.

References

[1] Saab AB. A history of high technology [internet]. [cited 2020-02-14]. Available from: https://saabgroup.com/about-company/history/

[2] Saab AB. Tidslinje [internet]. [cited 2020-02-14]. Available from: https://history.saab.com/tidslinje/

[3] Saab AB. Company In Brief [internet]. [cited 2020-02-14]. Available from: https://saabgroup.com/about-company/company-in-brief/

[4] Håland WC. The new Carl-Gustaf M4: Lighter-Better-Smarter. Small Arms Defense Journal. June 2017; Volume 9 [cited 2020-02-12]. Available from: http://www.sadefensejournal.com/wp/the-new-carl-gustaf-m4-lighter-better-smarter/

[5] Jenzen-Jones NR. Recoilless Weapons. Small Arms Survey Research Notes. December 2015; Issue 55. Available from: http://www.smallarmssurvey.org/fileadmin/docs/H- Research_Notes/SAS-Research-Note-55.pdf

[6] Saab AB. Carl-Gustaf M4 [brochure]. September 2014. Available from: https://saab.com/globalassets/commercial/land/weapon-systems/support-weapons/carl- gustaf-m4/image-download/carl-gustaf-m4_8pg_brochure_d6.pdf

[7] Saab AB. Carl-Gustaf M4: Smart just got smarter [internet]. [cited 2020-02-27]. Available from: https://saab.com/land/weapon-systems/support-weapons/carl-gustaf- m4/?gclid=Cj0KCQjwm9D0BRCMARIsAIfvfIbDtZpUxLVMQkMNCkomt5iQ2MAwpuWi0upIlwUKf 2EVKH5gi0uldAwaAnAhEALw_wcB

[8] Army Recognition. Top most modern Land RWS RCWS Remote Controlled Weapon Station combat vehicles. 26 February 2020. [cited 2020-03-03]. Available from: https://www.armyrecognition.com/weapons_defence_industry_military_technology_uk/top_mo st_modern_land_rws_rcws_remote_controlled_weapon_station_combat_vehicles.html

[9] Saab AB. Trackfire RWS: Remote Weapon and Sensor System [brochure]. Available from: https://saab.com/globalassets/commercial/naval/precision-engagement/remote-weapon- station/trackfire/trackfire_brochure_2012.pdf

[10] Saab AB. Saab förser svenska marinen med ytterligare Trackfire RWS-system. 26 February 2018 [cited 2020-02-13]. Available from: https://saabgroup.com/sv/media/news- press/news/2018-02/saab-forser-svenska-marinen-med-ytterligare-trackfire-rws-system/

[11] SOFF. Saab får en beställning av FMV på Trackfire Remote Weapon Station [internet]. [cited 2020-02-13]. Available from: https://soff.se/medlemsnyhet/saab-far-en-bestallning-av-fmv-pa- trackfire-remote-weapon-stations-saabgroup/

[12] Kongsberg. Protector Remote Weapon Station [internet]. [cited 2020-03-03]. Available from: https://www.kongsberg.com/kda/products/defence-and-security/remote-weapon- systems/protector-rws/

[13] Choi EH, Ryoo JB, Cho JR, Lim OK. Optimum suspension unit design for enhancing the mobility of wheeled armored vehicles. Journal of Mechanical Science and Technology. 2010; 24: 323-330 DOI: 10.1007/s12206-009-1102-0

[14] Försvarsmakten. Pansarterrängbil 360 [internet]. [cited 2020-02-14]. Available from: https://www.forsvarsmakten.se/sv/information-och-fakta/materiel-och- teknik/mark/pansarterrangbil-360/

[15] Försvarsmakten. Terrängbil 16 [internet]. [cited 2020-03-03]. Available from: https://www.forsvarsmakten.se/sv/information-och-fakta/materiel-och- teknik/mark/personterrangbil-6/

[16] Karlsson L. Konceptstudie: Fordonsinstallation av Carl-Gustaf [degree project]. Karlstad: Karlstad University; 2018 [cited 2020-02-13]. Available from: http://www.diva- portal.org/smash/get/diva2:1244607/FULLTEXT01.pdf

[17] Meriam JL, Kraigne LG. Engineering Mechanics: Dynamics. 7, SI version. Singapore: John Wiley & Sons Inc; 2013

[18] Nordling C, Österman J. Physics Handbook for Science and Engineering. 8:13. Lund, Sweden: Studentlitteratur AB; 2014

[19] Donald E, Jacobsen CS, Jacobsen SS. Ballistics: Theory and Design of Guns and Ammunition. 2 ed. Boca Raton, FL: Taylor & Francis Group; 2014.

[20] Engineering Design Handbook: Recoilless Rifle Weapon Systems [pamphlet]. Alexandria, VA: Department of the Army Headquarters United States Army Material Command; 1976. Available from: https://books.google.se/books?id=vfCMQVOF3CsC&pg=SA10-PA20&lpg=SA10- PA20&dq=recoilless+rifle+mechanisms&source=bl&ots=fdZZm1o82X&sig=ACfU3U0umyICBOzl ECm_iXAVyTqrYlmjHA&hl=sv&sa=X&ved=2ahUKEwjy3oWAk- _nAhX0AxAIHeNnBqgQ6AEwIHoECA8QAQ#v=onepage&q=recoilless%20rifle%20mechanisms& f=false

[21] Wu B, Zheng J, Zhang K, Tian Q, Yu X, Zou Z. Tribology of rotating band and gun barrel during engraving process under quasi-static and dynamic loading. Friction. 2014; 2(4): 330-342 DOI: 10.1007/s40544-014-0061-3

[22] Mizokami K. The Army’s Recoilless Rifle Is Getting a Huge Upgrade: Laser-Guided Warheads. Popular Mechanics. 2 October 2018. Available from: https://www.popularmechanics.com/military/weapons/a23708392/army-recoilless-rifle-carl- gustav-laser-guided-warheads/

[23] Fredriksson R, Hellberg V. Calculation of Fluid Dynamic Loads on a Projectile During Firing: Development of a CFD-modelling Approach [master’s thesis]. Linköping: Linköping University; 2016 [cited 2020-03-09]. Available from: http://www.diva- portal.org/smash/get/diva2:944956/FULLTEXT01.pdf

[24] Private communication within the company

[25] Williams D. Mechanics (including force, mass, and acceleration). Anaesthesia & Intensive Care Medicine. July 2017; Volume 18, Issue 7: 364-367 DOI: 10.1016/j.mpaic.2017.04.012

[26] Ritter AC, Needham C, Duckwort JL, Bailie JM, Wiri S. Computational modeling of blast exposure associated with recoilless weapons combat training. Shock Waves. 2017; Volume 27: 849-862. DOI: 10.1007/s00193-017-0755-3

[27] Shea D. Artillery on the Fly – The Carl Gustaf 84mm Recoilless System. Small Arms Review. 2004; Volume 7 [cited 2020-02-14]. Available from: http://www.smallarmsreview.com/display.article.cfm?idarticles=165

[28] Lastdokument CG M4 [internal company document]

[29] Carl-Gustaf M4 Description [internal company document]

[30] Dursun T, Büyükcivelek F, Utlu Ç. A review on the gun barrel vibrations and control for a main battle tank. Defence Technology. October 2017; Volume 13, Issue 5: 353-359 DOI: 10.1016/j.dt.2017.05.010

[31] System description Trackfire RWS [internal company document]

[32] Patil SR, Krishna S, Gawade SS. Praparation, Characterization and Performance Analysis of BTO Based High Yield Strength Electro-Rheological Fluid in Artillery Gun Recoil System Using FEA Approach. Materials Today: Proceedings. 2018; Volume 5, Issue 2 DOI: 10.1016/j.matpr.2017.11.512

[33] Pettersson D, Johannesson H, Persson JG. Produktutveckling: Effektiva metoder för konstruktion och design. 2. Stockholm: Liber AB; 2013

[34] Lilliesköld J, Eriksson M. Handbok för mindre projekt. 1. Stockholm: Liber AB; 2013

[35] Breiler A, Michanek J. Idéagenten: En handbok i att leda kreativa idéprocesser. 4. Malmö: Arx förlag; 2015

Appendices

Appendix 1 – Gantt-Chart

Appendix 2 – Evaluation Matrix

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Appendix 3 – List of requirements

The List of Requirements was developed using a previous study on vehicle integration between CG M4 and the Trackfire, along with feedback provided from the Life Guards regarding that study. Additional customer input as well as background research on the CG M4, Trackfire and the Patria 360 was used to establish the following List of Requirements.

Requirements regarding the system

R1: The system should integrate barrels for CG M4 on the Trackfire RWS Comment: M1-M3 barrels are considered too heavy.

R2: The system should be able to carry at least one CG M4 barrel.

R3: The construction should use the same interface for the integration used for the current Primary Weapon Interface.

R4: All barrels should be adjustable horizontally and vertically so that all barrels can be aligned.

R5: The system needs to be operable both while parked and while moving.

R6: One barrel should be fireable without the recoil affecting the position of the other barrels.

R7: Each subsystem should have a maximum weight of 20 kg. Comment: This is to make demounting of the system from the Trackfire easier, and to make sure the parts can be carried individually.

R8: Each subsystem must pass an impact test of 1 m without the functionality being affected.

R9: The system must be able to withstand regular levels of ESD without the functionality being affected.

R10: The system should be designed so that required maintenance of the system is minimised.

R11: All current CG ammunition should be usable.

R 12: The integration needs to exhibit enough flexibility to ensure that no parts of the system the Trackfire are damaged while firing.

R13: The system must be able to manage shock and vibrations arising from the new Life Cycle User Profile.

R14: The system should have a maximum weight of 100 kg, provided that the system is well balanced.

R15: The system must not require that any dimensional changes are made to the Trackfire or the CG M4 barrels.

R16: The system should be integrated so that the current secondary weapon interface can be used as usual.

R17: The barrels should be able to fire at least six shots each before they have to be realigned.

Wishes regarding the system

W1: The system should be able to carry at least four CG M4 barrels.

W2: The barrels should be equipped with splinter guards.

W3: The system should be provided with protection from tree branches and other things that might cause damage to the system.

W4: The system should require minimum changes to the Trackfire and original mechanisms and interfaces.

W5: The system should not require usage of loose tools while mounted and demounted.

W6: Manual carrying of the barrels, while unattached to the system, should be comfortable.

W7: The system should be tiltable so that the barrels can be pointed vertically, directed away from the line of sight. Comment: This enables usage of the Trackfire sight systems without the system having to look threatening. This is important if used during peace times.

W8: The barrels should revert to their original position after fired.

Requirements regarding environmental aspects

R18: No environmentally hazardous materials are to be used in the system (i.e. the system must follow the EU-laws of REACH).

R19: The system must be able to withstand long-term UV-radiation.

R20: The system must be able to withstand temperature variations from -46°C to +71°C.

R21: The system must be able to withstand submersion in water for a minimum of one hour without water entering the system and affecting its functionality.

R22: The system must be able to withstand subjection to salt spray without functionality being affected.

R23: The system must be able to withstand subjection to oils and liquids without functionality being affected.

Requirements regarding safety aspects

R24: The barrels must be positioned so that no surrounding personnel or equipment are hurt or damaged by the blast or back blast while fired.

R25: The subsystems must pass an impact test of 2.1 m without them becoming dangerous to use.

R26: Mounting and demounting of the subsystems must be quick and smooth.

R27: The system must withstand high levels of ESD.

Appendix 4 – Concept selection

Concept Selection

Concept descriptions

Ideas of concept solutions extracted from the Morphological matrix are described below. All concepts regarding positioning of barrels (designations beginning with a C) are, in theory, meant to be compatible with those concerning concepts of attachment (designations beginning with an A), and concepts of protection (designations beginning with a P). With this said, this may not practically be possible.

Model and position

Integration of 1 barrel

C1.1: Integrate 1 barrel by attaching it in the current interface. The barrel can be loaded while attached.

Integration of 2 barrels

C2.1: Integrate 2 barrels by placing one in the interface and the other on a table above. The barrels will have to be drawn out to enable loading.

C2.2: Integrate 2 barrels by placing one in the interface and the other in a drawer above. The barrels will have to be drawn out to enable loading.

C2.3: Integrate 2 barrels by placing them next to each other on a table. If placed some distance apart, the barrels can be loaded while attached.

Integration of 3 barrels

C3.1: Integrate 3 barrels by placing one barrel in the interface, two on top in a fence. If placed some distance apart, the barrels can be loaded while attached.

C3.2: Integrate 3 barrels by placing one barrel in the interface, two on top in drawers. The barrels will have to be drawn out to enable loading.

C3.3: Integrate 3 barrels by placing one barrel in the interface, two on top on a table. If placed some distance apart, the barrels can be loaded while attached.

C3.4: Integrate 3 barrels by stacking them on top of each other in drawers. The barrels will have to be drawn out to enable loading.

C3.5: Integrate 3 barrels by placing them all next to each other on a table. The barrels will have to be drawn out to enable loading.

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Integration of 4 barrels

C4.1: Integrate 4 barrels by placing one in the interface, three on top like in a fireplace. The barrels will have to be drawn out to enable loading.

C4.2: Integrate 4 barrels by placing one in the interface, three on top like on a boat. The barrels can be loaded while attached.

C4.3: Integrate 4 barrels by placing one in the interface, three on top like on a staircase. The barrels will have to be drawn out to enable loading.

C4.4: Integrate 4 barrels by placing one in the interface, three on top on a table. The barrels will have to be drawn out to enable loading.

C4.5: Integrate 4 barrels by placing one in the interface, two on top, one on top of that, in a fence. The barrels can be loaded while attached.

C4.6: Integrate 4 barrels by placing one in the interface, two on top, one on top of that, in drawers. The barrels will have to be drawn out to enable loading.

C4.7: Integrate 4 barrels by placing two next to each other, and to next to each other above the first two, like in an oven. If placed some distance apart, the barrels can be loaded while attached.

C4.8: Integrate 4 barrels by placing two next to each other, and to next to each other above the first two, like in an oven. The barrels will have to be drawn out to enable loading.

C4.9: Integrate 4 barrels by placing them in a wheel. The barrels will have to be drawn out to enable loading.

C4.10: Integrate 4 barrels by placing them like a flower. The barrels can be loaded while attached.

Recoil and attachment

A1: Use existing pic.rail; clamp or click/insert into fitting to force the barrel to stay in position. Combine with rubber clamp to dampen recoil. Comments: The pic.rail would make sure the barrel stays in position; it will not be able to rotate or move axially or horizontally. Problems: The pic.rail might not be strong enough.

A2: Use a claw or clamping screws to keep the barrel in position. Combine with rubber clamp to dampen recoil. Problems: The claw can force the barrel to keep its horizontal position but might not be able to keep it from rotating or moving axially.

A3: Use existing pic.rail; insert into fitting provided with springs for recoil dampening and positioning. Combine with a clamp or claw for additional barrel stability. Problems: Will the pic.rail be strong enough for this?

A4: Attach wire dampeners to the barrel for positioning. Problems: The wire dampeners might not be stiff enough? How are the dampeners attached to the barrel? Will they require new brackets attached to the barrel?

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A5: Use existing pic.rail; attach rail to a piece of construction mounted on rods provided with springs for recoil dampening and positioning. Possibly combine with clamp or claw for additional barrel stability. Comments: The pic.rail would make sure the barrel stays in position; it would not be able to rotate or move horizontally. The springs would dampen the recoil and return the barrel to its original axial position. Problems: The pic.rail might not be strong enough to withstand the rotation

A6: Insert barrel into a sleeve that acts as a stop mechanism. Provide the stops with springs to dampen the recoil and for positioning. Problems: Might require new brackets attached to the barrel?

A7: Attach barrel to a swing that swings back and forth when the barrel is fired. Attach barrel by using clamps to keep the barrel in position. Problems: Spacing issues?

A8: Attach new brackets to the barrel to enable an attachment that allows rotation. Mount on rods provided with springs for recoil dampening and positioning. Problems: Will require new brackets attached to the barrel.

A9: Attach new brackets to the barrel to enable a “clicking” stop mechanism. Mount on rods provided with springs for recoil dampening and positioning. Comments: Same spring principle currently used. Problems: Will require new brackets attached to the barrel.

A10: Use clamp/claw/clamping screws to attach the barrel to a construction mounted on rods provided with springs for recoil dampening. Comment: This will allow rotation of the barrel. Problems: Will the barrel keep its axial position?

Protection

P1: Use a lid or lids to cover the construction.

P2: Protection is by default provided from the construction.

P3: Use a covering clamp to protect important parts of the barrel.

P4: Clamp a cone to the barrel to prevent branches from reaching it.

Evaluation and Elimination

All concepts were tried in evaluation matrices; one matrix for concepts concerning model and positioning, and one matrix for concepts concerning recoil and attachment. The purpose of using the evaluation matrix was to compare each concept with each requirement, to see if they were fulfilled. Some requirements were only applicable for concepts regarding one of the two groups. Requirements regarding environmental aspects, impact tests, and ESD, were not included in the matrices, since these were not considered at this stage of the concept generation. An additional requirement was introduced to the matrix concerning concepts of model and positioning: E1 – The concept can be combined with at least one of the concepts for recoil and attachment.

Concept A1 was immediately eliminated since it was deemed not strong enough to handle rotation and recoil forces of a barrel. A2 and A10 were eliminated because they could not guarantee that the barrels would keep their axial position long enough to fire six shots without having to be realigned. Also, concept A4 was eliminated due to uncertainties regarding stability. Because concepts C4.9 and C4.10 could not be combined with any of the concepts for recoil and attachment, these were also eliminated.

The same principle was applied for the elimination matrix; the two groups of concepts were tried in two different matrices. Apart from the concept that did not fulfil the defined requirements, concepts C3.1, C3.4, C4.6, C4.7 and A3 were eliminated due to uncertainties regarding stability, and whether or not these concepts would be realisable.

Concepts that were approved and chosen to evaluate further were:

C1.1, C2.1, C2.2, C2.3, C3.2, C3.3, C3.5, C4.1, C4.2, C4.3, C4.4, C4.7, C4.8 A3, A4, A5, A6, A8, A9

A number of 5 individuals at SBD were shown the remaining concepts and asked to rank their three top choices from each of the two groups. The concepts were on each occasion discussed at length, to see if some concepts could be combined and/or developed further.

The by far most popular concept for attachment was A5. Concepts A4, A6 and A9 all got four points each.

While evaluating the concepts for attachment, two new concepts came to be developed; both of them combining the ideas of two of the other most popular concepts:

A11: A concept that included both the axial recoil system of concept A6, and the rotational dampening system of A9.

A12: A concept that combined the spring rod of A5, and the wire dampeners of A4.

Further evaluation resulted in three new concepts, all inspired by concept A12: A13, A14 and A15.

Concept A15 gave rise to concept A15, which in its turn, inspired the development of concept A17.

Concepts A11-A17 are described as follows:

A11: New brackets are attached to the barrel. The brackets have two pockets; one provided with rubber lining, and one with limited space. A lever or locking mechanism is inserted into the rubber lined pocket, designed to dampen the rotational recoil. Another lever in inserted into the other pocket, designed to dampen the axial recoil.

Since a lot of new concepts were developed during this process, all based on- or inspired by previous concepts, these new concepts were chosen to continue the process as ‘round 2’, leaving A1-A10 belonging to ‘round 1’. A11, A12, A13, A14, A15, A16 and A17 where thus tried in a decision matrix. A17 came out the winner; using symmetry and strength, the recoil of the barrel can be dampened axially, and hindered with some flexibility in rotation. This construction would be relatively simple while strong and flexible.

Selecting concepts for positioning of the barrels was a simpler process, since these concepts did not include too many construction details, but rather focused on where the barrels were to be placed in relation to each other and the Trackfire. Concepts C4.4 and C4.8 were the clear winners in this evaluation. Concept C4.4 would be advantageous regarding the fact that the user could choose whether to attach one, two, three, or four barrels, while still keeping the centre of gravity at the centre of the Trackfire, and thus maintaining the balance of the system. The drawback, however, would be that if four barrels were to be attached, more mass would be spread out towards the sides and above the Trackfire, which would lead to the need of a large counter mass to keep the centre of gravity at the centre of the elevation axis.

Concept C4.8 would gather the combined system mass in a more compact construction, making it easier to counter the mass. Though unlike concept C4.4, this construction would require attachment of either two or four barrels to maintain the system balance.

Concepts C4.4 and C4.8 were tried against each other in a decision matrix, where C4.8 came out the winner.

Now, the two winning systems were to be combined. Three ideas were developed: F1, F2 and F3.

No matrices were necessary to make the final decision between these three concepts; F2 was based on the idea of placing the two upper barrels a bit further ahead than the two lower barrels, to simplify the ammunition loading process. However, the back blast from the barrels would not allow this. Due to the limited amount of space allowed for the integration, the rods were placed on a diagonal line over the barrels, rather than on each side. The space issue was also why concept F3 was eliminated.

As a result of the Concept selection process, concept F1 was chosen as the final concept solution. A detailed concept description follows.

F1: Four barrels are attached, using the stacking principle of the “oven”. The construction consists of four “boxes”, all of the exact same design. These boxes are attached back-to-back, and bottom-to-bottom. This is to ensure that the weight of each subsystem is kept to a minimum, and make demounting of the subsystems as simple as possible. The construction of the four boxes is mounted on a baseplate that is attached in the PWI of the Trackfire. The baseplate is also meant to hold a counter mass required to keep the centre of gravity at the centre of the elevation axis. The barrels are provided with customised brackets designed to withstand forces that are transferred during firing of the barrel. These brackets are attached to blocks mounted on rods. The rods are provided with springs to dampen the firing recoil. The blocks are free to rotate around the rod axes, allowing for some rotational flexibility, although this concept mainly focuses on preventing rotation of the barrels, meaning that the new brackets need to exhibit a certain level of strength.

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Appendix 5 – Concept sketches

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Appendix 6 – FEA results

Axial recoil

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Rotational recoil

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Full recoil

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