DEPARTMENT OF THE ARMY TECHNICAL BULLETIN TB 9-1377-200

DEPARTMENT OF THE AIR FORCE TECHNICAL ORDER TO 11P-14

PROPELLANT

ACTUATED DEVICES

DEPARTMENTS OF THE ARMY AND THE AIR FORCE

NOVEMBER 1965

WARNING

The propellant charges contained in propellant actuated devices function at various burningrates, and yield relatively large amounts of energy and impetus, according to design.

The same degree of caution should be exercised when handling propellant actuated devicesas is used when standard ammunitions are handled. Inadvertent functioning, forcing, dropping,severe jarring, or throwing could result in damage to equipment and/or injury to personnel.

TB 9-1377-200/TO 11P-1-14

TECHNICAL BULLETIN DEPARTMENTS OF THE ARMYNo. No. 9-1377-200 AND THE AIR FORCETECHNICAL ORDERNo. 11P-1-4 WASHINGTON, D.C., 8 November 1965

PROPELLANT ACTUATED DEVICES

CHAPTER 1. INTRODUCTION..................................................................... Paragraph PagePurpose and scope.................................................................. 1 1Reporting of bulletin improvements ......................................... 2 1References.............................................................................. 3 1History..................................................................................... 4 1Uses........................................................................................ 5 2

CHAPTER 2. DESCRIPTION OF PROPELLANT ACTUATED DEVICESGeneral ................................................................................... 6 3Gas-generating devices........................................................... 7 3Stroking devices...................................................................... 8 5Special purpose devices.......................................................... 9 8Systems .................................................................................. 10 11

CHAPTER 3. BASIC DESIGNGeneral ................................................................................... 11 20Motion or time functions .......................................................... 12 20Load........................................................................................ 13 21Weight and size (envelope) ..................................................... 14 22Environment............................................................................ 15 22Heat loss ................................................................................. 16 23

CHAPTER 4. DESIGN TECHNIQUESSection I. INTRODUCTION

General ................................................................................... 17 24Design requirements................................................................ 18 24

Section II. METHOD OF FIRST ORDER APPROXIMATIONSGeneral ................................................................................... 19 24Stroke to separation ................................................................ 20 24Stroke time.............................................................................. 21 25Peak pressure ......................................................................... 22 26Propellant charge weight ......................................................... 23 26Propellant web......................................................................... 24 28Cartridge case volume............................................................. 25 28Igniter charge .......................................................................... 26 28

Section III. DESIGN STRENGTH CALCULATIONSGeneral ................................................................................... 27 28Safety factors .......................................................................... 28 29Temperature effects ................................................................ 29 29Stresses .................................................................................. 30 29Distortion-energy theory .......................................................... 31 29Length of thread engagement.................................................. 32 32

Section IV. DESIGN PROCEDURESGeneral ................................................................................... 33 32Gas-generating devices........................................................... 34 32Stroking devices...................................................................... 35 33Systems .................................................................................. 36 34

Section V. COMPONENT DESIGNCartridge ................................................................................. 37 34Body and chamber .................................................................. 38 37Piston ...................................................................................... 39 38Firing mechanism.................................................................... 40 38Locking mechanisms ............................................................... 41 41Seals ....................................................................................... 42 41

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Section VI. SPECIAL PROBLEMS ............................................................ Paragraph PageGeneral ................................................................................... 43 43Shear pins ............................................................................... 44 43Damping systems.................................................................... 45 43High-low systems .................................................................... 46 44Protective coatings .................................................................. 47 45Dissimilar metals ..................................................................... 48 45

CHAPTER 5. BALLISTIC DESIGN AND ANALYSISSection I. BALLISTIC DESIGN

General ................................................................................... 49 47Propellant parameters ............................................................. 50 48Refinements to first order approximations ............................... 51 49Development of propellant charge design................................ 52 57

Section II. MATHEMATICAL ANALYSIS OF INTERIOR BALLISTICSCatapults and removers........................................................... 53 60Thrusters ................................................................................. 54 65Initiators .................................................................................. 55 69

CHAPTER 6. DESIGN EXAMPLESSection I. GENERAL

Purpose................................................................................... 56 70Scope...................................................................................... 57 70

Section II. M3 CATAPULTGeneral ................................................................................... 58 70Design requirements................................................................ 59 70First order approximations ....................................................... 60 70Component layout ................................................................... 61 72Cartridge ................................................................................. 62 73Tubes ...................................................................................... 63 74Trunnion.................................................................................. 64 77Block ....................................................................................... 65 79Firing mechanism.................................................................... 66 80Locking mechanism................................................................. 67 81Cap ......................................................................................... 68 81Minor parts .............................................................................. 69 82

Section III. M3A1 THRUSTERGeneral ................................................................................... 70 83Design requirements................................................................ 71 83Component layout ................................................................... 72 84First order approximations ....................................................... 73 84Cartridge ................................................................................. 74 85Body........................................................................................ 75 85End cap................................................................................... 76 86Piston assembly ...................................................................... 77 86End sleeve and locking mechanism......................................... 78 88Breech..................................................................................... 79 89Firing mechanism.................................................................... 80 89Trunnion.................................................................................. 81 89

Section IV. M4 INITIATORGeneral ................................................................................... 82 90Design requirements................................................................ 83 90First order approximations ....................................................... 84 91Component layout ................................................................... 85 91Cartridge ................................................................................. 86 92Cartridge retainer .................................................................... 87 93Chamber (body) ...................................................................... 88 93Cap ......................................................................................... 89 94Firing mechanism.................................................................... 90 94Firing-pin housing.................................................................... 91 96

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CHAPTER 7. PERFORMANCE EVALUATION ............................................. Paragraph PageGeneral ................................................................................... 92 97Instrumentation........................................................................ 93 97Fixtures for performance evaluation ........................................ 94 105Development evaluation program............................................ 95 110Qualification and analysis evaluation program......................... 96 112

APPENDIX I. CONVERSION OF DISTORTION ENERGY EQUATION TOMORE USEFUL FORMS FOR PROPELLANT ACTUATEDDEVICES ................................................................................ -- 116

APPENDIX II. TABLE OF WALL RATIOS...................................................... -- 118APPENDIXIII. DERIVATION OF EQUATION USED IN DETERMINING

LENGTH OF ENGAGEMENT OF THREADS .......................... -- 120APPENDIXIV. DERIVATION OF WEB THICKNESS EQUATION FOR

TELESCOPING TUBE DEVICES ............................................ -- 121APPENDIX V. DERIVATION OF EQUATION FOR BYPASS TUBE

PRESSURE ............................................................................ -- 122APPENDIXVI. REFERENCES........................................................................ -- 124GLOSSARY......................................................................................................... -- 125

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CHAPTER 1

INTRODUCTION

1. Purpose and Scope. This bulletin is intended forthe dissemination of such general and technicalinformation concerning Propellant Actuated Devices .ismay be necessary for their care, handling andutilization. It may also be used as a reference book forall using arms and services. This bulletin is the firstpublication of its type and pertains to the history andbasic fundamentals of Propellant Actuated Devices. Itdiscusses only the basic theory and principlesunderlying the functioning and design of most devices inthis class; it does not attempt to discuss the mechanicaldetails or operating procedures that differentiate onemodel from another. General reference is made tospecific models to give the reader an overall picture ofthe development of Propellant Actuated Devices fromthe earliest date of concept.2. Reporting of Bulletin Improvements. The directreporting by the individual user of errors. omissions andrecommendations for improving this bulletin isauthorized and encouraged. DA Form 2028(Recommended Changes to DA Publications) will beused for reporting these improvements and forwardeddirect to the Commanding Officer, Frankford Arsenal,ATTN: SMUFA-M 4320, Philadelphia, Pa., 19137.3. References. Appendix VI contains a list ofreferences pertaining to Propellant Actuated Devices.Detailed information relative to specific applications canbe obtained from applicable technical manuals, as listedin DA Pam 3104.4. History. a. Prior to World War II, escape from adisabled aircraft in flight occurred in environments andat speeds that were physiologically tolerable; therefore,muscular effort usually was sufficient to separate theman from his plane. As speeds increased, it becamemore difficult to leave the aircraft safely when troubleoccurred. The technique of turning the ship onto itsback, sliding open the canopy, releasing one's safetybelt, and falling out was no longer feasible.

b. In 1943, the U.S. Army Air Corps made asurvey of emergency bail-outs that had occurred in1942. The results showed that 12.5 percent had beenfatal and 45.5 percent had resulted in injury. A similarstudy of bail-outs from fighter aircraft for the year 1943showed that 15 percent had been fatal and 47 percenthad resulted in injury.

c. The Germans were the first to take effectiveaction. A German directive was issued in 1944 requiringthat all fighter aircraft be equipped with ejection seats.The British followed with a directive in 1945 requiringthat all fighter aircraft with speeds greater than 400 mphbe equipped with ejection seats.

d. The problems of escape from pusher-typeairplanes were studied by the Aircraft Laboratory atWright Field as early as 1940. At least oneexperimental airplane made during the war is reportedto have been equipped with an escape mechanism, butit was not until 1945 that our Air Force and Navy beganserious development work on ejection seats. In August1945, the Pitman-Dunn Laboratories of the FrankfordArsenal were requested to develop ejection devicesunder the cognizance of the Special Projects Branch,Aircraft Laboratory, Engineering Division, Air MaterielCommand. Initial performance requirements of theejection devices were established on the basis of dataand information from the Aircraft and Aero-MedicalLaboratories of Engineering Division, Air MaterielCommand. With the formation of the Air Research andDevelopment Command in 1950, these laboratorieswere assigned to Wright Air Development Center.

e. Before gun-type devices could be used onpersonnel ejection seats, it was necessary to determinetolerable acceleration levels for the human body and theminimum velocity of separation necessary for ejectedpersonnel to clear the aircraft structure in flight. TheAero-Medical Laboratory had been conducting acontinuing study to determine the physiological

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limitations of the human body in the various flight suitswhich have been developed. Table I summarizes thepresent limitations outlined in the military specificationcovering the design of propellant actuated devices.

Table I. Physiological Limitations for PersonnelEjection

Maximum MaximumDirection of ejection acceleration rate of change

(g) of acceleration(g/sec)

Upward................................ 20 250Downward............................ 12 125Rearward (seat positioning) . 6 60

f. The first ejection seat catapult was standardizedin 1947 and designated the M1 Personnel Catapult. Thedesign and development of the M1 and M2 canopyremovers followed in quick succession. These earlydevices were mechanically initiated; i.e., cocked firingpins were released by rotating or withdrawing a sear.The "choke coil," bell-crank rod, and cable-actuatedsystem left much to be desired from a reliability,simplicity, and maintenance standpoint.

g. In 1949, Frankford Arsenal developed apropellant gas pressure source which was designated aninitiator. Concurrently, the Arsenal redesigned theexisting devices to incorporate a pressure-operatedfiring mechanism. The propellant gas was transmittedby hydraulic hose assemblies from the initiators to thefiring mechanisms.

h. With the advent of the B-52 airplane and itsrequirements for multi-crew, multi-functional, integratedescape system, it was realized that a new form ofpropellant actuated device (PAD) could furnish thrust toposition ejection seats, unlock hatches, stow controlcolumns, etc. In 1951, with the enthusiastic support ofthe airframe contractors and Wright Air DevelopmentCenter, Frankford Arsenal commenced the design and

development of the first series of thrusters, designatedM1, M2, M3, and M5. Since that time many new andvaried applications for propellant actuated devices havebeen found in the escape system and other weaponssystems for various services.

i. Propellant actuated devices are commonlysupplied by the Air Force as Government FurnishedEquipment (GFE). Current development andmanufacture is accomplished primarily by the MunitionsCommand at Frankford Arsenal. Approximately 175propellant actuated devices and cartridges arefabricated and over one-half have been standardizedand are available off the shelf.5. Uses. a. Although propellant actuated devices weredeveloped originally for emergency escape fromaircraft, they have been used for many other short-duration, high-force applications, such as ejecting radiobeacons in the event of a crash, supplying gas pressureto operate hydraulic pumps in missiles, releasing bombsor jettisoning stores from aircraft, and rammingprojectiles into the breech of a howitzer. Propellantactuated devices are useful in these applicationsbecause of their reliability, simplicity, light weight, smallsize, and ability to withstand long periods of storageunder extremes of environment without impairment ofreliability.

b. Propellant actuated devices have beenproposed for parachute and cargo separation, reductionof landing shock, landing gear extenders, Gatling gunand missile rotators, and life raft inflators. Applicationsin the form of rotational motors for augmenting orstarting standard engines and operation of a variedfamily of such devices in space, where weight and bulkare at a premium, is also practicable. In addition, gasservo mechanisms would eliminate some of thecommon problems inherent in hydraulic systems bysubstitution of gas which is more suitable to applicationsinvolving high temperatures and radiation. All suchdevices are capable of full output on command and maybe time phased after triggering as desired.

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CHAPTER 2

DESCRIPTION OF PROPELLANT ACTUATED DEVICES

6. General. a. The first aircraft pilot catapults andassociated devices powered by propellants were called"Cartridge Actuated Devices" (CAD), a name whicharose from the similarity in appearance between theirpropellant containers and the cartridge case for anordinary rifle. As new applications were developed, thissimilarity disappeared, but the name continued to beused. Many of the older records will show this name.OTCM 37418 dated 12 April 60 was published to changethe name of future developments of these items to"Propellant Actuated Devices" (PAD), it beingconsidered that this name more nearly expresses theirprincipal characteristic.

b. The propellant actuated devices described inthis chapter have been divided arbitrarily into threecategories: gas-generating devices, stroking devices,and special purpose devices. Although special purposedevices could be classified as essentially gas generatorsor stroking devices, they have been separated because,of specific applications.

c. Various tables list data on the physical andperformance characteristics of propellant actuateddevices already developed. Although rocket-assistedcatapults are beyond the scope of this manual, theperformance possible with these devices is compared tothat of conventional catapults.

d. Some propellant actuated devices combine theoperations of several subdevices. Such a device is theT28 initiator which combines release with amechanically operated initiator. The operation of thisand other devices incorporating separate functions is notdescribed, since an understanding of the individualfunctions is all that is necessary to understand the mostcomplex of these devices.

e. Several aircraft escape systems and missilesystems are described in order to illustrate theapplication of propellant actuated devices and

demonstrate their interrelationship in actual systems.The various means of transmitting energy from deviceto device in a system and proposed energy transmissionmethods also are discussed.7. Gas-Generating Devices. a. There are two basictypes of gas-generating devices: short duration"initiators" and long duration "gas generators." Thesedevices consist of vented chambers containingcartridges and firing mechanisms. The firingmechanisms may be operated electrically, by gaspressure, or mechanically.

b. Initiators are designed primarily to supply gaspressure to operate the firing mechanisms of otherpropellant actuated devices, but they may be used assources of energy for operating piston devices such assafety-belt releases and safety-pin extractors. Initiatorsare used extensively in aircraft to operate the firingmechanisms of propellant actuated devices, since theyeliminate cumbersome cable-pulley systems andprovide a more reliable method of triggering. Insystems where the propellant actuated device is remotefrom the initiator, intermediate initiators (gas-actuated)are used as boosters. For systems where propellantactuated devices are fired in a sequence, initiators orother PAD's may contain combustion train elements(delay elements) to delay propellant ignition for aspecific time to permit completion of another operation.A typical initiator is shown in figure 1. Comparative datafor several existing initiators are given in table II.

c. Gas generators differ from initiators since aninitiator supplies gas for much less than 1 second, whilea gas generator may supply gas for several minutes.Gas generators (fig. 2) have been used to supply gasflow to spin turbines as well as for supplying pressure tooperate pumps which supply hydraulic pressure tomissile controls. Comparative data for gas generatorsare given in table III.

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Figure 1. Mechanically operated initiator.

Table II. Comparative Data for InitiatorsWeight Chamber Delay Peak pressure†

Model (lb) volume (sec) (psi)(in.*)

Mechanically operatedM4 ................. 1.0 2.4..........2 600(12)M12................ 1.0 2.4..........1 600(12)M3 ................. 0.9 2.3............ 1000(16)M29................ 1.6 2.3............ 1000(15)M27................ 0.3 0.6............ 1200(15)T30E1 ............ 0.3 0.6............ 1200(15)M30................ 1.1 2.6..........2 1500(15)M32................ 1.1 2.6..........1 1500(15)M8 ................. 2.2 4.3............ 1800(30)

Gas operatedM6 ................ . 1.0 2.4..........2 600(12)M33................ 1.0 2.4..........1 600(12)M5 ................. 0.9 2.3............ 1000(15)M28................ 0.3 0.6............ 1200(15)T31E1 ............ 0.3 0.6............ 1200(15)M10................ 1.1 2.6..........2 1500(15)M31................ 1.1 2.6..........1 1500(15)M9 ................. 1.8 4.3............ 1600(30)†Peak pressure in 0.062 in.3 gage located at the end of alength of MS-28741-4 hose. The number following thepressure indicates the length of hose in feet between theinitiator and the gage.

Figure 2. Gas generator.

Table III. Comparative Data for Gas GeneratorsWeight Chamber Operating Operating

Model (lb) volume pressure time(in.3) (psi) (sec)

T3 .................... 25 100 2,000 90T4 .................... 30 50 1,500 480XM7 ................. 0.75 0.3 †500 0.9† At the end of 2 feet of MS-28741-4 hose.

d. In the past few years, considerable progress hasbeen made in miniaturizing initiators. For example, atypical initiator, the M3, has a chamber volume of 2.3cubic inches and weighs 0.9 pound. This device hasbeen miniaturized in the form of the T25 initiator whichhas a chamber volume of only 0.65 cubic inch and

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weighs 0.33 pound. This miniature initiator duplicatesthe performance of the M3 initiator when used with hoselengths between 3 and 15 feet.

8. Stroking Devices. a. General.(1) Stroking devices include catapults,

removers, thrusters, and ejectors. Thesedevices can be divided into two groups:those which separate permitting theescape of propellant gasses (opendevices) and those that do not separate(closed devices).

(2) Closed devices are more difficult todesign since a method of stopping thepiston or stroking member at the end ofstroke is required. The unit also must beable to withstand the maximum pressuredeveloped as no gas escapes from thesystem.

b. Catapults.(1) The catapult was developed for

emergency ejection of personnel fromaircraft. In this application, it serves is a

connecting member between thecrewman's seat and the aircraft structure.The catapult is a telescoping "open"assembly which is mounted in the aircrafton trunnions. The firing mechanism ismounted in one end of the catapult alongwith a cartridge containing at primer,igniter, and propellant. When thecartridge functions, the propellant gas fillsthe catapult and causes it to extend (fig.3). As the catapult extends, it ejects theseat from the aircraft. Table IV lists theexisting catapults and presentsperformance data for these devices as aguide to what has already provedpracticable in catapult design.

(2) Rocket-assisted catapults sustain thrustand thus increase ejection height, withoutexceeding acceleration maximums.Performance data for several rocket-assisted (catapults are presented in tableV.

Table IV. Comparative Data for Conventional CatapultsStroke Weight Maximum Maximum Rate of change Weight of(in.) propelled velocity acceleration of acceleration device

(lb) (fps) (g) (g/sec) (lb)

M6†.................................................................. 21 350 26 9 120 32M4A1 ............................................................... 45 412 37 8 70 7T15 .................................................................. 50 340 60 17.................. 11M2†.................................................................. 60 312 48 13 100 15M1A1 ............................................................... 66 312 64 15 160 8M5A1 ............................................................... 66 312 64 15 160 8T16E2 .............................................................. 71 600 23 14.................. 24T10 .................................................................. 72 363 71 17 130 16T18 .................................................................. 76 350 80 20.................. 31M3A1 ............................................................... 88 465 72 15 100 25†Multi-shot training catapult.

Table V. Comparative Data for Rocket-Assisted CatapultsCatapult Weight Total Impulse Maximum Maximum Rocket grain Weight of

stroke (In.) propelled (1b) (lb sec) velocity (fps) acceleration (g) weight (lb) device (lb)

T20 ................................................. 23 325 1,100 35 15 2.8 22XM10 .............................................. 34 350 1,650 35 12 6.0 26XM9 ................................................ 36 350 1,650 35 12 5.8 24XM12 .............................................. 40 350 1,800 40 12 6.6 29XM8 ................................................ 40 350 1,800 40 12 6.6 27XM7 ................................................ (†) 595 6,300 120 15 30.4 65† An all-rocket catapult.

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Figure 3. Operation of a conventional catapult.

c. Removers.(1) Removers (fig. 4) are "open" telescoping

devices developed to remove thecanopies from aircraft prior to personnelejection. Comparative data for variousremovers are presented in table VI.These devices are similar in design tocatapults with one important exception:

removers are de-maximum pressureproduced by the burning propellant in theevent of restrained motion of thepropelled load. This feature is describedas being able to withstand "locked-shut"firings. Also, greater acceleration ispermissible with signed to be capable ofretaining the removers (table VI) since

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Figure 4. Typical remover.

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Table VI. Comparative Data for Removers

Stroke Weight Peak Stroke Method Weight of(in.) propelled thrust time of device

(lb) (lb) (sec) initiation (lb)

T18† ................................................................ 12 320 6,000 ------ Gas 19.0M4 ................................................................... 19 300 4,100 0.1 Gas 3.8M5 ................................................................... 19 1,000 8,100 0.15 Gas 3.9M1A1 ............................................................... 23 311 3,040 0.13 Mechanical 2.1T13E1 .............................................................. 23 1,000 5,500 0.2 Gas ------T19† ................................................................ 24 230 6,000 ------ Gas 25.5M3 ................................................................... 26 311 3,145 0.15 Gas 4.4T8 .................................................................... 26 300 3,100 0.15 Gas 4.3M2A1 ............................................................... 28 311 3,145 0.15 Gas 4.4

† Electromechanical-ballistic canopy remover-actuator.

human physiological limitations are not afactor. The only limit on acceleration andrate of change of acceleration is thestrength of the aircraft structure.

(2) Electro-mechanical removers, notillustrated, utilize an aircraft's electricalpower system to allow operation of thecanopy in normal use. In emergencies,jettisoning of the canopy is accomplishedby means of a ballistic system initiated bythe pilot or other crew member.

d. Thrusters.(1) The thruster was developed to exert a

thrust, through a short stroke, to move aweight or to oppose a force. The deviceconsists of a chamber, piston, firingmechanism, and a cartridge. Thrustershave been used for operations such asseat positioning, stowing of equipment,hatch or canopy unlock, and canopyejection. Thrusters are closed devices;that is, the main piston does not separatefrom the device under any operatingcondition including "locked-shut" and "no-load" firings.

(2) Buffer or damper mechanisms (fig. 5) areused occasionally in conjunction withthrusters and, in some cases, are madean integral part of the thruster. They areused to restrict the velocity andacceleration of the propelled loadbecause of structural or humanphysiological limitations. Thrusters havebeen developed that function in theirusual manner, but also at the end of astroke, bypass gas through high-pressure

flexible hose or tubing to initiate otherpropellant actuated devices. In thisapplication, the thruster ensures theproper sequencing of operations. Anexample is one of the T25 thrusters usedin the F-106B aircraft escape system.This thruster unlocks the canopy and, atthe completion of stroke (after the canopyis unlocked), bypasses gas to fire thecanopy remover (fig. 6). Each thruster isdesigned to operate against specificconstant or varying forces.

e. Ejectors. These devices (fig. 7) consist of abody, an outside tube (slug), a firing mechanism, and acartridge. When the cartridge fires, the expandingpropellant gas ejects the slug and extracts the load towhich it is attached. A series of electrically and gasinitiated ejectors has been developed to eject dragparachutes. Table VII presents comparative data on thesize and performance of existing ejectors. This tablelike all of the others, is presented merely to show therange of devices already developed as a guide fordetermining the feasibility of proposed devices.Ejectors are applicable to many missile and dronerecovery systems and have potential Use as automaticmortar, grenade, or rocket launchers and for chest typereserve parachute deployment.

9. Special Purpose Devices. a. General. A numberof propellant actuated devices have been developed for"special" applications. Included in this category arecutters, releases, and electric ignition elements.

b. Cutter. Cable cutters have been developed thatsever cables (such as electrical cables) prior to theremoval or ejection of a canopy or seat, or the firing of amissile. Although most cable cutters were developed tosever a single cable, a cutter (T3) was designed to sever

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Figure 5. Oil damped thruster.

Figure 6. Emergency Rescue F-105B Aircraft.

a bundle of 41 electrical wires prior to the removal of theaircraft canopy. The T3 cutter has a blade attached tothe forward end of the piston. Gas produced by burningpropellant in the cartridge in the cutter propels the pistonforward, driving the blade into the wires which are to be

severed. The blade of the cutter may be coated toprevent electrical shorting as the blade passes throughthe current-carrying wires. Other cutters have beendesigned to sever the reefing lines of parachutes.Unlike cable cutters, reefing line cutters are

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Table VII. Comparative Data for Ejectors

Weight of Ejected Maximum Methoddevice (lb.) Weight Length velocity of Stroke

(lb) (in) (fps) initiation (in)

T1E1................................................................ 1.0 0.3 5 125 Mechanical 5.0T7 .................................................................... 2.0 1.0 6 340 Gas 3.0T8† .................................................................. 2.6 1.0 5.5 375 Gas 3.0T9† .................................................................. 2.6 1.0 5.5 375 Gas 3.0T10† ................................................................ 2.6 1.0 5.5 375 Electrical 3.0T11† ................................................................ 2.6 1.0 5.5 375 Electrical 3.0

† These units differ only in the mounting angle of the base plates.

mechanically initiated. (Fig. 8 shows a typical reefingline cutter.) The firing mechanism of the reefing linecutter is attached by lanyard to the shroud of aparachute. When the shroud lines are pulled taut by theopening parachute, the cable (sear) is pulled out of theend of the cutter, cocking and releasing the firingmechanism. The firing pin strikes the primer in thecartridge which ignites a delay element. After apredetermined delay, the cartridge is fired and the

propellant gas propels the cutter blade forward. Theblade shears the reefing line, passing through the holein the end of the cutter. A whole family of cartridges hasbeen developed to provide different delay times (2-, 4-,6-, 8-, and 10-second delays). The sear-type firingmechanism may be operated by pulling the cable (sear)from any angle up to and including 180° to the cuttermain axis.

Figure 7. Parachute ejector.

Figure 8. Typical reefing line cutter.

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c. Releases.(1) Releases have been developed that

disconnect the parachute from a crash-locator beacon, suspend and releasesingle lug bombs, release external storesfront aircraft, and pull safety pins fromother propellant actuated devices.

(2) The release designed to pull the safetypin of another propellant actuated deviceis shown in figure 9. It consists of acylinder (body), piston with integral pin,and locking mechanism. The release pinreplaces the safety pin in the firingmechanism of a propellant actuateddevice. The device does not contain acartridge. Propellant gas supplied to therelease unlocks the piston and causes it toretract and withdraw its pin from the firingmechanism of the device assembled to it,thereby arming the device.

(3) The type of release shown in figure 9 iscommonly used in aircraft escapesystems to unlock the firing mechanismsof initiators used to fire catapults. Inthese systems, the release is actuatedautomatically at the end of the pre-ejection cycle. This prevents personnelejection prior to performing suchoperations as seat positioning and canopyremoval.

d. Ignition Elements.(1) The electric ignition element is a device

designed to replace the firing pins andpercussion primers used with gas ormechanically fired propellant actuateddevices. Ignition elements have beendeveloped that are capable of being firedby an electrical power source such as anaircraft 28-volt dc supply. The firstignition elements developed were

designed to pass 0.5 ampere without firingand to fire when the current was 1.0ampere. This early series of ignitionelements used the body of the element fora ground. A later series of ignitionelements was designed with 4 internalpins, insulated from the body of thedevice (fig. 10). Two pins areinterconnected and provide a testingcircuit separate from the firing circuit.The other two pins are connected to thefiring circuit. This device is designed witha 1.5 ampere no-fire and a 3.5 ampereall-fire qualification.

(2) The two pins in the firing circuit areconnected to a wire filament in theelement. This wire is coated with anignition bead which is ignited when thefilament is heated by passing the requiredcurrent through it. Ignition of the beadsets off the main charge of the element.

(3) To improve the reliability of electricallyinitiated systems, auxiliary firing sources,such as electromagnetic impulsegenerators, have been developed.Electromagnetic impulse generatorscontain several bar magnets and a coil.Movement of the handle or trigger on thegenerator changes the reluctance in themagnetic circuit, generating a current inthe coil. These units have indefinite life,are unaffected by environmentalextremes, and present a fixed impedancefor circuit checking.

10. Systems. a. Aircraft Escape Systems.(1) Seat escape systems.

(a) Initially, relatively simple systemsfor canopy removal and seatejection provided for the escape of

Figure 9. Release.

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Figure 10. Electric ignition element.

personnel from fighter aircraft. Inthese systems, two separateoperations were required, andmechanical interlock ensured theorder of actuation. As the operationof aircraft became more complex,escape systems were expanded toinclude pre-ejection operations,such as stowing the control columnor positioning the seat, thus freeingthe pilot from these operations. Thedevelopment of escape systems forbomber aircraft necessitated thatinitiation be possible from severalpoints, provision be made for theescape of many crewmen and forthe stowage of equipment, crewmenbe oriented with respect to theescape exit, and delays or pausesbe part of the escape sequence.

(b) A schematic of an escape systemused in the F104B aircraft ispresented in figure 11. When thedee ring (1) is pulled, three cablesattached to it are pulled actuatingfour initiators. One M27 initiator (2)supplies gas pressure to fire theXM13 thruster (3). The XM13thruster unlocks the aircraft canopyand also twists a torque tube whichactuates an M27 initiator (4). Thisminiature initiator supplies gaspressure to fire two XM11 thrusters(5) which jettison the aircraftcanopy.

(c) Concurrently, a second M27 initiator(6), actuated by pulling the dee ring(1), supplies gas pressure to initiatean M15 thruster (7). This retractingtype thruster positions the pilot'slegs by tightening cables attachedto the pilot's ankles; as the piston ofthe thruster retracts, it actuates anM27 initiator (8), supplying gaspressure to initiate the XM10catapult (9) which ejects the pilotfrom the aircraft.

(d) The third initiator actuated bypulling the dee ring (1) is an M32delay initiator (10) which suppliesgas to fire the XM10 catapult (9)after a 1-second delay. Thisinitiator is insurance against failureof the M27 initiator actuated by theleg-positioning thruster to fire thecatapult.

(e) The fourth initiator actuated by theoriginal pull on the dee ring is anM30 delay initiator (11) whichcontains a 2-second delay element.After the delay element burns, thepropellant charge in the initiator isignited and supplies gas pressurethrough the manifold (12) to cablecutters (13), which release thepilot's legs. To insure that thecables retaining the pilot's legs are

12

Figure 11. F-104B Escape System, schematic diagram.

severed, a mechanical tripperignites an M32 initiator (15)containing a 1-second delayelement. After the delay, gaspressure from the initiator issupplied through the manifold (12)to the cable cutters (13). Gas fromthe M32 initiator (15) is alsosupplied to an M28 initiator (16)which acts as a booster andsupplies gas to operate the pilot'sMA-6 lap belt release (17) and agas generator (18). The gasgenerator supplies gas to anactuator (19) which separates thepilot from the seat.

(f) To summarize, the pilot pulls a deering and the canopy is unlocked andejected, his legs positioned, the seatejected, his legs freed, the lap beltopened, and he is separated fromthe seat, all in the proper sequence,and with parallel systems to insure

operation of the catapult and leg-positioning cable cutters.

(g) As part of the complete system, aseparate M27 initiator (20) isprovided so that the canopy can beunlocked and jettisoned, withoutinitiating the seat-ejection system.This initiator may be actuated bythe pilot (21) or from outside theaircraft (22).

(h) The F104D aircraft is a two-seataircraft with two independentescape systems. Each system isidentical to that described abovewith one exception. As in thesingle-seat aircraft, the externalcanopy jettison ring (22) isconnected to an M27 initiator (20) inthe front seat to remove the frontcanopy; however, the ring also isconnected to an M45 delay initiator,which delays 3 seconds andremoves the aft canopy.

13

The delay avoids any possibility ofthe forward canopy striking the rearcanopy as may occur should theybe jettisoned simultaneously.

(2) Capsule escape systems.(a) An escape system should allow the

crewmen to separate safely fromthe aircraft throughout the aircraft'saltitude and speed range, and todescend, with the necessarysurvival equipment, to the earth'ssurface in a physical conditionpermitting him to survive and, ifnecessary, evade or escape enemyforces. The ejection-seat escapesystem is effective in the regionbelow 600 knots IAS (indicated airspeed). Beyond 600 knots, theprobability of a safe escape with anejection-seat escape system rapidlydecreases. The Air Research andDevelopment Command requiresthat escape capsules with protectiveand survival devices be used in allnew aircraft with speeds exceeding600 knots EAS (equivalent airspeed) † and operational altitudesexceeding 50,000 feet.

(b) Figure 12 shows a nose capsuledesign based on the configuration ofan F104 type aircraft. The ejectablenose capsule is stabilized by threeswept-back, thick-wedge airfoils.

(c) The complete escape system (fig.13) is set into operation by a singleoperation of the pilot, the raising ofhis seat handle or handles (1). Thisaction starts a dual initiation systemfor all units which absolutely mustwork for a successful escape.Either or both initiators (2 and 3) firea gas generator (4) which suppliesgas pressure to actuate the pilot'sbody and foot restraint systems (5).The gas generator also suppliespressure to extend the stabilizingwedges (6, 7, and 8). Themovement of the upper wedgeunlocks the capsule air vent (9). Assoon as the top wedge (6) andeither of the lower wedges (7 or 8)are fully extended, they removestops in a valve (10). Gas from thegenerator (4) then forces a shuttle in

the valve forward and actuates fourexploding bolts A (11 and 12), a0.5-second delay initiator (13), andthe rocket motor (14). The fourexploding bolts are the onlystructural connections between thenose capsule and the rest of theairframe. If for some reason thevalving system (10) does notoperate satisfactorily, a 1-seconddelay initiator (15), previouslyactuated by the dual initiators (2and 3), will fire the rocket motor,structural disconnects (explodingbolts), and a 0.5-second delayinitiator (16). The rocket motorthrust insures separation andsufficient trajectory for parachutedeployment, even in "off therunway" escapes (fig. 14).

(d) The purpose of the two 0.5-seconddelay initiators (13 and 16) is topostpone arming the parachutelaunching sensor (17) action untilthe rocket has propelled the capsuleto maximum speed. If the capsulehas not exceeded the safeparachute launching speed at thattime, the pilot chute ejector (19) isfired, pulling the high and low speeddrogue chutes (19) out into theairstream. The drogue chutesextract the heavy main parachutebox and the main parachute isdeployed. At initial deployment, themain parachute is reefed so that itsopening shock will not be too great.After suspension line stretch, cuttingof the reefing line allows fullparachute deployment. If the pilotsenses a failure of the parachutelaunching system, he can fire asecond ejector cartridge manually(20). This is the end of the dualinitiation sequence.

(e) The remaining phases whichenhance safe escape, but are not,absolutely necessary, are actuatedfrom single sources. At the time thecapsule starts away from the parentaircraft, a lanyard from the aircraftpulls on a valve (21) in the capsuleallowing pressure remaining in the

† Equivalent air speed is the Indicated air speed corrected for compressibility. Though the difference between IAS and EAS isnegligible at low speeds and low altitudes, impact pressure upon the pitot tube at high speeds increases, causing the airspeedindicator to show values above normal.

14

Figure 12. Nose capsule.

gas generator to operate the headrestraint device (22). Anotherlanyard from the parachute riserstarts a 6-second delay initiator (23)at the time of parachute launch.This initiator releases pressure froma bottle (24) to prepare the capsulefor a landing on land or in the water.The pressure from the bottleactuates a propellant charge toshatter the glass-like radome (25),exposing a sheet metal structurewith predictable shock-absorbingcharacteristics, and allowing thecapsule's center of gravity to becloser to the ground at the time ofcontact. This reduces the capsule'stumbling tendencies in the wind.Simultaneously, gas from thepressure bottle releases the lowerriser of the parachute (26),positioning the capsule for the mostdesirable landing attitude, and gasfrom the bottle also inflates floats inthe stabilizing wedges (27). Thefloats at the ends of the lowerstabilizing wedges support the aftend of the capsule so that it isapproximately level, and reasonablystable in the water.

(f) After the capsule contacts theground or water, the pilot can, at hisdiscretion, pull a handle (28) in thecockpit to release the parachuteriser (29).

b. Missile Systems.(1) A propellant gas generator was developed

to replace the compressed gas bottle usedto pressurize the hydraulic fluid in theNIKE-AJAX guided 'missile. It wasinstalled in a missile and successfullytested on the ground.

(2) Another gas-generating system has beendeveloped for possible use in the NIKE-HERCULES guided missile. It wasdeveloped as a backup for the current,ethylene-oxide system. It has not as yetbeen used, although it has been groundtested. It is described here as anexample of missile applications.

(3) In this system, propellant gas from the T4gas generator in the auxiliary powersupply is used to operate a double-actingpump which supplies fluid to the actuatorsat 3,000±250 psi at a flow rate to meettactical demands for all anticipatedmissile maneuvers. The system isrelatively light in weight, simple in design,requires little ground maintenance, andmay be stored for long periods of time.

(4) The auxiliary power supply for the NIKE-HERCULES guided missile operates inthe following manner: Prior to launching,the T4 gas generator (fig. 15) is initiatedby the T14E2 electric ignition element.The ignition element ignites the igniterwhich, in turn, ignites the fast-burning

15

Figure 13. Nose capsule escape system, schematic diagram.

16

Figure 14. "Off the runway" ejection sequence.

propellant contained in the chamber. Asthis propellant burns, it ignites the mainpropellant charge (sustainer) contained inthe series of tubes which makes up thegas generator. The walls of the propellantgrains are inhibited so the propellant mustburn from end to end as a cigarette. Asthe stub end of the propellant stick burns,it ignites a primer cord which ignites thepropellant in the next tube, and so theburning continues for 8 minutes.

(5) Figure 16 shows the entire auxiliary powersupply system. The gas produced by theburning propellant passes through a filterin the gas generator, through an externalfilter and pressure release valve, into ashift valve (2), where it is directed intoone end of a double-acting pump. Thedouble-acting pump transforms gasenergy (3) to hydraulic fluid energy (4).By means of a 2 to 1 differential piston

area, the hydraulic fluid is pressurized to3,000 psi as the piston is stroked. Thefluid is forced through the actuatingmechanism (5) and the spent fluid isreturned to the opposite side of the pistonat a low pressure. When the pistonbottoms, the shift valve (2) exhausts thehigh pressure gas and reverses thedirection of the gas piston. The hydraulicfluid becomes pressurized in the oppositedirection, and these cycles continue untilburnout of propellant in the gas generatoroccurs (approximately 8 minutes).

(6) The surge accumulator (6) absorbs surgesof fluid and maintains a constant flowwhen the pump reverses direction. Theoil reservoir (7) contains the fluiddisplaced when the piston rod is in thepump chamber and provides backpressure in the system.

17

Figure 15. T4 gas generator.

Figure 16. NIKE-HERCULES auxiliary power supply system.

18

c. Energy Transmission in Systems.(1) In early aircraft escape systems, all

propellant actuated devices weremechanically initiated. This mechanicalinitiation required elaborate cable pulleyarrangements to release cocked firingpins by rotating or withdrawing sears. Thedrawbacks of this system are obvious.

(2) Gas-initiated systems gradually replacedthese early systems. Gas systems useteflon-lined, steel-braided hose andstainless steel tubing to transmit the gasfrom the gas-generating device to thepropellant actuated device to be operated.The gas-initiated systems not only providea more reliable means of initiating asystem of devices, but also permit the useof delay initiators and bypass thrusters tosequence operations in the system.

(3) Electrically initiated systems havereliability comparable to gas-initiatedsystems. The weight of electrical systemsis less than gas systems since allinitiators, couplings, check valves, andhigh-pressure hose can be eliminated;however, an auxiliary power source mustbe provided. Where the propellantactuated device and the initiating deviceare some distance apart, no boosterinitiators are needed. Electrical systemsoffer the advantage of economy, smallersize, easier installation, and lessmaintenance, as well as permittingcontinuity checks by pilot or ground crews.The disadvantages of electrical systemslie in their need for an external powersource and possible danger of accidentalfiring caused by stray radiation, etc.

19

CHAPTER 3

BASIC DESIGN

11. General. a. Propellant actuated devices arebasically simple devices containing a minimum numberof parts. They are light in weight, yet strong enough towithstand the maximum pressure created by burning thepropellant they contain. The materials selected for usein these parts are compatible with the propellant, igniter,and primer at various temperatures and in the functionaland storage conditions to which the parts are exposed.

b. Constant awareness of basic concepts must bemaintained when designing propellant actuated devices.Certainly the most important concept is that of reliability.Determination of how these devices will operate inconjunction with other components in a system must beestablished along with a reliable method of initiation anda simple but sure method of installation.

c. Standard parts are used wherever possible, andwhen special parts are necessary, they are designed sothat they are manufactured easily. All parts ofpropellant actuated devices are interchangeablebetween similar units, and under no conditions may thefunctional reliability of a device be dependent upon theselective fit of any or all parts. Propellant actuateddevices are designed for ease of proper assembly andwherever possible, parts are made nonreversible so thatit is impossible to assemble a component backwards.12. Motion or Time Functions . a. The function timefor propellant actuated stroking devices is the timeinterval from initiation of operation to the completion ofa stroke. This interval may vary from as little as a fewmilliseconds (some thrusters) to a quarter of a second(some catapults). Thrusters containing dampingdevices may take more than one-half a second tocomplete a stroke.

b. In the system shown in figure 17, amechanically operated initiator is connected to a thrusterby a length of hose. When the lanyard is pulled, theinitiator cartridge is fired. The burning propellant in the

initiator generates gas which flows through the hose tothe thruster. When sufficient gas pressure is exerted onthe thruster firing mechanism, the thruster cartridge isfired. As the propellant burns in the thruster, thepressure in the thruster chamber increases and causesthe thruster piston to extend, moving a body (load). Acurve showing the relationship of pressure to time withinthe thruster is presented in figure 18.

c. Point A in figure 18 represents the instant theinitiator functions and point B represents the momentthe thruster firing mechanism is operated. Point C is thetime internal gas pressure is first noted in the thruster,and point D is the time peak pressure occurs. Point Erepresents the instant the thruster piston is fullyextended.

d. If it is assumed that piston motion starts at pointC (when pressure is first developed in the thruster), theactual work cycle of the device extends from point C topoint E. However, thrusters normally have initial lockingarrangements (to prevent the piston from extendingprior to the time the thruster cartridge fires), and theinitial lock is released when the pressure reaches someintermediate point between C and D.

Figure 17. A simple PAD system.

20

Figure 18. Pressure-time curve for system offigure 17.

e. Every effort is made to minimize the time frompoint A to point C. The exception to this is in the designof the delay initiator. The time from point A to point B isincreased intentionally to establish a specific sequenceof operations. The delay function of the initiator is amajor consideration in designing elaborate systems.The span of time from B to C is referred to as ignitiondelay (the interval between actuating the firingmechanism and the beginning of sustained rise ofpressure in the propellant chamber).

f. The C to D span may be the most important forit is during this pressure rise time that such importantperformance characteristics as rate of change ofacceleration are determined. Furthermore, this C to Dspan affects the selection of propellant, propellantgeometry (perforations and web, etc.), internal volume,and expansion ratio (the ratio of final internal volume toinitial internal volume). The time from C to D variesfrom a few milliseconds for releases and initiators to 100or more milliseconds for some catapults. The ballisticdesign chapter 5 of this manual discusses this importantinterval in detail.

g. Peak pressure (point D) also is important sinceit determines maximum acceleration, charge weight,and the working pressure the unit must withstand. Thisworking pressure affects the piston size, the wallthickness, material selection, and overall weight.

h. Finally, the interval from point D to point Erepresents the remaining time required to complete thepiston stroke. Most of the piston movement occursduring this interval, and so it is during this time that

velocity and acceleration can be controlled mosteffectively. Without acceleration control, the maximumvelocity normally occurs at time E, the end of the stroke.

i. Acceleration and rate of change of accelerationof a device are controlled by the selection of internalballistic parameters. Occasionally, further control iseffected by the addition of a buffer or damper. Externaldampers were used in earlier propellant actuateddevices, and internal dampers have been usedsuccessfully in several recently designed thrusters.Figure 5 illustrates the operation of an oil-dampedthruster. The spring acting against the floating piston iscompressed or extended as the buffer fluid reacts totemperature changes. When the thruster is fired, theexpanding gas drives the floating piston against thefluid, exerting pressure on the main piston. The mainpiston begins its stroke when the pressure buildup issufficient to shear the locking pin (fig. 5). The fluidsurrounding the main piston is then forced through theorifice into the volume between the floating piston andthe main piston. The velocity of the main piston is afunction of the viscosity of the buffer fluid, the orificearea, and the difference in force due to the samepressure acting against a large area on one side of themain piston and on a considerably smaller area on theopposite side.

j. Motion is not only controlled by grain design andby the addition of dampers but may also be controlledballistically by metering the flow of propellant gasthrough an orifice. A high-low system is an example ofballistic control. In a high-low system, the propellant isburned in a chamber and the gas is bled from thischamber into a much larger chamber through an orifice.Thus, the propellant is burned at high pressures (whichare conducive to good burning) while the stroke iscontrolled by the low pressure gas in the large chamber.

k. A pressure relief valve can also be used tocontrol the motion of a propellant actuated deviceballistically by dumping the gas that would causeexcessive acceleration. Throughout the stroke, thevalve opens and closes to maintain a nearly constantpressure within the device.13. Load. The load experienced by the piston of athruster is the total of all forces acting on the thruster.Propellant actuated devices may be subject to loadswhich assist as well as resist motion. These loadsinclude the inertia forces of the mass of the body beingpropelled and the moving parts of the propellantactuated device, initial and final locks (if used), friction

21

forces, and damping forces (if a damper is used). Inaircraft installations, friction and bending forces may bepresent in the tubes of catapults and removers as aresult of aircraft maneuvers and aerodynamic loads.14. Weight and Size (Envelope). a. Weight and size,although subordinate to reliability, generally are criticalconsiderations in aircraft or missile installations. Thedesign of the propellant actuated device is dependentupon a specific space allocation, which can result inmounting problems, insufficient actuator stroke for thetask, and complicated mechanical and ballistic designs.As an example, space limitations can cause a deviceswhich could be fabricated easily from a single long tubewith piston, chamber, and end connections all on thesame axis, to be designed with telescoping tubes or in afolded or stacked configuration, as shown in figure 19.

b. To reduce weight, it is necessary to operate withworking stresses which approach the yield stresses ofthe materials used. The sizes of the parts are adjustedand readjusted to provide safety factors whichexperience has indicated will produce a reliable item.The safety factors used are covered in paragraph 28.

c. The selection of materials for propellantactuated devices entails more than just strength andweight consideration. Resistance to corrosion, ease offabrication, and resistance to erosion and chemicalaction with propellants or damper fluids also are factors.15. Environment. a. In aircraft applications,propellant actuated devices are exposed totemperatures within the range of -65° to +200°F.Propellant, primers, and all mechanical parts must be

selected so that they operate throughout this range withminimum variation in performance. Particular attentionmust be given to the selection of nonmetallic materialswhich may age and cease to function properly. Thecoefficient of expansion and the viscosity of dampingand buffing fluids also are important considerationsbecause of this wide temperature range.

b. Propellant actuated devices are supplied assealed units to prevent moisture or dirt entering duringlong storage periods (as long as 3 years either on ashelf or mounted in an aircraft). As added insurance,cartridges are hermetically sealed, and are replacedperiodically to prevent propellant aging from adverselyaffecting performance.

c. Threaded connections must be capable ofwithstanding torque tests as insurance against looseningwhen exposed to vibrations encountered in handling,shipment, or installation. A Nylok pellet, inserted in thethreaded joint, creates sufficient friction to preventloosening, yet the device may be disassembled byapplying sufficient torque. Staking the threads is notconsidered an acceptable way of meeting vibration(torque) requirements if the device contains a cartridge,since the device may require disassembly.

d. If a propellant actuated device can survive a 6-foot drop onto concrete, it can withstand the maximumshock which will occur in service. Devices, therefore,are designed to withstand this drop test, which meansthat the propellant grains will not shatter and the firingmechanism will not function as a result of the shock.The design of shear pins used to retain the firing pins in

Figure 19. Thruster with stacked configuration.

22

gas-actuated device is critical: the pins must withstandthe shock of the drop test and yet shear when the firingpin is subjected to a specific gas pressure. The conceptof shear pins is presented in chapter 4.16. Heat Loss. a. A highly theoretical discussion ofheat loss is unnecessary in the design of propellantactuated devices. It is important, however, that severalfactors be understood. To minimize heat loss, the metalsurface in contact with the hot propellant gas should bekept to a minimum, consistent with the chamber volumerequired. Heat loss has a great effect on devices whichretain or produce hot propellant gas for a long period oftime (gas generators) ; the chamber walls absorb heat,thus lowering the temperature of the gas in the chamber

and, consequently, reducing the pressure of the gasremaining in the chamber.

b. In transferring hot gas from one chamber toanother, as with initiators, teflon-lined hose is usedprimarily because it absorbs less heat than stainlesssteel tubing and introduces less friction loss than rubberhose.

c. In preliminary designs of propellant actuateddevices, it is common to assume the devices to be 8 to10 percent efficient. No attempt is made to calculatethe actual losses due to heat and friction, but rather, theabove efficiency is assumed and adjustments in energyrequirements are made during testing.

23

CHAPTER 4

DESIGN TECHNIQUES

Section I. INTRODUCTION

17. General. This chapter provides a basic knowledgeof the preliminary design of propellant actuated devices.Methods of approximating parameters not generallygiven in design requirements are presented. Materials,safety factors, and methods of calculating wall strengthsand selecting tube sizes to be used in propellantactuated devices are discussed. The design ofindividual components of the devices is described, andthe use of protective finishes and dissimilar metals isoutlined.18. Design Requirements. The customary startingpoint in the design of propellant actuated devices is therequirements which list in detail the size, weight,strength, and performance of the device. A typical listof design requirements includes the following.

a. Maximum envelope dimensions.b. Maximum weight.

c. Method of initiation.d. Minimum mounting strength (structural loads).e. Open or closed type system.f. Initial and/or final lock requirements.g. Propelled mass.h. Velocity.i. Maximum acceleration.j. Maximum rate of change of acceleration.

k. Ignition delay.l. Resisting or assisting forces.

m. Strokes (must be compatible with h, i, and jabove).

n. Special requirements such as bypass and bufferor damper requirements.

Section II. METHOD OF FIRST ORDER APPROXIMATIONS

19. General. Not all significant parameters are definedin design requirements. The design requirements mayspecify acceleration, rate of change of acceleration, andvelocity, but, not the stroke necessary to satisfy theserequirements. Stroke and velocity but not accelerationmay be specified for thrusters. The envelopespecifications may give exterior dimensions but not theinternal volume and expansion ratio nor the propellantcharge and cartridge size. The unspecified parametersmust be determined by the designer in conjunction withthe ballistician. Methods of approximating stroke, stroketime, working pressures, and propellant charges arepresented here. The last parameter is treated in greaterdetail in chapter 5.

20. Stroke to Separation. a. The requirements forcatapults, removers, and occasionally thrusters specifyterminal velocity, v, maximum acceleration, am, andmaximum rate of change of acceleration, a°. Thestroke, S, of such devices can be estimated by using thefollowing equation, the derivation of which is containedin chapter 5.

b. The M5 catapult, for example, has the followingperformance characteristics when fired at 70°F.:

† The quantities used here are the actual quantities measured during the development of the M5 Catapult. They are used in

these equations to illustrate the usability of the equations. The acceleration and rate of change of acceleration are usually given asspecified maxima. The values of these two quantities to be used in these equations for preliminary design are chosen by the designerfrom experience. Chapter 6 gives step-by-step use of the equations for some examples.

24

Using equation (1) to determine the necessary stroke,

The actual stroke of the M5 catapult is 66 inches.c. The relationship of stroke and velocity for

several values of acceleration also is shown graphicallyin figure 20. The performance curves were plottedusing equation (1). The maximum acceleration curvesshown were chosen near those which are acceptable for

pilot ejection catapults. Using the 15g curve of figure 20instead of the equation would have yielded a similarresult. To use the curve, locate the intersection of thedesired final velocity (abscissa) with the curverepresenting the allowable acceleration. The ordinate ofthis intersection is the required stroke, which in theexample is 65 inches.21. Stroke Time. The time tm, required for a propellantactuated device to complete its stroke may be estimatedfrom the equation:

Figure 20. Curves for estimating performance.

25

(2)Where a° is the maximum rate of change ofacceleration. The use of equation (2) is demonstratedby the following calculation which was made todetermine the stroke time of the M5 catapult. The M5catapult has the following performance characteristics:

The stroke for the M5 catapult actually is 0.220 seconds.22. Peak Pressure. a. The relationship between peakpressure, P, and piston area or tube area, A, may beestimated by using Newton's Law (F=ma) andsubstituting PA for force, F, where m is the propelledmass and am the maximum acceleration.

PA=mam (3)Equation (3) may be used to determine the piston ortube area if a specific pressure is desired, or it may beused to determine the peak pressure if the area isestablished.

b. The characteristics of the M5 catapult are usedagain in the following calculation as an example of howto use equation (3). The propelled mass is 312/g slugsand the tube area is 2.65† + square inches. Therefore:

The actual peak pressure in the M5 catapult is 1800 psi.23. Propellant Charge Weight. a. Catapults andRemovers.

(1) A first order design approximation of thepropellant charge weight for catapults andremovers may be found by using figure21. This figure is based on the equation:

Where:c=charge weight (grams)

W=propelled weight (pounds)k=a constant (6.25X10-5 for catapults and 5.38X

10-5 for removers)v=terminal velocity (fps)

(2) Equation (4) is a simplification of equation(31) presented in Chapter 5. Thederivation of the constants§ used inequation (4) is presented in "Refinementsto First Order Equations," in Chapter 5.

(3) To use the curves of figure 21 inapproximating the propellant charge in acatapult (the M5 catapult for example)find the intersection of the terminalvelocity (64 fps) abscissa and the catapultcurve. The ordinate of this point (0.26gm/lb) is the ratio of the charge weight tothe propelled weight. Since the propelledweight is 312 pounds, multiply the ratiofound in figure 21 by 312 pounds and theapproximate charge weight is found to be81 grams. This is a reasonable estimatesince the actual charge weight of the M5catapult is 84.5 grams.

(4) A similar procedure is followed whenestimating the charge weight of aremover, except the remover curve isused.

b. Thrusters.(1) Figure 22 is used, in a manner similar to

that outlined above, to estimate thepropellant charge for a thruster. Twocurves are presented in figure 23,showing two groups of propellants ofdifferent impetus which are used instroking devices. The curves are plottedfrom equation (5) which is derived inchapter 5.

Where:c=charge weight (grams)k=a constant (based on the propellant used)Fr=resistive force (pounds)S=stroke (inches)

† Refer to footnote on page 24.‡ Chosen on the basis of installed dimensions and dimensions) of standard tubing.§ Different constants are used for catapults and removers since the characteristic propellant composition and energy losses for

these two types of devices are different.

26

Figure 21. Curve for approximating propellant charge for catapults and removers.

27

Figure 22. Curve for approximating propellantcharge for thrusters.

(2) To determine the charge weight for athruster, calculate the energy expended indoing the required work (in inch pounds).Then find the intersection of thatparticular abscissa with the curverepresenting the propellant to be used,and the ordinate of that intersectionrepresents the approximate charge (ingrams).

24. Propellant Web. The web is the minimumthickness of the grain between any two adjacentsurfaces of the propellant and the initial propellant webin inches, w, may be estimated from equation (6):

w=1.4 C'Ptm (6)where C'=pressure coefficient of linear burning rate ofthe propellant (of the order of 2 X 10-4 in./sec/psi). Asbefore, P is peak pressure (1,800 psi) and tm is stroketime (0.210 sec), for the M5 catapult.

Therefore:W= 1.4 X 2 X 10-4 X 1,800 X 0.210W=0.11 inchThe actual web is 0.110 inch.

This equation may be applied to catapults, removers,and thrusters, remembering that it is only a first orderapproximation.25. Cartridge Case Volume. a. The cartridge casevolume is usually estimated in one of two ways,depending upon the size of the individual propellantgrains. If the grains are "small" and will be orientedrandomly when loaded into the cartridge case, theloading density is taken to be about 30 in.3/lb ofpropellant. For an example, suppose it is estimated that8 grams of propellant in the configuration of a cylinder0.25 inch long by 0.10 inch outside diameter arerequired for a thruster application. The case volumerequired would then be estimated as:

30 in.3/lb X 8 gm x lb/454 gm = 0.53 in.3

Additional volume also must be provided for the casecap and igniter charge retainer. This must bedetermined after estimation of the igniter charge volumeby a preliminary design of the head cap.

b. If "large"' grains are to be used, they may beloaded iii some definite geometrical armament. Thegrains are then stacked in the cartridge with theircenterlines parallel to the centerline of the case. Thecase volume is then estimated by the size and numberof the grains and their geometrical arrangement. This isdiscussed in section II, chapter 6, in the design exampleon the M3 Catapult.26. Igniter Charge. The igniter used in most propellantactuated devices developed up to the present time hasbeen black powder. A rule of thumb that has evolved toestimate igniter charge weight is the use of about 40grams of black powder per pound of propellant. Thisestimated igniter charge may have to be increased ordecreased depending upon results of firings between -65° F. and 200° F.

Section III. DESIGN STRENGTH CALCULATIONS

27. General. a. In most propellant actuated deviceapplications, minimizing the weight of assemblies is aprimary consideration. For this reason, materials whichpossess a high strength-to-weight ratio, such as heat-treated alloy steels and high-strength aluminum,

commonly are used. Critically stressed port ions ofcomponents of propellant actuated devices are designedso that material is used efficiently.

b. Resulphurized steels are never used, since

28

they contain iron sulphide "stringers" or microstructuralsulphide inclusions, oriented in the direction of working,and normal to the most critical stress, and thus areinadequate in devices with high internal pressures.28. Safety Factors. a. Safety factors used in thedesign of propellant actuated devices may appear low,but they are adequate because they are subjected onlyto controlled loads.

b. Safety factor of a part is established as a ratioof the limiting stress to the design stress. All conditionshaving an effect on the stress is included in thedetermination.

c. Limiting stresses of pressure containingstructures is based on the minimum yield strength of thematerial, and the design stress is based on theDistortion Energy Theory in accordance with the vonMises-Hencky Concept. Utilizing this theory, theminimum factor of safety of the cylindrical section orwall of the pressure chamber is 1.15.

d. The limiting stress of all other components alsocorresponds to the minimum yield strength, but aminimum factor of safety of 1.5 is applied. In the caseswhere shock or impact loads are applied, the minimumfactor of safety is 2.0.29. Temperature Effects. Temperature has a markedeffect on the mechanical properties of metals at hightemperatures. The burning of propellant in the device isfor so short a time that the metal parts are unable toabsorb much heat; consequently, a negligibletemperature increase is experienced. In addition,propellant actuated devices are not exposed to ambienttemperatures exceeding 200° F., and the change instrength at 200° F. is small and may be neglected.30. Stresses. When calculating the sizes of metalparts to withstand the internal pressures of propellantactuated devices, it is necessary to consider thestresses at the weakest part of the tubes, commonly atthe undercut at the end of the threads. The gaspressure inside the device produces a direct radialcompressive stress which is greatest on the inside wall,and induces a tangential stress (hoop stress) which isgreatest also at the inside wall. In undamped strokingdevices, the stresses are biaxial (radial and tangential),but occasionally a longitudinal stress is introduced in thetube due to axial loading and the stresses becometriaxial. Biaxial stresses put greater strains on materialsthan triaxial stresses when the directions of strain aredirected as they are in cylindrical pressure vessels.

31. Distortion-Energy Theory. a. The distortion-energy theory of failure (von Mises-Hencky) is theaccepted criterion for the design of ductile materialsunder combined loads. This theory defines anequivalent stress that exists for a combined loading.The distortion-energy equation for triaxial stresses givenin equation (7),

is shown in more useful forms in equations (8) and (9).The conversion of equation (7) to the forms of (8) and(9) is shown in appendix I.

Where:P=maximum pressureY=yield strength of materialW=wall ratio

When a device is designed to withstand only biaxialstresses, equation (10) may be used.

b. The convenience of these forms of thedistortion-energy equation is apparent when it is realizedthat the internal pressure, P, can be estimated and thestrength of the material, Y, may be found in mostengineering handbooks. The wall ratio (ratio of OD toID) and a tube size can then be calculated. Appendix IIcontains a table of wall ratios for values of P/Y from0.010 to 0.200. This table was calculated from theformulas presented in this section. Figure 23 presentscurves of P/Y as a function of W for biaxial and triaxialstresses, based on the tables of appendix II.

c. The wall ratio, W, may be used to determine thetube size. Tubing is supplied in standard sizes and itmay be necessary to use a tube which is stronger thanrequired (higher W) to avoid the expense of usingspecial size tubing. Tubing sizes are presented inmilitary standards.

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Figure 23. Biaxial and triaxial strength curves (sheet 1 of 2).

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Figure 23. Biaxial and triaxial strength curves (sheet 2 of 2).

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d. The tables of appendix II or figure 23 also maybe used to determine the maximum permissiblepressure when the tube size is specified. For example,the maximum pressure permissible with a tube whosedimensions are 1.500 outside diameter and 1.248 insidediameter may be found as follows:

Assuming that there are triaxial stresses, P/Y=0.170 isobtained from the tables in appendix II. If the material issteel with a value of Y=125,000 psi, then P=0.1770 X125,000 =21,250 psi.

e. Conversely, the maximum pressure could havebeen estimated and the wall ratio taken from the table offigure 23. From the estimated OD or that specified bythe envelope drawing, the necessary ID can becalculated. The tubing size specified in the militarystandards most closely approximating these dimensionswould be used.

32. Length of Thread Engagement. After calculatingthe tubing size necessary to withstand the stressesinvolved, the second most important calculations arethose for determining the length of engagement ofthreads. Threads are designed in accordance withBureau of Standards specifications. The length of thesethreads may be calculated by using equation (11). (Thederivation of equation (11) is given in appendix III.)

Where:L=length of engagement of threadsP=maximum internal pressureS3=shear strengthR=major radius of female (max)d=minor diameter of male (min)

This equation includes a 1.5 safety factor to allow fortolerances and the distribution of stresses within theengagement.

Section IV. DESIGN PROCEDURES

33. General. a. Typical procedures are presented herewhich, with some variations, are used in the design ofpropellant actuated devices. The procedures havearbitrarily been divided into three categories: gas-generating devices, stroking devices, and (multi-device)systems. The design of special purpose devices (suchas cable cutters and gas operated trigger mechanisms)is similar to that of gas-generating and stroking devices,so it was not considered necessary to discuss theseseparately.

b. The discussion of systems, unlike those for thegas-generating and stroking devices, does not presentdesign procedures, but rather presents material on howsystems are established and their reliability maintained.34. Gas-Generating Devices. a. The designrequirements for gas-generating devices specify thepressure that is to be generated and where it is to bemeasured. For example, an initiator may be required toproduce a pressure of 500 psi in an 0.062-cubic-inchchamber at the end of a 15-foot tube. Using theenvelope specified, the designer estimates the internalvolume of the initiator, the volume of the tubing to beused, and the volume of the chamber in which thepressure is to be measured (fig. 24).

Figure 24. Simple PAD system using an initiator.

b. The ballistician uses these three values toestimate the propellant charge necessary to produce therequired pressure. The method of estimating thispressure is described in the ballistics design discussion(chap. 5). The designer then calculates the maximumpressure which may be developed in the initiator whenthe device is fired "locked shut." (The chamber is closedso that the internal volume of the chamber must containall of the gas generated by the burning propellant.) Thestrength of the walls is calculated from the "locked shut"pressure, using the curves or tables describedpreviously.

c. To estimate the locked-shut pressure, the "gaslaw" is approximated as shown below:

† The smallest possible OD and largest possible ID are used. The numbers 0.016 and 0.008 are tolerances.

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Where:P=maximum gas pressure (psi)V=volume (in.3)C=charge weight (lb)F=the impetus of the propellant (ft-lb/lb)

The factor 12 is used to permit the use of inch units inthe gas law. Rewriting equation (12) using theequivalents indicated, and introducing a factor (454) topermit the charge to be given in grams, yields

d. To illustrate the use of this equation, assume aninitiator is to be designed with an internal volume of 2.3cubic inches. The ballistician determines that 3 gramsof propellant of F=360,000 ft-lb/lb is required. Applyingequation (13),

Since the maximum pressure which can be produced is12,400 psi, this value and the value of Y correspondingto the material may be used in the curve (fig. 23) todetermine the wall ratio and, therefore, the thickness ofthe wall.

e. It is common practice to fabricate the first modelof a device (workhorse model) out of steel and to makeit considerably stronger than necessary so that theoperation of the device and the actual pressures whichare generated can be studied. This workhorse modelalso permits repeated firings whereas the final product,in most cases, is designed as a one-shot item.Considerable fabrication cost and time may be saved bythe liberal use of removable portions on original testmodels of propellant actuated devices. These portionscan be removed and modified without necessitatingredesign of the complete device.35. Stroking Devices. a. The design procedure forstroking devices is more complex than that for gasgenerators. After the design requirements have beenexamined and the stroke length and stroke timeapproximated, it must be decided whether to use anopen or a closed system and whether or not to use adamper to control the stroke. (A closed system is

sometimes a military requirement: e.g., thrusters.) Thedecision on the damper is based on the estimated stroketime and required velocity or acceleration. Damperdesign is discussed in paragraph 45.

b. The next consideration is the envelope of thestroking device. The envelope dimensions may bespecified with a complete drawing or only a fewmaximum dimensions may be given. In the latter case,the designer determines all dimensions. The designernow positions the trunnions on the envelope accordingto the eventual installation of the device. (The purposeof using trunnions for mounting is to permit selfalignment; and thus avoid bending loads in strokingdevices.) With all of the above completed, it is thendetermined whether the envelope will permit thenecessary stroke. Thrusters have been developed withas many as 3 moving tubes (fig. 25) to reconcile thenecessary stroke with the specified envelope.

c. It is now possible to compute the initial volume(available to the powder gases) and the final volume(the volume at end of stroke or where the tubesseparate) and determine the expansion ratio. Theexpansion ratio of a device is the ratio of the finalvolume to the original volume. It is customary inpropellant actuated devices to limit the expansion ratioto 3 to 1, although several devices have had ratiosgreater than 4 to 1.

d. In an effort to enlarge the initial volume of adevice (and therefore reduce the expansion ratio), manydevices are designed with holes in the walls of the insidetubes to permit gas to flow around the tubes as well aswithin the tubes. Figure 25 shows a thruster with thisdesign feature. Gas flowing outside as well as within thetubes also eliminates large pressure differentials andpermits the inside tube walls to be made thinner andlighter.

e. Ballistics, in conjunction with the design, nowdetermines the charge and cartridge sizes necessary.These determinations are critical for devices usingpyrotechnic delay elements, since the delay elementsmust fit inside the cartridge case with the propellant.The maximum pressure to be developed is alsodetermined. If the device is to bypass pressure at theend of stroke, it must be insured that sufficient energyremains in the device after completing its stroke topermit the proper energy bypass.

f. The next step is to fit a firing mechanism to thedevice and design the individual components. Anychanges in design that are necessary are made, and a

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Figure 25. T28 Thruster.

workhorse model is fabricated and tested. Theprocedure then becomes one of modification and retestuntil the design specifications are satisfied with the mostefficient arrangement of components.

g. A portion of the design and testing phases maybe eliminated by using computers. An analog computerhas been used for analyzing a catapult's performancetheoretically under various acceleration loads andfriction forces.36. Systems. a. Multi-component PAD systemsgenerally are designed by the air-frame or missilemanufacturer under the direction of the cognizantagency. However, in the design of propellant actuateddevices, systems can be improved by eliminatingdevices or combining several operations into one deviceto improve reliability and guarantee proper operatingsequence of the system.

b. The sequencing of operations is determined by

experience with previous systems, but the testing phaseis the major determinant. Systems are tested onbreadboard mockups and on rocket sleds at variousspeeds to determine the overall operation of eachdevice in conjunction with every other device.

c. The operation of devices in a system may besequenced by mechanical means such as gear trains orstatic lines; however, the most common method isthrough pyrotechnic delays and bypass fittings on theends of propellant actuated devices. Many pyrotechnicdelays have been standardized, but their metal partsoften are modified to insure the proper fit in the variouscartridge cases. The tubing, hose, and gas fittings usedin these systems are also standardized. Various fittingsand types of hose or tubing have been studied, butstandardization has not reached the point of determiningequivalent lengths of hose for fittings, as is done in thehydraulics industry.

Section V. COMPONENT DESIGN

37. Cartridge. a. General.(1) The cartridge (fig. 26) is a metal can

which contains the propellant, igniter, andprimer. It is designed to burst open fromthe pressure of the propellant gases. Thecan (case) is hermetically sealed to keepout moisture (moisture interferes seriouslywith performance). The hard