A Method for Determining the Effects of Overpressure from Small/Medium Weapons Fire Abstract August 2011

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2 Small Arms Air Plaform Inegraion A Meho for Deermining he Effecs of Overpressure from Small/Meium Weapons Fire Absrac Augus 2011 Seven L. Backer Crane Division, Naval Surface Warfare Cener (NSWC Crane) Com (812) DSN Seven.backer@navy.mil 2

3 Small Arms Air Plaform Inegraion Small/Meium Caliber Weapons on Air Plaforms SH-60S Arme Helicoper GAU-21 (.50-cal) M mm 20 mm Weapon Sysems RAMICS Aircraf Skin Limis 3

4 Shockwaves Shockwave - a region across which here is a rapi pressure, emperaure an ensiy rise, usually cause by a boy moving supersonically in a gas or by a eonaion Characerisics: Near-isconinuous pressure rise Exponenial ecay. Posiive Phase uraion. Relaively shor uraion. Negaive phase. Depenen on angle of incience. 4

5 Shock Waves from Gunfire Non-ieal source. Source is no a eonaion. Similar o Shocking Up 5

6 Shock Waves from Gunfire Shocking Up 6

7 Shock Waves from Gunfire Measuremen may see boh projecile shockwave (N-wave) an he Muzzle Blas 7

8 Shock Measuremens PCB Moel 137A23 Blas Probe (Incien Pressure) Enevco Moel 8515C-15 Pressure Sensor (Reflece Pressure) 8

9 Incien Pressure vs. Reflece Pressure (Ieal) 9

10 Angle of Incience 10

11 Downrange Disance (in) GAU-21 Daa Posiion P S I W A V E , 30 6, 20 6, 10 6, , , , , Off Axis Disance (in) Table 1. Raw Daa Tes Peak Incien (Sie-On) Overpressure (psig) Posiive Phase Duraion (ms) Incien Impulse (psi-ms) m S Table 2. Some Calculae Daa Tes Reflece Overpressure Incien Impulse (psi-ms) Calculae Equivalen Weigh of TNT (lbs)

12 Biggs, Inroucion o Srucural Dynamics, MIT, Assume unampe linear spring-mass sysem DLF y s - Generaes a General Response Equaion y y - For Triangular Force Inpu, y y 0 cos sin y f ( )sin 0 s ( ) 0 f f ( ( ) ) 1 0,, - Subsiuing, Inegraing an Simplifying, DLF DLF 1 1 cos sin sin sin (, ) cos, 12

13 Dynamic Loa Facor (DLF) Differeniaing, equaing o 0 an ploing versus T/T, Righ Sie (/T)>5 Lef Sie /T<0.1 13

14 Using DLF Require Values From Pressure Measuremens T = Posiive Phase Duraion P r = Peak Dynamic Pressure applie o surface From Srucure T n = Naural Perio f» Reference () gives a formula o eermine he naural frequency of a fla plae wih all of he eges fixe or simply suppore (Table 36; cases 15&16): K Dg 1 2 wa 4 where, K 1 =23.6 for a recangular plae wih fixe eges an K1 = 11.5 for recangular plae wih simply suppore eges E = Moulus of Elasiciy for maerial = Poisson s Raio for he maerial g = graviaional consan w = uni loa per uni area incluing weigh of plae a = lengh of shor ege of plae 14

15 GAU21/H-60S on full rear rain Impinges on an 18 X 7.25 panel T n = 3.88 ms for fixe eges T n = 7.97 ms for imply suppore ege Wors pressure case from GAU-21 esing P r = psi T = ms T/Tn = for Fixe DLF max = 0.33 T/Tn = for Simple DLF max =

16 Equivalen Saic Pressure P eq = P r * DLF max Fixe Eges P eq = psi * 0.33 = 6.65 psi Simply Suppore Ege P eq = psi *0.17 = 3.42 psi 16

17 Alernaives an Caveas Alernaive - Dynamic FEA Only he simples of srucures can be han cranke. FEA may be ineviable. Doesn ake ino accoun flexing of he supporing srucure. Pressure profiles for weapons are har o come by an o no mach pressure versus isance equaions for explosives 17

18 Conclusions Tha s why helicopers on fall ou of he sky when hey fire heir weapons. 18

19 Small Arms Air Plaform Inegraion Thank you for your ime an aenion! For more informaion on NSWC Crane, please visi Images were ownloae via publically accessible websies 19