New Extended Range Shoulder-Fired 40 mm Grenade System

Transcription

1 New Shoulder-Fired Grenade System Danie Els a Hennie Pieterse b Marius de Bruin c a Dept of Mech and Mechatronics Eng, Univ of Stellenbosch, South Africa dnjels@sun.ac.za b Rippel Effect Weapon Systems Pty (Ltd), Silver lakes, Pretoria, South Africa hennie@rippeleffect.co.za c Denel Land Systems Western Cape, Denel Pty (Ltd), Somerset West, South Africa Marius.deBruin@dlswc.co.za 22nd Small Arms and Cannons Symposium DCMT Shrivenham, UK August

2 1 Weapon Systems Design 2 Analysis Free recoil energy limitations 3 Final system 4 ERLP Design Specifications 5 2

3 I This section consists of: Overview of type ammunition. Overview of weapon systems. Design objectives of new extended range ammunition. 3

4 40mm 46mm Standard Ammunition (Low Velocity) Low pressure chamber High pressure chamber Vent holes Cartridge case High/low pressure propulsion system Effective range Maximum range 76 m/s 375 m 430 m Maximum pressure 13 MPa Projectile 4

5 Weapon Systems M79 M203 5

6 Weapon Systems... HK69 A1 AG36, XM320 6

7 Weapon Systems... M4/XM320 and M16A2/XM320 L85A2/L17A2 7

8 Weapon Systems... XRGL40 8

9 Design The new Low Pressure (ERLP ) round was developed with the following objectives: Extending the range as much as possible for tactical reasons. Keeping the recoil energy below 60 J in accordance with TOP , when fired from the XRGL40 or from under-barrel configurations such as the L85A2/L17A2 so that a maximum of 100 rounds/day/man can be fired. Minimizing the propulsion pressure for weapon safety and use in existing weapons. Modifying the M118 based cartridge case to prevent accidental loading in weapons where it may be unsafe. 9

10 This section consists of: II Analysis Maximum recoil energy limitations. Different weapon system mass parameters. Recoil energy formulas. Calculation of maximum allowable muzzle velocity. Simple external ballistics model. Calculation of maximum allowable range. Maximum recoil energy is the main design constraint 10

11 Free recoil energy limitations for shoulder fired weapons on Free recoil energy number of rounds 0 J to 20 J Unlimited firing 20 J to 40 J 200 rounds/man/day 40 J to 60 J 100 rounds/man/day 60 J to 80 J 25 rounds/man/day Greater than 80 J No shoulder firing Test Operations Procedure (TOP) , U.S. Army Safety Evaluation of Hand and Shoulder Weapons. K. Blankenship, et al. Shoulder-Fired Weapons with High Recoil Energy:Quantifying Injury and Shooting Performance. USARIEM Technical Report T04-05, M79 as reference has recoil energy of about 40 J 11

12 Weapon Systems Properties Total Barrel Empty mass length Weapon system [ kg ] [ mm ] HK69 A XM320 (Stand Alone) M M4/XM XRGL L85A2/L17A M16A2/M M16A2/XM

13 calculations Free recoil energy E E = 1 2 m W [( mp + αm g m W ) v e ] 2 (1) with: m W = weapon mass [kg] m P = projectile mass [kg] m g = propellant gas mass [kg] v e = projectile muzzle velocity [m/s] v g = propellant gas velocity [m/s] α = v g /v e 1.75 (contribution of exit gasses) The muzzle velocity v e for a given recoil energy E 2mW E v e = (2) m P + αm g 13

14 130 Maximum muzzle velociy for E = 40J to 60J Maximum muzzle velocity [m/s] Std LV ERLP XRGL40 (5kg) XM320 (2.3kg) Grenade mass [g] ERLP 200 g projectile with 120 m/s muzzle velocity 14

15 y ½ρC d Av 2 v v 0 θ 0 Simplified 2D external ballistics model [ẍ ] ÿ = ρc dav 2m G [ẋ ] with: ρ = air density = 1.2 kg/m 3 C d = drag coefficient = 0.20 to 0.23 A = sectional area = π m 2 g = gravitation = 9.81 m/s 2 ẏ m G g [ ] 0 g x (3) v = ẋ 2 + ẏ 2 (4) Initial values: x 0 = 0 m, y 0 = 0 m, ẋ 0 = v 0 cos θ 0 m/s ẏ 0 = v 0 sin θ 0 m/s 15

16 900 Maximum range for E = 40J to 60J 800 ERLP (840m) Maximum range [m] Std LV (435m) XRGL40 (5kg) XM320 (2.3kg) Grenade mass [g] ERLP Maximum range of 840 m and effective range of 800 m. Live firings with radar measurements has given a maximum of 890 m. 16

17 III Analysis This section consists of: Investigate the internal ballistics properties of system Establish changes to reduce maximum pressure 17

18 PA Simplified internal ballistics model ẍ = PA ( m m = m 1 + r ) 2 tan(α) tan(α + β) R2 with: P = pressure [ Pa ] A = barrel projected area [ m 2 ] R = barrel radius [ m ] r = projectile radius of gyration [ m ] α = barrel helix angle [ rad ] β = friction angle (tan β = µ) [ rad ] m= projectile mass [ kg ] x α (5) 18

19 V 0 A From ideal gas laws assume no heat transfer, no leakages and that propellent is fully burnt. Approximate pressure as a simple blowdown system P(x) = P 0 ( V 0 V 0 + Ax ) γ (6) with: P 0 = initial pressure [ Pa ] P = pressure [ Pa ] V 0 = initial volume [ m 3 ] A = barrel projected area [ m 2 ] γ = heat capacity ratio (change to compensate for losses) 19

20 Equation of motion of projectile from (5) and (6) d 2 x dt 2 = vdv dx = P ( ) 0A V γ 0 m (7) V 0 + Ax Integrate with respect to velocity v, then ve 2 = 2P [ ( 0V 0 m Ax ) 1 γ ] e (γ 1) V 0 with: v e = muzzle velocity x e = barrel travel distance (8) Equation (8) can be used to calculate the influence of low pressure chamber volume and the effect of a shortened barrel. 20

21 /P 0 P M79 with LV cartridge =1.297 x e =0.3m (V 0 V 0 )/A A 0 =13.380cm 2 V 0 =20.795cm V 0 /V 0 ERLP Doubling of low pressure chamber volume reduces peak pressure by about 40%. 21

22 1.00 Velocity reduction compared to M79 /v e v e XM x e 0.7 /x e of short barreled underslung weapons is 95% compared to that of the M79 reference. 22

23 Final system Based on the M118 cartridge. The low-pressure chamber volume was doubled compared to the M406 round with M118 cartridge. Different propellents were tested and the final configuration has a maximum pressure of 12 MPa to 14 MPa. Optimization of the high pressure chamber and vent holes is still in progress. 23

24 IV ERLP Design Specifications Projectile mass 200 g 120 m/s (short barrel: 115 m/s) Maximum range 840 m (short barrel: 800 m ) Effective range 800 m Maximum pressure MPa Cartridge length 51 mm (Safety & performance) Obturator (Efficiency) 24

25 40mm x 51mm (ERLP) 40mm x 46mm Standerd Velocity HE 25

26 V We have designed and verified an extended range system that has met all our objectives. The ERLP round has an effective range of 800 m. The recoil energy is below 60 J for weapons with a mass of 5 kg or more. The recoil energy can be dangerously high from lighter weapons. This necessitates that the ERLP round be prevented from being loaded into such weapons. Existing weapons require modification to fire the round. The propulsion system resulted in a pressure of MPa, which is in the same range as the standard low-velocity systems, thereby not reducing the fatigue life of the chamber or barrel of existing weapons. More than 400 shots have been fired successfully 26