GURPS Tactical Shooting

[sir_pudding]

Originally Posted by Anthony

I believe that the ultra-tech standard is that deflection effects are assumed to be incorporated in DR, it's just that they function as a multiplier rather than an adder, and can basically be rolled into the whole armor quality modifier.

Doug, IIRC, has said that the vehicle DR in High-Tech was done based solely on linear thickness. I could be wrong, I suppose.

[DouglasCole]

Originally Posted by sir_pudding

Doug, IIRC, has said that the vehicle DR in High-Tech was done based solely on linear thickness. I could be wrong, I suppose.

Linear from the direction of 'averaged axis of the attack,' which is somewhere between "most useful gaming abstraction" and "vague to the point of uselessness," true. But we're not building real vehicles or designing real body armor here, we're playing a game. "Good enough to facilitate fun without completely shattering suspension of disbelief for the genre being emulated" is pretty much the yardstick.

I was a bit surprised during the LT playtest that the "deflection" thing was allowed/encouraged. When PD went away, slope of armor more or less went into "more DR," but "the blow whanged away and didn't do anything due to deflection" sort of went away.

Don't get me wrong: it's a real-world phenomenon. But it's a bear to model well in GURPS and its demise was not really missed.

[Anthony]

Originally Posted by sir_pudding

Doug, IIRC, has said that the vehicle DR in High-Tech was done based solely on linear thickness.

That might be true, but where available I'd bet on it being based on RHAe, which is to say 'someone else did the math or testing to figure out how much effect deflection has'.

[DouglasCole]

Originally Posted by Anthony

That might be true, but where available I'd bet on it being based on RHAe, which is to say 'someone else did the math or testing to figure out how much effect deflection has'.

Well, yeah. Linear thickness of RHAe, with conversions of thickness along the axis of impact of alternate materials (40mm of aluminum armor, angled at thus-and-such degrees) into RHAe where direct RHA equivalents weren't available.

[DanHoward]

Williams worked out a formula to determine the additional energy required to penetrate a plate as the angle of impact increases from normal. All of this is in Chapter 9.

E* = E/Cos A

E* is the actual energy required
E is the energy required if the attack hit normal to the target
A is the angle of impact.

[Orienda]

That probably works fine for melee weapons and armor of all sorts, but doesn't cover the windshield case in tactical shooting, where in addition to requiring energy to penetrate, it can also cause the object to be deflected off from its intended course.

[cosmicfish]

Originally Posted by DanHoward

Williams worked out a formula to determine the additional energy required to penetrate a plate as the angle of impact increases from normal. All of this is in Chapter 9.

E* = E/Cos A

E* is the actual energy required
E is the energy required if the attack hit normal to the target
A is the angle of impact.

That is not an accurate formula - all that is doing is compensating for the effective thickness, while still erroneously assuming that the same amount of energy is being imparted during the collision. As far as back-of-the-envelope calculations go, I would square that number to represent the additional difficulty in penetration due to decreased energy transfer.

[DanHoward]

He determined the forumula after experimental anaylsis. If you look at the results from his experiments against various types of plate and feed the parameters into his formula you get very similar results.

[Anthony]

Originally Posted by DanHoward

Williams worked out a formula to determine the additional energy required to penetrate a plate as the angle of impact increases from normal.

If we assume his equation is accurate, it implies that sloping armor makes it worse. The actual thickness of armor which must be penetrated is T/Cos A (i.e. if the armor is 5mm thick, and you come in at a 45 degree angle, you must penetrate 7mm armor). However, the exponent of E with regard to T is normally greater than 1, and his testing results in an exponent of exactly 1.

If you want to armor X area, a flat plate requires X*T*d total volume of armor. An angled plate requires X*T*d/cos A total volume. Thus, for the same weight, you can either have a 7mm thick flat plate, or a 5mm thick plate that's at a 45 degree angle.

[cosmicfish]

Originally Posted by DanHoward

He determined the forumula after experimental anaylsis. If you look at the results from his experiments against various types of plate and feed the parameters into his formula you get very similar results.

Are the test parameters and data available?