[HT] Airburst question (HE-AB & ABF)

[General Lee]

Hi,

I'm in doubt about how airburst works in some situations.

In High-Tech, p. 174-175, the ABF (Annular Blast Fragmentation) and the Airburst projectile option (commonly HE-AB) were described.

In p.174, when describing HE-AB it is stated that this type of warhead inflicts fragmentation damage only. The ABF is already considered as airburst.

So, when looking for SAM (Surface-Air Missiles) that are equivalent to Igla-S (9K338/SA-24 "Grinch") I look into FIM-92 stats. But, the stats presented in High-Tech are for the FIM-92A version, that have a slight different warhead than the actual version ( -C) of the FIM-92. According to the public domain, the FIM-92C have an ABF warhead and FIM-92A have an Blast Fragmentation warhead, that I could assume that is HE-AB. Igla-S, in its turn, have a directed-energy blast fragmentation warhead that I don't know how to classificate it in GURPS. I tended to put it as a HE-AB warhead, also.

In the stats for the FIM-92A, the damage is 6dx3 (3d+2) cr ex.

So, if it hits a target, what is the maximum number of hits possible? How the HE-AB warhead works in this case?

Thank you.

[Ulzgoroth]

Fragmentation damage is explained on p414-415 of the basic set. There's technically no maximum on the number of hits that can occur, but the likely number is a few.

If you score a 'direct' hit, I'd assume the range modifier for the fragmentation roll is zero, otherwise it would be determined from the scatter distance.

[General Lee]

Originally Posted by Ulzgoroth

Fragmentation damage is explained on p414-415 of the basic set. There's technically no maximum on the number of hits that can occur, but the likely number is a few.

If you score a 'direct' hit, I'd assume the range modifier for the fragmentation roll is zero, otherwise it would be determined from the scatter distance.

Ok. I'm aware of how frag works in game, but would you concur that it will cause some poor results, or unrealistic ones, for SAM missiles.

For example, I roll 8 in the attack (homing attack) (had to roll 12 or less - "10 + 4 - 2[countermeasures]"). So it was a direct hit. But, as it is an airburst I assume that it explodes at some distance from the target (a Mi-24 Hind) (5 yards). The HE-AB description saids that this type of attack does fragmentation damage only. In fact, at 5 yards, the explosive damage is divided by 15 which could at maximum inflict 7 Hit Points, most probably 1.

So, I had to roll 19 or less (15 + 6[for SM] - 2 [distance]). I rolled 10. Therefore, I have 4 (four) hits (automatic 1 [for hi]t + 3 [success by 9]).

The Mi-24 have DR 5 in the body, with some areas more reinforced at DR 25 (cockpit, passenger compartment' floor).

Suposing that all four hits were in the less protected areas in the body (DR 5). We would have an average damage of 7 HP {[(3*3.5) +2] - 5} per hit, hence a total average of 28 HP! For a direct hit from a SAM!

ABF warheads deals these situations better in my judgement . Or, I am missing something?

[Phoenix_Dragon]

Originally Posted by General Lee

Suposing that all four hits were in the less protected areas in the body (DR 5). We would have an average damage of 7 HP {[(3*3.5) +2] - 5} per hit, hence a total average of 28 HP! For a direct hit from a SAM!

For a small man-portable SAM detonating in proximity (NOT a direct hit!) and hitting nothing vital (No engines) on one of the most heavily-armored helicopters, that doesn't sound too surprising.

From everything I can find, neither of these missiles would use the "airburst" rules. While the Stinger has an ABF warhead, it's not fused like GURPS's ABF warheads (Which seem to be both warhead and trigger); probably why it's not listed as one in the weapon table, in fact. It is a delayed-impact fuse. The Igla appears to be the same, but with the addition of a magnetic fuse to trigger it on a near miss. They can score direct hits, and such hit with either of those missiles is going to do a lot more!

[Ulzgoroth]

Originally Posted by Phoenix_Dragon

For a small man-portable SAM detonating in proximity (NOT a direct hit!) and hitting nothing vital (No engines) on one of the most heavily-armored helicopters, that doesn't sound too surprising.

From everything I can find, neither of these missiles would use the "airburst" rules. While the Stinger has an ABF warhead, it's not fused like GURPS's ABF warheads (Which seem to be both warhead and trigger); probably why it's not listed as one in the weapon table, in fact. It is a delayed-impact fuse. The Igla appears to be the same, but with the addition of a magnetic fuse to trigger it on a near miss. They can score direct hits, and such hit with either of those missiles is going to do a lot more!

I doubt that the Stinger actually has an ABF warhead, unless you've got a good source for that. Wikipedia claims it does, but nobody else seems to, and it makes little sense for a weapon that is impact fused and characterized as 'hit to kill'.

I don't know why the High Tech writeup characterizes it as HE-AB or what behavior is intended. Or, indeed, how to correctly model the missile's delayed-impact HE warhead when no stats are provided for the missile impacting the target.

[Nereidalbel]

Originally Posted by Ulzgoroth

I doubt that the Stinger actually has an ABF warhead, unless you've got a good source for that. Wikipedia claims it does, but nobody else seems to, and it makes little sense for a weapon that is impact fused and characterized as 'hit to kill'.

I don't know why the High Tech writeup characterizes it as HE-AB or what behavior is intended. Or, indeed, how to correctly model the missile's delayed-impact HE warhead when no stats are provided for the missile impacting the target.

The missile would roll for slam damage as Imp, based on relative speed vs the aircraft, as opposed to absolute speed. If the missile penetrates, it's an internal explosion, otherwise, it's a contact explosion.

[Ulzgoroth]

Originally Posted by Nereidalbel

The missile would roll for slam damage as Imp, based on relative speed vs the aircraft, as opposed to absolute speed. If the missile penetrates, it's an internal explosion, otherwise, it's a contact explosion.

You could do that of course, but it's a horribly crude method.

[doulos05]

Originally Posted by Ulzgoroth

You could do that of course, but it's a horribly crude method.

Because the high explosives in SAMs are so incredibly precise... :D

[General Lee]

Originally Posted by Phoenix_Dragon

For a small man-portable SAM detonating in proximity (NOT a direct hit!) and hitting nothing vital (No engines) on one of the most heavily-armored helicopters, that doesn't sound too surprising.

From everything I can find, neither of these missiles would use the "airburst" rules. While the Stinger has an ABF warhead, it's not fused like GURPS's ABF warheads (Which seem to be both warhead and trigger); probably why it's not listed as one in the weapon table, in fact. It is a delayed-impact fuse. The Igla appears to be the same, but with the addition of a magnetic fuse to trigger it on a near miss. They can score direct hits, and such hit with either of those missiles is going to do a lot more!

Well, of course that a SAM often inflict minor damages, but in average we are speaking of such poor results as I have explained that almost all the time a helicopter would fly away even when received a good hit (I write direct hit above, but it cause some confusion).

ABF warhead is described in the AIM-9L Sidewider stats, which have the same function as "air-killer" as SAM's. I thought it is credible that modern warheads could be ABF. The only issue is how many frags exists in a given warhead. Stinger would have less than Sidewider, but by how many?

I tended to concur with the delayed-impact fuse, so the "blast fragmentation" warhead is not necessarily an airburst (HE-AB) in GURPS terms. Actually, I think that it is HE only.

But, when there is a proximity fuse (magnetic, eletronic, laser etc.) it would work as HE-AB. In that, the issue is still there. How many frags exists? The actual rule for definition of the number of hits is not satisfactory for situations like that. Someone have a suggestion how to improve it?

[Ulzgoroth]

Originally Posted by doulos05

Because the high explosives in SAMs are so incredibly precise... :D

The method of deciding impact damage is crude. It's crunching the actual missile into low-information GURPS stats and feeding it through the collision rules...

You could call the impact damage crude, but nobody would really care. Though I would say that ABF, shaped charge, and some fragmentation type warheads are pretty precise when you get down to it.

Originally Posted by General Lee

ABF warhead is described in the AIM-9L Sidewider stats, which have the same function as "air-killer" as SAM's. I thought it is credible that modern warheads could be ABF. The only issue is how many frags exists in a given warhead. Stinger would have less than Sidewider, but by how many?

Not all anti-aircraft missiles use ABF warheads.

Alternatives include blast-fragmentation of various sorts, continuous-rod warheads (probably behaves like beehive?), shaped charges, and in one case a trio of very high speed penetrating rockets that can punch through light armored ground vehicles.

Originally Posted by General Lee

But, when there is a proximity fuse (magnetic, eletronic, laser etc.) it would work as HE-AB. In that, the issue is still there. How many frags exists? The actual rule for definition of the number of hits is not satisfactory for situations like that. Someone have a suggestion how to improve it?

I do not think that you have much of a case that fragmentation rules need to be revised because a bad shot with a low-powered missile is unlikely to shred an aircraft. Though the fact that shrapnel cutting damage precludes hitting vehicle vitals seems a bit wrong...

Also, by my numbers even a proximity burst actually is likely to give a Cold War Light Helicopter a bad time! The shrapnel roll will be at 15 + 4 (for SM), resulting in a 50% chance of 4 hits, each for 3d+2 cutting -3 dr. If each hit causes 13 injury the OH-6A will be going down, and the other two models hanging by a thread. Assuming none of the fragments hit the glass and took out the pilot! It'll also shred a light monoplane pretty well, except the armored Piranha.

A full-size fighter has enough mass to soak up the damage without being knocked out, and under the RAW isn't likely to take serious side effects, which may be a bit odd...but this is with a bad hit, remember. (Early blast/fragmentation warhead sidewinders had the delightful habit of exploding in the target's jet outlet. And 6dx3 internal explosion damage will mangle anything in High Tech pretty well.)

I also don't see a good reason not to allow the blast effect to damage the target, if it's close enough. Even if a proximity 'hit' counts as a yard off, 6d cr is not a negligible effect.

Tangential issue: What is the damage from an explosion to targets in the target hex, but not hit by the projectile? Full? Or treated as one yard and divided by 3?