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Old 10-20-2018, 08:48 AM   #1
johndallman
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Default [Basic] Throwing things with TK

Since Telekinesis power is expressed in terms of ST, most circumstances of throwing things can be handled using the Throwing rules on B. 355-6. However, I have a different case to solve.

In our occult WWII campaign, there's a character with TK ST 13, who's spotted that throwing shaped-charge anti-tank grenades that way allows him to save carrying a grenade launcher around. Since the launcher is a PIAT, that's a considerable saving in weight and convenience, and allows a much better rate of fire.

We do want to use PIAT grenades, rather than M1 bazooka grenades, because we're British, and also because PIAT grenades have a larger diameter, more explosive and better penetration than bazooka rounds (100mm rather than 75mm). The PIAT delivery system was definitely worse than the bazooka, but we're dispensing with that.

My character is the party's armourer, so I'm trying to work out if TK ST 13 allows the grenades to be thrown fast enough to trigger their standard impact fuze, or if we need a more sensitive fuze, and if that will be safe enough to carry around. Obviously, it would be good to be able to use standard grenades without needing to change the fuze.

So, how much force can one exert with TK? Basic Lift for ST 13 is 34lb, about 15Kg. That's the weight you can lift overhead with one hand in one second. So you've moved it about two metres in one second, against gravity, and with negligible friction. So that's about (2 + 9.81) Newtons for each Kg of weight, or about 175 Newtons for 15Kg.

A PIAT grenade weighs about 1.5Kg all-up, so applying 175N for 1 second would accelerate it at 115 m/sec/sec, leaving it moving at 115m/sec. That's well in excess of the launch velocity on a PIAT, about 75-80 m/sec, but a slower acceleration, so there's no risk of premature detonation.

However, it isn't going to work this well, because TK has a range of only 10 yards, unless you buy that up. Starting the grenade behind you makes aiming difficult, so we have about 9m to accelerate it. That takes about 0.4 seconds, at the end of which it's travelling at about 45 m/sec.

That seems like a plausible figure. The normal impact fuze will doubtless go off at less than the normal muzzle velocity for a PIAT, because the grenade has a fair amount of aerodynamic drag. So the characters do need to source a more sensitive fuze, but the difference isn't vast. If we get one that needs a 25 m/sec impact to go off, that's still reasonably drop-safe, since that requires a 32 metre fall. The packaging for these grenades applied some care to ensuring that the fuzes were protected, and they can be put back in it after modifications.
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Old 10-20-2018, 09:48 AM   #2
Anaraxes
 
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Default Re: [Basic] Throwing things with TK

This page tells me soldiers were unhappy with the effort to cock a PIAT, which required a "draw weight of 200 pounds (90 kg)". That's presumably also the force the spring will exert to launch the projectile. If we take that as BL, I get ST 32.

(I doubt anyone ever loaded a PIAT one-handed, and for that matter wouldn't care about doing so in under one second. The quad-time double-handed lift would only call for ST 11, which at least matches the anecdotes about soldiers of small stature struggling to load the weapon while not requiring a superhuman to do it at all. But in this case, we're trying to figure out how to throw the grenade quickly, certainly under a second. TK is theoretically a "pair of hands", so we might get a discount on the one-handed BL as well.)
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Old 10-20-2018, 09:49 AM   #3
Nereidalbel
 
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Default Re: [Basic] Throwing things with TK

You can resolve the aiming issue by using a simple tube of sufficient length. You could even just use cardboard tubes, which are cheap enough to either drop when you need to run away, or, they can be burned if you really need a fire.

If you're using TK to throw something as an attack instead, it has the same thrown weapon range as if you'd thrown it yourself, plus the up to 10 yards starting point for the throw. I see no reason why this couldn't set off the impact fuze, especially if you source a slightly more sensitive one.
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Old 10-21-2018, 01:51 AM   #4
vicky_molokh
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Default Re: [Basic] Throwing things with TK

I'm assuming the GL and the TK throw an approximately same trajectory. As a result, if they have a comparable throw range, they have a comparable velocity. If they have a comparable velocity, they should have a comparable chance of triggering the fuse upon impact. Range of a throw of course depends on the interaction of TK ST with the mass of the projectile cross-referenced with the throwing range table.

(By comparison, the tube trick is likely to be underwhelming because with TK13 you are limited to moving your 'hands' across the tube at 13y/s [unlike when throwing stuff without moving the hands to another hex].)
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Old 10-21-2018, 02:35 AM   #5
RogerBW
 
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Default Re: [Basic] Throwing things with TK

The cocking effort isn't all the force that goes into launching the projectile - there's both the spring and a powder charge, and firing the weapon recocks the spring. (Usually.)

I haven't been able to get details of acceleration tolerances, but the 425 impact fuse originally used on the PIAT often didn't detonate the charge (it needed a solid square impact on the target), and in early 1944 it was replaced by the 426 graze fuse which was rather more sensitive.
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Old 10-21-2018, 04:16 AM   #6
johndallman
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Default Re: [Basic] Throwing things with TK

Quote:
Originally Posted by RogerBW View Post
I haven't been able to get details of acceleration tolerances, but the 425 impact fuse originally used on the PIAT often didn't detonate the charge (it needed a solid square impact on the target), and in early 1944 it was replaced by the 426 graze fuse which was rather more sensitive.
Good find! That led me to what appears to be the right document reference (AVIA 44 434) at the Public Record Office, and I've requested a quote for a copy of the document.
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Old 10-21-2018, 04:14 PM   #7
Anaraxes
 
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Default Re: [Basic] Throwing things with TK

Actual primary sources. Sweet.
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Old 10-21-2018, 05:29 PM   #8
smurf
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Default Re: [Basic] Throwing things with TK

According to wiki the muzzle velocity was 250ft per sec or around 83 yards per second (rounded down). The BL for ST13 is 33lb that is enough to fling the round 13 yards per second.

However PIATs were reported to work 75% of the time. This could mean capping the ability at a max of 12 or under. My concern is would the PIAT have the enough energy: 13/83 yards per second or 15% of the normal energy used to fire the round?

To do what the character would like to do, it maybe better to fling anti tank mines around. The MK2 mine was only 8.5lb and the MK5 was 12.5lb (1943+).
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Old 10-22-2018, 01:27 AM   #9
johndallman
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Default Re: [Basic] Throwing things with TK

Quote:
Originally Posted by smurf View Post
However PIATs were reported to work 75% of the time. This could mean capping the ability at a max of 12 or under.(1943+).
The problem was the original impact fuze, which has been replaced by the point in the campaign that we've reached:
Quote:
Originally Posted by RogerBW View Post
... the 425 impact fuse originally used on the PIAT often didn't detonate the charge (it needed a solid square impact on the target), and in early 1944 it was replaced by the 426 graze fuse which was rather more sensitive.
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Old 10-22-2018, 03:09 AM   #10
RogerBW
 
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Default Re: [Basic] Throwing things with TK

The numbers usually quoted are ~75% detonation chance with the original 425 impact fuse (some say "75% failure rate" but I think this is probably a transcription error), ~90% with the 426 graze fuse.

(That's "in the field" observations – for testing, I believe, they had a cleaner setup with square-on impacts, and it was the awkwardness of real-world situations that led to the higher proportion of glancing shots and therefore failures to detonate.)
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