Maintenance of weapons

[mbear]

But Btech missiles are a lot like cannons, themselves.  There is a launch tube, that is loaded from the rear, or even the side  Even if each missile is in its own self contained cannister, you need some kind of sealing mechanism to keep the exhaust from going back into the feed system.

That could easily be handled by having a U-shaped exhaust tube that directs the exhaust out the front of the launcher. Something like the plenum and uptake stack used by Mk 41 VLS. Here's a picture to show what I mean.

You would move the plenum and uptake into the individual missile container instead of the launcher itself. Then the canister is moved into place to launch out the "barrel" of the launcher.

If the missiles are in self contained cannisters, you need to deal with the empties before you load the next one.  Then there's the feed mechanism and the magazine.

Those are good points.

The empty canisters could self-destruct upon launch. I think there are some modern tank cannons that use consumable cases for storage. When fired, the propellant burns up most/all of the shell's packaging.

Or the missile canister could be squished by the next fully loaded missile cell dropping into place. (I do something similar with aluminum soda cans after I've drunk the contents. ;) )

Or maybe the canister is ejected from the launcher by using heated air from the 'Mech's heat sink system that's been compressed.

[Apocal]

That's a good point. 

But Btech missiles are a lot like cannons, themselves.  There is a launch tube, that is loaded from the rear, or even the side  Even if each missile is in its own self contained cannister, you need some kind of sealing mechanism to keep the exhaust from going back into the feed system.  If the missiles are in self contained cannisters, you need to deal with the empties before you load the next one.  Then there's the feed mechanism and the magazine.  The closest analog I can think if is the  old Mk 26 missile launchers.

RE: exhaust in the feed system
Missiles can get blasted by their own exhaust gasses without issue, generally speaking. Like the Mk. 26 you posted; there is no protection for the second missile on the rail from the first's exhaust. The problem with allowing stuff like dirt to build up in an autocannon is there are fairy tight mechanical tolerances involved: if nothing else, you have the round engaging with the barrel and the case having to extract without snagging anything. A little too big (even from normal thermal expansion) and nothing works.

But there isn't really an equivalent for missiles because rails aren't that tight (IME) and are fairly tolerant of deviations because they have to be.

That isn't to say there aren't things that go wrong -- there absolutely are. It just isn't stuff like gasses causing them. Missile maintenance, would be more about the launcher's function, largely regularly checking its integrity and testing it, since there isn't a hard-and-fast function check like with a firearm or a cannon dry-fire. Especially with a Mech since you'd be dealing with routine and prolonged periods of shock (stomping around on hard-packed ground, landing on top of a building after jump jetting, generally getting banged around during fights). 

[RifleMech]

A laser 'barrel' IIRC should really be a vacuum tube so you do not get heat bloom or diffusion through particles.

Wouldn't it need to be check to see if if its still sealed and nothing is warped from heat?

[Orin J.]

i doubt a pressure sensor that'd pick up if the pressure inside of the firing chamber is still correct would be hard to incorporate, and that'd relegate it to a diagnostics check rather than needing a teardown.

[The_Caveman]

The real cost of maintaining large cannons would probably out-strip that of maintaining a laser, because friction of the rounds against the rifling grooves or barrel walls WILL wear the gun out, and it WILL need to be either re-lined or replaced.  Most of the old battleships were only good for a few hundred rounds per barrel before requiring gun replacement.  The old railroad cars with the enormous siege guns used in WWI and WWII had individually numbered rounds that had to be fired in order, because each one was a few mills larger than the previous to account for barrel wear and expansion due to stress.

I don't think you'd have a conventional barrel construction in an autocannon. The combination of rate-of-fire and projectile caliber with repeat followup shots are just too damaging. There are current-day medium caliber naval guns capable of burst fire in the 120 RPM range and after firing a few dozen shells they need to cool for half an hour or more. Even with better materials, such a weapon would wear out far too quickly if required to fire hundreds of shots per hour like a 'Mech autocannon in a pitched battle.

More likely I think you'd have the gun constructed as a sleeve-and-liner system where most of the structural strength comes from a fixed outer sleeve that is fitted with a network of coolant channels. This would be a low-wear part whose main job would be dissipating heat and containing the hoop stresses on the inner liner. The removable liner would be a "dumb" metal pipe made out of a high-wearing steel (or in fancy models even a ceramic) and fitted with a quick-change mechanism so techs could slide them out and pop in a new one every few hundred rounds without the need to rip out the entire cannon and disassemble it.

Because the inner liner is a sacrificial part, it could be a lot thinner and possibly light enough for a vehicle crew to do the change on their own for the AC/2 and AC/5 in the field. And because most of the barrel's stiffness comes from the outer sleeve, replacing a liner wouldn't severely alter the barrel harmonics. You'd just have to run a handful of practice shells through the gun to verify the point of aim and you'd be good to go.

With a system like that in place, cannon maintenance wouldn't be enormously expensive. Spent metal liners could even be recycled, by re-forging the tube in a hydraulic mandrel until the inner diameter was correct and friction-welding copper or aluminum sheet to the outside as a thermal shim (and re-cutting rifling, though I suspect nearly all ACs are smoothbores due to ammunition preference).

[RifleMech]

i doubt a pressure sensor that'd pick up if the pressure inside of the firing chamber is still correct would be hard to incorporate, and that'd relegate it to a diagnostics check rather than needing a teardown.

Probably but sensors go bad.

I don't think you'd have a conventional barrel construction in an autocannon. The combination of rate-of-fire and projectile caliber with repeat followup shots are just too damaging. There are current-day medium caliber naval guns capable of burst fire in the 120 RPM range and after firing a few dozen shells they need to cool for half an hour or more. Even with better materials, such a weapon would wear out far too quickly if required to fire hundreds of shots per hour like a 'Mech autocannon in a pitched battle.

More likely I think you'd have the gun constructed as a sleeve-and-liner system where most of the structural strength comes from a fixed outer sleeve that is fitted with a network of coolant channels. This would be a low-wear part whose main job would be dissipating heat and containing the hoop stresses on the inner liner. The removable liner would be a "dumb" metal pipe made out of a high-wearing steel (or in fancy models even a ceramic) and fitted with a quick-change mechanism so techs could slide them out and pop in a new one every few hundred rounds without the need to rip out the entire cannon and disassemble it.

Because the inner liner is a sacrificial part, it could be a lot thinner and possibly light enough for a vehicle crew to do the change on their own for the AC/2 and AC/5 in the field. And because most of the barrel's stiffness comes from the outer sleeve, replacing a liner wouldn't severely alter the barrel harmonics. You'd just have to run a handful of practice shells through the gun to verify the point of aim and you'd be good to go.

With a system like that in place, cannon maintenance wouldn't be enormously expensive. Spent metal liners could even be recycled, by re-forging the tube in a hydraulic mandrel until the inner diameter was correct and friction-welding copper or aluminum sheet to the outside as a thermal shim (and re-cutting rifling, though I suspect nearly all ACs are smoothbores due to ammunition preference).

Built in cooling, along with stronger recoil and ammo feed systems, would help explain why Autocannons are so much heavier than Rifle Cannons.

[SCC]

Built in cooling, along with stronger recoil and ammo feed systems, would help explain why Autocannons are so much heavier than Rifle Cannons.

Autocannons are so heavy because Battledriods was pretty much bad by a bunch of guys in a garage without any thought to balance.

[Daryk]

Naval weapons, at least, have barrel lives in the thousands of rounds: http://www.navweaps.com/Weapons/WNUS_5-62_mk45.php

[Apocal]

Naval weapons, at least, have barrel lives in the thousands of rounds: http://www.navweaps.com/Weapons/WNUS_5-62_mk45.php

That's a modern and relatively low-powered weapon. Kovax was referring specifically to old battleships and NavWeaps has the old Mk7 16" with a barrel life of 290-350 rounds. Other battleship guns are in the same ballpark.

[Daryk]

The muzzle energy of the ERGM isn't exactly low power ("only" half of a rail gun), and still has a barrel life in the thousands of rounds (1,500 to 3,000; see footnote 7a under ammunition).  And 127mm is a bit more in the realm of what a 'mech would mount.  Hilarious art aside, no 'mech is walking around with a 406mm cannon.

[Caedis Animus]

I think the highest caliber on any known AC-20 toting unit in Battletech is a 200-to-210mm Ultra AC on some Clan Omnimech, either the Summoner or the Ebon Jaguar.

[Daryk]

Agreed, that's what I remember too.

[The_Caveman]

The muzzle energy of the ERGM isn't exactly low power ("only" half of a rail gun), and still has a barrel life in the thousands of rounds (1,500 to 3,000; see footnote 7a under ammunition).  And 127mm is a bit more in the realm of what a 'mech would mount.  Hilarious art aside, no 'mech is walking around with a 406mm cannon.

Much lower rates of fire than 'Mech autocannons though.

The Mk45 gun tops out at 20 RPM. Based on shell weight, an AC/5 of similar bore diameter is shooting 3-round bursts. Since regular ACs put all the shells on the same location and Ultras in double-rate mode don't (as well as the TacOps rapid-fire ACs rule and the old Solaris rule permitting a full-power shot every 2.5 seconds at a significant heat penalty), it is strongly implied that the time of a burst is very short. Probably upwards of 120 RPM for the cyclic rate.

Faster rates of fire accelerate barrel wear as the barrel has less time to cool between projectiles and prolonged exposure to corrosive propellant gases. It would only get worse for the bigger ACs (the AC/20 producing as much heat as a large laser does not make me optimistic for its barrel life).

[Daryk]

Based on shell weight, I think an AC/5 with a similar bore would be firing single rounds (or two at the most), with the extra weight going to propellant.

[Orin J.]

we aren't trying to untie the gordian knot of how battletech ammo works, we're talking about maintenance. and it's not like we have a set bore for a given AC size, anyways. best to work with an average there i'd think....

i doubt a pressure sensor that'd pick up if the pressure inside of the firing chamber is still correct would be hard to incorporate, and that'd relegate it to a diagnostics check rather than needing a teardown.

Probably but sensors go bad.

and the diagnostics would pick that up too, what's the point here?

[The_Caveman]

Based on shell weight, I think an AC/5 with a similar bore would be firing single rounds (or two at the most), with the extra weight going to propellant.

A volley of AC/5 is somewhere in the neighborhood of 50kg. Complete rounds for 5-inch class guns are 15-25kg. They're not loading upwards of 30kg of propellant behind the shell, there would be no point. You can't propel a projectile faster than the combustion speed of the propellant, no matter how much of it you use, and physics restrains most chemical propellants to 2000-3000 m/s--hence why hydrogen/helium light gas guns are used for micrometeoroid simulations.

Besides, if ACs are single-shot weapons, there is nothing significant to differentiate them from the primitive rifle cannon. If the answer is propellant or projectile, that can be easily retrofitted to the older designs. A large-bore burst-fire weapon is the most convenient explanation for the ways ACs behave relative to everything else. Anything else requires lots of handwavium or mental gymnastics to justify.

[Daryk]

We're definitely looking at different tables.  The ERGM by itself is 50kg, and the lightest shell I see on the page I linked is 29kg.  Propellant charges run from 8.3kg to 18.6kg.

[Colt Ward]

And you have no idea how that weight could be distributed . . . heck, you could have a flush of some noble gas as part of firing the AC which would factor into the 'weight' per shot.

IMO you are really trying to dig down into the weeds since are are told Autocannon classes are done by size- not how many shells are fired, how often or their weight.  So some descriptions in the past for AC/5s made them sound like RACs currently are- a spinning gatling barrel shooting out smaller rounds- and I want to say we have a description of one huge bore single shot, and everything in between which all depends on the model.

The most you can break down on a AC is that they have a barrel, a breech, a firing mechanism, and a recoil absorbing shock system to put it back in battery along with mechanisms to aim.

[grimlock1]

i doubt a pressure sensor that'd pick up if the pressure inside of the firing chamber is still correct would be hard to incorporate, and that'd relegate it to a diagnostics check rather than needing a teardown.

Temperature sensors would be my go-to.  Thermocouples are very rugged, and just about anything that misbehaves will probably start by overheating a bit.

Probably but sensors go bad.


and the diagnostics would pick that up too, what's the point here?

Yes. Yes they do. I spent a fair bit of time in a previous job learning how to distinguish between bad sensors, dead sensors, unplugged sensors and a sensor that really is telling you that something bad is happening.

[SCC]

I think one thing people constantly over look is that BT is a world of mature, stagnate even, technology. I'm pretty sure that most people here are aware that the Pentagon doesn't exactly have the most aggressive IT upgrade. Well one of the factors that contributes to that is the restless advance of tech, but in BT things seem to have stopped some time ago, so maintaining gear is easy.

[RifleMech]

we aren't trying to untie the gordian knot of how battletech ammo works, we're talking about maintenance. and it's not like we have a set bore for a given AC size, anyways. best to work with an average there i'd think....

Probably but sensors go bad.


and the diagnostics would pick that up too, what's the point here?

And diagnostics never go wrong? ???  A sensor could say things are good even when they're bad couldn't it?

A volley of AC/5 is somewhere in the neighborhood of 50kg. Complete rounds for 5-inch class guns are 15-25kg. They're not loading upwards of 30kg of propellant behind the shell, there would be no point. You can't propel a projectile faster than the combustion speed of the propellant, no matter how much of it you use, and physics restrains most chemical propellants to 2000-3000 m/s--hence why hydrogen/helium light gas guns are used for micrometeoroid simulations.

Besides, if ACs are single-shot weapons, there is nothing significant to differentiate them from the primitive rifle cannon. If the answer is propellant or projectile, that can be easily retrofitted to the older designs. A large-bore burst-fire weapon is the most convenient explanation for the ways ACs behave relative to everything else. Anything else requires lots of handwavium or mental gymnastics to justify.

If we go with 2 shots per round, based on rules in TacOps, then each round for an AC/5 weighs 25kg. However that would vary since the size Autocannons varies so widely.

There's still the ability to rapid fire with Rifle Cannons can't do. That'd be a total of 4 rounds, 100kg of AC/5 ammo, per turn fired, going by TacOps rules. A Medium Rifle Cannon has 9 rounds of ammo. So that's pretty close to the same number of times the weapons can fire. 10 AC/5 (double tapping) 9 MRC. So AC/s do seem to have better propellant than RCs. To compensate for the rapid firing they need to be heavier to deal with the the rapid cycling of ammo and the recoil. So the AC/5 is 3 tons heavier than the MRC.

That's looking at the rules though. Fluff wise ACs can be firing a single shot to 10 or more.

[grimlock1]

And diagnostics never go wrong? ???  A sensor could say things are good even when they're bad couldn't it?

It's possible, but highly unlikely that a sensibly designed system will give you a false green.  That assumes you are taking readings from a good place in the inference space. 

A smart designer sets up the system so the simplest possible sensor will send a voltage to an analog-digital converter(ADC), and that converter will send a signal to the Diagnostic Interpreter, including error correction and sanity checks.  The DI looks to see if the reading is A: timestamps, checksums and other book keeping are in order, B: that the reading is within the happy band, and checks specific values known to indicate problems.  The thermocouple controllers at my old job would read 511^oC if the wire to the probe was unplugged.   C: that the variation on the signal is sufficiently random.   That last is important.  I get nervous when I see voltage v time graph and dead flat line. That's telling me there may be a problem.

[dgorsman]

That, and procedure.  There will be a number of visual inspections done during maintenance to spot trouble that wouldn't show up on electronic diagnostics.

[Colt Ward]

Visual inspections would be to look for . . .

Discoloration in material/paint, warping of a flat surface, buckling, smoke stains, excess fluid/grease in wells/low areas, oil/lubricant burns (burned oil will leave a yellowish brown residue), grass or other debris that sticks to a flat surface where it should have fallen, excessive carbon build up or scoring, excessive weathering for internal components (for example thermal liner that indicates solar/UV exposure b/c of break down), water in what should be sealed assemblies (my fav where headlights & turn signals- "See Private, that turn signal is running low on blinker fluid!  Go get some from Maintenance pronto, we do not want it to dry out!"), gray rubber seals (dried out, but not cracking- might be saved), cracked rubber seals, exposed wiring, flaking paint (why is it flaking?), rings in the paint around mounts/bolts, and . . . that is about it for what I remember for now.

You will also be checking for any difficulty opening hatches/access ports or unsteady brackets/mounts

[RifleMech]

It's possible, but highly unlikely that a sensibly designed system will give you a false green.  That assumes you are taking readings from a good place in the inference space. 

A smart designer sets up the system so the simplest possible sensor will send a voltage to an analog-digital converter(ADC), and that converter will send a signal to the Diagnostic Interpreter, including error correction and sanity checks.  The DI looks to see if the reading is A: timestamps, checksums and other book keeping are in order, B: that the reading is within the happy band, and checks specific values known to indicate problems.  The thermocouple controllers at my old job would read 511^oC if the wire to the probe was unplugged.   C: that the variation on the signal is sufficiently random.   That last is important.  I get nervous when I see voltage v time graph and dead flat line. That's telling me there may be a problem.

So it can fail and the more complicated it is the more ways it can break? 

[grimlock1]

So it can fail and the more complicated it is the more ways it can break?

Anything can fail. Yes, more elements in the system create more points of failure. And it is possible that a failure can be something unforeseeable.  But in 99.9999% of cases, the failure modes are understood and if they are understood you can build your system so that you distinguish between bad data and data that is telling about something bad.

The point is that even though the diagnostic systems add to the maintenance load, they pay for themselves in time and equipment saved.

Visual inspections would be to look for . . .

Discoloration in material/paint, warping of a flat surface, buckling, smoke stains, excess fluid/grease in wells/low areas, oil/lubricant burns (burned oil will leave a yellowish brown residue), grass or other debris that sticks to a flat surface where it should have fallen, excessive carbon build up or scoring, excessive weathering for internal components (for example thermal liner that indicates solar/UV exposure b/c of break down), water in what should be sealed assemblies (my fav where headlights & turn signals- "See Private, that turn signal is running low on blinker fluid!  Go get some from Maintenance pronto, we do not want it to dry out!"), gray rubber seals (dried out, but not cracking- might be saved), cracked rubber seals, exposed wiring, flaking paint (why is it flaking?), rings in the paint around mounts/bolts, and . . . that is about it for what I remember for now.

You will also be checking for any difficulty opening hatches/access ports or unsteady brackets/mounts

Enough buckling or warping to wreck a laser or PPC might not be visible to the eye. But solid state components that are approaching end of life will likely start showing some thermal discoloration.

[Colt Ward]

Sure, but I was not just talking about the immediate weapon- I was talking about general inspection.  The PPC or large laser that is putting off more heat may have some buckling in the cooling jacket caused by shock damage (hello shaped charge) and while the sensors may tell you the jacket has a problem, part of the first step is a visual inspection.  Buckled cooling jacket would likely mean crushed/crimped coolant flow so you do not get the spec flow rate through the tubing to move the heat to the heat sinks (as discussed, really radiators) and you can determine what tools you might need if you see damp surface around the buckled area or on any surfaces under the buckled area (like hull or internal structure) . . . which would also mean you are leaking some coolant.  What I have seen is b/c of the viscous nature of the fluid, it will be 'dirtier' than the surrounding painted/sealed metal or composite surfaces since debris will stick to it.

Again, shock damage could cause warping of the aiming gimbals & rods for any type weapon (hello, +1 TH penalty for accuracy) which you might be able to see . . . even if you get a sensor error, you will still use the Mk I Eyeball as your first inspection tool.  If you cannot visually spot any flaws, then you take out your precision tools to inspect components.

[grimlock1]

Sure, but I was not just talking about the immediate weapon- I was talking about general inspection.  The PPC or large laser that is putting off more heat may have some buckling in the cooling jacket caused by shock damage (hello shaped charge) and while the sensors may tell you the jacket has a problem, part of the first step is a visual inspection.  Buckled cooling jacket would likely mean crushed/crimped coolant flow so you do not get the spec flow rate through the tubing to move the heat to the heat sinks (as discussed, really radiators) and you can determine what tools you might need if you see damp surface around the buckled area or on any surfaces under the buckled area (like hull or internal structure) . . . which would also mean you are leaking some coolant.  What I have seen is b/c of the viscous nature of the fluid, it will be 'dirtier' than the surrounding painted/sealed metal or composite surfaces since debris will stick to it.

Again, shock damage could cause warping of the aiming gimbals & rods for any type weapon (hello, +1 TH penalty for accuracy) which you might be able to see . . . even if you get a sensor error, you will still use the Mk I Eyeball as your first inspection tool.  If you cannot visually spot any flaws, then you take out your precision tools to inspect components.

Objection withdrawn.

[RifleMech]

Anything can fail. Yes, more elements in the system create more points of failure. And it is possible that a failure can be something unforeseeable.  But in 99.9999% of cases, the failure modes are understood and if they are understood you can build your system so that you distinguish between bad data and data that is telling about something bad.

The point is that even though the diagnostic systems add to the maintenance load, they pay for themselves in time and equipment saved.

I can't help think of the later Star Trek series, The Next Generation and later where whenever something when wrong they'd yell and tap out commands on a view screen to fix the problem. I always wondered what if it was the computer screen that was wrong? Or just dirty?
https://youtu.be/-KDviXJCfHg

Who or what does the diagnostics on the diagnostics systems?

[SCC]

Given that 'Mechs can sit in storage for at least 100 years, often in seemingly less then ideal conditions, and then be brought to battle readiness by people who have never been trained on some of it's systems (LosTech), and that none of this is a major task, I some how doubt that 'Mechs require all that much maintenance.