Just *why* can't vehicles use DHS?

[Kit deSummersville]

I can think of at least one instance of a cheractor being burned by brushing up against a heatsink vent coming down out of a mech (H. Mehta on Huntress in the Twilight of the Clans books, though for the life of me I can't remember the H name she had).  Made it seem like only the heatsink radiators got really hot, and not other parts of the mech.  If mech armor is a poor heat conductor (likely, if it resists being blown off by lasers) than that would be pretty reasonable, and another reason mechs would tend to be very hot.

I think there was a story in Shrapnel of a MechWarrior with a prisoner on the arm of his Marauder firing his PPC repeatedly and cooking the poor guy....

[GoldBishop]

I think its a combination of factors -- Open Construction of vehicles (do not track Missile or Ballistic weapon heat) and double heat sinks being too bulky to "squeeze" into an open chassis frame (doesn't fit on small, streamlined chassis effectively or cannot be covered with enough armor to protect it).

For me and my players, the balance between rules and fluff kinda balances out.  We usually dive into the TechManual to justify anything, so this is what I've come up with (in case it comes up again):

Under Constructing Vehicles section, first item that jumped out at me was under Combat Vehicles: Myths vs Reality - Myth Number 3... 2nd started paragraph on p.92
"Finally, despite their structural weaknesses, vehicular chassis also shed waste heat more efficiently; the thermal output from ballistic systems and missile launchers has a negligible effect on vehicles. Energy weapons, however, still require the addition of heat sinks."
...

Then I did a quick search for Double Heat sinks and found the following (fluff, p.221) :
"Star League-era double heat sink technology vastly improved upon the standard heat sink with a larger, more powerful radiator system that enhanced the effectiveness of the existing heat pumps and coolant lines. The effect was a bulkier exchange system—roughly two hundred percent larger—for the same physical weight. The increased bulk and other factors proved too problematic for vehicle design, however, and limited its application to ’Mechs and aerospace craft. Even the more compact Clan versions have yet to overcome this limitation. ..."

...Hopefully this (or whatever was previously written) was worthy enough of an answer.  Its sufficient for me and mine in my corner of the interwebs  ;)

[massey]

My own head-canon is that what we think of as a "heat sink" in-game, really isn't any one type of thing.  A heat sink isn't a big air conditioning unit that is built into the mech.  A person in-universe wouldn't say "my mech has 15 heat sinks" just like they wouldn't say "my gauss rifle does 15 points of damage".  It's a game term that would be translated into a significantly different form.  (Note: there very well might be some statement somewhere in one of the books where a character says exactly that, but if there is, I think it's bad writing).

Instead, a "heat sink" is a set of construction techniques and materials that are known to dissipate heat.  These get abstracted into 1 ton, 1 critical components for gameplay, but that's not how a character in-universe would think of them.  Critical damage in the game would represent smashing something that was important, and now the mech doesn't cool quite as well.  So, you're going to have cooling lines that run through the mech.  You're going to have cooling jackets around the weapons, exhaust ports that get rid of superheat gases, surface area, specialized metals that better resist the effects of higher internal temperatures, etc.  Everything from where ammo is stored, to how your myomer bundles are wrapped around your weapon housings.

"Double heat sinks" or "Freezers" are a slang term for advanced Star League construction techniques that radically reduce heat.  It's a bulkier system, and it really limits weapon placement within the mech (you can't cram things together as tightly).  This is represented by the higher number of crits they take up.  But it's not like a super air-conditioner, it's a variety of advanced heat management systems within the mech.

This would be why mechs (originally, I don't know about how it is now with all the optional rules) can't mix and match double and single heat sinks.  It isn't like plugging in a new AC unit -- you've got to make significant changes to the internal layout of the whole thing.

Vehicles can't use them because these advanced construction techniques just aren't used in vehicles, for whatever reason.  A vehicle's traditional "heat sinks" would be very different in design from a mech's.  Improved myomer shielding doesn't really help a vehicle that doesn't use myomers.

[haesslich]

Welding gloves protect the hand from heat nicely. I'm sure some infantry uniform manufacturer included similar fabrics in their gloves.

It may insulate you from the heat but it also means you bake to death as your body heat is trapped in there with you and has no way to get out.

Those cooling suits tankers in the Devastator wear are probably Nomex lined... and have cooling pumps that attach to a cooling system in the chair just like a Mech's.

[Sockmonkey]

Another thought: Mechs generally have a much larger surface area to volume ratio than tanks do. Tanks have a lot mode space contained inside a smaller surface area, while mechs tend to have lots and lots of surface area for the same volume, what with all the arms and legs. Double heat sinks, on a recordsheet, occupy more crit slots than singles, but perhaps part of that abstraction is representing that they require more surface area to mount than a single does. It's possible that vehicles in general just don't have enough free surface to mount a useful number of double heat sinks. The surface of the tanks still has to have weapon ports, sensors, etc. so maybe there just isn't enough space to mount doubles in any useful numbers. Think of the 'fins' on a reseen Battlemaster's shoulders. I believe those are fluffed to house heat sinks. Where on a tank are you going to find a place to mount those big, armored fins without being a hinderance or adding significantly to the size of the tank?

That would apply to tanks operating in a vacuum where the cooling surfaces have to be out in the open to function, but in-atmosphere all it takes is a small opening so you can pump in outside air over them. The volume isn't an issue.
What would be is the time, money, and resources to retool all the factories to produce vehicle chassis compatible with a new system.

The cockpit of a mech would have a small separate cooling unit built in as part of the life support system, which is how things like that are done in real life. It's not really practical to cool humans and heavy machinery with the same system because machines can run hotter and handle bigger temperature swings than a person. Wouldn't stop some of the reactor heat radiating up into the head of course, but it does explain why a lot of mechs have a separate head unit in the first place. It would help isolate the cockpit from the hottest bits.

[SCC]

The other problem with the surface area thing is that presumably the surface area is proportional to the volume the component takes up, which means that Clan DHS have twice as much volume/surface area and dissipate twice as much heat, so replacement should be possible.

Expect that HS in BT aren't radiators which worry about surface area, they're heat pumps, basically air conditioners, no surface area needed. In fact the closest thing to heat sinks we get in BT are the 'Mechs themselves, the heat gauge would be a representation of how close to saturation it is.

[Col Toda]

The open and closed system works as a good explanation . I been in a game in which I encountered a non- canon hover tank that had double heat sinks but it tracked all weapon heat just like a mech . The designer put in so much tech in it one cost 40 million C Bills if memory serves . Efficacy VS cost not great vs anyone except the Clan who just would  not normally exploit the design weakness due to combat style .

[YingJanshi]

Whatever the technobabble explanation is, I suspect it's related to why a fusion engine installed on a tank requires heavier shielding than the one on a 'Mech, and why an XL engine requires a bigger fraction of a tank's total item slots than of a 'Mech's total critical slots.

Well that's partly because the engine in a 'Mech is greatly shielded by the torso of the 'Mech itself. The pilot gets nowhere near it. But it's different on a vehicle, the crew compartment is right up against where ever the engine is, so it needs the extra shielding to protect the crew. (At least, that's how I've always explained it.)

[Scotty]

Well that's partly because the engine in a 'Mech is greatly shielded by the torso of the 'Mech itself. The pilot gets nowhere near it. But it's different on a vehicle, the crew compartment is right up against where ever the engine is, so it needs the extra shielding to protect the crew. (At least, that's how I've always explained it.)

A good effort!  Now explain why Torso-Mounted Cockpits don't require extra shielding on the engine ala tanks.

[SCC]

I figure that it's that environmental sealing that 'Mechs get for free. Of course one problem is that that extra mass is said to include transmission, which makes me wonder where mass is budgeted for a 'Mechs musculature, which presumably increases in weight as the 'Mech gets bigger and/or faster.

[skiltao]

Well that's partly because the engine in a 'Mech is greatly shielded by the torso of the 'Mech itself. The pilot gets nowhere near it. But it's different on a vehicle, the crew compartment is right up against where ever the engine is, so it needs the extra shielding to protect the crew. (At least, that's how I've always explained it.)

That's an old favorite, yeah. :)  Though like SCC is saying, it doesn't apply to designs that don't have distinct heads, and while it addresses the issue of mass it doesn't address the issue of slots. Any thoughts on how to connect it to the double heatsink issue?

[Tegyrius]

A good effort!  Now explain why Torso-Mounted Cockpits don't require extra shielding on the engine ala tanks.

Life is cheap but BattleMechs aren't?

[YingJanshi]

A good effort!  Now explain why Torso-Mounted Cockpits don't require extra shielding on the engine ala tanks.

Because even a Torso Mounted cockpit is still it's own sealed, shielded thing; even if it is physically closer to the engine than a normal head mount.

[idea weenie]

I figure that it's that environmental sealing that 'Mechs get for free. Of course one problem is that that extra mass is said to include transmission, which makes me wonder where mass is budgeted for a 'Mechs musculature, which presumably increases in weight as the 'Mech gets bigger and/or faster.

I've figured that the extra internal structure and extra musculature is part of the Mech's Engine weight.


But yes, torso mounted cockpits should have a mass penalty to reflect that they are closer to the Mech's engine.  By reducing the distance between the pilot and engine, you need extra physical shielding to make up for it.

[Sockmonkey]

I figure that it's that environmental sealing that 'Mechs get for free. Of course one problem is that that extra mass is said to include transmission, which makes me wonder where mass is budgeted for a 'Mechs musculature, which presumably increases in weight as the 'Mech gets bigger and/or faster.

The only numbers that fit are ones that have the musculature be included in the engine weight. Otherwise the engine weights would increase linearly and the internal structure weight would increase on the curve instead of the other way around.

[Scotty]

Because even a Torso Mounted cockpit is still it's own sealed, shielded thing; even if it is physically closer to the engine than a normal head mount.

But why (or more specifically how) is that any different from a crew compartment on a vehicle?  Especially a single crew vehicle?

(Hint: it's because it isn't, and the rules are arbitrary and do not reflect anything remotely resembling realism.  It's a fool's errand.)

[Tai Dai Cultist]

(Hint: it's because it isn't, and the rules are arbitrary and do not reflect anything remotely resembling realism.  It's a fool's errand.)

It's actually because Catgirls are used as reactor shielding to make DHSs possible, and Catgirls won't go near tanks.  (Annapuma and Unipuma excepted)  Generally only mechs and ASFs are sufficiently kawaii.

[SCC]

But why (or more specifically how) is that any different from a crew compartment on a vehicle?  Especially a single crew vehicle?

(Hint: it's because it isn't, and the rules are arbitrary and do not reflect anything remotely resembling realism.  It's a fool's errand.)

Not really, 'Mechs have single person cockpits for the most part, where as tanks have multi-person crew compartments that probably take up a good chunk of their volume and that wrap around the engine, they may also need to shield infantry bays so it makes sense to shield the entire reactor.

The only numbers that fit are ones that have the musculature be included in the engine weight. Otherwise the engine weights would increase linearly and the internal structure weight would be increase on the growing curve instead of the other way around.

So this stuff is removed when the engine is put into a tank, right?

[YingJanshi]

But why (or more specifically how) is that any different from a crew compartment on a vehicle?  Especially a single crew vehicle?

(Hint: it's because it isn't, and the rules are arbitrary and do not reflect anything remotely resembling realism.  It's a fool's errand.)

Um...because like I said even Torso Mounted cockpits are a sealed unit. As in 'Mechs can work in vacuum just fine and vehicles can't unless they devote tonnage to Environmental Sealing.

[Sockmonkey]

So this stuff is removed when the engine is put into a tank, right?

If the rules were consistent about it, yeah. A tank's suspension tracks and electric motors aren't going to weigh as much as the legs of an equally massive mech would.

[Scotty]

Um...because like I said even Torso Mounted cockpits are a sealed unit. As in 'Mechs can work in vacuum just fine and vehicles can't unless they devote tonnage to Environmental Sealing.

And what possible reason is there for it to cost tonnage to seal a vehicle but not a 'Mech? ::)  Especially, once again, for single crew vehicles.  By every measure a Gabriel or a Savannah Master should require identical tonnage to a 'Mech of the same construction for their engine and to have a sealed crew compartment, on account of having exactly one crewmember (just like a 'Mech) and having their crew compartment exactly as far from the engine as a 'Mech with a Torso-Mounted Cockpit.

But they don't, because vehicles aren't allowed to be as good as 'Mechs.  It's arbitrary, it has been arbitrary from the very beginning, it will continue to be arbitrary.  That doesn't mean the decision to make them worse is bad, it just means that it was definitely a decision, and not something borne out of realistic concerns and considerations.

[cpip]

And what possible reason is there for it to cost tonnage to seal a vehicle but not a 'Mech? ::)  Especially, once again, for single crew vehicles.  By every measure a Gabriel or a Savannah Master should require identical tonnage to a 'Mech of the same construction for their engine and to have a sealed crew compartment, on account of having exactly one crewmember (just like a 'Mech) and having their crew compartment exactly as far from the engine as a 'Mech with a Torso-Mounted Cockpit.

The handwave I'd go with is the neurohelmet. As far as I know, tankers in the BTU are still using control surfaces that would be more familiar to a 20th/21st century tank operator than the loadout on a 'Mech. So therefore, the shielding/sealing space that a 'Mech cockpit has, is instead additional control surfaces and electronics on a Savannah Master.

(It's a weak handwave, to be sure. But it's the best I could argue if someone insists on coming up with a 'realistic' solution. Neurohelmets wouldn't justify 'Mechs that aren't humanoid bipedal either...)

[Scotty]

if someone insists on coming up with a 'realistic' solution.

I have identified the problem.

[SteelRaven]

The easiest answer would be Tanks use a different type of engine but Fasa era fluff already indicated that Tank engines have been salvaged to repair mechs. Head cannon, the Fusion Engine for tanks use the same parts but are ultimately constructed differently. Many other things could also play a part not reflected in the construction rules for the the sake of game simplicity, much like how we have different calibers for the AC/5 but any AC/5 ammo is AC/5 ammo for any AC/5 regardless.

It's a game, don't overthink it.     

[Daryk]

It is a game, but using the Savannah Master example, you're not going to fit a three-ton cockpit into that thing.  Also remember that vehicle fusion engines have to add 50% of their mass for extra "shielding".  It's already baked in.

[YingJanshi]

And what possible reason is there for it to cost tonnage to seal a vehicle but not a 'Mech? ::)  Especially, once again, for single crew vehicles.  By every measure a Gabriel or a Savannah Master should require identical tonnage to a 'Mech of the same construction for their engine and to have a sealed crew compartment, on account of having exactly one crewmember (just like a 'Mech) and having their crew compartment exactly as far from the engine as a 'Mech with a Torso-Mounted Cockpit.

But they don't, because vehicles aren't allowed to be as good as 'Mechs.  It's arbitrary, it has been arbitrary from the very beginning, it will continue to be arbitrary.  That doesn't mean the decision to make them worse is bad, it just means that it was definitely a decision, and not something borne out of realistic concerns and considerations.

Dude, the whole point of this thread was to try to find an in-universe justification of why the rules are a certain way. Of course the out of universe answer is gonna be "game balance". Duh. But that misses the entire point of the thread.

[RunandFindOut]

Dude, the whole point of this thread was to try to find an in-universe justification of why the rules are a certain way. Of course the out of universe answer is gonna be "game balance". Duh. But that misses the entire point of the thread.

No, you are missing HIS point.  That the rules are arbitrary and difficult to impossible to justify in universe as well.  The rules were created arbitrarily out-of-universe and done in such a way that you can't actually find a good justification for them in universe.  Pretty any much explanation ends up falling flat if it's not allowed to stand without any question. 

The extra fusion engine tonnage was specifically added to reduce the amount of weapons tonnage available to vehicles so heavy tanks wouldn't have so much available.  The double heat sink rule was added after those were created because allowing them on tanks made them too competitive for mechs.  In both cases little to no thought was given to why those rules should be the case from an in-universe perspective.  And this resulted in the current situation where people frequently point it out because the lack of forethought has caused those rules to require much more suspension of disbelief.  Singling them out for attention.

[Revanche]

That the rules are arbitrary and difficult to impossible to justify in universe as well. 

But that is breaking the premise of the question: the search for an in-universe answer. Just because one individual cannot creatively solve the answer doesn't mean no one can. There are plenty of places where people enjoy staying within the bounds of the universe and seek creative answers.

However, I think it might be best for those of us that do ask in-universe questions just ignore the responses that don't play by the requested rules. Neither party has to convince the other it must be done in-universe or from the behind-the-scenes perspective.

I--for one--subscribe to the extra shielding needed when removed from the inherent protection of a 3-ton cockpit. Someone can shoot that down (for only for their head canon), but I'll replace my head canon when a better answer is provided.

[SteelRaven]

That the rules are arbitrary and difficult to impossible to justify in universe as well.

If you take the rules for game as literal interpretation, yeah. Your just going to bang your head against the wall. Take it as a abstract interpretation and you got some room for logic and head canon. Was this aspect of Tanks a after thoughts from the creators, yes. But unless you have a time machine, we have to make the best of it unless you want to ret-con allot of tanks out of existence.

I'm sticking with my head canon that tank fusion engine and mech fusion engines use the same parts but are ultimately different.   

[skiltao]

And what possible reason is there for it to cost tonnage to seal a vehicle but not a 'Mech? ::) 
<snip>
It's arbitrary, it has been arbitrary from the very beginning <snip> and not something borne out of realistic concerns and considerations.

I don't think it's unrealistic to use cheaper construction on vehicles than on 'Mechs. It's a doctrinal (or logistical) barrier rather than a purely technological one, sure, but it is something the books give some consideration to.

The easiest answer would be Tanks use a different type of engine but Fasa era fluff already indicated that Tank engines have been salvaged to repair mechs.

That's ultimately a semantic problem with how the word "engine" is getting parsed.

So therefore, the shielding/sealing space that a 'Mech cockpit has, is instead additional control surfaces and electronics on a Savannah Master.

you're not going to fit a three-ton cockpit into that thing.  Also remember that vehicle fusion engines have to add 50% of their mass for extra "shielding".  It's already baked in.

Oh hey, those are good points. I doubt there's many vehicles where the 1.5x engine multiplier isn't better than paying 3 tons per crewmember.

That the rules are arbitrary and difficult to impossible to justify in universe as well
<snip>
In both cases little to no thought was given to why those rules should be the case from an in-universe perspective. 

That's your opinion. In some ways, I agree with it. But it's super shaky ground unless you personally witnessed the events in question, or interviewed someone who did, or can present an exhaustive survey of all BattleTech stuff ever written.

And even if it's true, it isn't a useful point to make. That initial arbitrariness doesn't tell us anything about the surrounding constraints. And while the constraints may seem so tight as to make an explanation impossible, that doesn't actually mean that explanation is impossible--it just means you identify the constraints and put them up for discussion.