thrust limits from structure

[Ishmael]

I had the idea that structure should provide a limit to how much thrust a ship can endure without breaking up.
Following an idea that the mass a structure can support is dependent of the structure's total cross-sectional area it would appear that the amount of support a point of structure can provide follows a square/cube relationship.

If I assume that the standard structure point per 50 dtons allows support for 1G, then for 2G's of support, we'd need 2.83 structure points; 2^(3/2) or 2^(1.5) per 50 dtons.
5G's of support would need 11.2 structure points per 50 dtons.

Reversing this procedure can give the amount of thrust a hull can take when damaged. A damaged hull that has 4 remaining structure points per 50 dtons can accelerate by up to 2.5 G's without collapsing due to over-stress; 4^(2/3).

This should limit super-battleships, somewhat, and make them 'act' like super-battleships instead of giant fighters that can zip about.
Naturally, adding massive armor should impact performance, but tracking mass is a complication that can be handled at a later time.

For ships that are built using monocoque structures where the hull IS the structure, then hull points could be treated as structure points. As the hull gets blown away, the structure points are blown away as well with new limits to acceleration being re-calculated each turn that damage is taken.

just as idea

 

[AndrewW]

There go the small fast fighters then. Small craft up to 90 tons only have 1 structure point.

 

[BP]

Not sure quite what you are driving at - a ship should have no problem with 'breaking up' except due to external pressure or thermal loads.

Area is related to mass via density - which is non-uniform and hardly realistically definable. I.e. engine spaces are gonna mass a lot more than cargo holds. And cargo holds and fuel tanks are gonna change mass significantly.

Also, just because something is bigger, doesn't mean it has greater limits on maneuverability or thrust (do some research on U.S. aircraft carriers . In fact, 6Gs is not a lot when talking structure (though, it is when talking humans).

Pressure in atmo can be an issue (dispersed hulls), but plasma and wind shear (and hail and fauna) is a much bigger concern. Submersed is a different issue entirely...

 

[rinku]

The assumption of 1G as a standard doesn't hold, since the same hull can have 6G drives without any problems, and 2-3G drives are very common. There's also the issue of gravitics - by defininition a standard Traveller grav drive ship has grav compensation that can match its thrust, so it's not clear if *any* stress is taking place on the internal structure.

Trav ships are also pretty rugged by default. 4pts of crystaliron armour ends up giving a hull about 15cm thick. On a vessel that's around 20-30 metres long (as most of the standard ships are), that's a pretty strong shell.

 

[DFW]

If I assume that the standard structure point per 50 dtons allows support for 1G,

What are you basing that assumption on?

 

[rinku]

Hey! Did DFW and I just agree on something?

 

[DFW]

Hey! Did DFW and I just agree on something?

:shock:

 

[Ishmael]

There go the small fast fighters then. Small craft up to 90 tons only have 1 structure point.

Actually, small craft can have much more structure when using the High Guard SRD where 'structure can be reinforced. I also am proposing monocoque contruction techniques where hull points can act as structure points even though it'd take damage from hull hits. Hulls can be reinforced too.

In fact, that's why I made the assumption that 1 structure point can hold up a 50dton ship in 1 G; the basic hull is clearly the bottom line base model hull which would not have been too terribly over-engineered. Otherwise structure and hull reinforcements would not be neccessary.

There's also the issue of gravitics - by defininition a standard Traveller grav drive ship has grav compensation that can match its thrust, so it's not clear if *any* stress is taking place on the internal structure

This also allows for grav drives to be used in a "1G" basic hull, I suppose. Grav drives seem to be the only ones available in the core SRD, yet the game should have support for non grav drives such as mentioned in High Guard.

It looks like handling this issue would end up beyond the scope of the simple game in that it would also require tracking ship's mass, surface area and material strengths and masses.

I just feel that structure should be used for more than just 'hit points' for a ship/vehicle.

btw, I served on a carrier for 4 1/2 years...they must obey the same physics as everyone else. They are very fast but not very manuverable at speed...certainly less than a 'Schnellboot' moving at the same speed.
A small boat can be lifted with a sling...a carrier would end up cracking in half....

so much for a hard science approach, eh?
I'll just go back to my own stuff instead

 

[rust]

I just feel that structure should be used for more than just 'hit points' for a ship/vehicle.

I have been thinking about using some combination of hull + armour and
structure to determine the crush depth of Mongoose Traveller vehicles, si-
milar to the way GURPS Traveller does it with armour and frame strength.
The result would probably a formula where the hull + armour would provi-
de a basic value and the structure a modifier (e.g. x1, x2, etc.).

However, since I am currently not using Mongoose Traveller vehicle stats
for submarines, I have not worked out anything.

Edit.:
I have determined arbitrarily that a Traveller starship without armour and
reinforced hull has a safe depth of 200 meters (this fitted well into my cur-
rent setting).
For ships without a spherical or otherwise pressure resistant hull each 5 %
of reinforced structure could double this safe depth (400 m, 800 m, etc.).

 

[DFW]

In fact, that's why I made the assumption that 1 structure point can hold up a 50dton ship in 1 G; the basic hull is clearly the bottom line base model hull which would not have been too terribly over-engineered. Otherwise structure and hull reinforcements would not be neccessary.

There is nothing is the design rules that makes it problematic to design a 50t ship without additional structural reinforcement beyond the standard hull, an have 6G acceleration, . It doesn't violates anything with physics. So, I still don't know how you came to that conclusion.

 

[Ishmael]

So, I still don't know how you came to that conclusion.

then don't worry about it.

It appears that the base ship/vehicle rules are too simplistic to do what I want to do, so I'll work with other stuff ( and because it won't be based on Mongoose rules, I'll work with it elsewhere and not muddy the waters here )

 

[AndrewW]

Actually, small craft can have much more structure when using the High Guard SRD where 'structure can be reinforced. I also am proposing monocoque contruction techniques where hull points can act as structure points even though it'd take damage from hull hits. Hulls can be reinforced too.

Yes they can at the cost of more tonnage. For say a 10 ton fighter this is .5 tons for every structure point added. When you've only got 10 tons to work with this adds up quickly, especially if you want to be putting in larger drives to use the extra structure...

 

[DFW]

Actually, small craft can have much more structure when using the High Guard SRD where 'structure can be reinforced. I also am proposing monocoque contruction techniques where hull points can act as structure points even though it'd take damage from hull hits. Hulls can be reinforced too.

Yes they can at the cost of more tonnage. For say a 10 ton fighter this is .5 tons for every structure point added. When you've only got 10 tons to work with this adds up quickly, especially if you want to be putting in larger drives to use the extra structure...

I think the data that Ish is missing is the strength of the future hull material that Traveller presumes. Without those figures, detailed assumptions like this can't be made.

 

[CosmicGamer]

Hows this
- some cars can reach close to 1G on a skid pad
- many cars can brake at over 1G
- a formula one race car can generate 1.5G acceleration
- a formula one race car can generate 5G braking
- aerobatic planes and fighter jets can generate over 9G when turning
- the space shuttle can reach up to 3G at launch
- the Apollo 16 on reentry hit over 7G

Personally, I think Traveller space craft are sturdy enough that I wouldn't worry about how much acceleration they could handle.

 

[rinku]

Ishmael,

Thinking some more about it, I think your idea is good (though not for every campaign), but you may be approaching it from the wrong direction.

As I mentioned, standard Traveller starships are very rugged. Perhaps what you're looking for is to de-ruggedise them? That is, *reduce* the hull/structure on ships as a cost saving for those which can do without it?

After all, the average Free Trader boosts out to 100D at 1G, jumps, then comes in from 100D at 1G. It's likely to undergo extra stress during re-entry, though the jury is out as to how contra-G affects this.

Yet that Free Trader has the same armour, proportional hull and structure as a 3G mercenary cruiser which you would think gives better structural integrity since it has less mass and volume. There would be wiggle room there to reduce the FT's structure - it appears overengineered to me.

My gut feeling is that bigger ships would need to allocate proportionally more structure to acheive the same structural integrity as a smaller one. Can't remember if High Guard addresses this - standard ships are similar enough in size that a flat value per 50 tons works.

 

[DFW]

Ish, I remembered this from MGT HG/Book 2 errata:

Page 59
Add this footnote;
Note that small craft under 70 tons can achieve Thrust ratings greater than 6. This is not possible on bigger ships due to stress limitations on larger hulls.