Carried vessel/craft design trivia

[Major B]

I'm trying to figure out a good house rule for designing landing feet or skids and what type(s) of landing cradles would be necessary for carried craft.

For the first part - remember the landing feet on the original type S deckplans from S7? There may have been rules for them in Bk2 or Bk5 but I know there are no rules for those in MT. Have any other systems incorporated landing skids or feet?

Second part - most of the designs I'm familiar with (and those are too few) have what I'd call "fitted" berths for carried craft rather than hangars where any craft can find a home (the Azhanti High Lightning is the only design with such I can remember). So a standard cutter or ship's boat (being tubular designs) would need some sort of cradle if they were to be berthed in a bay or hangar. Has anyone seen a workup on the dimensions such a crade would take up? Or how much one would cost?

Any ideas or dim memories from any system would be welcome.

 

[sabredog]

1) Nope, no specific rules for landing gear in CT.

2) The only things they had in HG and Book 2 were the costs of carrying small craft depended on the size of the ship carrying them (1000ton- no extra cost of volume) and if they were carried inside, outside, or what the config of the ship was.

 

[flykiller]

I have pretty much just 20 dton gigs, all with keel skids for any ground-side landings. they follow a standard airlock layout so they all fit in standard 26-30 dton gig bays. see my deckplan link below. couldn't think of a better way to manage the vaccuum/atmo and ship/ship transition. the starwars/startrek hanger-bay approach looks better in a movie, and probably works better in a game, but there's just no room for it in hg2 ship rules, and I just can't accept it anyway.

 

[far-trader]

I'm trying to figure out a good house rule for designing landing feet or skids and what type(s) of landing cradles would be necessary for carried craft.

For the first part - remember the landing feet on the original type S deckplans from S7? There may have been rules for them in Bk2 or Bk5 but I know there are no rules for those in MT. Have any other systems incorporated landing skids or feet?

Nothing specific in B2 or B5. For house rules I've long (always?) lumped it in with the "bridge" tonnage and streamlining expense in those rules. I think many others have too. And then simply handwaved just what type of system it was. Skids, wheels, feet, fixed or retractable, whatever.

As far as I recall no system has done them, not even TNE FF&S. Though you could in that I suppose. Just designing non-powered wheels sufficient for the craft in question. Never thought of it in the day though. Maybe T5 will address it

Second part - most of the designs I'm familiar with (and those are too few) have what I'd call "fitted" berths for carried craft rather than hangars where any craft can find a home (the Azhanti High Lightning is the only design with such I can remember). So a standard cutter or ship's boat (being tubular designs) would need some sort of cradle if they were to be berthed in a bay or hangar. Has anyone seen a workup on the dimensions such a crade would take up? Or how much one would cost?

Any ideas or dim memories from any system would be welcome.

T4 went into this a bit. As did TNE FF&S with a little more detail.

B2 only specifically allowed small craft (under 100tons) and vehicles to be carried. All such were carried at their tonnage for no extra cost and it was up to the individual to handwave if it was a hanger, cradle, docking ring or whatever.

B5 went a little further, allowing different carriages and large craft (over 100tons), some requiring extra tonnage (or wasted tonnage) and a price for some fittings.

It was (and is afaik) still an imperfect system that largely ignores the problem of the nesting dolls of the same size fitting inside each other.

I once worked out the rough hanger sizes to fit the standard cylindrical small craft designs and they all came to around 6 times the volume for a squared hanger allowing clearances of 1.5 all around. If I recall correctly. Even fitted (conformal) hangers needed about 2 times the volume when accounting for walls and minimal clearances. Again iirc.

 

[robject]

For the first part - remember the landing feet on the original type S deckplans from S7? There may have been rules for them in Bk2 or Bk5 but I know there are no rules for those in MT. Have any other systems incorporated landing skids or feet?

T5 has options for various landing gear, including defaults that vary based on the hull configuration. Streamlined hulls come standard with landers and lifters, I think.

Second part - most of the designs I'm familiar with (and those are too few) have what I'd call "fitted" berths for carried craft rather than hangars where any craft can find a home (the Azhanti High Lightning is the only design with such I can remember). So a standard cutter or ship's boat (being tubular designs) would need some sort of cradle if they were to be berthed in a bay or hangar. Has anyone seen a workup on the dimensions such a cradle would take up? Or how much one would cost?

No knowledge. Current T5 rules allow cramped hangars or spacious ones for carried craft (in addition to fitted-niche and docking-ring options), but no mention of cradles.

 

[morfydd]

T5 has options for various landing gear, including defaults that vary based on the hull configuration. Streamlined hulls come standard with landers and lifters, I think.



No knowledge. Current T5 rules allow cramped hangars or spacious ones for carried craft (in addition to fitted-niche and docking-ring options), but no mention of cradles.

Docking rings come closest to being cradles ..but a good portion of the carried craft is hanging out the back end..

Better solution is the Spacious msall craft bay ie doubele the volume and you have a cradle..or a lot of them and you have a bay

 

[robject]

Docking rings come closest to being cradles ..but a good portion of the carried craft is hanging out the back end..

Better solution is the Spacious msall craft bay ie doubele the volume and you have a cradle..or a lot of them and you have a bay

Agreed. I put the question to Marc yesterday and he replied:

We talk about grapples [...]
Most hangars are small and hold a craft rather tightly. ([...] I think we need to address "big" spacious hangars).

We have docking rings that hold standard small craft by the nose.

But your comment shows we need a standard system for holding craft in place... something [performing a function similar to] automatic tiedowns so that rows of small craft are held tightly in a hangar as the big ship moves.

And since Marc is currently working on the starship revision to T5*, perhaps he'll add an option.


* in bursts of activity. Compare Vigor versus Endurance...

 

[Tellon]

I have always regarded landing "gear" as part of the "wasted space" or as a part of the internal structure of the humm (when calculated) --

I kinow the rules (FWICT) is that there is nothing in there *specifically* for landing gear

But like it was mentioned above -- non-powered wears with a cost -- maybe taking up a bit of volume -- just like a grapple --

 

[Major B]

Thanks to everyone for all the feedback, but I'm a little disappointed that someone hasn't already figured out something I can use.

Any more ideas or suggestions, please let me know. In the meantime I'll have to see if I can come up with something that passes first look.

 

[Major B]

remember the landing feet on the original type S deckplans from S7?

I just checked the deckplan for the Type S. The two aft landing feet recesses are shown to be 2x2 squares, so with some risk one might assume that each was about 2 Td.

The forward foot isn't shown on the plan. Since the nose is smaller and presumably lighter, perhaps the front foot is half the size of the rear feet at 1 Td. Alternatively, since there is only one forward foot, maybe it needs to be the same size as the rear feet.

Without knowing the size of the front foot, it appears that the combined volume of the feet is either 5 or 6 Td. That is 5% or 6% of the hull volume.

Does 5% to 6% of hull volume seem to be a totally unscientific but good rule of thumb for planning?

 

[robject]

Does 5% to 6% of hull volume seem to be a totally unscientific but good rule of thumb for planning?

It seems to me that, since most player starships do in fact land, that rather a better rule of thumb would be to award ships extra tonnage if they do not have landers, and assume the default is "some sort of landing gear is figured in already".

 

[far-trader]

I just checked the deckplan for the Type S. The two aft landing feet recesses are shown to be 2x2 squares, so with some risk one might assume that each was about 2 Td.

I always figured them as half height bays, at most, so 1dton each. And that just so I could run various stowaway and critter infestation fun and the occasional manual deployment crisis

The forward foot isn't shown on the plan. Since the nose is smaller and presumably lighter, perhaps the front foot is half the size of the rear feet at 1 Td. Alternatively, since there is only one forward foot, maybe it needs to be the same size as the rear feet.

I think I've gone both ways on that, though again just half height, so half your tonnage assessment. I think it was Scarecrow who made the front one (a narrow foot) double as a stairway from the forward airlock just behind the bridge. I liked that idea a lot.

Does 5% to 6% of hull volume seem to be a totally unscientific but good rule of thumb for planning?

Seems a bit excessive to me. I'd probably go with 1% or 2%, though my preferred method (noted above iirc) is to just handwave it as part of the bridge tonnage.

 

[far-trader]

It seems to me that, since most player starships do in fact land, that rather a better rule of thumb would be to award ships extra tonnage if they do not have landers, and assume the default is "some sort of landing gear is figured in already".

In those cases (i.e. unstreamlined ships*) I figure in place of landing gear they have (and need) more attitude control thrusters (which I also subsume into bridge tonnage).

* though even they may land on airless worlds, or if you're of the gravitics wonders crowd they can even land of worlds with atmospheres

 

[sabredog]

Seems a bit excessive to me. I'd probably go with 1% or 2%, though my preferred method (noted above iirc) is to just handwave it as part of the bridge tonnage.

I've always gone the same route figuring that "Bridge" tonnage was as much a catch-all for avionics, flight control surfaces (or directional thruster controls), landing gear, and all the myriad things not explicitly detailed, but implied as part of the "controls the ship" components. Same way that all things related to life support and living space come out of generic staterooms, and ramps, cargo locks and lifts come out of "Hold".

I'm not of the magic contra-grav crowd, though, so I also don't allow anything over 1000 tons to land unless the starport is A or B, and even then the upper max is 2000 tons. So that also solves a lot of those issues.

 

[Major B]

I always figured them as half height bays, at most, so 1dton each.

That makes sense given the shape of the hull and would cut down on the percentage of hull required. I think 5-6% is excessive too. That's why I posted it - to get more ideas.

I think it was Scarecrow who made the front one (a narrow foot) double as a stairway from the forward airlock just behind the bridge. I liked that idea a lot.

I like that idea too. I'll dig through the gallery to see if I can find his workup.

Seems a bit excessive to me. I'd probably go with 1% or 2%, though my preferred method (noted above iirc) is to just handwave it as part of the bridge tonnage.

I've always gone the same route figuring that "Bridge" tonnage was as much a catch-all for avionics, flight control surfaces (or directional thruster controls), landing gear, and all the myriad things not explicitly detailed, but implied as part of the "controls the ship" components. Same way that all things related to life support and living space come out of generic staterooms, and ramps, cargo locks and lifts come out of "Hold".

You've both hit on exactly the reason for the question. I'm trying to figure out a way to allocate tonnage in the design sequence so that the design does a better job of translating into a deckplan. So, rather than steal accomodations space for other purposes on the deckplan, the designer chooses how much space for each feature in the design sequence and can then directly port those allocations over to a deckplan and start laying it out.

This is a bit harder in MT because you don't have the large space allocated to 'bridge' that can be used for other purposes in the deckplan.

I'm not of the magic contra-grav crowd, though, so I also don't allow anything over 1000 tons to land unless the starport is A or B, and even then the upper max is 2000 tons. So that also solves a lot of those issues.

Size limit was going to be a future discussion topic. Thanks for saving me the trouble of a new thread.

 

[atpollard]

Landing Gear are almost always depicted far larger than necessary. Sand compacted enough to walk on without sinking, will support 1 metric ton per square meter. So a ship with 1 square meter of landing pads per metric ton of ship can safely land on a beach or a plowed (but not muddy) field. A concrete landing pad will support at least 10 times as much, or a conservative 10 metric tons per square meter of landing pad (actual values are probably twice that).

Turning the problem around, each 1.5m square on the deckplan dedicated to landing pads will support 22 to 50 metric tons of starship on a concrete tarmac or 2.25 metric tons of ship landing in a plowed field.

 

[aramis]

Arthur, 10 Metric Tons is about 1 displacement ton...

Concrete tends to damage at 0.7MPa (about 70 tons per square meter).

Class of Materials Load-Bearing Pressure (pounds per square foot)
Crystalline bedrock 12,000
Sedimentary rock 6,000
Sandy gravel or gravel 5,000
Sand, silty sand, clayey sand, silty gravel, and clayey gravel 3,000
Clay, sandy clay, silty clay, and clayey silt 2,000
Source: Table 401.4.1; CABO One- and Two- Family Dwelling Code; 1995.
http://www.concretenetwork.com/concrete/footing_fundamentals/why_soils_matter.htm

the above is static loads, but... it's roughly 30 tons per square meter for sedimentary rocks, and 60 for bedrock.... in short, the landing gear shown is, in fact, all too small for anything less than engineered reinforced materials. (The Type S is shown with 8m² of LG, and a third and/or 4th leg not shown, and is 815 tons unloaded per MT IE... or about 100 Mg per m². )

 

[Major B]

Thanks Arthur!

Turning the problem around, each 1.5m square on the deckplan dedicated to landing pads will support 22 to 50 metric tons of starship on a concrete tarmac...

So, to land on an improved surface (at a downport) and assuming that necessary hydraulics would not require more than 3m height inside the hull directly above the 1.5 m2 'foot' ...

that would be 6.75 kl internal per 50 Tm of ship weight.

...or 2.25 metric tons of ship landing in a plowed field.

or 148.5 kl (6.75 x 22) per 50 Tm if you want to make wilderness landings.

 

[aramis]

that 50 Tm (properly Mg, megagrams) is between 2 and 10 tons displacement, using MT or TNE masses.

A scout courier should have a ground pressure under 20 Mg/m² for reasonable landing options.

Also, keep in mind that landing gear systems may include folding components.

Further, reasonably, you can get multi-stage hyrdaulics to about 3:1 without excessive flexibility. (I've seen that on various construction equipment with 3 and 4 stage rams, and frequently on jacks, as well.) So your presumption of 3m tall isn't of need viable, and you can probably halve that.

A quick review of MTIE, and I get a range of masses (unloaded) per Td of 3Mg/Td (Mercenary) to about 20Mg/Td (Gazelle), with most in the 8-10 range.

 

[atpollard]

I hate making metric calculations since I am too familiar with Imperial units, but we use 4000 pound per square inch compressive strength concrete to design heavy traffic areas (like a truck loading dock). Unless I messed up the conversion, 4000 PSI should be 2765 Metric Tons (aka Mg) per square meter, so the concrete landing pad should be able to support VERY HEAVY concentrated loads. Here in Florida, everything (99% of our projects) is built on sand and we use 2500 pounds per square foot for our design calculations (roughly your 3000 psf quoted value with an engineer ‘chicken factor’ to appease the government regulators who are sure that the contractors will not compact it properly during construction). Again, unless I messed up the conversion, 2500 PSF should be about 12 Metric Tons per square meter, so the concrete slab at the landing pad needs to be thick enough to spread the concentrated load from the landing gear across the compacted sand below.

Ultimately, the load limit on the landing pad would be 12 metric tons per square meter of total landing pad area, with a safety limit of perhaps 1000 metric tons per landing leg (to absorb the potential impact loads from a less than soft touchdown).

Using your bedrock value for a “Class E” starport, would indicate a limit of about 57 metric tons per square meter of landing leg foot.

EDIT: Major B, [a 1.5 m square of 'landing gear' per 128 Metric Tons of Starship and a minimum of 1 landing leg per 1000 Metric Tons of Starship.]

SLIGHTLY OFF TOPIC:
The density values of 3-20 metric tons per dTon (average 10) are correct for MegaTraveller (and I assume TNE), but really stink when compared to real world vehicles. Modern Submarines packed full of nuclear reactors with dense shielding, living spaces that make prisons seem spacious, and enough armor to withstand the crushing depths of the ocean are less than 13.5 metric tons per dTon. The concept of launching ‘brick starships’ into orbit strains credibility for me. Starships are mostly air (crew occupied spaces) and liquid hydrogen [both about 1 metric ton per dTon] and the entire starship should be far less dense than indicated in MegaTraveller [closer to an average of 4 metric tons per dTon in my opinion, like the Saturn V, Apollo CM and Space Shuttle].

Simply changing the Traveller structural components from steel (like the Hull rules describe) to aluminum should cut their weight in half.