Kinunir-class landing gear

[Maitrejeanthierry]

(That question has probably been asked before but I can't find any reply. Sorry for the cross-post, just in case.)


Do Kinunir-class ships have wheeled undercarriages or simple skids ?

Since Streamlined ships are supposed to be able to land aircraft-style, my money would be on wheels, but is that the case ? Is that even reasonnable ?

Do ships this size (1200+ Dtons) often make planetside landings in your TUs ? I mean, not in case of emergencies, but during routine operations ?

 

[atpollard]

I don't know of any official answer in a published source, but skids tend to be more common on ships in general (per illustrations).

I looked into the issue of landing gear on general starships as a matter of curiosity one time. The results were surprising.

First issue becomes "How much does a starship weigh?", which is ultimately either unknown or rules version specific. Aircraft and historic spacecraft in general, tend to be around 4 metric tons per Traveller displacement ton.

The second issue is that a starship is huge. A 100 dT scout is larger than the space shuttle and heavier than the heaviest transport aircraft. Look at the landing gear on the AN-225 Transport and a scout ship will probably have larger landing gear ...

The third issue becomes pavement design. This was my original question (How thick is the pavement at a starport?). Real world airport runways tend to be around 0.3 meters thick (about a foot) of concrete. Traveller starships will require closer to a meter of concrete to keep the landing pads in the illustrations from punching through the concrete.

For a 1200 dT ship like you ask, the object is comparable in size to a fully loaded warehouse or medium-rise office building. How many wheels will be needed to make an office building mobile? The foundation needed to support it on four or six landing legs (without punching through the landing pad) is measured in meters of thickness.

An ironic consequence is that water landings become preferable for large ships .

I hope that some of this is useful.

 

[aramis]

as a reference data set...
Antonov AN225 Mriya max TO is 640,000 kg
Boeing 747-8I max Takeoff weight is 442,253 kg
Airbus A380-F max TO is 590,000 kg
C5B Galaxy max takeoff weight is 381,000 kg.
Boeing C17 Globemaster max TO is 265,350 kg


The Scout/Courier is, according to MT, 840 metric tons empty, 941 loaded.

 

[DaveChase]

I think a bit of this question's answer depends on if you have or allow grav plates (or something similar).

If you don't the psi will poke holes in almost anything in most of the ship designs.

If you do allow them, do they take power? If so what happens when you run out of fuel or power?

Dave Chase

 

[aramis]

Assuming a type S has 4 square meters of landing gear, that's just a bit shy of 236 tons/m²...

Concrete has a typical compressive strength of 4000psi (27586kPa) which is 2759 or so tons in 1G at rest.

As commonly shown, the type S has about 6 to 8 square meters of landing strut.

Don't land hard - need to touch at under 10m/s - but once down, a type S is actually well within concrete's compressive strength.

 

[whartung]

as a reference data point...
C5B Galaxy max takeoff weight is 840,000 lb (381,000 kg).

The Scout/Courier is, according to MT, 840 metric tons empty, 941 loaded.

that's 2.2x the max TO of the C5B... empty.

It's (mostly) about ground pressure.

So, an empty SC, 840,000kg would need landing gear totaling 42m2 of landing surface to have a ground pressure equivalent to a passenger car (200 kPa, or about 29 psi). That would be three skids 2x7m long. Obviously there's no requirement for it to be comparable to a passenger car. An M1 Tank, Fyi, has about 1/2 the ground pressure of a car (big treads ftw).

I just use a car as a familiar comparison. And it is perhaps something to consider when landing in the wilderness. Can a Scout ship lift itself out of deep sand?

I never consider a streamlined ship "taking off like an aircraft", I consider it more "taking off like the Millennium Falcon" (float up a little bit, then point and shoot in to space). Streamlined ships are not airframes, and don't have the surfaces (or need) to generate lift.

 

[McPerth]

I understand weels would be a problem due to the sheer weight of such starships (as Kinunir), but, OTOH, I see them as easing taxing along the landing pods, if they have to, so easing the starport funciton at large.

Most Traveller starport despict landing pods as a place where ships land and stay for the lenght of their planet time, but I guess some kinds of hangar (albeit gigant ones, see the germa sumbarine shelters in WWII would not suffice for a 100 dton ship) should also be possible, both for staying in planet and for maintenance/repairs.

I can envision ships taxing along the starport to them or to parking zone, allowing for the landing pods to be used for more ships (and so increased traffic), either taxing by weels or by "low power" grav.

This said, most starship pictures (both, Traveller and other sci-fi sources) feature the landing gear as simple skids, without weels (more so if grav tech is in the speciffic setting).

 

[atpollard]

... but once down, a type S is actually well within concrete's compressive strength.

But not a 200 ton Free Trader which will have roughly the same footprint and twice as much weight.
... Or a 400 ton Fat Trader with only a little larger footprint and quadruple the weight.

 

[atpollard]

I understand weels would be a problem due to the sheer weight of such starships (as Kinunir), but, OTOH, I see them as easing taxing along the landing pods, if they have to, so easing the starport funciton at large.

I actually like wheels as a concept myself, but common truck tires (like on a tractor trailer) only support about 2.2 tons per tire. So Aramis' Scout needs over 400 truck tires, and a Free Trader would need twice as many!

You could go with those giant tires like mining trucks use, but they are going to show up in a deck plan if you expect to retract those monsters.

Since the issue is spreading weight across a larger area, tracks actually make more sense. The tracks on an Abrams allow travel over the sand (wilderness landings) at about 30 tons per track (about 30 tracks for Aramis' Scout). o:

 

[PFVA63]

It's (mostly) about ground pressure.

So, an empty SC, 840,000kg would need landing gear totaling 42m2 of landing surface to have a ground pressure equivalent to a passenger car (200 kPa, or about 29 psi). That would be three skids 2x7m long. Obviously there's no requirement for it to be comparable to a passenger car. An M1 Tank, Fyi, has about 1/2 the ground pressure of a car (big treads ftw).

I just use a car as a familiar comparison. And it is perhaps something to consider when landing in the wilderness. Can a Scout ship lift itself out of deep sand?

I never consider a streamlined ship "taking off like an aircraft", I consider it more "taking off like the Millennium Falcon" (float up a little bit, then point and shoot in to space). Streamlined ships are not airframes, and don't have the surfaces (or need) to generate lift.

Hi,

I did some similar calcs awhile ago, and ended up with pretty much the same conclusions that you appear to be suggesting (with flat bottom landing skids on most of the stuff craft that lift and land by gravitics.)

PF

 

[McPerth]

I actually like wheels as a concept myself, but common truck tires (like on a tractor trailer) only support about 2.2 tons per tire. So Aramis' Scout needs over 400 truck tires, and a Free Trader would need twice as many!

Maybe some better materials to make the wires has been developed...

You could go with those giant tires like mining trucks use, but they are going to show up in a deck plan if you expect to retract those monsters.

Not if you deinfalte them. Such way they can occupy quite low space when retracted, and only inflated when detracted for landing.

Since the issue is spreading weight across a larger area, tracks actually make more sense. The tracks on an Abrams allow travel over the sand (wilderness landings) at about 30 tons per track (about 30 tracks for Aramis' Scout). o:

Tracks use to destroy the pavement they go through, unless rubber (or similar) protectors are used. While I agree they could be a good solution to most those problems, some way to protect them shoulc be used or the maintenance cost of the starport itself would skyrocket.

 

[DaveChase]

Assuming a type S has 4 square meters of landing gear, that's just a bit shy of 236 tons/m²...

Concrete has a typical compressive strength of 4000psi (27586kPa) which is 2759 or so tons in 1G at rest.

As commonly shown, the type S has about 6 to 8 square meters of landing strut.

Don't land hard - need to touch at under 10m/s - but once down, a type S is actually well within concrete's compressive strength.

Slighty correct.

6 inch Concrete test cylinder can have 4000 psi, so can a 12 inch test cylinder.

But that does not mean that a 6 inch thick concrete slab will hold up as well as a 12 inch concrete slab under that kind of localized pressure.

Weather, foundation (what is under the concrete), pressure sudden or gradual, extreme tempatures over time, certain chemicals, what the concrete is made of.

Is it pervious or not? Is there a slope or does liquid pool in places?
Was the Concrete poured during hot or cold? Was the concrete pour all at the same tempature?
Was the Concrete pour continuous or did some set up quicker than other part during the pour?
Was it sealed or finished or sealed after finishing?

Are the landings along the sheer, straight down or slightly of plane?
Is the slab checked (has planned breaking points place in it) or just one huge slab?
Are there anchor supports into the rock table?


A lot of the above will determine if 3000 psi, 4000 psi or greater psi will last very long under use.
Of course footing and foundation and the ground make a lot of difference

I will not go into the Engineering aspect of concrete, but I will say that if done properly and poured correctly, concrete will last 1,000 of years (depends on the concrete material and of course environment.)

Dave Chase

 

[rancke]

I actually like wheels as a concept myself, but common truck tires (like on a tractor trailer) only support about 2.2 tons per tire. So Aramis' Scout needs over 400 truck tires, and a Free Trader would need twice as many!

Truck tires would presumably be better at higher tech levels. Though TL9 is only two levels above common truck tires, so they might not be 25 times better (Assuming 16 wheels).

I'm inclined to go with anti-gravity and no wheels at all. Just ease the whole vessel down on the ground to rest on its belly.


Hans

 

[HiverLord]

My assumption (such as it is) is that any suitable starport (probably C-class or better, but not sure about D) would be constructed with suitably-designed and constructed landing area support (deep pylons, thick landing pads, on top of, or very close to bedrock, etc) which should be able to withstand the weight under most conditions (at least for the common, smaller starships). At least that's the assumption I make for most starports IMTU.

And IIRC, per canon many starports can handle up to 5000-Td ships landing (or I've read references to that somewhere in the past, long ago...) Imagine the structure needed to withstand THAT weight...

 

[aramis]

My assumption (such as it is) is that any suitable starport (probably C-class or better, but not sure about D) would be constructed with suitably-designed and constructed landing area support (deep pylons, thick landing pads, on top of, or very close to bedrock, etc) which should be able to withstand the weight under most conditions (at least for the common, smaller starships). At least that's the assumption I make for most starports IMTU.

And IIRC, per canon many starports can handle up to 5000-Td ships landing (or I've read references to that somewhere in the past, long ago...) Imagine the structure needed to withstand THAT weight...

Typically around 50K metric tons...

 

[Carlobrand]

Unspoken in all this is how you'd land a wheeled spacecraft in the absence of a landing strip. Naval craft and scouts would have to be built to handle wilderness landings, and hovering down on pads works better for that than trying to find a big flat area that'll accommodate your wheels.

If it's possible to land on the hover, it's really the best way. You don't have to spend a fortune building a runway, you don't need to buy extra land for it, you don't have to worry about craft having a high speed accident because a landing strut breaks.

 

[SpaceBadger]

This discussion is bringing to mind some of the SF (esp Jerry Pournelle) in which spaceports were really seaports, and spacecraft landed on the water.

 

[McPerth]

And IIRC, per canon many starports can handle up to 5000-Td ships landing (or I've read references to that somewhere in the past, long ago...) Imagine the structure needed to withstand THAT weight...

As I've been in some discussions about if there's a maximum size for ships t oland and never found the reference (aside from IN bses servicing ships larger than 1000 dton in orbit), please, if you find this reference make me know about it.

This discussion is bringing to mind some of the SF (esp Jerry Pournelle) in which spaceports were really seaports, and spacecraft landed on the water.

In MT (the only ship design system I know well enough to talk about that includes mass) some ships would sink on water, unless they use grav propulsion or some kind of inflable support.

 

[aramis]

As I've been in some discussions about if there's a maximum size for ships t oland and never found the reference (aside from IN bses servicing ships larger than 1000 dton in orbit), please, if you find this reference make me know about it.

There is no reference I've seen, per se, but there is the limit on book two hulls being 5K. ISTR a 5KTd being grounded in some adventure... but we see 2KTd and 3KTd landing planetside in The Traveller Adventure.

 

[Icosahedron]

My take on this has generally been a handwave - I tend to ignore the whole question of how a starship lands unless it is directly relevant to the plot (and I've never had such a case).

However, any GM has to have some ideas lurking in the background just in case...

My thought is that grav tech has always grown up alongside spaceflight (except for the earliest days) and IMTU M-drives incorporate grav drives for landing. For this reason, runways are not used IMTU, all spacecraft are VTOL.

The smallest vessels (small craft and some PC ships) may use landing struts if their shape isn't compatible with belly-landing, but most larger vessels should be capable of landing on the belly and moving by means of surface-effect grav (however that works).

An alternative might be some form of high-tech pad on the belly of the ship that moves it along in the manner of a snake or caterpillar. Nanotech could help there and keep ground pressure to a minimum.

Water landings certainly occur IMTU and many starports have lakes for just this purpose, but I've always been uncomfortable with the physics of water landings - specifically since most ships are shown with the drives at the rear and without some form of 'always on' grav compensation the weight distribution would have them bobbing around tail-down...