Grav Vehicles, Grav Drives

[AnotherDilbert]

No, the a/r is 4 dtons, way more than 4 tons. If the 4 dT is the external size, then it is the size of the largest trucks one can rent without a class B license, a 26' truck with a capacity of about 45 m³ = 3 dT. That could easily be 30 tons by various Trav rules.

By LBB3 the basic air/raft is a 4 tonne vehicle that can carry 4 people plus 4 tonnes of cargo.

By LBB2 it requires a 4 Dt garage onboard ships.

Only spacecraft is measured in displacement tons, that is not used for other equipment, as far as I understand.

 

[AnotherDilbert]

Given Cr600,000 to work with, I can design something that hits around 30 metric tons payload, but it flies like a bat outta hell when it's not loaded.

Edit: Ooh, 50 tons!

With Striker we can build cheap grav vehicles, but 10 weeks endurance at TL8 isn't quite that easy...

 

[Carlobrand]

With Striker we can build cheap grav vehicles, but 10 weeks endurance at TL8 isn't quite that easy...

True, the 10-week design is at TL9 with a fusion plant, but then I can't get the gravs until TL9 either. The old game introduced gravs and fusion plants at TL8, which they thought was gonna happen 30 years ago.

There are some game-mastery things one can do to set more realistic limits on the air/raft. We'd need to concentrate the thrusters over the rear half to keep the load balanced, and then the thing would somersault if we hit full power while not carrying cargo, so we'd either need to redesign it to carry weight in the center - maybe move motor, controls and seats to amidships left and right - or cap the speed if we want the traditional seats and engine compartment forward. If we don't need hyper-speed, we can stick to traditional truck designs.

 

[kilemall]

Of course we can build sub-orbital or orbital grav vehicles, but we end up with something less efficient than a small craft. Once we have M-drives they are superior for space and orbital interface.

Pretty sure we worked out a grav truck that was millions cheaper then the smaller small craft. The equation changes with larger small craft and time value of G speed.

 

[kilemall]

The original frame of reference was "car with antigravity", and in 1977-82, 120 kmh was significantly faster than cars could legally travel in the US.

This is because at the time they wrote the game, the US national speed limit was 55 MPH (88 kmh). It wasn't raised again until the mid 1990s. The canonical CT vehicle you're discussing is the Speeder (TL 8, like the Air/Raft), and, surprisingly, even it wasn't supersonic.

But (dead horse abuse alert!) once you get above the atmosphere, neither drag nor frictional heating is a constraint.An canonical Air/Raft can easily exceed that 19,000 fpm (100 m/s) in vertical ascent in a vacuum. In the lower atmosphere it's drag-limited to 8m/s if ascending flat, 33m/sec if nose-up, because it has the aerodynamic characteristics of a heavily-starched flying carpet. Streamlining can enable far better performance than that, but as-written they're not particularly streamlined.
I agree, but for slightly different reasons. They're only "realistic" if you're operating in the lower atmosphere with vehicles that look like TL7 ground cars and have 0.1G (Air/Raft) to 1G (Speeder) thrust after neutralizing their own weight.

They're far too conservative because they do not account for aerodynamic optimization, nor do they even consider exo-atmospheric operation aside from "going to orbit".

Basically, given the stated capabilities of an Air/Raft, it could reach any point on Earth (20,000km distance) within 4 1/2 hours: 1 hour and 15 minutes to 100km altitude, 3 hours above the atmosphere (would be 2 1/2 hours but escape velocity limits peak speed), and 15 minutes getting back down again. Average ground speed is 8000kmh. Shorter trips would have lower average ground speed since the climb/descent would be a larger portion of the trip.

A speeder built like a scaled-down X-15 could easily go Mach 3+ in atmosphere. But then, when an Air/Raft can effectively travel at Mach 6+ over the longest distances, why would you need one?

And all of this discussion is about TL 8 grav vehicles that don't have much extra thrust left over after hovering -- once you get to TL9 and up designs, lack of thrust is no longer an issue.

Given the pricing and the stats, I always considered the classic air/raft to be a personal all-purpose jeep/helicopter.

 

[Carlobrand]

Given the pricing and the stats, I always considered the classic air/raft to be a personal all-purpose jeep/helicopter.

Given that it first shows up as a craft carried by the scout/courier, it's probably intended as a means for a scout to get around with his equipment without needing to lift off and then land a building-sized ship every time he needed to go a few milles in the wilderness. Features were no doubt designed with that mission in mind.

 

[Grav_Moped]

....Why would we not be able to fly upside down? It's just inconvenient, especially in an open-topped vehicle.

It may be a lorry, but it's a flying lorry. It is manoeuvring in 3D like an aircraft or submarine...
This is supposed to show a helicopter looping...

My thoughts were more in terms of something like a helicopter coming to an abrupt halt (not quite as quickly of course -- less available drag -- but you get the idea) for normal flight, or a Mercury/Apollo/Gemini capsule for the hot re-entry case.

Even if you could fly an Air/Raft upside-down it shouldn't make a difference. While a helicopter directs its lift mostly along the rotor-shaft axis, an Air/Raft directs its lift mostly away from the planetary center because antigravity.

If vehicle orientation doesn't matter to antigrav drives, you could point it straight up and keep going indefinitely (unlike a helicopter). There's nothing in the canon description that says orientation matters. As I noted, I just assumed it did because hey, it's a car and cars are always right-side-up.

D = at²/2 if we are accelerating fully without slowing down.

Correction appreciated. It was after 0200 hrs local...

 

[Grav_Moped]

Given the pricing and the stats, I always considered the classic air/raft to be a personal all-purpose jeep/helicopter.

Works for me. Open-topped, it's an antigravity Pinzgauer

Closed, it's an antigravity VW Vanagon.

...only slightly larger.

Come to think of it, given the authors' experience, it might have been conceptualized as a double-cab M35 Deuce-and-a-half (wiki) that can fly.
Or maybe a MAN KAT1 truck (looks like an overgrown double-cab Pinzgauer).

Given that it first shows up as a craft carried by the scout/courier, it's probably intended as a means for a scout to get around with his equipment without needing to lift off and then land a building-sized ship every time he needed to go a few milles in the wilderness. Features were no doubt designed with that mission in mind.

That too.

 

[AnotherDilbert]

True, the 10-week design is at TL9 with a fusion plant, but then I can't get the gravs until TL9 either. The old game introduced gravs and fusion plants at TL8, which they thought was gonna happen 30 years ago.

The grav modules have no specified TL in Striker? So should be available at TL-8 as specified in LBB3?

Fusion is available at TL-8, but vehicle and ship size fusion is TL-9.

 

[AnotherDilbert]

Come to think of it, given the authors' experience, it might have been conceptualized as a double-cab M35 Deuce-and-a-half (wiki) that can fly.
Or maybe a MAN KAT1 truck (looks like an overgrown double-cab Pinzgauer).

The M35 is about the right size, the Pinzgauer is too small (by payload).

 

[Carlobrand]

The grav modules have no specified TL in Striker? So should be available at TL-8 as specified in LBB3?

Fusion is available at TL-8, but vehicle and ship size fusion is TL-9.

Oop, you're right, per Striker errata, grav generators are available starting at tech level 8. Doesn't change till MegaTraveller.

 

[Straybow]

By LBB3 the basic air/raft is a 4 tonne vehicle that can carry 4 people plus 4 tonnes of cargo.

By LBB2 it requires a 4 Dt garage onboard ships.

Only spacecraft is measured in displacement tons, that is not used for other equipment, as far as I understand.

For CT, apart from supplements such as Striker, there is essentially no differentiation (read: complete confusion) between mass and displacement. If the vehicle requires 4 dT of garage, then it is approximately 4 dT in size, and that translates to far bigger than 4 passengers and 4 tons mass cargo (a crew cab pickup truck).

 

[Condottiere]

If an air/raft is released into orbit above it's rated ceiling, it's an uncontrolled descent.

 

[Grav_Moped]

If an air/raft is released into orbit above it's rated ceiling, it's an uncontrolled descent.

If it's in orbit...
1. ... it's not descending, because orbit is altitude plus sufficient velocity to maintain that altitude.
2. ... it's below its rated ceiling. The description says that this is at least orbital altitude (but doesn't say how high an orbit).
3. ... there's enough gravity to hold it in orbit. This means there's something there for the lifters to twist into acceleration, deceleration, or lateral movement. Maybe not much acceleration, but with enough time it'll be able to decelerate to begin a descent -- and the farther down it goes, the more control authority it gets.

If you're trying to discuss orbital altitude without orbital velocity; that is, shoved out of the vehicle bay of a stationary (not orbiting) spacecraft at 36,000km altitude (the altitude of geosynchronous[sic] orbit around a Size 8 world), it might be difficult to get the craft to stop tumbling if it was ejected with some rotation* (fun, no?) until it falls several thousand km. It won't really matter until much deeper in the gravity well, though, and by that point there'll be enough gravity for the lifters to be able to straighten it out and start to slow the descent.


* Difficult task, +DMs: Air/Raft, Zero-G Combat.
One attempt per 10 minutes.
DM+1 for each subsequent attempt, cumulative.
Critical failure restarts "subsequent attempt" +DM to zero.

Also, each occupant must throw to avoid vertigo (as per hazardous conditions under Vacc Suit rules)...

 

[Timerover51]

I am looking at the overhead of the air raft in Supplement 7: Traders and Gunboats, page 24. It shows a vehicle that is two 1.5 meter squares wide and three 1.5 meter squares long. The overhead shows no cargo space, and the front 1.5 meter length appears to be the power plant, while the seating area shows 4 seats, each occupying a single 1.5 meter square. The stated capacity is 4 passengers and 4 tons of cargo, with unlimited endurance.

Now, I also have a digital copy, and hard cover copy as well, of the U.S. Army manual for vehicles from 1953. The jeep in the manual could carry a crew of 2 and three passengers in a space of about 60 inches by 60 inches. A square of 1.5 meters is 59 inches on a side. Allowing for only 2 passengers to make things a bit more comfortable for the back seat riders, that would still be 4 persons per 1.5 meter square. A carryall truck for passengers looks like it will hold 8 persons in a space of 1.5 meters by 3 meters. The half-ton Chevy pickup shown looks like it has a cargo bed of about 80 inches by 60 inches.

Putting this into carrying capacity for an air raft and it looks like it would break down as follows. The first 1.5 meters in length is the power unit, including whatever drive is assumed, with the lifting modules located on the bottom along the length. The second 1.5 meter length is the passenger compartment, with a capacity of 8 persons in comfort, or say 4 persons in vacuum suits. The last 1.5 meters in length is the cargo bed, at call it 60 inches by 120 inches, or at least about 3/4 to 1 ton of cargo, by mass. Adding slings on the side, the air raft can lift 4 tons mass of cargo slung underneath. If you have the passengers carrying equipment in the passengers space, then you could carry 4 passengers and probably a quarter ton or so of gear behind them.

Now, if you cube out the air raft into 1 Traveller dTon blocks, four 1.5 meter cubes, you actually only have 3 dTons of volume for the vehicle. I assume the extra 1 dTon is used to allow for access space inside of the ship carrying it. Otherwise, you could stretch the cargo bay a bit, and give it 2 tons of carrying capacity. Of course, if the cargo is heavy, then even with the 1.5 by 3 meter cargo bed, you might get 4 tons in. Small arms ammunition averages about 40 cubic feet per ton, so you probably could load 4 tons on the standard air raft, depending on how high you would want to carry cargo behind the passengers. Realistically, the air raft should have a crew cab for the passengers and operator, and not simply an open air compartment.

 

[wellis]

Why aren't air/rafts fully enclosed in general? Why are they open air? I mean isn't there potential danger of wind chill and having to endure the elements, and the danger of being pulled out of the air/raft by the wind, with it being open and all?

 

[Carlobrand]

Why aren't air/rafts fully enclosed in general? Why are they open air? I mean isn't there potential danger of wind chill and having to endure the elements, and the danger of being pulled out of the air/raft by the wind, with it being open and all?

They started life as something carried by Scout/couriers. Presumably whoever created them had the idea of giving the scout an unrestricted view of his surroundings.

 

[kilemall]

They started life as something carried by Scout/couriers. Presumably whoever created them had the idea of giving the scout an unrestricted view of his surroundings.

I always figured it was to have an open-topped exploratory jeep/buggy feel.


Be logical to at least have a canvas/other futurey cover for inclement weather, perhaps a Jetsons bubble top.

 

[Carlobrand]

I always figured it was to have an open-topped exploratory jeep/buggy feel.


Be logical to at least have a canvas/other futurey cover for inclement weather, perhaps a Jetsons bubble top.

Well, 100 kph is 62.5 mph, freeway speed, so a ragtop option is certainly practical. I'd certainly try to argue a gamemaster into allowing it. It beats getting your seats soaked. I hate soaked seats.

 

[Grav_Moped]

I always figured it was to have an open-topped exploratory jeep/buggy feel.


Be logical to at least have a canvas/other futurey cover for inclement weather, perhaps a Jetsons bubble top.

Also simplifies fields of fire for small-arms carried by the occupants.