CT Only: Big Far Trader (Type R2)

[AnotherDilbert]

Grav lifters (as I interpret them from the Air/Raft description) have thrust that's different in different directions. Against the local gravity field, it's local gravity plus 0.1G. Downward, it can be as high as local gravity plus 0.1G (because it can fall at local gravity and push (pull?) downwards at 0.1G beyond that). Perpendicular to the local gravity field, it's just 0.1G.

Grav drives it just provides thrust, just like a helicopter rotor.

A grav vehicle will have different performance on different planets:

The movement rate is determined as outlined in the vehicle design rules in Book 3,but instead of subtracting 1 from the G-rating of the vehicle's drives, the local gravity is subtracted instead.

An air/raft is just a particularly low performance grav vehichle. On a low gravity world it will be quite a bit more sprightly, e.g. on a size 4 world with about 0.5 G it would have a top speed of about 700 km/h.


Grav or M drives does not change the mass, weight, or inertia of the craft, it just provides thrust, the same thrust regardless of local gravity (at least somewhat close to a gravity source).

 

[whartung]

Not relevant. Grav, lifters, thrust plates. It ALL equals x amount of thrust. AND, unlimited deta-v. As long as you have more "thrust" than gravity pulling on you you can slow to a hover out in space over the part of the planet you want to land on and slowly go straight down.

But that's the problem, smaller drives against larger worlds do NOT have "more "thrust" than gravity". Unlimited Delta V can prepare a ship to keep it from getting in to a hole it can't get out of, but once in it, it's kind of stuck.

 

[Proneutron]

But that's the problem, smaller drives against larger worlds do NOT have "more "thrust" than gravity".

Large or small is not relevant, drives have the G rating they have for the hull they are driving, large drive or small drive. Please give an example of what you are talking about. Also where did I state that a ship with a drive that has a lower G rating than the G's of the planet can climb out???????

 

[Fovean]

Originally Posted by CT Striker B2 p19
The movement rate is determined as outlined in the vehicle design rules in Book 3,but instead of subtracting 1 from the G-rating of the vehicle's drives, the local gravity is subtracted instead.

Thank you for this, I knew I had seen this somewhere once upon a time, and not having Striker myself could not remember where. Too bad there’s no BFB (Big Floppy Book) for Striker, Snapshot, etc. Cheers

 

[Proneutron]

Thank you for this, I knew I had seen this somewhere once upon a time, and not having Striker myself could not remember where. Too bad there’s no BFB (Big Floppy Book) for Striker, Snapshot, etc. Cheers

There is no other logical way to do it. No one would subtract 1G when on a 0.5 G world.

 

[Fovean]

There is no other logical way to do it. No one would subtract 1G when on a 0.5 G world.

Well, this is what I asked about up-thread, a rule stating that local gravity gets subtracted from a vehicle’s potential. I’ve been doing it for years IMTU and now I finally have a rules reference to hang it on.

 

[Proneutron]

Well, this is what I asked about up-thread, a rule stating that local gravity gets subtracted from a vehicle’s potential. I’ve been doing it for years IMTU and now I finally have a rules reference to hang it on.

I understand. But it's straight physics. No need for a game rule. Just as there is no game rule that two objects of different mass dropped from the same height on an airless world "fall" at the same rate. This would be the rule unless there is a game rule written otherwise.

 

[Grav_Moped]

Grav drives it just provides thrust, just like a helicopter rotor.

A grav vehicle will have different performance on different planets:


An air/raft is just a particularly low performance grav vehichle. On a low gravity world it will be quite a bit more sprightly, e.g. on a size 4 world with about 0.5 G it would have a top speed of about 700 km/h.


Grav or M drives does not change the mass, weight, or inertia of the craft, it just provides thrust, the same thrust regardless of local gravity (at least somewhat close to a gravity source).

You're citing Striker. I'm going off the LBB3:'81 p. 25 description that doesn't adjust top speed for local gravity, and whose text strongly suggests that its top speed is limited by aerodynamic drag/stability considerations.

From that description, its "nullgrav modules" work by neutralizing weight (gravity effects) rather than by generating a force vector opposing gravity.

It's not a "helicopter", it's a "blimp".

 

[Grav_Moped]

And if an Air/Raft can lift 4 tons for Cr600,000 (while displacing 4 tons -- yes, different tons, but...), how much of the cost of a starship hull could go toward including "nullgrav modules" in its construction?

 

[Proneutron]

And if an Air/Raft can lift 4 tons for Cr600,000 (while displacing 4 tons -- yes, different tons, but...), how much of the cost of a starship hull could go toward including "nullgrav modules" in its construction?

WAY too many Crs at that ratio

 

[Proneutron]

From that description, its "nullgrav modules" work by neutralizing weight (gravity effects) rather than by generating a force vector opposing gravity.

That is true only if the "null grv modules" are spec'd by mass of the vehicle/object for a certain performance. If not then they cannot be working that way.

 

[Grav_Moped]

WAY too many Crs at that ratio

Yes and no.
Basic hull is Cr100,000/ton, Air/Rafts are Cr150,000/ton. Not a viable explanation, except:

For a 1G ship, it only needs to neutralize at most 25% of the ship's weight to lift off from a Size 10 world. The MD takes care of the rest.

That means you only need 1/4 of an Air/Raft per ton. That brings the cost down to Cr37,500/ton -- 37.5% of the base hull cost per ton. Which isn't outlandish.

An extra "up to 0.25G, and only to reduce a world's gravitational effects" wouldn't significantly change space combat.


It's a cute rationalization and I might go with it IMTU, but there's an issue with canon ship designs: how do they rotate to vertical to get the maneuver drives pointing up?

 

[Grav_Moped]

That is true only if the "null grv modules" are spec'd by mass of the vehicle/object for a certain performance. If not then they cannot be working that way.

It works if it's volume based in the same way maneuver and jump drives are.

 

[AnotherDilbert]

And if an Air/Raft can lift 4 tons for Cr600,000 (while displacing 4 tons -- yes, different tons, but...), how much of the cost of a starship hull could go toward including "nullgrav modules" in its construction?

According to Striker we would need a ~3 Dt, MCr 4.4, 1 EP grav drive to lift a 200 Dt (say about 2000 tonnes) Free Trader.

If you are in a spacecraft, just use a proper M drive.

 

[Proneutron]

It works if it's volume based in the same way maneuver and jump drives are.

Volume based M drives in Trav ARE effected by planetary G level. J-drives are irrelevant as not moving anything in our frame

 

[AnotherDilbert]

You're citing Striker. I'm going off the LBB3:'81 p. 25 description that doesn't adjust top speed for local gravity, and whose text strongly suggests that its top speed is limited by aerodynamic drag/stability considerations.

Let's see what LBB3'77 says:

Helicopter (6) CR 1,000,000. Single engine rotary wing aircraft capable of vertical take-off and landing, as well as maneuverability in tight places. This craft weighs one ton with a capacity for one ton of cargo and passengers. Range: 600 km; maximum speed: 250 km per hour. ...
Air/Raft (8) CR 6,000,000. Also known as a flier, the air/raft relies on solid state null gravity modules for lift and propulsion. Four independent, individually replaceable modules (CR 1,000,000 each) insure a maximum of safety. Loss of one module reduces lift by one-quarter. The standard air/raft weighs 4 tons and can carry a payload of up to 4 tons including pilot and passengers. Cruise speed is 100 km per hour with unlimited range and endurance. Normally, air/rafts are open topped; ...

Note that helicopters and air/rafts are described the exact same way, yet we know helicopters are very sensitive to gravity and air density. We can't really say that the air/raft is insensitive to local gravity from this description.

Also note that "null gravity modules" are described as providing "lift", somewhat generalised a lifting force aka thrust.

Nothing is said about it's aerodynamics, but as it is open-topped you probably don't want to go much faster than 100 km/h anyway...

 

[AnotherDilbert]

From that description, its "nullgrav modules" work by neutralizing weight (gravity effects) rather than by generating a force vector opposing gravity.

It's not a "helicopter", it's a "blimp".

But a grav drive produces forward motion, requiring thrust aka force. A-grav does not just neutralise weight.

See LBB2'81:

Air/Raft (8) Cr600,000, 4 tons. A light anti-gravity vehicle which uses null-grav modules to counteract gravity for lift and propulsion.

It "counteracts", not neutralises or negates. It specifically provides "lift" and "propulsion", aka vertical and horizontal force aka thrust, just like a helicopter. In fact "lift" means aerodynamically produced lifting force, so, if anything, it's implied that propellers and/or wings are involved, again just like a helicopter.


Contragrav from TNE somehow just barely counteractes local gravity leaving vehicles drifting in the wind, requiring some other locomotion system to be useful, but that is a rather different animal...

 

[AnotherDilbert]

An extra "up to 0.25G, and only to reduce a world's gravitational effects" wouldn't significantly change space combat.

But the LBB2 movement system says that spacecraft are affected by the full gravity of nearby celestial bodies, so it would not be compatible with canon.

... but there's an issue with canon ship designs: how do they rotate to vertical to get the maneuver drives pointing up?

MT has an explanation, see SSOM. I prefer not to quote it, to protect sensitive readers.

 

[AnotherDilbert]

Basic hull is Cr100,000/ton, Air/Rafts are Cr150,000/ton.

As I believe already stated, not the same "ton".

Spacecraft hulls are specified in displacement tons of about 14 m³.

Vehicles are specified in metric tons (tonne) of 1000 kg.

A spacecraft would require about ten times as many "null grav modules" as you assumed.

 

[Grav_Moped]

Let's see what LBB3'77 says:


Note that helicopters and air/rafts are described the exact same way, yet we know helicopters are very sensitive to gravity and air density. We can't really say that the air/raft is insensitive to local gravity from this description.

Also note that "null gravity modules" are described as providing "lift", somewhat generalised a lifting force aka thrust.

Nothing is said about it's aerodynamics, but as it is open-topped you probably don't want to go much faster than 100 km/h anyway...

The description (as with the one in '81) does not adjust performance for local gravity, indicating that discretionary thrust -- what's left over after weight neutralization -- is constant regardless of local gravity. Therefore, the non-discretionary thrust ("lift") must vary by local gravity. Striker grav drives work under a different paradigm.

(It also doesn't adjust it for atmosphere, though the ability to reach orbit implies that the top speed in vacuum is at least orbital velocity -- after that, it's limited by inability to stay close enough to the planet for the nullgrav modules to work.)