A lot of worlds over 1g gravity. How do 1G thrust ships take off?
A
Anonymous
Guest
dragoner said:
Using your definition an electric car is reactionless. The difference in mass between a charged and discharged battery is almost nothing.
edit: I've looked at wikipedia's definition and they say" A reactionless drive is a device producing motion without the exhaust of a propellant ". They define propellant as " propellant or propellent is a chemical substance used in the production of energy or pressurized gas that is subsequently used to create movement of a fluid or to generate propulsion of a vehicle, projectile, or other object "
So according to wikipedia, my electric car is also reactionless.
Wikipedia are usually good on science, but this topic is sci-fi not science, and it looks like it was therefore written by a sci-fi author.
I guess there is no accepted definition of a reactionless drive, nor wil there be until one is construfted. I've always assumed it meant "does not rely on newton's 3rd law of motion".
AnotherDilbert
Emperor Mongoose
Yes, that is baked into the constant in the Lift = constant × v² relationship.phavoc said:
I'm sure the Subbie has worse characteristics, so worse constant, than any real aircraft, but that should be insignificant compared to the v² term.
Basically, the Subbie can fly with enough thrust (and two to three times bigger wing area). I really think that is good enough for a game...
According to https://en.wikipedia.org/wiki/Airbus_A380#Specifications has a max take off weight of 575 tonnes and a thrust of about 4 × 350 kN = 1400 kN which gives a thrust to mass ratio of 1400000 / 575000 / 9.8 = 0.25.phavoc said:
By Newtons Second (F=ma so F/m=a) the thrust to mass ratio is by definition the same as the g-rating.
And of course the Subbie has a g-rating = thrust to mass ratio of 1, hence four times the A380.
Sorry, I don't do Google spyware.phavoc said:
But, yes, the A380 has a larger wing area than the Subbie. So the Subbie needs bigger wings, but that is counteracted by a higher take off speed made possible by the greater thrust to mass ratio:
AnotherDilbert said:
So, as far as I can see nothing says the Subbie can't fly, it only needs bigger wings, well within the margin of error for a game illustration.
Yes, with current TL-7/8. Stellar tech is apparently better.phavoc said:
SSOM, p3 explains this in detail. It's even canon, as far as I know. Basically the thrust from drives is vectorable (at reduced efficiency).phavoc said:
If it can't fly and land with a big fat M-drive, it can't fly or land with an anti-grav drive, since both provide the exact same thing: thrust.phavoc said:
I fail to see the handwavium. It's just simple Newtonian mechanics (slightly simplified).phavoc said:
TNE FFS does this in detail, with mass and all. Old-school M-drives are included as an alternative tech.
Using the volume as a proxy for mass is just a simplification, to make the ship design system much less complicated. Using actual mass means that we have to recalculate the M-drive and hence P-Plant hence crew hence staterooms, etc, etc, every time we change a tiny detail in the ship. Most players seem to not enjoy that...
The ship has a mass and a thrust, we just don't keep track of all that detail. It has enough thrust to produce the specified g-rating for the nominal mass.phavoc said:
If you want to keep track of all the detail use FFS with all the trimmings.
?? Says who? I've never seen any such statement?phavoc said:
As far as I know spacecraft most certainly can't do 8 g turns with just a 1 g drive. With wings it might be able to do it in atmosphere.
That is not correct. CT does not do petty detail like mass, but MT and TNE certainly does.phavoc said:
As per MT RM, p56, Overview of Technology, Traveller uses real world physics with a few specified exceptions, such as M-drives and Jump drives. But it is a game so we don't always keep track of every little detail.
Does a helicopter nullify gravity? Can we load a heli with infinite mass?phavoc said:
Anti-grav does exactly the same as the rotor of a heli; it provides thrust. Any excess thrust after we have compensated for gravity can be used for propulsion.
This means an ineartialess drive:phavoc said:
Anti-grav does not remove mass, it just provides thrust.phavoc said:
It's a game, it has to be playable, so it is simplified. Unless you want to run relativistic orbital mechanics every time you land a ship? How good is the average player at tensor algebra?phavoc said:
Yes, that is a simplification in MT, but not in TNE. Use TNE if you want a bit more detail, but even that is of course highly simplified.phavoc said:
MT IE gives the example of a 400 Dt SDB with fairly heavy armour. It has a mass of ~11 ktonne, so about 30 tonnes per Dt. Bigger ships would have less extra mass, since hull surface increases more slowly than hull volume.
A 1 g anti-grav drive provides exactly the same benefit as a 1 g M-drive: 1 g of thrust, but only in a planetary gravity well. M-drives work everywhere cost as much but works in space too, so are always better.phavoc said:
To you, but not too me. Is it common sense to mount a helicopter rotor on all aircraft so that they can land vertically?phavoc said:
All design systems says that grav drives have a significant cost. Why would they suddenly be free? Should M-drives be included in the hull too?phavoc said:
Edit: If you want in your game, just say that you use it because you feel like it?
The design sequence in MT has a specified way of including grav drives in spacecraft if you wish, but none of the standard spaceship actually do.phavoc said:
I would disagree, I would rank the rules and specified procedures higher than some random artistic illustrations.phavoc said:
Most ships can land at most starports with a 1 g drive, as SSOM specifies.phavoc said:
I agree that tail-sitters would make more sense, but they are the exception in Traveller.
Lift is just thrust in a specific direction. A 2 g drive shouldn't have any problem overcoming a 1.1 g gravity field.phavoc said:
Moppy said:
Leaving aside that; the thing is that the only variable in the equation is time, as mass and thrust are constants. One could get super fiddley about when the G's of the planet can over come the G's of thrust vs the mass of the vehicle (something we don't know), then again one can also launch using the momentum imparted by the planet's rotation with an orthogonal vector and reactive force. Nevertheless, it's complicated.
AnotherDilbert
Emperor Mongoose
You truncated the wiki quote:Moppy said:
The electric car is not a closed system since is in contact with the road. The required reaction is on the road.
That is the strict physics definition.Moppy said:
The more everyday definition is probably the first sentence in the wiki quote "A reactionless drive is a device producing motion without the exhaust of a propellant".
I prefer the everyday definition (without any base in the game) since it doesn't make a mockery of physics as we know it.
A
Anonymous
Guest
AnotherDilbert said:
That definition's quite badly written then. All they needed to say was it classical closed system making a propulsion device. That is, no matter is exchanged over the boundary and no net external force is experienced.
AnotherDilbert said:
I don't accept that there is a strict/agreed definition, because it's a made up thing. We've also been over this before but that first everyday definition you've chosen to use also works for an electric car. They really should not have written it this way as we've both got into trouble over it now.
AnotherDilbert
Emperor Mongoose
It's wiki, not a physics textbook.Moppy said:
Given that the context is obviously a space drive, it's not too bad...
Condottiere
Emperor Mongoose
1. The Lockheed Starfighter was a wonderful piece of engineering, meant to be flown by an experienced pilot for the interceptor role; also, Lockheed went around bribing everyone they could who had a say in the military procurement process to buy it.
2. Upto technological level fifteen, Traveller has no reactionless drive; how inertial compensators function is the mystery.
3. As I recall, it was retconned that manoeuvre drives can angle thrust downwards like a Harrier, at a cost of efficiency.
2. Upto technological level fifteen, Traveller has no reactionless drive; how inertial compensators function is the mystery.
3. As I recall, it was retconned that manoeuvre drives can angle thrust downwards like a Harrier, at a cost of efficiency.
A
Anonymous
Guest
AnotherDilbert said:
Wikipedia is actually very good for mainstream science and they can replace a physics textbook - but this is a sci-fi topic.
Apologies for the delay in a response, it was a busy day at work.
Yes, the Type-R does have horrible characteristics when it comes to aerodynamics. The thick wingroots would create tremendous drag. While wings of any sort provide a modicum of lift, the amount of lift generated by the wings is not enough for takeoff.
You cannot use Newtons second law for aerodynamics. Lift calculations using surface area and mass and drag are required as part of the equation to determine lift. This is a non-sequitur as far as an atmospheric airframe goes.
Clearly you don't understand the nature of the internet, spyware or PC security. If you are willing to use this website and, I suspect, you've used Google search engine, then you can easily view the images in complete safety. And I'm betting you use at least one of the major search engines, thus you can use the link and insert it into your choice of "free of Google spyware" search engines to show the comparison of wing area to a person (or as best as fake imagery for non-existent starships go). Your loss.
You forget that starships don't take off like aircraft (e.g. no runways at most starports). For example, to cite canon literature, GURPS starports P76 design states "At most SPA downports, each starship berth is a free-standing, paved area with a wall around it. The landing starship drops right into the berth, and flies straight up and out when its business is done". Therefore a ship must be able to take off and land vertically under it's own power with no ability for wings to provide lift.
Unfortunately that's not how aerodynamic laws work.
Since we are continuing the discussion on lift and lifting bodies and what the rules state, there is a glaring gap between rules and reality. While a scout class, or even a free or Type-R trader could indeed generate lift using the body of their craft, this is both insufficent to glide as well as to gain altitude. The relatively small amount of lift would be offset by their mass, thus the advantages of lift would only be possible during a descent, and only at high speed.
According to SSOM p2, thrust plates are able to provide a 25% thrust margin at a 90 degree angle, with only 10% in the opposite direction of the thrust plate. Moving to page 3 it states "Lateral Thrust: Since the output of a drive fall to 25% when it is providing lateral thrust, it would seem that a 4G maneuver drive is required for a starship to hover above the ground on a planet with a 1G field. In fact, because a starship obtains full thrust directly aft, hovering is often done in a nose-up attitude"
SSOM goes on to discuss gyroscopes at the center of a ship to control direction. However, as you have pointed out quite often, it's not in the design system, therefore it obviously cannot exist.
To take that point further, SSOM further states (we are still on p2-3) that ships can have both internal gravity controls in the floor AND separate inertial compensators. Neither made into, for example HG v1, so should their existence be assumed due to this oversight? If we agree on yes, the anti-gravity should also be assumed. If no, then ships do not have inertial compensators OR grav floor plating unless it is specifically called out in the design process. If we accept "but it's mentioned elsewhere" then we must also accept the following from GURPS Starships p40 - "For extra detail, a ship required to fly in an atmosphere must have enough lift to compensate for its weight. This lift can come from three different locations: the hull, contragravity or vectored drives. One or both of the latter two are required if unstreamlined ships want to move around in an atmosphere - they don't get any lift from the hull" The section goes on to provide a simple calculation for lifting surface required. But it's also only functional in GURPS since it specifies loaded mass. It further goes on to state if the hull itself is unable to provide enough lift then more vectored thrust or CG modules are required.
So we have at least one version of Traveller that explicitly acknowledges CG being available in starships. Plus it specifically acknowledges the fact that with CG ANY ship may enter atmosphere.
Nothing in that statement makes it possible for big, fat ships, with big, fat drives, to maneuver sufficiently delicately to make it down to a standard starport pad. Wings require distance, and as the F104 shows, landing at high speeds can be rather deadly for the crew.
As seen in any aeronautical engineering handbook, not Newton's second law when it comes to calculating lift. It's not that simple.
Volume is not a good arbiter for mass. Empty masses differently than full. I realize it's a game, however if we are looking for simplification the use of CG for lift in a starship solves everything and makes formulas and wings and lift go away. It also makes all the pretty pictures that have been part of Traveller fit.
Well, as you pointed out, SSOM describes the M-drive usage, and it states a ship must have a M-drive rating equal to 4 if it plans to hover in a 1G atmosphere. So it would seem that few starship would be able to hover on their own since a 4G rating is not as common on the lower end.
The initial statement came from me. And you've once again ignored the point of the original statement. A ship has a 1-G drive rating. That same ship, using it's wings, could pull an 8-G maneuver. So we have both a thrust rating and a force rating using the same measurements. And this thrust rating is the same in both vacuum and atmosphere. Hence the mish-mash statement.
P56 of the MT Referee manual states - OVERVIEW OF TECHNOLOGY - Traveller makes certain assumptions about the nature of future technological developments. In addition to the progressive refinement of existing equipment and methods,
several areas of future technology have been postulated. Traveller bases its technology on a series of logically explainable developments even if they may be far beyond any present science." They clearly state they are guessing, or "postulating". Nowhere does it state they take real world physics to make up the technical background. Like the rest of us it's extrapolation and guesswork and fancy. Lanthanum jump grids, zuchai crystals and Grandfather all fall within the fancy part of things and not real world physics.
CT didn't do a lot of "petty" details. The lack of a statement doesn't imply it doesn't exist. Utilizing your logic the designers could have simply decided stating that starships logically have CG is too "petty" to mention, much like mass. Other systems, such as GURPS spent a lot of effort to include mass in the system.
The answer is no. Helicopters obey the laws of aerodynamics (they have lift because their rotor acts as a wing). A helicopter rotor actually provides no thrust. By angling the rotor and/or the helo forward you are able to move forward (or backwards). As SSOM states, thruster plates CAN do all of the above. They are magical like that. But also per SSOM to hover takes a 4G M-drive. So your statement is false per the rule.
AnotherDilbert said:
Yes, the Type-R does have horrible characteristics when it comes to aerodynamics. The thick wingroots would create tremendous drag. While wings of any sort provide a modicum of lift, the amount of lift generated by the wings is not enough for takeoff.
AnotherDilbert said:
You cannot use Newtons second law for aerodynamics. Lift calculations using surface area and mass and drag are required as part of the equation to determine lift. This is a non-sequitur as far as an atmospheric airframe goes.
AnotherDilbert said:
Clearly you don't understand the nature of the internet, spyware or PC security. If you are willing to use this website and, I suspect, you've used Google search engine, then you can easily view the images in complete safety. And I'm betting you use at least one of the major search engines, thus you can use the link and insert it into your choice of "free of Google spyware" search engines to show the comparison of wing area to a person (or as best as fake imagery for non-existent starships go). Your loss.
AnotherDilbert said:
You forget that starships don't take off like aircraft (e.g. no runways at most starports). For example, to cite canon literature, GURPS starports P76 design states "At most SPA downports, each starship berth is a free-standing, paved area with a wall around it. The landing starship drops right into the berth, and flies straight up and out when its business is done". Therefore a ship must be able to take off and land vertically under it's own power with no ability for wings to provide lift.
AnotherDilbert said:
Unfortunately that's not how aerodynamic laws work.
Since we are continuing the discussion on lift and lifting bodies and what the rules state, there is a glaring gap between rules and reality. While a scout class, or even a free or Type-R trader could indeed generate lift using the body of their craft, this is both insufficent to glide as well as to gain altitude. The relatively small amount of lift would be offset by their mass, thus the advantages of lift would only be possible during a descent, and only at high speed.
AnotherDilbert said:
According to SSOM p2, thrust plates are able to provide a 25% thrust margin at a 90 degree angle, with only 10% in the opposite direction of the thrust plate. Moving to page 3 it states "Lateral Thrust: Since the output of a drive fall to 25% when it is providing lateral thrust, it would seem that a 4G maneuver drive is required for a starship to hover above the ground on a planet with a 1G field. In fact, because a starship obtains full thrust directly aft, hovering is often done in a nose-up attitude"
SSOM goes on to discuss gyroscopes at the center of a ship to control direction. However, as you have pointed out quite often, it's not in the design system, therefore it obviously cannot exist.
To take that point further, SSOM further states (we are still on p2-3) that ships can have both internal gravity controls in the floor AND separate inertial compensators. Neither made into, for example HG v1, so should their existence be assumed due to this oversight? If we agree on yes, the anti-gravity should also be assumed. If no, then ships do not have inertial compensators OR grav floor plating unless it is specifically called out in the design process. If we accept "but it's mentioned elsewhere" then we must also accept the following from GURPS Starships p40 - "For extra detail, a ship required to fly in an atmosphere must have enough lift to compensate for its weight. This lift can come from three different locations: the hull, contragravity or vectored drives. One or both of the latter two are required if unstreamlined ships want to move around in an atmosphere - they don't get any lift from the hull" The section goes on to provide a simple calculation for lifting surface required. But it's also only functional in GURPS since it specifies loaded mass. It further goes on to state if the hull itself is unable to provide enough lift then more vectored thrust or CG modules are required.
So we have at least one version of Traveller that explicitly acknowledges CG being available in starships. Plus it specifically acknowledges the fact that with CG ANY ship may enter atmosphere.
AnotherDilbert said:
Nothing in that statement makes it possible for big, fat ships, with big, fat drives, to maneuver sufficiently delicately to make it down to a standard starport pad. Wings require distance, and as the F104 shows, landing at high speeds can be rather deadly for the crew.
AnotherDilbert said:
As seen in any aeronautical engineering handbook, not Newton's second law when it comes to calculating lift. It's not that simple.
Volume is not a good arbiter for mass. Empty masses differently than full. I realize it's a game, however if we are looking for simplification the use of CG for lift in a starship solves everything and makes formulas and wings and lift go away. It also makes all the pretty pictures that have been part of Traveller fit.
AnotherDilbert said:
Well, as you pointed out, SSOM describes the M-drive usage, and it states a ship must have a M-drive rating equal to 4 if it plans to hover in a 1G atmosphere. So it would seem that few starship would be able to hover on their own since a 4G rating is not as common on the lower end.
AnotherDilbert said:
The initial statement came from me. And you've once again ignored the point of the original statement. A ship has a 1-G drive rating. That same ship, using it's wings, could pull an 8-G maneuver. So we have both a thrust rating and a force rating using the same measurements. And this thrust rating is the same in both vacuum and atmosphere. Hence the mish-mash statement.
AnotherDilbert said:
P56 of the MT Referee manual states - OVERVIEW OF TECHNOLOGY - Traveller makes certain assumptions about the nature of future technological developments. In addition to the progressive refinement of existing equipment and methods,
several areas of future technology have been postulated. Traveller bases its technology on a series of logically explainable developments even if they may be far beyond any present science." They clearly state they are guessing, or "postulating". Nowhere does it state they take real world physics to make up the technical background. Like the rest of us it's extrapolation and guesswork and fancy. Lanthanum jump grids, zuchai crystals and Grandfather all fall within the fancy part of things and not real world physics.
CT didn't do a lot of "petty" details. The lack of a statement doesn't imply it doesn't exist. Utilizing your logic the designers could have simply decided stating that starships logically have CG is too "petty" to mention, much like mass. Other systems, such as GURPS spent a lot of effort to include mass in the system.
AnotherDilbert said:
The answer is no. Helicopters obey the laws of aerodynamics (they have lift because their rotor acts as a wing). A helicopter rotor actually provides no thrust. By angling the rotor and/or the helo forward you are able to move forward (or backwards). As SSOM states, thruster plates CAN do all of the above. They are magical like that. But also per SSOM to hover takes a 4G M-drive. So your statement is false per the rule.
AnotherDilbert said:
AnotherDilbert
Emperor Mongoose
So, the shape of the Subbie wasn't carefully designed in a windtunnel by a professional aerospace engineer. I believe very few Traveller craft are, so by that measure no Traveller spacecraft would ever fly, in atmosphere or in space.phavoc said:
Thrust isn't an aerodynamic force. Thrust is defined in terms of Newton's laws. Aircraft most certainly obeys Newton's laws of motion. Aerodynamics have nothing to do with thrust to mass ratio, which is a measure of engine power, not wing area. So, what is your point?phavoc said:
I believe I have a basic grasp of how a web-browser works. I certainly consider the tracking software (js+cookies) deployed by Google (and others) on most major websites is spyware.phavoc said:
I don't allow Google javascript or cookies in my regular browser, this forum (and even Google search) works perfectly well anyway.
Most starports don't need runways, since most spacecraft can land perfectly well with only the M-Drive. Only ships with 1 g drives trying to land in higher gravity needs special handling. And, obviously, only craft with wings or other aerodynamic lift needs runways.phavoc said:
So this aircraft that could land and even gain altitude with less power than the Subbie, is clearly impossible?phavoc said:
Martin-Marietta X-24
Did you miss the next paragraph?phavoc said:
SSOM said:
So, a craft with a 1 g M-drive can hover laterally for a few minutes in a 1 g gravity field.SSOM said:
I don't believe I have ever said that. I have said that systems that are in the design system but are not included in most standard craft, cannot be assumed to be generally deployed, e.g. anti-grav drives in MT.phavoc said:
No:phavoc said:
But they are missing in LBB2, and for the brief time I only had LBB1-3, I didn't assume anything about at least inertial compensators, as far as I remember.HG'79 said:
phavoc said:
GUPRS 4e Starships said:
I really don't think this supports your argument. Yes, contragrav (not anti-grav) is available, but, no, it's not generally deployed on all ships. Just like MT it seems.GUPRS 4e Starships said:
But TNE has contragrav (not anti-grav) as standard on spacecraft. I don't take that as indicative of any other edition, as neither did TNE have regular M-drives.
In that case why would an anti-grav drive with vectorable thrust of say 10 MN be better than a M-drive with vectorable thrust of 10 MN?phavoc said:
And I have never tried to do that. But Newton's Laws applied perfectly well to thrust.phavoc said:
Agreed, but that is the simplification chosen in some editions of Traveller. And in the real world in the case of containers: A container may be classed by volume (TEU), but also has a mass limit so that standardised trucks, cranes, and ships can handle them.phavoc said:
No, as your quote from Gurps makes clear mass does not disappear just because you say contragrav. The contragrav drive must be dimensioned for a specific mass, and combined with aerodynamic lift and M-drive thrust it can make a ship fly with a maximum mass, but not more.phavoc said:
Note that most editions of Traveller, including MgT, does not have contragrav, but anti-grav. Anti-grav differs by supplying thrust that can both lift and propell the craft (like a helicopter). Contragrav can only lift, but not propell the craft (like a balloon).
Except, as already quoted, the M-drive can be overdriven for a short while, so that a ship can hover for a few minutes.phavoc said:
Note that M-drive overload is in MgT2 too, see Core, p160.
OK, I completely fail to see the point. What does a crafts turning ability have to do with whether it can accelerate enough to escape a gravity well?phavoc said:
They start with what we have, and then they add some fictional tech such as M-Drives and Jump drives.phavoc said:
Or if you prefer GURPS:
GURPS Traveller said:
Agreed.phavoc said:
Possible, but I find it unlikely, since the movement system specifically say that spacecraft does not have a magic button to avoid gravity.phavoc said:
Yes, just like MT and TNE, so?phavoc said:
Not by any definition I have ever heard:phavoc said:
Lift is the force imposed on a craft from the fluid flow over it, perpendicular to the flow. https://en.wikipedia.org/wiki/Lift_(force)
Thrust is a reaction force imposed by accelerating a mass, in Traveller extended to reactionless drives. https://en.wikipedia.org/wiki/Thrust
In short:
"A fixed-wing aircraft generates forward thrust when air is pushed in the direction opposite to flight. This can be done in several ways including by the spinning blades of a propeller, or a rotating fan pushing air out from the back of a jet engine, or by ejecting hot gases from a rocket engine.
...
Rotary wing aircraft and thrust vectoring V/STOL aircraft use engine thrust to support the weight of the aircraft, and vector sum of this thrust fore and aft to control forward speed. "
I think you missed my point; Just saying anti-grav or contragrav does not make you immune to gravity or inertia.phavoc said:
Sitting in an air/raft in flight you feel the full force of gravity and are bound by it to the planet, just like in a heli. The anti-grav (or contragrav) only provides a countervailing force to keep it aloft. That force is limited, so can only lift a certain amount of weight.
That means that a craft, with anti-grav or not, can only carry a specified amount of weight, not infinite amount as you tried to state earlier:
phavoc said:
If a craft was completely disconnected from local gravity it would no longer orbit together with it and the planet would quickly accelerate away from the craft in its orbit, leaving the air/raft in space with no way of getting back to the planet.
Also note that the lifting force of anti-grav in an air/raft is not dependent on local gravity, so it can carry more load (or be faster) in low gravity and less in high gravity. (CT Striker, Book 2, p19.)
As already noted SSOM, p3 (and MgT) allows the M-drive to be overloaded, so a ship can hover with a 1 g M-drive for a few minutes.phavoc said:
So you mean that contragrav can selectively bend and unbend curved space-time as it sees fit? Yikes, that is worse than reactionless drives...phavoc said:
As above, if an air/raft is not bound by gravity it would no longer be bound to the local planet or star system, but fly off in space as the planet accelerated away rotating in its orbit.
I have no idea how countergrav actually works, but anti-grav is pretty straight forward, e.g.:
This hints that countergravity works similarly (except no propulsion):CT Striker said:
GURPS Starships said:
I believe MgT uses anti-grav, not contra-grav.
I don't understand your argument. If we don't use wings to land on runways, then lift is irrelevant. Without wings we balance on the drive's thrust like a rocket, whether the thrust is provided by anti-grav or M-drive.phavoc said:
Again, I fail to understand your argument.phavoc said:
The Launch is a much bigger and more capable vessel, hence it costs more. Is that a problem?
The Launch specifically does have a 1 g M-drive and no anti-grav drive. We could easily add an anti-grav drive (and some more power) for MCr0.5 or so, or for roughly the same cost enhance the M-Drive to 2 g. Neither is free.
Obviously the enhanced M-Drive is better since it works in space too.
Of course neither the air/raft nor the Launch has any aerodynamic lift, they have no wings, they use their thrust to stay aloft.
Um, so you agree that thrust plates are superior to anti-grav units, yet you want to add anti-grav units in addition to the thrust plates?phavoc said:
Now I fear you are being deliberately obtuse. Of course there is a difference between a drawing directly illustrating a rule, and an artistic illustration depicting a cool scene.phavoc said:
Now take this picture made by ShawnDriscoll:
http://forum.mongoosepublishing.com/viewtopic.php?p=934255#p934255
It is beautiful, but what does it tell me about the rules? I would say nothing.
Again, SSOM, p3, specifies that the M-drive can be overloaded a short while, so can hover and land vertically with a 1 g drive.phavoc said:
I don't dislike it, I just find it unnecessary and counterindicated in some editions (CT, MT, MgT). In some other editions (TNE, T5) they are standard.phavoc said:
Yes, just like I assume that ships that do not state that they have Sandcaster turrets lack them. Sandcasters are perfectly acceptable and some ships have them, but most don't.phavoc said:
Yes, in GURPS some ships have contra-grav and some don't. I don't find that that supports the argument that all spacecraft must have it to be able to land.phavoc said:
And in TNE nearly all spacecraft have contra-grav as standard, but I don't see that that says much about any other edition, especially CT or MgT.
I agree MgT is closest to CT and perhaps MT as a more detailed CT, hence I prefer to take hints from CT rather than other editions when I consider MgT.
I fear that is inevitable, given that we have small snippets of information here and there. I use whatever I find useful, from any edition I am familiar with, as long as it's not directly contradicting.phavoc said:
I hope people can ignore what doesn't interest them.phavoc said:
A
Anonymous
Guest
About overloading the drive to land:
Traveller is its own universe, but it's heavily western-influenced and the Imperium is very strict on control within its borders.
I doubt the regulators will allow a craft to be certified for powered landing if it needed to overload its drive to do so.
If the master chose to use a craft in such a manner over a city, they would certainly be arrested or reported. If not by the Imperium, but by the city they flew over.
A 12 meter (40 foot) asteroid will take out a city center. A mishandled starship is a doomsday rock with a nuclear reactor.
It's probably fine over an independent low-tech world outside of a major empire, if only because there is nothing they can do about it. Don't land and ask for provisions though.
Traveller is its own universe, but it's heavily western-influenced and the Imperium is very strict on control within its borders.
I doubt the regulators will allow a craft to be certified for powered landing if it needed to overload its drive to do so.
If the master chose to use a craft in such a manner over a city, they would certainly be arrested or reported. If not by the Imperium, but by the city they flew over.
A 12 meter (40 foot) asteroid will take out a city center. A mishandled starship is a doomsday rock with a nuclear reactor.
It's probably fine over an independent low-tech world outside of a major empire, if only because there is nothing they can do about it. Don't land and ask for provisions though.
AnotherDilbert said:
No need to carefully design. It wouldn't be able to generate enough lift due to it's design. Which is why when lift is being supplied by anti-grav generators all Traveller craft will function as designed without wild gyrations of logic to find reasons why the might be able to take off and land.
AnotherDilbert said:
Clearly you have missed the point of the conversation. You have been trying to put forth the view that Traveller ships don't need CG/AG to take off or land because of lots of other reasons. You have attempted to use Newton's second law to demonstrate your point. As I (and all books on aerodynamics will confirm) keep saying you cannot use that law to describe aerodynamic lifting effects. Nothing more, nothing less.
So the point is that formula is useless in trying to justify or explain lift. TL;DR - you need more variables in your math.
AnotherDilbert said:
You don't turn that off/block them with your browser settings? It's pretty easy to do that. And you do realize that utilzing Google search works the same, regardless of if you are looking at text only or images. Those links were from Google and thus if you had put that into your browser and selected "Images" at the top you would have gotten the same visual response as I did - all without catching a cybercold from Google "spyware". Or use the links in the browser you prefer to find the same data.
AnotherDilbert said:
You do realize that lift (from surfaces) is only generated while an object is in motion, correct? With no wings, winglets or other lifting surfaces crafts like the launch, ships boat or modular cutter can't even fit with this model. Lift would require continual forward momentum, and the heavier the craft is, the more momentum is required to generate it. Landing with only M-drive means dropping down as a tail sitter. If they are returning conventionally the would still need to change their orientation, which would be rather challenging to go from horizontal to vertical.
AnotherDilbert said:So this aircraft that could land and even gain altitude with less power than the Subbie, is clearly impossible?
Martin-Marietta X-24 lifting body. It did indeed fly - after it was dropped from a B-52. All of the models could fly - after being dropped. They never took off on their own. The space shuttle can land on it's own, and even gain altitude, too. However it's quite disingenious to make it out like either of these craft could ever take off. Basically they are able to do controlled descents, with the lift generated by their bodies/wings allowing this to happen. Neither is capable of taking off in the same fashion. Add some rockets to anything and it can fly. People have added JATO bottles to cars and made them fly (if inadverdently).
AnotherDilbert said:
I did not. But you are ignoring the previous statement, also found in SSOM. A ship requires 4G M-drive rating to hover. At 25% lateral power (that's 1G), it can land. So the point made by SSOM remains - ships need 4G capabilities to hover in a 1G environment. Let me emphasize your own words to prove the point - "By gradually shifting the direction of thrust a hovering starship can slowly "fall" forward and settle into a horizontal (that is, lateral) landing position." (emphasis mine). The precursor statement there - a HOVERING starship. You've already acknowledged that statement, yet you try to obfuscate. Sorry, it's quite clear in black and white in the book.
AnotherDilbert said:
While very detailed in some areas, MT sidestepped this somewhat. But they aren't the only version to do this.
AnotherDilbert said:
The point was that one design system calls them out, another does not, thus they are implied. And, logically, if they are called out as separate systems in SSOM, then the inclusion of inertial dampening fields with g-plating is assumed. Much like the assumption that starships are able to take off and land with antigravity lift. You can't split the hairs both ways and say "oh, this one is ok to assume, but not that one". Well, that's incorrect. You are, of course, allowed to split hairs and assume such a thing. But logically it doesn't make sense.
AnotherDilbert said:
You are ignoring the section in the same book that speaks of can your ship fly on it's own, or does it need help. Most of the ships in GURPS Starships list contragravity modules. Though it's certainly not a requirement for those ships that never make planetfall. So I would say the preponderance of the design evidence supports this idea - at least in GURPS. CG and AG are interchangeable terms as far as a discussion on lift is concerned. Where they differ is that CG is typically (not universally) thought to address the nullification of gravity and allows for ascent/hovering/descent. AG would allow cover the same, but also would allow lateral movement. But for the purpose of this discussion they are equivalent (e.g. takeoffs and landings).
AnotherDilbert said:
How is this germane to the discussion? Shall we also talk about how useful, or not, flames along the side of the ship would be?
AnotherDilbert said:
We are discussing lift, not thrust. Lift is more than thrust. If you want to talk equations then use this: L = Cl * A * .5 * r * V^2. You need to quote Possio not Newton if you are talking aerodynamics.
AnotherDilbert said:
Yes, volume-based measurements rather than actual mass does make for easier tracking for gaming. Though, as an aside, most people don't realize that a TEU is the volume of a 20' standard container. So the older 40' containers are 2 TEU (and, to further muddy the waters, many ocean-going containers are now standardized at 48', and road/rail containers (in the US at least) are now 53'. In theory a TEU should probably now be 24' (a 20% increase). Which is a good example of why standards that don't appreciably change a lot are good).
AnotherDilbert said:
My quote from GURPS indicated that both mass and CG are present in the design system and on most ships that are atmospheric capable. Plus the system acknowledges that even with aerodynamic streamlining the ships are too massive to fly unaided without CG. And that if you wanted lift from aerodynamics you had to take into account mass. You conveniently leave that out of your rebuttal.
Most editions of Traveller don't differentiate (even assuming they mention it) between CG and AG. But on the capabilities of both we are in agreement.
AnotherDilbert said:
Per SSOM, to do this the M-drive would require a 400% overdrive. Please show me where in reality any engineer or designer would implement a system that requires a 400% (even assuming the system was capable of such an increase) overdrive just to accomplish a normal every-day activity.
The overdrive rule is quite specific, and still not enough power to make this work under the rules of SSOM: Overload Plant (Engineer) A favourite of engineers on action vids, the power plant
can be overstressed on a temporary basis to provide the ship with more Power points. A successful Difficult (10+) Engineer (power) check (1 round, INT) will increase the ship’s current Power points by +10% during the next round. If the check fails with an Effect of –6 or less, the power plant suffers a critical hit with Severity 1, as detailed on page 160. This check suffers a cumulative
DM-2 each time it is attempted after the first. This penalty can be removed by performing maintenance on the power plant, a procedure that requires Engineer (power) and 1D hours. And you conveniently ignored the fact that the risk to damage the power plant is cumulative each time it's attempted. This is NOT something anyone would realistically consider a normal activity, let alone something you would do every time you attempt to land or takeoff.
AnotherDilbert said:
As an expression of capabilities the terms are the same (e.g. G-force for thrust, G-force for expression of the force being applied to an object in a gravity well. But I suggest we drop this particular item as the discussion is going nowhere.
AnotherDilbert said:
Actually I prefer the GURPS definition. But you had cited the MT one, and they are different. The GURPS definition, and rules, clearly outline how to determine if your ship has enough inherent ability to take off/land vertically, and clearly states (acknowledges and adds CG lifting capabilities to the designs). I love the fact that you have quoted "the laws of physics still apply - with a few exceptions necessary to the game". The laws of aerodynamics and how lift is generated are one of those laws that still apply. Ergo GURPS has acknowledged that fact and called out the need for CG lifting to make the starships work.
AnotherDilbert said:
Agreed, hence the need for the inclusion of lift through CG and not trying to make wings work when they would not.
AnotherDilbert said:
More specifically, for helicoptor - "Understand each element of the limit equation L = ½ ρv2ACL. L signifies lift force, measured in Newtons; ρ signifies air density, measured in kilograms per cubic meter; v2 signifies true airspeed squared, which is the square of the speed of the helicopter relative to the oncoming air, expressed in meters per second. In the equation, A signifies rotor disk area, which is simply the area of the rotor blade, expressed in meters squared. CL signifies the dimensionless lift coefficient at a specific angle of attack, which is the angle between the chord line of the rotor blade -- an imaginary line drawn through the middle of an airfoil extending from the leading edge to the trailing edge -- and the oncoming air. CL is dimensionless, in that no units are attached to it; it is simply displayed as a number.
Identify the values for each element of the lift equation. In the example of a small helicopter with two blades, the rotor disk travels at 70 meters per second (v). The coefficient of lift for the blades is 0.4 (CL). The planform area of the rotor disk is 50 meters squared (A). Assume international standard atmosphere, in which the density of air at sea level and 15 degrees Celsius is 1.275 kilograms per cubic meter (ρ).
Plug the values you have determined in to the life equation and solve for L. In the helicopter example, the value for L should be 62,475 Newtons.
The value for CL is typically determined experimentally, and cannot be determined unless you first know the value of L. The equation for the lift coefficient is as follows: CL = 2L/ρv2A." - (Sciencing.com)
There you go. Now you've heard a new definition.And it's more than Newton's 2nd law.
AnotherDilbert said:
Agreed. Neither gravity, nor inertia nor mass. They simply nullify the G rating. After that you still need to move around and stuff.
AnotherDilbert said:
Now this presents an interesting conundrum and one that I hadn't really thought about. Within a starship it's mentioned specifically about grav plating (and in some instances there is mention of inertial compensators). But elsewhere it sometimes just talks about internal gravity. An air-raft isn't a good comparison, so let's use the G-carrier since it, like a starship, is fully enclosed. I think we agree that starships can use purely gravitic drives. The G-carrier uses AG for both lift and propulsion. I can't recall seeing anywhere in any design sequence about inertial compensators or grav plating for vehicles. It could be assumed that they do not have it, but if a launch has it, why not a G-carrier? I'd like to think vehicles would not have such a thing, but since these vehicles are capable of making orbit (and in MT family cars were capable of interplanetary travel, with no mention that they would make the journey in zero-G), do they also have an inherent inertial dampening/grav plating built into them?
but this has nothing to do with loading mass into a starship.AnotherDilbert said:
AnotherDilbert said:
I haven't cracked open my Striker books in some time. I don't recall something similar in other versions related to speed of grav vehicles being dependent upon local gravity conditions. That would certainly change things for gaming purposes. Local vehicles might receive an upgraded system in higher gravity environments, thus they would be faster and more maneuverable than standard vehicles being brought in by players (or the reverse for lower G worlds). This also begs the question of how hard/easy is it to change the settings on your vehicle to accommodate this, or even if you can change them.
AnotherDilbert said:
Nowhere does it state you can overload by 400%. As you pointed out upthread, in MGT v2 about overloading power, the limitation is 10%. Thus you cannot get enough power through overloading (not to mention the cumulative risk each time you attempt to do so.
Nope. Never said that.AnotherDilbert said:
AnotherDilbert said:
If starships exiting jumpspace don't bring with them the direction and velocity of the star system they were in, then I would say the average air raft rider is safe from being flung into space. So if you want to open that can or worms you are really going to make the system complicated. I have no issue with things as they stand. People used to say the same thing about what would happen if you flew through the air. I think we are relatively safe on this point.
AnotherDilbert said:
I think you've made the point that just because something is hinted at, if it's not in the rules it's not there.
And I agree neither of us has a good understanding of how CG or AG actually works.
AnotherDilbert said:
The discussion has always centered around how ships are able to maneuver, land and takeoff. You have argued that ships, like the Type-R can use their wings to generate lift. You have also argued that ships could act like a tail sitter to use the drive as this way. However you have yet to state how a ship enters atmosphere normally using it's wings or hull as a lifting body and then transitions to a vertical position, then lowers itself on it's drive, and slowly lowers it's nose to the ground using an overloaded powerplant. The sheer amount of logical jumping around to avoid the useage (as detailed in GURPS) is rather high. And, if you recall, the description of landing pads which indicate vertical ascent/descent. And even the pretty T-5 picture you provided of what a starport looks like. Those ships have got to maneuver while on the ground, and since most don't sport wheels, the option of overloaded thrusters seems rather silly.
AnotherDilbert said:
Who cares if it's drive is anti-grav or thruster plate or HePLAR? That wasn't the point. You state that the launch doesn't have an anti-grav drive. It says this where? According to SSOM anti-grav drives are overtaken by thruster plates due to higher efficiency at TL11. So a TL9/10 launch can't utilize them due to TL restrictions. And CT doesn't mention that option (maybe a revision does, dunno off top of my head).
Anti-grav modules aren't terribly expensive and can easily be part of the cost of the hull.
AnotherDilbert said:
I'm not, nor have I ever, been debating about the efficacy of thruster plates versus anti-grav drives. This question isn't germane to the discussion. And it's applicability is limited to MT. Why are you bothering to inject this?
AnotherDilbert said:Now I fear you are being deliberately obtuse. Of course there is a difference between a drawing directly illustrating a rule, and an artistic illustration depicting a cool scene.
Now take this picture made by ShawnDriscoll:
http://forum.mongoosepublishing.com/viewtopic.php?p=934255#p934255
It is beautiful, but what does it tell me about the rules? I would say nothing.
Well, why don't we use a useful image to answer that question? Since you are concerned about Google spying on you I won't share any links, but they are easy enough to find. The GURPS starport cover (you've quoted from it, so you should have a copy in hand) has an image of a S-class scout in the air above a warehouse between very large towers. One could say 'it's flying' in a horizontal direction with it's landing gear down, however the amount of lift would be negligible from it's surface and the amount of drag would negate what it could be generating - unless it was moving at or above mach speeds. So that would be a clue towards it having CG lift capabilities (which, in fact, it does explicitly have in it's GURPS ship description).
There are other illustrations out there if you search for them (including in your Starports book. On page 12 there is, what appears to be, a ship taking off/landing in a vertical position. P16 has an illustration for multiple ships in 'pits' where they are only able to descend vertically to get to the pad. P43 has a far trader sitting on a small pad next to a body of water. p46 shows a Type-R coming into a landing at a very large arcology. This one is telling because unless there are long runways in those docking ports the only way a ship can dock is to float in under CG (and even overloading the M-drive to hover and land is debased here because there is no room to do so). On pg76 where it offers more description of downport berths it specifically states, "Many feature retractable roofs that can completely enclose the berth once a ship has landed". Which matches the description earlier in the section that a ship would vertically enter and leave the berth.
AnotherDilbert said:
Again, as you pointed out, overloading a powerplant to produce enough power to overload the M-drive is limited to 10% overage, and each time raised the cumulative risk of a drive failure.
AnotherDilbert said:
I don't think it's counterindicated at all. What I think is that some designs specifically acknowledge it, others ignore it or don't think it's important enough. M-drive propulsion methods are distinct and separate from lifting mechanisms. And what we see are SOME of the editions stating it outright, but most just ignore it.
Explaining how things work, at a basic level, is part of the narrative of a gaming universe. I don't need to know how the toilet flushes. But a single sentence explaining how a starship lands or takes off from the ground is an easy add. The challenge becomes finding a balance between explanations, inference, and leaving things so wide open that its' confusing. This is where non-verbal things, such as useful illustrations and artwork, can fill in a lot of the blanks. Especially when the game system talks of extrapolating current tech. If we accept an air raft, a grav tank or even a grav belt or a grav fork lift, then assuming assigning that same useful tech to something like a starship is logical and common sense extrapolation.
AnotherDilbert said:
Not sure what this means. If I am understanding what you are saying here, I think it is safe to assume that if a ships description does not state it has sandcaster turrets that it does not have sandcaster turrets installed. Indeed they are perfectly acceptable and some ships have them, some do not. But for those that do have them I believe you'll find it in the ship description.
AnotherDilbert said:
I agree that not all spacecraft must have it to land. We've seen designs that are tail sitters that do not have it. But those are explicit designs and it's clear how they work. I would say a Subsidized liner needs CG to land. I would say a free trader needs it. I would say a modular cutter needs it. I would say the standard shuttle is a maybe (it's wing surface is pretty big relative to its' body). Then again, we have to determine just where the vessel is landing. Assault shuttles coming down on a field to deploy troops would need it since the risk of landing like an aircraft and hitting unseen debris or soft earth makes it very risky. CG equipment means it can get in and out with far less risk - and in smaller spaces, too.
You and I seem to share similar, if opposite fervor towards explaining and understanding the rules. Hopefully we are entertaining the others here.
Condottiere
Emperor Mongoose
1. Even a monogee thruster would generate a quarter gee vectorable lift when quartered; if might make gliding down smoother and somewhat more controllable.
2.
2.
AnotherDilbert
Emperor Mongoose
Of course there is every need to carefully design any real spacecraft, but illustrations made by artists rarely take physics into consideration, e.g. many Traveller spacecraft would have difficulties flying in a straight line because the M-drives are not balanced around the centre of mass.phavoc said:
Game illustrations are not engineering drawings, and we cannot possibly require them to be.
This particular part of the discussion started with comparing the drive trust of a Subbie and a A380.phavoc said:
Aerodynamic lift has nothing to do with M-drive trust. Wings or other lift will get you nowhere without drive thrust.
Aerodynamics can tell you the force of lift, but Newton's second is needed to tell you how the aircraft will move exposed to that force.
Yes, and hence Google shows me no pretty images...phavoc said:
Obviously.phavoc said:
Obviously.phavoc said:
But they can, as SSOM explains.phavoc said:
You stated specifically that a Subbie could not possibly fly or gain altitude. I tried to demonstrate with an example that an aircraft could do exactly that even without any wings:phavoc said:AnotherDilbert said:So this aircraft that could land and even gain altitude with less power than the Subbie, is clearly impossible?
Martin-Marietta X-24 lifting body.
The X-24 could indeed glide to landing (without drive trust) and gain altitude (with drive trust). I find it difficult to believe that a stellar tech craft with wings and superior thrust cannot do what a TL-6 aircraft without wings can do.phavoc said:
If you actually read the section in SSOM you would find:phavoc said:
Yes, you can do it, and, no, the drives won't explode.SSOM said:
There is no sidestepping, the MT design system provided an easy way to incorporate anti-grav drives, but the standard ships specifically does not have them.phavoc said:
Agreed, since LBB2 says nothing about this either way.phavoc said:
No, not when the other systems are inconsistent with that assumption, as CT and MT are.phavoc said:
Of course ships can take off with anti-grav, and it might be convenient, but not necessary.
I find your "logic" rather unconvincing.phavoc said:
Example: In TNE the normal drives are reaction drives that require large amounts of reaction mass to function. I can of course not take that to mean that CT ships can't fly, since they don't have the tankage for reaction mass.
CT specifically state that no reaction mass is needed, just as MT specifically state that anti-grav is not generally deployed.
This part?phavoc said:
I fail to see that this states that contragravity is needed or generally deployed. CG (or wings) is only needed if M-drive thrust is insufficient.GURPS 4e Starships said:
You seem to ignore the explicit statement that contragravity drives are not generally deployed, or necessary.
GURPS 4e Starships said:
To get more specific the Akkigish-class subbie does not have contragravity, whereras the Colresh-class (TL9) subbie (with a lower thrust to mass ratio) does have it.
Note that the Colresh-class specifically include CG to compensate for low M-drive thrust.Gurps Starships said:
The 0.6 g Harper-class Launch (TL9) does have contragrav, but the 2 g Quatarmain-class launch (TL10) does not.
It seems contragrav is generally an option for less capable low-tech craft in GURPS, e.g. the TL9 Patrol Cruiser has contragrav, but the TL10, TL11, and TL12 versions does not.
Except that is is specifically no so. Some spacecraft have it, some don't. It is explicitly not needed.phavoc said:
Almost, but not quite. AG can provide lateral thrust and take you to space, CG alone does not and cannot. CG cannot even provide positive lift to make a craft ascend, it just makes the craft lighter so that the necessary thrusters can more easily make the craft rise.phavoc said:
According to MT they cost about the same. Why would I prefer the AG drive over the M-drive when they both provide the same trust, but the M-drive also works in space?phavoc said:
You want AG drives to be standard. I would say an M-2 drive is better than an M-1 + AG-1 drive for the same cost, so would be the more likely choice.
Except when we are talking about drive thrust, which has nothing to do with aerodynamics.phavoc said:
And since drive thrust can be vectored, it can be used to provide a lifting force without involving aerodynamics. Cf Hawker Harrier.
Look: it can magically hover with neither aerodynamic lift, nor anti-gravity:
CG is certainly available, just as AG was in MT. But most ships? I will not bother counting, some ships have, some don't. It cannot be generally assumed, even in GT.phavoc said:
You misrepresent the source. It is clearly stated that the sum of drive thrust, CG trust, and aerodynamic lift must be enough to fly the ship. Enough drive trust is enough, without either CG or wings.phavoc said:
You ignore e.g.:
GT Starships said:
GT Starships said:
Clearly a craft with a 1 g M-drive can take off from a world with <1 g surface gravity in GT. CG or wings are only needed if M-drive thrust is too low.
All editions I am familiar with use one or the other, not both.phavoc said:
In SSOM M-drives explicitly has this capability, as already quoted.phavoc said:
That is about the power plant, not the M-drive. And you are quoting MgT2, not SSOM. As usual the details differ between editions.phavoc said:
As far as I can see GT clearly state that spacecraft need enough lifting force to take off from any combination of drive thrust, CG, and aerodynamic lift. Enough drive thrust is quite enough on its own, as shown by the many GT spacecraft without CG.phavoc said:
So I find your conclusion entirely unwarranted.
AG is the magic button that ship clearly lacks, otherwise gravity effects would be optional, not mandatory, in the movement system.phavoc said:
Very well, by some definitions a helicopter rotor produces thrust, and by some other definition lift.phavoc said:
Either way it produces a vectorable force, which can be used to hover or propel the craft, just like AG thrust.
I assume you mean the craft's weight in the local gravity field.phavoc said:
But that is incorrect, an anti-grav drive simply provides a limited amount of thrust. Load it with too much mass and it will not lift.
A 10 MN anti-grav drive does absolutely nothing that a 10 MN M-drive can't do just as well.
I'm not talking about artificial gravity from grav plating. The GCarrier does not have it (by MT), nor does it need it since it is not intended for space.phavoc said:
This is not a setting; increasing thrust, and hence load capacity, would require a bigger drive and more power. Colloquially, add more anti-grav modules.
Sitting in an air/raft or GCarrier in flight does not make you weightless, you are still affected by the local gravity field. This is not stated anywhere, as far as I know, but my conclusion, because:
Given that ships explicitly carry their velocity vector with them that does not say much...phavoc said:
JTAS24 said:
That is what you are saying, by implication.phavoc said:
Either the air/raft and its passengers are affected by gravity normally, or they will fly off in space. Gravity (curved space-time in general relativity) is the perceived force that bounds the craft to the planet and prevents it from flying off in space (or rather the planet to fly away from the craft).
Obviously?phavoc said:
I don't see any jumping around.phavoc said:
A) Normally ships visit the Highport, and don't land at all.
B) If they must land, ships land on their thrusters, and lowers the nose at the last minute, as described in SSOM, p3.
C) In case the drive thrust is lower than surface gravity, extra lift can be provided by aerodynamic lift, and then a runway is used to land, as described in e.g. Gurps:
Gurps Starports said:
Gurps Starports said:
Despite what you are maintaining, Gurps does not mandate default use of contragrav, or preclude atmospheric landings on runways.
You specified an MT Launch, according to the description it's a TL-15 craft with only one locomotion system, an M-drive, and no anti-grav drive.phavoc said:
I disagree. Lets look at the drive options for a Subbie in MT:phavoc said:
Note that the Grav suspension cost is identical to the cost in CT Striker.
We can see that an anti-grav drive costs about the same as a 1 g thruster plate based M-drive.
As I have said quite few times, they cost about the same, so why not use a 2 g drive instead of an M-drive plus an anti-grav drive?phavoc said:
Yes, that might be an Iiken-class (TL9) scout with CG, not a Suleiman-class (TL10).phavoc said:
Is that supposed to say anything about ships in general?
There is no illustration on p12, but on p11 we have a spacecraft that appears to balance on its tail exactly as SSOM describes?phavoc said:
Yes, it shows a Subbie apparently flying horizontally, which it of course entirely shocking for an aircraft with wings.phavoc said:
It might, or might not, be trying to dock with the turret. If so, it might be a Colresh-class (TL9) with CG, or an Akkigish-class without CG caught in a tractor beam.
Again this tells me nothing about spacecraft in general.
You studiously ignore the reference provided:phavoc said:
The cumulative risk is easily removed by routine maintenance.SSOM said:
Ok, how do you explain e.g. the effect of gravity on spacecraft movement as described in LBB2? If spacecraft generally had anti-grav, they could counteract this at will, but that appears to not be the case.phavoc said:
Quite, but the only specific descriptions descriptions I can recall is SSOM and the use of runways in Gurps and T5.phavoc said:
Yes, as long as we keep in mind that each picture is a specific situation describing a special case. That special case should not be impossible, but neither is it necessarily the general case. If the artist has read and understood the rules at all, that is.phavoc said:
Yes, but only if it's very cheap. Grav thrust in CT, MT, and MgT is not especially cheap.phavoc said:
Yes, that is what I mean. Just like anti-grav drives, if the design system includes them.phavoc said:
We probably mostly agree. Our small disagreements leads to one large consequence, seemingly.phavoc said:
The Liner is originally unstreamlined and not intended to land. The cutter and shuttle have plenty of thrust from their M-drives, a little more wouldn't make much difference.phavoc said:
I agree that a Free Trader would need more thrust to land in high gravity, but since it is already marginally profitable it does not need expensive "nice-to-have" equipment. Any reasonable starport has shuttles.
I don't see why; anti-grav provides exactly the same thing as thruster plates: thrust.phavoc said:
Edit: Missed this:
What family car? Grav vehicles are too expensive to be regular family cars and are not very capable of interplanetary travel. Note that grav vehicles have minimal thrust outside a planets gravity well (RM, p56 again). They also do not generally have extended life support, so are unsuitable for trips over a few hours.phavoc said:
Oh, I think we can safely assume they have stopped reading this long ago...phavoc said:
Annatar Giftbringer
Emperor Mongoose
Haha well some of us are still reading! When threads evolve into... well something way beyond what’s generally necessary for day-to-day gaming, I tend to find them both entertaining and a great source for information, so please keep going
I’ll try to sum up my own thoughts, theories and observations on the subject this weekend - sometimes I wish I had more time to spend participating in forum discussions and not just lurking...
Old School
Mongoose
I quit reading a while ago, but at whatever point I left, I am in complete agreement with phavoc.
AnotherDilbert
Emperor Mongoose
Sorry, I missed this.
A planet with a surface gravity of 1 g accelerates ships by exactly 1 g (downwards).
Drive thrust divided by mass gives the acceleration the ship is capable of, say M-1 = 1 g. We don't know exact thrust or mass, nor do we need to, just the effective g-rating (=acceleration).
If the ships g rating is higher than the planets surface gravity, it can accelerate away from the planet faster than it falls down, hence escape the gravity well.
Or did I misunderstand you completely?
No, this is trivial. 1 g is just a standard measure of acceleration.dragoner said:
A planet with a surface gravity of 1 g accelerates ships by exactly 1 g (downwards).
Drive thrust divided by mass gives the acceleration the ship is capable of, say M-1 = 1 g. We don't know exact thrust or mass, nor do we need to, just the effective g-rating (=acceleration).
If the ships g rating is higher than the planets surface gravity, it can accelerate away from the planet faster than it falls down, hence escape the gravity well.
Or did I misunderstand you completely?
Agreed.dragoner said:
