Atmospheric operation of small craft, incorrect assumptions
- Thread starter DFW
- Start date
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DFW said:
Ok, so in this case the hull's aerodynamics would control how rapidly the ship could go from orbit to land rather than how agilely, and explains why traders and other time-is-money based ships would favor at least standard hulls if not streamlined ones. (Yes, that's outside the rules, but must of this discussion is anyway
, so....)And yeah, I get that your "1 mph" figure is meant to represent "a slow rate that won't cause any trouble", so I'll spare you the "but then it would take days to get to orbit" sarcasm.
It seems that this whole discussion hinges on whether or not M-drives can thrust off-axis or alternately at what angle of attack a "standard" hull becomes aerodynamically unstable.
I suspect that the real truth of the matter is that when Traveller was first conceived, the concept for ships was that they "float" like airships in the gravity field, and need extra control surfaces or reaction jets for fine control during landings and liftoffs. The gravity drives are maybe just not nimble enough to provide a lot of "final approach" maneuvering.
Sorry, but that still does not convince me at all. If you assume a graviticbarnest2 said:Go check out my earlier posts on evading an AIM-9
drive, you also have to assume that the enemy is aware of its properties,
so he will simply use a type of missile with a proximity fuse and submuni-
tions that create a threedimensional "killing zone" with a radius that is
bigger than the distance the hovering grav vehicle can fly when beginning
to accelerate from speed zero the moment its sensors can identify the
incoming missile - no escape hatch left, as much chance to survive as a
tank attacked with cluster bombs.
hdan said:
Each version treats that subject a little differently I believe. MT: "A standard-hull ship may still enter atmosphere but is very ungainly and ponderous, capable only of making a controlled glide to the surface. Getting it back into space requires an elaborate launch setup and considerable expense."
Here is where it gets plain bizarre. To be able to "glide" means you have lift from the body of the craft. If so, you wouldn't need an "elaborate launch setup" to get "airborne" again as you could use a runway. When you get into writing these types of rules it is best to at LEAST consult someone with a lttle knowledge of the subject...
rust said:Sorry, but that still does not convince me at all. If you assume a graviticbarnest2 said:Go check out my earlier posts on evading an AIM-9
drive, you also have to assume that the enemy is aware of its properties,
I'm talking physics NOT tactics and equipment designed to deal with anti-grav. Since I never broached THAT, I wouldn't even imagine I'd convince you of something I didn't speak of.
I've not seen any real description of the hypothetical grav plane's performance characteristics, nor any real discussion of its hypothetical opponent's performance, nor any real discussion of aerodynamics. Without that, this thread seems empty....
Aerodynamics and its structure.will have an affect on the grav-plane's performance
How many Traveller ships are rated for more than 6g's?
How many modern fighters are rated for less than 10 g's?
I seriously doubt a grav-plane could outmanuver a plane like an Extra EA-300 or Zivko Edge 540 unless grav drive is truly an inertia-less drive like described in E.E.Smith's Skylark series space opera.
Both are rated for -10 to 12 g's and have roll rates in excess of 400degrees per second
I'd give the grav plane would have a more useful speed range and better climb rate ( if it had thrust greater than 1.25 g's or whatever modern fighters these days have )
Other abilities may be questioned in light of the lack of details about it except that its a grav-plane.
come on!
discuss aerodynamics already!
Aerodynamics and its structure.will have an affect on the grav-plane's performance
How many Traveller ships are rated for more than 6g's?
How many modern fighters are rated for less than 10 g's?
I seriously doubt a grav-plane could outmanuver a plane like an Extra EA-300 or Zivko Edge 540 unless grav drive is truly an inertia-less drive like described in E.E.Smith's Skylark series space opera.
Both are rated for -10 to 12 g's and have roll rates in excess of 400degrees per second
I'd give the grav plane would have a more useful speed range and better climb rate ( if it had thrust greater than 1.25 g's or whatever modern fighters these days have )
Other abilities may be questioned in light of the lack of details about it except that its a grav-plane.
come on!
discuss aerodynamics already!
Ishmael said:
This thread seems to be generating an awful lot of heat with only glimmers of light, but I couldn't pass this one.
You're confusing sustained G's with peak G's.
Traveller spacecraft are rated in terms of sustained thrust (expressed in terms of G's of constant acceleration in a vacuum). This does NOT imply that their hulls aren't rated for higher stresses, especially in terms of those intended to operate in an atmosphere. In any case, the thrust rating of craft only has direct relevance in space or a vacuum world. In an atmosphere the craft is going to have a top speed, acceleration profile and agility determined by its aerodynamics (which is where this thread started...).
Those peak G's you refer to occur not from direct thrust, but during maneuvers, when the craft's own momentum is working against it. No pilot will survive 10Gs for very long. To clarify: 10G's is an acceleration of 100 metres per second PER SECOND. That's a change in velocity of 360kph in one second. NOT something that is going to happen by just opening up the throttle and kicking in the afterburners in level flight.
Also, There's no reason that the technology used to prevent a fighter pilot from passing out or dying under high *peak* Gs can't be used in a spacecraft (i.e. a guy in a vacc suit strapped into an acceleration couch looks a lot like a pilot in a pressure suit strapped into a fighter's seat... in both cases they'll be able to take a few extra G's and operate fine).
HAVING SAID ALL THAT...
A basic Traveller small craft isn't a jet fighter, and even a Starfighter isn't optimised for atmospheric work. I would expect that pound for pound (which is rarely going to be the case) a purpose built atmospheric craft is going to out-perform a spaceship or a multi-role craft.
When would a spacecraft ever be able to 'feel' accelerations greater than its own engines can produce unless it runs into something or is hit by something?
Its own frame/structure should be optimized such that it is able to accept such accelerations primarily along the axis of thrust from its main engine. To overbuild too much adds mass without benefit so a spaceship would not be stressed for off axis accelerations.
Spaceships, at least in Traveller, are hugely armored and thus have greater mass than otherwise expected which works against maneuvering unless grav-drives are actually Doc Smith's inertialess drives. I don't believe that they are.
Now, I don't use Mongoose's version of Traveller because I prefer my own rules to those shown in the SRD (in part because of arguments such as this), but shouldn't the max number of G's that a ship can 'pull' be limited to that determined by the ship's structure rating? Naturally those ships intended to operate in atmosphere may indeed have structure rated for higher accelerations.
I guess that in the end, the real question is whether a plane that can pull a 12-g turn can change direction and facing faster than a ship than can do 6-g straightline accelerations ( decelerate to a stop then accelerate at 6-g's in the opposite direction vs. a 12-g turn whose radius is set by the limit of 12-g's ) and of course, missiles can pull more G's in a turn/climb/etc. than a plane.
Its own frame/structure should be optimized such that it is able to accept such accelerations primarily along the axis of thrust from its main engine. To overbuild too much adds mass without benefit so a spaceship would not be stressed for off axis accelerations.
Spaceships, at least in Traveller, are hugely armored and thus have greater mass than otherwise expected which works against maneuvering unless grav-drives are actually Doc Smith's inertialess drives. I don't believe that they are.
Now, I don't use Mongoose's version of Traveller because I prefer my own rules to those shown in the SRD (in part because of arguments such as this), but shouldn't the max number of G's that a ship can 'pull' be limited to that determined by the ship's structure rating? Naturally those ships intended to operate in atmosphere may indeed have structure rated for higher accelerations.
I guess that in the end, the real question is whether a plane that can pull a 12-g turn can change direction and facing faster than a ship than can do 6-g straightline accelerations ( decelerate to a stop then accelerate at 6-g's in the opposite direction vs. a 12-g turn whose radius is set by the limit of 12-g's ) and of course, missiles can pull more G's in a turn/climb/etc. than a plane.
I still think the turning plane would win. It retains its speed through the turn and is already travelling when it come out of the turn.
The 6G craft however has to decelerate and stop. At, lets say, a full deceleration of 6G's, the ship would only decelerate at a rate of 60m/s, which means it would take a good few seconds before you came to a full stop and then started accelerating in the other direction.
For instance, say a 6G craft is travelling at 300m/s (just below the speed of sound). It would take a full 5 seconds to come to a stop, and another 5 to accelerate up too the same speed again. I'm not sure how long a 12G turn would take at these speeds, but I would guess it would be less than 10 seconds.
The 6G craft however has to decelerate and stop. At, lets say, a full deceleration of 6G's, the ship would only decelerate at a rate of 60m/s, which means it would take a good few seconds before you came to a full stop and then started accelerating in the other direction.
For instance, say a 6G craft is travelling at 300m/s (just below the speed of sound). It would take a full 5 seconds to come to a stop, and another 5 to accelerate up too the same speed again. I'm not sure how long a 12G turn would take at these speeds, but I would guess it would be less than 10 seconds.
DFW said:
It's a game. On these types of things I don't think the authors cared if it followed the rules of the universe. They were creating a ficitional universe only with some basis in science. They wanted such a rule for the game, so they did it and tried to explain it away somewhat. CT had streamlined ships able to land on a planet and unstreamlined ones being forced to stay in orbit even with a grav drive. Non-sensical, but simple, easy, and fun for a game.
