[Black Wolf]

OK - less Zero Grav, more Zero Air resistance, but they at least point in the same direction to get you physics buffs thinking along the correct lines. I'm writing some prelims for a sci fi story, and I'm considering the way my Space fighter is going to manoeuvre. I don't want to use retro rockets exactly for the primary rotation around the Y axis, so I came up with an alternative plan. Imagine a ship that looks pretty much like a Y Wing, excepot with the engines slightly farther apart. If on of those engines stopped firing, would the craft turn around its centre of gravity (presumeably at least relatively close to the pilot) with a reasonable degree of speed? And would it work as well, to reorient the ship at least, when going at high speeds? I know you'd have to give it at least equal force in the opposite direction to change your actual vector, but I'm just wondering about that sort of systems practicality in a combat situation.

I know it's fairly elemental, but I  want to get the basics sorted out before I commit too much to paper, and I need to be sure about these sorts of things, or I'kll have no end of people nitpicking my work. Thanks.

[ZylonBane]

Originally posted by Black Wolf
OK - less Zero Grav, more Zero Air resistance

Sorry, you lost me right there. Huh?

[Black Wolf]

err... Physics in space basically. I know it's not very clear..., and I'm sorry - it's kind of hard to describe...

[Flipside]

Hmmmmm... If you are talking in space, I'm really not sure, certainly, in an air environment, this would be so, since one wing is now 'dragging', it's a shaky, but not uncontrollable effect, but I think in space it would either do absolutely nothing or be similar in effect to a handbrake spin, the hard part wouldn't be turning, it would be coming out of that turn in any predefined direction. Maybe you could use something more along the line of the 'vectored thrusters' used on modern fighters, which just alters the direction the thrust leaves the jet by using an adjustable cone. This is what allows modern fighters to strafe to a certain degree.

Flipside

[pyro-manic]

Yeah - TVC is definitely the way to go - perhaps have Harrier-style exhaust ports on the sides of the engines, that can open and twist to thrust in any direction.

Oh, or you could look up some info on the latest X-plane (either the X-36 or the X-76, can't remember, but it sort of look like the F16, and it's white), 'cos that's a testbed for advanced TVC systems.

[magatsu1]

sounds like the Babylon five fighters. They would fire their engines on one side of the ship inorder to rotate "on the spot"

[Shrike]

Or you could just use the DMTMBTC drives.

[StratComm]

The Bab5 fighters were a little off in the way they turned; the center of mass of their designs would be somewhere in or just behind the cockpit, forward of the engines.  In that configuration you would have a turn as well as a spin.  Shutting down one engine will produce torque and turn the ship, but it would also cause the ship to enter a flat spin that would require the other engine to fire for an equal amount of time alone to come out of.  You would not have uneven thrust for very long, as to get your ship turning and then let it rotate until you need to bring it out.  The effect would be most pronounced if the engine is perfectly adjacent to the ship's center of gravity, as this would control how it handled in turns.

[Rampage]

I would say, "Yes, it will create rotational torque if the two engines exert equal forces at opposite points from the ship's center of mass.  Just picture a rod.  If you exert a force at the end of the rod, it will rotate.  It's the same case here."

[aldo_14]

Would it rotate, or cause the craft to move forward at an angle, though?  Using the above example, if you push end of a rod, it doesn't pivot round a static point, but moves forward as well.  I think.

[Flipside]

In zero G, the energy from the jet is transferred directly to the mass of the fighter in the direction the jet is going, I'm not certain, but I would have thought that a thrust not lined up with the centre of mass would cause the mass to pivot around it's centre, the problem is that the jet's would have to be only barely on either side of the centre, and the turn angle would have to be low, because the velocity of the turn would increase exponentially. Possibly It it's like pushing a rod in Zero G, the further from the centre you push, the faster the rod would spin.

Flipside

Edit : Just a thought, but if used right, this could actually be useful. Because the change in direction would be less the faster the object was moving, so moving slowly you would be highly manouverable, but you would sacrifice manouverability for speed

[ZylonBane]

Originally posted by Black Wolf
it's kind of hard to describe...

Not really.

"In a near-vacuum microgravity environment..."  <-- there, see?

[Stryke 9]

It'd turn, but it'd have ****e cornering, and would still be moving forward, and slightly to the direction the ship would be turning in. For anyone not an experienced pilot, it could very well spin out, in fact. Also, it'd be pretty inefficient. Basically a bad way to go compared to RCS jets and the like, but since in space you typically have a few hundred thousand miles of elbow room I guess it wouldn't be such a big deal.

[StratComm]

Actually, the common "but why do you have wings in space" can be justified by manuvering thrusters.  The farther the thruster is from the ship's center of mass, the more rapid the turn will be.  Using main thrust for manuvering isn't really an option, since you'd be wasting a lot of main thrust under normal conditions producing equal-and-oposite torques on your ship if you were using that approach (plus, if an engine goes out, you can't do better than a big circle; that happened to the Bismark in WWII, a big German battleship.  She lost her rudder and was picked apart by allied fighters, not something you'd want to happen in space combat).  A better alternative is to have booms extending from your ship with thrusters at the end, but these would be vulnerable and somewhat fiddly anyway.  The third option is to design the ship with bulky, fin-like extensions with the thrusters on the end, nothing that would change the center of mass but enough to move the manuvering thrusters farther away.

And in reality, in space, you wouldn't necessarily want your engines burning all the time.  It's a waste of fuel and you'd wind up going uncontrollably fast all too quickly.

[Sandwich]

There's essentially zero difference between what you describe, BW, with a single engine firing off-center, and what RCS thrusters are.

The main difference is that with RCS thrusters (assuming the simplest scenario where each pair of the 6 thrusters are located along a different XYZ axis), you usually have 2 firing in tandem, either together or in opposite directions. If both fire together, the object will change position, not orientation. But if, say, both thrusters situated along the same axis fire in directions opposing each other by 180 degrees, you get a change in orientation, not position.

So the question remains, if only ONE thruster fired, what would the result be? Logically, it would transfer half of the energy into rotational movement, and half into directional movement. Realistically, I haven't a clue.

Oh, and in a vacuum, the speed of the object does not affect the rotational movement at all. Also, if you had 2 objects travelling at the same speed (say 1Kps), and your point of observation was one of those objects, than the resultant position/orientation changes in the other object - relative to the 1st object - will be identical to what they would be were both objects at a standstill.

Wow, that turned into quite an essay...