www.ditl.org

The impulse engines weren't exactly located center of mass before the addition so I'd say Starfleet is ok with dealing with that issue.

Fair enough, I stand corrected.

That wouldn't matter in space anyway . Also if one can truly manipulate gravity one can to a certain extent manipulate mass as well.

Actually in space it matters a great deal. Unlike a ground vehicle you don't have gravity and friction to keep all four tires on the ground. Unlike an aircraft you don't have aerodynamic surfaces to make gross corrections (aka. the F-4). In space all you have are your engines, and if you're fighting them all the time then you're wasting tremendous amounts of fuel.

Now, the visual evidence we have of Trek ships and their engine locations vs. CGs does seem to indicate that it's not a problem for Starfleet. They either don't care about the added energy use, wear on the components, and general inefficiency of off axis thrust or they have found a way to selectively reduce the mass of the ship to different degrees in different locations.

So while I agree that for Starfleet it's a non issue you couldn't be more wrong about off axis thrust not mattering in space.

The lack of friction and gravity is exactly why you can put the engines anywhere on the ship and have it move in the direction of thrust. Friction and gravity are the only reasons that it would not work in an atmosphere (the various assymetric aircraft designs not withstanding, different dynamic).

Vic wrote:The lack of friction and gravity is exactly why you can put the engines anywhere on the ship and have it move in the direction of thrust. Friction and gravity are the only reasons that it would not work in an atmosphere (the various assymetric aircraft designs not withstanding, different dynamic).

If you have an engine off axis in space, you'll just have a spinning disaster, not a viable ship.

The awesomeness of the SSV Normandy SR-2...with its brand new Thanix Cannons:



And firing torps!

stitch626 wrote:

Vic wrote:The lack of friction and gravity is exactly why you can put the engines anywhere on the ship and have it move in the direction of thrust. Friction and gravity are the only reasons that it would not work in an atmosphere (the various assymetric aircraft designs not withstanding, different dynamic).

If you have an engine off axis in space, you'll just have a spinning disaster, not a viable ship.

Only if you have opposing engines on each end, this is the reason why the shuttle has so many thrusters around the vessel.

If only one thruster is hit the shuttle will move in the direction of that thruster only.It takes an opposite facing thruster on the other end of the shuttle fired at the same time to achieve a spin.

Just that simple, no need to make it more complicated than it already is.

Vic wrote:Only if you have opposing engines on each end, this is the reason why the shuttle has so many thrusters around the vessel.

If only one thruster is hit the shuttle will move in the direction of that thruster only.It takes an opposite facing thruster on the other end of the shuttle fired at the same time to achieve a spin.

Just that simple, no need to make it more complicated than it already is.

Vic, I don't think you understand the idea of rotation and center of mass as well as you think you do. If the point of thrust is not behind the center of mass, there will be rotation. How much rotation there is will depend on how much thrust to how much mass, and how far off center the point of thrust is, but there will be rotation. On aircraft off center thrust can be compensated for by using the control surfaces to create an opposing rotation by redirecting airflow. On a spacecraft however the only way to compensate for an off center thrust is to have another source of thrust that is either placed an equal but opposite distance off center or which is directed opposite of the direction of rotation. The former is certainly a more idea set up than the latter, but it is still not as idea as putting all thrust directly behind the center of mass, as a failure of one engine means the ship is stuck.

As far as this applies to trek ships, most of the federation ships have their thrust above or below (relative to the orientation of the ship) their center of mass. Without some correction mechanism, this set up would impart a rotation termed pitch, the ship would climb or dive, and end up going in circles.

Are you talking about warp speed or impulse drive? If warp speed, remember that the warp nacelles create a warp field around the ship and the entire ship travels in subspace via that field. If it's impulse, you'll notice that on most of the starships that have saucer sections, the impulse thrust ports are on the aft section of the saucer, in effect pulling most of the ship's mass (stardrive section) and pushing the saucer, and they're not far off of the center of mass that they can't compensate somehow, either by the SIF, or by sheild manipulation, or changing gravitational properties of the ship.

We're talking about any sort of thrust. Warp must be ignored in this sense because it doesn't follow physics to begin with (well, not much anyway).

And the issue is that any thrust not in line with the cog (up/down and left/right, forward/back doesn't matter) will cause a rotation unless countered by more thrust, which in turn lowers efficiency.

My Search-FU is obviously weak, I can find many descriptions of the equipment used. But I cannot find descriptions of how you steer in space, this would illustrate my point perfectly.

...uh, no comment on the pictures I posted?

Vic wrote:My Search-FU is obviously weak, I can find many descriptions of the equipment used. But I cannot find descriptions of how you steer in space, this would illustrate my point perfectly.

Actually it would prove you're wrong. You steer via off axis thrust. You accelerate significantly only with on axis thrust. If your axis of thrust does not pass through your center of gravity then all you do is spin like a top. If you're not that far off then you can counter the rotational tendency with thrusters else where to counter the spin but you can't just slap engines on spacecraft where ever you please and expect it to work.

alright, let me illistrate, lets pretend we have an imaginary (and exagerated) spacecraft who's shape looks something like this:
______________
/ \
O-----------------------------------------------------------------< CM >------------------------------------------------------------O
\______________/

The big box is the craft with CM representing the center of mass...the two circles on the ends of the wings are the engines....

now if you were to fire both simultaneously then you would be okay, they are both located vertically on the Center of Mass so no up-down spin and their both equidistant from the Center of Mass horizontally so the ship will fly forward.

If however you were to thrust with just one of those engines, there would still be not up-down spin because the engine is on the CM vertically, however the ship would begin to spin in the left-right direction because the thrust isn't behind the Center of Mass.

EDIT, okay the whole box thing was a fail because I used spaces that the forum took out but the principle is still the same, just imagine the box thing around the CM