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# How would a ship pitch up and down and move in that direction with no drift?

Discussion in 'General' started by HateDread, Dec 1, 2013.

This last post in this thread was made more than 31 days old.
1. ### HateDreadTrainee Engineer

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Hey guys,
Just curious as to what was suggested in terms of ship movement. If you were flying in a direction, then pitched up or down, the thrust would now push you in that direction + your pre-existing drift from before you pitched, so you'd be moving somewhat diagonally between your old pitch and your new pitch.
How does the game suggest it gets around this? I'm not saying it should be ultra-realistic. I'm just genuinely interested in the physics at work here - how the forces are being applied.
(I may or may not be trying to make my own flight model, and am having trouble getting any non-Newtonian flight working in space... trying to pitch up leads to the aforementioned drifting, which is the most realistic but most frustrating way to play).
Regards,

2. ### DocTannerJunior Engineer

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763
There are lots of unrealistic bits of physics in this came, but what you're talking about is - fortunately - not one of them.

First, to recap: thrust and velocity are both vectors. Like you described, vectors can be added together to form a new vector. So, if I apply forward thrust of 10m/s^s for five seconds, then pitch up 90 degrees and again apply forward (previously upward) thrust in the same amount, I end up with two vectors: 50m/s "down" and 50m/s "forward", relative to our current facing. Thanks to Pythagoras, we can then calculate that our actual velocity is 70.71m/s at 45 degrees down-forward. Since the direction of our velocity vector isn't the same as our heading, it feels like we're "drifting".

Now, on to your question: Why doesn't your ship in SE do this? Well, it actually does. However, there's also a feature they've called "inertial dampeners". When the dampeners are on, the ship automatically fires thrusters in order to counteract any velocity on a vector other than thrust vector. Or, to simplify: they use thrusters to stop you in each axis independently, unless you are currently accellerating in that axis. So, if you're moving "down" when you're not telling it to accelerate down, it automatically accelerates "up" to stop you. The net effect of this is to keep you moving roughly in the direction you are burning.

You can turn off inertial dampeners with the 'z' key.

3. ### HateDreadTrainee Engineer

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Hi Doc,
Thanks for the reply!
The part of this idea that confuses me is the force required to reverse/negate a significant forward velocity. Comparing the thrusters on the rear of a ship with those on its underside, for example, reveals how weak the 'up' force would be, and thus how hard it should be for the ship to negate the pre-existing forwards velocity. How then does one pull up so smoothly, with such reduced drift? (If I am understanding you correctly, that is).

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5. ### K^2Apprentice Engineer

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A good analogy to think about is an airplane. When it performs a turn, it's the wings that provide the force necessary to change direction. The force is perpendicular to direction of motion, as with any turn that preserves speed. Note that the engine only has to work to compensate for drag. If you picture a space ship performing a constant speed turn, it does not need any forward thrust. Only a perpendicular "lift" to carry it through the turn. So the fact that your bottom thrusters aren't as powerful as your main thrusters doesn't prevent you from making a smooth turn. It does, however, limit possible turn radius. To make a tighter turn at the same speed, you have to apply more force.

For smaller ships, it might be easier to point the ship into the turn and use main thrusters for manuver. I suspect, once we have multiplayer and weapons, we will see fighter pilots doing just that. Adding significant thrusters in each direction is just extra weight which cannot be spared. On larger ships, however, it might be easier to just have thrusters pointing in all directions as is done currently.

Realistically, a long, narrow ship should have much easier time banking than turning. That would make it prudent to install significantly more thrusters on the bottom than top and sides, and then just banking into the turn. However, I'm getting the feeling that SE uses the same value for moment of inertia around all axis, which means a turn in any direction would require the same time. Hopefully, that's something the devs are planning to improve.

6. ### HateDreadTrainee Engineer

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Thanks, mate. I'll check them out. Although this gets more game-specific than an analysis of how to accomplish it, I can reverse-engineer a bit to try to understand.

Ahhh, yes, I was just thinking about aircraft... of course! The control surfaces and wings 'force' (nice pun) the craft to ascend upwards (locally) when it pitches, resulting in a curve as you said. What approaches can one take to calculate this? Particularly formulas.
Also, at the risk of side-tracking myself, how is maximum velocity calculated? Obviously we're not Newtonian here, but I'd be interested in the logic used.
Kind regards,

7. ### K^2Apprentice Engineer

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174
Centripetal acceleration of an object going through a turn is v²/R, where v is velocity and R is the turn radius. Multiply that by ship's mass and you have the necessary thrust.

Maximum velocity is an arbitrary limit in this game. There is no reason for ships to stop accelerating. If I had to guess, I would say that the particular limit is chosen to make sure there aren't any significant problems with collisions.

8. ### RalirashiApprentice Engineer

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306
In SE ships use gyroscopes for turning, rather than thrusters. Thrusters are used only for linear motion.

9. ### K^2Apprentice Engineer

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174
Gyroscope only changes attitude of the ship. A turn is a maneuver that changes direction of travel. You cannot do that without thrusters thanks to the Newton's first and third laws.

If you are flying with the "inertial dampener" assist, you will notice thrusters firing when you perform a turn. If you are flying without it, you'll notice that change of attitude does not change direction in which you are moving. You have to fire up the thrusters yourself if you want to travel in a different direction.

10. ### ryudragon27Trainee Engineer

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i felt really smart after both reading and understanding whats in this thread, nice topic