Jun 22

General Flight Mechanics

backgrounder (19)

General Flight Mechanics? What’s that?

General Flight Mechanics is the first academics lesson in the Legacy Instructional Series, and presents an elementary look at spaceflight in Star Citizen. This guide is created for people who have never experienced any sort of six-degree-of-freedom (6DOF) simulator before. Much of this is explaining the semantics of spaceflight, discussing the interaction of the Intelligent Flight Control System (IFCS) with both the pilot and the ship, and how to think in a way conducive to successful piloting.

Exercise videos provide new players with a more hands-on experience – currently, there is only one video associated with this particular lesson: Exercise GFM1-1: Flight Check.

 

The Six Degrees of Freedom

A spaceship has three axes: lateral, longitudinal, and vertical.

All six degrees of freedom are manipulations that occur about these axes. Three are translational, and three are rotational.

Source: S1-T8A-UFM-000 (Courtesy of Nimrod77)
Source: S1-T8A-UFM-000 (Courtesy of Nimrod77)

 

The ship can be translated (in simple terms: moved) with lateral strafe, longitudinal strafe, and vertical strafe.

The ship can be rotated with pitch, roll, and yaw, which correspond to rotations about the lateral, longitudinal, and vertical axes, respectively.

Currently all six of these “degrees of freedom” can be manipulated independently from one another. Limitations of controllers (not even most HOTAS setups have six independent analog axes) and players (asking new players to use 6DOF would result in high attrition) result in the need for an in-depth “fly-by-wire” system – the IFCS.

The core function of the IFCS is taking the prescribed inputs above (“strafe the ship left” or “pitch the ship up”) and determining which thrusters need to fire, in what direction, and for how long. This is done to prevent needing an analog axis for every single thruster on the ship, as well as a superhuman pilot.

 

Orders (levels) of Control

The next layer of the IFCS delves into control systems, so they are described briefly below.

Zero-order (position) control: Direct control over the physical position of whatever axis you are manipulating. In a simulator that is based on realistic physics, this isn’t very likely as it doesn’t allow for physics to occur when control inputs are made. Zero-order control over the strafe axes would mean that going 50% right on the lateral strafe would result in the ship flying itself to halfway between the origin and the right boundary of the Arena Commander map. 50% right on the yaw input would result in the ship’s nose being rotated to 90 degrees right of whatever is considered to be the “zero” axis of the map. A good example of zero-order control are real-time strategy (RTS) games – one only needs to right click on the ground somewhere, and the selected unit will walk or run itself to that location without any further input.

First-order (velocity) control: Control inputs translate into rates of change (velocity/rotational velocity). First-order control over the strafe axes would mean that going 50% right on the lateral strafe would result in the IFCS accelerating your ship until it is going half of your top speed to the right. 50% right on the yaw input would result in the ship’s nose rotating to the right at half of its maximum rotation speed. Good examples of this are (obviously) some space simulators and even the WASD movement controls of most shooters (note that aiming in shooters is usually zero-order).

Second-order (acceleration) control: Control inputs translate into accelerations. This is the thinnest this “layer” of the IFCS could (reasonably) be. Second-order control over strafe axes would mean that going 50% right on the lateral strafe would accelerate the ship at half its maximum acceleration (determined by thruster power, layout, weight, etc.). The ship would continue to accelerate in this manner (well, at least until the speed limit imposed by Cry Engine). 50% right on the yaw input would result in the ship’s nose accelerating rotationally at 50% of the maximum just as above. The nose would continue to spin faster and faster until reaching a Cry Engine limit (if there is one). Note that releasing the stick would not stop the spinning, but merely the rotational acceleration. A good example of this is Elite: Dangerous with flight-assist off.

By now you are probably wondering which levels of control are possible in Star Citizen. Here’s the answer:

Coupled mode:  First-order strafing / First-order rotation

Decoupled mode:  Second-order strafing / First-order rotation

Under the current flight model, the only time to pilot has direct control over his acceleration is when strafing in decoupled mode.

Why is this important to note?

Mentality matters. To be successful, the pilot must remember that in most situations he is not directly accelerating his ship. It’s easier to think of it this way: in most circumstances, you are inputting a desired velocity vector, and the ship’s IFCS is accelerating as needed to match that desired vector. Remembering that you are not directly controlling your ship, and that your IFCS is, will be fundamental to understand what happens during maneuvering – particularly when it comes to the influence of g-effects on your avatar, additive strafing, and complex maneuvering, all of which will be covered in more detail in later lessons.

Alright, I get it. I input the desired velocity vector, and my ship matches it. So, how does this help me fly?

The first step is figuring out how to keep track of your current velocity vector. This can be described as your movement in the game world at any given time, expressed in both magnitude and direction. In other words – you need to know which way you are going, and how fast.

This leads to what is perhaps the most useful HUD element in the game – the Total Velocity Indicator (TVI).

TVI

The total velocity indicator gives you one of the two pieces – the direction of your velocity vector. The reason it doesn’t look like a vector is because the vector extends directly out from your ship and into the TVI. In a way, the TVI can be thought of as the “head of the velocity arrow”. Simply, it shows where your ship is going – where it will be in the future. If the TVI lies on top of an asteroid, and you make no changes, your ship will hit the asteroid.

ATVI

There’s also an indicator for the tail of the same arrow, which is opposite in direction from the TVI and indicates the direction you are coming from. This is called the Anti Total Velocity Indicator (ATVI). In general, it is usually only visible for most users when they are flying backwards in some way. You ATVI indicates the direction that your ship is coming from.

Source: S1-T8A-UFM-000 (Courtesy of Nimrod77)
Source: S1-T8A-UFM-000 (Courtesy of Nimrod77)

 

With the TVI, you can keep track of the exact direction your ship is traveling at any time. But how fast? The other value of the ship’s velocity vector is the magnitude, expressed in meters per second (m/s). This one, at least currently, it more difficult to determine.

The velocity tape on the left side of the HUD gives an indication of velocity, but doesn’t tell the full story. It only indicates velocity in the forward direction. In other words, if you were traveling at 200 m/s directly right, the velocity tape would read 0 m/s. Because of this, at least until CIG adds a true velocity indicator, velocity in directions other than forward can only be approximated by the pilot based on visual indications (dust going by the cockpit) and based on the pilot’s spatial awareness during maneuvers. Regardless, maintaining awareness of both your direction and magnitude of velocity is essential for combat maneuvering. This will be covered in more detail later.

Let’s look at some examples. . .

First, a ship at rest guns his throttle to 100% (or strafes directly forward – the effect is the same).

ss+(2015-03-31+at+01.46.05)

 

The ship’s IFCS sees the pilot is inputting a desire for full velocity forward, and uses thrusters and the main engine to accelerate the ship until reaching that velocity, at which point the thrusters shut off.

ss+(2015-03-31+at+01.49.04)
Here’s what what the result would look like in-game. Note that the TVI is centered.

 

Next, a ship at rest guns his throttle to 100% and strafes right (or leaves throttle at zero and strafes forward and right – the effect is the same). Note that the throttle can be thought of as just another strafe input that gets mixed with whatever lateral/vertical/longitudinal strafe inputs the pilot puts in otherwise.

ss+(2015-03-31+at+01.42.29)

 

The ship’s IFCS sees the pilot is inputting a desire for full velocity, but at a 45 degree angle offset right from the nose, and uses longitudinal and lateral thrust as well as the main engine to accelerate the ship until matching that velocity vector, at which point the thrusters shut off.

Finally, we’ll examine rotation. A ship at rest – both translationally and rotationally – inputs full right yaw.

The IFCS sees a deflection in the ship and determines what the maximum rotational velocity for the ship should be (currently limited by the IFCS to prevent out-of-control spins). It then uses opposing thrusters on either side of the ship to affect a rotational acceleration until reaching that rotational velocity, at which point the thrusters shut off. If the stick were to be returned to center, the reverse would happen until the ship rotation is stopped.

 

Newton Hurts My Brain

Luckily, the IFCS makes most ship movement fairly intuitive for the new pilot. Only when attempting complex maneuvers, particularly in the heat of battle, will this knowledge become important. The most important takeaway is remembering that, as a pilot, you are telling your IFCS what you want the ship to do, and the IFCS determines what actual accelerations need to happen to meet your desire.

As always, if you have questions, feel free to comment here, and the LIS team will do its best to answer!

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6 comments

  1. Nimrod77

    As always Whitesnake, great job. Excellently crafted lesson from a professional.

  2. ArrghhScott

    Wow, well done. My brain hurts now.

  3. Saoldian

    I feel like I’m back in flight school, but with a twist! Nice work, great job! Do you find decoupling in a turn faster than using the space brake? I can’t tell which one is faster.

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