Flight dynamics in
aviation
Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air craft such as hot air ...
and
spacecraft
A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
, is the study of the performance, stability, and control of vehicles
flying
Flying may refer to:
* Flight, the process of flying
* Aviation, the creation and operation of aircraft
Music
Albums
* ''Flying'' (Grammatrain album), 1997
* ''Flying'' (Jonathan Fagerlund album), 2008
* ''Flying'' (UFO album), 1971
* ''Fl ...
through the air or in
outer space
Outer space, commonly shortened to space, is the expanse that exists beyond Earth and its atmosphere and between celestial bodies. Outer space is not completely empty—it is a near-perfect vacuum containing a low density of particles, pred ...
. It is concerned with how forces acting on the vehicle determine its
velocity
Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity is a ...
and
attitude
Attitude may refer to:
Philosophy and psychology
* Attitude (psychology), an individual's predisposed state of mind regarding a value
* Metaphysics of presence
* Propositional attitude, a relational mental state connecting a person to a pro ...
with respect to time.
For a
fixed-wing aircraft
A fixed-wing aircraft is a heavier-than-air flying machine, such as an airplane, which is capable of flight using wings that generate lift caused by the aircraft's forward airspeed and the shape of the wings. Fixed-wing aircraft are distinc ...
, its changing
orientation
Orientation may refer to:
Positioning in physical space
* Map orientation, the relationship between directions on a map and compass directions
* Orientation (housing), the position of a building with respect to the sun, a concept in building de ...
with respect to the local air flow is represented by two critical angles, the angle of attack of the wing ("alpha") and the angle of attack of the vertical tail, known as the
sideslip
A slip is an aerodynamic state where an aircraft is moving ''somewhat'' sideways as well as forward relative to the oncoming airflow or relative wind. In other words, for a conventional aircraft, the nose will be pointing in the opposite directio ...
angle ("beta"). A sideslip angle will arise if an aircraft yaws about its centre of gravity and if the aircraft sideslips bodily, i.e. the centre of gravity moves sideways.
[Flightwise - Volume 2 - Aircraft Stability And Control, Chris Carpenter 1997, Airlife Publishing Ltd., , p.145] These angles are important because they are the principal source of changes in the aerodynamic forces and moments applied to the aircraft.
Spacecraft flight dynamics involve three main forces: propulsive (rocket engine), gravitational, and atmospheric resistance.
[Depending on the vehicle's mass distribution, the effects of gravitational force may also be affected by attitude (and vice versa), but to a much lesser extent.] Propulsive force and atmospheric resistance have significantly less influence over a given spacecraft compared to gravitational forces.
Aircraft
Flight dynamics is the science of air-vehicle orientation and control in three dimensions. The critical flight dynamics parameters are the
angles of rotation
In mathematics, the angle of rotation is a measurement of the amount, of namely angle, that a figure is rotated about a fixed point, often the center of a circle. A clockwise rotation is considered a negative rotation, so that, for instance ...
with respect to the three
aircraft's principal axes about its
center of gravity
In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weight function, weighted relative position (vector), position of the distributed mass sums to zero. Thi ...
, known as ''roll'', ''pitch'' and ''yaw''.
Aircraft engineers develop
control system
A control system manages, commands, directs, or regulates the behavior of other devices or systems using control loops. It can range from a single home heating controller using a thermostat controlling a domestic boiler to large industrial c ...
s for a vehicle's orientation (
attitude
Attitude may refer to:
Philosophy and psychology
* Attitude (psychology), an individual's predisposed state of mind regarding a value
* Metaphysics of presence
* Propositional attitude, a relational mental state connecting a person to a pro ...
) about its
center of gravity
In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weight function, weighted relative position (vector), position of the distributed mass sums to zero. Thi ...
. The control systems include actuators, which exert forces in various directions, and generate rotational forces or
moment
Moment or Moments may refer to:
* Present time
Music
* The Moments, American R&B vocal group Albums
* ''Moment'' (Dark Tranquillity album), 2020
* ''Moment'' (Speed album), 1998
* ''Moments'' (Darude album)
* ''Moments'' (Christine Guldbrand ...
s about the center of gravity of the aircraft, and thus rotate the aircraft in pitch, roll, or yaw. For example, a
pitching moment
In aerodynamics, the pitching moment on an airfoil is the moment (or torque) produced by the aerodynamic force on the airfoil if that aerodynamic force is considered to be applied, not at the center of pressure, but at the aerodynamic center o ...
is a vertical force applied at a distance forward or aft from the center of gravity of the
aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
, causing the aircraft to pitch up or down.
Roll, pitch and yaw refer, in this context, to rotations about the
respective axes starting from a defined equilibrium state. The equilibrium roll angle is known as wings level or zero bank angle, equivalent to a level
heeling angle on a ship. Yaw is known as "heading".
A
fixed-wing aircraft
A fixed-wing aircraft is a heavier-than-air flying machine, such as an airplane, which is capable of flight using wings that generate lift caused by the aircraft's forward airspeed and the shape of the wings. Fixed-wing aircraft are distinc ...
increases or decreases the lift generated by the wings when it pitches nose up or down by increasing or decreasing the
angle of attack
In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...
(AOA). The roll angle is also known as bank angle on a fixed-wing aircraft, which usually "banks" to change the horizontal direction of flight. An aircraft is streamlined from nose to tail to reduce
drag making it advantageous to keep the sideslip angle near zero, though aircraft are deliberately "side-slipped" when landing in a cross-wind, as explained in
slip (aerodynamics)
A slip is an aerodynamic state where an aircraft is moving ''somewhat'' sideways as well as forward relative to the oncoming airflow or relative wind. In other words, for a conventional aircraft, the nose will be pointing in the opposite directio ...
.
Spacecraft and satellites
![Space launch flight diagram improved](https://upload.wikimedia.org/wikipedia/commons/8/80/Space_launch_flight_diagram_improved.png)
The forces acting on space vehicles are of three types:
propulsive force (usually provided by the vehicle's engine thrust);
gravitation
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stron ...
al force exerted by the Earth and other celestial bodies; and
aerodynamic lift and drag (when flying in the atmosphere of the Earth or another body, such as Mars or Venus). The vehicle's attitude must be controlled during powered atmospheric flight because of its effect on the aerodynamic and propulsive forces.
There are other reasons, unrelated to flight dynamics, for controlling the vehicle's attitude in non-powered flight (e.g., thermal control, solar power generation, communications, or astronomical observation).
The flight dynamics of spacecraft differ from those of aircraft in that the aerodynamic forces are of very small, or vanishingly small effect for most of the vehicle's flight, and cannot be used for attitude control during that time. Also, most of a spacecraft's flight time is usually unpowered, leaving gravity as the dominant force.
See also
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References
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Aerospace engineering
Aerodynamics
Spaceflight concepts