QUADCOPTER TECHNICAL TERMS

Some of the terms used to described quadcopter characteristics are "borrowed" from the flight characteristics definitions of airplanes and helicopters. Where there is a difference or similarity, I will point that out to you.

THRUST

The vectored force of the quadcopter's (4) rotors which forces the quadcopter in a specific direction.

DRAG
The resistance of the free air working against forward frontal surface(s) of the quadcopter and is in opposition to thrust.

LIFT 
The rotation of the quadcopters rotors supplies a downward thrust which in turn pushes the quadcopter upwards. More information here:

Bernoulli's Principle 

GRAVITY

Gravity is the effect of 1) the earth's movement as it moves through space, 2) its rotational speed relative to its axis, and 3) the effects up other objects (planets) mass upon the earth.

More simply put, an object's mass will tend to be accelerated toward the center of the earth at a constant rate of 32 feet per/second/second (not a typo). This is referred to sometimes as the "pull of gravity". More on gravity here:

Newton's Theory Of Gravitation

CENTER OF GRAVITY

Not to be confused with gravity. From Wikipedia:

"The center of gravity (CG) of any aircraft is the point over which the aircraft would balance. Its position is calculated after supporting the aircraft on at least two sets of weighing scales or load cells and noting the weight shown on each set of scales or load cells. 

The center of gravity affects the stability of the aircraft. To ensure the aircraft is safe to fly, the center of gravity must fall within specified limits established by the aircraft manufacturer." 

The CG of a quadcopter can be slightly off, and still fly well because it has a joystick trim function to effectively counteract any slight CG imbalance.

TORQUE

Torque is the action of external forces to move an object about an axis. In the case of quad, this axis passes vertically through the CG. Quadcopters counteract this rotational effect of torque, by using (2) matching pairs of adjacent rotors.

YAW

The quadcopter's flight computer can modify the speed of any of the rotors individually to effectively rotate the quadcopter on its vertical axis located at or very near the quadcopters CG. This is called Yaw.

Quadcopters have trim controls to allow for this although somewhat limited. However they can give relatively good hovering characteristics in very light wind.

By controlling torque, the quadcopter can adjust its direction or heading. Quadcopters have multiple pre-programmed flight movement vectors that work in combination to control the quadcopter using joysticks. 

PITCH

Pitch is the upward or downward tilt of the quadcopter's nose. Quadcopters can pitch nose up, or pitch nose down. The nose is marked (paint, lights, decals and other markings) and is used by the flight computer as a central reference point.

All joystick controls on the transmitter are referenced to the nose position. Example: A quadcopter is taking off nose forward and your are behind it. If you push the RT stick forward the quadcopter's nose will pitch down. If you pull back the RT stick, the quadcopter nose will pitch up or tail will pitch down.

ROLL

Roll is a fixed wing (airplane) technical term for 1) the aircraft lowering a wing or 2) the aircraft rotating around its longitudinal axis (an imaginary front to back down the center of the aircraft). The airplane uses an aileron to create drag or lift by deflecting airflow and the lowering or raising the lift on that wing.

One wing will move downward, the other wing will move upward and the aircraft will roll around the longitudinal axis of the airplane. The quadcopter accomplish much the same maneuver, although somewhat limited, by decreasing the RPM (Revolutions Per Minute) of the 2 rotors on the side to be lowered. 

BANK

A bank can be a combination of a pitch and roll to an airplane. Combined with the rudder or yaw control, the aircraft can "bank a turn". This banking is done on an airplane with a moveable part of the wing called an "aileron" for the roll portion and the rudder for the yaw. Both used in a coordinated fashion. 

There are no ailerons on a quadcopter. The term aileron as used for a quadcopter is actually an airplane term for movement called a "slip". When talking quads, bank means move either left or right of the flight path, usually by lowering one side of the quadcopter.You can add yaw in the same direction of the bank get a better and/or quicker turn. Not required, though.

VECTORED THRUST

The thrust of any given rotor is combined with all the others and is controlled by the quadcopters flight computer. The flight computer changes each individual rotors speed to maneuver the aircraft up or down, left of right, forward or backwards and in any combination the pilot dictates using a two, 4-way flight controls called joysticks. The two flights controls are:

1) The left joystick (manages: motor & yaw). This control acts as throttle (rotor RPM) when pushed forward or pulled backwards and controls the rotors speed (RPM). More RPM will make the quadcopter ascend, less RPM will make the quadcopter descend.

Pushing left on the left stick will yaw the quadcopter counter-clockwise. Pushing right on the left joystick will yaw the clockwise. Left joystick movement will snap back to center position when released and the quad will sty at approximately the same heading.

2) The right joystick (manages: pitch & roll) when pushed forward will tilt the nose down causing the quadcopter to move forward, when pulled back it will raise the nose causing the quadcopter to move backwards.

Pushing the right stick to the left will cause the quadcopter to roll (slip) to the left, pushing the stick to the right will cause the quadcopter to roll (slip) to the right. The right joystick will center itself when released. 

ANGLE OF ATTACK

The angle in context of quadcopters refers to the angle the rotor (also called a blade or propeller or prop) slicing through the air horizontally. It is generally referred to as "pitch". Pitch is the number of inches a rotor blades advances per turn expressed in inches.

The rotor angle of attack (pitch) is fixed in all quadcopter rotors. The pitch, diameter of the rotor and speed of the motor powering the rotor determines how much lift (downward thrust) is created. Generally, the bigger the motor turning the rotor, and/or the larger the rotor, the more thrust is generated.