www.nasa.gov

National Aeronautics and Space Administration

STEM LEARNING:

Advanced Air Mobility: The 

Science Behind Quadcopters

Reader—Student Guide
2 | ADVANCED AIR MOBILITY: THE SCIENCE BEHIND QUADCOPTERS READER STUDENT GUIDE

ADVANCED AIR MOBILITY (AAM)

When most people think of aircraft, they usually think 

about airplanes that travel at great speeds and cover 

large distances while flying routes between airports. 

More and more, however, new types of aircraft are 

transporting people and equipment to urban and rural 

locations where traditional airplanes cannot access. 

These new aircraft range in size from small cargo 

carrying drones to passenger-carrying air taxis, and 

carry out short range missions. 

NASA is leading the nation to quickly open this new era 

in air travel called Advanced Air Mobility, or AAM. The 

vision of AAM is that of a safe, accessible, automated, 

and affordable air transportation system for passengers 

and cargo capable of serving previously hard-to-reach 

urban and rural locations. 

According to recent NASA-commissioned market 

studies, by 2030 there will be as many as 500 million 

flights per year for package delivery services and 750 

million flights per year for air taxi/metro services. AAM 

will help ensure this new airspace is properly managed.

Compared to airplanes and helicopters, the aircraft that fly in this new airspace are small. This, along with where they 

fly, makes it unrealistic to continuously track or control these aircraft using radar or satellite technology. Many of these 

aircraft are Unmanned Aerial Vehicles, or UAVs, meaning they are self-flying or autonomous. 

Figure 1. AAM is a system of safe, accessible, affordable, and

automated air transportation for passengers and cargo in urban 

and rural locations. Credit: NASA
ADVANCED AIR MOBILITY: THE SCIENCE BEHIND QUADCOPTERS READER STUDENT GUIDE | 3 

QUADCOPTERS

Some of the aircraft controlled in the AAM system 

are quadcopters, similar to commercially available 

drones. The term quadcopter refers to the fact that 

they use four propellers to fly.

Several manufacturers are working on larger 

versions of quadcopters capable of carrying cargo 

and people. In fact, several prototypes have 

already flown! Prototypes are working models used 

by engineers to test whether a design works as 

expected.

Figure 2. NASA scientists use this quadcopter for experimentation. 

Credit: NASA, David C. Bowman

NEWTON’S THIRD LAW AND QUADCOPTERS

Figure 3. Newton’s third law 

explains the upward motion 

of a quadcopter. 

In 1687, English scientist Sir Isaac Newton published his now famous three laws 

of motion. These laws describe how forces and objects interact to affect motion. 

Newton’s third law of motion states that for every action, there is an equal and 

opposite reaction. 

When a quadcopter’s propellers spin, they push air downward. Using Newton’s third 

law, this represents the action. For Newton’s law to be true, there must be an equal 

and opposite reaction. This reaction is an upward force pushing on the quadcopter. 

Once this force exceeds the force of gravity pulling the quadcopter downward, the 

quadcopter begins to move up. 
4 | ADVANCED AIR MOBILITY: THE SCIENCE BEHIND QUADCOPTERS READER STUDENT GUIDE

For a quadcopter to fly, it must be capable of three different types of movement: 

vertical movement, lateral movement, and rotational movement. Based on 

Newton’s third law, each of these can be achieved using the quadcopter’s four 

propellers.

When the propellers spin, they push air 

down. Similar to a helicopter, pushing the 

air down is the action in Newton’s third law 

of motion. The reaction is a force, called 

lift, which pushes the quadcopter up. Each 

of the propellers will create lift, and the 

total lift for the quadcopter will be the sum 

of the four propellers’ lifts. The total force 

of the lift must be stronger than the force of 

gravity for the quadcopter to take off. Once 

in the air, the quadcopter can hover with 

no vertical movement by having the forces 

of lift and gravity equal.

When the force of lift acts straight upward, 

the quadcopter moves vertically. But, when 

lift acts at an angle, it can also move laterally. 

This is because part of the force of the lift is 

upward and part of it is to the side, resulting in lateral movement that can be from 

side-to-side or forward and backward.

Lateral movement occurs by varying the speed of the propellers. Increasing the 

speed of the two propellers on one side of the quadcopter and/or decreasing the 

speed of the two propellers on the other side creates uneven amounts of lift on the 

two sides. The lift created on the side with the faster spinning propellers is greater 

than the lift created on the opposite side. The result is that the quadcopter moves 

in the direction of the side where less lift is created.

The final type of movement happens when the quadcopter rotates. 

This type of movement relies on a force called torque, a twisting force 

that causes rotation. When a propeller spins, this force is produced. 

And, according to Newton’s third law of motion, an equal and 

opposite force is produced as well.

We see this in action when we look at a helicopter like the one in 

figure 7. When the blades on top of the helicopter (the rotor) spin, 

torque is created. The equal and opposite force rotates the body of 

the helicopter in the opposite direction of the blades’ rotation. Since 

this would make the helicopter unusable, a tail rotor is added. It 

creates a force that counteracts the torque and stops the helicopter 

from rotating uncontrollably.

MOVEMENT OF A QUADCOPTER

Figure 4. Drones move in three 

different ways.

Figure 6. When lift acts at an angle, it 

causes lateral movement. 

Figure 5. Gravity and lift act on a 

quadcopter. 

Figure 7. This S-64 heavy-lift helicopter uses the 

tail rotor to balance out the torque created by the 

rotor. Credit: NASA, Tony Landis
ADVANCED AIR MOBILITY: THE SCIENCE BEHIND QUADCOPTERS READER STUDENT GUIDE | 5 

Torque also affects a quadcopter when its propellers spin because each propeller 

individually creates torque when it rotates. All four torques are added up to 

determine the total torque acting on the quadcopter. Engineers have come 

up with a clever way of counteracting this torque—two of the propellers spin 

clockwise and two spin counterclockwise, as shown in figure 8. This results in two 

propellers creating torque that acts clockwise and two creating torque that acts 

counterclockwise. Thus, the forces cancel each other out.

This torque can also be used to create rotational movement for the quadcopter. In 

figure 8, when propellers 1 and 3 rotate, they produce counterclockwise torque 

(remember, equal and opposite reactions). If these propellers rotate faster than 

propellers 2 and 4, the counterclockwise torque acting on the quadcopter will 

be stronger than the clockwise torque acting on it. This results in the quadcopter 

rotating counterclockwise. Of course, if propellers 2 and 4 rotate faster than 

propellers 1 and 3, the quadcopter will rotate clockwise.

While having pairs of propellers 

rotating in opposite directions 

effectively controls the torque 

acting on the quadcopter, it 

presents a new problem for 

engineers. If propellers spin in 

opposite directions, two of the 

propellers push air upward while 

two push air downward. When 

you combine these forces, the 

total lift is zero and the quadcopter 

cannot take off. To overcome 

this, engineers use two different 

propeller blades. In figure 9, you 

can see that the leftmost propeller has the left edge higher in the front while 

the other has the right edge higher. This design changes the direction the air 

is pushed by the two propellers, meaning that when they spin in opposite 

directions, they actually push the air in the same direction.

Figure 10 shows a quadcopter with the propellers numbered and their directions 

of rotation indicated. This quadcopter weighs 4 Newtons (N), meaning that 

gravity pulls it downward with a force of 4 N.

Figure 8. Propellers spin in different 

directions to cancel out the torque. 

Figure 10. Top view of a quadcopter 

showing propellers rotating clockwise and counterclockwise.

Figure 9. Propeller blades can have different 

angles. 
6 | ADVANCED AIR MOBILITY: THE SCIENCE BEHIND QUADCOPTERS READER STUDENT GUIDE

To determine the movement of the quadcopter, the following rules are used:

Rules for Determining the Movement of the Quadcopter:

1. Rules for determining vertical movement: To calculate the total lift, add up the lifts created by each of the four 

propellers. 

• If the total lift is greater than the force of gravity (4 N), the quadcopter moves up. 

• If the total lift is equal to the force of gravity (4 N), the quadcopter doesn’t move vertically. 

• If the total lift is less than the force of gravity (4 N), the quadcopter moves down.

2. Rules for determining lateral movement: 

• If the lifts of propellers 1 and 4 add up to more than the lifts of propellers 2 and 3 added together, it moves right.

• If the lifts of propellers 2 and 3 add up to more than the lifts of propellers 1 and 4 added together, it moves left.

• If the lifts of propellers 1 and 2 add up to more than the lifts of propellers 3 and 4 added together, it moves 

backward.

• If the lifts of propellers 3 and 4 add up to more than the lifts of propellers 1 and 2 added together, it moves 

forward.

3. Rules for determining rotational movement: 

• If the lifts of propellers 1 and 3 add up to more than the lifts of propellers 2 and 4, it rotates counterclockwise.

• If the lifts of propellers 2 and 4 add up to more than the lifts of propellers 1 and 3, it rotates clockwise. 

• Otherwise, there is no rotational movement.
ADVANCED AIR MOBILITY: THE SCIENCE BEHIND QUADCOPTERS READER STUDENT GUIDE | 7 

Using the rules for determining the movement of the quadcopter, determine and fill in the missing information in the chart:

Lift Produced (N)

Vertical Movement 

(None, Up, or Down)

Lateral Movement 

(None, Right, Left, 

Forward, or Backward)

Rotational Movement 

(None, Clockwise, or 

Propeller Counterclockwise)

1

Propeller 

2

Propeller 

3

Propeller 

4

1.25 1.25 1.25 1.25 Up None None

1.2 1.2 0.8 0.8 None Backward None

0.25 0.25 0.5 0.5 Down Forward None

1 1.5 1 1.5 Up None Clockwise

1.5 0.5 1.25 0.75 None Backward None

0.5 0.5 None Right None

2 1 1 1 Up Right and Backward Counterclockwise

0.25 1 1 0.25 Down Left None

Figure 11. Completed chart showing the lift produced by each of the four propellers and what movement that causes.
8 | ADVANCED AIR MOBILITY: THE SCIENCE BEHIND QUADCOPTERS READER STUDENT GUIDE

READING COMPREHENSION QUESTIONS

1. Why does NASA believe that there will be a need for AAM as an air traffic management system in the near future?

2. If a system like AAM is not put in place, what sort of problems might arise?

3. Hovering is when an aircraft is in the air but remains motionless. For a quadcopter to hover, why must the forces of 

lift and gravity be equal?

4. Keeping mind how the propellers are used to balance out the torque, could you create a drone with just three 

propellers? If so, how? If not, why?

5. How does the quadcopter in figure 10 move if propellers 2 and 3 rotate faster than the other two propellers?

6. Look at the data in figure 11. Why would propellers 1 and 4 producing more lift than propellers 2 and 3 make the 

quadcopter move to the right?
ADVANCED AIR MOBILITY: THE SCIENCE BEHIND QUADCOPTERS READER STUDENT GUIDE | 9 

1. In science, a law describes what will happen under certain conditions every time, whereas a theory explains why 

something happens. Why is Newton's third law of motion a law and not a theory?

2. Sir Isaac Newton devised three laws of motion. Investigate these laws. How would his first and second laws of 

motion be important in determining how a quadcopter works? 

3. Read through the article found at https://www.nasa.gov/aero/taking-air-travel-to-the-streets-or-just-above-them/. 

What is NASA’s role in AAM and what other groups or organizations are involved?

4. Some air taxi prototypes have two rotors on top and no tail rotor. How is this possible when the rotors produce 

torque? 

GOING FURTHER

GLOSSARY

Advanced Air Mobility (AAM)—a safe and efficient air transportation system for short range aircraft

Lateral movement—movement to the right, left, forward, or backward

Lift—force that pushes upward (against gravity)

Newton’s third law of motion—for every action, there is an equal and opposite reaction

Prototype—an early model of something that can be used to test its functionality 

Rotational movement—spinning around an axis

Torque—a twisting force created when something rotates

Unmanned Aerial Vehicle (UAV)—small aircraft that can be remotely or autonomously controlled

Vertical movement—movement up or down
EP-2020-04-519-HQ

National Aeronautics and Space Administration

Headquarters

300 E Street SW

Washington, DC 20546