Why Do Drones Have 4 Propellers

Why Do Drones Have 4 Propellers?

Quadcopter UAVs (Uncrewed Aerial Vehicles) are the most common type of drones in the market. These tiny crafts use four rotors, each consisting of a motor and propellers.

But why do drones have four propellers? 

The reason why drones need four propellers is because of stability. Four propellers distribute the drone’s thrust and weight evenly. This makes it possible for the drone to hover and turn without tilting or swaying. 

That said, you’ll be surprised to know that four propeller mechanics are considered relatively inefficient for flight.

As a drone enthusiastic, I would explore this interesting conundrum as I unravel why four propellers are still the favored option.

The Significance Of Propeller Count In Drone Design

The Significance Of Propeller Count In Drone Design

Considering that propellers are the key elements in getting the drone airborne, the propeller count is a crucial factor. While four is preferred, you must have seen drones with one, two, or even three propellers.

To know what are the advantages of using a quadcopter design in drones, let’s first understand the science behind what propellers do.

When propellers spin, they force the air downwards. Now, per Newton’s third law of motion, every action has an equal and opposite reaction.

So, this downward thrust creates an upward pushing force, or lift, on the drone. Once this lift exceeds the force of gravity, the drone begins to fly.

Now, the required thrust can also be achieved by two or maybe three spinning propellers. So, why aren’t most drone propeller configurations like this?

That’s because you might be able to get the drone airborne with two propellers but will lose out on control.

Flying a two-propeller drone at high speeds and maneuvering it with accuracy and stability is nearly impossible.

Perhaps, with technological progress in control algorithms, two propeller drones may become functional.

Let’s now talk about three propeller drones. This design is rarely seen in the market because the torque generated by three propellers is difficult to balance, leading to instability.

Like the two-propeller drones, these drones also offer restricted maneuverability when compared to quadcopters.

Understanding The Aerodynamics Of Quadcopters

Three types of movements, i.e., vertical, lateral, and rotational, are required for a quadcopter to fly with stability and control. All these are taken care of by the four propellers. Here’s how.

The vertical movement or lift is achieved when the propellers push air downwards, and the counter force creates an upward thrust. Once the drone is airborne, it can hover as long as the forces of lift and gravity are equal.

For lateral movement, the speed of the propellers needs to be varied. By reducing/increasing the speed of propellers on one side, an uneven lift is created.

The propellers spinning faster have greater lift than the other side. This allows the drone to turn in the direction of the propellers with lower lift.

The rotational movement depends on a force called torque, which is created by the spinning motion of propellers.

An equal and opposite force to this torque rotates the drone in the opposite direction of the blades.

To balance this torque, a pair of diagonal propellers spins in the anticlockwise direction while the other pair spins in a clockwise direction. 

This might lead you to wonder if the two propellers that spin anticlockwise and push the air upward could prevent take-off.

The reason that does not happen is because the blades of two diagonal propellers are designed differently. 

By raising the edge of the propellers, engineers are able to make the propeller spin anticlockwise yet push air downwards. That’s some amazing quadcopter aerodynamics, right?

If you want to read more about the scientific rules and numbers that determine the movement of a quadcopter, this guide by NASA will be quite helpful.

Advantages Of Using Four Propellers In Drones

Advantages Of Using Four Propellers In Drones

We will address the deficiencies inherent to a four-propeller design in subsequent paragraphs. For now, here are the benefits of four propeller drones:

1. Smooth Cruising Operation

The balance and stability created by the four propellers give a smooth flying experience.

Your drone becomes easier to maneuver and can withstand winds and counter high speeds.

2. Hovering Prowess

The four-propeller drone technology makes it possible for quadcopters to hover in the air.

The drone’s rotors produce a lift force equivalent to the gravitational pull to balance the two forces and keep the drone afloat in mid-air. 

3. Simple To Use

Most modern quadcopters are software-controlled digital devices with electronic stabilization systems. This makes them easy to use, even for beginners.

With fixed-wing drones, one needs to be an expert pilot. And even then, you never know when the landing might go awry!

4. Low Cost

Quadcopters do not have too many moving parts. Their mechanical design consists of fixed propellers mounted onto simple motors. This makes their cost reasonable compared to some other drones.

5. Safety

The small blades of a quadcopter make it relatively safer if there is a crash. The damage or injury in case it plummets to the ground would be minimal.

Refer to my previous article for more insights into why propellers are dangerous and measures to stay safe when flying a drone.

Propeller Configuration Comparisons

Propeller Configuration Comparisons

We have already examined the benefits that four propeller blades hold over lesser configurations in terms of stability and control.

But as I pointed out in the beginning, the quadcopter design advantages have their limitations.  

Four propeller blades might offer more thrust but are an efficiency nightmare! The four blades continually maintain a speed difference in order to keep the drone flying.

This is a drain on the energy source. As a result, quadcopters are only capable of short flights lasting 20-30 minutes. This shortcoming also applies to propellers with six or eight blades.

In contrast, fixed-wing and single-rotor drones only need sufficient energy to lift and carry them forward. This makes them more energy-efficient and capable of longer flights.

It also makes them faster. I’ve often seen racing drones in my local drone racing club. Most of them have two propellers.

The reason is that with these drones, a quick motor reaction is more important than thrust.

A two-blade propeller is sufficient to lift these ultralight drones while bestowing them with speed and quick reaction time. 

Also, unlike quadcopters, it is possible to use gas engines as the power source for fixed-wing drones. This reduces the overall cost of flight while increasing flight time exponentially.

However, the simplicity, stability, and ease of control are some quadcopter design advantages that find favor with drone hobbyists and manufacturers.

Future Trends In Drone Propeller Configurations

Future Trends In Drone Propeller Configurations

The future of drones is bright, and this applies to the components that make them fly as well!

Researchers are experimenting with varied propeller configurations and designs that keep the drone afloat and stable while maximizing efficiency. 

Amazon’s Prime Air delivery drone is a hybrid model that combines the advantages of fixed-wing and rotor-based designs. This allows the craft to hover as well as land and take off vertically.

Researchers at MIT have come up with a unique toroidal propeller for commercial quadcopters.

The unique looping blades of the propeller offer similar thrust as present propellers but significantly reduce the noise levels and enhance efficiency.

The search for new drone tech that makes it possible to fly without propellers is also on. These bladeless drones use an impeller or a rotating centrifugal pump to fly.

Such drones will remove the dangers posed by spinning propellers and make them safer for everyone.

Conclusion

Two, four, or none, who knows what the future of propeller configuration tech holds? At present, the quadcopter stability and control cater to the needs of hobbyists and professionals alike.  

The reliability and control offered by quadcopters make them the top choice for beginners as well. While we eagerly await future trends in drone propellers, for now, the aerodynamics of quadcopters will ensure you have a smooth flight.

The next time you marvel at a hovering quadcopter, you will know the science behind its elegant aerial dance!

FAQ

1. What are drone propellers made of?

Plastic and carbon fiber are the most commonly used materials for drone propeller design.

2. Will quadcopters be used for large-scale transport?

Unlikely. Owing to the inefficiency of the four-propeller design, they are likely to remain popular in small drones only that are used for limited flight times.

3. What are six and eight-propeller drones called?

Six and Eight propeller drones are called Hexacopters and Octocopters, respectively.

Author
Diptesh Das

Diptesh Das is your friendly ‘content maniac’ and drone enthusiastic! Being passionate about content writing. He is a firm believer of the power of words and thereby ended up leveraging them to create an impact by sharing his drone knowledge and experiences.

Leave a Comment

Your email address will not be published. Required fields are marked *