We all know drones can’t fly without propellers; they’re necessary components. But exactly how many can they have? Would just one propeller suffice?
When we ask for a recommendation at a drone shop, we ordinarily get shown a quadcopter. Perhaps that means no less than four propellers suffice.
The truth is that there are many different types of drones on the market — ones you don’t get to see too often. Each type may come with a different number of propellers and made with different parts, hence, may have a different frame design.
In this post, we’ll be getting into the specifics to explore what the range of possibilities actually looks like. You’ll also find out why a drone design may be significantly more popular than another as you read on.
To kick things off, let’s consider the lowest possible number.
You may have seen single-propeller aircraft before. However, their design is oftentimes deceiving and there are more components affecting airflow than just the one, big propeller.
Let’s see if one propeller can facilitate drone flight.
A drone can technically fly with one propeller, as shown by two different project models called the Ball-Drone and the Monospinner. However, single-propeller drones aren’t commercially available. A lot more development is required before they can even be remotely useful.
In other words, single-propeller drones aren’t stable enough to shoot steady footage. Their development is still in their early stages where lift and (some sort of) control is prioritized.
Multiple-propeller designs, on the other hand, are simpler to construct and allow the pilot to accomplish a lot more.
Still, the projects offer interesting insight into a design that’s seemingly underexplored.
The Ball-Drone makes use of a 3D printed frame and four air vanes to compensate for the lack of control that a single-propeller drone comes with. And since it uses servos, it may be considered slightly cheaper to make than a typical quadcopter.
The Monospinner, on the other hand, targets simplicity and uses even fewer components.
The propeller is its only moving part and it has no actuators. The battery and electronics are the only other main components.
At the same time, the researchers achieved their goal of enabling “controlled flight”. The Monospinner can maintain its position during flight and is controllable in the horizontal direction.
It does have an unorthodox way of taking off though — you have to toss it like a frisbee. And considering the angle it flies at, it’s not particularly safe to be around.
You may be wondering why a single moving part is a big deal. After all, don’t helicopters work the same way?
The truth is that they don’t.
A helicopter’s main rotor system does consist of a single large propeller, but it also has a tail rotor system. Its steering mechanism requires dozens of moving parts.
As a side note, this is also why helicopters have to be maintained regularly.
The comparison with other flying machines puts into perspective the impressiveness of the small, single-propeller drones, though they still have a long way to go.
Now, let’s move on to familiar territory. We’ve all seen multi-rotor drones as they’re actually available to the public. So, surely a hobby drone can work with just two propellers?
The thing to remember here is that some flight properties only improve as you increase the propeller number. Therefore, the answer depends on the drone’s intended use. Take a look.
A drone can generally have up to eight propellers, though the system can be scaled up to support even more. The minimum count depends on the user’s goals. It will realistically need at least two propellers for stability and at least three propellers for fair weather resistance.
We’ve already gone through the single-propeller design and why it’s not implemented (or explored) by drone manufacturers. Here’s what you can expect with bicopters, tricopters, quadcopters, and the more powerful models.
A two-propeller design typically resembles a V, with the propellers being positioned at the two ends.
Once we increment the number of propellers to two, we start to find balance — which is what drone flight is all about.
The two propellers generate thrust and spin in opposite directions to keep the drone from spinning out. And compared to the other designs, a two-propeller design allows for a pretty fast horizontal speed.
Two propellers also mean only two motors are at play. This reduces the current draw and maximizes flight times. In fact, the bicopter’s endurance is one of its biggest advantages.
So, why don’t we see two-propeller models in the drone community then?
Well, modern drones boasting such a design do have a niche purpose. They’re often used in indoor facilities, usually to inspect places that are otherwise inaccessible.
However, two propellers still aren’t ideal for stability. Bicopters lose their value outdoors as even a little bit of wind could bring it crashing down.
Similarly, a two-propeller design makes forward and backward motion pretty difficult. Pilots have little steering control over a basic bicopter.
Three-propeller designs combat some of the issues pilots face with the use of bicopters. They’re typically shaped in a T or Y, again with the propellers mounted on the ends.
The extra propeller immediately boosts stability, and this time to a reasonable extent. Tricopters operate just fine outdoors and can easily withstand a light breeze.
Similarly, the third propeller gives way to more thrust and increases the payload capacity of the drone. Pilots have a little bit of freedom with the equipment they can attach to it.
The three-propeller design also allows for a wider range of motion compared to the two-propeller design.
Now, I previously said the two propellers in a bicopter spin opposite to each other to ensure balance. How do things work with a tricopter then?
Here’s the deal: three-propeller designs are relatively complex. To put it simply, the two front propellers create lift while the third propeller counteracts spin to keep the drone steady.
The tail motor can rotate over its axis and has a lot of moving parts. So, should the drone go down, that motor is usually the first to fail.
Ultimately, the range of functions a tricopter offers makes three propellers the minimum (if not the preferred) count for hobby drone models.
The four-propeller design is the industry standard. Quadcopters are, by far, the most popular type of multi-rotor drones. They can be configured in more than just one or two shapes, though they typically resemble an X.
There are a bunch of factors that influence commercial manufacturers and DIY builders to opt for the four-propeller design.
We’ll be diving into those in the next section but for now, let’s consider the most important point: balance.
The four propellers work in pairs to offer controlled maneuverability.
But just like there’s balance during an actual flight, there’s also balance in the features. Four-propeller designs are simply a safe bet for everything a pilot may consider, including stability, flight times, control, and price.
And at the same time, quadcopters aren’t built in a complex way. This means they’re easy to repair and a basic model can even be put together quickly from scratch.
So, to answer the main question, four propellers are an incredibly attractive choice for drones.
The options don’t just end at four propellers. But this is where you step out of the hobby drone league and move on to costly, professional models.
You can continue adding pairs of propellers as long as the rest of the drone’s components can support them (and the high energy consumption).
However, drone manufacturers usually max out at eight propellers. This is simply because there’s no need to go further; an eight-propeller design already packs quite the punch.
The main expectation from a design with so many propellers is power.
Hexacopters and octocopters create a lot of lift and have an impressive payload capacity. So, they are typically used for commercial purposes.
Their stability is unparalleled when compared to the smaller drones and they rarely go down in the form of an accident.
We now know how many propellers drone models can realistically have. But as I’ve mentioned, the number mostly turns out to be four. Here are the reasons why.
Most drones are quadcopters because the four points of thrust allow for propulsion that is balanced and super easy to control. They are maneuverable and don’t have a complex system under the hood unlike conventional helicopters and tricopters. Plus, their production is economical.
There are a few things to unpack here. However, most points are related to mechanical simplicity in one way or another.
To start with, they’re easy to manufacture. Quadcopters use fixed propellers that are mounted onto simple motors. There are no anti-torque motors to complicate things.
In other words, their mechanical design isn’t particularly a task to be solved. DIY builders can assemble a quadcopter in minutes.
This is also why the conventional helicopter design doesn’t really have a place in the market of small drones.
Quadcopters are low-cost compared to other drones that come with too many moving parts. This gives manufacturers an extra incentive.
On the other hand, quadcopters also heavily benefit pilots. They’re popular because there’s truly a demand for them in the multi-rotor drone space.
Their use is not only safe but also super simple. Most modern quadcopters are digital devices, in the sense that they’re software-controlled. There’s little risk of things going wrong.
It’s important to remember that toy drones are a large part of the industry. Bicopters don’t offer the easy motion control most hobbyists are looking for and hexacopters are a bit of an overkill. This leaves quadcopters as the balanced option.
There are a few disadvantages that come with quadcopter though. This is why they don’t completely drown out the competition.
Quadcopters are less efficient compared to single-rotor drones. The four propellers continuously vary in speed to allow the drone to remain stable. This wastes a lot of energy.
You may also have noticed that quadcopters don’t really come in large models. This limitation isn’t ideal for demanding use.
This question has already been indirectly answered a few times throughout this post. Still, I believe the answer’s worth reiterating considering our topic.
Most drones have an even number of propellers to cancel out the torque produced by each propeller pair without the need for a complex tail rotor system. The net torque of zero maintains the balance of thrust throughout the drone and keeps it from spinning out.
So, in the manufacturing stage, it’s simply a no-brainer to add another propeller to a drone with an odd number of propellers.
The drone will be easier to engineer and the additional propeller results in better stability.
If you’re wondering why the torque produced affects drone flight, I recommend checking out my separate article on the working of propellers. It covers most of the basic concepts you’ll need to know about throughout your journey.
To wrap it all up, quadcopters are definitely at the top of the ladder when it comes to small-scale drones. They have the perfect blend of power and portability.
However, a drone can have different numbers of propellers and each layout has its own spot in the community.
All drones are not quadcopters. Quadcopters are drones that use four propellers mounted onto four fixed motors. They’re simply very popular multi-rotor drones, examples of which include tricopters, hexacopters, and octocopters. In other words, all quadcopters are drones — not vice versa.
Whatever drone a pilot goes for, compromises are bound to be made. A change in the propeller count always shifts the advantages and disadvantages of a drone model.
But as we’ve learned today, there’s a lot that can be done with a single moving part. Drone flight, at its core, is possible with just one propeller.
If you’re truly enthusiastic about the extent of what drones can accomplish, I suggest experimenting on your own using the abundance of resources available. But with anything you do, it’s always best to keep safety first.