Can Drones Auto-Rotate Like A Helicopter?

I was flying my drone the other day, and as I was looking up at it, I wondered what would happen if it suddenly lost power? Would it be able to auto-rotate and land safely? Well, I did some research and here’s what I found!

Drones that are available on the market have a fixed-pitch rotor design, which means they are not capable of auto-rotation. For a drone to be capable of auto-rotation, its rotors would need to have a variable pitch design like a helicopter, although some drones do have this design and are capable of auto-rotation.

To find out more about the mechanics of auto-rotation and exactly how it would work on a drone, keep reading!

What Exactly Is Auto-Rotation?

Auto-rotation is a state of flight where the primary rotor system of a helicopter or an aircraft similar to it, such as a drone, turns by air moving up through the rotor rather than using the engine power to drive the rotor.

The movement of air upwards allows the blades to turn or rotate automatically without the assistance of the motor. This is possible because of the design of the rotors. In order for this to be possible the aircraft needs to have variable pitch propellers.

Video showing helicopter landing using autorotation

Why is it important?

All helicopters have this sort of design for their rotors, as it would be disastrous if a helicopter were to lose power in the air without the ability to land! This is important because it gives the pilot the ability to control a glide down to the ground if an engine happens to fail.

Engine failure in a helicopter is the most common reason for this feature. Another reason why it is essential to have auto-rotation is that a quadcopter that is capable of auto-rotating is less likely to become damaged in a crash.

This is largely a possibility because the pilot that is operating the quadcopter will have more options for bringing the quadcopter to the ground gently if something goes wrong, whereas a quadcopter without this ability is most likely just going to drop out of the sky and crash into the ground.

Drone crashing out of the sky suddenly.

Common Errors When Auto-Rotating

Here are just a few of the main errors pilots make when in an emergency and attempting to auto-rotate:

  • Lowering the nose of the aircraft suddenly when you lose power.
  • Not being able to maintain the Rotor Revolutions Per Minute(RRPM) during the descent.
  • Flaring or rounding out at the wrong height, either too early or too late.
  • Failing to level out the aircraft before touch down.
  • When flaring, do not do it too aggressively.

Why Can’t Drone Propellers Auto-Rotate?

In order for a quadcopter to be able to rise into the sky, it needs force to be created. This force needs to either equal or exceed the force of gravity.

The spinning of the quadcopters propeller blades pushes air downwards. As the propellers push air down to the ground there is an equal but opposite reaction force(Newtons Third Law).

When this happens the air pushes the rotor up and therefore the drone is lifted up, this force created is called thrust. The faster the rotor and propellers spin, the greater the lift created. The drones thrust that it creates must be greater than the weight of the drone in order for it to actually take off.

Using its propellers a drone can do 3 things:

Hover Still  In order for the drone to hover, the net thrust of the rotors pushing the drone up must be exactly equal to the gravitational force pulling it down.

Ascension – This is done by increasing the amount of thrust created by the drone rotors so that the upward force is greater than the weight of the drone and the pull of gravity. When this happens, the drone starts climbing.

Vertical Descend – For the drone to come back down, it would require the pilot to do the exact opposite of ascension. By decreasing the rotor speed, so the thrust created by the rotors is reduced.

Can a Passenger Drone Auto-Rotate?

Probably the best passenger drone that exists at the moment is the Ehang 184. The Ehang 184 is a fully automated drone that will transport its passengers from point A to point B without the passenger needing to control anything!

It is truly the next step in human transportation. But, what happens if there is some sort of motor failure? Is this passenger drone capable of auto-rotation?

The Ehang 184 is an X-8 multi-rotor drone, and this means that it has 4 points creating thrust, and each of these points consists of 2 motor-propellers. This means that if one of the motors were to fail or die mid-air, the drone would not just flip over and come crashing down to the ground.

The problem lies in the fact that, like most consumer drones on the market, Ehang 184 has a fixed-pitch rotor that has been optimized for creating thrust because of the heavyweight it needs to carry and it is not designed for auto-rotation.

Passenger drones are still being developed and fine-tuning is definitely still being conducted by the companies involved in making these drones!

Can a Drone With Fixed-Pitch Rotors Auto-rotate?

It is actually nearly impossible for a drone without fixed-pitch rotors to do an autorotation landing. But, notice how I said nearly! It is possible for a drone to have an auto-rotation landing as long as some very specific factors are met:

  • Firstly, you need to have a forward center of gravity or CG.
  • Secondly, you need to be facing into the wind for it to work.

To meet the center of gravity requirements, you need your battery to eject itself out of the drone, which would also explain why you lost power in the first place.

When this happens, it fills the requirements needed for the center of gravity condition, and this is required for the proper forward speed from when you are just hovering.

In terms of wind direction, there is literally nothing you can do to control this! All you can do is hope in the event that you do lose power, you are lucky enough to be facing the wind.

If these conditions are met, then the drone propellers might just auto-rotate, and the drone might survive the landing!

Why Aren’t There More Variable-Pitch Propeller Drones?

If you do your research or you have read the rest of this article, then you probably have realized that a variable-pitch propeller system design seems to be superior.

A quadcopter with a low RPM(Revolutions Per Minute) will usually spend less energy on air drag so that the drone will perform more efficiently.

There’s also the fact that if drones were to be developed with a variable-pitch rotor, they would be capable of auto-rotation and be able to land safely if the motor were to stop working suddenly or it loses power while in the air.

With the research I’ve done, I have seen a few quadcopters that have variable-pitch rotors but they seem to be mostly in the development stage. The main reason why smaller quadcopters and drones do not have a variable-pitch rotor is that this system is very complicated.

Final Thoughts

Basically, the design of a quadcopter or drone is different from that of a helicopter, and the main difference is that drones have a fixed-pitch rotor, and helicopters have a variable-pitch rotor. Because of this, drones are unable to auto-rotate while in the air in order to land safely if a problem were to occur in the air.

If your motor were to suddenly stop working in the sky then your drone is most likely dropping like a brick! In terms of battery, life drones don’t usually just fall out of the sky, so you do not have to worry about this happening!

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