What is Vortex Ring State? How To Prevent It? (2023 Updated)
Have you ever heard of the Vortex Ring State? If you haven't, don't worry – you're not alone. In fact, until recently, this phenomenon was relatively unknown, even to experienced drone pilots.
But that's all changing now, as the Vortex Ring State is becoming more and more understood. And as drones become increasingly popular, pilots need to be aware of this potential hazard.
So what is the Vortex Ring State? Put simply, it's a condition that can occur when a drone is descending too quickly. As the drone falls, the rotors create a vortex of air – similar to a tornado. This vortex of air can cause the drone to lose lift and can even cause it to crash.
The Vortex Ring State is sometimes referred to as the "dead man's curve" because it can be so dangerous. But fortunately, there are ways to avoid it. In this article, we'll take a closer look at the Vortex Ring State and what drone pilots need to know about it.
Table of Contents
Defining Vortex State
A vortex ring state, also known as "settling with power" or "the hole," is a dangerous flight condition that can occur when a helicopter or other rotary-wing aircraft descends too quickly into its downwash.
In a vortex ring state, the airflow around the rotor blades begins to swirl in a Vortex. This can cause the lift on the blades to be greatly reduced and, if not corrected, can lead to a crash. To understand how this happens, it's helpful to think of the blades as a set of spinning wings.
As the blades spin, they push air down. This downward flow of air is called the "downwash." When you descend too quickly into your downwash, the airflow can become turbulent and start to swirl around the blades. This swirling Vortex of air can cause the lift on the blades to be significantly reduced.
How are Vortex Rings formed?
A vortex ring forms when a mass of fast-moving fluid is injected into a mass of motionless fluid. The moving fluid at the outer core of an imaginary toroid slows down and rotates back towards the inner core due to friction between the two different masses of fluids.
Due to the constant injection of mobile fluid into the inner core, this fluid regains speed. However, the inner core can never quite "catch up" to the outer core's speed because of the fluid friction. The result is a continuous and rotating torus or doughnut-shaped ring.
The most common way that vortex rings are formed is by air being forced through a small opening, such as the exhaust on an aircraft engine.
As the air accelerates through the small opening, it spins and forms a vortex. This spinning Vortex of air can then be injected into the main body of air, where it will start to rotate.
A vortex ring state can also occur when a helicopter or other rotary-wing aircraft descends too quickly into its downwash. As the aircraft descends, the rotors create a vortex of air. This vortex of air can cause the lift on the blades to be greatly reduced and, if not corrected, can lead to a crash.
Factors promote the Formation of a Vortex Ring
Several factors can promote the formation of a vortex ring. These include:
- The size of the opening through which the air is flowing: The smaller the opening, the more likely it is for a vortex to form.
- The speed of the air: A vortex is more likely to form when the air is moving more quickly.
- The density of the fluid: The likelihood of a vortex forming increases with the density of the fluid.
- The temperature of the fluid: A vortex has a higher chance of forming when the fluid is colder.
The best ways to Prevent or get out of a Vortex Ring State
If you fly drones frequently enough, you will ultimately experience a vortex ring state. On the other hand, modern drones are less susceptible to vortex ring formation, for reasons we will address later.
Regardless of the benefit, understanding the mechanism of a vortex ring state and how to recover from one is important.
Controlled Rate of Descent
The most important factor in avoiding a vortex ring state is to maintain a controlled rate of descent. A good rule of thumb is to descend at a rate no faster than 1/2 the rate of the rotors' rpm.
For example, if your rotors are spinning at 1000 rpm, you should descend at a rate no faster than 500 feet per minute.
If you find yourself in a vortex ring state, you should first stop descending. You may need to increase power to maintain altitude, but stopping the descent as quickly as possible is important.
Once you have stopped descending, you can then start to recover by slowly flying out of the vortex. It is important to fly out of the vortex slowly, as sudden movements can worsen the situation.
One of the reasons that modern drones are less susceptible to vortex ring states is that they have angled rotors. The angle of the rotors helps to prevent the downward flow of air from becoming turbulent and swirling around the blades.
Another reason that modern drones are less susceptible to vortex ring states is that they have larger rotors. The larger the rotors, the more lift they generate and the less likely it is for a vortex to form.
So there you have everything you need to know about vortex rings and how to avoid them. Remember these tips next time you're out flying, and you'll be sure to stay safe and avoid any potential accidents.
Land with some Forward Motion
Although drone firmware should prevent you from descending quickly enough to generate a vortex ring, it is nevertheless recommended that you do not descend vertically in a straight line.
We propose slowly descending in a forward manner to your selected landing site. If you don't have access to a corridor, consider descending in a spiral manner.
Move Sideways to Recover
If you enter into a vortex ring state, you should first increase power to maintain altitude and then try to move sideways and out of the vortex. It is important to move slowly and deliberately, as any sudden movements could make the situation worse.
Vortex ring states are something that all drone pilots need to be aware of. By understanding the factors which promote the formation of a vortex ring, as well as the best ways to prevent and recover from one, you can ensure that you stay safe while flying.
So remember, when in doubt, descend slowly and always be aware of your surroundings. Thanks for reading!