By Lauren Nagel
These days it seems like drones are everywhere - delivering packages, inspecting buildings, filming movies, and much more.
As they become a more common sight, it can be useful to be able to identify the different types of drones you see.
This guide will help you differentiate between the different types of drones and UAVs.
In this article, we will explore:
- Drone definitions (UAV vs. Drone vs. UAS vs. RPAS)
- Fixed wing, rotary and powered-lift drones
- Power sources (electric, solar, gas, hybrid, hydrogen, and laser-charging)
- Types of drones such as helicopters, quadcopters, eVTOL, and more
Figure 1: Mavic Pro quadcopter drone in action (Photo by Pedro Henrique Santos)
1. Drone Definitions (UAV vs. Drone vs. UAS vs. RPAS)
A ‘Drone’ is defined by the Merriam Webster dictionary as “An unmanned aircraft or ship guided by remote control or onboard computers”.
It is used interchangeably with ‘Unmanned Aerial Vehicle’ (UAV), which shares the same definition.
Saying the aircraft is ‘unmanned’ strictly refers to the fact that the pilot is not on board, as passenger-carrying drones are already proving quite feasible. This becomes a bit more complicated when we start to discuss eVTOLs, but we will cover that in a later section.
An additional point to note is that ‘drone’ and ‘UAV’ generally refer only to the aircraft itself, whereas there are other terms that include all components that make the drone fly: UAS and RPAS.
A UAS, unmanned aerial system, is defined as “an aircraft and its associated elements which are operated with no pilot on board”.
The RPAS definition is more detailed and refers to “a remotely piloted aircraft system, its associated remote pilot station(s), the required command and control links and any other components as specified in the type design”.
The main difference between the two, according to the ICAO, is that in practice, UAS must receive special airspace accommodations and be kept away from other aircraft, whereas RPAS can be integrated into airspace alongside manned aircraft.
The technical difference between the two is that RPAS can only be piloted from a remote pilot station (RPS) whereas UAS may be piloted from an RPS or a ground control station (GCS).
2. Fixed Wing vs. Rotor-Wing vs. Powered-lift Drones
Similar to manned aircraft, drones can be categorized based on the structure of their lift-producing surfaces.
Fixed Wing Drones
Figure 2: eBee X fixed wing UAV
First off, as the name suggests, fixed wing drones have wings that do not move, they are bound to the body of the drone. They may have control surfaces that turn and rotate, such as ailerons and rudder, but the wings themselves are fixed. Figure 2 shows one such example, the eBee X by AgEagle, which has just one forward thrusting propeller located behind the fuselage and wings. In this system, lift is generated by the forward thrust of the aircraft coupled with the aerodynamic shape of the wing.
Pros of fixed wing drones are that their aerodynamic shape allows them to remain airborne for long periods of time, so they can cover large areas and are energy efficient. This is ideal for missions that require the drone to be airborne for hours or days, such as surveillance and climate monitoring.
Further reading: Comparing UAV Power Systems
The main cons are the steep learning curve for operators, the ample space required for take-off and landing, and the fact that they cannot hover in place.
For rotary-wing drones, the rotor-blades rotate around a central mast, forcing air downwards and creating the vertical lift required for the aircraft to become airborne. All vertical take-off and landing (VTOL) aircraft fall into this category, including small and large helicopters and multicopters. Rotary-wing drones may have a single rotor or even up to 16+ rotors generating thrust.
Pros of rotary-wing drones are that they are simpler to operate initially and can hover in place, allowing them to fulfill a wide variety of roles. Basic models are also relatively inexpensive, so small rotary drones are a great place to start for those wanting to get into the industry.
The main cons relate to their short flight time, as generating upward and forward thrust requires a lot of energy, thus restricting the range and endurance of the vehicle.
Powered-lift drones occupy a fascinating middle ground between fixed wing and rotary drones, using elements of both to complete a flight.
Rotors are used for VTOL-style take-offs and landings, then once airborne, the aircraft transitions to forward, fixed-wing-style propulsion. As such, they benefit from the low space requirements of rotary drones, while also having the improved aerodynamics and efficiency of fixed-wings.
There are several types of powered-lift drones, namely tiltrotors, tiltwings, and drones with two perpendicular sets of rotors.
For tiltrotor drones, the rotors themselves rotate in order to transition from vertical to horizontal thrust during flight. The Skywalker X 8 VTOL is a great example, with three rotors transitioning between copter and fixed wing mode.
Slightly different in design, tiltwing aircraft undergo a more dramatic in-flight transition as the rotors are fixed to the wings themselves, so the entire wing undergoes a rotation during the conversion from lift-off to forward flight.
Tiltrotors and tiltwings are also referred to as convertiplanes as they are converted from one configuration to another.
The third type describes drones that use perpendicular sets of rotors for lift-off and forward flight, neither set rotating or changing position. In this scenario, one set of rotors is operated only for take-off and landing while the perpendicular set is used only during portions of the flight requiring forward thrust.
While seeming to make the best of both worlds, powered-lift drones are quite complicated to design, which explains why they are not more common. Designing a system that can transition between configurations while remaining stable is challenging, though once achieved, the result is a highly versatile aircraft.
3. Power Sources - Electric, Solar, Gas, Hybrid, Hydrogen, and Laser-Charging Drones
The majority of rotary drones on the market today are fueled by electric power from lithium-ion polymer (LiPo) batteries, though many new power sources are being explored.
Electric / Battery Powered Drones
LiPo batteries are rechargeable and lightweight, thus ideal from a design perspective. This is the most common power source for drones, which we cover in detail in our Guide to LiPo Batteries.
Solar power has also been employed as a source of electricity, with solar cells mounted on the upper surface of the drone. This concept could turn the industry on its head as it would effectively eliminate flight time limitations as long as the sun keeps shining.
That said, solar cells require significant surface area and have almost exclusively been used with fixed-wing models.
One fully solar-powered quadcopter was built by an engineering team at the University of Singapore. The design carried little more than the solar cells and rotors themselves, but it was still an impressive vehicle.
At the other end of the spectrum, gas-powered drones have become major players for carrying out long-distance missions.
While electric motors are more efficient than combustion motors, gasoline has about 50x the energy density of LiPo batteries, so maintains the energy advantage.
There are several possible fuel options for gas-powered drones, such as unleaded gasoline, two-stroke motor oil, nitro-based gasoline, and diesel.
Most gas-powered drones have a fixed wing configuration since they can more easily accommodate larger engines. Their aerodynamic shape produces so much natural lift that little gas is needed to achieve flight times of many hours or even days.
On a record breaking flight, Vanilla Unmanned’s diesel-powered VA001 drone not only stayed airborne for five full days, but when it landed, they found it had an extra three days worth of fuel on board.
Thus far, gas motors have been uncommon in rotary drones, as a heavier motor and fuel system is required.
Figure 5: VA001 diesel-powered drone (Photo: vanillaunmanned.com)
Furthermore, they can be noisy and require ignition of the motor to start. That said, some models are in development, such as the Goliath quadcopter, which uses a single gas-powered motor to power four propellers.
A third category of drones has emerged that boasts not one, but two power-sources. Hybrid-powered drones are changing the game and can come in different configurations, such as gas/battery-powered or battery/solar-powered.
The performance of these vehicles is unparalleled and they have been breaking all kinds of records with both rotary and fixed-wing aircraft.
Skyfront’s Perimeter 8 octocopter is a great example, using electronic fuel injection to convert gasoline into electricity in-flight. The novel system provides the aircraft with a record 5 hours of no-load hovering flight time, 10 times longer than the best battery-powered drones on the market.
Also to come is proof of concept for the PHASA-35, a high altitude long endurance (HALE) hybrid drone advertised to have a flight time of up to one year in the stratosphere. The drone operates on solar power during the day and battery power at night, with a 35 m wingspan to provide ample lift. The drone’s developers believe the drone could take over many of the current functions of satellites, such as delivery of telecommunications networks, weather monitoring, and surveillance.
Hydrogen and Laser-Charging Drones
Two other power sources to mention are hydrogen fuel cells and laser-charging of batteries in-flight.
Hydrogen fuel is a clean and energy-dense power source with a lot of potential in the drone, aviation and general transportation industries.
South Korean company Doosan claims their DS30W drone is the "world's first mass manufactured hydrogen fuel cell drone". It is truly unique as it has a rotory-wing octocopter design, yet it can achieve 2 hours of flight time.In April of 2020, the DS30 drone delivered over 15,000 protective masks to residents on the remove Gapa, Mara, and Biyang Islands off the Southern cost of South Korea.
Figure 6: DS30 drone by Doosan delivering face masks to remote South Korean islands (Photo: business wire)
Laser-charging of drones is a technology that has been on the scene since 2012. Recently, a team of researchers at Northwestern Polytechnical University in Xianyang, China demonstrated their laser-charging drone that can stay airborne indefinitely. They use an "intelligent visual tracking algorithm" to keep the laser beam targeted on the drone so it never loses power.
4. Types of Drones
Now that we’ve covered the ways that drones can be classified, let’s look at some specific types of drones available.
Quadcopters, Hexacopters and Octocopters
Multi-rotor drones are perhaps the most recognizable form of UAV, complete with a compact body, multiple arms, and high RPM propellers.
They come in a variety of sizes and are named for the number of rotors they have: quad = 4 rotors, hexa = 6, octo = 8. Following the same rule, a drone with 16 rotors would be called a hexadecacopter.
These drones can take on a single or coaxial rotor configuration, which describes the layout of the rotors.
Single rotor configurations have just one rotor in a given vertical section whereas coaxial configurations have two, either completely or partially overlapping.
Many drones are piloted by visual line of sight (VLOS), where the pilot has the vehicle in view for the duration of the flight, and controls it based on observation. Other drones are piloted via first-person view or FPV, whereby the cameras on the drone deliver footage to a set of FPV goggles or a monitor so the pilot can fly the drone remotely from an onboard perspective.
Further reading: Drone Design Calculations and Assumptions
Though it was once a niche segment of the drone industry, demand for helicopter drones is growing, with the market projected to be worth $11 billion USD by 2027.
Operating on the same principle as manned helicopters, heli-drones use a single or coaxial rotor to generate vertical lift, partnered with a tail rotor to counter torque. Like multirotor drones, a perk of helicopters is that they can take-off and land virtually anywhere.
That said, drone helicopters are unique in that many are powered by gas, except for very small models that are powered by batteries. There are exceptions to this rule, of course, such as AeroVionment’s VAPOR 55 helicopter, which is all electric and manages a payload of up to 10 lbs.
A significant societal benefit of helicopter drones is their potential to replace humans in dangerous missions.
Manned helicopters play a big role in operations such as search and rescue, disaster relief, fire fighting support, etc., jobs that involve flying in challenging terrain with potentially poor flight conditions.
Unmanned helicopters could change this by delivering supplies to inaccessible areas, flying in smoky or windy conditions, and even evacuating humans from hazardous situations. All this could be accomplished without having to send a human crew into the field. Designed precisely for this purpose, Laflamme Aero’s LX300 helicopter can fly in severe weather and has a payload of up to 90 kg, enough to carry the average adult.
The electric VTOL aircraft (eVTOL) category encompasses all electrically powered VTOL vehicles, but for the purposes of this article, we will focus on a large and highly competitive segment of the industry: urban air mobility (UAM).
This new mode of transportation has the potential to reduce transportation-related emissions and cut down on commute times, acting as a sort of aerial Uber.
As such, there is an ongoing race to see who can design and manufacture a safe and efficient eVTOL vehicle for transporting people around urban areas, with companies such as Archer, Joby Aviation, Lilium, and Vertical Aerospace leading the pack.
Archer's Midnight eVTOL aircraft is designed to carry a pilot plus four passengers and is capable of flying up to 100 miles.
If all goes well, many major cities could have eVTOL taxi programs by the end of the decade.
Figure 9: Archer Midnight eVTOL (photo: Archer website)
Within the eVTOL category there are purely electric vehicles and also hybrid eVTOL vehicles, which most commonly use a combination of battery power and gas power. Hybrid aircraft are important players in the UAM movement as battery technology is still evolving to support extended flights independently.
The Bell Nexus 4EX for example is built to be able to run on battery power or hybrid gas-electric power, offering flexibility and greater flight time between charges.
That said, a major driver in the industry is the mandate to offer more sustainable transportation solutions, so many companies are still focusing their development efforts on going fully electric.
eVTOL vehicles can also be hybrid in nature in that they are designed for pilot-optional flight, meaning they can be operated manually onboard, piloted remotely, or pre-programmed for a flight. This versatility will come in handy as society gets used to the idea of inner-city travel via drone, appreciating a certain amount of redundancy.
High Altitude Long Endurance (HALE)
HALE drones are aptly named for their purpose of flying high altitude, long endurance (HALE) missions.
To give you an idea of what this means, ‘high altitude’ drones are expected to fly above 60,000 ft and ‘long endurance’ flights are expected to be days, months or even years long.
Many HALE drones are intended for military use, designed for long-term surveillance, intelligence and reconnaissance operations. Others may be used as sub-orbital or pseudo-satellites, performing functions such as weather monitoring and telecommunications network delivery.
Figure 10: RQ-4 Global Hawk (Photo from the U.S. Air Force website)
The most widely used HALE aircraft to date is perhaps the Northrop Grumman RQ-4 Global Hawk, powered by a Rolls-Royce AE 3007 turbofan engine and most notably used by the U.S. Air Force (USAF).
Capable of flying up to 60,000 ft for over 32 hours, it has mainly been employed for the military purposes described above.
We hope that this article has provided you with a greater understanding of the diversity of drones in the industry. The field still faces many challenges such as obtaining government certifications, overcoming design limitations, and building trust with consumers.
With much development underway, it won’t be long before these aircraft become bigger and better, offering a more permanent service to society.
Further reading: The Future of Wind Tunnel Testing for Drones