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Introduction
Unmanned aerial vehicles (UAVs) have evolved from hobbyist toys to critical tools with applications spanning across various industries. As the demand for UAVs with extended flight endurance continues to grow, propulsion system technologies have risen to the challenge. This blog article explores how cutting-edge UAV propulsion systems are enabling lightweight, fuel-efficient designs, revolutionizing long-endurance missions in both commercial and military sectors.
Understanding UAV propulsion
Over the years, the UAVs have been employed by wide range of industries including mining, security, healthcare, wildlife, forest, disaster management, traffic management, urban development, and agriculture among others. The use of unmanned aerial vehicles can provide these industries a superior option to gather highly precise remote data in real-time in a cost-efficient manner as with higher safety compared to piloted aerial vehicles.
Defense and Security have also deployed advanced UAVs for a wide variety of critical missions. They provide capability to fight effectively in urban areas against widely dispersed forces, while minimizing collateral damage and achieving information superiority. The UAVs have become one of the essential constituents of all militaries to perform intelligence, surveillance, and reconnaissance missions. Their roles have expanded to areas including electronic attack, suppression or destruction of enemy air defense, network node or communications relay, combat search and rescue and many others. The increasing demand and reliance on UAV in warfighting and peacekeeping operations has doubled the pace of UAV-related R&D in recent years.
The employment of UAVs by various industries and in Defense and Security missions are enabled by their propulsion system to provide them with the necessary power to propel the aircraft for forward flight or hover. Propulsion systems can advance the flight time or endurance of a UAV which is influenced by the propulsion technology used and is dependent on the aerodynamic design and amount of fuel carried. To fulfil the energy requirements of a large variety of UAVs, several variants of piston-engines and electric motors have been designed by the market players.
The type of propulsion depends on the type of UAV and desired performance. UAS are categorized in a variety of ways based on vehicle attributes including the type of aircraft (fixed wing or rotorcraft), flight altitude (high, medium, low), weight, speed, etc. In general, larger aircraft use larger engines that confer higher altitude, longer endurance and more payload capacity than smaller vehicles. The main propulsion system types are electric systems and gas systems. Both systems can be used to drive propellers or ducted fans.
If the performance required of a UAV is similar to the performance of conventional aircraft, the propulsion system may also be similar. Many UAVs will weigh more than 1,000 pounds, fly at subsonic and supersonic velocities at altitudes below 60,000 feet, maneuver at 9g’s or less, and will be maintained in ways similar to current military or commercial aircraft. These UAVs will not require unique propulsion technology. For example, a UCAV may require a gas turbine engine that can operate at much more than the 9g forces that limit manned vehicles.
The potential benefits of a propulsion system are measured by their impact on the costs of the whole UAV. Lightweight, more fuel-efficient engines permit usage of expensive payload for a given mission without significantly affecting the size and cost of the UAV. Although promising, the performance of propulsion systems in unmanned aerial vehicles still needs to be significantly improved to meet the requirement for executing increasingly difficult missions. In recent years, electric propulsion system has gained more popularity amongst small or mini UAVs for its apparent advantages: quiet operation, easy and safe to handle and store, precise power management and control.
Nevertheless, for some UAVs, the propulsion system is a critical limiting technology. These include subsonic High Altitude Long Endurance (HALE) UAV that must operate above the altitude limits of current engine technologies and Micro UAVs that are very low-cost, high-performance vehicles.Researchers are developing new engine technology, new designs, or even new fundamental research and propulsion concepts for these new classes.
UAV propulsion system types
UAVs (Unmanned Aerial Vehicles) can be powered by a variety of propulsion systems, each with their own advantages and disadvantages.
Primary propulsion requirements include reliability, high power density, excellent efficiency, and low total cost of ownership. In addition to these primary requirements, their secondary needs are for the engines to be as small, light, quiet and vibration-free as possible.
Gasoline engines: Gasoline engines are commonly used in larger UAVs, such as military drones. They are more powerful than electric motors, and can provide longer flight times and greater ranges. However, gasoline engines are heavier and more complex than electric motors, which can make the UAV less agile and more difficult to control.
Jet engines: Jet engines are typically used in high-performance UAVs, such as military drones or research aircraft. They are very powerful, and can provide very high speeds and altitudes. However, jet engines are also very heavy and expensive, and require a lot of fuel to operate.
For deeper understanding of UAV propulsion and applications please visit: Advancements in UAV Propulsion: From Hobbyists to High-Tech Frontiers
Lightweight Propulsion Systems
Traditional internal combustion engines and bulky power sources have long been the standard for UAV propulsion. However, advancements in lightweight materials and miniaturization technologies have led to the development of innovative propulsion systems that significantly reduce UAV weight. Among these lightweight solutions are electric motors, hydrogen fuel cells, and efficient rotary engines.
Electric Propulsion Systems
Electric motors have emerged as a game-changer for UAVs, offering a combination of energy efficiency and reduced weight.
Electric motors are commonly used in small UAVs. They are lightweight, efficient, and provide a high degree of control over the UAV’s flight. Electric motors can be powered by batteries, which is a major advantage since they are clean and easy to recharge. The downside, however, is that the battery life can be limited, which can restrict the UAV’s flight time and range.
With advancements in battery technology, electric UAVs can achieve longer flight times and carry larger payloads. Additionally, electric propulsion systems produce minimal noise and emissions, making them ideal for both commercial and military missions.
Hydrogen Fuel Cells
Hydrogen fuel cells present another groundbreaking propulsion option for long-endurance UAVs. By converting hydrogen into electricity through a chemical reaction, these fuel cells offer higher energy density than traditional batteries. Hydrogen fuel cell-powered UAVs can operate for extended periods, making them suitable for surveillance, environmental monitoring, and search and rescue missions.
Efficient Rotary Engines
Rotary engines, renowned for their compactness and versatility, are being adapted for UAV propulsion. These engines provide high power-to-weight ratios, enabling UAVs to carry heavier payloads without sacrificing endurance. Their efficient design minimizes energy loss, resulting in better fuel economy and extended flight times.
Reciprocating Piston Engines (RPE)
Their principle is: A mixture of petroleum distillates and air are pressurized as an enclosure collapses. Consequently, the temperature increases with the pressure. An ignition event occurs causing a rapid combustion of the fuel and air mixture. This forces the enclosure to expand with great force, a motion that is translated to a lever-arm mechanism (more specifically, a crankshaft), converting reciprocating motion into rotating motion.
Reciprocating piston engines have been employed very widely .General Atomics: MQ-1B Predator which has height ceiling of 25,000 ft employs 4 stroke, 150lb weight engine and generates 115 hp @ 5800 rpm. Pioneer UAV RQ-2B, which has height ceiling of 15,000 feet employs 2-cylinder 2-stroke that generates 26 hp. Honeywell MAV whose height ceiling is 10,500 feet utilizes Heavy fuel engine 5.5 lb RPE that generates 4.2 bhp @ 8200 rpm.
The technical issues associated with an RPE are crankshaft weakness, noise, vibration, seals, and high temperature. There is perpetually alternating torsional stress on the crankshaft. This constant flipflopping of the crankshaft stresses over long periods can fatigue the shaft, leading to cracks, breakage, and concomitant engine failure. Vibrational characteristics of a reciprocating piston engine can also cause problems. The engine can shake itself out of mounts, or break apart at high revolutions per minute. Moreover, reciprocating piston engines (RPE) have many pressurized seals that can fail, leading to significant power loss or engine failure. Additionally, if waste heat is not carried away from the engine fast enough, the system can overheat and lead to seizure or fire.
Wankel Rotary Engines
In rotary engines Rotor performs the function of piston of a reciprocating engine. It directly transmits the pressure of the combustion gases to the eccentric shaft as a turning moment. They are much quieter than reciprocating engines, have lower vibration than reciprocating engines and produces higher power output for similar displacement. The Wankel rotary engine approach has not only a fewer parts count, but also has less overall stress points, resulting in a better reliability factor.
The technical issues associated with rotary engine systems are exhaust temperature, compression seals, engine cooling and oil burn-off. A disadvantage of this design is the reduced fuel efficiency 50% higher fuel consumption than comparable diesel engines, a drawback that has been somewhat lessened as the technology evolves. Liquid-cooled engine adds to weight and complexity, failure modes. Higher electromagnetic and thermal signatures compared to diesel engine. They tend to be more expensive to buy, due to lower manufacturing volumes, but their TCO (Total Cost of Ownership) for a UAV application is less than most of the other engines, as Wankel engines have few moving parts to service and deliver excellent reliability and endurance between overhauls.
Wankel rotary engines currently are installed into some of the world’s most successful and proven platforms. These platforms include Textron’s Shadow, IAI Malat Searcher, Elbit Hermes 450, Leonardo’s Falco, IAI MBT Harpy and Harop, Schiebel’s Camcopter and the UK’s Watchkeeper programme. RQ-7A Shadow 200 with height ceiling of 14,000 feet has 23.5 lb, 208 cc rotary engine that generates 38 bhp @ 7800 rpm.
Gas Turbine Engines
All jet engines, which are also called gas turbines, work on the same principle. The engine sucks air in at the front with a fan. A compressor raises the pressure of the air. The compressed air is then sprayed with fuel and an electric spark lights the mixture. The burning gases expand and blast out through the nozzle, at the back of the engine. As the jets of gas shoot backward, the engine and the aircraft are thrust forward. As the hot air is going to the nozzle, it passes through another group of blades called the turbine. The turbine is attached to the same shaft as the compressor. Spinning the turbine causes the compressor to spin.
A gas turbine engine comes in various forms, and the three common are the jet turbine engine, turbofan engine, and turboprop engine. A turbofan works on a similar principle as a jet turbine, except that more work is sapped from the high energy exhaust gas to drive a fan mechanism, trading off some direct thrust for additional fan driven thrust . A turboprop engine operates on a similar principle as a turbofan, except that instead of a fraction, almost all of the high-energy output is used to drive a turbine that is gear coupled to a propeller. A turboshaft is similar to the turboprop except that the power is supplied to a shaft rather than a propeller (used extensively for rotorcraft)
The advantages of gas turbine engines are: high power density; tremendous thrust capability; not limited by sound barrier like the tips of propeller blades; decent efficiency at 30% load; insensitivity to fuel quality; can use of air bearings eliminate need for auxiliary lubricating fluid or oil. The technical issues associated with a gas turbine engine are high energy rotation, high temperature, blade balance and vibration, blade wear, blade cooling, bearing wear. The disadvantages of gas turbine engines are: expensive, loud, jet wash, complexity, very high velocity rotation and high internal temperatures.
Northrop Grumman: RQ-4A Global Hawk with height ceiling of 65,000 ft employs 1586 lb Turbofan that generates 8,290-lb thrust. General Atomics: Predator B with 50,000 ceiling employs 700 shp turbofan.
UAV Turbines Unveils Microturbine Propulsion System for Drones
UAV Turbines has announced the inaugural flight of its Monarch 5 engine, a miniature version of the type of propulsion system usually found in much larger aircraft. The company unveiled what it claims is a “first-of-its-kind microturbine propulsion system” at Griffiss International Airport in Rome, NY. The aim of the new turboprop technology is to provide mid-sized commercial and military drones with a reliable, efficient, safe, heavy-fuel propulsion system.
Many medium-sized commercial drones are powered by gasoline engines, which can be noisy, unreliable and weak in terms of power output. UAV Turbines says their new propulsion system is quiet, easier to maintain and safer than current designs.
The commercial UAV market is expected to see significant growth in the coming years, particularly as regulations catch up to enable use cases that require bigger and better drones, such as medical and cargo delivery and transportation.
“After years of innovative and intensive design and engineering work, we are elated to see our first Monarch propulsion system take flight in a TigerShark airframe from Navmar Applied Science Corp.,” said Kirk Warshaw, CEO of UAV Turbines.
“This flight is proof positive that our team is without peer in the development of small turboprop engine systems. Our attention now turns to working with commercial and military partners to develop airframes around our Monarch 5 propulsion system, similar to the manner that manned aircraft are designed and developed. Furthermore, we believe our Monarch engine’s capabilities will be instrumental in driving the urban air mobility and defense industries forward in making unmanned aircraft systems (UAS) as commonplace as airplanes, trucks and ships for both commercial and defense use.”
Rocket Propulsion
Rocket systems are self-contained flight vehicles, which carry their fuel and oxidizer internally and boost their payloads to high velocity. A rocket is propelled by a chemical reaction that generates extreme pressure gradients and high-velocity particles that exit a nozzle. The resulting momentum exchange provides impulse over some duration, accelerating the rocket’s mass.
The advantages of rocket propulsion systems are: high power density; mature; with long history of operation, and self-contained energy source for use in low-oxygen environments. The technical issues associated with rocket propulsion are explosion, fire, and propellants. The disadvantages of rocket propulsion systems are: inefficiencies at low speeds; high rate of fuel usage; low endurance; complex control system and expensive guidance components.
Propulsion derived exclusively from rocket power tends to be used in applications where the asset is not expected to return home. However, for use in a UAS, it is more likely to see rocket power as a means of takeoff assist, such as in the RQ-2B Pioneer.
MIT Developing Mach 0.8 Rocket Drone for the Air Force
MIT’s AeroAstro labs is working to develop a drone that can fly at speeds up to Mach 0.8, or roughly 614 mph. Dubbed the Firefly, the drone is essentially a mini-rocket and has a similar shape to a zeppelin. It is designed to launch from a fighter jet and collect data or distract enemy weapons systems. A solid rocket presents some unique challenges, and the team had to slow the fuel burn rate to meet the requirement that the rocket fly at Mach 0.8 for 2 to 5 seconds. A typical rocket this size burns its fuel in just a few seconds, and slowing the burn rate can reduce the pressure to the point that combustion is not possible at all.
The solution was found by mixing ammonium perchlorate propellant with an oxamide inhibitor. “We use this burn-rate suppressant, which—via chemical decomposition—cools the flame and changes the flame structure so that it actually burns slower,” says doctoral student Tony Tao to MIT Technology Review. The slow-burn propellant will power the 2- to 3-pound Firefly for up to 3 minutes, well within the Air Force’s requirements.
Built out of titanium through additive manufacturing, the Firefly is one of the first 3D-printed rockets. Difficulties emerged due to the combustions close proximity to the electronics, as the temperatures could overwhelm the drone’s controls. After considering design modifications, the MIT team decided to put an insulating layer between the engine and electronics instead.
Electrical propulsion
Due to the higher efficiency and better reliability comparing to conventional combustion engines, electrical systems with no greenhouse gas emission and low noise and vibration attract much more attention.
Electric Motor-Based Systems
Electric motors serve as powerplants to create rotational motion from electric power. For electrically based propulsion systems, electric motors are used as the powerplant because they can be easily coupled with propellers as the propulsion effecter; all that is needed is a continuous source of electricity.
Electric motors are universal in usage, widely understood, simple in concept and operation, low cost due to economies of scale, and very easy to obtain. With regard to small (or large) electrically based UAS propulsion applications and technical issues, the concern is less over the electric motor and more over a consistent, sustainable, reliable electric power source with sufficient endurance to power the electric motor.
The advantages of electric motor-based systems are: Electrically powered, Low maintenance, Reliable, Robust, Less issues surrounding overheating as opposed to thermodynamic engines, High torque, Scalability and Quiet. The disadvantages of electric motor-based systems are: Electromagnetic interference, Requires large currents, Potential sensitivity to water and other conductive liquids
Battery-Based Systems
Batteries are electrochemical storage devices that serve as vessels for a reversible chemical reaction. Composed of cells, they do not require fuel or oxygen; they are self-contained units whose potential energy is only liberated when a load is applied across the terminals. In general, it consists of one or more voltaic cells, each of which is composed of an anode and cathode connected in series by the conductive electrolyte
There are different types of batteries for UAS applications. Rechargeable batteries are preferred, Lithium batteries tend to be lighter and have higher-energy density per unit mass than other self contained energy storage systems. To date, the most economical battery is the basic cylindrical 18,650 (18 mm diameter with 650 mm length), with a capacity of 2,000mAh.New variations in chemistries and crystalline structures (such as polymers, hydrides, gels, new crystalline structures, and exotic doping materials) are leading to ever-improving battery technology.
A significant issue with batteries relates to the recharge and discharge rate. Batteries have a wide dynamic range of behavior in various temperature conditions, and behave best when operating at their preferred operating temperature. High current loads can overheat batteries due to internal resistance, and a short circuit can cause deformation or bursting from rapid gas formation
The advantages of battery-based systems are: they are silent and lightweight; efficient (reduced levels of waste heat); no waste products; self-contained; no external reactants required; reduced complexity; no moving parts; rechargeable; uses electric motor as the prime mover. has advantages, including reliability, maintenance, control, and high-altitude operational benefits.
The disadvantages of battery-based systems are: limited endurance, battery recharge delays due to current limits and recharge rates, heating associated with rapid recharge; battery discharge may be efficient, but recharge process is inefficient, heating do to internal resistance; performance sensitivity to environmental temperature conditions; and hazardous chemicals (corrosive internal chemistry).
Photovoltaic
Solar cells convert the energy of electromagnetic radiation (at a frequency above the threshold frequency of the photoelectric material) into an electric power source by means of the photoelectric effect. With sunlight as an effectively cost-free and inexhaustible resource, there is a growing demand to harness solar power for long-endurance systems to which it may be reasonably applied. Unfortunately, the intermittent availability of solar power (weather and/or daylight permitting) necessitates either short-term operation during peak sunlight hours, or some sort of auxiliary power storage.
Traditional approaches use a battery system as an energy storage system. An example of this is the AC Propulsion SoLong UAS. This aircraft is designed to be as light as possible to efficiently operate off the battery in low-sunlight conditions. During full-sunlight conditions, the solar panels generate enough power for both vehicle operation and battery charge recuperation. This arrangement has field-proven continuous flight of over 48 hours, and providing continuous sunlight is available during the day, claims are made that it can run indefinitely.
Solar-powered systems using photovoltaics are being explored for use in High-Altitude, Long Endurance (HALE) applications, “which hold the potential for unlimited flight”. The renewable energy source of sunlight can power a reverse electrohydrolysis reaction, creating hydrogen fuel that can be used later to power a fuel cell when sunlight is not available.
Large surface areas are required to collect enough radiant solar energy to gain enough reserve power from available photovoltaic arrays at current efficiencies. Moreover, this need for enough sunlight intensity restricts flight of solar-based systems to operation in the mid-latitude regions.
The advantages of photovoltaic-based systems are: Primary energy source not carried onboard, silent, no moving parts; can be used in regenerative fuel cell applications (reverse electrohydrolysis); uses electric motor as the prime mover. They have higher reliability, low maintenance, control, and high-altitude operational benefits.
Fuel Cell: Proton Exchange Membrane
Fuel cells, as an advanced power generation technology, are regarded as alternative power sources in electrical systems because they offer higher energy density to extend the duration of flight. For the same energy capacity, the weight of fuel cells is 3.5 times lower than that of lithium-ion batteries, resulting in much preferable specific energy.
A fuel cell derives usable power from supplied chemical reactants in the form of an electric current. There are a wide variety of fuel cells, including proton exchange membrane, phosphoric acid, molten carbon, solid oxide, methanol, and alkaline.
The proton exchange membrane fuel cell (PEMFC) is the most promising technology for use in UAS propulsion systems. The molecular hydrogen is exposed to a platinum catalyst. The catalyst causes the hydrogen to ionize into its constituent protons and electrons. The electrolytic membrane separating the anode and cathode allows only the protons (hydrogen stripped of its electron shell) to pass through. At the cathode, oxygen combines with the protons in an electrochemical oxidation process, requiring electrons. This draws the electrons liberated in the anode across a load; the current produced can be used as a source of power.
The use of a PEMFC has advantages over a strictly battery-based system, such as better endurance and better replenishing characteristics (refill hydrogen tanks as opposed to recharging the battery); They are quiet, low-moving parts; zero-emission signature; higher-energy density than battery; reversible reaction has regenerative properties; uses electric motor as the prime mover that has advantages, including reliability, maintenance, control, and high-altitude operational benefits.
The disadvantages of the PEMFC-based systems are: expensive (platinum catalyst); pressurized components (inside fuel cell and liquid hydrogen); complexity as compared to a battery system; catalyst sensitivity; and humidity/water management.
UAV propulsion system trends
In addition to thrust, propulsion systems for modern aircraft must provide high fuel economy, low weight, small size (to limit drag), and extremely high reliability. The primary engine performance metrics are minimum total fuel burn (while meeting aircraft performance requirements) and reliability levels commensurate with permissible aircraft loss rate (1 per 108 departures for commercial aircraft).
The major types of UAV engines include: turbo-fan engines, turbo-prop engines, piston engines, wankel engines, electrically propelled engines, solar power propelled propulsion systems, and hybrid engines. All types of aircraft (including UAVs), engines and fuel typically account for 40 percent to 60 percent of gross takeoff weight, and the performance of the propulsion system has an enormous effect on air vehicle performance.
The gas turbine engine is vastly superior to alternative engines in all propulsion metrics. The power-to-weight ratio of gas turbines is three to six times that of aircraft piston engines. Gas turbines can also operate for long periods of times (4,000 to 8,000 hours) between overhauls, compared to 1,200 to 1,700 hours for aircraft piston engines. The small piston engines in current UAVs are replaced every 100 hours or less of service. The difference in reliability, measured by in-flight shutdown (IFSD) rate, is even greater.
The gas turbine engine efficiency deteriorates dramatically when its size is reduced. This fact limits its use for low-power and long duration applications, due to fuel weight. Large gas turbines can exceed 55% thermal efficiency, but turbine engines tend to be too inefficient for applications below about 200 kW — when idling, they are less efficient than ICEs in cars. So they are only found in bigger drones and in those that demand fast flight.
The small gas-turbine when replaced with one or more turbocharged 4-stroke Diesel engines can result in increases in efficiency and decreases in fuel consumption can result. These advantages can translate to increases in range and/or flight duration, plus a reduction in fuel tank volume and weight.
Experts say ICE technologies that include two and four-stroke cylinder engines, Wankels, and diesel technology are seeing advances that make them good candidates for some kinds of UAV applications.Automakers that include Mazda, Honda, and VW now make diesels with aluminum cylinder blocks as a means of reducing weight. Advanced aluminum alloy cylinder heads are capable of withstanding the pressures diesel fuel creates because the size is small enough to withstand it. But the vibration associated with the impulse torque during combustion can be severe, and this issue is still an area of research.
Wankels in UAVs typically are in the 4 to 100 hp range. Durability is one research area for these power plants. For example, Wankel engine maker UAV Engines Ltd. says that its engines typically need minor maintenance after about 50 hrs and a more major workover after about 200 hrs. But, says Len Louthan – a Wankel engine expert involved in applying Wankel diesel engines to military electrical power generation applications – UAV makers are looking for Wankels able to run for about 1,000 hrs before needing serious maintenance.
Engine technology company LiquidPiston Inc. have redesigned Wankels to overcome its traditional limitations of especially fuel efficiency. Company CEO Alec Shkolnik has a Wankel engine design that’s essentially been inverted, and he says it can increase flight endurance by more than 50 percent — the maximum length of time that an aircraft can spend in cruising flight. “We developed what we call the X4 engine, which is like the old Wankel rotary engine, but flipped inside out,” Shkolnik said. “It solved a lot of the challenges the Wankel used to have while giving it this new thermodynamic cycle upgrade.” Future unmanned aerial vehicles, like Lockheed Martin’s Fury, pictured here, could benefit from the Wankel engine derivative developed by LiquidPiston, which should reduce heat signature and increase flight endurance for military drone.
This trend among UAV manufacturers has significantly reduced the dependence of UAVs on fossil fuels. Recently, hydrogen fuel cells have emerged as viable alternatives to fossil fuels. They offer improved reliability, safety, and low maintenance compared to internal combustion engines. Also, UAVs powered by fuel cells operate longer than battery-powered counterparts and have better power to weight ratios.
The adoption of Electric motors and batteries is growing, however lower energy density (Rechargeable lithium-ion batteries typically come in the 0.9 to 2.63 MJ/L range compared to 34.2 MJ/L Ordinary gasoline.) means they will be confined to powering only small UAVs for the near future. The UAV propulsion system market is estimated to capture a market value of $363.8 million in 2016 with electrically-powered segment accommodating the highest share, according to report by ReportLinker .
Fuel-Efficient Propulsion Systems
Fuel efficiency is paramount for long-endurance UAV missions, ensuring maximum flight time and range while minimizing the need for frequent refueling. UAV designers are turning to innovative propulsion technologies to achieve better fuel efficiency, including:
- Hybrid Systems: Combining electric and internal combustion engines in hybrid propulsion systems optimizes energy use, allowing UAVs to switch between power sources based on flight conditions, further extending endurance.
- Aerodynamic Enhancements: Advanced aerodynamics, such as streamlined airframes and wing designs inspired by birds, reduce drag and energy consumption, enhancing fuel efficiency during flight.
- Energy Recovery: UAVs equipped with energy recovery systems can capture and store energy generated during descent or gliding phases, utilizing it during critical phases of the mission to save fuel.
Hybrid propulsion
Orbital UAV, an Australian designer and manufacturer of propulsion systems for unmanned aerial vehicles (UAVs), has signed a deal with Northrop Grumman to design and develop a hybrid system for a vertical take-off and landing (VTOL) UAV, the company announced in April 2020. The system will combine an electric motor, which has yet to be selected, with the company’s flight-proven heavy-fuel engine. A hybrid system will allow greater payload to be carried. Under the contract Orbital UAV will develop, supply, and support two initial hybrid propulsion systems for integration into what the company described as Northrop Grumman’s small UAV development platform. Work will be performed at Orbital’s facility in Perth, Western Australia.
The Air Force is investing in LiquidPiston’s X-Engine technology to create a hybrid-electric propulsion system to power emerging technologies like unmanned aircraft systems (UAS) and orbs, the company announced on March 2021. The Small Business Technology Transfer (STTR) contract worth $150,000 was awarded through AFWERX to support Agility Prime, a program developing electric vertical take-off and landing (eVTOL) aircraft for commercial and military use.
UAS and eVTOLs are being developed with battery-powered propulsion systems which have limited their range of flight. The X-Engine technology would use fuel to power a generator and charge the aircraft’s batteries extending its flight time and range, according to the company. “Today’s solutions for power and energy are held back by a lack of technological innovation; gasoline engines are inefficient, diesel engines are big and heavy, and while the world wants to go electric, batteries lack significantly compared to the energy density of fuel,” Alec Shkolnik, CEO and co-founder of LiquidPiston, said in a statement. “The X-Engine solves these challenges, and with this contract, we look forward to showcasing the value a hybrid-electric configuration can bring to unmanned flight.”
The X-Engine runs on JP-8, diesel, and other heavy fuels but is 30 percent more fuel-efficient than a diesel engine, according to LiquidPiston. It is also five to 10 times smaller and lighter than a diesel engine and is two to four times more fuel-efficient than a small turbine. The Army also awarded LiquidPiston a Small Business Innovation Research (SBIR) contract in December 2020 to develop the X-Engine platform for small tactical generators.
Market Growth
The global UAV propulsion system market is estimated to reach $10.76 billion in 2033 from $8.36 billion in 2022, at a CAGR of 2.33% during the forecast period 2023-2033 in terms of value. The growing demand for such unmanned aerial vehicles is expected to be the primary driving factor for the growth of the global UAV propulsion system market.
The global UAV propulsion system market is expected to be driven by defense and government applications due to the high capital investment involved in the development of the propulsion system. Military applications being one of the largest end-use application sector of the market, such investments are thus quite helpful for its overall growth.
Several countries across the globe are now allocating large sums of funds for their defense budgets. The idea behind it is to tackle the growing challenges in counter terrorism operations, intelligence, counter insurgency, and surveillance. This move is expected to be one of the biggest driving factor for the growth of the global UAV propulsion system market.
However, commercial applications are expected to witness a high growth rate during the forecast period due to an increase in the usage of UAVs in commercial applications leading to investment in technologically advanced propulsion systems.
The inherent benefits of integrating an electric-propulsion system to different UAV platforms is also driving adoption of electric propulsion technologies at a much faster pace than their other counterparts. For instance, an electrical propulsion system provides more flexibility in the installation of machinery as they are compact in nature, and due to the absence of several moving components of the drivetrain, they weigh less and hence contribute toward weight savings and endurance enhancement of a particular UAV model. Besides, the emergence of global green emission initiatives has encouraged adoption of eco-friendly propulsion technologies, such as electric propulsion.
In addition to this, with the constant advancements in the field of technology, several manufacturers are now trying to integrate AI in these unmanned aerial vehicles. The objective behind this integration is to provide features such as dynamic visual surveillance and target tracking capacity. Such developments are also influential factors that drive the growth of the global UAV propulsion system market.
The following are the drivers for the global UAV propulsion system market:
- Rising Procurement of Unmanned Aerial Vehicles by Defense Forces
- Growing Focus of Manufacturers on Lightweight and Fuel-Efficient Drone Engines
The following are the challenges for the global UAV propulsion system market:
- Notable Incidents of Engine Failure and Improper Functioning
- High Investment Costs and Supply Chain Complexities
The following are the opportunities for the global UAV propulsion system market:
- Focus of Manufacturers on Developing Sustainable Propulsion Systems for UAVs
- Ongoing Developments of Electric VTOL Aircraft
UAV Propulsion System Market Segmentation Analysis:
The global market is divided into three different types: conventional, hybrid, and full electric. In propulsion systems that use electricity, electric motors are used to drive propellers with the power stored in batteries. Electric propulsion systems are becoming more popular quickly because they make less noise, don’t need as much maintenance, and are cheaper.
Hybrid propulsion is made up of two engines: a thermal engine that keeps the motor turning all the time, and an electrical engine that makes more power when it’s needed. Most of the hybrid systems are on UAVs that carry heavy loads. But the traditional type isn’t used as much on the market because it doesn’t work as well.
The target market is segmented into civil and commercial, and military. Many companies and organizations are working on new technologies. For example, hydrogen fuel cells have become an alternative to Li-ion batteries in smaller drones, and their weight-to-power ratios are getting better and better quickly.
Recent trends in UAV Propulsion System Market:
- Increasing demand for electric propulsion systems: Electric propulsion systems have become increasingly popular in the UAV industry due to their high efficiency, low maintenance, and low noise levels. With the increasing demand for drones for delivery and other commercial applications, the demand for electric propulsion systems is expected to grow.
- Advances in battery technology: The development of high-performance, lightweight batteries has been a major driver of the growth in the UAV industry. With advancements in battery technology, drones can now stay in the air longer, fly further, and carry heavier payloads.
The Asia-Pacific region is expected to generate the highest demand for UAV propulsion systems during the forecast period. This increasing demand is mainly due the increasing orders for different UAV configurations for a plethora of military and commercial applications. Investments in the drone start-ups are projected to grow in several countries in the region necessitating the implementation of well-defined regulatory policies.
There are however some factors that are creating a roadblock in the fast-moving development of the market. One primary area of concern is the lack of clear operating regulations for UAV. Due to lack of such clearly defined mandates, there are chances of technology abuse going unpunished or unregulated. Recently, the government of India had put restrictions on the use of drones. The ban is now set to be lifted with clear guidelines defined by the government before the use of drones in public, commercial, or government controlled areas. For instance, in August 2018, India permitted the use of UAVs for commercial mapping, surveys and photography after elucidating the necessary regulations
Top companies include United Technologies Corporation (US), UAV Turbines, Inc. (US), UAV Propulsion Tech (US), UAV Engine Ltd. (US), Sky Power GmbH (Germany), Safran SA (France), Rotron Power Ltd. (UK), Orbital Corporation (US), LaunchPoint Technologies Inc. (US), Hirth Engines GmbH (Germany), GE Aviation (US), Ballard Power Systems Inc. (US), Austro Engine GmbH (Germany), 3W International GmbH (Germany), Rolls Royce Holdings, Rotax Aircraft Engine, Honeywell International
Major Five Small and Tactical UAV Fuel Cell Companies:
AeroVironment Inc.: AeroVironment Inc. operates its business through a unified segment. The company offers UAV fuel cells for small and tactical UAVs.
Ballard Power Systems Inc.: Ballard Power Systems Inc. operates its business through the Fuel cell products and services segment. The company offers small and tactical UAV fuel cells under the brand, Ballard FCair.
Doosan Corp.: Doosan Corp. operates its business through segments such as Electro-Materials BG, Mottrol BG, Industrial Vehicle BG, Doosan Digital Innovation BG, Others, DHC, DI, DEC, and DE. The company offers fuel cell powerpacks for small and tactical UAVs.
Elbit Systems Ltd.: Elbit Systems Ltd. operates its business through a unified Reportable Segment. The company offers UAV fuel cells for small and tactical UAVs.
H3 Dynamics Holdings Pte. Ltd.: H3 Dynamics Holdings Pte. Ltd. operates its business through a unified segment. The company offers small and tactical UAV fuel cells under the brand, AEROSTAK .
Recent Developments
The global UAV propulsion system market has seen several recent developments.
In November 2022, PBS INDIA announced its plans to launch the PBS TJ200 turbojet engine in 2023, designed primarily for modern UAV and UCAV systems.
In October 2022, BRP-Rotax GmbH & Co KG suspended the delivery of aircraft engines to “countries with unclear usage” following reports of engines being used on Turkish combat drones.
In July 2022, General Atomics Aeronautical Systems, Inc. (GA-ASI) tested a PT6 E-Series model turboprop engine from Pratt & Whitney Canada on GA-ASI’s MQ-9B Remotely Piloted Aircraft (RPA).
Finally, in April 2022, Suter Industries announced that their Suter TOA288 24hp UAV engine was selected by Volansi to provide propulsion for their VOLY M20 and VOLY 50 Series Vertical Take-off and Landing (VTOL) drones.
Commercial Applications
Long-endurance UAVs are revolutionizing commercial industries, such as agriculture, surveillance, and cargo delivery. In precision agriculture, UAVs can monitor vast fields for crop health, soil conditions, and irrigation needs, optimizing farming practices and increasing yields. For surveillance and monitoring, UAVs equipped with fuel-efficient propulsion systems offer extended coverage and real-time data collection, supporting various industries, including security, infrastructure inspection, and environmental research.
Military Missions
In the military domain, long-endurance UAVs play a critical role in intelligence, surveillance, and reconnaissance (ISR) missions. Armed with fuel-efficient propulsion systems, military UAVs can conduct prolonged surveillance missions over hostile territories, gather critical intelligence, and support ground operations, without the need for frequent refueling or recharging.
Conclusion
Advancements in UAV propulsion technologies have opened up a new era of long-endurance UAV missions. Lightweight and fuel-efficient propulsion systems, including electric motors, hydrogen fuel cells, and efficient rotary engines, are driving innovation in commercial and military applications. As these technologies continue to evolve, we can expect even longer and more efficient UAV missions, ushering in a new era of aerial exploration, data collection, and surveillance across industries worldwide.
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