The Role of Hybrid Propulsion in Extending UAV Mission Endurance – ePropelled

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What comes to mind when most people think of UAVs is probably a drone, and indeed, many UAVs are smaller, unpiloted vehicles. However, not all UAVs are drones in the strict sense, as they can be highly complex and highly sensitive pieces of equipment used by the military in strategic deployment.

One of the most famous and iconic UAVs to date is the General Atomics MQ-1 Predator, which used up to 100-octane reciprocating aircraft engine fuel and was used to great effect by the U.S. military in Iraq and Afghanistan. Its crucial strength was that it could stay airborne for hours, reducing risk to pilots while gathering information, and in some cases launching missiles.

UAV Propulsion

Hybrid propulsion allows a vehicle to combine multiple fuel or power sources to improve performance. Just like a hybrid car uses electric power and gas, a UAV can use an internal ICE (internal combustion engine) and electric power to propel itself forward.

The benefits and disadvantages of using an ICE in a UAV include:

Benefits

• Internal combustion engines are ideal for situations where UAVs need power for an extended period or mission.

• ICE allows easy and fast refuelling. The tank can be filled immediately on their return, and they can be sent out again quickly.

• ICE engines provide plenty of power, which enables UAVs to carry heavier loads.

Disadvantages

• ICE engines require regular maintenance and repair to continue working. They can also be harder to repair as ICE systems are complex. Both of these things mean a UAV running on ICE power might not be available when needed.

• ICE engines can be noisy, which makes them unsuitable for spy and covert work.

• ICE systems can be weighty, which can impact the speed and reach of the UAV.

What is an Internal Combustion Engine (ICE)?

In the context of UAVs, ICE is short for Internal Combustion Engine. Internal combustion engines work by burning fuel such as gas or diesel. To be able to burn this fuel, an ICE must first mix the fuel with air and then ignite this mix. It’s the energy from this combustion reaction that generates the power needed to propel a vehicle.

The internal combustion engine is a type of engine that has been in use since the 1800s, so it’s certainly not a new idea in itself. In fact, until very recently, when we began utilising electric energy for vehicle propulsion, it was the only fuel option in use for many vehicles, including planes and aerial drones.

What is an Electric Propulsion System (EPS)?

EPS, also known as electric propulsion systems, are, in their simplest form, batteries. UAVs get the energy they need for propulsion from these batteries, which allow them to fly.

Source of electrical energy for UAVs

There are several sources of electrical energy that UAVs can use:

Battery:

The first, like an electric car, is a battery. A battery is designed to store electrical energy and release it to active and maintain the propulsion system of the UAV. RQ-4 Global Hawk UAVs used by the U.S. military use lithium-ion batteries for propulsion.

Charging stations:

Some batteries are rechargeable, which means that by plugging them in, you can charge up the electric energy source of a UAV, rather than having to replace the battery. For example, the needs to be recharged after a mission.

Solar:

It makes sense that a vehicle that spends most of the time in the air uses solar panels to recharge its battery. Which is precisely what some UAVs like this one do.

Generators:

Some UAVs, like the ones available from epropelled.com, are designed to use a scaled-down internal combustion engine to run a small generator. This generator can be used to make energy to top up the UAV’s batteries while flying.

The benefits and disadvantages of using an EPS in a UAV include:

Benefits

• EPS fuelled UAVs contain fewer moving parts. This means they are easier to repair than a UAV running on an ICE system.

• EPS are much quieter than ICE-fuelled UAVs, making them well-suited to spy and covert work.

• UAVs with EPS can be easier to control accurately for delicate and subtle tasks.

Disadvantages

• EPS fuelled UAVs will run for as long as ICE-powered ones, because batteries run out quicker than Gas. This means EPS UAVs are only suitable for shorter missions.

• EPS fuelled UAVs cannot lift as much weight as an ICE-powered version, which means its used in war zones and relief zones may be more limited.

• ESP UAVs rely on more complicated tech, which means there is a greater chance that it can go wrong.

• EPS UAVs also need to be charged after each mission. This means their turnaround time is longer, and could cause delays before they can be utilized again.

UAV Hybrid Propulsion

From the information above, you can see that both ICE systems and EPS offer some excellent benefits when applied to UAV propulsion. However, you will also be able to see that there are some distinct disadvantages to choosing either ICE or EPS power options for UAV propulsion.

What is UAV Hybrid Propulsion?

UAV hybrid propulsion is when unmanned aerial vehicles use a combination of ICE and EPS as fuel. The main benefits of UAV hybrid propulsion include that it allows them to fly long distances while also being able to switch into quiet mode when they arrive at their target.

The good news is that many UAVs are now starting to use hybrid propulsion systems that combine internal combustion engines with the use of electric power. In this way, they can reap the benefits of both types of power systems while negating some of the major disadvantages present when only a single power system is used.

Let’s look at the benefits of using hybrid propulsion in the field of UAVs in more detail

Benefits Of Using Hybrid Propulsion Systems In UAVs for Military Missions

The first and perhaps the most important benefit of using hybrid propulsion systems in UAVs is that they extend mission endurance.

Increased mission endurance

Extended UAV mission endurance is all about making sure that an unmanned aerial vehicle can stay in the air for as long as possible. Extended mission endurance via a hybrid power system means that the UAV uses a small ICE to generate electricity, which is then used to propel the vehicle forward or to charge up its batteries while it’s in the air. This allows UAVs not only to travel longer distances but also to cover more ground and complete the task at hand without needing to refuel or recharge.

Increased operational flexibility

Operational flexibility for UAVs includes being able to take off and land on a range of terrains, being able to carry a range of tools, and being able to fly in all kinds of weather.

This type of operational flexibility is important because it means a single drone can be used across a wider range of missions, including delivery and search and rescue. This helps to save the military money and time as they will not need to wait for a specialised UAV for a particular job.

This increased operational flexibility is achieved by switching between gas and electric when required. For example, in bad weather, gas will provide more power for a safer takeoff, while a UAV can then be switched to electric power to stay enabled for more delicate and responsive manoeuvring.

Increased stealth

Stealth in a UAV is all about minimising the risk that it’s seen or heard. Stealth is important, especially in military applications, because it means the enemy is not alerted to the presence of the UAV and the mission is not compromised. Hybrid propulsion can help UAVs achieve better stealth because it allows them to switch to electric power, which is much quieter than gas. This means gas can be used to ensure that the UAV can travel a long distance to reach its destination, and then electric power can be used once it arrives, ensuring that stealth is maintained as the mission objective is executed.

Better fuel efficiency

Fuel efficiency is the rate at which a UAV uses fuel. Electric-powered UAVs use fuel faster, which can limit their range. However, when electric power is combined with gas in a hybrid power system, UAVs can still travel long distances and spend a greater length of time in the air without needing refueling. This means missions will not need to be terminated before they are complete.

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Originally published at https://epropelled.com on July 8, 2025.