Starter-generator integration in UAV engines: beyond just starting the engine
Ask the majority of people what a starter-generator does in a UAV engine, and they will tell you it starts the engine. This is technically true, but this defines about 10 percent of what this component actually does when a mission is conducted. When the engine has reached operating speed, the starter-generator switches to generation mode and becomes the main electrical power source of everything running onboard. Understanding this dual role is important for any engineer making propulsion or system architecture decisions for a UAV platform.
How Does a Starter-Generator Work?
A starter-generator is a single device that has two distinct modes of operation. During engine start, it acts as an electric motor, powered by a battery to crank the UAV engine until it reaches self-sustaining combustion speed. When that speed is attained, the unit automatically goes into generator mode. Since then, it transforms mechanical energy with the running engine into electrical energy, which is distributed to avionics, payload systems, autopilot hardware, and any other electronics onboard. This design avoids the requirement of an independent starter motor and an independent generator – the latter would add weight, complexity of wiring, and other sources of failure. Instead, there is a single integrated unit that performs both functions during the flight.
What the Generator Function Actually Powers
In the majority of professional UAV systems, electrical load during the flight is critical. The starter-generator unit’s generator side is tasked with providing power to an array of systems that are essential to the success of the mission. These loads include:
- Flight control computers, autopilot hardware, etc., which need constant, controlled voltage during the mission.
- Sensors and cameras, such as EO/IR payloads and LIDAR systems, which require constant power over extended periods of flight.
- Communications and data link equipment connects equipment that must be kept at a consistent power level to prevent signal degradation during the mission.
- Battery charging systems are where the generator continuously charges the onboard batteries to ensure that there is always a backup of power.
The Safety and Backup Benefit
Among the most significant and least discussed benefits of a starter-generator setup is what it would offer in case something goes wrong. During an engine failure incident in a UAV, the built-in generator ceases to provide its power. When the platform is powered by a generator that constantly charges an onboard battery, the battery contains usable power. This energy can be used to energize the flight control and other key systems. It enables the platform to experience a controlled descent or emergency landing.
A battery-only UAV system exhausts its resources as the mission progresses and reaches the end of a long flight with little backup capacity. The starter-generator integration also guarantees that the electrical redundancy is implemented passively, without the operator being required to operate the power states manually.
Weight and Integration Considerations
The issue of weight plays a crucial role in designing a UAV hybrid propulsion system. Each additional starter and each additional generator add both mass and wiring complexity. A well-designed starter-generator unit, such as that which has been specifically designed to operate on the engine platform of a UAV, can weigh as little as 2 kg and still provide a reliable electrical output over a wide RPM range. The integration also minimizes the number of parts, which in turn minimizes the number of failed parts that may occur during a mission.
Conclusion
When you are defining or developing a UAV platform requiring onboard power generation, mission electrical reliability, and minimal system mass, the starter-generator system of your UAV engine is a decision that will impact the entire platform, not just the propulsion stack. Zanzottera Technologies designs UAV engines with exactly these integration requirements in mind, combining efficient power output with built-in compatibility for starter-generator systems built for professional and industrial mission profiles. Connect with us and talk about the appropriate engine configuration to use in your application.
FAQs
Can a starter generator replace a dedicated UAV generator entirely?
Yes, in the majority of UAV engine designs it can. When the engine is operating, the generator mode can provide constant electrical power to all onboard systems,, eliminating the necessity of a dedicated generator unit.
What happens to onboard power if the UAV engine fails mid-flight?
When the engine is stopped, the generator is also stopped. The starter-generator, however, constantly charges onboard batteries during the flight, which serve as a backup source of power to flight control systems in order to manage a safe descent.
Does starter-generator integration affect UAV engine weight significantly?
A well-designed starter-generator unit will add only a small amount of mass (usually about 2 kg) but will eliminate the combined mass of an individual starter motor and generator, making the overall system lighter.
Can a starter-generator be used on both fixed-wing and VTOL UAV platforms?
Yes. Starter-generator systems are applicable in the fixed-wing, VTOL, and hybrid UAV platforms. The design has been compatible with the single cylinder and the multi-cylinder engine configurations of a variety of displacement sizes.
