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C3 to C5 Conversion Kit: Transforming Your Drone for Standard Scenarios
In the world of drones, European regulations have established different classes (from C0 to C6) based on characteristics and permitted uses. Recently, C5 and C6 classes have gained importance as they are intended for more complex operations in the specific (standard) category. A C3 to C5 conversion kit is a set of accessories designed to enable a drone originally certified as class C3 to meet the technical requirements of class C5. In other words, it allows transforming a C3 drone into a C5 drone by adding safety equipment and modifying certain parameters without the need to purchase a new drone.
The primary purpose of this kit is to enable existing drones to operate in more demanding operational scenarios (such as EASA’s STS-01 standard scenarios) while complying with current regulations. The benefits are clear:
- Expanding the operational scope of your drone (enabling flights in environments and missions not permitted for a C3 drone),
- Reducing costs by avoiding the need to invest in a new platform,
- Enhancing operational safety through additional systems such as parachutes and emergency flight termination systems.
Given the initial lack of C5-marked drones on the market, these conversion kits have become the best solution for complying with European standards without waiting for new models.
Comparison Between C3 and C5 Drones
A typical C3 drone must meet the following requirements, among others:
- Maximum takeoff mass (MTOM) < 25 kg
- Maximum dimension < 3 meters
- Exclusively powered by electricity
- Unique serial number
- Remote identification system
- Geo-awareness system
- Lights for attitude control/night flight
- Low battery warning system for both aircraft and ground station
- Secure data link to prevent unauthorized access to command functions
On the other hand, the C5 classification is intended for specific category operations under the STS-01 standard scenario, which allows VLOS (Visual Line of Sight) flights in controlled areas. A C5 drone must meet most C3 requirements but with key safety additions.
In particular, a C5 drone cannot be fixed-wing (unless tethered) and must include means to safely terminate flight and mitigate impact energy. This involves two critical systems:
- A Flight Termination System (FTS) that allows motor shutdown in case of emergency.
- An Impact Energy Reduction System, typically an automatic deployment parachute or another device that slows descent.
Additionally, the C5 drone (or its conversion kit) must provide control link monitoring (C2), with visual/audible alerts for signal weakness or loss. Another added requirement for C5 is a selectable low-speed mode, limiting speed to 5 m/s. Converting a C3 drone to C5 does not change its fundamental specifications (weight, size, etc.), but it adds safety equipment and stricter operational requirements.
Impact of the Conversion on Performance
In return for these minor performance reductions, the drone gains critical safety capabilities. A C5 drone can operate with confidence that, in the event of a critical failure (e.g., motor failure, signal loss), its FTS will cut power, and the parachute will deploy, ensuring a controlled descent. This drastically reduces impact energy in case of a crash.
Thanks to these enhancements, a converted C5 drone can operate in previously restricted environments, such as flights over populated or urban areas within an STS-01 scenario, meeting the required safety conditions. In short, the conversion expands mission possibilities at the cost of a slight reduction in raw performance but with a significant leap in safety and regulatory compliance.
Requirements and Testing for the Conversion Kit
Implementing a C3 to C5 conversion kit is not just about adding hardware; it involves meeting strict technical requirements and passing verification tests to ensure the modified drone complies with regulations. At a high level, the kit and the combined drone must demonstrate compliance with all additional C5 requirements while maintaining the original C3 requirements. Below are the main requirements and associated tests:
Compatibility and Non-Alteration of Original Design
- It must not exceed the original MTOM
- It must not surpass the declared maximum dimensions
- The drone must remain stable and maneuverable under normal and failure conditions
Proper Physical Integration
The kit must include clear installation instructions and use existing interfaces on the drone (e.g., dedicated parachute mounts). No invasive modifications to the drone (such as drilling new ports) are allowed; if the drone lacks an interface, the kit must provide an adapted solution. During evaluation, it is verified that the attachment is secure, no parts detach in flight, and that the kit’s presence does not interfere with critical elements (e.g., free-moving propellers, unobstructed sensors, and GPS signal reception).
Electrical and Software Systems
The kit must not require firmware modification of the drone; at most, it may include instructions to adjust parametersin the original software (such as enabling the low-speed mode). Compatibility with drone firmware versions must be specified, and after any firmware update, the kit’s functionality must be retested.
Flight Termination System (FTS)
The kit must incorporate a reliable FTS that, when activated, immediately cuts propulsion. This FTS must be independent of the drone’s automatic flight control and allow both manual and automatic activation.
Impact Reduction System (Parachute)
Unless the drone is tethered, it must include an impact energy reduction system. This parachute must deploy quickly if the drone enters free fall, reducing descent speed to safe levels. Some kits integrate automatic free-fall detection (IMU-based) to deploy the parachute without pilot intervention.
Low-Speed Mode
The drone must have a low-speed mode that limits speed to 5 m/s. It is verified that activating this mode effectively prevents exceeding this limit.
Link Monitoring and Alerts
A C5 drone must monitor control link quality (C2) and alert the pilot of issues, using at least four signal strength levels (strong, medium, weak, lost), with distinct alerts for weak signal (caution) and imminent loss (warning).
Security and Cybersecurity
Installing the kit is not just “plug and play”; manufacturers must conduct rigorous testing to ensure the converted C5 drone is as safe and compliant as required by regulations.