ISSUE 011 Autumn 2021 Candela C-7 hydrofoil speedboat dossier l In conversation: Robert Hoevers l Battery recycling focus l Vehicle dynamics insight l ZeroAvia hydrogen-electric aircraft digest l Motor materials

attitude to a computer, which adjusts the boat’s actuators as needed to maintain balance. This is no coincidence. Candela’s engineer Kristian Sloth Lauszus previously worked on UAV flight controllers before designing and building the control system for the C-7, and the dynamics of the latter are not wholly different from the former, especially given that above 16 knots the boat does indeed fly above the water. Small wonder then that the speedboat’s control system is referred to in-house as the “flight controller”. The core part of the first stage of the control process – the sensor inputs – are acceleration readings from an accelerometer, along with measurements from a gyroscope, while speed and position are calculated using GPS. “The accelerometer and gyro comprise our inertial measurement unit, which integrates with the GNSS receiver directly onto the board of the flight control computer,” says Lauszus. Both the accelerometer and gyroscope are similar to those used in smartphones or UAVs, being low- cost, free of moving parts, and widely available. “Many of these types of sensors were originally designed for UAVs, which can rapidly flip in the air, and so they can measure changes in movement of up to 300°/s,” Lauszus explains. He adds that the inertial estimates are calculated at a rate exceeding 100 Hz, ensuring more than enough actionable data inputs for the control loop, which sends commands to the foil actuators at 100 Hz. “Speed readings from the GNSS are also important, because the lifting force generated by the foil is proportional to the square of the boat’s speed, so if you double the speed you get four times the force; hence the faster you move. It’s therefore critical that the control system has a good speed estimate to keep the boat stable.” At the very front of the C-7 are two ultrasonic sensors, each measuring the distance between the hull and the water; two are used to give redundancy. “The power used by the pilot and flight control systems is really low,” Lauszus says. “Of course, the main bus from the battery is 400 V, and that’s great for the motor, but a DC- DC converter steps that down to 12 V for the control system. “So-called ‘take-off’ is handled by the flight controller. Initially, the angle of attack of the aft and front foils are set in such a way as to pitch the boat up in order to lift it out of the water. Once the correct altitude is reached, the pitch is normalised to balance the boat parallel to the water. “The process is performed in reverse during ‘landing’, with the nose pitching up just before landing, similar to when an aircraft flares when it comes in to land.” State observer systems on the flight controller serve to verify the integrity of data, and the boat is programmed to land and operate in slow mode for safety purposes in case of any errors. Hull materials and hydrodynamics In the earliest design stages for the C-7’s hull, very little was defined – only that it had to fly, and would therefore need to be as light as possible. The first prototype was built in an aerospace carbon fibre factory, made Judicious mechanical and software engineering enables the C-7 to make banked turns ;Oe C »s fliNOt controller ReeWs the boat balanced while foiling, with IMUs for inertial readings, .N:: for sWeed and ultrasonics for hull-to-water distance 28 Autumn 2021 | E-Mobility Engineering