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54 Digest | Griff 135 brushless direct current (BLDC) units. “A standard BLDC motor can withstand some rain, snow and other weather-related issues, but we are now developing new customised, Norwegian- made motors that can withstand all environmental challenges, including salt water,” Forde says. “We will be performing the first tests with them in March.” The intention is to qualify them to the IP66 standard. While the Griff 135, like the rest of the family, can be configured with four motors or eight, the power supply system remains essentially the same, apart from the number of motor controllers. The flight control software accommodates both configurations, with the choice being made during the build process. Designed for the Griff 135 and each individual set-up and motor combination, the propellers are folding two- or three- bladed units made from carbon fibre reinforced plastic. Forde says their design was the result of extensive calculation and testing to find the optimum combinations of diameter, rpm, aerofoil section, pitch, twist and number of blades, together with motor windings and voltage. In its eight-motor configuration, the 135 has two-blade propellers that have a diameter of 38 in and a pitch of 11 in, while with four motors it uses three-blade props with a diameter of 42 in and a pitch of 22 in. The blades are made in cooperation with Czech company Mejzlik. Suitable large, high-quality foldable propellers are not easily available off the shelf, so Griff Aviation is patenting its own hubs and folding mechanism. This includes a triple redundant locking mechanism to hold the blades in their flight position, thereby meeting certification requirements, and a tensioning system that prevents unwanted motion while preserving balance. Control and comms The flight control system (FCS) is an industrial-grade MP2128 autopilot from MicroPilot, running software written by the same company. Comms between the autopilot and the battery management system enable the autopilot to limit power demands and bring the aircraft back to base if there is a problem, Forde explains. “There is a full set of active telemetry, and we have settings to decide how the FCS reacts to low battery and other warnings,” he says. So far, Griff has supplied standard 2.4 GHz data links from various suppliers with sufficient bandwidth for video as well as telemetry. In each case they are specified to meet a customer’s requirements while complying with local spectrum allocation and RF transmission regulations. Similarly, the ground control system software can run on either a tablet computer or a more elaborate dual- screen system in a Peli case to suit the application. The simplest version of the two-screen interface puts a map and the programmed mission on one screen and the live video feed and aircraft instruments, telemetry and warnings on the other. As with the FCS, the software running it is from MicroPilot, but Griff is developing its own. Payload support Central to the facility to ready the aircraft for flight without the need for tools is Griff’s patented Switch And Lock (SAL) system, which replaces separate connectors and fasteners for batteries and payloads with combined connectors and quick locks. At the front and rear of each battery box, for example, is an end plate that contains two recessed tracks, one straight and one L-shaped. The straight track slides on to the guide rail in each end piece, while the L-shaped track receives the stud on the end of a locking lever, forming a cam surface that locks the battery into position as the lever is pushed home. February/March 2020 | Unmanned Systems Technology This view of a landing leg and skid shows the CNC-machined strengthening ribs in the leg and the spring-loaded linkage that forms the shock-absorbing system (Courtesy of Griff Aviation)