Issue 39 Unmanned Systems Technology August/September 2021 Maritime Robotics Mariner l Simulation tools focus l MRS MR-10 and MR-20 l UAVs insight l HFE International GenPod l Exotec Skypod l Autopilots focus l Aquaai Mazu

45 bases. Other expected applications include search & rescue, infrastructure inspections, agricultural spray, and seed distribution for reforestation and agricultural missions. “The MR-10 has an endurance of up to 35 minutes, and the MR-20 up to 45 minutes, but of course there’s a sweet spot for how much payload and batteries end-users will want to install, to optimise the flight time and effectiveness of the platforms for their specific operations,” CEO of MRS Tom Nickell says. “Both models use a lot of the same design points on their airframes and propellers – in fact, the MR-20 is only about 12 cm wider than the MR-10, despite their significant weight disparity,” he says. “The fundamental differences are in the tailoring of their motor-propeller combinations for thrust and efficiency, and in their frame size and standard battery weight.” A third platform, the Dauntless, is still in development, and will be offered as a quadrotor or octorotor. Once completed, the octorotor version is expected to offer end-users an efficient payload of 45 kg, with a MTOW of 140 kg. It will have an estimated flight time of up to 25 minutes with 18.5 kg of batteries, or up to 60 minutes or more if configured with a hybrid generator powertrain. While major details about the Dauntless remain under wraps, MRS spoke to us about the key engineering choices made on the MR-10 and MR-20 that have enabled the payload-to-MTOW ratios across its fleet. Hull architecture The four arms running between the hubs and motors of both UAVs are carbon fibre tubes, which are commonly used for their high strength-to-weight ratio as well as general availability. The tubes attach to the hub via mounts made from additively manufactured acrylonitrile styrene acrylate (a thermoplastic widely used in 3D printing and the automotive industry for its UV resistance and mechanical properties). For the rest of the crafts’ structural parts, however, the use of carbon fibre composite has deliberately been limited, with MRS largely favouring aircraft grades of aluminium instead. These include combinations of aluminium 5052, 6061 and 7075 across the frames, decks and structural support components. Although aluminium is heavier than carbon composite, workability and ease of use have proven vital for mounting heavy payloads in different configurations, and the wide availability of aluminium parts helps ease manufacturing, maintenance and repair. “The battery box has a payload- mounting plate in the bottom of its enclosure, which gives flexibility and saves weight when it comes to attaching different sensors, sprayers or package containers underneath,” Nickell notes. “Also, the hubs on both the MR-10 and MR-20 have elongated mounting decks on their upper and lower sides, allowing payloads to be mounted above or below, with further hardpoints on the sides in case users need flexibility as to where they can put mission-critical attachments.” Extensive simulation and testing have identified the degree and spread of mechanical stresses that payloads can impart on the UAVs’ structures – both in flight and when static – and to confirm that aluminium has been the smarter choice for enabling MRS’ targeted payload capacities. Nickell adds that upcoming development plans include further simulations and tests to identify which aluminium parts can be swapped out for near-identical composite pieces, to further reduce weight without compromising structural integrity. And although carbon composite is not typically thought of as a very cost- effective material, MRS has found enough mass-produced carbon parts that cost less than CNC-machined aluminium, making continued research into this area worthwhile. MRS KittyHawk MR-10 and RavenHawk MR-20 | Digest Unmanned Systems Technology | August/September 2021 Extensive tethered indoor flight tests were performed on the KittyHawk and RavenHawk before moving to outdoor flight trials