We all know normal multicopter drones are effective at hovering and Vertical Take-Off and Landing, they can’t travel long-distance as efficiently as aircraft with fixed wings. This has been listed as their main disadvantage. But not any more. A team of students from the Singapore University of Technology and Design (SUTD) is trying to get the best of both worlds with the Transformable HOvering Rotorcraft (THOR).
According to the design team, THOR’s design inspiration came from the samara seed, ‘helicopter’ tree seed that is capable of flying long distances because of its stable shape. The concept was earlier raised in 1913 called the monocopter, it was “structurally efficient”, the whole frame is used to generate lift, but “strategically inefficient.” The lack of counter-rotational systems meant the pilot and cargo would have needed to spin with the rest of the aircraft, making it impractical to actually ride in.
Usually, when aircraft makers want to hover and cruise, they simply fix rotors onto rotating wings, but with THOR the wings become rotors, transitioning in mid-air and spinning around a central module like a single-bladed helicopter. THOR manages to achieve very high structural efficiency by using all of its aerodynamic surfaces in both vertical and horizontal flight modes, transforming from a flying wing into a sort of whole-body spinning bicopter thing that you really need to see to believe.
How THOR actually works?? It has two modes of flight: hovering mode (H-MOD) and cruising or fixed mode(C-MOD). When transitioning from hover mode to fixed-wing mode, the wings rotate into alignment. When the drone is in hover mode (left), it can rotate its wings (servos) by 90 degrees (middle) to transition to cruise mode (right). And when in cruise mode, it can do the reverse to switch to hover mode. During this transition, centrifugal force of switch is used to move the ballast, a weight in an aircraft used to bring the center of gravity into the allowable range, to keep the aircraft balanced.
Two key points in the innovative design are First are the bearings placed between the drone’s body and the wings. The bearings allow the wings to rotate appropriately depending on what flight mode is used. Second is the motor power, primarily in hover mode. The motor must have sufficient power during the transformation so that THOR doesn’t just fall to the ground. It needs enough power to create the instantaneous transformation without losing altitude, but not so much power that the motor will break the wings.
As you can see from the video, the design still needs a bit of work, as transitioning from one mode to the other isn’t seamless. With the exception of the servo and bearing used for wing rotation, THOR uses every other structural component in both hovering and cruising modes, making it highly efficient relative to hybrid designs. It’s very much a prototype, and both the hardware and the software controller need some optimization, but look how innovative the design is.
The UAV business is now getting a world of extremes. At one end, you’ve got hobby-grade consumer gear, which has improved dramatically in the last couple of years, and at the other end, you’ve got the military gear tough, rugged. There are no real standards for industrial-grade drones yet, but it is a continually growing market as all sorts of companies in all sorts of areas start to discover the power and potential of unmanned aerial systems. The advantage lies in its applications as the commercial world can see the benefits of industrial-grade UAV tools. It’ll be interesting to see what sort of machinery and standards develop in this space over the next few years.
Applications of THOR seems to be endless i.e. anything that requires both long range and an agile hover, and because of its inherent potential to scale, it can be made smaller than other hybrid platforms,which will unlock many possibilities where current hybrid UAVs are too big or bulky to operate! These include agriculture, surveillance, and package delivery, all of which are hot topics in drone development as of the moment. I really hope this turns out to be a platform for the development of the next-generation unmanned programs.