Samara Autorotating Wings (SAW)

The SAW project takes inspiration from the graceful falling of maple seeds, sometimes more fondly known as helicopter seeds. The main purpose of SAW platform is for precision aerial deployment of lightweight payloads at a relatively low-cost. It is ideal for applications such as precision reforestation projects, sensor deployments for remote sensing such as detection of natural disasters such as forest fires, flood, or monitoring of wild life, agriculture, gases and chemicals, weather detection and so on. This project has currently been explored in the following five focal points.

1. Optimized Wing Planform

Maple seed and SAWs

The size and shape of the wing affects how fast the platform rotates, how fast it drops, its pose and coning angle. Therefore, the wing planform of SAW is carefully chosen in order to achieve the slowest drop speed, a decent rotation speed, which also affects the glide slope. The parameters being chosen include wing length and chord length, with a third order polynomial to ensure the shape remains smooth. A flat plate airfoil is used as the size of the platform is relatively small and the airfoil effects are considered minimal. Blade Element Theory is used to model the platform in 6 degrees-of-freedom free-fall scenarios, with various algorithms such as gradient descent and genetic algorithm are used to find the optimum solution. Various optimization methods are discussed in the following papers.

2. Collaborative Units and Mid-Air Separation


SAW units can be joined together as a rotor hub, looking rather like a flower. In this configuration, they can collaboratively work together, achieving better resilience as tough wind conditions. At a desired altitude, the units can exit the collaborated form, splitting to individual units and continuing their trajectory towards each respective landing locations. To achieve this, a unique de-centralized separation mechanism is designed, the separation manoeuvre is first simulated and then verified in a special experiment setup. More details can be found in -

3. Solar-cell Wings


Once SAW lands at a designated place, the payload sensor can begin collecting its data. Its service life can be extended indefinitely by integrating solar cells as a multi-functional wing structure. As the solar cells’ structure only allow them to be sliced in a specific way, an optimization is performed to find the best place to slice the solar cell, forming the main wing and the flap. More details can be found in -

4. A Flapless SAW Design

Flapless SAW

An alternative to using a flap for glide trajectory control of SAW is explored by using a thrust unit. The thrust unit can provide a precise and directional forces, which can be used to effectively change the tip path plane of the autorotating platform. The optimum location of the thrust unit is found via the use of Genetic Algorithm, with the cost function being mainly the glide slope and stability of the platform. Simulations and experiments are performed and the results can be found here -

5. Optimized Glide Slope and Diving Mode


SAW is a platform that uses a single actuator (a flap) and its only driving force is gravity. This puts SAW in the same category as other platforms relying on gravitational potential energy to make their journey, such as parafoils and gliders. Unlike the parafoils and gliders which may use two or more actuators, SAW only uses one. We attempt to achieve the maximum potential of SAW platform, striving to achieve the best glide slope by optimising the flap shape and size, and optimising the control method. The result is an average 28.9 degrees of glide slope.


One way to tackle adverse weather conditions (which SAW is vulnerable to) is by quickly passing through them. We introduce a new flight mode - the Diving Mode. Using the same flap (so no additional actuators are needed), SAW can be invoked to enter dive at any point during its autorotating flight. And the transition is bi-directional, meaning it can go from autorotation to dive, or the reverse, at any desired instance. The transition is also extremely quick, requiring less than a second for a full transition. Interesting details on this can be found in -

Single Actuator Monocopter (SAM)

The idea to achieve controllable flight with a single actuator is one that is fancied by many and achieved by a few recently. SAM brings flight efficiency and dynamic stability of the craft to the table.

1. Efficient 5-DOF Controllable Flight with Single Actuator


Monocopters have so far used two actuators to achieve flight and control, a thrust unit and a flap. In this work, we use only the thrust unit to achieve both. By changing the thrust in a certain manner during each cycle of rotation, SAM can translate vertically and laterally. As compared to other single-actuator UAVs, SAM has much higher flight efficiency as the wing helps in producing useful aerodynamic lift and provides passive stability. The wing planform and location of the thrust unit is optimised to achieve the best performance. Simulations and experiment results can be found in -

2. Semi-rigid Foldable Wing Structure

Currently a work in progress. Details will be updated at a later stage.