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Drone Taxonomy

Drones come in many different shapes, sizes and configurations, ranging in weights from a few grams up to a few tonnes, and can be conveniently divided into four main categories: (1) Horizontal Take-off and Landing (HTOL); (2) Vertical Take-off and Landing (VTOL); (3) Hybrid; and (4) Bio-Based. 

Drone taxonomy

Horizontal Take-off and Landing (HTOL)

Typically, HTOL drones require a runway to take-off and land in a similar way to a conventional aeroplane, and often utilise a fixed-wing configuration. 

Vertical Take-off and Landing (VTOL)

VTOL drones typically use a rotor (or multiple rotors) configuration to provide vertical take-off and landing capability, as well as horizontal propulsion through the air in a similar way to a conventional helicopter. 


Hybrid drones combine the characteristics of HTOL and VTOL drones, and are typically able to take-off and/or land vertically before transitioning to horizontal flight, for example by using a dual system to combine fixed-wings with rotors or by using tilt-rotor or tilt-body mechanisms.  


Bio-based drones are either bio-inspired involving mimicking flight mechanisms from the natural world, such as flapping wings, or bio-in-the-loop involving experimental efforts to control living birds and insects, for example by sending control signals to the animal’s brain or muscles. 

Drone Safety Features

Like almost all aircraft, drones have multiple layers of redundancy built-in to their systems to maximise safety, with all key features having backups upon backups. Ultimately, if something does go wrong, drones fail in a safe and controlled manner, for example by deploying a parachute for a safe and gentle touch-down. The University of Southampton is working closely with a spin off company developing a state of the art architecture that further increases the integrity of the onboard electronics to improve the safety of drones.

As technology improves, the reliability of drones as well as the number of safety features on board is also increasing; many drones can autonomously avoid obstacles using a variety of onboard sensor arrays. In most cases higher degrees of autonomy improve the safety of drones. For example, most autonomous drones that lose the signal from the operator can be programmed to automatically return to their launch site, whereas drones with lower degree of autonomy would not know their location and may not be able to land in a safe area. Broadly, the greater awareness of its environment a drone has, the more possible courses of action it has at its disposal in the event of a failure. Some state of the art research drones can pick safe emergency landing areas, such as empty fields, from the air.

Existing Drone Regulation in the UK

Larger drones or those that operate for extended periods over populated areas are subject to rigorous case-by-case approval by the Civil Aviation Authority. These drones fall into the higher risk categories of drone operations called “Specific” and “Certified”.  As part of this process, the airworthiness of the aircraft is established as well, the nature of the operation and any hazards that could be encountered. This ensures that the risk of something going wrong on the aircraft is minimised and that detailed response plans are immediately available to mitigate the effects of any problems experienced.  A document called the “Operating Safety Case” is used to encapsulate all this information.

It is important to note that the vast majority of drones being flown are those that are available directly to consumers. These are often considered to be toys and are therefore not subject to regulation as the the damage they can inflict is very small owing to their small mass. Strictly, any drone that is below 250g in the UK is considered a toy and is not subject to as strenuous regulation as heavier and larger drones.

In order to prevent the possibility of conflict with other crewed aircraft, all large scale drone operations in the UK currently require their own airspace to which they have exclusive access. Whilst this eliminates the risk of conflict, it detracts from the airspace other aircraft are able to fly in and is not a long term solution. As part of this research project, we are investigating the incremental integration of crewed aircraft into the same airspace as drones as the next step to a fully integrated airspace.

Safety features
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