Design of unmanned aerial vehicles
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Επίσκοπος, Ιωάννης
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Abstract
Contrary to conventional aircraft design, the design of Unmanned Aerial Vehicles
(UAVs) with Vertical Takeoff and Landing (VTOL) capabilities lacks a standardized,
coherent methodology of development. This thesis aims to develop such a methodology
for two different configurations and apply it for numerous unmanned aerial vehicle
instances of various scales, purposed for aerial firefighting. A literature survey on
firefighting aircraft and VTOL UAVs indicates that the water quantities required in
firefighting correspond to aircraft of significantly greater size than any non-military
drone. The survey also shows that the basis of firefighting aviation is the ability of
heavy cargo transport.
These observations function as guidelines for the early conceptual design procedure
called “sizing”. Sizing refers to the use of mission requirements and statistical data on
existing aircraft to approximate the aircraft’s weight and size. The procedure is
conducted on three scales of each configuration, for payload capacities that collectively
range from 100 to 2,000 kilograms. Elements from conventional airplane and helicopter
design are combined to initially produce a total of six VTOL, firefighting UAVs of
various sizes that use a plethora of propulsion systems.
The configurations studied and sized are the tail-sitter and the multicopter. Tail-sitters
are fixed-wing aircraft capable of hovering vertically, with their tail facing the ground,
hence their name. Multicopters are rotorcraft powered by more than two lift-generating
motors.
The sizing of the electric multicopters results in an extreme scaling rate with respect to
endurance, which is confirmed by a direct comparison of a petroleum-powered and an
electric large-scale multicopter with the same mission requirements. A brief literature
survey reveals that the low energy density of batteries compared to hydrocarbons is the
main explanation. Our attempt to further upscale the multicopters for improved
firefighting capacity produces a 27-ton quadcopter matching the capabilities of the S 64 Aircrane heavy-lift helicopter.
Each VTOL configuration has its own inherent issues requiring attention. The tail-sitter
configuration instigates stability problems during flight, takeoff, and landing, which
directly affect tail size and landing gear placement. The multicopters’ entirely vertical
operation is highly energy consuming, leading to increased weight.
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Keywords
Tail-sitter, Vertical takeoff and landing, Unmanned aerial vehicles, Multicopters