The Future Challenges and Opportunities of Unpiloted Aviation
Figure 1:
Intel Shooting Star Mini Drone
Summary: In “The Future Challenges and Opportunities of Unpiloted Aviation”, Ahamad Tawsif Chowdhury explores the numerous applications of drones to solve problems in both industrial and domestic settings as well as how this relatively new technology is being developed. In early stages of drone engineering, there have been different types of designs such as fixed-wing drones and rotorcraft drones. These drones are being used in many different fields such as the military, healthcare and entertainment just to name a few. Researchers and engineers are also finding novel ways to enhance drone technology, diversifying their designs and how they are used. This includes innovations such as the constructions of communication networks with drones as well as stepping into biomechanics by taking inspiration from nature for design. However, there are some disadvantages to drones such as their vulnerability to being hacked. Chowdhury discusses how engineers are tackling these issues and pushing the boundaries of drone technology; this new field of “drone craft” engineering could be the solution to many of the world’s engineering challenges.
An
unmanned aerial vehicle (UAV), also known as a drone, is an aircraft or
spacecraft which is controlled without the presence of a pilot on board. This
means that they can be used even when a physical pilot is not available or if
there is significant risk to the pilot’s life - such as in the military - in
which case the drone can be controlled remotely. In her article on space.com,
Elizabeth Howell states that “drones don’t require rest, enabling them to fly
as long as there is fuel in the craft and there are no mechanical difficulties”
Types of Drones
There are two categories that drone can be separated into. Each of these have specific features and functionalities that give them an upper hand in certain situations while also having weaknesses that detriment their performance in other situations. One major property that differs between these two groups is the wing system. It is important to differentiate between wing system and wing design; wing design is the specific attributes of an individual wing whereas a wing system is how a collection of wings are designed to work (or move) together.
One
such system is the fixed-wing system, drones with this wing system are
essentially miniature versions of conventional aircrafts. It is the most
obvious attempt at small scale, unpiloted aviation. An chapter in The Future
of Drone Use defines fixed-wing as “aircraft that use fixed, static wings
in combination with forward airspeed to generate lift”
Figure 2: Raven
being launched by hand
The
Raven was developed in 2002 for the US military with a width of 1.4m and a
weight of 2kg
Fixed-wing
drones can achieve significant speeds in the forward direction but cannot hover
and have more difficulty in yaw motion than other types of drones. Drones can
vary in size. An example of a large fixed-wing drone is the Predator air
vehicle used by the US military which is 27ft (8.2m) long and has a 49ft (15m)
wingspan
Another
wing system is the multirotor wing system which is used by rotorcraft drones.
Rotorcrafts can be defined as “aircraft that use rotary wings to generate lift”
Figure 3:
Amazon Prime delivery drone
Both designs have their strengths and drawbacks and meet the needs of different challenges. Rotorcraft drones are great for the situations that require the ability to manoeuvre with precision e.g. cinematography, intricate delivery routes with sharp turns, surveillance. Fixed-wing drones are more advantageous in long-distance journeys where the flight path is somewhat straightforward such as in long-distance delivery or small-scale model experimentation for large aircraft design. Fixed-wing drones are useful for model experiments because most conventional aircrafts also fly using a set of wings with that same wing system; this system still has numerous variable properties that can change the flight mechanics of the aircraft such as number of wings, wing design, orientation etc.
Rotorcraft – Fixed-Wing Hybrids
There
are also drones that cannot be perfectly described as rotorcrafts or fixed-wing
drones. As Gunarathna and Munasinghe state in their paper on the development of
hybrids, these drones utilise designs from both systems to achieve have
vertical take-off and landing capabilities of rotorcrafts and the long distance
flight advantages of fixed-wing aircrafts
In
the same paper, Gunarathna and Munasinghe use the Sky Scout drone as an example
of great hybrid drone design. The drone is designed as two separate pieces for
each wing system where their respective dynamics are modelled separately. Most
flight manoeuvres are done using either one of the two wing system dynamics so
the separate modelling is ideal as it is much simpler than a combined model.
However, during transitions from one system to the other, there is some
coupling from both systems where moments in the same direction work together;
this isn’t a significant issue as the time taken for transition is quite small
which minimises the disturbance it causes to the drone’s stable flight.
Figure 4:
Motor placement of the hybrid UAV. M1-M4 are the quadrotor motors and M5 is the
pusher propeller. Servo1 and Servo2 are the left and right aileron control
servos whereas Servo 3 and Servo5 are the elevator and rudder control servos
Table 1:
Flight control system components
We
can see that the fixed-wing platform is designed to be aerodynamic. However,
when the four rotor wings are added to the body, its aerodynamic property is
reduced and much more drag can be expected during flight. This is something
that could be improved in future designs – possibly by having the rotor wings
fold onto or into the main fixed-wing body – but was kept in Gunarathna’s and
Munasinghe’s research as its purpose is mainly to test the feasibility of
hybrid drone designs.
Figure 5:
Propeller speeds and resulting quadrotor motion
Figure 6: Flight
transition. Uf is the vertical velocity and the V is the forward velocity
The quadrotor wing system has four controls: throttle, pitch, roll and yaw. These account for the six dimensions of motion during the slow and stable movement of the rotorcraft mode flight. This mode can be used for vertical take-off and landing (shown Figure 6). The transition from rotorcraft mode to fixed-wing mode is initiated by the forward-facing pusher propeller which gives the drone a forward speed that could not be easily achieved by the rotor wings. Then the static wings produce lift so that the drone can be kept at the mission altitude which was achieved during the rotorcraft mode. As the static wings generate more lift, the rotor wings responsible for holding altitude are slowly turned off. Once the drone reaches cruise speed, the rotorcraft system is fully shut down.
The
team conducted multiple flight tests to gain experimental data for a reliable
conclusion. The final flight test started with a hovering altitude of 15m after
which the mode transition was initiated. The drone took 60m to fully change
modes and reach a cruise speed of 13ms-1. Soon after it was brought
back to a hover quite quickly (this final process is not described in detail).
Figure 7:
Graph depicting 3D flight path of final flight test
However, there are some problems during the first transition. Firstly, the altitude of the drone dropped slightly when the rotor wings power was decreasing while the pusher propeller power was increasing. Secondly, the drone requires 60m to fully transition from one mode to the other which is not dissimilar to having a runway like conventional fixed-wing drones. There is also the wider issue of where these drones would be needed as most users require only one of the two wing systems.
This
is one example that illustrates how hybrid wing system drones are very feasible
and could lead to more manoeuvrability freedom; the concept is even being
explored in large military aircrafts such as the Lockheed Martin F-35B which
has video footage online
Drones Inspired by Nature
Drone technology is developing to be more like nature because organic flying machines perform much better than human-made ones.
One
issue with fixed-wing drones is that they don’t have relatively long flight
times and it can be difficult to increase the battery size on the drones. This
led Dr Dan Edwards and others from the US Naval Laboratory to look into how
birds use thermals – plume of warm, rising air – to fly for longer
The
team developed a software called Autonomous Locator of Thermals (ALOFT) which
guides fixed-wing drones to thermals so that they can exploit the upward
movement of the warm air to gain altitude. The effect of using ALOFT is seen in
the flight time of an unmanned SBXC sailplane. Before using ALOFT it flew for 3
minutes, with ALOFT it was able to fly for 5 hours.
Figure 8:
Soaring algorithms like ALOFT can be used to keep unmanned sailplanes flying
for longer durations, a benefit that may improve the kind of surveillance and
reconnaissance data they provide
Another disadvantage of drones is that they can be bulky or
hard to manoeuvre. This is why a group of engineers decided to build a drone
modelled after a bat
Multi-drone Cooperation
A
single drone has many capabilities by itself but multiple drones connected in a
digital network can do much more in terms of surveillance, mapping and
communication. However, there definitely is a limitation in terms of cost;
buying multiple standard drones can be very expensive. To get around this issue,
an article in IEEE Vehicular Technology Magazine discusses how low cost mini drones
can be used for these types of networks to overcome financial obstacles
Due
to their size and limited power supply, mini drones are relatively slow and
have a low load capacity. This means that they are very limited as individuals.
However, their low cost can be exploited as a benefit when they are synced
together. The power consumption of a network of UAVs can be minimised by using
mini drones which do not require a high power supply. For example, engineers at
MIT have designed chips that go on board mini drones to run off only 2 watts of
power
Figure 9:
Engineers at MIT have taken a first step in designing a computer chip that uses
a fraction of the power of larger drone computers and is tailored for a drone
as small as a bottlecap
One challenge that comes from single drone use is that they have to communicate directly to the grounded pilot which means that the link is over a long distance. The researchers have identified that this type of communication leads to high propagation delays as the data has to go from the drone to the ground and then back unlike in a network where it only has to travel to the nearest relevant drone and back. Another weakness in the communication system is that it is volatile, relying on the sole connection between the drone and ground.
One big advantage of a mini drone system is that it extends the range of communication and surveillance from just the range of one drone. As mentioned, the network is more reliable because if one drone or link is eliminated then data packets can be sent to ground via a different route on the network (assuming one is still available). This is of high importance in the context of military use where drones can be targeted or can be easily damaged if caught in crossfire. New drones can be added to an existing network to create new nodes and arcs.
The network can be easily constructed and reconstructed if the need arises. For example, if multiple drones from a certain part of the network are no longer operational then the other drones can reposition – whether physically or on the digital network – to build a new network to get the best efficiency from the remaining drones.
Another
interesting use of drone networks is for entertainment e.g. light shows. Intel
developed a drones called the Shooting Star Drones which are small and compact,
having dimensions of 384 x 384 x 93mm
Table 2:
Intel Shooting Star Drone Specifications and Operational Conditions
Figure 10:
Intel Drone Light Show at The Olympics
From this evidence we can see that drones are capable of
more when they are being used together in a network. However, there are still
weakness in the drones being used for these networks but technology in the
future may lead to mini drones being made to be tougher and more powerful while
keeping their low costs.
Drones in Healthcare
The healthcare sector is one that can
also benefit greatly from drones. Due to the ease of use and minimal size of
drones, as they do not need to accommodate for an onboard pilot, they are
incredibly useful for quick, unplanned transportation. This is particularly
useful in the healthcare industry where supplies need to be sent to wherever
disaster may strike.
A 2017 article in The International
Journal Of Clinical Practice (IJCP) outlines the common uses of
unpiloted aviation in these scenarios:
“Common drone applications in medicine include the provision
disaster assessments when other means of access are severely restricted;
delivering aid packages, medicines, vaccines, blood and other medical supplies
to remote areas; providing safe transport of disease test samples and test kits
in areas with high contagion; and potential for providing rapid access to
automated external defibrillators for patients in cardiac arrest.”
This quote outlines how drones can be
used in transporting many different medical resources and equipment. Most of
the cargo being carried by drones in these medical emergencies are light and
compact enough that a small drone can carry them to their required destination.
Figure 11:
Flirtey is a company that uses drones to deliver food, water and first aid kits
Another interesting point mentioned in
the article is that drones can be used to transport rapid access samples and
test kits to places that have a high risk of infection. In the recent events of
the Corona virus outbreak (also known as COVID-19), drones can quickly
transport test kits to suspected patients so that the threat can be identified
and treatment can be rapidly initiated. Sample transportation is also a very
possible use for drones as “the race is on to develop a vaccine”
As of Saturday 14th March
2020, the COVID-19 situation has reached greater heights and has led
universities to halt lectures and postpone many extra-curricular and student
societal events until further notice of improvements. For example, the
University of Southampton has brought forward the Easter holidays by a week,
cancelled their Varsity 2020, and postponed graduation
We can see from this that the breakout
of a viral infection has forced institutions to take measures to prevent large
numbers of people from gathering. This is because human contact can put healthy
individuals at risk which is why drones would be a much better alternative for
the purposes of delivering goods such as food or medical aid. This is further
reinforced by the fact that the infection rate of this new virus is very high,
starting from the 3rd of March 2020 there has been an increase of
more than 1300 cases in the United Kingdom in the span of 2 weeks
Figure 12:
United Kingdom COVID-19 Cumulative Infection Number
Drones are unpiloted so no pilots are
put in danger of infection when a drone comes into contact with an infected
population. The use of drone technology could be incredibly beneficial to
fighting this novel outbreak and illustrates how they can be designed and
adapted for a wide range of challenges.
Digital Vulnerability of Drones
As drones become more commercialised, new models come out designed specifically for light use. These are often made to be cheap which leads to low digital security. Therefore, these types of drones – especially ones that connect to a controller via Wi-Fi – are quite vulnerable to being hacked. Ottilia Westerlund Rameez Asif assess the security of the Parrot AR Drone 2.0 and the Cheerson CX-10W to investigate ways in which drones can be hacked.
Both these drones operate on open Wi-Fi networks to which multiple users can connect to. This means that the IP addresses of these linked to the two drones can be easily attained and attacks can be made. (Westerlund & Asif, 2019)
The paper outlines a number of possible attacks that can be used to make a drone no longer operational. One of these attacks is the Denial of Service (DoS) method which overloads the Wi-Fi network with pings so that the target drone is overwhelmed by requests and becomes inaccessible. Thus, the drone’s user can no longer send information from their controller.
Another method is the de-authentication attack where the hacker “de-authenticates” the user from the drone and then immediately connects to it with their own controller. The article can be read for more examples.
In
the context of more expensive drones such as those in the military, the use of
blockchain could be a new, secure way of sending encrypted data between a drone
and the ground
We can see that digital vulnerability is a significant issue as it puts a drone into danger of losing connecting with its controller or of being controlled by an unknown, unauthorised user. This is especially dangerous with military UAVs which have more expensive and possible dangerous equipment. However, there is research being done on possible defences such as the use of blockchain.
Conclusion
Drone technology tackles many challenges including limited mobility and security with innovations such as nature-inspired designs, networks, hybrid wing-systems and more. Drones are used in the military, healthcare and entertainment; they are likely going to be more essential our regular technology.
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