UWE Bristol Engineering showcase 2015

Max Wright
BEng – Mechanical Engineering
Project Supervisor
Dr Jason Matthews
Conceptual Design of a UAV for Non-Civilian Operations
Introduction
Currently in use by the British Army to combat the global war on terror is the
Desert Hawk 3 (DHIII), an Unmanned Aerial Vehicle developed in 2006 by
Lockheed Martin. The DHIII is designed to be a portable, hand launched and
skid recovered, versatile surveillance device with changeable payloads. This
device was an update to the original Desert Hawk carried out by the Skunk
Works team at Lockheed. The original was heavier and could stay in the air
for thirty minutes less than the DHIII.
The DHIII’s use in Afghanistan has primarily been reconnaissance, providing
eye in the sky surveillance and situational awareness. Used by artillery units,
often in Forward Operating Bases, their purpose is base security, the support
of infantry patrols and target acquisition for artillery and air strikes. They can
be a vital weapon in a units arsenal and can change the tide of a battle;
knowing an enemies whereabouts and movements is key to success in
combat.
Problems With The Desert Hawk 3
Upon communication with a British Army Royal Artillery Unit some problems
were indentified:
•It can't be used in rain
•It can't be used in fog
•It becomes unstable in winds over 15 knots
•It struggles in temperatures below -5 and above +50
•The endurance can be reduced when the batteries are affected by heat
damage
Modeling
A desert Hawk 3 model was constructed on SolidWorks:
Airfoil Selection
The program Xfoil was used to determine an appropriate airfoil . This
program produced 2D coefficients of lift and drag at various angles of attack
(AOA) for 3 selected airfoils, NACA 2412, NACA 6412 & NACA 8414.
Cl/Cd
120
100
80
60
40
20
0
Cl/Cd vs AOA
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
AOA
NACA 2412
NACA 6412
NACA 8414
After NACA 8414 was chosen, wing parameters were decided upon and 3D
lift values were determined . Once appropriate parameters were selected
SolidWorks models were constructed for the improved design. The
subsequent design the Marsh Harrier I.2 is shown below.
Flow simulations were conducted applying side winds to the two UAVs to
determine displacement and head wind to determine lift and drag values,
the data gathered was analyzed. The pictures below detail a contour plot and
flow trajectories for the DHIII simulation.
Project summary
To determine a solution to the problems,
weight was added through the changing of
materials and the adding of heavier and
more powerful engine. Airfoil selection was
conducted using Xfoil and wing geometry was
decided upon.
Project Objectives
The objective of the project was indentify one
or more problems with the Desert Hawk 3
Unmanned Aerial Vehicle and work to find a
solution. The negatives with the UAV were
determined to be its susceptibility to wind
and wet conditions.
Project Conclusion
In conclusion the project was a success in that
it provided a solution to the designated
problem. Engineering methods were
employed using theoretical and experimental
calculations to detail the difference in
displacements when adding weight to the
UAV. Although there were other options
adding weight to the UAV proved most
feasible given the limited information
accessible.
There are many further improvements that
would be applied to the design if it were
being taken further, firstly symmetrical airfoils
for the tail would be selected to provide
stability. Further work would be conducted to
improve the design of the wing likely tapering
them towards the ends to reduce induced
drag produced at the tips. Manufacturing
processes would be studied to indentify the
most appropriate technique to apply in order
to provide the best product.