UWE Bristol Engineering showcase 2015

Elizabeth Forward
MEng Mechanical Engineering
Project Supervisor
Tushar Dhavale
Variable Pitch Propeller For High Powered UAV Application
Initial Designs
The initial designs were based up the
current mechanisms in industry, not
necessarily only aviation, that are
used to control pitch. The first
concept below is similar to the
hydraulic push-pull rods that are used
in maritime propellers.
The second concept below is based
on a the gearing system seen in a car
differential system. This gearing
system is already used in aviation
industry to control pitch, e.g. geared
pitch control is used on the C130-J
Hercules aircraft.
Stage 1 Design
This was the first major design
iteration that the study undertook.
The design below is the final concept
to emerge from this stage 1 iteration.
It shows a design that is compact and
contained within the main propeller
base plate.
The main rod of the mechanism runs
through the middle of the motor and
it is this rod that would actuate the
pitch control. The mechanism would
work as the rod would be connected
to the propeller blades via offset 3D
universal connectors. Thus
transposing the vertical displacement
to a rotational movement.
However, as the concept had been fully
sketched, it became apparent that the
size of the mechanism rod , a diameter
of 2mm, would not be substantial
enough to support the forces induced
by the working propeller.
Stage 2 Design
Due to the issues uncovered in the
stage 1 design development with the
mechanism rod’s diameter being too
small, it was decided that the actuating
mechanism would be situated below
the motor. This in itself produced a
number of issues such as the increased
total size of the mechanism and the
design of a system that would
incorporate both the motors rotational
movement and the mechanisms
vertical displacement. The final
concept for the design stage can be
seen below.
CAD Incorporated Design
This was the final stage of the design in
which all the previous concept were
analysed and compared in order to
produce the most suitable design. The
final design comparison came down to
two very similar designs and thus a
design comparison matrix was
completed in order to provide a fair
decision in down selecting to the final
design. The final concept, as shown
below was completed in CAD. It uses a
pin and joint system at the attachment
point between the mechanism arms
and the propeller blade to allow for
both the vertical to rotational
movement of the blades pitch change.
Underneath the motor is a bearing
system taken from a skateboard
bearing; this allows the rotation of the
propeller around the stationary motor
and the vertical displacement from the
servo.
Project summary
This project is based on the design of a mechanism
that allows for the adaption of a fixed pitch propeller
into a variable pitch propeller for the application in
high powered unmanned aerial vehicles (UAV’s)
namely a high performance, 3.4m ,radio controlled
gliding wing. The use of variable pitch propellers in
radio controlled aircraft is becoming more common
however, there is not much to be seen of variable
pitch propellers in the high performance sector.
Project Objectives
This study was mainly aimed as a concept design
study for the first year, thus the following points
where see as the main objectives.
o Design Initial Concepts
o Improve and Down Select Concepts
o Select the Final Design Concept
o Theoretically Annalise
o Select Appropriate Material
o Produce a Rapid Prototyped Model
It was decided that the first concept
would be the best option to progress
with . This was due to the size of the
system and thus the gearing system
would be to small to design and
prototype accurately.
Project Conclusion
It was concluded from this first year of the study that,
even though there had been some delays along the
way, that Concept 3C shown as the CAD design was
the most suitable design for the use in the high
performance gliding wing.
It is understood that in the following year, this design
will mostly likely be adapted due to further
information and data that will become available
about the design through more in depth analysis.