19-11-2012, 05:18 PM
Design of an Ultra-Lightweight Autonomous Solar Airplane for Continuous Flight
[attachment=40239]
Introduction
Development of unmanned aerial vehicle (UAV) has attracted the attention
of several agencies and university laboratories over the past decade, due to
their great potential in military and civilian applications.
There are a dozen commercial autopilots (Micropilot, Procerus, etc.) which
combine tiny dimensions, low weight and quite efficient navigation capabilities.
Despite all this, they usually use limited CPU power which restricts the control
of the airplane to classic control methods like separated PID loops and doesn’t
allow the onboard execution of more complex algorithms, for example, those
of image processing.
On the other side, there is a lot of research in Universities in various fields,
such as SLAM4, hardware design, control, navigation, trajectory planning, etc.
But whether they are done on VTOL5 systems or fixed-wing model airplanes,
the embedded system is often over-dimensioned, compared to the airplane
itself, in order to have high computational capabilities and efficient sensors.
Airplane Overview
Mechanical Structure
The approach we chose for the design of the airplane was to combine the
knowledge of aerodynamics engineers and the experience of lightweight model
airplanes designers. The starting point for this design was the model airplane
ofWalter Engel that holds the world record for flight duration of over 15 hours
with 1 kg of battery. Sky-Sailor version 1 is basically a motor-glider with a
structural weight of only 0.6 kg for a wingspan of 3.2 m and a wing surface
of 0.776 m2 (Fig. 1). The resulting total weight including motors, propeller,
solar cells, batteries and controller is around 2.5 kg.
Solar generator, Battery and Propulsion System
As explained in the introduction, one major challenge is the power management
that has to ensure continuous flight over days and nights.
A total of 216 silicon solar cells, divided in three modules, cover an area
of around 0.512 m2. In terms of efficiency, the better choice would have led
us to GaAs Triple Junction cells with efficiencies of 27-28 %, but taking into
account the impact of the weight on the required power for levelled flight, the
better choice is RWE-32 silicon cells with 16.9 % efficiency. Furthermore, the
flexibility of those thin cells is also an advantage for their integration on the
wing.
The cells are encapsulated using a mechanically favorable symmetrical
laminate combined with a fiber glass reinforced plastic coating. This encapsulation
is non-reflective. Thus, we obtain a flexible arrangement easily integrable
on the plane and connectable to the power circuit. At maximum sun
conditions, the available power is 28 W for each module, which makes a total
of 84 W.
Ground Control Station
The control of the airplane is executed onboard but there is a link to a ground
control station through a serial radio modem that allows a baudrate of 9600
bps. The goal is to:
• download and upload airplane and control parameters, but as well the
flight plan, before the takeoff,
• get a visual feedback of the state of the airplane once airborne, modify
flight plans on-the-fly,
• retrieve and record the telemetry for flight analysis, system identification,
etc.
[attachment=40239]
Introduction
Development of unmanned aerial vehicle (UAV) has attracted the attention
of several agencies and university laboratories over the past decade, due to
their great potential in military and civilian applications.
There are a dozen commercial autopilots (Micropilot, Procerus, etc.) which
combine tiny dimensions, low weight and quite efficient navigation capabilities.
Despite all this, they usually use limited CPU power which restricts the control
of the airplane to classic control methods like separated PID loops and doesn’t
allow the onboard execution of more complex algorithms, for example, those
of image processing.
On the other side, there is a lot of research in Universities in various fields,
such as SLAM4, hardware design, control, navigation, trajectory planning, etc.
But whether they are done on VTOL5 systems or fixed-wing model airplanes,
the embedded system is often over-dimensioned, compared to the airplane
itself, in order to have high computational capabilities and efficient sensors.
Airplane Overview
Mechanical Structure
The approach we chose for the design of the airplane was to combine the
knowledge of aerodynamics engineers and the experience of lightweight model
airplanes designers. The starting point for this design was the model airplane
ofWalter Engel that holds the world record for flight duration of over 15 hours
with 1 kg of battery. Sky-Sailor version 1 is basically a motor-glider with a
structural weight of only 0.6 kg for a wingspan of 3.2 m and a wing surface
of 0.776 m2 (Fig. 1). The resulting total weight including motors, propeller,
solar cells, batteries and controller is around 2.5 kg.
Solar generator, Battery and Propulsion System
As explained in the introduction, one major challenge is the power management
that has to ensure continuous flight over days and nights.
A total of 216 silicon solar cells, divided in three modules, cover an area
of around 0.512 m2. In terms of efficiency, the better choice would have led
us to GaAs Triple Junction cells with efficiencies of 27-28 %, but taking into
account the impact of the weight on the required power for levelled flight, the
better choice is RWE-32 silicon cells with 16.9 % efficiency. Furthermore, the
flexibility of those thin cells is also an advantage for their integration on the
wing.
The cells are encapsulated using a mechanically favorable symmetrical
laminate combined with a fiber glass reinforced plastic coating. This encapsulation
is non-reflective. Thus, we obtain a flexible arrangement easily integrable
on the plane and connectable to the power circuit. At maximum sun
conditions, the available power is 28 W for each module, which makes a total
of 84 W.
Ground Control Station
The control of the airplane is executed onboard but there is a link to a ground
control station through a serial radio modem that allows a baudrate of 9600
bps. The goal is to:
• download and upload airplane and control parameters, but as well the
flight plan, before the takeoff,
• get a visual feedback of the state of the airplane once airborne, modify
flight plans on-the-fly,
• retrieve and record the telemetry for flight analysis, system identification,
etc.