INGENIEUR
Systematic Design Process
Figure 2 shows a typical design process of an
aircraft including a UAV being adopted by an original
equipment manufacturer (OEM). Feasibility studies
are conducted to propose suitable configurations
of the UAV to meet the end-user’s requirements,
scope of supply, operations and other demands. At
the same time, the proposed design must comply
with airworthiness requirements and other flight
safety requirements.
The flight control and autopilot designs are
very important systems of the UAV to ensure the
fulfilment of its flight missions, precise waypoints
and navigation control. Figure 3 shows how the
flight control design is being implemented in the
conceptual, preliminary and detail design phases.
This flowchart shows the steps required to
assist in the design of a control system that will
give good flight responses and precise tracking of
the UAV’s motions, manoeuvrability and waypoints
guidance and control. The aerodynamics, stability
and control derivatives are required to evaluate
the UAV’s responses which initially could be
estimated using semi-empirical methods and
computational fluid dynamics (CFD). However, the
measurement of the aerodynamics, stability and
control derivatives of the UAV using wind tunnel
testing is more reliable and accurate. As such the
wind tunnel test of the airframe is simply a must in
the overall design of UAVs.
In the stability and control analysis, the UAV
should be able to be trimmed under normal flight
conditions for all flight cases within the required
performance envelope (i.e. at various speeds,
altitudes and g-loads within the envelope). The
open-loop response (i.e. inherent stability) for all
flight cases must be well analysed because the
flight control strategy has to be designed based
on the UAV’s open-loop responses. Then, the
Stability Augmentation System (SAS) is introduced
to ensure stable flight in adverse flight conditions,
such that it would achieve good control responses
(i.e. Level 1 flying qualities). Once the transient
response of the UAV has been improved using
SAS, the Command Stability Augmentation System
(CSAS) is designed to meet the demand or target
position within acceptable steady-state error
when the flight is disturbed from its programmed
paths and flight conditions. Finally, the autopilot
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system is designed to ensure the UAV is able to
maintain its position and waypoints accurately. A
stable UAV will return to its original waypoints if
being disturbed by turbulence or wind gusts. But
the ability to follow the programmed commands
depends on the sensitivity and stability of the
UAVs.
System Integration and SIL/HIL Testing
The overall design process for system integration
and testing are shown in Figure 4. There are
two major phases (circled by the dotted lines),
which are the design process and flight testing.
The intersection between those two boxes is the
activity for parameter tuning of the control system
which involves software-in-the-loop (SIL) and
hardware-in-the-loop (HIL) simulation activities. It
is a process where the aerodynamics, stability and
control of the airframe are simulated with software
and hardware integration.
In flight testing, the auto stabilizer performance
based on the SAS and CSAS design is tested and
evaluated. The other systems such as Airborne
System, Ground Control System (GCS) and Flight
Safety System that are being integrated into the
UAV system must also be tested together during
the flight testing. The final outcome of the design
process plus the SIL/HIL testing will be a well-
designed UAV prototype. This design process could
be used as a guideline especially for UAVs that are
classed as more than the micro UAVs, such as the
long range to high altitude long endurance UAVs
and also for tactical and combat UAVs (TUAV and
CUAV).
In addition, a well-documented design process,
analysis and testing is useful for UAV certification.
Furthermore, the documents could be used in the
future as design references and databases for
further developments of UAVs.
Issues and Challenges Facing the
Malaysian UAV Industry
Figure 5 shows the life-cycle of a UAV with respect
to design and build, certification, operation, and
service and maintenance. If we procured UAVs
from a supplier, apart from the cost of the UAV