Introduction
At  Sydney University, current research in Unmanned Aerial Vehicles (UAVs) has produced promising results towards the development of fully autonomous capabilities.  Previous experience with instrumented UAVs include the experimental KCEXP series UAVs, and the UAV Ariel.  An aircraft currently being operated is the UAV named Brumby.  Like its namesake, it is designed to operate in rugged environment.  Being developed primarily to provide a flight research platform in support of various research activities, UAV Brumby is also used to enhance skills in airframe design and fabrication, instrumentation, flight control systems, and operational aspects of UAVs.  It forms the basis of a technology demonstrator for many aspects of aeronautical engineering.  Current UAV related research activities include the following:

• Wind-tunnel and flight based experimental research in aerodynamics and flight performance;
• Modelling of engine/propeller performance and aircraft stability characteristics;
• High fidelity aircraft model development for simulation based control system validation;
• Trajectory optimisation and autonomous guidance for unmanned aircraft;
• Sensor fusion strategies for state estimation using multiple redundant sensors, including Global Positioning Systems (GPS);
• Using GPS for aircraft attitude determination;
• System Identification methods and neural networks for fault detection and reconfiguration;
• Robustness analysis of control laws in the presence of uncertain dynamics and wind gusts;
• Robust nonlinear high-performance manoeuvre tracking for autonomous aircraft;
• Autonomous launch and recovery of a UAV;
• Terrain Following and Terrain Aided Navigation;
• Integration of available UAV technologies into operational systems;
• Real-time fight control software synthesis; and
• Design and fabrication of airframe components using advanced composite materials.

Experimental Systems Overview

Flight Platforms
The flight platform is a delta wing unmanned aerial vehicle, designed with a standard dual fin, pusher propeller configuration.  It employs an extremely modular construction for simple and cost effective manufacture, as well as high maintainability and damage recovery.  Already prototyped as a multi-purpose flight research vehicle, it has been demonstrated as a stable flight platform well suited to flight navigation research.

The vehicle is designed to fly in excess of 100 knots and currently has an endurance of 1/2 to 1 hour flight time.  The aircraft has the capacity to carry up to six kilograms payload when remotely piloted, or four kilograms when operated autonomously. Furthermore, the maximum design weight will be extendable by an additional 3-5 kilograms once the initial flight test program is complete.  This is initially constrained to keep within the Australian Civil Aviation Orders Part 95.21, relating to model aircraft which permits a maximum Operational Empty Weight (OEW - that is maximum take-off weight minus fuel) of 25 kg.  Previous UAVs operated by the research group have been flown outside these regulations (maximum weight of 36 kg), requiring a Civil Aviation Safety Authority (CASA) Australia Permit To Fly.  The group has also flown UAVs within controlled airspace with the co-operation of CASA and the Federal Airports Corporation (FAC), and is working with CASA to formulate new regulations specifically for UAVs.  Hence, there is growth potential for the proposed airframes.

The payload bay runs the length of its 1.5m tubular fuselage with two interchangable areas allocated for sensor payloads (approximately 300x220x200mm each), and a possible third area within the nosecone.  This should accomodate most airborne sensor packs while being shielded from the flight critical electronic equipment located at the rear of the aircraft.  Initially, up to approximately 200 watts of electrical power will be available for the sensor payload.

Primary Navigation Sensors
The aircraft will be equipped with a coprehensive flight instrumentation suite that allows the implementation of a stability control system for navigation way points. This includes;

 Sensors:

•     3-axis rate gyro and 3-axis accelerometer set
•     angle-of-attack/angle-of-sideslip/airspeed probe
•     aircraft attitude reference sensor
•     control position transducers
•     1-4 GPS units for position/velocity/attitude reference

Actuators:
    Control over 12 (or more) actuators for flight controllability, guidance, and for operation of on-board equipment.

All primary control and navigation equipment will be boxed into line replacement units for fast turnaround, and will be individually shielded against any EMI that may be created by the payload.  To maintain overall systems safety, it will be an initial requirement to prevent any interaction between the onboard payload sensors and the primary navigation system.
 

Experimental Methods

Test Site
Requirements:
 Airstrips:
         strip requirement: grass/dirt 300m
         2 or 3 airstrips for all wind utilisation

 Ground units:
        Real-time computer ground stations to report a/c position, attitude, speed, and altitude of all flying aircraft, and payload status.

        Remote control pilot(s) for flight test program, for remotely piloted take-off and landing,
   and advanced manoeuvering.

The initial tests will be carried out under the model aircraft category ( < 25kg OEW) to avoid regulatory contstraints.  When the aircraft has accrued 20+ flying hours on-site, the aircraft's payload weight will be increased, and the appropriate authority will be sought to achieve fully autonomous flight capability.
 

Flight Testing Procedures
During the initial phase of the program, one aircraft will be operated on a number of consecutive flights to collect data.  To improve reliability, it is planned to then have 3-4 airframes on flight rotation to account for possible maintenance difficulties, and improved turn-around time.

Each flight will be nominally carried out by a remote control pilot, (on standby if flight is autonomous), and a ground engineer, who is responsible for monitoring the aircraft status via the ground stations, and providing advice to the R/C pilot.

Additional crew may be required to operate and collect data from additional sensory equipment that is telemetered separately from the primary flight control system. However, this requirement should diminish over the course of the test flight program as the data acquisition process becomes automated.
 
 
Current Rapid Prototype Delta UAV Brumby (#1 and #2)

3-view of prototypes #1 and #2 – undercarriage and bump stop not shown
 

The fuselage is constructed with sandwich composite of fibreglass/Nomex which results in a very stiff, strong and light structure. The wings are foam cores sheeted with aircraft plywood and fibreglass. The fins are foam core sheeted with balsawood. Investigations are underway to build tooling for fibreglass/Nomex composite wings and fins to facilitate a higher maximum Take Off Weight (TOW) and a small production run.

The aircraft is currently piloted remotely via a JR10SX, a 10 bit pulse code modulated system with ten control channels available. Servo actuators are JR 4721 rated at 8.6 kg-cm of torque. The aircraft has dual onboard receivers to provide redundancy, each with its own battery pack, switch harness and wiring loom. One receiver controls the inboard elevons, throttle and the left fin's rudder. The other controls the outboard elevons, the right fin's rudder, nosewheel steering and engine cutoff. The aircraft can be flown on either set of controls.

The Zenoah 74 cc engine has a built in spring starter to facilitate easy starting. The magneto ignition is very reliable and is lighter than many electronic ignition systems. The fuel is 90% petrol, 5% synthetic oil and 5% nitro methane. Currently two 1.2 litre tanks are located on the aircraft cg (centre of gravity). An optional 3.8 litre (1 gallon) tank is available.

Avionics power is currently provide by a 12 V 6.5 ah gel cell. This is soon to be replaced with a lithium ion battery which will result in a weight saving of 1.0 - 1.8 kg (depending on product availability). An alternator is currently being developed to provide up to 200 Watts of power and to reduce battery weight for extended flights.

The fuselage has two rails which contain captive nuts for the bolts which hold the four payload trays in place. Currently the payload trays are constructed from 4 mm plywood. Composite payload trays are under construction. All trays are 220 mm (8.66") wide. Trays #1 and #2 (the front two) are 300 mm (11.81") long each and are presently unoccupied and available for payload. Tray #3 is 400 mm (15.75") long and carries the fuel tank, onboard remote control receivers and associated electrical systems. An inertial navigation unit is intended to be mounted here also. Tray #4 is presently allocated for the onboard flight computer and associated flight sensors.
 

Increased Gross Weight (IGW) Version UAV Based on UAV Brumby

Animated Solid CAD Model of UAV Brumby Mk. II (844KB)

Proposed changes:

• 3W-120 cc engine
• Moulded wings and fins

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