Recent and Future Research for Bird-like Flapping MAVs of NPU Prof. B.F.Song Aeronautics School of Northwestern Polytechnical University

Main point  Introduction  Summary of PY-1  Some Research Developments in Flapping Wing’s Aerodynamics and Mechanism  Fix-wing MAVs developed in NPU  Wing Tunnel and Some Special Test Tools

0 Introduction  In 2000, a research team in NPU (Northwestern Polytechnical University) began to study flight mechanism and make some flight test models of bird-like flapping MAVs  In 2004, a successful flight test mode, called as PY-1, is achieved.

The parameters of PY-1 wing span 100 cm weight 280 g cruise time no less than 12 min flight speed 5-15m/s mission equipment weight 20 g flapping frequency 5~10 Hz flapping angle 64 deg power motor + polymer A clear image about ground objects has obtained by the colour video camera on-board.

 At present, the research team is doing research on the bird-like flapping MAV with 25-50cm wing span and it will be of independent or half-independent flight capacity.

our research plan for flapping wings with no more than 50 cm and the problems to be solved wing span 100 cm mission equipment weight 20 g flight speed 5 ～ 10 m/s cruise time no less than 10 min. flight control radio control present Flapping MAV wing span 25~50 cm mission equipment weight 20 g flight speed 5 ～ 10 m/s cruise time no less than 10 min. flight control independent or half-independent flight capacity future Flipping MAV improving lift and propulsion efficiency of flapping wing improving flapping mechanical efficiency and reducing energy loss improving energy storage ， reducing structure weight ， increasing cruise time increasing flight stability and flight capacity independent or half- independent flight capacity aerodynamics of bird-like MAV bionic flapping mechanism flexible wing techniques Integrated battery and structure Micromation and integrated equipments on board innovate flaping wing MAV or sub-syetems

1 Summary of PY-1 PY-1 prototype

Based on The Aerodynamic Performance Prediction System of Flapping Wing (APPSFW) developed by our research group, the aerodynamic characteristics of PY-1 could be predicted. Aerodynamic Characteristics

V= 7m/s F=8Hz V= 10m/s F=8Hz (a)(b)  Some aerodynamic characteristics of PY-1

V= 8m/s F=10Hz V= 10m/s F=10Hz (c)(d)

principle and prototype of flapping mechanism system  Flapping Mechanism System

 Fabrication and Flight test (a) Designing (b) Laser cutting

(c) Machining (c) Assembling

 In early flight test, the PY-1 could fly at about 30 m height for 10 minutes. the color camera and photo taken in the air

PY-1 in flight

2Some Research Developments in Flapping Wing’s Aerodynamics and Mechanism  Aerodynamics  Aerodynamic Performance Prediction System of Flapping Wing (APPSFW) according to J.D.Delaurier’s aerodynamic model using modified strip theory influence of vortex-wake, partial leading edge suction and post stall is included contributions of sectional mean angle of attack, camber and viscous friction drag are also taken into account

The developed code can calculate the following aerodynamic characteristics of flapping wing in equilibrium flight: average lift average thrust the input power required the propulsive efficiency

 Numerical Simulation of Finite Span Flapping Wings Using Unsteady Euler Equations With the moving grid strategy, a time accurate unsteady Euler Solver based on dual-time stepping method is developed. The developed code is able to calculate the unsteady flow field around the flapping wings in three-dimensional flexible flapping and twist motions as well as to evaluate the lift and the thrust output for different wing motions.

 Investigation of Numerical Solutions of Unsteady Navier-Stokes Equations for Wings at Low Reynolds Number Based on the dual-time stepping method, the unsteady compressible Navier-Stokes equations at low Reynolds is solved. The flow field around a rectangular wing and NACA0006 cross section in the motion of flap and twist is calculated.

 The Investigation of unsteady flow mechanism of airfoil in arbitrary motion at low Reynolds number The flow filed around the airfoils in ups-downs motion, the airfoils in pitching motion and the airfoils in ups - downs /pitching combination motion are simulated and the lift and trust characteristics are investigated, respectively. The influence of frequency, amplitude of airfoil motion is investigated and some conclusion can be drawn from the computational results:

a) The airfoil in symmetric ups- downs motion can produce only thrust b) In the asymmetric ups-downs motion of flap, the larger frequency up and lower frequency down of airfoil can produce significant lift c) The mean angle of attack of pitching airfoil has an great effect on the airfoil’s average lift d) In ups - downs /pitching combination motion of airfoils, the most favorable aerodynamic characteristics is achieved when the phasing between the pitching and ups - downs motion is approximate 90 degrees.

 Study on Principle of Flapping Mechanism  Type 1 This Flapping Mechanism can insure the symmetry of two flapping wings in flapping motion, but it is more complicated and heavier.

 Type 2 The less components lead to lighter weight. The motion of flapping wings is asymmetric, but it shows no problem in practical flight test, because of the high frequency.

 Type 3 designed to make the flapping motion be symmetrical Most simple and light Be of great potential to study further

3 Fix-wing MAVs developed in NPU  developed more than 14 different Fix-wing MAVs  maximum dimension from 40cm to 20cm  flight endurance from less than 3min to more than 15min.  Some of them can carry color video camera and transmit images of the objects back to the ground station.

Pictures Max. Dimension WeightFlight TimePayload 40cm136.4gAbove 15min10g 40cm128gAbove 15min10g 35cm86.4gAbove 5min10g 35cm80.5gAbove 5min10g  The specifications of the Fix-Wing MAVs.

Pictures Max. Dimension WeightFlight TimePayload 30cm75.3gAbove 5min10g 25cm145gAbove 810g 24.5cm65.5gAbove 5min10g 20cm74gAbove 3min- 20cm68.5Above 5min10g

 To demonstrate the developed the Fix-wing MAVs prototypes, a large amount of flight tests have been done.

 Wind Tunnel In NPU, a Low Turbulent Flow Wind Tunnel (LTFWT) has being built to research low Reynolds number flow characteristics of MAVs. Test model of a flexible fixed-wing MAV 4 Wing Tunnel and Some Special Test Tools

lift-to-drag ratio curvelift coefficient curve

drag coefficient curve

 Some special test equipments and manufacture tools force and moment test table of the motor/ propeller combination center of gravity measurement instrument

inertia measurement apparatus laser cutting tool

Thanks a lot !