Mitigating the Effects of Atmospheric Turbulence:

Toward More Useful MAVs

AOARD‑08-4061

Simon Watkins, Mujahid Abdulrahim*, Cees Bil, RMIT University, Australia*University of Florida, USA

Contact; simon@rmit.edu.au

Mitigating the Effects of Atmospheric Turbulence:

Toward More Useful MAVs

AOARD‑08-4061

Simon Watkins, Mujahid Abdulrahim*, Cees Bil, RMIT University, Australia*University of Florida, USA

Contact; simon@rmit.edu.au

The Challenge: Maintain Steady MAV Flight in Atmospheric Turbulence

The Challenge: Maintain Steady MAV Flight in Atmospheric Turbulence

MAVs will gain information when there is no direct line of sight, thus willmainly be used in cities, or other complex terrain, where ambient turbulencelevels are high. The above depiction illustrates potential roll and pitch inputsthat natural fliers have evolved to cope with, but which remain a significant challenge to MAVs, particularly as their scale reduces. Note:

• A standard size person (presumably with standard size lungs)• Complexity – significant changes in small distances• Vorticity (especially at top, 1/3rd from start and at end)

Overall Objective: Pursue passive and active strategies to reduce the disturbances to MAVs when flying in turbulent wind environments as found close to the ground in complex terrains.

Methods: Utilise prior outdoor measurements to replicate turbulence in tunnels of varying sizes and perform two types of experiments:

1) Fundamental fluid-mechanic experiments, measuring dynamic forces and pressures on airfoils

2) Flying experiments, where piloted, instrumented MAVs are flown in a large scale flying facility whilst measuring MAV motions, control inputs and upstream flow conditions

Overall Objective: Pursue passive and active strategies to reduce the disturbances to MAVs when flying in turbulent wind environments as found close to the ground in complex terrains.

Methods: Utilise prior outdoor measurements to replicate turbulence in tunnels of varying sizes and perform two types of experiments:

1) Fundamental fluid-mechanic experiments, measuring dynamic forces and pressures on airfoils

2) Flying experiments, where piloted, instrumented MAVs are flown in a large scale flying facility whilst measuring MAV motions, control inputs and upstream flow conditions

Facilities and EquipmentFacilities and Equipment 2x3x9m Tunnel, replicates small-scale

turbulence via grids to ~14% intensity for fluid-mechanic measurements on airfoils and MAVs

Flight test tunnel, replicates large-scale turbulence up to ~25% intensity for flying MAV experiments, with photogrammetry & real-time upstream flow documentation

Micro dynamic force balance (MDFB), flight data loggers, 4 robust turbulence probes, velocity & pressure transducers fixed wing and rotary MAVs, (various scales)

2x3x9m Tunnel, replicates small-scale turbulence via grids to ~14% intensity for fluid-mechanic measurements on airfoils and MAVs

Flight test tunnel, replicates large-scale turbulence up to ~25% intensity for flying MAV experiments, with photogrammetry & real-time upstream flow documentation

Micro dynamic force balance (MDFB), flight data loggers, 4 robust turbulence probes, velocity & pressure transducers fixed wing and rotary MAVs, (various scales)

MDFB Probes Flapping MAV on MDFB

Time-Averaged -Cp DistributionTime-Averaged -Cp Distribution

Turbulence=1.8%

Turbulence=6.2%

Turbulence=12.8%

Suction surface pressure distribution as a function of incidence

Data obtained from central span chordwise pressure taps on 1.9% thick, 2:1 AR SLS aerofoil with integral pressure taps. Suction side results only – colour indicates amplitude of negative Cp

Effect of increasing ambient turbulence level is shown to delay the onset of stall, and reduce separation

Pressuretap locations

Standard Deviation Cp DistributionStandard Deviation Cp Distribution

Turbulence=6.2%

Turbulence=12.8%

Standard deviation gives a indication of the magnitude and location of the transient flow region, such as flow separation and reattachment zone. Note change in scaling of amplitude

The effect of increased turbulence is to keep this location closer to the leading edge, and to increase its intensity

Turbulence=1.8%

α=2°

α=6°

α=8°

α=10°

α=12°

Turbulence = 1.8% Turbulence = 14%

Spectrograms reveal effects of turbulence on laminar separation bubble

Flying ExperimentsFlying Experiments Tunnel top section configured to

replicate IAS of 8m/s into a light wind, city conditions as well as smooth flow (bottom picture) in car test section

Attempting steady flight, on-board logging of 6 DOF and control inputs in smooth and turbulent flow

6 video cameras with reflective markers on MAVs for photogrammetry

Upstream velocity (u,v,w) measured simultaneously at 4 spanwise locations at 1250Hz

Fixed wing MAVs and 3 scales of rotary wing

Parametric variation of span, CG location, MOI and mass

Tunnel top section configured to replicate IAS of 8m/s into a light wind, city conditions as well as smooth flow (bottom picture) in car test section

Attempting steady flight, on-board logging of 6 DOF and control inputs in smooth and turbulent flow

6 video cameras with reflective markers on MAVs for photogrammetry

Upstream velocity (u,v,w) measured simultaneously at 4 spanwise locations at 1250Hz

Fixed wing MAVs and 3 scales of rotary wing

Parametric variation of span, CG location, MOI and mass

Flight test videosFlight test videos

See www.project240.net/mav_turbulence See www.project240.net/mav_turbulence

Comments Comments Fixed wing - low pilot

workload in smooth flow, high in turbulent (C-H*: 5-10), frequent terminal departure, highest sensitivity in roll

Rotary wing - high pilot workload under smooth flow, only small increase in turbulent flow (C-H: 3-4), all successful landings, lowest sensitivity in roll

Parametric studies, flapping and active control– ongoing research

Fixed wing - low pilot workload in smooth flow, high in turbulent (C-H*: 5-10), frequent terminal departure, highest sensitivity in roll

Rotary wing - high pilot workload under smooth flow, only small increase in turbulent flow (C-H: 3-4), all successful landings, lowest sensitivity in roll

Parametric studies, flapping and active control– ongoing research

*Cooper-Harper rating – used to evaluate handling qualities of aircraft

Future PossibilitiesFuture Possibilities Further dynamic surface pressure and force measurements on

airfoils to understand physics and flight inputs and as

potential inputs for gust alleviation (feeling the air) Flying instrumented birds and insects in conjunction with

Oxford Flight Group to gain insight in to natural mechanisms for gust alleviation.

Fixed vs rotary vs flapping - efficiency and gust response?

Further dynamic surface pressure and force measurements on airfoils to understand physics and flight inputs and as

potential inputs for gust alleviation (feeling the air) Flying instrumented birds and insects in conjunction with

Oxford Flight Group to gain insight in to natural mechanisms for gust alleviation.

Fixed vs rotary vs flapping - efficiency and gust response?

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