Peregrine Falcons Inspire New Thermal Soaring Strategy for UAVs

This post describes how pilots and birds exploit thermals (rising columns of air) to reduce the energy required to stay airborne.  Designers of unmanned aerial vehicles (UAVs) are particularly interested in exploiting thermals due to the limited amount of fuel that UAVs can carry.

Glider pilots tend to follow a set of simple rules developed by Helmut Reichmann that involves flying the glider in a spiral that tries to stay within the thermal.  Although effective if the thermal is well structured, the Reichmann rules are less useful in turbulent conditions.  More sophisticated approaches have been developed but these require significant computing power making them unsuitable for UAVs.

A team lead by Zsuzsa Ákosat at the Eötvös University in Hungary has been studying the flight of peregrine falcons using video and GPS tracking.  Rather than trying to maintain a consistent spiral, peregrine falcons constantly change the direction of their spiral.  Simulations suggest that this strategy allows the falcons the search the thermal 'space' more efficiently, especially when thermals are small (radius of 100 to 200 meters).  The strategy also works well even in turbulent conditions.   

Further work is underway to determine the magnitude of improvement over Reichmann's rules and the conditions under which this strategy is optimal.  The strategy appears to be computationally simple but the exact algorithm used by the falcons is still under investigation.  The paper lists a number of anatomical features of falcons that may also provide significant advantages over the way UAVs are currently constructed. 

This paper is intriguing not only in identifying a new soaring strategy by studying peregrine falcons but also in the extensive analysis of this strategy that allowed the researchers to better understand the context in which the strategy applies.  This should help UAV designers to better understand the principles and test whether they have been able to successfully apply the principle.

Abstract: Thermal soaring saves much energy, but flying large distances in this form represents a great challenge for birds, people and Unmanned Aerial Vehicles (UAVs). The solution is to make use of so-called thermals, which are localized, warmer regions in the atmosphere moving upwards with a speed exceeding the descent rate of birds and planes. Saving energy by exploiting the environment more efficiently is an important possibility for autonomous UAVs as well. Successful control strategies have been developed recently for UAVs in simulations and in real applications. This paper first presents an overview of our knowledge of the soaring flight and strategy of birds, followed by a discussion of control strategies that have been developed for soaring UAVs both in simulations and applications on real platforms. To improve the accuracy of simulation of thermal exploitation strategies we propose a method to take into account the effect of turbulence. Finally we propose a new GPS independent control strategy for exploiting thermal updraft.

Comments: 19 pages, 11 figures
Subjects: Biological Physics (; Other Quantitative Biology (q-bio.OT)
Journal reference: Zsuzsa \'Akos et al. 2010 Bioinspir. Biomim. 5 045003
Cite as: arXiv:1012.0434v1 []

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