Hovering isn’t difficult if you’re top heavy

Did you know that top-heavy structures are actually far more likely to maintain their balance while hovering in the air compared to those with a lower center of gravity?

According to Jun Zhang, a Professor at NYU’s Courant Institute, the recent findings are indeed counter common perceptions that flight stability can be achieved only through a relatively even distribution of weight – and may offer realistic new design principles for hovering aircraft.

As the Wright brothers demonstrated 100 years ago, the key challenge of flight is maintaining balance.

Yet, while insects took to the air 400 million years earlier, their flight stability remains a mystery because of the complex aerodynamics of their flapping wings.

The NYU researchers approached this enigma by creating experimental conditions required to achieve stable hovering in mechanical flyers.

To do so, they designed a range of pyramid-shaped “bugs” constructed from paper that hover when placed in an oscillating column of air – essentially mimicking the effect of flapping wings. The team then captured the experiment with high-speed videos to analyze the nature of the airflow around the bugs.

To gauge which types of structures best maintained their balance, the researchers created paper bugs with various centers of mass. Top-heavy bugs were made by fixing a weight above the pyramid, and low center-of-mass bugs bore this weight below.

Surprisingly, results indicate that the top-heavy bugs hovered stably while those with a lower center of mass could not maintain their balance.

The team also demonstrated that when the top-heavy bug tilts, the swirls of air ejected from the far side of the body automatically adjust to keep it upright.

“It works somewhat like balancing a broomstick in your hand,” Zhang explained. “If it begins to fall to one side, you need to apply a force in this same direction to keep it upright.”

For bugs, it is aerodynamical forces that provide this stability. Yet, as noted above, the lessons learned from these studies could definitely be put to good use in designing more stable and maneuverable flapping-wing robots.