What makes a fly,fly

How does an insect fly,Bird and airplane wings are curved on top and flat at the bottom,due to which air that flows over the wing is faster than air that flows below the wing. In insects,the wings are flat and corrugated,but can cut the air at much higher angles,thus enhancing the flow over the wing. The difference between the air pressures on either side of the wing creates a force called lift,which propels the insect upward and forward. However,as Cambridge University zoologist Charles Ellington found,insect flight defies the laws of traditional aerodynamics—the lift produced by insect wings is less than half of what is aerodynamically required to lift the weight of the insect,Ellington found. “Unlike birds,which can glide or flap their wings slowly to fly,insects must flap hundreds of times per second (they have extremely fast muscles in the thorax for this) to generate enough force to stay airborne. The smaller you are (the length of an average insect is 4-5 mm),the faster you must flap,” says Sane.

In a 1999 paper in Science magazine,Michael Dickinson,at the Department of Integrative Biology,University of California,Berkeley,and his associates,including Sane,report that insects use what’s known as ‘delayed stall’—flapping wings rapidly during upstroke to create a curling vortex of air and low pressure above the wing—to propel themselves upward,and that they also rotate and change the direction of the wing in the middle of a flap to fly even higher. As Dickinson et al write,‘The wingstroke of an insect is typically divided into four kinematic portions: two translational phases (upstroke and downstroke),when the wings sweep through the air with a high angle of attack,and two rotational phases (pronation and supination),when the wings rapidly rotate and reverse direction.’

Insects have an incredibly quick response system. “They see the world differently. For instance,if you put an insect under a standard light bulb,it will see the bulb blink like disco lights. The frequency of the bulb is 50 Hz,which means it turns on and off 50 times a second,and this is something the human eye does not notice,but the insect eye does,” Sane says. In a 2007 paper in Science magazine,Sane and his former colleagues at the Department of Biology,University of Washington,Seattle,conclude that while some insects may use vision to stabilise flight,they also have halteres and antennae that detect gyroscopic forces and send information to the nervous system,thus enabling rapid course control. Playing a high-speed video of a fly performing complex aerial manoeuvres to alight on a glass,Sane notes that unlike fixed-wing aircraft which must ramp up to a certain speed before they can take off,insects can take off from a static position. “The fact that insects have a high degree of course control has made engineers interested in making flapping-wing robots,” says Sane,who has made a robotic fly flap in oil to emulate insect flight. ‘There can be applications in the defence sector and for surveillance. These robots can reach places where fixed-wing planes cannot.’

KR Sreenivas,a professor at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR),Bangalore,studies insect flight from an engineering point of view. In a project funded by the Department of Science and Technology,Government of India,and the Air Force Office of Scientific Research,US,Sreenivas and his team at JNCASR work on developing efficient theoretical and experimental models of micro air vehicles that emulate insect flight. “Amateurs and research teams have already developed many battery-powered prototypes,but most of them can fly for just 10 or 20 seconds at a stretch and carry only very light cameras and equipment. Our lab tries to improve the endurance and load-carrying capacity of such vehicles,” says Sreenivas. Among the optimisations Sreenivas has come up with is asymmetric flapping of wings—that is,the time taken to execute a downstroke is less than the time taken to complete an upstroke. “When the ratio between time taken for downstroke and upstroke is 0.7,we find that it leads to a dramatic difference in the flow field,generating additional lift,” he says,adding that there are other ways,such as incorporating hinge joints in wings,to improve the performance of a small flapping vehicle.

At the aerospace research consortium at the Indian Institute of Science,Bangalore,which includes Wipro,Boeing and HCL,Ramachandra Budihal,a software architect with Wipro,says micro air vehicle development is still at a nascent stage. “Advances in nano-technology are needed to maintain SWAP (size,weight and power) ratios in such small machines. As I see it,it will be another five or six years before you see real world applications of insect flight,” he says.

Meanwhile,you can always watch the Star Wars Wookiees buzz about planet Kashyyyk in their fluttercraft.