How Birds Take Flight With Such Ease
New research breaks down the fundamentals required to smoothly go from perched to airborne.
Ben Parslew听had a problem: His robots weren't very good at jumping.听Parslew,听an听aerospace engineering researcher听and lecturer at the听University of Manchester, studies the mechanics of flight. Along with his research team, he had turned to robots to better understand how flying machines might听be able to launch themselves into the sky like birds. But听while avians seem to effortlessly听become airborne, Parslew's听robots, which were听relatively simple听constructions, didn鈥檛 find it quite so easy.听Some would听flip over in the air and听land upside-down. Others remained stable in the air but jumped in the wrong direction. And still others fell over before they got off the ground in the first place.
Something was clearly not working here. So Parslew and his听team decided they needed to back up and first study how exactly听a bird launches itself into the air.听鈥淭hat was kind of motivation for doing this study, to understand why our robots are failing and why birds succeed with such apparent ease,鈥 Parslew says.听
听conducted听was听published last month in the journal听Open Science. Using computer analysis, the researchers found that when听birds take off, they simultaneously control two motions: the direction they鈥檙e jumping in and the amount they听rotate (pitch) their body as they accelerate, Parslew says.听Such coordination allows them to remain balanced during launch.听
To conduct the听study, Parslew鈥檚 team created computer models using听data from two studies of birds with different takeoff styles: one was led by Pauline Provini, who researches evolutionary biology at the French National Museum of Natural History in Paris, using听, and another was听led by Havalee Henry, now an orthopaedic surgery resident at Yale New Haven Hospital, on听.
"That鈥檚 the kind of approach we took," Parslew says, "looking at birds in nature as a sort of dataset, but then also building our own theoretical models and computational models.鈥
In addition to discovering the importance of pitch and direction, the researchers found听that birds are specially听built for this kind of takeoff because of听a certain sponginess, or cushioning, in their leg joints that lets them extend their听legs for a smooth and fluid movement during the jump.听This extra flexibility听in combination with their jump direction and proper rotation allows for a stable takeoff, he says.听
Diamond Dove taking off.听Video:听Dr. Pauline Provini/Functional Morphology Lab/Mus茅um National d'Histoire Naturelle听
The team听also confirmed that the wings听don鈥檛 contribute at all to the physics of the initial听jump鈥攊t鈥檚 all about the legs. This听can be seen in听Provini鈥檚听video of a Diamond Dove taking off. The bird lowers听its trunk by flexing its legs, and then extends its听hip, knee, and ankle to push the body in the direction of takeoff.
鈥淲hat is interesting is the fact that the wings are still up when the bird leaves the perch,"听Provini says, "meaning that they are not involved in the first propulsion.鈥澨
Parslew鈥檚 modeling also showed that a bird's听ability to grip a perch is beneficial for听taking off: It allows them to launch听at more angles听than when they are standing with their feet on flat ground.听
"The big impact of having a perch to apply torque to is that it means you can jump in many more directions鈥攆rom very shallow to very steep," Parslew says.听"Without a perch you have a much narrower window of jump directions, and if you try anything outside of this window you tip over."听
The听Diamond Doves, for instance,听jumped at angles around 20 degrees shallower than birds with feet that aren't made for gripping, Parslew says.听Contrast that with the Guinea Fowl: With their fee flat on the ground, they have a much more limited range of jumping angles.听听
While this听new research helps scientists understand听bird flight听and takeoff better,听Parslew hopes that听it will also translate to robotics research.听听These findings could make drones more efficient, he says, and听perhaps one day听they will听even be able to perch and take off themselves鈥攚ithout doing any unexpected flips.听
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