From the first days of flight, engineers have looked to birds for inspiration when designing aircraft. Most efforts have focused on how they fly, but Ephrahim Garcia at Cornell University in Ithaca, New York, believes birds have a lot to teach us about landing, too. He is designing an aircraft that can land vertically by “perching” like a bird.
The perching plane is being developed to address an enduring problem with uncrewed reconnaissance planes: they find something interesting to look at but can’t inspect it properly because they don’t have enough fuel to keep flying over the area for any length of time, and so have to return to base. “If you could land the plane on the edge of a nearby building you could continue surveillance of an area, keeping that very useful asset out there,” says Garcia.
“If you could land the plane on a building you could continue surveillance”
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Since runways are hard to come by on the tops of buildings, an uncrewed aircraft would have to land vertically. Existing vertical landing craft, such as helicopters or Harrier jump jets – which use variable-swing jet exhausts – are too heavy and require too much fuel to make them suitable for pilotless surveillance.
Instead, Garcia believes that by mimicking the way birds come in to land, he can bring an aircraft to a gentle stop using aerodynamics alone. Birds can manoeuvre in ways irreproducible by conventional aircraft because they can dramatically alter the position of their bodies, says Garcia (Journal of Aircraft, vol 5, p 1386). When a bird wants to perch, it flares its wing feathers, angling them against the airflow, then does the same with its tail feathers as it lowers them. This configuration produces as much drag as possible, Garcia says, slowing the bird enough for a safe touchdown.
When Garcia’s plane is preparing to land, the wings rotate upwards to force the fuselage down, creating strong drag (see Diagram). The tail extends away from the body on a long boom, which is articulated so the tail can droop down to provide varying degrees of drag as it moves.
Once landed, the aircraft would not be able to take off again, but would remain perched on the building taking pictures for as long as required.
The idea has shown promise in wind-tunnel tests on models, but work is still at an early stage. “The tough part is morphing the aircraft so it doesn’t stall, otherwise we lose control,” says Garcia. “And bringing the tail down too quickly results in a tumbling plane.” The big test will come in December, when Garcia is planning to fly a perching plane with a 2.5-metre wingspan. He has yet to decide what kind of undercarriage the plane will land on. “It might have spikey feet, like a bird, with vibration-absorbing legs,” he says.
Using the tail to switch from flight to perching is a nice idea, says Ron Fearing, a specialist in bio-inspired flight at the University of California, Berkeley. “Being able to provide this manoeuvrability to an aircraft is a very challenging problem,” he says.
