|
|
          |
Exulans - A Love Affair with the Birds
The human infatuation with birds has a long history. Our forest-dwelling forebears admired and envied them - after all, birds possess wings to outwit the monkey's two major anxieties: snakes and the fear of falling.
Some of the earliest gods are bird-gods, such as Quetzalcotal, the feathered serpent of the Toltecs. But not all gods are make-believe ...
"In the past hundred years of aircraft development we haven't overcome some fundamental problems," explains Joachim Huyssen, inventor and aerodynamics engineer at Pretoria University. "One of them is our dependence on runways. Our other need to keep the weight as low as possible. If you look at nature, you see the aerodynamic form of a bird differs considerably from modern aircraft . The most notable difference is that aircraft do not have a long tail wing. Neither do they have very specific tail surfaces. If we too can create aircraft that are tail-less, we can create a great mass advantage. Most interestingly, by doing away with the tail, we have the option of developing an aircraft that will be able to land independently of runways."
The earliest flying machines were poor facsimiles of our feathered friends, clumsy mechanical imitations that were just too heavy. As in most love affairs, these initial setbacks made us rather despondent. We turned from the skies to the drawing-board for our inspiration. Aeronautical design departed from mother nature's paradigm. Powerful engines were used to thrust tons of metal into the sky; fixed wings and tails were incorporated into our constructions. Function took the place of form: it worked, but it didn't look pretty.
Human flight is barely a hundred years old. Birds are the product of 85 million years of evolution, so it stands to reason we can still learn a thing or two.
The Exulans plane mimics the albatross by incorporating something called variable wing-sweep, for in-flight control. Just as birds trim their wings for greater stability, so the Exulans, by virtue of a hinge that connects an inner wing to an outer wing, can sweep its wings forward. In this way, it can be trimmed for slower flight without reducing its overall lift.
Professor Edward Matthews from Pretoria University says that with the short landing and take off needs of the Exulans, it will allow the plane access to remote locations where conventional infrastructures like runways are not available.
The Exulans is the brainchild of Joachim Huyssen who conceived it as an undergrad in 1989. Since then it has grown into a major research project within the department of mechanical engineering.
Two years later, flight-testing commenced. First, the structural strength was tested by applying various loads to the wings. Thereafter it was mounted on a trailer test-rig with the freedom to move about on a single axis. Finally, tethered flights were performed using a vehicle mounted test-platform. The success of these tests hastened the next big step: untethered flight.
The fateful day arrived: an altitude launch from a hot-air balloon. All did not go according to plan ...
Joachim Huyssen explained that Exulans 1 was not intended for the full flight programme. They needed publicity for the funding of the project and therefore decided to do the flight. A hot air balloon was chosen as a launch method so that if something did go wrong there would be a parachute on board to save both pilot and hardware. As the glider dropped its tether under the balloon, it went into a negative climb attitude during launch, and the sudden speed build up was too high. The pilot's correction to pull the aircraft out of the dive caused it to oscillate and caused negative wing failure. Fortunately, the parachute deployed successfully and Huyssen and what was left of Exulans I floated safely to the ground.
In the final stage, the team would like to enable an aircraft of this concept to take off without a runway. To do that they would have to add a considerable power plant, but will be looking to do that in the next millennium.
If the Exulans teaches us anything, it's that good technology develops out of dialogue with nature. But then again, paying close attention to your partner is the basis of any successful love affair.
Contacts
|
There is a fossil that goes by a similar name - Quetzalcotalus, a member of the pterodactyl family, that had a wingspan of 12m.This ancient bird has become an inspiration for a new type of aircraft being developed at the University of Pretoria. It called the Exulans - and like Quetzalcotalus, it has a wingspan of 12m, and no tail.
In the field of aviation, this represents a return to empiricism - the recognition that when it comes to flight, the elegance of nature is hard to beat. But it's also hard to copy.
Joachim continues: "We observe birds, and especially in terms of their qualitative aspects of flight, we look specifically at their method of control during take off, flight and landing. One bird that is of particular interest is the albatross - it is regarded as the bird with the highest efficiency. It is a relatively heavy bird with regard to the wing size, although the wing span is quite large but it definitely has the best lift to drag ratio in nature."
It is this innovation that makes short-field landings possible. Until now, only helicopters or Harrier jets have been able to achieve this. The Exulans offers a cheap, elegant alternative.
The first tests were conducted using a scaled-down radio-controlled model. Construction of the first full-scale prototype, a glider called the Exulans I, started in 1993. Made of a carbon fibre composite, it only weighed 65 kilograms!
Undaunted, the team are pressing ahead with the construction of the Exulans II. There will be structural changes to prevent the failure of Exulans I, but the basic shape will stay the same.
