Conventional Aircraft Modified And Programmed With
Characteristics Of Possible Future Airliner
The German Aerospace Center has been performing flight tests to
simulate and study the flight characteristics of large 'flying
wing' configurations to prepare for future aircraft designs. These
have been tested and evaluated using DLR's ATTAS (Advanced
Technologies Testing Aircraft System) research aircraft.
DLR ATTAS Aircraft
Although the pilot is flying an aircraft resembling a small
passenger plane, it feels like he is sitting in an aircraft with
the fuselage and wings blended into a single entity. In addition to
conventional mechanical flight controls, ATTAS is also equipped
with an electrical flight control system. This allows the
researchers to intervene in the flight control system using special
hardware and software and give ATTAS the flight characteristics and
performance of an entirely different aircraft.
"With its special control technology, ATTAS can behave like
other aircraft while in the air," explains Dirk Leisling, a
researcher at the DLR Institute of Flight Systems. "This gives us
the opportunity to simulate aircraft that do not even exist yet,
and to see where we still need to make improvements."
Artist's Rendering Of Flying Wing Aircraft
First, the aircraft simulation is created using a computer,
where a mathematical model defines the dynamic behaviour of the new
design. This is transferred to the flight control system of ATTAS.
The pilot can then test and evaluate the performance of the new
aircraft design first hand under real flight conditions. ATTAS is
capable of simulating not only 'standard' airplanes, but aircraft
with an entirely different aerodynamic design as well. The 'flying
wing' configuration is a very promising concept for future
airplanes. Flying wings are aircraft resembling fish such as rays
or skate. While ATTAS, like all previous passenger aircraft,
consists of a cylindrical fuselage with wings and a tail unit, the
configuration simulated in the flight tests has a somewhat
triangular fuselage. At the tail, two vertical stabilisers that are
tilted slightly outwards replace the conventional combination of a
tail fin/rudder and a tailplane/elevator. There are four engines
under the additional wing area. "The peculiar shape of the aircraft
improves its lift characteristics, which in turn increases
efficiency," explains Leisling regarding the advantages of the
flying wing. It is no surprise that flying wings have a great
chance of becoming the aircraft of the future and are currently the
subject of many studies.
The flying wing model used in the DLR tests is based on a design
developed as part of the EU project NACRE (New Aircraft Concepts
Research). It is a wide-body aircraft designed for long-haul
flights and able to accommodate up to 750 passengers. With a length
of 65 metres, a height of 19 metres and a span of nearly 100
metres, the maximum take-off weight of the simulated flying wing is
roughly 700 tons. Its four engines provide a maximum total thrust
of 1425 kilonewtons.
Aircraft Comparison
During the test flights the scientists explored the flight
characteristics by examining individual manoeuvres, such as
deliberately varying the aircraft attitude. Using a simulated
instrument landing system, the pilots tested landing approaches on
a virtual runway. Each manoeuvre was followed by an evaluation of
the flying wing's handling characteristics, which showed that the
flying wing aircraft is difficult to control due to its unusual
shape. Only the introduction of an additional control system
developed at DLR brought about the desired results. This type of
control system prevents the aircraft from responding adversely to
pilot inputs by initiating appropriate counter-manoeuvres.
"The flight test confirmed our assumptions," said Leisling about
the results. "There is a limit to handling a modern, completely
uniquely-shaped aircraft without coordinated flight control laws.
We can only achieve the flight characteristics we want by using
appropriate computer and control technology."
The preliminary results of theoretical investigations could only
be confirmed in a 'tangible' way by carrying out simulations during
a real flight test; even high-quality simulations on the ground are
limited in this respect. Even after 25 years of service, ATTAS is
still of great value to aviation research as a flying
simulator.