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12
CASE STUDY
Test Facilities
With its 9.1 square meters of jet surface
space, the NWB facility is the second largest
low-speed wind tunnel within the organization.
At the facility, wind speeds of up to 300
kilometers per hour are achieved, roughly
comparable to the speed at which a commercial
aircraft takes off and lands, at a
power consumption of 1.6 megawatts. On
commission of aeronautical industry and
research organizations, studies are conducted
primarily into the dynamic load behavior
of aircraft, helicopters and propulsion
units.
Apart from this, the NWB is also a test
partner for the motor sport sector, to include
commissioning contracts from the
Formula 1. The wind tunnel experts in
Brunswick have even tested such unusual
items as bicycle helmets, lights and a complete
sailboat with rigging in their tunnel.
Manipulation – the right way!
In aircraft development, it is of key importance
to – at a very early stage – be able to
evaluate the handling characteristics and
the level of dynamic loads that occur. This
is the only way to keep development risks
low and, thereby, keep close track of development
costs. Consequently, taking measurements
of model aircraft movement in
the wind tunnel is an important field of activity
at the NWB. Models of the new giant
A380 passenger jet “flew” in the wind tunnel
in order to furnish designers with data
on the aircraft’s dimensioning, as well as
load estimates of the structural design during
flight maneuvers and wind gusts.
In most wind tunnels, model planes are
moved in the measurement path using an
elaborate mechanical lever construction,
whereby the stem supporting the model
extends beyond the measurement path,
and is kept in a Cartesian arrangement
from outside of the air stream with the help
of mechanisms arranged in series.
This solution, however, has the drawback
that the required complex movements
cannot be conducted with the desired speed
and dynamics at the necessary level of
rigidity.
Special parallel kinematics
in the tunnel
Some of these drawbacks can be avoided
with the help of the so-called Stewart platform,
which is used in flight simulators
for pilot training. As of 2000, NWB has also
been using 6-axis parallel kinematics with
hydraulic bars of variable length. The results,
however, have never been entirely
convincing. First, due to the operating
principle, the hydraulic bars lack rigidity,
while the inertia of the valves limits the dynamics
and accuracy of the model’s movement.
Second, the continuously switching
valves excited vibrations in the models,
thereby corrupting the results of the measurements.
The solution based on the flight simulator
also proved unsuitable for the motor racing
measurements. The hydraulic platform
stood on the floor, therefore precluding the
customary wind tunnel measurements during
which the vehicle model is held from
above, while a conveyor belt a very short
distance beneath it was moved. However,
this arrangement can scarcely be implemented
in any other way to simulate the relative
movement of the vehicle and track.
In addition, the hydraulic system was
costly to maintain, and bore the risk of
hoses bursting or becoming loose and soiling
the measured section with oil.
The kinematics and operator interface were developed for the
DNW technicians in accordance with the special needs of flight tests
Loss of control over the valuable models, which are “packed”
with measurement technology, must be avoided at all costs
All pictures: P. Koerber
motion world 1/2007