|Robot made to measure
Measuring air currents on an Airbus model
Flying with more payload, and no more fuel than necessary: Airbus is working to achieve this goal by optimizing the wings. In the concept phase for the new A400M transport aircraft, this involves measuring flow conditions on the wings of a model. Flow data are determined at various points with the aid of a KUKA robot, which in this case is literally “made to measure”. Analysis of these data makes it possible to pinpoint and eliminate areas of turbulence which would otherwise increase fuel consumption.
Airbus Deutschland GmbH was formed over the course of six decades through the merger of a number of major German aerospace firms; it develops and manufactures about one third of the European Airbus. On behalf of its parent company, Airbus S.A.S. (Societé par Action Simplifiée), Toulouse, the company also supplies spare parts to the fleet of some 2,600 Airbus aircraft worldwide.
Airbus S.A.S. has approximately 44,000 employees at present. The group accounts for nearly half of all passenger aircraft manufactured worldwide. Of its shares, 80% are held by EADS N.V., and 20% by BAE Systems.
In the business year 2000, Airbus Deutschland, at that time under the name EADS Airbus GmbH, achieved sales of 3.849 billion euros with some 16,500 employees. Airbus’s Germany subsidiary has operations at seven locations, with the greatest concentration lying in northern Germany. This includes, for example, the company headquarters in Hamburg and the center for wing equipment for Airbus widebody aircraft in Bremen.
The Bremen facility, which was established in 1924 by Focke-Wulf Flugzeugbau AG, is also responsible for the production of smaller sheet metal components and for structural assembly within the Airbus manufacturing alliance. This includes, for example, metal landing flaps and the rear structural zone of the Eurofighter central fuselage section.
With regard to wing equipment, Airbus Bremen is also tied into development work for the A400M military transport aircraft. This is intended as the successor to the Hercules C-130 and Transall C-160, which are still in operation after about 30 years. Airbus plans call for the A400M to make its maiden flight in 2007. The participating nations have ordered a total of 196 aircraft. Their objective is to be able to respond quickly when humanitarian and military cargoes need to be delivered to crisis regions. This sturdy aircraft is to be equipped with four turboprop engines, and will be designed to carry a payload of more than 30 tonnes to a range of almost 4,000 kilometers, with a maximum speed of approximately 780 km/h.
“In order to meet the specifications with regard to payload, we are conducting tests aimed at optimizing the wings in the gas-dynamic research facility of our aerodynamic testing center”, explains Eva-Maria Mendez Montilla of the Wind Tunnel Department at Airbus in Bremen. “Here miniature engines and model turbines are used to generate thrust, which is used to simulate the effects occurring on the wings. The test facility also makes measurements of air currents on half-models and model components.”
Since spring 2001 these tasks have been carried out with the help of a KR 30/15L six-axis jointed-arm robot from KUKA Roboter GmbH, Augsburg, Germany. The robot has a reach of three meters, and is also mounted on a linear unit, giving it a remarkable radius of action. It measures the air currents on a model of the FLA 5.1 (Future Large Aircraft), a preliminary study for the A400M. The fuselage of the model is constructed in 1:15 scale, while the proportions of the propeller are 1:17.
Advantages of the robot
“Our primary requirements for the robot are flexibility and reproducible repeatability. This is because it has to locate defined positions in a measurement grid”, explains Eva-Maria Mendez Montilla. “In addition, it must not block more than a small part of the measuring area so as not to influence the results of the measurements. For this reason, KUKA equipped the robot with an arm extension.”
This ability to “keep out of the way” is a decisive advantage six-axis jointed-arm robots have over gantry systems. In fact, the KUKA robot replaced just such a system, whose too-numerous and relatively inflexible axes generated resistance in the measuring area, thus influencing the boundary flow. Furthermore, six-axis robots have a more flexible kinematic system and therefore more freedom within the work envelope.
What is more, the robot always knows the actual position of the measuring probe in the coordinate system, and is consequently able to communicate with the measurement data processor. This dialog results in considerable time savings. Features equivalent to those provided by the robot could be implemented in a gantry system only with significantly greater effort and expense.
In addition, the KR 30/15L is much easier to work with, since KUKA sells it together with a PC-based controller and a control panel equipped with a familiar Windows man-machine interface.
The KUKA robot, which was supplied by the company SMT-Systeme Roland Rüb, from Syke, Germany, was chosen over other six-axis robots. The competitors’ robots all had an “upper arm” which was too thick for this application, and a sixth axis which was too bulky. Moreover, the Airbus group had already had positive experience with robots from KUKA.
The SMT contract included the robot together with its KR C1 controller, the 3.5 meter long linear unit, and a higher-level process program. This is necessary in order to generate a measurement grid for measuring currents on the FLA’s outboard propeller. SMT also carried out a feasibility study, integrated and installed all of the components, and put them into operation.
Measurements for optimized wings
The KR 30/15L is installed in an open-jet measuring gallery. Unlike an enclosed wind tunnel, this allows access from three sides. Another difference is that in an open-jet measuring gallery only current measurements are possible, not force measurements. Currents could also be measured in a wind tunnel, but the model would not be accessible.
“In order to measure the air currents, it is necessary to place a virtual surface grid over a corresponding grid on the half-model located in the measuring gallery”, says Eva-Maria Mendez Montilla about the process. “Once the two surface grids have been adjusted so that their coordinate points are superimposed, we can measure a wide variety of currents at different points on each individual cross-section.”
The KUKA robot does this by guiding a five-hole directional probe mounted on a holder. The head of the probe has five bevelled edges, each of which has an aperture. The differences in pressure between these measuring points can be used to determine the angle of the airflow.
The robot moves over the points on the model specified in the program, and sends a signal to the controller as soon as it reaches each point. The angle of the 300 mm x 300 mm measuring field guided by the KR 30/15L is changed regularly during the measuring procedure, and the controller must be able to take account of these motions.
Eva-Maria Mendez Montilla: “The flow conditions which are measured ultimately give us information about air stream separation and thus resistance which would occur during flight. The goal of our research is high cost-effectiveness through lower fuel consumption. Because if an aircraft can fly a particular route using less aviation fuel, it can then carry more payload. This results in significant benefits from both an economical and an ecological point of view.”
Author: Jürgen Warmbold, freelance technical journalist, 27327 Martfeld, Germany