Transformation at the push of a button

The new actuator in the wind tunnel
The new actuator in the wind tunnel
It seems like magic, but is pure physics: metal parts that have a memory and remember their shape. If they are cooled or heated, they return to their original shape. This is often demonstrated by means of a paper clip: no matter how you bend it – if you then immerse it in temperate water, the clip returns to its original shape within seconds. This amazing effect is made possible by so-called shape-memory alloys. The international research facility ETW European Transonic Windtunnel GmbH, located in North Rhine-Westphalia, makes use of these intelligent materials – and thus expedites wind tunnel tests for aircraft many times over.

In its wind tunnel, ETW measures the currents and loads to which aircraft are exposed during takeoff, landing and when cruising at altitude. Such tests are being carried out to determine the flight characteristics and operations of future aircraft under development under real-life conditions. However, ETW does not use real aircraft for the tests, but models which are on average 25 times smaller than their role models. In order to achieve realistic conditions in terms of fluid mechanics that are similar to those of a large aircraft, the models are tested at up to 4.5 times the atmospheric pressure and at low temperatures of -160 degrees Celsius in pure nitrogen gas.

Movement as if by magic

The tests at ETW are now standard in the development of new aircraft. The effect of adjustable control surfaces, such as ailerons or airbrakes, must also be tested. Up to now, their adjustment has been costly and cumbersome due to the inhospitable conditions in the wind tunnel. In order to change the position of the airbrakes, for example, the test must be interrupted, the channel opened and the model transported to a special climatic chamber, where the airbrake can be reset by hand. It takes about half a day and costs of €30,000 or more are incurred by the time the model is back in the cold wind tunnel. When investigating the effect of control surfaces on a medium-haul aircraft, this may add up to several hundred thousand euros and delays in the test program of a few days, which could be avoided by remote adjustment of the control surfaces.

A groundbreaking joint project by Deharde GmbH in Varel and ETW revolutionizes this complex process with the help of remote control that is based on shape-memory alloys: The team has developed a mechanism that allows control surfaces on the aircraft to be moved in the wind tunnel at the push of a button. In this process, the actuator, which is made of shape-memory alloys, is heated to a certain temperature and the surface takes on a different defined position as if by magic. What used to take half a day is now possible within seconds.

LuFo funding makes groundbreaking project possible

ETW and Deharde have been researching the use of shape memory alloys in the wind tunnel since 2016 in collaboration with Boeing and NASA. In January 2018, the project received the Boeing Performance & Innovation Award. The prize is awarded to teams that significantly increase Boeing's competitiveness and productivity.

A prototype of the new actuator has already been successfully tested in the ETW pilot wind tunnel. The goal is to use this method as the standard procedure for wind tunnel tests in a few years' time and make the costly modification measures superfluous. What is more: Deharde could also transfer the extremely robust and compact technology to other areas – to be used wherever space is at a premium or where aggressive environmental conditions would impair the function of motors. A striking example: ventilation louvers in a chemical storage facility or fire dampers in areas subject to explosion hazards.

The project was only made possible thanks to financial support from the German aviation research program LuFo. This success once again demonstrates the positive impact of research funding.