Rotation Test Stand @museum.de

So is it a home-made weather station? A wooden drilling rig? Or maybe an antique helicopter?

Far from it! This unusual wooden structure is what’s known as a Rotation Test Stand – a Rundlaufapparat. It’s one of several dozen devices developed by the Lilienthal brothers to carry out their basic physics research.

It’s actually the precursor of our present-day wind tunnel, which is used to study the aerodynamic properties of shapes and materials. If you set the top of the Rotation Test Stand in motion, the two panels at the ends of the arms start to turn. Air flows around them, so they’re subjected to a certain level of air resistance. To maintain the motion, that air resistance has to be overcome. And that takes more or less energy, depending on the shape of the panels, their texture and the angle of the tilt.

Lilienthal realised that smooth surfaces cut through the air differently when compared to porous, textured or feathered surfaces. A 60 degree tilt, say, behaved differently from a 90 degree tilt. To test the various parameters and make the required forces measurable, he varied the weights in the centre of the test stand. They indicate the lift force.

The Lilienthal brothers recorded several tens of thousands of experiments with the Rotation Test Stand. They were the first to find a way of making the forces operating during lift visible and measurable. The Rotation Test Stand was developed as part of the research for their book on bird flight, which laid out the theoretical foundations of aircraft design.

If you’d like to learn more about the workings of this impressive device and see it in action, please have a word with a member of staff. We’ll be delighted to provide a demonstration.