Down the rabbit hole again. I got a request for a paper by German physicist Albert Betz that I didn’t have. Betz, a well known figure in the field of wind energy, was a prolific researcher in the early days of aerodynamics. He published from the teens through the 1940s. He’s famous for the Betz limit that describes how much energy a wind turbine can extract from the wind.*
That request set off a long search for the paper in question. Previously, I’d found that one of his papers was still be hind a paywall after all these years. (See Betz: Everything You Need to Know about Wind Turbines Was Written in 1927.) I ran into the same problem once again—publishers are still trying to make money off of Betz and other long-dead academics.
This time the minions at Google had swooped in and copied an entire book and while it wasn’t what I was looking for, it was interesting nonetheless.
Wind-Energie und ihre Ausnutzung durch Windmühlen (Wind-Energy and its use by Windmills) was not only in German, but it was also in Old German Script.[1]
No, I didn’t read it so I am not going to review it. I did page through it and found a few photos that were of interest.
Figure 42 shows a post mill probably for pumping water because of the nearby canal. The caption calls it an “old fast-runner type” with poor blade profile with a tip speed of 2.5, assuming I am reading this right.
Figure 43 shows what the Germans call a windrose or what we know as a multiblade farm windmill. The 15 meter diameter Hercules windmill was built in Dresden, a place better know for faience or pottery. I think the caption says that this size is the limit for a windmill like this to be effective.
Figure 44 is the reason I took the time to copy these illustrations. This fast-runner windmill was built by Aerodynamo on Berlin’s Kürferstendamm. This was Kurt Bilau’s company and that’s his design. The caption goes on to note the air brakes (or more correctly flap brakes) toward the end of the blades (bremsflappen?). The caption says to see Figure 48 for an explanation. I couldn’t find a Figure 48. Could it be that Google missed it? It’s hard to tell, the figures are not in a numeric sequence.
Figure 45 is described as an “Adler” windmill in a pasture in Holstein. This windmill uses fewer blades than the multiblade windmill and each blade is an airfoil, not a simple curved sheet of metal. The caption says it will have a tip speed ratio of 2.5 to 3.5
The entire book is worth a look, but be advised it’s heavy sledding unless you’re
*More correctly called the Betz-Joukowsky limit.
[1] Betz, Albert. Wind-Energie und ihre Ausnutzung durch Windmühlen. Vandenhoeck & Ruprecht, 1926. Google-Books-ID: 7Lw3AAAAMAAJ.
