Environmental Engineering Reference
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Client and contractor agreed on a compromise which was to
build rotor blades of 50 m length in hybrid construction. A
hexagonal steel frame bar takes-up the loads. It is shrouded with a
shell of glass-fibre compound providing the aerodynamic form. This
solution suited the engineers from MAN but it was much heavier
than a self-supporting blade of glass-fibre compound. Therefore
the entire system design had to be revised.
This meant the principle of consequent lightweight construction
Hütter had in mind was thrown overboard. He was no longer deeply
involved in the practical realisation of GROWIAN as he had retired
from the chair of the Institute of Structure and Design at DFVLR
already in 1976. The Institute of Aircraft Design (IFB), where he
was still acting director at that time, was no longer involved in the
GROWIAN project.
17.7
Limit of Feasibility
Hütter saw better opportunities to realise his academic ideas
through cooperation with Voith GmbH from Heidenheim. Wolfgang
Weber, one of the last to complete his doctorate proceedings under
Hütter's reign, was already working there. Together with Weber,
who later was appointed Professor of Business Engineering at
the University of Applied Sciences in Aalen, Hütter designed an
extreme high-speed 265 kW wind turbine trying to push his light-
weight construction philosophy to the maximum. The system was
a 2-blade downwind turbine. The 52 m rotor diameter gave it the
name WEC-52. In order to reduce weight of the nacelle, the energy
was transmitted through a tapered gearbox and a fast shaft in the
tower to a second gearbox, which just as the generator was easily
accessible at the bottom of the tower.
When the system was put into operation in October 1981 on
the test field in Schnittlingen, which had been re-opened two years
before, it was the biggest wind turbine built in Germany to that
date. However the test run lasted only a few months. Hütter had
tried to maximise the performance coefficient of the rotors with
an extremely high speed at the blade tip of more than 100 m/s.
The aerodynamics of such speeds requires very slim blade profiles,
and that stretched the issue of rigidity to its limits.
The extremely slim rotor blades were bending during certain
critical operation modes. When braking, torsion forces afected the
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