2 research outputs found
Full Electric Helicopter Anti-Torque
On the way to complete electric flight, the electrification of helicopter subsystems is an essential milestone. This paper discusses the design of an electric helicopter anti-torque system, which uses Kopter's AW09 helicopter as a platform and shall be tested in ground tests. Analysis of state of the art anti-torque devices for helicopters has helped to identify concepts, which are suitable to be combined with electric propulsion and actuation. Engineering models are used to estimate the power benefits of varied tail rotor RPM, enlarged and steerable vertical stabilizers and drag reducing devices, which cover the rotor in forward flight.
In connection with operational benefits viewed from the OEMs perspective, an architecture is proposed which consists of an electric driven shrouded tail rotor, an electric pitch actuation system and additional aerodynamic surfaces, like a steerable vertical stabilizer and a drag optimized tail rotor cover. The systems were developed according to the results of a safety analysis to meet the requirements of CS-27. The electric tail rotor drive is designed with an internal level of redundancy that allows to compensate for subsystem failures
Adsorption, Ordering, and Metalation of Porphyrins on MgO Nanocube Surfaces: The Directional Role of Carboxylic Anchoring Groups
The
understanding of porphyrin adsorption on oxide nanoparticles including
knowledge about coverages and adsorbate geometries is a prerequisite
for the improvement and optimization of hybrid materials. The combination
of molecular spectroscopies with small-angle X-ray scattering provides
molecular insights into porphyrin adsorption on MgO nanocube dispersions
in organic solvents. In particular, we address the influence of terminal
carboxyl groups on the adsorption of free base porphyrins, on their
chemical binding, on the metalation reaction as well as on the coverage
and orientation of adsorbate molecules. We compare the free base form
5,10,15,20-tetraphenyl-21,23<i>H</i>-porphyrin (2HTPP) with
the carboxyl-functionalized 5,10,15,20-tetrakisÂ(4-carboxyphenyl)-21,23<i>H</i>-porphyrin (2HTCPP) and show that without carboxylic anchoring
groups the free base form metalates on the nanocube surface and adopts
a flat-lying adsorbate geometry. The saturation limit for flat-lying
adsorption on nanocubes with an average edge length of 6 nm corresponds
to 90 ± 14 molecules per particle. This limit is surpassed when
2HTCPP molecules attach via their terminal carboxyl groups to the
surface. The resulting upright adsorption geometry suppresses self-metalation,
on the one hand, and allows for much higher porphyrin coverages, on
the other (at porphyrin concentrations in the stock solution of 2
×
10<sup>–2</sup> mol·L<sup>–1</sup>). UV–vis
diffuse reflectance results are perfectly consistent with conclusions
from SAXS data analysis. The experiments reveal concentration dependent
2HTCPP coverages in the range between 0.4 to 1.9 molecules nm<sup>–2</sup> which correspond to the formation of a shell of upright
standing porphyrin molecules around the MgO nanocubes. In contrast,
after adsorption and metalation of nonfunctionalized 2HTPP the resulting
porphyrin shells are in the range of a tenth of a nanometer and thus
too thin to be captured by SAXS measurements. Related insights advance
our opportunities to prepare well-defined nanohybrids containing highly
organized porphyrin films