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This publication shows advantages and possible applications for variable transmission drivetrains within rotorcraft. The power requirement of a generic helicopter with constant and variable rotor speed was calculated. Various drive train technologies that support a variable transmission were described. The prospects of this technology, its influence on the dynamic behaviour of a rotor and further areas that need to be investigated extensively are presented. This technology is applicable to some rotorcraft architecture. Requests from the rotorcraft industry underline the necessity for future rotorcraft using variable rotational speeds. However, the A160 or the EC145 and Mi-8 already show the potential of this technique. Reduction of required power of the rotor should be possible and also an extension of the flight envelope towards higher flight speeds, higher altitudes, better manoeuvrability, etc. By using a variable transmission gearbox, turbine and auxiliary units can still be driven at their design point, independent of the current rotor speed. Excessive loads may occur when discrete speed transmission are used. Frictional or fluid transmissions with continuous variable ratio may fail due to overheating. Other continuous concepts are favoured. The design of a variable speed rotor focuses specifically on its dynamic behaviours and on structural and geometrical optimisation to avoid operation at rotational speed resonance frequencies. Morphing structures may support this. Some rotorcraft architectures can benefit from a variable speed rotor technology. It probably will increase efficiency, decrease noise levels, fuel consumption and CO 2 production, and the flight envelope may be extended.

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Plasma etching is an integral part of semiconductor integrated circuit (IC) processing and is widely used to produce high-resolution patterns and to remove sacrificial layers. Bottom anti-reflective coatings (BARCs) under the resist absorb light to minimize reflectivity during lithography and are typically opened during pattern transfer using plasma etching. High etch selectivity is required in the BARC opening process to minimize resist loss to allow further substrate etching. Because the plasma etch process combines physical bombardment and chemical reaction, the factors affecting etch rate and selectivity are complex. The results are related to etch conditions and the chemical nature of polymer. This paper addresses plasma etch properties as they relate to polymer type and etch gas composition. Polyacrylate, polyester, and polymers containing nitrogen and halogens have been investigated. The research was carried out by a series of designs of experiments (DOEs), which varied the flow rate of Ar, CF 4 , and O 2 in plasma gas. The selectivity of BARC to resist depends not only on the carbon content but also on the different ways polymer compositions and structures respond to an oxidizing gas, a reducing gas, and plasma bombardment. Based on a polymer decomposition mechanism, we discuss what could happen physically and chemically during the polymer's exposure to the high-energy reactive plasmas. We also modified the Ohnishi parameter for the polymers containing nitrogen and halogen using our polymer decomposition theory. The contribution of nitrogen and halogen in the etch equation can be positive or negative depending on the chemical properties of the plasma.

Ionic liquids (ILs) have been used effectively in many applications for reducing problems related to friction and wear. In this work, the potential of ILs as an anti-wear and extreme pressure lubricant additive for high load-carrying gearbox applications such as helicopter transmissions has been studied. Two halide-free ILs: $${{\rm{P}}_{8881}}{\left({{\rm{BuO}}} \right)_2}{\rm{PO}}_2^ - $$ P 8881 ( BuO ) 2 PO 2 − (1) and $${{\rm{P}}_{8881}}{\left({{\rm{MeO}}} \right)_2}{\rm{PO}}_2^ - $$ P 8881 ( MeO ) 2 PO 2 − (2), which are blended at 5 wt% each into a standard non-additivated FVA2 base oil (BO) are examined. Their solid—liquid interface, friction and load-carrying capacity, and wear (scuffing) behavior are studied on the nano-, lab-, and component-scale, respectively, at a different range of temperature and loading conditions by using the atomic force microscopy (AFM), Schwing—Reib—Verschleiß (SRV) friction tests, and Brugger tests, as well as forschungsstelle für zahnräder und getriebebau (FZG) back-to-back gear test rig. The AFM analysis shows nearly no change of adhesion over the full range of studied temperature for the IL blends compared to the BO. Similarly, IL blends demonstrate a very stable coefficient of friction (COF) of around 0.16, which even decreases with increasing test temperatures ranging from 40 to 120 °C. A clear reduction in COF up to 25% is achieved by adding only 5 wt% of the investigated ILs in the BO, and the Brugger tests also show a pronounced enhancement of load-carrying capacity. Finally, on the component-scale, a significant improvement in gear scuffing performance has been observed for both used IL blends. A detailed characterization of the wear tracks from the SRV friction tests via the transmission electron microscopy (TEM) revealed the formation of a phosphate (P—O)-based amorphous tribo-chemical layer of about 20 nm thickness. Therefore, this work may present an approach for ILs to be used as an additive in conventional lubricants due to their ability to enhance the lubrication properties, making them an alternative lubricant solution for high load-carrying gearbox applications.