Aerodynamics – Part 1
In 2009, all stakeholders of the aviation industry committed to a set of ambitious climate action goals, namely:
- improving fuel efficiency by 1.5% per annum between 2009 and 2020;
- reaching net carbon-neutral growth from 2020;
- reducing global net aviation carbon emissions by 50% by the year 2050 relative to 2005.
Since then, an impressive number of technological solutions contributing to the 2050 goal have been proposed, and many related projects have been initiated. One of these has been the development of EV aircraft.
Elsewhere numerous aircraft (air-frame and engine) technologies as well as sustainable aviation fuels, operational and infrastructural measures have been pursued.
The road-map proposed by the aviation industry stakeholders focuses on technologies and the design of future aircraft. The technology road-map timeline has been plotted out all the way to 2050. In the short-to-mid-term, i.e. until about 2035, new commercial aircraft will still be “evolutionary” with developments deploying the traditional tube-and-wing configuration, and turbofan engines will be powered by conventional jet fuel or a sustainable drop-in equivalent.
From 2035 on-wards, one can expect “revolutionary” new aircraft configurations and propulsion systems to be ready for entry into service, provided the economic framework conditions are favourable to their implementation. These radically new aircraft designs include, among others, blended wing bodies, strut-braced wings, as well as hybrid and battery-electric aircraft.
The reader should be aware that as each new generation of aircraft is put into service, which is every 15 – 20 years, the fuel burn per available seat-km is typically 15 to 25% less than the aircraft models that they replace. These reductions in fuel burn reduce the costs of operation and ultimately lessen the seat price. Of course, this has the disadvantage also of creating a price point that invites more customers, which sells more airplanes, resulting in more CO2 emissions. This cycle of economy forcing more emissions is part of the overall plan inherent in the Aircraft Technology Roadmap.
Evolutionary aircraft technologies
Continuous progress is being achieved in all areas of evolutionary technologies, namely aerodynamics, materials and structures, propulsion and aircraft equipment systems. Some examples of technologies that have recently made noticeable progress are natural and hybrid laminar flow control and new high-bypass engine architectures. In aircraft systems, evolutionary technologies could be provided in such areas as electric landing gear drives and fuel cells for onboard power generation. By applying combinations of evolutionary technologies, fuel efficiency improvements of roughly 25 to 30% appear possible. However, further progress to the tube-and-wing configuration (see Figure 1) powered by turbofans are becoming more and more difficult to conceive around 2035.
Aerodynamics
Aerodynamic technology has been progressing continuously throughout the past decades to produce new designs with significantly reduced drag. An aerodynamic technology that has been pursued over many years and has recently made recent progress in development is Laminar Flow Control. This technology allows considerable drag reduction by preventing turbulence in the airflow over the aircraft’s surface.
Figure 1 – Traditionally Designed Aircraft – Tube and Wing
Natural Laminar Flow (NLF) Control achieves laminar flow only by designing the surfaces of the wings and other aircraft parts with a suitable shape. From some test flight results, the fuel-saving potential of NLF for an 800-nautical mile flight would be around 4.6%. In todays’ environment, fuel costs are typically 10% – 12% of an airline’s operating expenses.
Another way to create laminar flow conditions is Hybrid Laminar Flow Control (HLFC), which uses boundary-layer suction to maintain laminar flow over the aircraft surface. This technology is particularly suited for swept wings and fins.
Figure 2 shows how conventional, laminar, natural laminar and hybrid laminar flow differ from one another. The diagram demonstrates where the turbulence (indicated by circular patterns) takes place, which is a detriment to the efficiency of the wing’s performance.
Figure 2 – A Comparison of Conventional, NLF, LFC, and HLFC techniques
Novel Aircraft Configurations
While all current commercial aircraft have a conventional tube-and-wing configuration, novel configurations with higher fuel efficiency benefits are also considered for future air-frames. Design concepts currently seen as most promising by research establishments include: strut-braced wing (see Figure 3), blended wing body, double-bubble and box-/joined-wing aircraft. All these designs are significantly more environmentally friendly than conventional aircraft designs, not only more fuel-efficient, but also quieter.
Figure 3 – Strut-Braced Wing Configuration
The Strut-Braced Wing configuration studied at DLR is characterized by a fuel-efficient design with a large span and rear-mounted open-rotor engines. Indications are that the efficiencies possible using this design would be from 10 – 15% in improvements over the current design state. Much of the early design work on these types of projects is performed by High Performance Computers.
Articles which follow in this website will further consider these and other aspects of the Aircraft Technology Roadmap.
Materials in this presentation have been taken from the Aircraft Technology Roadmap Report.
Our intent with web pages such as this is to take pieces of that report and represent them with a focus on how aviation will transition from the current state to a Green Aviation state.
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