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DALLAS — The Boeing 787 Dreamliner has been the next leap in commercial aviation technology. Among its several innovations, and arguably the most significant one is its Bleed-less system, a radical departure from traditional bleed-air architecture.
This new design has enabled the Dreamliner to establish a new benchmark for efficiency, reliability, and passenger comfort, making it the best representation of the future of the aviation industry.
In this article, we delve into the Boeing 787's Bleed-less system in depth, examining how it works, what it offers, and why it marks a turning point towards more-electric aircraft.
Traditional Bleed Air Systems: The Old Standard
The majority of commercial aircraft before the 787 utilized engine bleed air extensively to power various systems. Bleed air is pressurized air tapped from the engine's high and low compressor stages and used for:
- Cabin pressurization
- Air conditioning
- Wing and engine anti-icing
- Starting the other engine(s) and the APU
- Hydraulic and pneumatic systems
It is typical in most contemporary aircraft engines to redirect compressed air towards other parts of the engine. This is referred to as "bleed air." An aircraft's bleed air system serves a range of different functions, some of which (although not all) include cooling turbine fan blades, pressurizing the aircraft cabin and lavatory water tanks, and warming various aircraft components to prevent them from freezing.
The majority of gas turbine aircraft engines use a bleed air system. This design utilizes the relatively hot (200–250 °C), high-pressure air that is cycled through the compressor section of the engine. Air may be bled at any point in the compressor section, and the fact is engine-dependent.
In some instances, air is bled from more than one stage of the compressor because of the change in pressure and temperature characteristics of the gas as it travels through each stage. This air is routed through the aircraft to various components using a series of pipes, regulators, and valves.
Although this configuration has existed for decades, it is not without serious disadvantages. Bleed air robs the engine of thrust and fuel efficiency. It also requires an extensive duct system, valves, and pressure regulators, which are heavy, complex, and require more maintenance, according to the University of Colorado.
On Board the Boeing 787: Welcoming the Bleed-less Design
The Boeing 787 Dreamliner was the initial production aircraft to eliminate engine bleed air usage for its environmental control systems (ECS).
The aircraft utilizes electric compressors driven by generators installed on the engines to provide cabin pressurization and air conditioning. It is a foundation of the aircraft's more electric architecture, a design philosophy that seeks to substitute pneumatic and hydraulic systems with electricity.
This design progress offers excellent performance, efficiency, and maintenance advantages, making the 787 one of the most sophisticated aircraft in the skies.
How the Bleed-less System Functions
- Electric Compressors
Instead of drawing in air from engines, the 787 draws in atmospheric air, which is compressed using electric compressors. The onboard power system of the aircraft, comprising four engine-mounted generators and two auxiliary power units (APUs), supplies power to the compressors.
- Filters and Heat Exchangers
The compressed air is conditioned and cooled by heat exchangers and high-quality filtration systems. It enables the accurate control of temperature and humidity inside the cabin, resulting in a more comfortable ride for passengers.
- Cabin Air Distribution
After being conditioned, the air is pumped through the cabin through a duct system. The system reconditions part of the cabin air through HEPA (High-Efficiency Particulate Air) filters, further enhancing efficiency and quality.
- Selective Bleed Air Use
While the 787 is positioned as "Bleed-less", it still uses some limited bleed air for life-sustaining operations such as engine cowl anti-icing and hydraulic reservoir pressurization, where electrical solutions are not yet so convenient. Nor is it completely reliant on being bleed-less, according to TransGlobalTraining.
Advantages of the Bleed-less System
- Better Fuel Economy
Among the primary advantages is a 3% improvement in fuel efficiency. Conventional bleed systems draw high-pressure air from engines, thereby reducing the available thrust. The 787 does not suffer from energy loss because it uses electricity, saving engine performance and overall fuel usage.
- Simplify Engine and Weight
No bleed air manifolds, valves, or titanium ducting are needed, and the engine design is greatly simplified. This results in a lighter engine weight, lower manufacturing costs, and fewer areas of potential failure.
- Improved Cabin Comfort
The electrically driven ECS facilitates:
- Higher humidity
- More stable cabin temperatures
- Better air quality
- Lower noise levels
This enhances the flying experience, particularly on long-distance flights, and alleviates traveler fatigue.
- Simple Maintenance
Traditional bleed systems have high maintenance expenses and require regular servicing of pressure regulators, valves, and ducts. With the streamlined electrical ECS design of the 787, there are fewer moving parts, resulting in less frequent maintenance, which lowers maintenance expenses and enhances aircraft availability.
- Environmental Benefits
With more efficient fuel use, there is less carbon output. Boeing has achieved a 20% increase in overall fuel efficiency for the 787 compared to previous-generation aircraft, aligning with industry targets to reduce CO2 emissions (Simple Flying).
The Broader More-Electric Aircraft Vision
The Bleed-less system of the 787 is a component of a broader strategy for more-electric aircraft, whereby:
- Hydraulic and pneumatic systems are replaced with electric ones
- Electrical systems, including flight control, wing de-icing, engine start, and hydraulics, are powered electrically
Hydraulic System Evolution
- The 787 maintains three hydraulic systems (left, right, and center)
- The center hydraulic system employs two high-flow electric pumps rather than engine-driven pumps
- 5,000 psi electric pumps instead of 3,000 psi on legacy aircraft, minimizing component size and weight
These modifications not only enhance fuel efficiency but also improve operational durability and safety through added system redundancy.
Industry Background: A Fresh Angle
Boeing was courageous to introduce this design to a commercial airplane. Interestingly enough, neither Airbus nor Boeing has incorporated the no-bleed system on any other aircraft:
- The Airbus A350 retains a conventional bleed air system
- Boeing's new 777X also follows an old-school approach
This renders the 787 an exceptional case study in the implementation of more-electric concepts to wide-body commercial transport aircraft.
The bleed-less design of the Boeing 787 rendered it 20% more fuel-efficient compared to its predecessors. Through the removal of bleed systems, the risk of air contamination incidents is eliminated, which has been a cause of concern in conventional aircraft designs in the past. Electrical wing anti-ice systems in 787 use 50% less power than pneumatic systems.
Challenges, Considerations
Although the advantages are evident, certain aviation professionals have raised concerns about the complexity of maintenance in electric systems, particularly as they age. Electrical malfunctions are more challenging to identify than mechanical malfunctions, and any malfunction in large power systems may cause a cascade effect.
Nonetheless, Boeing has implemented redundant power systems and sophisticated diagnostic technologies to reduce such risks. Ultimately, with the ongoing advancement of more electric technologies, these risks will likely diminish.
Conclusion: A Game-Changer in Aircraft Design
The Boeing 787 Dreamliner's Bleed-less system is not just a technological advancement but a strategic leap forward that enhances performance, saves money, and drives the industry toward a more sustainable future.
Through its deviation from conventional engine bleed air systems, Boeing has:
- Enhanced fuel efficiency
- Reduced maintenance loads
- Increased passenger comfort
- Enabled industry environmental goals
While it takes other producers as long as it will to catch up, the Dreamliner's success sets an overwhelmingly powerful precedent. As the aviation industry continues to move toward all-electric propulsion and cleaner flight, the 787's Bleed-less system will be seen as a pioneering benchmark.
Featured image: Brandon Farris/Airways
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