No-Bleed Systems

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No-Bleed Systems.

Advance aircraft and spacecraft systems are, so far, one of the most revise areas in aviation industry. From the very beginnings, these system are twine together to the aircraft’s performance. Every year, more systems are tested, review, and redesign into better advance applications. A response to ensure the continuity for aircraft performances in aviation industry, is still to be consider, a foremost line of duty. Aircraft’s designs and systems, allocate many applications such as the next generation in avionics and other sub-systems. With new methodologies and technological advancement in aerospace industry, aircraft’s systems can address better operational implementations and provide feedback for safety environments.

In recent years, most aircraft’s systems shaped the way in which aviation is heading. A main focus on these developments is the systems redesigning phase. A redesigning phase, reinforce the aircraft performance by means of previous insight to attain aircraft deficiency. By acknowledging system’s background, it allows better proactive and reactive processes in the line of safety and performance. A very important aspect, is the overall endurance. Endurance approach must convey through all aircraft’s systems. These systems are the driving motor of the aircraft; without a proper integration, it could lead to a total structural failure. When a system(s) is not properly addressing and/or acting as the requirement states, it is consider to be inefficient. Providing efficient work capacity through all systems is a minimum and essential condition. As part of an unending process, aviation industry is recurring to research implementations to address situational awareness regarding aircraft’s systems and performance. The continuity of providing support to research areas, are very advantageous to this industry. It leads to address deficiencies in products, systems, services, safety factors, and human developments.


One of the most important key component in an aircraft’s systems, is the APU. Currently, the auxiliary power unit (APU) is mainly a ‘gas turbine engine’, which supplies energy to different systems. It is also a self-sufficient system, when the aircraft is in ground operations. Among the current APUs, there is the 131-9 Honeywell series. “The 131-9 Honeywell series measures 32.8 inches/cm in the front and 52.0 in/cm on the sides; it is rated EGT is 1100 degrees Fahrenheit and a rotor speed of 48,800 rpm for maximum rated (Honeywell Aerospace, January 2008, pg. 2/2).” This APU is light weight and affordable maintenance operational cost in comparison to other commercial brands.

With a great deal of service hours (> 10,000 hrs.) for MTBCR and MTBUR, this APU meets the minimum noise requirement and is also cost efficient. The design cost for low cost on aircraft maintenance, with a total annual cost of $1,946 vs other competitors high prices (Honeywell Aerospace, November 2007, pg. 2/4, second paragraph).

Another revolutionary concept has being develop by Airbus DLR German Aerospace Centre and Parker Aerospace, a proton exchange membrane fuel cell system (PEMFCs). Similar fuel cell concepts has comes from the aerodynamic principles and extensive work to improve the overall aircraft performance. “This new fuel cell system consist a hydrogen tank, heat exchangers, and fans in the tail section; while the fuel cells will be positioning in the cargo hold (The Flying Engineer in General Aviation, September 18, 2012, third paragraph).” Fuel cell systems can improve the aircraft design, from gas engine to better auxiliary power system. Leading to environmental friendly and efficient systems since produces low emissions and better noise attainment.

A small but easy to correct fault was found in this system, when doing an inclination test. “The system decreases the voltage of the cell when is positioning at an angle of 30 degrees. Since the by-product of the system is water (10 liter of pure water), its management creates an instability (G. Renouard-Vallet, J. Kallo, A.K. Friedrich, J. Schirmer, M. Saballus, and G. Schmithals, 2010, Pg. 273-276).”

As an approach to a conceptual aircraft, a visionary design will allow room to a broad course of actions. The general idea, is to pursue systems that contributes to reinforce previous designs; while allowing new concepts for advance aircrafts. A design will intend to address concepts for cost, environmental factors, performance, and design comparison. Let start by comparing the previous two model, as they will provide insight for best choosing.

The 131-9A APU is a remarkable approach for this conceptual design. To begin, the 131-9A maintenance cost, makes it affordable and the overall design has proven to be an efficient one; with new implementation to make it environmental friendly, this design is a great choice. Moreover, the materials used complement the concept for light weight systems and fuel consumption. Light weight system, allows room for more cargo or passengers, and better fuel performance. These APU model provides power to the pneumatic system. The next generation of fuel cell systems is headed into a new approach, to eliminate the gas engine APU system. By redesigning the current APUs operational aspects, these fuel cell also meet the requirement of light weight systems. This last approach not only allows room for other implementations as for the 131-9A, but also betters the main engines performance. The PEMFC system is still on a research phase. Its achievements, will be address by the year 2015, with the Airbus A320 flight test. The environmental factors of this design are the one of the best applications. This fuel cell concept, is based on a hydrogen and oxygen chemical interactions. Leaving the environmental factors in a good quality standard, for non-pollutant systems.

“Currently, the Airbus, A 320 APU emits 0.15 HC (g/kg), 2.05 of CO (g/kg), and 10.10 of NOx (g/kg) (Antonio Filippone, 2012, pg. 148, table 5.5).” With a new approach to fuel cell system, this APU will be absorbed completely by an advance system. “It acts as an independent source, capable of providing power to other systems (The Flying Engineer in General Aviation, September 18, 2012, third paragraph).” Furthermore, the standards addressed by the PEMFC’s can be stated as follow.

With the production of water, water vapor, electrical power, heat and inert gas; it does not produce CO2 or NOx. The water can be used to fill water tanks and be distribute for lavatories, galley, and humidification. Minor adjustment to the pH of the water are needed to make it drinkable (Martin Keim, Josef Kallo, K. Andreas Friedrich, Claudia Werner, Martin Saballus, Florian Gores, 2013, Pg.330-338).

A conceptual fuel cell system, will be ideal for this for a commercial blended wing aircraft design. Conceptual cost and performance for this system, is intrinsically related to overall aircraft design. Cost is always a topic to be address by the aviation industry, questions as: It is affordable? What about the maintenance and other operational cost? Are the manufacturer willing to process such implementations? And, will the FAA allowed such designs (safety factors involve)? All these questions cannot be answer if the first step to advance system is not pursue. With better research applications, the operational, safety and performance this questions are address. “The cost for the Honeywell 131-9A APU, the annual labor cost per APU is $1,946 (Honeywell Aerospace, November 2007, pg. 2/4, bottom figure).”

The expected cost for the hydrogen fuel cell is still considerable high because of the refined fossil fuel system. More companies are currently focusing on this aspect, with composite material that allows better and more affordable parts and other means to acquire hydrogen fuel from resources such as other fuel combinations that provides enough energy to power the aircraft’s systems. This conceptual fuel cell is an adequate choice for the conceptual aircraft design. Therefore, the maintenance overhauls will be stated to be the same as the engines maintenance or every 2,800 hours as maximum is requirement. This design will manage fuel consumption, engine efficiency, environmental factors, and cargo capabilities.

Pneumatic vs. No-Bleed Systems. A typical pneumatic power system, is provided by the following: main engine bleed systems, auxiliary power unit (APU), and ground power unit system (GPU). Before the bleed air passes through this systems, it must be heated and pressurized. After the air is conditioned to proper standards, it will be used by other sub-systems such as the anti-ice, water, engine starting, hydraulic, air conditioning (AC), and pressurization of the cabin. The pneumatic system contains a manifold system which collects all the air driven by all other bleed systems and two air packs for each side of the aircraft. In this system, a valve divides the left side from the right side. If one side is closed from the other, the bleed air can still be provided by the one of the main engines, APU, and ground power unit when available.

The pilot controls the pneumatic system from the cabin by the flight control system. In the flight control system, the valve can be set to be open, auto, and close. In an open loop or access, the valves will allow a complete air flow from any component of the bleed system. On auto, the system provide bleed air as requires. When the valve are closed, the left side is completely closed from the right side of the pneumatic system. An independent electro-pneumatic or pneumatic system is compose of fans, heat exchanger, air cycle unit, air starter, and valves. This pneumatic system with pipes and valves add a considerable weight to the aircraft. Moreover, this system is not fuel efficient and requires bleed air taken from the engines.

In a no-bleed system, the air coming from the engines causes a loos of thrust. Since the conceptual aircraft does not requires the anti-ice and the hydraulic system to be powered by the pneumatic system, this allows better performance. The pneumatic system is then replace by an electrical system (no-bleed air), similar to the B787. With the incorporation of an electrical system, a light weight capability is also achieved. This electric system also needs a driven generator and an electrical driven compressor, for a continuous pressure and air flow. “The driven generator will be connected in series to the main engines and provide power to most of the aircraft’s systems (Boeing, 2008, Article 02, pg.2, paragraph 2).” The electrical system is powered by the engine driven and fuel cell generator (see figure a ). A typical compressor, approved by the FAA uses two to three stages; for the conceptual design this last one will be used as a safety requirement. Further research application will allow this system to use composite material to allow a down-size version with a light weight and operational achievements. Maintenance for the conceptual compressor will be perform daily, to ensure safety. The daily maintenance requirements include change of oil, refill air tank and pressure testing, and cleaning as stated in the instruction manual. Therefore, in a conceptual design, a compressor under the FAA regulation will be used.

For high pressure, the requirement for the air bottle must be between 1,000 psi and 3000 psi. Medium pressure (50-150 psi): it draws air from the compressor section of the engines. For low pressure, a four chamber pump can supply a continuous compressed air (FAA, 2012, Chap. 12, pg. (12-48)-(12-53)).

Environmental Control (Air conditioning and cabin pressurization). The environmental control system is compose of high efficient air and gaseous filters, four electric cabin compressors and air conditioning packs. “The cabin air comes from the ram air inlets on each side of the planes’ belly and won’t pass through the engines, says Mike Sinnett, the 787 project director (Marilyn Adams, 2006, paragraph 14).” The air coming from this inlets into the cabin pressurization and A/C. A light weigh standards for ozone elimination and oxygen converter are essential for the conceptual design. The air inside the cabin and the humidification must pass through two processes: a catalytic air pollution control (an ozone removal abater) and the high efficient filters. For optimum achievement, the ozone and oxygen converters are reinforce by a ceramic materials. “Moreover, these ceramic material allows residual particles attainment at a considerable activity of 20,000 flight hours (Ronald M. Heck, Robert J. Farrauto, Suresh T. Gulati, 2012, Pp. 361-372).”

The catalytic air pollution control unit and ram air inlets will be located under the aircraft’s belly. The air conditioning and cabin pressurization are electrically dependent from the driven compressor. In addition, “the electrical compressor drives the compress air by a speed motor. It flows through low pressure and the air conditioning packs for efficiency (Boeing, 2008, Article 02, pg.2-4, paragraph 3).” The pressurization and humidification process are set to be automatic and altered when needed. If the maximum passenger’s capacity is not achieve, this automated system compensates by adjusting the amount of pressures and humidification. A very important concept to be included, is the fuel consumption; which is achieved by this adjustable system.