The pneumatic system, chapter ATA 100-36, is also known as the engine bleed system. It basically supplies hot, high-pressure air for air conditioning, ice and rain protection, and pressurization systems. It can also be used for pressurization systems for seals, ejectors, drains, heating, radar pressurization system, on board oxygen generation system (OBOGS – on board oxygen generation system) and any other system that needs of hot or pressurized air from the aircraft.
There are important aspects of the pneumatic system such as its distribution, flow, temperature and pressure. Distribution depends on the pressure drop of its subcomponents and the presence of control valves. One feature is the flow division, which can be active or passive, and determines how much flow each branch of the system will reach.
A pneumatic system on a commercial aircraft usually has shut-off and pressure regulation valves for high and low stages of the engine compressor, pre-cooler, as well as flow and pressure control valves for user systems such as air -conditioning and frost protection.
According to certification requirements and security analysis such as Functional Hazard Analysis, Failure Mode and Effect Analysis (FMEA) and fault trees there is redundancy in the system. That’s why the aircraft have a system on the left and right sides of the aircraft.
The system and its components can be certified by analysis, testing or similarity. This is determined in a means of compliance analysis (MOC).
For testing, proof and burst pressure tests are performed. If the ducts have moving joints, fatigue and accelerated life tests may be required.
The analyzes required are usually of head loss, distribution or flow sharing, thermal performance and temperature. Other analyzes involve the control of pressure, flow or temperature, that is, the dynamics of the plant and its control. CFD analysis may also be required for duct breakage, pressure drop determination, air or Ram Air inlets and heat exchanger inlets (headers) for example.
A very important subsystem is that of indication and measurements of flow, pressure, temperature and fault detection. This subsystem has dedicated sensors for each task. The indication is shown to the pilot and has severity levels for flight safety. Failures can be over-temperature, over-pressure or unwanted leaks, which can mainly affect the structure or electronic equipment.
The main pneumatic system certification reports are: system description, safety analysis, test proposal, test results as per FAR 25 or 23 requirements, but also component qualification as per RTCA-DO-160.
To design a system of pressurized ducts with high temperature that runs through a large part of the aircraft, it is necessary to install expansion joints or ball joints, as well as supports attached to the primary structure of the aircraft. During operation, thermal expansion and displacement occurs due to pressure differences. Therefore, to design, it is necessary to know what are the forces and displacements suffered by the pneumatic lines. The forces generate stresses in bends, ducts and their joints that need to be compared to static and fatigue allowable materials. A certification requirement is knowing what loads are passed through the pneumatic system on the aircraft’s primary structures. The project needs the support of a CAD tool and a FEA-type structural analysis tool, such as NASTRAN or Adina.
The numerical tools that support the design and certification of pneumatic systems are CFD++, FEA (NASTRAN or Adina), Matlab/SciLab or Siemmens AMESim/Modelica (for control or transient regime) and Siemens FloMaster (for steady state). ATS also has tools specifically developed for Python and Excel applications.
ATS has experience in pneumatic system design, certification and testing, including simulation, analysis and installation.
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