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Centrisep EAPS, Design, Analysis and Test
Designing a helicopter intake protection system is a complex process that requires significant knowledge and experience. Every Centrisep EAPS design is tailored to a specific helicopter model. Pall’s design and engineering expertise ensures that optimum performance is achieved in the smallest envelope with the lowest weight possible. The designs are developed using sophisticated CATIA1 3-D modelling and simulation software. The steps include:
- Define Specifications
- Generate Engineering Design and Analyze Flow
- Create Prototypes
- Perform Qualification Testing
- Perform Flight Testing
Step 1 – Define Specifications
Pall’s experienced engineers work closely with helicopter design engineers to define product performance specifications for each helicopter type.The specifications will include:
Flow rate- Pressure drop
- Removal efficiency
- Scavenge system
- Maximum weight
- Filter and intake geometry
- Flow distortion at compressor entry plane
Step 2 – Generate Engineering Design and Analyze Flow
Pall engineers will produce an initial concept design. The new generation of Centrisep EAPS designs utilize composite materials to create complex geometries. The curved shape of the new units:- Ensures minimum pressure loss and optimizes flow distribution at the compressor entry plane
- Preserves the aesthetic, aerodynamic profile of the helicopter
Performance analysis is conducted, including the compressor entry plane because the Centrisep EAPS (and Inlet Barrier Filters) can interact with the downstream ducting. Depending on the specific design, the Pall parts kit can include or exclude the downstream duct.
After a series of reviews, the final design is agreed upon. Every helicopter model is unique, therefore significant engineering knowledge and experience are required for each design.
Design Analysis Tools
To achieve the optimum performance, several tools are used:
- CATIA1 3D modelling - uses the latest CATIA V5 CAD/CAM
- Finite element analysis (FEA) - uses computer software such as ABAQUS2/CAE and HyperMesh3 for linear, non-linear, and complete model analysis to produce highly accurate results.
Computational Fluid Dynamics (CFD) – Pall’s flow analysis engineers use an enhanced version of computer software such as FLUENT4 and FloWizard5. 
Step 3 – Create Prototypes
A prototype unit (or a rapid prototype model) will be produced to verify the following:
- Ease of manufacturing
- Installation interface
- Ease of maintainability
- Selected performance characteristics.
After the prototype evaluation is completed, design improvements are identified and incorporated.
The next stage is testing.
Step 4 –Qualification Testing
Before a Centrisep EAPS can be installed onto a helicopter, the unit must undergo a comprehensive suite of qualification (performance and environmental) tests, followed by flight testing.
Performance testing - To ensure that the Centrisep EAPS meets OEM and/or customer specifications, engineers conduct extensive testing in Pall’s own laboratory facilities. Pall scientists and technicians perform air filter and qualification testing using the following:
- Suction rigs (i.e., wind tunnels)
- High pressure flow equipment
- Temperature fatigue test units
- Other specialized test equipment
The following tests are performed:
- Air flow pressure drop (tested to ISO5167)
- Particulate removal efficiency
- Flow distortion at compressor entry plane
- Fan performance and erosion resistance
Environmental testing - Vibration, shock, acceleration, icing, EMC and bird strike testing are normally conducted at approved, independent test facilities.
- Icing Certification - Pall has extensive experience in icing certification for Centrisep EAPS designs. Note that the EAPS is never the limiting factor when flying into icing conditions. Generally the flight limitations are imposed by rotor or critical airframe components.
For a Centrisep EAPS design, a Pall engineer can prepare an icing certification report which predicts the design performance. The report is created using results from previous icing tests, as well as Computational Fluid Dynamic (CFD) Simulation. These reports have been widely accepted by the airworthiness authorities. As a result, laboratory or natural icing tests may not be required. Contact centrisep@pall.com for an icing report for your particular helicopter.
Each design can be certified for inadvertent entry into icing conditions. Some models have undergone winter trials and have subsequently been qualified for all-weather operation.
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Bird strike – The Centrisep EAPS has been qualified to meet the bird strike requirements of both FAR 29 (airframe) and FAR 33 (engines). When combined with a mesh screen, the unit provides excellent protection against foreign object impact and does not become clogged with debris.
Step 5 - Flight Testing
After the qualification (ground) testing is complete, the Centrisep unit can be installed on the helicopter for flight testing. The aim is to confirm the effects of the Centrisep EAPS on the helicopter’s performance and handling characteristics.
The flight test program is carried out on a fully instrumented helicopter and can include:
- Power effect (in hover and forward flight)
- Speed in forward flight
- Rate of climb
- Center of gravity changes
- Maneuverability
1CATIA is a trademark of Dassault Systèmes.
2ABAQUS is a trademark or trademark of ABAQUS, Inc., in the United States and other countries.
3HyperMesh is a trademark of Altair Engineering, Inc.
4FLUENT is a trademark of Fluent, Inc.
5FloWizard is a trademark of Fluent, Inc.
