The purpose of this blog entry is to provide guidance and advice for engineers involved in planning and conducting nacelle or engine bay cooling and ventilation tests. Test requirements as well as applicable regulation are reviewed in this entry, the first of three dedicated to cooling and ventilation tests.
So, what are some of the reasons that explain the need for nacelle or engine bay cooling and ventilation ground and flight tests?
- To characterize the air temperature surrounding a specific component
- To verify the overall heat management performance of the system
- To validate the existing thermal models
One could argue that the big engine manufacturers have dedicated facilities where they perform all sort of engine tests. However, on-aircraft testing may be required for a variety of reasons.
- Certification requirements
- Challenges related to systems integration
- Difficulty to model complex flows and airframe/nacelle/engine interactions
Turbofan engine (Image: NASA Glenn Research Center)
NACA scoop on Piper Twin Comanche PA-30 aircraft
Ventilation systems are paramount to ensure that our systems stay below limit temperature. Depending how the air flow is managed, we can categorize ventilation systems as passive or active.
- Passive ventilation systems rely on artifact such nacelle ventilation holes where the air flows freely from the engine Fan Duct into the core bay. NACA scoops and ducts to bring air to specific areas are other examples of passive systems
- Active ventilation systems force the flow to circulate across the nacelle / engine compartment or to impinge directly into a specific component. Examples of active systems include fans and exhaust or bleed air driven ejectors. Failure cases of active ventilation systems should also be considered
Aircraft level requirements for civil transport aircraft are included in FAA’s 14 CFR Part 25 sections 25.1041 (General), 25.1043 (Cooling tests) and 25.1045 (Cooling test procedures). In a nutshell, these requirements call for the most critical cases for component temperatures to be identified and assessed during flight and ground testing. EASA has equivalent CS-25 regulations.
Additional guidance can be found in FAA’s Advisory Circular AC 25-7D Flight Test Guide for Certification of Transport Category Airplanes, and in the draft of FAA’s Transport Airplane Propulsion Engine and Auxiliary Power Unit Installation Certification Handbook: “The Propulsion Mega AC”.
From ES3AERO we hope you find this entry interesting and useful and, more importantly, we would love to hear back from you! Did you like this entry? Would you like more specific information about how to conduct a nacelle and engine bay cooling and ventilation test? What other types of test would you like to hear about?
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