Nacelle and Engine Bay Cooling and Ventilation

Part 1/3

Are you working on an aerospace project that requires the completion of a nacelle or engine bay cooling and ventilation test? If that is the case, this entry might come in handy.

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.

Background

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 
tempfn

Turbofan engine (Image: NASA Glenn Research Center)

Understanding the nacelle and engine bay thermal environment is important to prove that the maximum temperatures are within component limits, ultimately demonstrating system reliability.

Capture

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
Certification requirements

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”.

You are now familiar with Nacelle and Engine Bay Cooling and Ventilation tests and their associated certification requirements. Visit Part 2/3 of this guide including specific details about the test content

Give us your feedback

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?

Please feel free to contact us using our “Contact” page to ask any questions, share your personal experience or even to propose what you would like to see next.

Sincerely,

The Company

0