Nacelle and Engine Bay Cooling and Ventilation

Part 3/3

ES3AERO's tips, recommended practice and checklist based on the team's experience

ES3AERO recommended practices

Based on ES3AERO’s team experience, the following tips may be useful to somebody tasked with conducting a nacelle or engine bay ventilation and cooling test.

Proper sealing: Nacelle or bay sealing should conform to the design intent, avoiding any leakage of hot gas from the engine core. Some examples on how to identify hot gas leakages:

→ First order temperature response to changes in engine power (lag response = no-leakage)
→ Marks and/or “bluing” traces across the air duct sealing surface
→ By applying chemical developers (e.g. Ardrox®) on the surface/s of interest

Limits for each component must be clearly defined before the test. This includes temperature and time exposure operating limits (component running at its nominal capacity), transient limits (maximum operating limit that can be exceeded for a certain period of time) and non-operating limits (for instance after engine shutdown on ground). Test Engineers should also have a good understanding of FADEC (Full Authority Digital Engine Control) logic and cockpit indications of LRU over-temperature and of any automatic protection thresholds. In addition, the action to be taken after reaching any limiting temperatures should be agreed with specialists in advance

– Instrumentation requirements should be defined and agreed between the Airframer Design Office and the Engine Manufacturer  and result defined in a Flight Test Instrumentation Definition requirements document or equivalent. Aero-thermal modelling will support the instrumentation requirements definition (temperature/pressure sensor type, accuracy, range, location, etc.)

 Temperature sensors: instrumentation generally consists of a mix of surface thermocouples placed on components of interest along with “bulk” air temperature measurements and any measurement of any fluid temperatures units are exposed to. Temperature sensitive stickers may also be useful if a simple, rough order of magnitude check of peak temperature is required at a specific location

Temperature sensors are typically placed around 1-1.5 inches from the component, skin temperature sensor must be properly isolated from the environment to avoid misreading

 Pressure sensors: pressure measurements may be required for ventilation model validation or to confirm whether intake or exhaust conditions are as predicted. A mix of total pressure (PT) and static pressure (PS) sensors might be required to calculate mass flow rates across specific sections (e.g. mass flow across a nacelle ventilation port can be derived with a PT, PS and a temperature sensor)

During instrumentation pre-checks confirm that PT > PS at an specific section when there is forward speed

 Infra-red cameras can be used to thermally image external areas if nacelle surface temperatures or exhaust impingement on aircraft structures is of interest or to measure external surface or component thermal emissivity. Care should be taken to select an appropriate wavelength for the medium in question, e.g. surface metal temperature vs hot gas leak

MoreAndSmarterSensorsAreComing-v2

Sensors array in aircraft engine (Image: Structural Monitoring Systems PLC)

Real time monitoring from telemetry or on-board need to be defined and set up before the test and should include appropriate features in terms of data stream transmission frequency and critical parameter readiness and visibility

→ Data stream should be transmitted at least at 2 Hz for temperature data and 8-10 Hz for pressure data
→ Histograms including all those critical components with a temperature limit defined. Temperature readouts should also be available, with a color system that ease to identify temperature exceedances (for instance temperature data turns red when limit exceeded)
→ Histograms including flight and ambient data (pressure altitude, airspeed, Mach, delta ISA temperature, etc.), as well as aircraft and engine configuration (flap configuration, landing gear configuration, engine spools speeds, bleed configuration, power extraction, active thrust mode, etc.)

Extrapolation of flight test temperature data will likely be required soon after the test is completed. The extrapolation method needs to be defined by the Design Office before the test, typically consisting on a degree by degree extrapolation from the actual temperature (component temperature) to the Max Hot Day (MHD) temperature defined in the Altitude vs. Ambient Temperature aircraft flight envelope

At a given altitude, the component temperature can be extrapolated to MHD as follows,
𝐶𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 𝑇𝑒𝑥𝑡𝑟𝑎𝑝@𝑀𝐻𝐷=𝐶𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 𝑇𝑎𝑐𝑡𝑢𝑎𝑙+(𝑇𝐼𝑆𝐴 𝑀𝐻𝐷−𝑇𝐼𝑆𝐴 𝑎𝑐𝑡𝑢𝑎𝑙)

And the component temperature margin can be then derived,
𝐶𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 𝑇𝑚𝑎𝑟𝑔𝑖𝑛@𝑀𝐻𝐷=𝐶𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 𝑇𝑒𝑥𝑡𝑟𝑎𝑝@𝑀𝐻𝐷−𝐶𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 𝑇𝑙𝑖𝑚𝑖𝑡

TEST PREPRATION CHECKLIST

We would like to conclude this entry with a basic checklist to double check whether you are ready to conduct your nacelle and engine bay cooling and ventilation test.

  • Nacelle and engine bay test relevant hardware configuration fully defined
  • Any delta hardware with final configuration identified and effect on cooling and ventilation understood
  • Engine test relevant software configuration fully defined
  • Any delta software with final configuration identified and effect on cooling and ventilation understood
  • Aircraft environmental envelope defined (altitude vs. ambient temperature), MHD temperature defined

Thank you for reading ES3AERO's Nacelle and Engine Bay Cooling and Ventilation Test Guide

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

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