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NOISE IMPACT OF ELECTRIC AND HYBRID PROPULSION IN AVIATION
Opportunities and Threats
Rod SelfISVR, University of Southampton
20th November 2018Greener By Design Conference -- London
What electric aircraft are:
Types of electric aircraft:
Drones
Small UAVs for package delivery and other roles
Types of electric aircraft:
Air Taxis
Images Curtesy NASA
Larger UAVs for urban and sub-regional passenger transport
Types of electric aircraft:
Hybrid Electric
Images Curtesy Zunum Aero
Replacement for short and medium haul passenger transport
What electric aircraft are not:
• Electric aircraft are not necessarily quieter than equivalent conventional aircraft
• Main noise sources: jet, fan, and airframe still present
• Combustor and turbine noise may be absent
• Electric motor noise is present
SAECA Project Results
• e-A320 v. A320neo – 900nm mission -- TO
SAECA Project Results
• e-A320 v. A320neo – noise v. mission length -- TO
SAECA Project Results
• e-A320 v. A320neo – Approach
More realistic concept aircraft do show noise gains
• E.g. Boing Sugar-Volt concept estimate is 22 EPNdB below Chapter 4
• However, more conventional concept aircraft have comparable gains
• Main noise gains of e-aircraft from increased propulsive efficiency
• More radical designs such as DEP may give greater gains
• But we are less sure how to estimate the impact
Estimating noise from novel aircraft – physical noise
• Because conventional aircraft have the same type of noise emission we know how to estimate changes
• More novel designs require understanding:
• In principle this is not a problem
New noise sources such as motor noise and BLI noise
New installation effects
New operational profiles
Estimating noise from novel aircraft – perception
• How people respond to noise depends on a number of factors – not just loudness
• Do current metrics, EPNL and Leq apply to novel aircraft?
Effective Perceived Noise Level
• Effective Perceived Noise Level (EPNL) is the current metric used to assess noise emissions for certification.
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• EPNL:
o Perceived Noise Level (PNL),
o duration effects, and
o tonal penalty based on the level of the strongest protruding tone.
• EPNL is not able to account for the perceptual effect of complex tones.o 1/3-octave banding for tone detection.
o Solely focused on strongest protruding tone.
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• Work at the ISVR shows Aures Tonality based metric better at predicting perception than EPNL when multiple tones are present
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Courtesy of Rolls-Royce plc - Advanced open rotor concept
Courtesy of NASA - Sceptor project
Annoyance model for DEP using Loudness, Roughness and AuresTonality as predictors (Rizzi et al., 2017)
Source: Kingan (2014)
• Small-size quadcopters (DJI Phantom and HS-200): Multiple complex tones distributed across the whole spectrum (significant content in high frequency).
• Drone noise certification: More sophisticated tonality methods needed.
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Tones -- A major potential problem for drones and air taxis
• Currently Leq used to measure community annoyance around airports
• Not always reliable
• Will need to be amended to reflect novel aircraft noise signatures
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Community Noise Considerations -- I
• The most annoying noise is a new noise
• Drones and other urban aircraft will increasingly affect people away from airports
• Visual intrusion from low altitude flights increases perceived noise substantially
• Public understanding and trust are major issues
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Community Noise Considerations -- II
• E-aircraft replacing current fleet:
– are likely to show substantial noise benefits but variation in noise signature will require novel metrics to reflect noise impact
– Will require additional source modelling and knowledge of operation to establish confident prediction of noise impact
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Conclusions and Requirements -- I
• Urban E-aircraft – Drones and Air Taxis:
– New noise source whose impact cannot be predicted with confidence
– Will require source modelling and knowledge of operation to establish confident prediction of noise levels
– Will require significant research on multi-model attitudinal response to establish appropriate metrics
– Will require establishment of low noise operational rules
– Will require public participation to maintain trust
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Conclusions and Requirements -- II
Thank you!