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!