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Optimum number of engines for transport aircraft employing electrically powered distributed propulsion

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Abstract

Realizing a significant reduction of enroute emissions with respect to greenhouse gases is one major challenge in aircraft design today. Conventional kerosene propulsion systems are going to reach their efficiency limits in near future and it will be very ambitious to fulfill the requirements for future aircraft transportation using conventional engines. Consequently, new approaches for propulsion system design and integration are required to further improve aircraft efficiency through synergy effects. In this paper, a universally electric, short-haul, medium-capacity aircraft utilizing electric motors and battery for motive power is used as datum. The focus lies on the impact of a distributed propulsion system on the aircraft design and flight performance and will not discuss the advantages and disadvantages of the used reference aircraft configuration. Initial studies were performed identifying that the critical design cases for electric motor sizing are the one-engine-inoperative (OEI) flight segments, i.e., the climb gradients required at take-off and landing as well as field length requirements. By increasing the number of installed engines (i.e., motor–fan combinations) the OEI performance requirements may be satisfied with a reduced amount of installed motor and battery system power. An integrated aircraft performance analysis is conducted to estimate the possible net benefit in terms of increased aircraft range when increasing the number of installed engines. Aerodynamic efficiency degradation is considered as well as weight impacts due to electric motor scaling and necessary system architecture modifications. The analysis shows that a 6 % increase in aircraft design range can be achieved when going from 2 to 4 installed propulsive devices.

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Abbreviations

AEO:

All engines operative

BCU:

Battery control unit

EIS:

Entry into service

EMS:

Electric motor system

FL:

Flight level

GPU:

Ground power unit

HTS:

High-temperature superconducting

ISA:

International standard atmosphere

MTOW:

Maximum take-off weight

OEI:

One engine inoperative

OEW:

Operating empty weight

PAX:

Passenger

SSC:

Second segment climb

SSPC:

Solid state power controller

T/O:

Take-off

TOC:

Top of climb

TOFL:

Take-off field length

UESA:

Universally electric systems architecture

A:

Wing reference area (m2)

D Fan :

Fan diameter (m)

FPR:

Fan pressure ratio (–)

GR:

Gear ratio (–)

\(\dot{h}\) :

Climb rate (m/s)

k int :

Interference drag factor (–)

k E :

Mass relief factor (–)

k FT :

Landing gear and engine factor (–)

L/D :

Aerodynamic efficiency (–)

m :

Mass (no subscript indicates aircraft mass) (kg)

n :

Number of propulsive devices (–)

P :

Power (kW)

Q :

Torque (Nm)

Ref:

Subscript indicating reference value

RPM:

Revolutions per minute (1/min)

T :

Thrust (N)

V :

Flight speed (m/s)

V 1 :

Take-off decision speed (m/s)

V 2 :

Take-off climb safety speed (m/s)

V DEAS :

Design dive speed (km/h)

φ25 :

Quarter chord sweep (rad)

Λ:

Wing aspect ratio (–)

δW :

Thickness to chord ratio at wing root (%)

η Motor :

Electric motor system efficiency (–)

η Prop :

Propulsor efficiency (–)

γ :

Flight path angle (°)

ρ :

Density (kg/m3)

ρ P :

Specific power (kW/kg)

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Acknowledgments

The authors like to acknowledge the work of all Bauhaus Luftfahrt team members participating in the conceptual design of the baseline aircraft.

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Authors and Affiliations

  1. Cassidian, Rechliner Straße, 85077, Manching, Germany

    Hans-Jörg Steiner

  2. Bauhaus Luftfahrt e.V., Lyonel-Feinigner-Straße 28, 80807, Munich, Germany

    Patrick C. Vratny, Corin Gologan, Kerstin Wieczorek, Askin T. Isikveren & Mirko Hornung

Authors
  1. Hans-Jörg Steiner
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  2. Patrick C. Vratny
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  3. Corin Gologan
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  4. Kerstin Wieczorek
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  5. Askin T. Isikveren
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  6. Mirko Hornung
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Corresponding author

Correspondence to Patrick C. Vratny.

Additional information

This paper is based on a presentation at the German Aerospace Congress, September 10–12, 2012, Berlin, Germany.

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Steiner, HJ., Vratny, P.C., Gologan, C. et al. Optimum number of engines for transport aircraft employing electrically powered distributed propulsion. CEAS Aeronaut J 5, 157–170 (2014). https://doi.org/10.1007/s13272-013-0096-6

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  • DOI: https://doi.org/10.1007/s13272-013-0096-6

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