Slide 1: Architectural performance assessment of an e-VTOL aircraft based on a ducted vectored thrust concept
Architectural performance assessment of an electric vertical take-off and landing (e-VTOL) aircraft based on a ducted vectored thrust concept Author: Dr. P. Nathena, Reviewer 1: Prof. Dr. P. Bardenhagenb, Reviewer 2: Prof. Dr. A. Strohmayerc, Reviewer 3: Prof. R. Millerd, Reviewer 4: Dr. S. Grimshawd
Slide 2: Abstract (continued)
Concept (DVTC) e-VTOL, which is specifically optimised to meet the low-noise vertical take-off, long range and high payload requirements of the RAM market. The specific aircraft analysed is the Lilium jet. The aircraft is 7-seater with a cruise speed of 300km/h and maximum take-off mass of 3, 175kg. The
Slide 3: 1. Architectural design space for e-VTOL aircraft
1. Architectural design space for e-VTOL aircraft The design of e-VTOL aircraft for passenger transport is a new field, see Thipphavong et al. (2018) and Whittle (2018). Five degrees-of-freedom (DOF) drive the design: payload, speed, range, noise and simplicity. These degrees-of- freedom are strongly
Slide 4: Multicopter, lift & cruise and tilt rotor architectures
lack cruise eciency, which limits their application to UAM markets only. A more detailed review of multicopter architecture can be found in Pradeep and Wei (2019). The second category of e-VTOL is the lift & cruise architecture. These merge the multicopter, for vertical take-off and landing, with a s
Slide 5: Ducted fan advantages and the Lilium jet
swirl. Another advantage of ducted fans is that the duct can contain a blade-off in the case of blade loss or bird strike making them safer than open propellers. The main disadvantage of ducted fans is that because of the higher disc loading, as discussed above, the hover power is higher than for pro
Slide 6: 2. Design of a DVTC e-VTOL aircraft
VTOL aircraft which can address the market needs of UAM and RAM without facing the same noise challenges as propeller concepts. This paper is structured as follows: Section 2 details the aircraft requirements and specification. Sec- tion 3 describes the approach to the analysis. Section 4, analyses t
Slide 7: Figure 2: The Lilium jet architecture
Figure 2: The Lilium jet architecture. Picture taken from Lilium (2019a). trade-off between noise, cruise power consumption, hover power consumption, redundancy, DEP packaging eciency, and engineering complexity. In the ref- erence architecture the number of ducted fans is n = 36, and the diameter of
Slide 8: Flight mission and phases
range. To begin the assessment, a flight mission is defined, shown in Figure 3. The mission can be divided into seven phases. The seven phases are made up of the four modes of flight listed below. Figure 3: Flight phases for an e-VTOL mission for simplified calculations • Hover: This is the period of th
Slide 9: Hover power and efficiency
where vj,h is the jet velocity at nozzle exit during hover and ˙ mh is the total mass flow through the fans during hover. The overall hover eciency can be written as η0,h = power to jet power from battery = power to electronics power from battery | {z } ηB,h · power to motors power from electronics |
Slide 10: Cruise power and efficiency
where Dcr is the drag of the aircraft, and vcr is the cruise velocity of the aircraft. The eciency in cruise can be written out as a product of eciencies as η0,cr = power to aircraft power from battery = power to electronics power from battery | {z } ηB,cr · power to motors power from electronics |
Slide 11: Climb and descent power
crafts drag and a component of its weight in the direction of flight. This can be written as Pcl = (P i Di,climb + MT OM · g · sin(Φ)) · vcl ηP,cl · ηD,cl · ηF,cl · ηP E,cl · ηM,cl · ηB,cl ..(10) During climb the altitude increases to 3000m and the speed increases from 150km/h to the cruise velocity
Slide 12: Range equation and aircraft performance
where th is the total time in hover, take-off and landing, ttr is the total time in transition, take-off and landing, tcl is the time in climb, and tcr is the time in cruise. This can be rearranged to give an expression for the time in cruise, and multiplying by the cruise velocity vcr gives a relatio
Slide 13: Cabin and wing drag
4.1.1. Cabin drag The ideal drag of the aircraft cabin, see Nicolosi et al. (2015) among others, can be calculated as Dc,ideal = CD,c · 0.5 · ρcr ·Sc,∅ · v2 cr = 248N, (16) where the cabin drag coecient is CD,c = 0.039 and Sc,∅ is the frontal area of the cabin. The frontal area of the cabin is Sc,∅
Slide 14: Wing and flap configuration; flap drag
Figure 4: Wing and flap configuration. The scales, sizes, proportions, details and measure- ments are not implemented in the real aircraft and shall serve only for illustrative purposes. Green areas mark the surfaces being used to calculate wing drag Dw and flap drag Df . The fan stage eciency ηF is eff
Slide 15: Induced drag and total drag
4.1.4. Induced drag The induced drag Di can be calculated, see Schlichting and Truckenbrodt (2001a,b), as Di = 2 ·(MT OM · g)2 ρcr · π · v2 cr · s2 w · e,(26) where for a canard configuration the Oswald factor is e = 0.83, see Kroo (2001, 1982). Substitution of the Oswald factor into Equation (26) gi
Slide 16: Variable area nozzle
the jet is defined by σ, the ratio of the diameter of the exit nozzle Aj and the area of the duct in which the fan is located Ad Aj = σAd.(30) For hover we set σh = 1.3 and for cruise σcr = 0.9 resulting in Aj,h = 0.0742m2 and Aj,cr = 0.0513m2. At hover the blade tip Mach number is Mab,tip,h = 0.45 a
Slide 17: Effect of a variable area nozzle on fan performance
Reduction in nozzle area y=1+f tan b2 y f hF 1.09 1.31 1.55 0.40 0.4 0.27 88% 83% Figure 6: Effect of a variable area nozzle on fan performance. At the cruise operating point, closing the exit nozzle area to σ = 0.67 would move the operating fan point so that it was identical to that of the hover op-
Slide 18: Fan and propulsive efficiency
that ducted fans with high flow coecients φcr = 1.31 can be designed during cruise flight at eciencies of ηF,cr = 0.83, while achieving peak performance in hover flight with a fan eciency of ηF,h = 0.88. There is little published literature on fans or compressors designed at these high flow coecients. H
Slide 19: Duct efficiency
The duct eciency is defined as ηD = power to jet power from flow = 1 − T ˙ Sd,irrev 0.5 · vcr ˙ mcr · v2 j,cr − v2 cr + T ˙ Sd,irrev , (35) where T ˙ Sd,irrev are the boundary layer losses in the duct due to viscous dis- sipation which can be calculated for the hover and cruise fan operating points a
Slide 20: Motor, power electronics and battery efficiency
giving a duct hover eciency of ηD,h = 0.964.(42) 4.2.4. Motor eciency The motor eciency ηM is defined as ηM = power to shaft power from motor (43) The motor eciency in cruise is assumed to be ηM,cr = 95% and in hover ηM,h = 92%. These are typical for commercially available motors. The variation betwe
Slide 21: Hover and cruise power
where the overall aircraft eciency during hover is η0,h = ηF,h · ηD,h · ηP E,h · ηM,h · ηB,h ≈ 59% and Pboard = 8kW through the whole flight. Substituting into equation (46) gives Ph = 2,570kW. (47) It is an interesting academic question to calculate maximum hover time which the power in Equation (46
Slide 22: Climb power
the speed raises to vcr = 300km/h. This means that the power changes through the climb phase. However, in practice this change is not large and for simplicity a mean altitude of 1500m with a mean climb velocity vcl = 275km/h is set. Taking the drag value from Table 2, the climb drag is Dcl = 1,698N.
Slide 23: Range result of 261km
tuting into Equation (14) gives a range R = vcr Pcr (·Es(1 − SOCmin) − th ·Ph − 2 · ttr ·Ptr −tcl ·(Pcl + Pdes)) + 2 · tcl · vcl = 261km. (57) The focus of this paper has been on providing a simplified method of calculating the realistic maximum range of a DVTC e-VTOL aircraft. The analysis shows tha
Slide 24: Noise emissions and acoustic liners
a duct and to the tip speed of the blade being limited to ub,tip = 154.38m/s, which is equivalent to a Mach number Ma = 0.45, see also Appendix B. In addition, acoustic liners are included in the duct. These are designed to reduce tonal noise through Helmholtz and porous liners. Sutliff (2019) and Au
Slide 25: Battery, powertrain and electric motor technologies
in excess of 350W h/kg by using different anode materials. In addition active research is underway in the development of solid-state bat- teries. Singh (2020) predicts that these will be commercially available within 5 years with an energy density in excess of 400W h/kg. The specific power required du
Slide 26: Parameter variation for range sensitivity
Input Range Aircraft variation eB[W h/kg] th[s] µb/µpl[−]R[km] (Section 4.4) DVTC-1 320 60 1.36 261 DVTC-2 250 60 1.36 181 DVTC-3 320 90 1.36 232 DVTC-4 400 60 1.36 353 DVTC-5a 320 60 2.30 337 DVTC-5b 400 60 2.30 448 Table 4: Parameter variation for an investigated e-VTOL aircraft architecture. All
Slide 27: Conclusions
physical understanding of the key trades. The analysis shows that if an available battery technology with energy den- sity of 320W h/kg is assumed then the 7-seater DVTC aircraft with a maximum take-off mass of 3,175kg can achieve a range of 261km. It is shown that the de- velopment of solid-state ba
Slide 28: References
M. Clarke, J. Smart, E. M. Botero, W. Maier, and J. J. Alonso. Strategies for Posing a Well-Defined Problem for Urban Air Mobility Vehicles. 2019. doi: 10.2514/6.2019-0818. URL https://arc.aiaa.org/doi/abs/10.2514/ 6.2019-0818. J. D. Denton. Loss Mechanisms in Turbomachines, volume Volume 2: Combus-
Slide 29: References
H. D. Kim, A. T. Perry, and P. J. Ansell. A Review of Distributed Electric Propulsion Concepts for Air Vehicle Technology. 2018. doi: 10.2514/6.2018- 4998. URL https://arc.aiaa.org/doi/abs/10.2514/6.2018-4998. S. Kim, D. Kim, C. Son, K. Kim, M. Kim, and S. Min. A full en- gine cycle analysis of a tu
Slide 30: References
F. Schieber. Procedure for Estimating the Combined Noise Level of Multi- ple Acoustic Sources. 2021. URL http://apps.usd.edu/coglab/schieber/ psyc707/pdf/AddedNoiseLevels.pdf. H. Schlichting and E. A. Truckenbrodt. Aerodynamik des Flugzeuges: Erster Band: Grundlagen aus der Str¨omungstechnik Aerodyn
Slide 31: References and Appendix A: Hover thrust calculation
R. Whittle. Air mobility bonanza beckons electric vtol developers. https://pdfs.semanticscholar.org/a132/ ba1a11012da261627597f1d074c3f3ea67e9.pdf, 2018. Accessed: 2010- 09-30. X. Ye, P. Li, and C. Li. Numerical investigation of grooved blade tips effect on the performance of an axial flow fan. Zhongg
Slide 32: Appendix B: Fan design
Equation (A.3) differs from the power consumption for open rotor systems P open h,ideal P open h = T 3/2 h p2ρhAd,tot ,(A.7) see Bittner (2005). Appendix B. Fan design The fan flow parameters for hover, cruise and climb are shown in Table B.5 and B.6. The fan calculation was undertaken at the mean rad
Slide 33: Fan flow parameters and operating points
where the rotor chord length is cr = 0.052m. The demonstrated procedure can be repeated for different radial cuts, but doesn’t change the architectural deci- sion making process. Pshaft ˙ m uj vin ∆h0 ub,mean Hover 47.98kW 8.65kg/s 97.59m/s 126.87m/s 5.41kJ/kg 116.86m/s Cruise 5.06kW 4.39kg/s 94.11m/
Slide 34: Nomenclature
Dcr Total drag in cruise flight Dc Total cabin drag in cruise flight Dc,ideal Ideal cabin drag in cruise flight Df Total flap drag in cruise flight Di Induced drag in cruise flight Dw Total wing drag in cruise flight dh Hub diameter ds Shroud diameter Eacc Accessible energy in the battery Es Total stored e
Slide 35: Nomenclature (continued)
Tα Total thrust required during the respective flight state T ˙ Sd,irrev,α Total losses due to viscous dissipation tcl Operational climb time tcr Operational cruise time tmax h Theoretical maximum hover time th Total hover time th,l Operational hover time during landing th,to Operational hover time d