Key Drivers for evtol Design Christopher Silva From VTOL to evtol Workshop May 24, 2018

Transcription

1 Key Drivers for evtol Design Christopher Silva From VTOL to evtol Workshop May 24, 2018

2 Can we use what we already know? Techniques and processes Aircraft / System design theory: Design Thinking, MDAO, IPPD, classic sizing Historical data from the fossil record Wind tunnel data from NASA and DoD (ntrs.nasa.gov, dtic.mil) Flight test data from NASA and DoD (ntrs.nasa.gov, dtic.mil) Weights of components and whole vehicles (NDARC theory manual) Procedures and operational requirements (various sources and regulations) Tools for high fidelity and low fidelity analysis Aeromechanics of rotors and wings Electric system models Structural analysis for normal loads and crash What do we know we don t know? e- versions of most of above What don t we realize we don t know? Unexpected consequences From VTOL to evtol Workshop, May 24,

3 NASA uses a suite of concept tools Design space exploration and optimization NDARC: Design/sizing RCOTools: OpenMDAO ANOPP/ANOPP2: Noise NPSS (special access): Engines (+motors) SIMPLI-FLYD (NASA): Handling qual/control CAMRAD II/RCAS/CHARM: Aeromechanics IXGEN (M4): Blade stiffness OpenMDAO: Execute jobs, optimize OpenVSP: Initial geometry Rhino (McNeel): Final geometry Needs: Structures, Transient Thermal, Cost/economics, Electric Accessories From VTOL to evtol Workshop, May 24,

4 NASA Concept Vehicles for Air Taxi Operations Explored design-space: payload, range, aircraft type, propulsion system Single-passenger (250-lb payload), 50-nm range electric quadrotor Six-passenger (1200-lb payload), 4x50 = 200-nm range hybrid side-by-side helicopter Fifteen-passenger (3000-lb payload), 8x50 = 400-nm range turbo-electric tiltwing Research areas identified to support aircraft development for emerging aviation markets, in particular VTOL air taxi operations These concept vehicles already being used as examples From VTOL to evtol Workshop, May 24,

5 power change (%) We need to model interactions early Rotor-rotor interactions impact performance, vibration, noise, handling qualities Quadrotor reduce cruise power by: Elevating rear rotors above front rotors Also reduces noise and vibration Forward center-of-gravity, so front and rear rotors trim closer to same thrust From VTOL to evtol Workshop, May 24,

6 RPM control means From VTOL to evtol Workshop, May 24,

7 Even at moderate speed may create high loads Quadrotor fixed pitch, hingeless; level flight and 2g turn Hub moment 2g 1g design load for lift-offset rotor design load for hingeless helicopter rotor From VTOL to evtol Workshop, May 24,

8 Rotor L/De Rotor-Rotor interactions can be beneficial You need analysis which captures wake interactions and aircraft system effects to make the right design choices Outboard advancing is quite a bit better than outboard retreating Twist trades between hover and forward flight need system effects Outboard advancing Peak L/De ~ 10.5 Peak b/d ~ Inboard advancing Peak L/De ~ isolated rotors = 8.9 Single Rotor = 7.7 8

9 Need light-weight, high-power batteries Baseline designs: battery installed & useable specific energy = 400 Wh/kg State-of-the-art = Wh/kg installed & useable electric quadrotor hybrid side-by-side battery fuel payload payload operating weight operating weight installed specific energy installed specific energy From VTOL to evtol Workshop, May 24,

10 Your battery details matter a lot for evtol Typical Li-ion battery discharge characteristics capacity reduction Account for efficiency reduction with discharge rate, and unusable energy From VTOL to evtol Workshop, May 24,

11 electric side-by-side need high discharge current capability current: I = xc Cruise efficiency: battery energy Hover efficiency: battery power From VTOL to evtol Workshop, May 24,

12 What is a representative Urban Air Mobility Mission? 6 place, 1200 lb payload Range = 75 nm Cruise V br with 10 kt headwind Takeoff and landing at 6000 ft / ISA Taxi: 15 sec at 10% power Transition: 10 sec at max power Cruise: capable of 500 fpm climb Reserve: V be Ref: Patterson, Antcliff, and Kohlman, A Proposed Approach to Studying Urban Air Mobility Missions Including an Initial Exploration of Mission Requirements AHS Forum, May 2018 From VTOL to evtol Workshop, May 24,

13 What known unknowns is NASA looking at? Handling Qualities Modeling NASA concept vehicles (the plant ) Simulating flying the vehicles (pilots and passengers) Operations in the airspace Near the vertiports (What is a vertiport?) En route air traffic (What rules? How many?) Contingencies, margins (20 minutes? Autorotation?) Structures Flight loads, dynamics, durability, and crashworthiness Acoustics Noise and annoyance From VTOL to evtol Workshop, May 24,

14 PROPULSION EFFICIENCY high power, light battery light, efficient, high speed electric motors power electronics and thermal management light, efficient diesel engine light, efficient small turboshaft engine efficient powertrains PERFORMANCE aircraft optimization rotor shape optimization hub and support drag minimization airframe drag minimization Red = primary RVLT focus Blue = secondary RVLT focus ROTOR-ROTOR INTERACTIONS performance, vibration, handling qualities aircraft arrangement vibration and load alleviation SAFETY and AIRWORTHINESS FMECA (failure mode, effects, and criticality analysis) component reliability and life cycle crashworthiness propulsion system failures high voltage operational safety OPERATIONAL EFFECTIVENESS disturbance rejection (control bandwidth, control design) all-weather capability Passenger acceptance cost (purchase, maintenance, DOC) NOISE AND ANNOYANCE low tip speed rotor shape optimization flight operations for low noise aircraft arrangement/interactions active noise control cabin noise metrics and requirements Quadrotor + Electric Side-by-side + Hybrid Tiltwing + TurboElectric STRUCTURE AND AEROELASTICITY structurally efficient wing and rotor support rotor/airframe stability crashworthiness durability and damage tolerance ROTOR-WING INTERACTIONS conversion/transition interactional aerodynamics flow control AIRCRAFT DESIGN weight, vibration handling qualities active control From VTOL to evtol Workshop, May 24,