Electric Propulsion for Vertical Flight Transformative Vertical Flight Workshop Arlington 2014 Mike Ricci Vice President, Engineering mricci@launchpnt.com 1
LaunchPoint Technologies High Performance Controls/Electromechanical ystems Maglev Train High power density, high efficiency electric motors/generators/electronics Electromechanical engine valve actuator Maglev Heart Assist Pump 2
LaunchPoint ual Halbach Array Motor High power density and efficiency 2.5 to 5 hp/lb at 95% efficient depending on speed, size, and configuration Ironless stator greatly reduces probability of winding fault to ground Fully encapsulated winding with heavy duty, high temperature phase insulation Patent Pending Magnets are mechanically retained from coming loose, optionally hermetically sealed in structure Integral impeller provides stator cooling air flow without need for motor to be in free air stream, reducing vehicle cooling drag Easily configurable for dual independent 3-phase windings or isolated phase configurations 3
Halbach arrays are a key enabler The field is concentrated on this side The field is cancelled on this side 4
Reduced Cooling rag pinning disks with small gap create turbulent, highly convective layer in contact with stator for cooling Centrifugal action pumps fresh air through the gap to ensure cooling even without high speed flow over motor Air velocity in gap between stator and magnets- from CF analysis Ram air and high velocity stream not required for cooling motor, low drag NACA inlet for cooling is sufficient CF analysis of Motor section showing temperature in air 5
High Power ensity Gen-et Heavy Fuel to Electricity 2 stroke, 2 cylinder heavy fuel engine by GE (Greg tevens Engineering) mated to LaunchPoint alternator 1 kw/kg for fuel to C bus conversion ubcontract to LaunchPoint Technologies Funded under a NAA contract with NIA 6
GE-LaunchPoint Gen-et 6 kw max continuous power <6 kg (13lb) for 6 kw (8 hp) gen set ~8 lb engine, 3 lb alternator, 2 lb electronics ~.4 lb/hp*hr BFC 95% efficient shaft C bus conversion at 25% power = 1.5 kw 97% shaft to AC, 98% AC to C Bus 7
Electric Tail Rotor ystem Concept Use our lightweight motors and fault tolerant controller architecture to drive tail rotor Transmission Turbine Accessory Gearbox Tail Rotor haft Tail Rotor Gearbox Optional energy storage in future design Power Cables Transmission Turbine eries Hybrid architecture Navy BIR N00014-13-P-1095 Accessory Gearbox Generator Electronics LaunchPoint Generator Motor rive LaunchPoint Motor 8
ETR irect rive Motor 9
ETR -- Generator riven off shaft PTO for tail rotor 10
Reliability Requirements FAA airworthiness requirements Part 27 FAR 27.695 states that for powered controls the system should allow continued safe flight and landing after any single failure. FAR 27.672 also states that After any single failure of a power operated system the rotorcraft is safely controllable within a practical operational envelope and can fly and land safely. FAR 27.571 indicates failure rate for catastrophic event should be extremely remote; and extremely remote is further defined by the FAA as between 10-7 and 10-8 per hour (see table 3-6 in FAA ystem afety Handbook) 11
Electric Propulsion Reliability C Bus Fault Tree for basic electric propulsion Control ignals Power upply Controller/ Inverter Bearings Motor Winding Gearbox Hazard If Loss of Output is Hazardous or Catastrophic, the basic electric propulsion system doesn t even come close to meeting FAA airworthiness of better than 10^-6/hr Bennet, Mecrow, Atkinson, Atkinson, afety-critical design of electromechanical actuation systems in commercial aircraft, IET Electric Power Applications, 2009 12
Gearbox vs irect rive? epends on your failure modes and severity Gearbox is generally lighter than direct drive since electric motor sized by torque iamond E-tar Conventional Helicopter Tail Rotor drive 13
Let s try 2 of everything *If* continued safe flight and landing is possible with 1 of 2 systems failed, this works But these two failures of independent motor/drives need to be isolated so one failure does not cascade over and fail the second system imply putting two controllers and motors on a shaft OE NOT provide isolation 14
Redundancy = Reliability??? ometimes but not always Redundancy may not be an option 15
Requirements for Fault tolerance Redundancy or degraded failure modes No single point failures Isolation of failures / segmentation No cascading failures Continued operation after 1 st single (worst case) failure etection of failures No latent failures 16
17 Parallel but NOT redundant R/C controller teardown
MIL-HBK-217F Est. Failure Rate.012*4*10*8 = 3.84*10^-6 /hr for a single device Times (30) devices = 1.1*10^-4 / hr for just the power devices 18
Failure Isolation MOFET can fail on or off Fail ON = explosion/fusing of part when opposite gate turns on If detected, still creates eddy current braking in phase All propulsive output lost in both cases ome Fault Tolerant Architectures Bennet 2009 Welchko 2004 19
ensing and Isolation are Key Full fault tolerance requires attention to detail! Redundant digital controllers with voting mechanisms Communication, voting logic Embedded software and hardware can fail P Monitor/control P Monitor/control P Monitor/control ingle Event Upsets in perfectly good hardware can cause software malfunction oftware needs to be designed to be fault tolerant as well (i.e. Toyota sudden acceleration and Michael Barr s expert witness testimony) Note 3 independent power busses required for isolation of power bus faults From Electric Boat Corporation, U 6320731 20
Electric Propulsion is Fly by wire But also Fly by software The electric systems involved in modern electric propulsion almost without exception have some software component oftware components in: Motor rives Battery Management ystem Generator controller and Engine controller 21
LaunchPoint Motor rive evelopment 3 lane drive in development 40 kw each 120 kw total ~3.8 kg total (per lane) 1.6 kg active and EMI filter 2.2 kg heat sink and fan >20 kw/kg without heat sink; 10 kw/kg including 22
ETR Failure Rate Calculations Multiple Lane esign Multiple C Busses Transmission Turbine Accessory Gearbox Generator Electronics LaunchPoint Generator LaunchPoint Motor Motor rive Failure of single lane is still 10-4/hr Tail rotor peak to nominal power is approximately 4X o with one lane failed normal operation remains possible, with some reduction in envelope (FR = ~10-4/hr) Even with 2of3 lanes failed pilot is able to retain full control with head into the wind (FR = 10-8/hr) 23
ETR ystem Weight Breakdown Alternator 12.7 kg Alternator Electronics 1 kg C Bus Cables 4.3 kg Motor Electronics (including heat sinks/fans and EMI filters) 8-10 kg Motor 20 kg Total 46 24
ETR Results Adds some weight (23 kg over shaft/gears) eries electric power transmission is less efficient than shaft & gears CAA paper data appears to show tail rotor shaft/gearbox failures between 5.7*10^-7 and 4.6*10^6 for Catastrophic Failure Airworthiness requirement 1*10^-7/hr Fault Tolerant ETR system can have lower FR (limited by bearings and seals) Fly By Wire allows redundancy, isolation & sensing while removing single point failure 25
Fault Tolerant Electric Propulsion Electric propulsion can potentially enable simpler ways to get to high reliability vertical flight N+1 or N+2 propellers can achieve high reliability with simple lower reliability drives on each propeller Removes most single point failures till need multiple (isolated) power busses, sources, and control signal paths 26
istributed Lift Motor Gears are now an option for greatly increased specific power 32 kw, 2500 rpm 4.8 kg 6.7 kw/kg 27
Motor and Rotor Optimization For a given fixed payload requirement, vehicle weight required to complete mission (VTOL, cruise) (Assuming direct drive motors) 28
Electric Machine esigns Machines we are working on/proposing 6 prototype 7.5 alternator ETR generator ETR motor Helicopter main rotor direct drive MW motor concepts 29
6 prototype 5 kw at 8400 rpm, 95% efficiency.7 kg mass 7 kw/kg Tip speed 67 m/s Out-runner design mall lightweight bearings Carbon fiber rotor plates 30
7.5 Gen-et Alternator 10 kw at 7500 rpm 16 kw at 12,000 rpm 1.5 kg mass 6.6 kw/kg @ 7500 rpm 10 kw/kg @ 12,000 rpm In-runner design Tip speed 75 m/s @ 7500 rpm; 120 m/s @ 12000 rpm Titanium plates, hermetically sealed, mechanically retained magnets Large structural margins to accommodate engine power stroke pulsation 31
13 Generator 82kW at 6200 rpm, 95% efficiency 12.7 kg 6.5 kw/kg Tip speed 98 m/s In-runner design Titanium rotor plates Expect 20% weight savings with CF 32
16.5 motor (Helicopter Tail Rotor) 82 kw at 3600 rpm, 94% efficiency 20 kg mass 4 kw/kg Tip speed 70 m/s In-runner design Heavy duty bearings Extended output shaft prag over-running clutches on each stack Titanium rotor plates Expect 15% weight savings with CF 33
7.5 96 kw with gear reduction 12,000 rpm motor, 2500 rpm output shaft 11 kg ~9 kw/kg 34
Helicopter Main Rotor Power (kw) peed (rpm) motor efficiency iameter (m) GearBox Weight (kg) Weight (kg) 200 400 92 1.2 131 0 200 6000 93 0.33 20 27 Working with collaborator Pascal Chretien Number of patents relating to electric/hybrid helicopter 35
MegaWatt scale possible High tip speed plus large diameter = greatly increased specific power Proposed 1 MW motor 200 m/s tip speed 1 MW at 6,000 RPM ~70 kg (projected) 95% efficient 26 diameter Up to 13 kw/kg 36
Mike Ricci Vice President, Engineering mricci@launchpnt.com (805) 683-9659 x244 Partial funding from ARPA Phase I BIR contract #W31P4Q-09-C-0109 Partial funding from NAA Phase I BIR contract #NNX10C84P 37