Watts up with the ultimate `green` aircraft ?

Developments in electric
propulsion in the
Deregulated sectors
Paul Dewhurst, Flylight Airsports Ltd
What are Footlaunched and Sub-115 Aircraft?
Footlaunched:
Must be Footlaunched
• Max 60 Kg unladen weight (inc fuel), or 70Kg for two place
• Max fuel capacity 10 litres
• Max stall speed 35knots (by default – V fast runners required!)
Generally fall into two groups – Paramotor and Powered Hanglider
Sub-115
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Single seat only
Max empty weight 115Kg – less fuel
MTOW 300Kg
Max stall speed 35 knots
Two main groups - Flexwing and Fixedwing
The Dream of Electric Flight
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Almost no engine noise
No emissions at point of use
Potential to use ‘green’ supply of charging power
Instant power and no warm up requirement
Reliable starting
Almost zero maintenance
Low vibration
Engine not affected by density altitude – only prop
No carb icing
Not oily!
Doesn’t care which way up it is – aerobatics?!
Feasibility
• powerful ‘rare-earth’ magnets for use in
electric motors
SmCo magnet holding
1000x it’s own weight
Feasibility
• lithium-polymer rechargeable cells
LiPo - lithium
polymer cells:
150 Whr/kg
1000 W/kg
LiPo
w1.siemens.com (Pictures of the Future – Fall 2007)
Electric vs. Petrol
• Energy content of petrol = 45 MJ/kg = 12.5 kWhr/kg of which ~30%
can be turned into power = 3.7 kWhr/kg
• 4-stroke petrol aero-engine power rating ~ 1HP/kg = 0.75 kW/kg
Electric vs. Petrol
• Energy content of petrol = 45 MJ/kg = 12.5 kWhr/kg of which ~30%
can be turned into power = 3.7 kWhr/kg
• 4-stroke petrol aero-engine power rating ~ 1HP/kg = 0.75 kW/kg
• High-tech. electric motors have an efficiency of ~90% and a power
rating of 6 kW/kg
• LiPo cell storage capacity is ~ 0.15 kWhr/kg
Electric vs. Petrol
• Energy content of petrol = 45 MJ/kg = 12.5 kWhr/kg of which ~30%
can be turned into power = 3.7 kWhr/kg
• 4-stroke petrol aero-engine power rating ~ 1HP/kg = 0.75 kW/kg
• High-tech. electric motors have an efficiency of ~90% and a power
rating of 6 kW/kg
• LiPo cell storage capacity is ~ 0.15 kWhr/kg (1/25 of net petrol)
• A 75 kW electric motor saves 85 kg in weight, but this only
corresponds to 13 kWhr of battery capacity = 4 kg of petrol
Electric vs. Petrol
• Energy content of petrol = 45 MJ/kg = 12.5 kWhr/kg of which ~30%
can be turned into power = 3.7 kWhr/kg
• 4-stroke petrol aero-engine power rating ~ 1HP/kg = 0.75 kW/kg
• High-tech. electric motors have an efficiency of ~90% and a power
rating of 6 kW/kg
• LiPo cell storage capacity is ~ 0.15 kWhr/kg (1/25 of net petrol)
• A 75 kW electric motor saves 85 kg in weight, but this only
corresponds to 13 kWhr of battery capacity = 4 kg of petrol
• Hence, an electric aircraft must be very efficient
How to do more
with less?
• Power requirement for level flight resolves
into:
Sinkrate x Weight = Thrust Horsepower*
550
• High speed = high Ld required
• Low speed = low span loading more important
than drag = our machines very suitable.
An electric airliner ?
Boeing 737 - 400: 60,000 kg max. (60 t.)
• 30 t. empty weight
• 15 t. payload (168 passengers)
• 15 t. fuel => LiPo cells = 2.25 MWhr capacity
Assuming L/D = 15 at 560 mph (= 10 MW aero)
and 60% efficient drive = 17 MW electrical
An electric airliner ?
Boeing 737 - 400: 60,000 kg max. (60 t.)
• 30 t. empty weight
• 15 t. payload (168 passengers)
• 15 t. fuel => LiPo cells = 2.25 MWhr capacity
Assuming L/D = 15 at 560 mph (= 10 MW aero)
and 60% efficient drive = 17 MW electrical
• Flight time = 8 minutes (=> 75 miles) !!
An Electric Paramotor
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Total weight ~ 120Kg
Sink rate ~ 4.2FPS
2Thp – 1.5Kw / .5 drive eff
3kWhr requirement
12kg cells = 1.8kWhr
Duration = 36 mins - less climb, 100%
discharge
An Electric Powered Hanglider
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Rigid wing best efficiency
Sink Rate ~ 2.5FPS
Weight 140Kg
1.4THP – 1kW / .5
2kWhr requirement
12kg cells = 1.8kWhr
Duration = 54 mins – less climb, 100%
discharge
More Cells, more duration?
• Pramotor limited by weight a person
can realistically carry on their back.
• Powered Hanglider limited by 60Kg
max weight with ‘fuel’
Good solution though for what
are essentially Self Launched
Gliders
Current Footlaunched Projects
Neil Andrews UK
Current Footlaunched Projects
Dr Ing Werner Eck - Germany
E-Lift system
• 10Kw direct drive brushless motor
• 14 cell Lithium Ion cell pack 31Ah fast
chargeable
• 61Kg max static ‘startboost’ – 52
continuous
• Own design folding prop
• 22Kg Paramotor system
• 22mins flight time no lift
• Climb height 800m
• Climb rate 1.2m/s
Elift System for Powered Hangliders
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Overall harness weight 28Kg
30 mins flight time – no lift
Climb height 1100m/3600’
Climb rate 1.8m/s
E-Lift measured values
flown on 10.03.08 with rigid wing Atos VR
1200
1000
altitude 1200m
Kapazität in 0,1Ah
Drehzahl in 10/1/min
Strom in Ampere
Schub in Newton
I-Vario in cm/s
Höhe in metern
Spannung in 0,25V
Leistungsabgabe in 10W
average motor power 7kW
800
Start thrust 61,5 kp
600
average thrust 31,5kp @ 48km/h
average climb rate1,8m/s
400
used capacity 29,8Ah
from 31Ah
200
low rpm at 1900 1/min
average current 175 A
constant voltage
at 47 Volt
climb time 11min.
13:32:34
13:32:21
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Current Footlaunched Projects
Yuneec – China!
E-Pac system
• 160mm direct drive brushless
motor 10kW, 1.2M prop
• 1.7kWh capacity
• 3 blocks of lithium polymer
cells
• 25Kg unit weight
• 50Kg max static thrust
• 25-35mins duration
Scalextric anyone!
Sub-115 projects
Randall Fishman – USA
‘Electraflyer Corp’
• 18Hp direct drive
motor(12Kg), folding prop
• Up to 5.6kWhr cell pack
(40Kg)
• 112Kg weight with large
pack
• 63Kg max static thrust at
1800RPM
• Experimenting with redrive
for greater thrust – 70Kg
(non folding prop)
• You can buy it now!
Werner Eck
Aeriane Swift Lite conversion
(SWIFT =Swept Wing Inboard Flap Trim !)
• 24:1 Ld max
• .65ms min sink
• 80Kg empty weight less
Cells
• 190Kg MTOW
• 1.5m/s climb rate
Werner Eck – Flylight Dragonfly
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In process!
65Kg less cells
185/ 200Kg MTOW
10:1 LD
Min sink 1.1m/s
3.5kW required
Around 50 mins
duration on 24kg cell
pack
Dr Eck – Aerola Alatus
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100Kg less cells
235Kg MTOW
27:1 LD
Min sink 0.8m/s
Yuneec
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E200 project
High wing strut braced conventional layout
Twin pylon mounted 10-15Kw motors
50Kg cell payload
Flying as giant RC model at present!
Video of test flights– show at end
Hummingbird
Hummingbird
Dr Paul Robertson
Paul Dewhurst
• 80 kg empty
• 250Kg MTOW
1m
• Tubular aluminium
• Fibre-glass fairings
• Fabric wing covering
• 10 m wingspan
• 6 m long
Hummingbird figures:
Glide Ratio L/D vs. Airspeed
• L/D max is ~18:1 at 45mph
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• Min sink ~ 200fpm
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10
• Stall speed ~ 32mph
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Aero. Power vs. Airspeed
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100
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Airspeed (mph)
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• Power reqd. to maintain level
flight = Drag × Airspeed
• Hence, propeller Thrust must
exceed Drag for climbing
Power (kW)
Glide Ratio L/D
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Airspeed (mph)
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Electric Powertrain
• Modelling of motor & prop. performance:Thrust & power required ?
• 200 kg weight with L/D = 18:1 @ 45 mph ⇒ 11 kgf
(=110 N @ 20 m/s, this is an aerodynamic power
requirement of 2.2 kW)
• Each motor/prop. must therefore produce 5.5 kgf @
45 mph airspeed to maintain level flight
• Extra thrust (x 5) is required for take-off and climb
Electric Powertrain
• Test modelling of motor & prop. performance
Theory
www.gylesaero.com
Experiment
Electric Powertrain
• Modelling of prop. characteristics allows
motor power (= current x voltage) to be
determined
Static thrust data 22"x12" 4-blade prop.
15
Expt.
Thrust (kgf)
Theory
• Good agreement
with theory - high
motor efficiency
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5
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1000
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Power (W)
2000
2500
3000
Electric Powertrain
• Twin brushless aero-motors, 10 kW each
Thrust at various airspeeds
5mph
45mph
70 mph
25
Prop. thrust (kgf)
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15
10
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Prop. pow er input (kW)
5
6
7
Electric Powertrain
• Twin cell stacks 12 x 3.7 V, 40 Ahr LiPo (3.5 kWhr)
• Integrated control system required for battery safety
Lithium
polymer cell
stack
Brushless motor
controller
Battery Management System
Throttle
lever
Pulse width
controller
Monitor individual cells:
• voltage (4.2 - 3.2 V)
• current (0 - 200 A)
• temperature (0 - 50 °C)
Brushless dc
aero-motor
31” x 12”
3-blade
CF prop.
Electric Powertrain
• Twin cell stacks 12 x 3.7 V, 40 Ahr LiPo (3.5 kWhr)
• Integrated control system required for battery safety
Lithium
polymer cell
stack
Brushless motor
controller
Battery Management System
Throttle
lever
Pulse width
controller
Monitor individual cells:
• voltage (4.2 - 3.2 V)
• current (0 - 200 A)
• temperature (0 - 50 °C)
Brushless dc
aero-motor
31” x 12”
3-blade
CF prop.
Electric Powertrain
Full-scale static tests
Static Thrust vs. Electrical Power
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Thrust (kgf)
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25
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Theory
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Expt.
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Power (kW)
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Powertrain testing – next step?
• First air tests will use an existing airframe
• An old Lazair; which meets <115kg rules
• …. and is a twin !
Hummingbird Performance
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Duration ~40 minutes
Range 35 miles
Max. rate of climb 650 ft/min
Max. speed 80 mph
(+80% more duration with additional cell packs)
But how are we going to charge the
batteries ?
• Mains power
• Wind turbine
• Fuel powered generator eg. LPG, fuel cell
Wind turbine
• Post-code check for windspeed (5.5 m/s avg.)
• 1.8 m dia., 35% efficient turbine will generate
~1500 kWhr of electricity per annum
• Assuming 67% charge efficiency = 270 recharges
• This equates to ~180 hours flying each year
www.reuk.co.uk
Wind turbine
• Post-code check for windspeed (5.5 m/s avg.)
• 1.8 m dia., 35% efficient turbine will generate
~1500 kWhr of electricity per annum
• Assuming 67% charge efficiency = 270 recharges
• This equates to ~180 hours flying each year
This is actually quite feasible
Note: if all the parts were made from aluminium, the
aircraft and wind turbine would cause ~1000 kg of
CO2 to be released during manufacture.
Costs?
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Lithium polymer cells around £150 kg
Life of cells circa 1000 cycles to deplete to 80% capacity
Mains recharge approx 10p kWh
No maintenance
Footlaunched:
Approx £4 per motorised flight hour electric
Approx £4 for petrol with 2 stroke IC motor + maintenance
Hybrid?
Fuel cells too heavy for us.
But how about ?:
• Electric drive with medium sized cell stack
• Small IC motor running at best fuel specific RPM – used as
generator
• Sized to provide cruise power at best Ld speed plus small
reserve
• Cells used for takeoff and climb boost and trickle charge in the
cruise
- Student study project at Cambridge
Conclusions
• Light electric leisure aircraft (especially those with a
soaring slant) are now just about feasible - on both
technical and economic grounds
• Battery performance will continue to increase - and
become cheaper
• A wind turbine offers a feasible and carbon-neutral
approach to re-charging the batteries between flights
• Hybrid-powered aircraft, particularly for GA, will
become a reality in the near future
Any questions ??