Electric aviation is still in its infancy, but with interest in the field clearly growing rapidly by the year … (see our recent coverage of the Siemens news for more on that.) … more and more conversations are popping up on online discussion forums.
One of our friends and readers, Peter Egan, recently shared rather interesting specs for a 100-seat plug-in hybrid (PHEV) aircraft — over on the Tesla Motors Club forum, but the idea seems worth sharing here. Perhaps it’ll kick off an interesting conversation.
Here’s the original posting in its entirety:
While the aviation industry is starting with 1 to 4 seat electric aircraft to mature technology, an indicative specification for a plug-in hybrid version of an industry standard 100 seat regional propeller powered aircraft could look as follows below. Tesla technology would be used in the battery system and in the ground ‘drone’ used to power the aircraft while taxiing to the runway.
In the attached image of a modified CRJ1000, I have left the turbofans in place to compare with the new electric drive layout.
The aircraft has a 100 km electric range. However, the batteries are mainly used on take-off with the turboshaft-generator APU contributing power on take-off and fully powering cruise flight, aircraft services and battery recharging.
The 100 km electric range, along with aircraft glide capacity, is kept in reserve in the event of turboshaft engine failure. The aircraft has one jet fuel burning turbine compared to three for conventional 100 seat aircraft – a large cost saving and a big start on the journey to fully electric aircraft. 800 kWh of usable battery storage for the 100 km range is expected to weigh 4 tonne. An electric range of 500 km for a 100 seat aircraft is likely some decades away.
This aircraft would compete with the 78 seat ATR72-600 and 86 seat Q400 turboprops and 100 seat CRJ100 on short hall routes.
100 seat plug-in hybrid electric aircraft – indicative specification
Cabin – 26 seat rows with two 2 toilets, two front doors, 4 emergency exits over wings
Cabin – 24 m long, 2.65 m wide, aisle headroom 1.90 m
Cargo hold – 20 cu.m, 4 m long, behind cabin
Cockpit – 4 m long
Tail – 4m long – houses propulsion equipment
– elevators/horizontal stabilisers mounted on propeller motors frame
Fuselage – 2.8 m wide, 3.0 m high, 32 m long
Wing area – 70 sq.m
Wing span – 27 m
Payload – 10.0 tonne including 3 tonne Cargo
Fuel – 4.0 tonne, 5000 litres
Typical operating empty weight – 20 tonne including 4 tonne flight power batteries
Maximum take-off weight (MTOW) – 32 tonne (2 tonne less aircraft with max. payload and max. fuel)
Flight battery – 800 kWh (2880 MJ), 4.0 T, with 40 x 100 kg modules each with 1152 x 70200 NCA Tesla cells
– module – 1152 cells in series, 1 cell parallel, each cell 18.36 W.hr, 3.6 V, 5.1 Amp.hr
– module – 4147 V (nominal)
– module – 1152 x 18.36 W.h = 21.15 kW.hour (nominal)
– battery – 21.15 kW.h x 40 = 846 kW.h (3046 MJ, 3GJ) – 5.75% above nominal capacity
Turboshaft APU – 1 tonne (including 483 kg PW127TS):
– Pratt & Witney PW127TS – 1864 kW class with 2386 kW take-off power ((813 H, 686 W, 1626 L, mm))
– 2 x 1000 kW generators, each with 1200 kW take-off capability
2 x motor/counter-rotating propeller units, each with:
– 2 x permanent magnet electric motors, 1200 kW continuous (1400 kWx4 = 5600kW for take-off),
weight 4×280 kg, 1120 kg, 4147 Volt (nominal), 337.6 Amp (likely rated to 400 amp)
All wheel drive (in-wheel motors) for taxiing and regenerative braking
Ceiling – 25,000 ft, 7620 m
Range at MTOW – 2500 km at cruise 301 kt, 558 kmh, 155 m/s
Range – battery (APU fails) – 100 km plus 10 km reserve plus altitude glide reserve plus battery reserve
Flight time without APU – 12 minutes at cruise plus reserves
Fuel economy Jet A-1 – 1.6kg/km average, 1.5kg/km cruise – 37% energy conversion to thrust
Fuel economy – Battery – 7.27 kWh/km (26.2 MJ/km) – 90% energy conversion to thrust
Take-off run – 1400 m
Price – US$30 m
At large airports with long taxi paths, a ground drone (cart) with Tesla driverless technology, and 200 kWh battery capacity (for numerous taxi runs before recharge), will power aircraft out to runway, disconnect and return to terminal. Planes will generally land with enough electricity stored to reach terminal. If needed, the plane could restart its APU.
Propellers set high on tail to be well out of the way in the event of tail strike on take-off.
Aircraft will recharge its batteries by plugging-in while being serviced at terminal gate – 1000 kW charger needed.
Aircraft accelerates faster down the runway as electric motors reach full power much faster than jet engine.
APU started at push-back, or at ground drone detachment where they are available. APU has sufficient power to recharge battery while at cruise.
Aerodynamic drag, rather than aerodynamic lift to carry aircraft weight, is the prime user of power at cruise. The weight of the batteries is mainly a concern at take-off.
25% improvement in fuel economy expected compared to 86 seat Bombardier Q400 turboprop.
Aircraft construction has ‘armoured cockpit’ and ‘propulsion unit tail’ constructed separately and bolted to hull. Fuel lines and power cables run in separate ducts on underside of hull for ease of construction and maintenance. Fuel stored in wings, flight batteries under floor ahead of the wings.
Plug-in hybrid systems could be trialled on a Bombardier Q400 with the electric motors/propellers mounted on the wing in place of the PW150A engines, with the PW127TS turboshaft engine and generators replacing the UTC Aerospace Systems APS 1000 in the APU bay.