Electric and hybrid propulsion are new ways to power aircraft using electric motors instead of relying only on jet fuel engines. The goal is to reduce carbon dioxide emissions, noise, and local air pollution, especially on short flights. This matters because aviation is hard to decarbonize, and every kilogram carried into the air must be justified.
Small training planes and short regional aircraft are likely to be the first practical uses.
Key Facts
- Electric power is P = IV, where P is power in watts, I is current in amperes, and V is voltage in volts.
- Energy used during flight is E = Pt, where E is energy, P is power, and t is time.
- Battery specific energy is often measured in Wh/kg, which tells how much energy a battery stores per kilogram.
- Propulsive efficiency compares useful thrust power to input power: efficiency = useful output power / input power.
- Hybrid-electric aircraft combine a fuel engine, generator, battery, motor, and propeller or fan.
- Battery-electric aircraft produce no exhaust during flight, but total emissions depend on how the electricity was generated.
Vocabulary
- Electric propulsion
- A system that uses electric motors to turn propellers or fans and create thrust.
- Hybrid-electric aircraft
- An aircraft that uses both stored electrical energy and a fuel-powered engine or generator to power its flight system.
- Specific energy
- The amount of energy stored per unit mass, usually measured in watt-hours per kilogram.
- Regenerative system
- A system that recovers some energy that would otherwise be wasted, although aircraft have fewer chances to use this than cars.
- Powertrain
- The complete chain of parts that converts stored energy into motion, such as batteries, generators, controllers, motors, and propellers.
Common Mistakes to Avoid
- Confusing energy with power is wrong because energy is the total amount available, while power is how fast it is used. A battery can store enough energy but still fail if it cannot deliver the required power.
- Assuming electric aircraft are always zero-emission is wrong because battery charging may use electricity from fossil fuels. In-flight emissions can be zero while life-cycle emissions are not.
- Ignoring battery mass is wrong because aircraft must lift every kilogram they carry. Unlike fuel, most battery mass remains throughout the flight even after energy is used.
- Thinking hybrid aircraft are just electric aircraft with bigger batteries is wrong because hybrids use a fuel engine or generator as part of the powertrain. This can extend range but adds complexity and maintenance.
Practice Questions
- 1 An electric motor needs 300 kW for takeoff and runs at that power for 5 minutes. How much energy does it use in kWh?
- 2 A battery pack has a specific energy of 250 Wh/kg and a mass of 800 kg. How much energy can it store in kWh?
- 3 A short regional route is more realistic for early electric aircraft than a long international flight. Explain using energy density, aircraft mass, and reserve energy requirements.