Q. Surely the future is battery electric vehicles?
A. Battery electric cars are amazing methods of reducing CO2 emissions, providing they are charged from renewable energy sources. However batteries have significant drawbacks that become apparent once you try to use them as an energy source to fly. One of these is low specific energy.
The combination of an IC engine and liquid fuel can deliver x 15 the energy amount to the rotors per kg than batteries.
Q. How heavy is a suitable IC engine?
A. Rotax 915 (101 kW continuous) weights 90 kg installed. This is less than one 22 kWh battery pack.
As a reference an Emrax 268 (best in class power density) outputting 110 kW continuous, weighs approx 28 kg including a controller/drive.
Q. Don’t internal combustion or IC engines add to global warming through CO2 emissions?
A. A range of sustainable aviation fuels (SAF) exist that allow an IC engine to have the same global CO2 emissions as a pure electric system charged from renewable energy.
The main reason they aren’t so widely used is they cost more than using CO2 emitting fossil fuels. However, for applications such as large multicopters this additional cost is not a significant burden as the utility value is so high.
Q. Don’t IC engines need regular overhauls?
A. Rotax 915 is rated for 1,200 hours between overhauls (TBO) with a goal of 2,000 like the Rotax 912. This compares well to 2,000 hours between overhauls for the electric motor in the Pipistrel Alpha Electro.
Q. How does this compare for the hydraulic system?
A. Hydraulic pumps and motors are typically designed for >8,000 hours.
Q. Aren’t hydraulic components heavy?
A. Hydraulic motors such as Hydroleduc M18 has a very high specific power. A 96kW shaft power motor weighs 5.5kg, less than the controller of an equivalent electric motor.
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