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Stielau Electric Helicopter

Oskar electric helicopter


Electric Helicopter
Oskar Stielau
Auckland, New Zealand

During September 2019, inventor Oskar Stielau, based in Auckland, New Zealand, started the development of an experimental electric helicopter. He starting formulating the idea of building an electric helicopter in 2014. The helicopter model is a conventionally powered Mosquito helicopter which he built in 2008 and Stielau flew as a gas-piston engine helicopter for 60 hours. The rotorcraft has now been completely converted into an electric helicopter.

The newly converted electric helicopter has one main electrically powered rotorblade, seven electrically powered tail propellers and batteries. "Measurements on the conventional tail rotor showed that it was very power hungry, and calculations indicated that drone motors driving fixed pitch props would use a lot less power." -Oskar Stielau. The mechanically driven tail rotor was removed and replaced with seven electrically powered propellers. The inventor has stated the tail rotor authority is fantastic with seven tail propellers. A video provides proof of his statement here on YouTube and the video also shows the skill of Stielau as a helicopter pilot. The helicopter can operate with only four tail propellers if three would fail; however, using only four propellers for the tail authority makes the propellers work extremely hard to control the yaw forces of the helicopter.

For the mechanical foot pedals to work as they do in a gas-powered helicopter, the pedal movement needs to be converted into an electric signal. This is done using a potentiometer which feeds the information into a microprocessor. The microprocessor then reads the analog input from the potentiometer, calculates the thrust needed and then converts it into a signal the tail motor controllers read for each individual tail propeller. The motors and their controllers are standard off-the-shelf drone equipment and work very well, according to the inventor.

The microprocessors know the main rotor motor torque at all times and automatically compensate for the tail propellers, for all main rotor torque variations. The inventor has stated it's really nice to fly the electric helicopter because it requires a lot less foot work than a conventional tail rotor. During startup, the tail motors automatically speed up as power is applied to the main rotor. The electric tail rotors are much more efficient than mechanical tail rotors, says the inventor.

Stielau made his first untethered test flight on December 9, 2020 in Auckland, New Zealand, and has also posted several other YouTube videos making test flights with his electric helicopter. (The date on the YouTube shows December 8, 2020 but that's due to the International Time Zone date change.)

As of February 2021, there are three batteries on the helicopter. One for the main rotor, one for the tail propellers and one auxiliary battery. According to Stielau, with these three batteries, the helicopter can fly normally for approximately 27 minutes. A hover-only flight would be approximately 22 minutes. Stielau is working on a design of doubling the battery capacity to the helicopter and the numbers look good. 

The installed electrical tail system (including the tail rotor battery) weighs less than the mechanical tail rotor system it replaces. The aircraft empty weight including batteries is 145 kg (320 lb) which is 30 kg (66 lb) more than the empty weight of the original Mosquito Air with a gas engine. Pilot weight to stay within weight and balance limits is specified as a minimum of 75 kg (165 lb) and a maximum of 85 kg (187 lb).

The electric helicopter has safety features including redundancy of the electric motors, controllers and in the future, the aircraft will have multiple microprocessors. As of 2020, the inventor already has the registration paperwork with the Civil Aviation Authority of New Zealand (CAA).


  • Aircraft type: Electric helicopter 
  • Piloting: 1 pilot 
  • Cockpit: Open cockpit
  • Cruise speed: Unknown 
  • Flight time: Approximately 27 minutes (with 3 batteries)
  • Hovering-only flight time: Approximately 22 minutes (with 3 batteries)
  • Payload weight range: Minimum 75 kg (165 lb) and maximum 85 kg (187 lb)
  • Electric Motors: 8 
  • Power source: 3 batteries (1 for the main rotorblade, 1 for the tail propellers, 1 auxiliary battery) 
  • Main rotorblade: 1 
  • Tail rotors: 7
  • Landing gear: Fixed tricycle leg landing gear 
  • Safety features: Redundancy in motors, controllers and microprocessors.