Proxflyer

Lore & Background

The Proxflyer rotor system achieves passive stability through a combination of three features. The typically 4-bladed rotor has a generally fixed geometry and is tiltably connected to the rotor shaft, enabling the rotor to tilt almost freely in any direction. The outer parts of the rotor blades have a pitch angle fixed relative to the rotational plane of the rotor, with the tips fixed to a ring encircling the rotor. The inner part of the rotor blades have a pitch angle fixed relative to a reference plane perpendicular to the rotor shaft; to achieve this, the blades are flexible and can twist in the longitudinal direction. This combination allows the rotor to respond to aerodynamic forces and tilt in any direction without introducing mechanical bending forces between the rotor and the rotor shaft, while still allowing control by tilting the rotor shaft in the desired direction of flight.

Altitude control is performed by varying the speed for both main rotors, while yaw control is achieved by increasing the speed of one rotor and reducing the speed of the other by the same amount. A horizontally oriented tail rotor controls forward or backward movement by shifting the helicopter's center of lift with respect to the center of gravity. The forward speed is limited because the rotors have a high tendency to tilt up to counteract any horizontal movement. This increased tilting tendency is an important part of achieving passive stability but makes it almost impossible to use the rotor system in anything but calm weather. The Proxflyer rotor system is designed for indoor use only.

Petter Muren built one-off prototypes, none of which were for sale. The Proxflyer rotor system was licensed to Interactive Toy Concepts, whose R/C helicopters—including Bladerunner and Micro Mosquito—are all based on the Proxflyer rotor design. The Bladerunner is considered by some to be the first successful indoor R/C helicopter. Up until the beginning of 2007, the total number of toy helicopters produced using the Proxflyer rotor system was estimated to be about one million. Helicopters utilizing the system are also used in some science projects around the world. Petter Muren's designs were showcased as part of the 1st US-European MAV event in Garmisch Germany (MAV-05).

Reader's Guide

The Proxflyer rotor system is notable for enabling the first successful indoor R/C helicopter, the Bladerunner, through a design that achieves passive stability without gyroscopes or active stabilization. By eliminating conventional cyclic and collective pitch controls, the system allows for simpler, lighter helicopters with fewer parts. The dual coaxial counter-rotating rotors keep the helicopter very stable relative to the surrounding air, while altitude and yaw are controlled by varying rotor speeds. A horizontally oriented tail rotor shifts the center of lift for forward or backward movement. The main benefits include passive stability, simple electronics without active stabilization, relatively simple mechanics, high efficiency, and a very low noise level. The main limitations are relatively slow forward speed and the inability to operate in wind, restricting the system to indoor use. The Proxflyer rotor system was licensed to Interactive Toy Concepts, which produced the Bladerunner and Micro Mosquito models. By early 2007, approximately one million toy helicopters using the system had been produced. The design has also been used in science projects and was showcased at the 1st US-European MAV event in Garmisch Germany.

Did You Know?

• The Proxflyer rotor system achieves passive stability without gyroscopes or any form of active stabilization.
• Altitude control is performed by varying the speed of both main rotors simultaneously.
• Up until the beginning of 2007, about one million toy helicopters using the Proxflyer rotor system had been produced.