Engineers at NASA’s Glenn Research Center have demonstrated a prototype magnetically levitated and propelled fan that could be the basis of a new generation of electrically powered aircraft.
The levitated ducted fan (LDF) is driven electromagnetically rather than by the gas generator at the heart of a conventional gas turbine. The fan blades are attached at their tips to a ring that rotates inside a static shell, suspended by force fields generated by permanent magnets. The fan and rotating shell, or rotor assembly, are made from preformed composite material while the static shell, or stator, is filament-wound composite.
The rotor assembly is suspended in place by magnetic fields generated within the stator. Instead of being mechanically driven by a turbine, as in a conventional turbofan, the rotor is turned by modulating the electromagnetic fields between the rotor and the stator. These time-varying fields interact with passive coils inside the stator to produce repulsive forces that magnetically suspend the rotor.
LDF programme manager Mark Klem says the rig tests of a small-scale, 3.8kg (8.5lb) rotor went well and prove the viability of the “Halbach rotor”, named after the pioneer of a magnetic propulsion technique used in particle accelerators. For an initial application, such as a 50-seat regional jet, LDF engines would require “up to 10mW of power on take-off and around 5mW in the cruise”, he says. “That’s a lot of power, so we think we’ll need a gas turbine for take-off [such as a dual-use APU] and use the LDFs for cruise.”
The concept is being explored as part of NASA’s low-emissions alternative power project. The agency says the fan is inherently stable once critical speed is reached, eliminating the need for complex active controls, and adds that the LDF reduces the operating concerns and costs associated with bearings, such as speed limits and lubrication.
Further steps to integrate the levitation and propulsion subsystem are being studied, although a NASA budget squeeze may cause the project to be put on ice.
GUY NORRIS/LOS ANGELES
Source: Flight International
