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PDD Gear Explanation

Actuator on Test

Flight Control Actuator Motor

A reliable electric aerospace control surface at just a fraction of the volume and mass of current technology looks like a real possibility in the coming years.  Magnomatics have been working with collaborators Triumph Aerospace, Romax and the University of Sheffield to develop a highly reliable and compact flight aircraft control surface actuator. 

Magnomatics have designed, built and tested a number of prototype electric motors as part of the Electro-Mechanical Magnetic Actuator Systems (EMMAS) project. This project has been co-funded by Innovate UK the UK Government Funding agency.  The electric motors use Magnomatics proprietary Pseudo Direct Drive (PDD®) technology.  The PDD integrates a permanent magnetic motor and a magnetic gear, resulting in a very compact electric motor.  When compared to current benchmark technology the results look very promising indeed. 

Two variants of the PDD have been designed, a basic machine and a second one using a fault tolerant (FT) stator winding and a fault tolerant control system developed by University of Sheffield.  Even with the fault tolerant winding the PDD is around half the mass of current technology with a conventional winding.

The PDD has a further benefit, low inertia.  This results in a very good response rate making it suitable even for military applications on unstable aircraft where a high bandwidth is required.  The low inertia and inherent torque fuse also protect the actuator system from jams or impacts.  Rather than failing, the magnetic gear in the PDD simply slips until the problem is removed.  It does this with no damage to the system components.  This means in turn that other actuator components such as end stops can be light weighted bringing further benefits for this type of actuation system.

All these features suggest that a PDD based actuator for flight control surfaces will be at least as reliable as the traditional hydraulic systems used today.  This is a key step on the way to the all-electric aircraft.  A number of aircraft manufacturers and leading suppliers are showing interest in this exciting new technology.