Implementation of electrical rim driven fan technology to small unmanned aircraft

Abstract

Aircraft propeller performance is significantly reduced when tip speeds become sonic causing the maximum attainable airspeed of the vehicle to be limited by the propeller diameter. There are also performance losses attributable to miniature Unmanned Aerial Vehicles as the propeller to hub diameter ratio is reduced. The research conducted indicated that re-arranging a Brushless DC Motor and propeller configuration, so that it becomes rim-driven rather than hub-driven, would provide some performance and operational advantages and could inspire the design of novel high-speed Unmanned Aerial Vehicle configurations powered by hub-less, multi-stage contra-rotating electrical fan-compressors. This investigation involved analysis, design and testing a prototype, low cost, concept demonstrator Rim Driven Fan device in order to assess the feasibility of applying this technology to Small Unmanned Aircraft. It was demonstrated that Rim Driven Fan technology could be successfully applied to lift and propel a Small Unmanned Aircraft. However, the performance testing of the Rim Driven Fan demonstrated that in its prototype configuration it would not be as efficient as a conventional Brushless DC motor and propeller. Keywords-rim driven fan; small unmanned aircraft; unmanned air vehicles; drone; brushless dc motors; hub-less fanI.

Performance Comparison between Copper and Aluminium Windings in a Rim Driven Fan for a Small Unmanned Aircraft Application

“…The FPR was calculated for the range of RDF speeds and the differential pressure generated across the fan rotor was established with (2).…”

“…Other benefits include less obstruction to the through-flow of fluids if used in an RDF or RDT application and the flexibility to install multiple rim driven devices in tandem. Some of the main disadvantages of rim drives are that they are: susceptible to efficiency reductions due to friction generated at the rim, for example from rim mounted mechanical bearings; they may require relatively high supply current frequencies to achieve fast rotational speeds and noise, vibration and harshness (NVH) problems can arise owing to the manifestation of eddy currents, cogging torque and torqueripple effects at the rim [2]. Some motors are more suited to rim drives than others, with the better types being induction motors (IMs) and brushless DC (BLDC) motors.…”

Review of Electrically Powered Propulsion for Aircraft

“…Rim driven fans (RDF) are also a form of ducted electrical fan in which the fan blades are attached at their tips to a rotating rim or duct structure [18]. Investigative research has been conducted on these devices [19] with the perceived benefits being increased fan pressure ratios gained by multi-staged contra-rotating compressor configurations and also miniaturisation and airflow efficiency gains through hub-less RDF configurations. Rim driven fans offer the prospect of achieving high electrically powered aircraft speeds extending into the supersonic region of flight.…”

Aerodynamic Analysis and Design of a Rim-Driven Fan for Fast Flight

“…This is because small single-stage rotors require prohibitively high rotational speeds to achieve high exhaust airspeeds owing to their hub-driven configuration. However, a promising solution appears in the form of Rim Driven Fan (RDF) technology which offers an alternative motor architecture with the potential for high thrust and exhaust air speeds to be achieved whilst maintaining relatively small fan inlet diameters [9]. This paper presents a performance analysis conducted on an RDF design with a relatively small fan diameter of 120 mm.…”