Design and Development of Three Bladed Propeller for Micro Air Vehicles

Abstract

National Aerospace Laboratories is having a major program on development of Micro Air Vehicles (MAV) for civil, surveillance and defense use. Its components development has been undertaken in various divisions of NAL. One of the configurations of NAL MAV having fixed wing is battery driven miniature motor and mini propellers. Efficient propulsion system plays a major role in deciding the endurance, payload and maneuverability of MAV’s. Design of efficient propellers for these classes of vehicles is a challenging task because of their lower operating Reynolds number as well as conservative power utilization to enhance the endurance. The propeller driven MAV’s demands different class of thrust, weight of propellers and geometrical constraints for its mission requirements. Already 2 bladed, fixed pitch, variable speed, 6 inch diameter propellers with different plan form has been carried out and reported. The present requirement is 3 bladed, fixed pitch, variable speed mini propellers to augment thrust and at the same geometrical constraints used earlier with a slight penalty on weight as well as power consumption, expected to be at reduced noise has been carried out to meet the mission requirements, is designed using minimum induced loss method. Eppler-193 airfoil is used in the design in view of its higher lift to drag ratios at low Reynolds numbers. Propeller CAD model is generated using SOLID WORKS and used for analysis as well as for fabrication. Performance estimation for this propeller is carried out using blade element momentum theory (NALPROPELLER code) and ANSYS FLUENT. The fabrication of mini propellers is carried out using three methods namely rapid prototype (RPT) using poly carbonate material and conventional vacuum casting using poly urethane material. However the propellers fabricated using these methods have lower structural integrity and prone to failure during the landing of MAVs. In view of this, fabrication of propellers using CFRP material with conventional casting using aluminum mold have been carried out. Fabrication of mould for 3 bladed mini propeller given the small thickness and twisted airfoil of high accuracy using 3 Axis NC milling is the most challenging work in realizing the product with sufficiently good accuracy. Fabrication of propeller mould using Aluminum alloy and three axis NC machine is carried out in house. The overall performance parameters like thrust, propulsive efficiency and motor power are evaluated using CFRP propeller and tested at uninstalled condition using the test setup specially developed by NAL, at low speed wind tunnel, CSIR-NAL for different wind velocities and propeller rotational speeds. This paper brings out the work carried out on design, development and testing of three bladed miniature propeller for MAVs at propulsion division, CSIR-NAL.