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Title:The effects of aero-propulsive coupling on aircraft with distributed propulsion systems
Author(s):Perry, Aaron Timothy
Director of Research:Ansell, Phillip J
Doctoral Committee Chair(s):Ansell, Phillip J
Doctoral Committee Member(s):Bretl, Timothy W; Elliott, Gregory S; Wissa, Aimy A; Kim, Hyun Dae
Department / Program:Aerospace Engineering
Discipline:Aerospace Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Distributed Propulsion
Aero-Propulsive Coupling
Flight Testing
Wind-Tunnel Testing
Electric Propulsion
Hybrid Electric Aircraft
Flight Dynamics
Abstract:A set of three experiments were performed at the University of Illinois at Urbana-Champaign to characterize the aeropropulsive coupling effects which are present for aircraft equipped with distributed electric propulsion (DEP) systems consisting of over-wing trailing-edge mounted (OWTE) arrays of ducted fans, and to identify the influence of those effects on aircraft dynamics. The first experiment consisted of low-speed wind-tunnel testing of an NACA 643-618 airfoil with an array of five ducted fans integrated into the upper-surface trailing-edge of the model at the center-span location. Testing of the airfoil model was performed at Re = 1x10^6, and data were acquired as a function of angle of attack and fan speed. Force and moment data were acquired from a three-component load cell, supplemented by chordwise pressure distributions in regions influenced by the fans, and planar PIV measurements of the fan-inlet flowfield region. Both uniform and mixed fan-speed configurations of the DEP array were investigated. The second and third experiments were based off of a modified Cirrus SR22 general-aviation aircraft geometry which featured a new wing design incorporating an array of four ducted fans into the upper-surface trailing edge of each wing at a mid-span location, in addition to removal of the traditional tractor propeller propulsion system. The second experiment consisted of low-speed wind-tunnel testing of a semispan model of the modified SR22 geometry at Re = 3.5x10^5; 4.5x10^5 and 5.5x10^5. Data were again acquired as a function of angle of attack and fan speed. Measurements of the forces and moments experienced by the model were acquired with a six-component load cell, and supplemental chordwise pressure distribution measurements were again taken in regions influenced by the fans. During testing of the semispan model, both steady and unsteady data were acquired to characterize the aero-propulsive coupling effects of the system. Again, both uniform and mixed fan-speed configurations were tested. The third experiment consisted of remotely-piloted flight testing of a sub-scale model of the modified SR22 aircraft. The flight-test vehicle was fully instrumented for measurement of the aircraft’s inertial and airspeed-based states through the use of an integrated inertial navigation system at the aircraft C.G. and a five-hole probe located on a boom at the nose of the aircraft. Pre-programmed excitation maneuvers were flown to produce datasets for parameter estimation. Results of the flight tests and wind-tunnel experiments were used to build a dynamics model of the sub-scale aircraft for an investigation into the influences of the propulsion system on the flight dynamics of a representative general-aviation aircraft. The major aero-propulsive coupling effects which were identified for this form of DEP included an increase in the stream-normal force with increasing fan speed primarily due to reduced pressure over the upper surface of the wing section in front of the fans, a decrease in stream-wise force with increasing fan speed due to the increased thrust of the fans, a decrease in pitching moment with increasing fan speed due to both changes in fan thrust and surface pressure distributions, and an increase in the rolling and yawing moments when fan speeds were asymmetrically increased and decreased simultaneously on the left and right wings of the representative models. Additionally, span-wise nonuniformities in pressure distributions, boundary-layer characteristics, and force and moment sensitivities to changes in fan speed were observed for cases where each of the fans were operated at non-uniform speeds. An assessment of the aerodynamic performance results from the wind-tunnel tests as well as dynamic simulations which were conducted using the model identified from wind tunnel and flight-test data were also performed to highlight the influence of the DEP system as it was integrated into a general-aviation type aircraft. The increased stream-normal force due to an increase in fan speed was identified as a beneficial aero-propulsive coupling effect which could be utilized to fly at slower speeds or to reduce the required wing area. The large increase in stream-wise force when the fans were uniformly set to a windmilling state, however, was identified as a negative aero-propulsive coupling consequence of this form of DEP. If the fans were to fail during flight, the DEP system would essentially act as a spoiler to greatly increase drag and reduce lift leading to potentially devastating results during critical phases of flight. The increased nose-down pitching moment produced by the propulsion system with increased fan speed and the dependence of the wing system stability on angle of attack and fan speed must also be carefully accounted for in the design of such an aircraft to ensure stability throughout the flight envelope. Finally, it was identified that the coupled rolling and yawing moments which are produced by asymmetrically increasing thrust on one wing and decreasing it on the other could be utilized effectively to aid in control of an aircraft equipped with this form of DEP.
Issue Date:2020-04-24
Rights Information:Copyright 2020 Aaron T. Perry. All Rights Reserved.
Date Available in IDEALS:2020-08-26
Date Deposited:2020-05

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