A conceptual design methodology for low speed high altitude long endurance unmanned aerial vehicles

摘要

A conceptual design methodology was produced and subsequently coded into aVisual C++ (GUI) environment to facilitate the rapid comparison of several possibleconfigurations to satisfy High Altitude Long Endurance (FIALE) unmanned aircraft (UAV)missions in the Low Speed (propeller driven aircraft) regime.Several comparative studies were performed to verify the applicability of traditionaldesign methods. The traditional computational design methodologies fail in several areassuch as high aspect ratio wing weight estimation and design, low Reynolds number wingdesign, high altitude engine performance, low Reynolds number drag estimation, unmannedaircraft design, and the conceptual design of unconventional configurations. Themethodology developed for this thesis was robust enough to allow not only forconsideration of these areas of inadequacy in traditional methods, but also to allow for theinclusion of advancements in the relevant technologies as they become more widelyavailable.The following configurations were evaluated for suitability to the Low Speed HALEUAV application: conventional, canard, twin boom, multiple fuselage (conventional orcanard), tandem wing, multiple fuselage tandem wing or flying wing configuration. Theconfigurations were compared on the basis of aircraft endurance for takeoff weights rangingfrom 2,000 to 20,000 pounds and wing loadings ranging from 5 to 25 lbs1fe.Initial drag estimates were made using traditional parabolic drag estimationtechniques. A more refined drag buildup was performed using a vortex lattice dragestimation for the lift induced drag (for all lifting components) and calculated skin frictioncoefficients for the parasite drag. Statistically based methods were used for othercomponents of drag having much smaller contributions. In addition, a statistical approachwas taken to the weight estimation of the major aircraft components. However, thisapproach made comparison of alternative configurations more difficult. Thus wing bendingmoments trends were evaluated and utilized in the development of weight saving values formultiple fuselage wing weight estimation.The comparative performance of each configuration is justified with direct referenceto the terms in the Breguet Endurance equation. Validation was performed where possibleon all modules and segments associated with the methodology, as well as for themacroscopic results. In addition, parametric studies on endurance were performed for theconventional configuration for geometric characteristics and operating conditions directlyand indirectly effecting the calculated endurance and generalized results presented. Finally, acase study was performed to demonstrate this capability.A new relation was developed for aircraft empty weight prediction, a low speedairfoil figure of merit was proposed, and new constants were offered for UAV fuselagelength prediction. In addition, horizontal and vertical tail volume coefficients were proposedfor all of the Low Speed HALE UAV configurations considered. It was determined that themultiple fuselage configurations showed comparatively superior endurance performanceacross a range of takeoff weights, with several other configurations demonstrating marginalendurance improvements. Finally, a highly flexible and robust computer based conceptualdesign methodology was developed and validated enabling the quick comparison of a greaternumber of possible configurations to satisfy a given mission for Low Speed HALE UAV'sand providing detailed drag and weight breakdown data.