Investigation of wing airfoils for low-speed high-altitude unmanned aerial vehicles

Аuthors

Brusov V. S.^*, Petruchik V. P., Kuznetsov A. V.^**

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: vsbrusow@mail.ru
**e-mail: alexkuzn@sumail.ru

Abstract

High-altitude low-speed unmanned aerial vehicles (UAVs) are designed to fly for many days in the stratosphere (within the range of altitudes from 25 to 30 km). Such UAVs can be considered as an effective alternative to artificial Earth satellites concerning carrying out such missions as Earth surface observation, meteorological service, telecommunications etc. The effectiveness of stratospheric UAVs is heavily influenced by their aerodynamic characteristics, which depend significantly on the properties of the used wing airfoils. Small values of the Reynolds number (Re = 3?104...5?105), which are typical for the operation of stratospheric UAVs, result from the conditions of low-speed high-altitude flight regimes. Such values of Reynolds number cause significant degradation of aerodynamic characteristics of wing airfoils. Thereby the problem of reasonable choice of the UAV wing airfoil becomes a very important part of the UAV design process. It is impossible to fulfill the numerous requirements for the stratospheric UAV, which often contradict each other, without successfully solving this airfoil choice problem. A comparative analysis of characteristics of possible versions of UAV wing airfoil was carried out to support the choice process. The following airfoil versions were considered: FX 63-137, WE 3.55-9.3, S1223 and Liebeсk LA2573А. The analysis, which was based on the previously published data, specified the FX 63-137 and WE 3.55-9.3 airfoils as the most suitable for further research. The appropriate experiments were conducted in the T-1 wind tunnel, which is installed at the MAI. The experiments were aimed at obtaining the following observed relationships for the airfoils: dependencies of the lift, drag and pitching moment coefficients on the values of the angle of attack and Reynolds number. According to the results of the wind tunnel tests, the maximum values of the lift coefficient were recorded for the FX 63-137 airfoil. These values lie within the range from 1.75 to 1.8. The maximum values of lift-to-drag ratio were recorded for the WE 3.5-9.3 airfoil. These values lie within the range from 55 to 60. Besides these investigations some wind tunnel tests were carried out to obtain aerodynamic characteristics of the UAV wing, which is equipped with the FX 63-137 airfoil and streamlined by the additional blowing flow from a rotating propeller. The test results demonstrate that the values of the wing lift coefficient increase by average 10-15% due to the propeller blowing whereas the values of the pitching moment coefficient decrease by approximately 25%. At the same time the drag coefficient values of the UAV wing increase by 10%-15% under the considered conditions. The experimental results, which are presented in the paper, can be used to support the process of aerodynamic design of the low-speed high-altitude unmanned aerial vehicles.

Keywords:

wing airfoil, aerodynamic characteristics, flight mechanics, wind tunnel , Reynolds number , angle of attack, drag polar, hysteresis loop, turbulence, nonsteady aerodynamics

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