AERODYNAMIC OPTIMIZATION OF THE ANGLE OF ATTACK OF THE WINGDESIGN OF A MQ-9 R EAPER UAV Ryan Kim

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AERODYNAMIC OPTIMIZATION OF THE ANGLE OF ATTACK OF

THE WING DESIGN OF A MQ-9 REAPER UAV

Ryan Kim

Thomas Jefferson High School for Science and Technology

ABSTRACT

In this paper I present the aerodynamic optimization of the angle of attack of MQ-9 Reaper wings

under turbulent airﬂow conditions. The background discusses the evolution of UAVs such as the

Hunter and their usages for different tasks, speciﬁcally within the last decade. The main procedural

stage consists of creating a criterion for choosing the most aerodynamic wing design by considering

certain aerodynamic properties and analyzing the lift and drag coefﬁcients using computer software.

At the end of the paper, the ﬁnal optimized MQ-9 wing design, along with its respective design

parameters, are presented and discussed.

Keywords UAV ·Aerodynamics ·Airfoil

1 Introduction

An unmanned aircraft system (UAS) comprises unmanned aerial vehicles (UAVs), control stations, and aircraft computer

systems. UASs can be beneﬁcial as they are remote locations where operators can set up communication systems to

control the UAV aircraft and analyze certain data. Of the parts of an UAS, the UAV is worthy of additional consideration

because it can be physically optimized to increase aerodynamic efﬁciency. UAVs are able to transmit data back to

the control stations about certain information such as altitude, aircraft speed, or even the detection of a target. Many

UAVs are designed to automatically respond to certain conditions, giving them a level of intelligence. For example, an

intelligent UAV may return back to the starting destination if it runs out of fuel [1]. It’s important to distinguish between

drones, which can only execute a pre-programmed task without making any changes during ﬂight, and UAVs, which

send information back to the control stations and execute certain tasks based on the decisions made by the controller.

Beneﬁts of UAVs include a lack of an airborne crew, low operational costs, ease of execution, and the convenience of

air travel [2]. Some applications include: photography, military and domestic surveillance, ﬁre detection and control,

surveying for mapping, and weather monitoring. Although this study does not aim to design the interior or even the

fuselage system of UAVs, it is worth noting that 220 kg of payload mass is removed just by locating the control system

at a remote location instead of keeping it on the aircraft. Many industries have started to mass-produce UAV aircraft

due to these beneﬁts.

Due to its wide range of uses, the UAV has drastically increased in popularity in the last few decades. The beneﬁts

and versatility UAVs offer has led to several countries investing in the rapid development and implementation of better

designs, with the majority of the UAV market lying in the military [3]. One type of UAV in particular, the Hunter UAV,

is commonly used in warfare for surveillance, espionage, target acquisition, and much more, especially by the US Army.

The motivation of this study is to optimize the airfoil geometry of a speciﬁc aircraft model, the MQ-9, which is a newer

and upgraded version of the MQ-1. The “M” refers to the Department of Defense designation of multi-role, and the “Q”

means that the aircraft is remotely controlled. The MQ-9 is relevant currently, as tensions rising between Ukraine and

Russia have incentivized the US to send MQ-9 and similar UAVs to the aid of Ukraine [4 ukraine]. Optimization was

done by changing its angle of attack to maximize its lift-to-drag (LD) ratio, a common measurement of aerodynamic

efﬁciency. Once the optimization process is ﬁnished, the airfoil is then applied to a 3D CAD model and compared to

the original design to see the aerodynamic improvements.

arXiv:2210.10013v1 [physics.flu-dyn] 18 Oct 2022

A plethora of studies examining the aerodynamic design of UAVs already exist. For example, Panagiotou et al.

conducted a study on Medium-Altitude-Long-Endurance (MALE) UAVs, emphasizing the conceptual and preliminary

design phases, while also running computer simulations as a part of their optimization technique [2]. While their

study was not specialized for Hunter UAVs (which are more commonly used for close-range operations compared

to the MALE UAVs which are more commonly used for longer distance operations), the methodology used in their

optimization study was rigorous and can be applied to the study of Hunter UAVs.

In Panagiotou et al. study, the ﬁrst stage was to create a conceptual design of the MALE UAV [2]. Eight engineers

were divided into four groups and they all came up with optimal UAV designs with different fuselages, tails, and wings

using CAD software. Many limitations were taken into account, such as the total weight of the aircraft which included

the payload weight, fuel weight, and empty weight, temperature, maximum speed, and much more. These limitations

reﬂected the terrain They also used the Breguet equation to estimate the required fuel for the ﬂight of the UAV. With

each of the four optimal designs that were created, the thrust-to-weight ratio (T/W) and the wing loading (W/S) were

calculated. The ﬁndings were that the team 2 had the best overall L/D ratio, with the design of a boom-mounted tail

conﬁguration featuring raked-type winglets and an airfoil-shaped fuselage.

Another study performed by Kontogiannis and Ekaterianris focused on small-sized UAVs, again utilizing a general

design that could possibly be implemented for different UAVs used for various tasks[5]. Again, they optimized wing

geometry after picking an optimal existing fuselage, that being the PARSONS-F2-49. Optimized wing features included:

wing twist, airfoil angle of attack, and type of winglet design. The study presented here, in contrast, focuses solely on

the Hunter UAV, which is used for military operations.

In the proceeding sections, the procedural stages and methodology are thoroughly discussed, the results of the simulation

runs are discussed and the most aerodynamic UAV is chosen, and the wing and airfoil are optimized on the best UAV

model, and ﬁnally the conclusion and ﬁnal UAV design concept are presented.

2 Methodology

In this experiment, the GW-19 airfoil and its angle of attack (AoA) is incrementally changed to ﬁnd the optimal AoA.

In aerodynamics, it is generally agreed upon that the best metric for aerodynamic efﬁciency is the lift-to-drag (L/D)

ratio [6]. This study, therefore, seeks to maximize the L/D ratio in order to determine the most aerodynamic AoA.

The program of choice was Flowsquare 4.0, which solves high-order differential equations to simulate two-dimensional,

incompressible ﬂows [7]. The chosen input airfoil was the GW-19 airfoil as it is the root airfoil of the MQ-9 Reaper.

Every angle was created in MATLAB and made into an input boundary condition ﬁle for Flowsquare to read and use

in the simulation as shown in Figures 1-3 [8]. For the Flowsquare parameter ﬁle, which was labeled grid.txt, certain

conditions were used to simulate the real environment that the MQ-9 Reaper UAV ﬂies in, assuming clear weather.

UAVs such as the MQ-9 Reaper operate at altitudes below 9,100 m and have a broad variety of altitudes to cruise in

based on the mission [9]. The altitude of 5,000 m above sea level was chosen for simplicity. The average pressure at an

altitude of around 5,000 m is 16.22 in Hg (mercury), which is approximately 54,930 Pa of pressure [10]. At this altitude,

air has a density of 0.746 kg/m-3 [11] and, according to the US Standard Atmosphere 1976 model, has a dynamic

viscosity of around 3.4 * 10-7 lb*s/ft2, which in standard units is 1.63 * 10-5 kg/(m*s). The last parameter needed

for the simulation is the relative velocity between the aircraft and the air, which will stay relatively constant for the

majority of the ﬂight. Because drag and lift are associated with the velocity squared, the maximum speed is chosen to

clearly show the difference between the different AoAs in their respective L/D ratios. The maximum speed of the MQ-9

Reaper is approximately 240 knots, or 123.467 m/s [12].

Other Flowsquare parameters were chosen purely based on simulation time constraints and preference, and every

simulation run kept the same parameters. A high-order scheme with a 4th order difference and 3rd order time integral

was used for the numerical scheme in the simulation. 5000 was the last time step used and each time step lasted around

6.1138 x 10-5 seconds. The reason for this choice was because when preparing the simulation by running pre-trials,

after around 3000 time steps, there seemed to be no changes at all to the x and y velocity vector ﬁelds. A simulation

was run for each AoA, 0 through 20 degrees in increments of 1 degree. Examples of the boundary condition with the

airfoil at various angles are provided in Figures 3-5. It is generally advised to not go above around 17 degrees before

airﬂow above the upper surface becomes detached, a phenomenon known as ﬂow separation [13].

The cruise velocity can be helpful to calculate the aircraft range to ﬁnd the fuel efﬁciency of the aircraft. Using the

lift-drag analysis provided by Flowsquare, the instantaneous air density and velocities were read from the collected

simulation data, and then converted to the ratios of drag and lift forces to drag (CD) and lift coefﬁcients (CL), respectively.

Next, the drag and lift coefﬁcients were approximated using NASA FoilSim JS, whose values are experimentally derived

[14]. The parameters used for FoilSim were a 2.2% maximum camber at 44.2% chord and a maximum thickness of

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AERODYNAMICOPTIMIZATIONOFTHEANGLEOFATTACKOFTHEWINGDESIGNOFAMQ-9REAPERUAVRyanKimThomasJeffersonHighSchoolforScienceandTechnologyABSTRACTInthispaperIpresenttheaerodynamicoptimizationoftheangleofattackofMQ-9Reaperwingsunderturbulentairowconditions.ThebackgrounddiscussestheevolutionofUAVssuchastheHunte...

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