Novel Hybrid Electric Motor Glider-Quadrotor MAV forIn-Flight/V-STOL Launching

Rafael Coronel B. Sampaio, Andre C. Hernandes, Marcelo Becker, Fernando M. CatalanoFabio Zanini, Joao L. E. M. Nobrega, Caio Martins

University of Sao Paulo - EESC - Mechatronics Group - Mobile Robotics - Aerial Robots Team (ART)Sao Carlos/SP, Brazil - 13566-59

rafaelc@sc.usp.br, carmonaroom@gmail.com, becker@sc.usp.br, catalano@sc.usp.br

Abstract—This work presents a novel lightweight electric UAVthat features fixed-wing motor glider aircraft and quadrotorhelicopter capabilities. This paper presents the hybrid con-cept, design, evaluation and operation of a MAV (Mini AerialVehicle) named Sharky, fully designed and crafted by ART(Aerial Robots Team), which may be a versatile flying robotto broaden the scope of a great number of autonomous/tele-operated missions. To illustrate, Sharky may be potentiallyuseful on precise positioning of sensors/equipment at any pointin water/ground/air areas. The MAV may aid atmosphericsensing, water sample collecting, precise positioning of sensorfor agriculture, surveillance of restricted/non-structured areas,such as post-disaster sites. The aircraft is morphologically andaerodynamically shaped to perform well defined and specificfeatures, e.g., 1) in-flight stable launching from a carrier, 2)gliding ability, 3) powered flight (motor-glider), 4) transitionbetween glider and quadrotor (and vice versa) and 5) base levellaunching either as a quadrotor or a motor glider. Sharkytransition (glider/quadrotor/glider) may be achieved at anytimeduring the mission. The aircraft center of mass is slightly shiftedto offer gliding/motor gliding stability. Because it is a quadrotor,Sharky may either work as an inverted pendulum problem.Thus, translations and rotations are easily achieved using partof the potential energy from center of mass unbalance. Still,Sharky is easily able to return back to glider/motor glider con-figuration by using the same principle. That helps minimizingbrushless motors usage and, therefore, battery consumption.Dynamic models are presented and analyzed. Sharky stabilityand controllability are first evaluated in VLM/Panels software.Secondly, wind tunnel analysis are run.

TABLE OF CONTENTS

1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12. NOVEL HYBRID MORPHOLOGY . . . . . . . . . . . . . . . . . 23. SHARKY TECHNICAL SPECIFICATIONS . . . . . . . . . 34. STABILITY WITH VLM/PANELS METHOD . . . . . . 65. WIND TUNNEL EVALUATION . . . . . . . . . . . . . . . . . . . . 66. RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77. PERSPECTIVES OF APPLICATIONS & MISSIONS 108. CONCLUSIONS & FUTURE WORKS . . . . . . . . . . . . . 10

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11BIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1. INTRODUCTIONThe potential usage of lightweight electric aircraft has ex-ponentially grown in the last years [1] [2] [3]. Mini AerialVehicles (MAVs) have become cheaper to set up, highlymaneuverable, offers good stability and are relatively easy

978-1-4799-1622-1/14/$31.00 c©2014 IEEE.

to be controlled. From the operational point of view, MAVsmay offer many advantages over large UAVs in determinedmissions - e.g., short range and precision tasks when ahigh level of maneuverability/controllability is required [4].Besides, the advent of ultra high energy density batteries,micro-electronics and light and resistant composite materialshave also aided small scale electric flying vehicles to beconstructed.

However, even high efficiency batteries present low energydensity/weight ratio, which is the major drawback of mobilerobotics. As for flying electric robots, energy capabilitydecreases as project requirements demand more payload.Such requirements directly impact mission range since lessbatteries means shorter mission time.

Considering outdoor applications where a MAV is desig-nated to a specific task, constructive/geographic/distance con-straints may detract the quality of the overall mission. Inexample, suppose a MAV is outbound to collect data froma given site far from the base. Most of the energy resource iswasted during the round trip journey. A MAV may be mor-phologically adapted to overcome mission constraints andoptimize battery charge utilization. One potential possiblesolution is to plant the MAV as near from the interest point aspossible. In-flight launching may considerably optimize theusage of a MAV.

This work presents a novel MAV that features motor-gliderand quadrotor qualities in the same frame. Sharky (Fig. 1) isa four electric engine delta wing shaped aircraft designed byAerial Robots Team (USP/EESC/LabRoM/ART). The MAV

Figure 1 - Sharky hybrid motor-glider/quadrotor MAV.

1

may offer two different flight characteristics in the sameaircraft. That may considerably broaden the range, quality,scope and success of precision missions. Gliding character-istics may allow energetic optimization to be achieved effi-ciently. Furthermore, gliding capabilities may be favorable tothe in-flight launching problem.

Sharky novel hybrid morphology is presented in Section2.. Project requirements and flight modes are outlined. InSection 3., main technical features of Sharky MAV are pre-sented, including dynamic modeling of aircraft and quadrotorconfigurations, brushless motors as well as the airfoil isdescribed. Section 4. presents evaluation by VLM/Panelmethods both for lateral and longitudinal stabilities, followedby frequency response results. Section 5. presents our windtunnel specifications in which a complete analysis of Sharkyaerodynamics was run. Wind tunnel results are followed bythe discussion of our findings in Section 6.. Perspectives ofapplications of Sharky MAV in a wide variety of missionsare presented in Section 7.. The feasibility of optimizing andbroadening the use of MAVs in the novel Sharky morphologyis addressed in Section 8..

2. NOVEL HYBRID MORPHOLOGYProject Requirements

Sharky is specially designed to act as a regular airplane in themotor-glider configuration and to present quadrotor capabil-ities. Both qualities require the MAV to be shaped aroundimportant project requisites, which have leaded Sharky to aparticular morphology. Sharky optimal design follows thefollowing requirements:

• Except for usual moving parts (propellers, flaps, aileronsand rudders) the whole structure must be rigid, fixed and noninterchangeable;

• The MAV foil must produce lift as any regular airplane;

• Foil must present considerable gliding ratio coefficient;

• The MAV must naturally present low moment coefficientwith no active control;

• The same motor group must work for both motor-glider andquadrotor configurations;

• All four motors must necessarily be symmetrically distantfrom each other in both airplane/quadrotor configurations;

• Altogether, motor-gliding and quadrotor operation must bestable;

Resulting prototype is a fixed delta wing airplane providedwith two mirrored vertical stabilizers comprehending a crossshaped structure. Such constructive features allow the MAVto perform coordinate longitudinal flight and also perform 6DoF omnidirectional maneuvers.

Brushless electric motors are strategically positioned at thetip of each one of the four foils. Thus, as long as Sharkyflies as a regular airplane, the electric motor group provideslongitudinal thrust to the UAV. Sharky is also provided withelevons that are used for increasing lift during take-off andlanding/approaching. Still, they act as flaps, elevators anddifferential ailerons. Besides, the MAV is endowed with two

mirrored vertical stabilizers, each one containing one rudderthat may be differentially operated. Thus, it may performcoordinate maneuvers as any other airplane.

Figure 2 shows Sharky in the motor-glider configuration.Thrust forces F1..4 are independently produced by the motorgroup denoted by the four motors M1..4. An interestingcharacteristic intrinsic to Sharky longitudinal dynamics is thatboth motor group and control surface commands (elevonsand rudders) may produce the necessary moments separately,so that the MAV may perform all maneuvers. In exam-ple, suppose Sharky flies in the motor-glider configuration,coordinate rolling, pitching and yawing moments may beachieved by the correct combinations between motor angularspeeds Ω1, Ω2, Ω3 and Ω4. In the other hand, suppose thatSharky is flying in the gliding configuration (motor group notoperating), the same maneuvers may be achieved by controlsurface deflections δ1, δ2, δ3 and δ4. Hence, Sharky activecontrol module characterizes a redundant active system. Afault tolerant system may be designed after well-tunning ofcontrollers as well as the control architecture configuration.Furthermore, one may resort to a great variety of combina-tions between motor group and surface controllers in order toimprove the MAV maneuverability and controllability, evenallowing aggressive maneuvers to be performed.

Regarding Sharky as a quadrotor (Fig. 3), omnidirectionalcoordinate flight (6 DoF) may be performed by the correctcombination between the angular speed of motors Ω1, Ω2,Ω3 and Ω4. Although it is expected that Sharky performs lowspeed hovering flight in this configuration, the combinationbetween correct surface command deflections δ1, δ2, δ3 andδ4 and motor group torques may improve maneuverability.That may be useful to expedite turns and translations, leadingto a more agile and maneuverable MAV.

Generally, Sharky is designed to meet the following fiveessential and critical phases:

• In-flight stable launching - The MAV must be able to bein-flight deployed from a carrier aircraft around a specificpoint of interest or even at medium-long distances;

Figure 2 - Sharky in the airplane configuration motorgroup and flight control surfaces.

2

Figure 3 - Sharky in the quadrotor configuration motorgroup and flight control surfaces.

• Gliding Ability - Sharky may glide as soon as it is launchedfrom the carrier aircraft.

• Powered Flight - The MAV may also fly assisted by themotor group;

• Airplane/Quadrotor Transition - The MAV may switchbetween motor-glider and quadrotor at any flight time;

• Base Launching - Sharky may perform vertical take-off/landing from/to any base level. Furthermore, Sharky maybe hand launched by a human operator.

Figure 4 shows a flight simulation that illustrates how Sharkymay perform the transition between motor-glider and quadro-tor.

3. SHARKY TECHNICAL SPECIFICATIONSConstructive Description

Sharky body is completely shaped in low-density high-resiliency bi-component polyurethane (PU) which leads toan extremely light frame. Although PU presents good me-chanical properties, the MAV is recovered with carbon fiber.The resulting fuselage is a lightweight resistant structure thatallows payload to be increased.

Withal, the MAV is more immune to vibration and maysupport mechanical stress. That is, Sharky is reinforcedto bear the forces due to inflow air stream impact duringtransport and in-flight launching.

A complete description of Sharky parameters is listed in Table1

(a) (b)

(c) (d)

(e) (f)

Figure 4 - Sharky in-flight transition ((b)-(e)) betweenmotor-glider airplane (a) and quadrotor (f).

Table 1 - Sharky Key Data Specifications.

Symbol Parameter Value

m Mass (equiped) 1.130 Kgb Wingspan 800 mm

Croot Root Chord 450 mmCoGx CoG x Coordinate 230.1 mmCoGz CoG x Coordinate 0.6142 mm

Ixx MoI About x Axis 0.047 Kg ·m2

Iyy MoI About y Axis 0.033 Kg ·m2

Izz MoI About z Axis 0.05 Kg ·m2

Ixz PoI About z Axis 0.0009 Kg ·m2

Ixz PoI About z Axis -0.0002 Kg ·m2

Iyz PoI About z Axis 0.002 Kg ·m2

3

Sharky Quadrotor Dynamics

Differently than the great majority of commercial quadrotors,Sharky quadrotor dynamics considers the fact that the mobilecoordinate system B and the MAV center of gravity are notcoincident. Figure 5 shows the coordinate frames used bySharky in the quadrotor configuration. Consider also theparameters presented in Table 2 for the quadrotor modeling.

Figure 5 - Sharky quadrotor coordinate axes, variablesand parameters.

Table 2 - List of Variables for SquidCop DynamicalModeling.

Variables Brief Description

[u,v,w]T CG velocity vector[p,q,r]T Body angular velocity vector[φ ,θ ,ψ]T Tait-Bryan CG orientation angles[xG,yG,zG]

T CG displacementm Quadrotor massI Quadrotor Inertia Tensorb Thrust factord Drag factorl Motors leverK Force-to-moment ratiocW1..6 Body drag coefficientsΩ1..4 Rotor speed[Fx,Fy,Fz]

T External applied forces[Mx,My,Mz]

T External applied torques[U1..4]

T Control action vector[F1..4]

T Thrust vector from propellersIM Rotors InertiaΩr Residual motors velocity

According to [5], external forces may be written as:

[FxFyFz

]= m

u+2(wq− vr)− xG(q2 + r2)+ ...+yG(pq− r)+ zG(pr+ q)

v+2(ur−wp)+ xG(pq+ r)− ...−yG(r2 + p2)+ zG(qr− p)

w+2(vp−uq)+ xG(pr− q)+ ...+yG(qr+ p)− zG(p2 +q2)

(1)

And the external torques may be written as:

[MxMyMz

]=

Ix p+(Iz − Iy)qr− Izx(pq+ r)+ ...+Iyz(r2 −q2)+ Ixy(pr− q)

Iyq+(Ix − Iz)pr− Ixy(qr+ p)+ ...+Izx(p2 − r2)+ Iyz(pq− r)

]Izr+(Iy − Ix)pq− Iyz(pr+ q)+ ...

+Ixy(q2 − p2)+ Izx(qr− p)

+

m

xG(wr+ vq)+ yG(w−uq)− zG(v+ur)

−xG(w+ vp)+ yG(up+wr)+ zG(u− vr)

xG(v−wp)− yG(u+wq)+ zG(vq−up)

+

qIMΩr

−pIMΩr

0

(2)

Where

I =[ Ix −Ixy −Izx−Ixy −Iy −Iyz−Izx −Iyz −Iz

](3)

And

Ωr = Ω1 +Ω3 −Ω2 −Ω4 (4)

External forces [Fx,Fy,Fz]T and moments [Mx,My,Mz]

T maybe written as:

FxFyFzMxMyMz

=

(cos(φ)sin(θ)cos(ψ)+ ...+sin(φ)sin(ψ))U1 − cW1u2

(cos(φ)sin(θ)cos(ψ)− ...−sin(φ)sin(ψ))U1 − cW2v2

(cos(φ)cos(θ))U1 − cW3w2

l(U2 − cW4 p2)

l(U3 − cW5q2)

Kl(U4 − cW6r2)

(5)

4

Where the control action vector may be related with therotation of the motors, such as:

U1U2U3U4

=

b b b bb −b −b b−b −b b bd −d d −d

Ω1

Ω2Ω3Ω4

(6)

Sharky Aircraft Dynamics

Figure 6 shows the coordinate frames adopted for Sharky inthe airplane configuration. Consider, also, the parameterspresented on Table 2 for the aircraft modeling.

Figure 6 - Sharky airplane coordinate axes, variables andparameters.

According to [5], external forces may be written as:

[FxFyFz

]= m

u+2(wq− vr)− xG(q2 + r2)+ ...yG(pq− r)+ zG(pr+ q)

v+2(ur−wp)+ xG(pq+ r)− ...yG(r2 + p2)+ zG(qr− p)

w+2(vp−uq)+ xG(pr− q)+ ...yG(qr+ p)− zG(p2 +q2)

(7)

And external torques may be written as:

[MxMyMz

]=

Ix p+(Iz − Iy)qr− Izx(pq+ r)+ ...Iyz(r2 −q2)+ Ixy(pr− q)

Iyq+(Ix − Iz)pr− Ixy(qr+ p)+ ...Izx(p2 − r2)+ Iyz(pq− r)

Izr+(Iy − Ix)pq− Iyz(pr+ q)+ ...Ixy(q2 − p2)+ Izx(qr− p)

m

xG(wr+ vq)+ yG(w−uq)− zG(v+ur)

−xG(w+ vp)+ yG(up+wr)+ zG(u− vr)

xG(v−wp)− yG(u+wq)+ zG(vq−up)

+ ...

qIMΩr

−pIMΩr

0

(8)

where I =[ Ix −Ixy −Izx−Ixy −Iy −Iyz−Izx −Iyz −Iz

]and Ωr = Ω1 +Ω3 −Ω2 −Ω4.

The rotation matrix is described as follows, considering cφ ascos(φ), sφ as sin(φ) and analogous for θ and ψ .

Rzyx =

[cψcθ cψsθsφ − sψcφ cψsθcφ + sψsφ

sψcθ sψsθsφ + cψcφ sψsθcφ − cψsφ

−sθ cθsφ cθcφ

](9)

Thus, the external forces [Fx,Fy,Fz]T and external moments

[Mx,My,Mz]T may be written as:

FxFyFzMxMyMz

=

Rzyx 0

0 Id

· ...

U1 − cW1u2 +Fs2x(δs2)+Fs4x(δs4)

U1 − cW2v2 +Fs1y(δs1)+Fs3y(δs3)

U1 − cW3w2 −∑4i=1 Fsiz(δsi)

l(U2 − cW4 p2)+ rs1zFs1y(δs1)+ rs2yFs2z(δs2)+ ...rs3zFs3y(δs3)− rs4yFs4z(δs4)

l(U3 − cW5q2)− rs1xFs1z(δs1)− rs2zFs2x(δs2)+ ...rs3xFs3z(δs3)− rs4zFs4x(δs4)

Kl(U4 − cW6r2)− rs1xFs1y(δs1)+ rs2yFs2x(δs2)+ ...rs3xFs3y(δs3)− rs4yFs4x(δs4)

+ ...

0

0

−mg

(10)

Where the control action vector may be related with therotation of the motors as:

5

U1U2U3U4

=

b b b b0 −b 0 bb 0 −b 0d −d d −d

Ω2

1Ω2

2Ω2

3Ω2

4

(11)

Brushless Motor Model

Each one of Sharky motors produce an average thrust of about11N and may be represented by a first order model, whichdenotes the transfer function between propeller speed and thecontrol signal:

M(s) =0.316

0.419s+1.52(12)

Sharky Airfoil

The choice of the MH-60 airfoil for the Sharky MAV tooksome sound characteristics into consideration, such as:

• Low drag coefficient (CD);• Low moment coefficient (CM);• Relatively high lift coefficient (CL);• Good performance at low Reynolds numbers;• Has been successfully used in tailless airplanes;

The MH-60 airfoil (see foil cross section in Fig. 7) is widelyused in flying wings and in well-know high performanceaircrafts (e.g., Boeing F3-B) and presents some of the abovecharacteristics [6].

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1−0.05

0

0.05

Figure 7 - Typical MH-60 cross section.

4. STABILITY WITH VLM/PANELS METHODComputational evaluation was run in XFLR5 software [7],which is an open source platform for longitudinal and lateralstability analysis of foils, wings and aircrafts subject to oper-ations at low Reynolds numbers. Software algorithms solvethe aircraft equations of motion and follow theoretical back-ground proposed in [8]. The software performs all necessarycalculations along/around stability axes on the determinationof the stability derivatives of the aircraft. An approximationof the UAV CAD model may be entirely designed. Firstly, theaircraft was defined as a series of panels, which are defined bylength (l), root (ci) and tip chords (ci+1), leading edge offsetat root and tip chords (hi and hi+1, respectively), dihedralangle and the object mesh itself for the VLM (Vortex LatticeMethod) analysis. Secondly, XFLR5 then performs CoG andinertia tensor calculation from the aircraft geometry. Allpoints of concentrated mass may also be included, whichare necessary to guarantee the reliability of simulation andalso to preserve Sharky mechanical characteristics as muchas possible.

Figure 8 shows Sharky panels in XFLR5 GUI. It is expectedto extract qualitative and quantitative information about lat-eral and longitudinal stabilities of the MAV.

Considering lateral stability, Figures 9 to 12 refers to velocityv along y axis, and rotation rates p, r and phi, respectively.

An input control gain of about 5/sec was considered, whichleads to the aircraft stability. Lateral eigenvalue is λ ≈−2.4193− 10.9770 j. Modes of vibration and damping ratioare f = 1.747Hz and ξ ≈ 0.215, respectively.

Regarding longitudinal stability, Figures 13 to 16 show ve-locity u along z axis, and rotation rates q, w and theta,respectively. An input control gain of about 10/sec was con-sidered. Sharky is longitudinally stable with an eigenvalueλ ≈ −0.5577 − 2.507 j. Modes of vibration and dampingratio are f = 0.404Hz and ξ ≈ 0.214, respectively.

Table 3 summarizes VLM/Panel analysis results for bothlateral and longitudinal stability.

Table 3 - Sharky lateral & longitudinal stability data.

Item Lateral Longitudinalλ −2.4193−10.9770 j −0.5577−2.507 jωn (Hz) 1.747 0.404ξ 0.215 0.214

5. WIND TUNNEL EVALUATIONUSP/EESC LAE 1 Wind Tunnel Specifications

Sharky aerodynamic features were experimentally extractedfrom LAE (USP/EESC) [9] closed circuit wind tunnel whichwas first designed as a 3/8 scale pilot wind tunnel for auto-motive industry purposes. Construction started in 1998 andwas finished in 2002. It is predominantly crafted with navalplywood. As automotive industry investment decreased andBrazilian aeronautic industry has considerably grew in thepast years, LAE wind tunnel became a multi task wind tunnelwhose instrumentation is specially focused on aeronauticaltests both for industry (i.e., EMBRAER) and academic pur-poses. Figure 17 shows the test section assembly in whichSharky is mounted.

Figure 18 presents a plan view of the LAE-1 closed circuitwind tunnel. The wind tunnel test section dimensions are 3.00m long, 1.30 m high and 1.70 m wide. The maximum designflow speed is 50 m/s, with a turbulence level of 0.25%. Forsafety and components long range issues, maximum velocityis limited to 45 m/s. An electric motor, with 110 HP, drivesan 8 blades fan with 7 straighteners localized downstreamthe fan. In the flow stabilization section there are two meshscreens of 54% porosity following by the 1:8 contractioncone designed using two 3rd order polynomials joined at45% inflection point. The tunnel is endowed with lowangle diffusers, low-drag corner-vanes and high-efficiencypropeller blades designed with a combination of CFD and

Figure 8 - Sharky VLM/Panel analysis.

6

5 10 15 20 25 30 35 40−1

−0.5

0

0.5

1

1.5

Time (s)

v (

m/s

)

v

Figure 9 - Linear velocity v in lateral stability evaluation.

5 10 15 20 25 30 35 40

−60

−50

−40

−30

−20

−10

0

10

20

30

Time (s)

p (

°/s

)

p

Figure 10 - Rolling rate p lateral stability evaluation.

5 10 15 20 25 30 35 40

−40

−20

0

20

40

60

Time (s)

r (°

/s)

r

Figure 11 - Yawing rate r in lateral stability evaluation.

5 10 15 20 25 30 35 40

−4

−3

−2

−1

0

1

2

3

Time (s)

ph

i (°

/s)

phi

Figure 12 - Euler rolling rate φ in lateral stability evalu-ation.

semi-empirical techniques. Besides, background noise isreduced to allow carried-out beam-form noise measurements[10].

6. RESULTSWind Tunnel Quantitative Evaluation

Wind tunnel tests were run at the real speed and scale thatSharky is expected to fly. Thus, Reynolds number is pre-served, which turns the experiment extremely favorable onreproducing real flight conditions. Wind speed at the testsection was around 85 Km/h. Data corrections follows ESDU

10 20 30 40 50 60 70 80

−0.8

−0.6

−0.4

−0.2

0

0.2

0.4

0.6

0.8

1

Time (s)

u (

m/s

)

u

Figure 13 - Linear velocity u in lateral stability evalua-tion.

10 20 30 40 50 60 70 80

−20

−10

0

10

20

30

40

Time (s)

q (

°/s

)

q

Figure 14 - Rolling rate q around in lateral stabilityevaluation.

10 20 30 40 50 60 70 80−0.2

−0.15

−0.1

−0.05

0

0.05

0.1

Time (s)

w (

m/s

)

w

Figure 15 - Linear velocity w in lateral stability evalua-tion.

10 20 30 40 50 60 70 80

−6

−4

−2

0

2

4

6

8

10

12

Time (s)

the

ta (

°/s

)

theta

Figure 16 - Euler pitching rate θ in lateral stabilityevaluation.

[11] norms for closed-circuit/closed-wall wind tunnels.

Figure 19 shows CL plot at elevon angles at 0. Maximum liftachieved is CL ≈ 0.6. Still, stall occurs at a angle of attackα ≈ 14. Zero lift coefficient happens at α ≈−3.

Figure 20 shows that minimum drag occurs at α ≈ 0. Aswas expected, CD raises as the angle of attack increases. An

7

Figure 17 - Sharky mounting inside the test section of theUSP/EESC/LAE Wind Tunnel.

Figure 18 - USP/EESC/LAE wind tunnel specifications.

0 5 10 15 20

0

0.1

0.2

0.3

0.4

0.5

0.6

Angle of Attack (°)

Cl

Cl

Figure 19 - Lift coefficients to baseline (α = 0).

important aspect that must be taken into account is that glideratio can not be ensured just by raising angle off attack.

0 5 10 15 20

0.04

0.06

0.08

0.1

0.12

0.14

0.16

Angle of Attack (°)

Cd

Cd

Figure 20 - Drag coefficients to baseline (α = 0).

Figure 21 shows both previous plots together. One importantanalysis may be done from the stall angle. At that point, it isnoted that CD raises faster as α increases.

0 5 10 15 20

0

0.1

0.2

0.3

0.4

0.5

0.6

Cl

Angle of Attack (°)

0 5 10 15 20

0.04

0.06

0.08

0.1

0.12

0.14

0.16

Cd

Cl

Cd

Figure 21 - Lift & drag coefficients to baseline (α = 0).

Figure 22 shows lift curves to different angles of attack anddifferent elevon angles. It is noted that CL considerablyincreases as elevon angle also increases. Furthermore, stallangle decreases. In such circumstances, the wing producesmore lift but stalls earlier than at the baseline with flatelevons. As it may be noted from the plot, the distancebetween curves is proportional to the difference betweenelevon angles. In other words, the elevon works appropriatelyand is in compliance with its design specifications. Figure 23shows Sharky drag polar.

0 5 10 15 20

−0.4

−0.2

0

0.2

0.4

0.6

0.8

Angle of Attack (°)

Lift C

oeffic

ient

Elevon Deflection −20°

Elevon Deflection −10°

Elevon Deflection 0°

Elevon Deflection 5°

Elevon Deflection 10°

Elevon Deflection 15°

Elevon Deflection 20°

Figure 22 - Lift coefficients to different elevon angles.

Figure 24 shows gliding ratio at different angles of attack.Maximum gliding ratio is observed at α ≈ 6. Figure 25shows distinct gliding ratios to different elevon angles. Itis noted that an elevon deflection δ ≈ 10 produces the bestgliding ratio (10 : 1) at the lower angle of attack (α ≈ 2).

8

0 0.1 0.2 0.3 0.4 0.5 0.6

0.04

0.06

0.08

0.1

0.12

0.14

0.16

Cl (°)

Cd

Cd

Figure 23 - Sharky polar of drag.

Besides, raising the elevon angle does not necessarily impliesgliding ratio increasing since drag raises as lift grows. Figure26 shows CL Vs. CD plot at the baseline.

0 5 10 15 20

−2

0

2

4

6

8

Angle of Attack (°)

Glid

e R

atio

Glide Ratio

Figure 24 - Gliding ratio.

Moment coefficient Cm linearly changes due to changes in liftcoefficient Cl . That is, aerodynamic moment raises as angleof attack raises (and, consequently Cl raises), as it may beseen in Figure 27. Longitudinal pitching tendency raises aswell, as Cm also increases (Figure 28).

0 5 10 15 20

−8

−6

−4

−2

0

2

4

6

8

10

12

Angle of Attack (°)

Glid

e R

atio

Elevon Deflection −20°

Elevon Deflection −10°

Elevon Deflection 0°

Elevon Deflection 5°

Elevon Deflection 10°

Elevon Deflection 20°

Figure 25 - Sharky gliding ration to variable α and elevondeflection.

Wind Tunnel Qualitative Evaluation

Figure 29 shows the vortex formation along Sharky left foil.It may be noted that streamlines begin to twist as the angle ofattack raises. The vortex starts right at the wing tip. Figure 30contrast is intentionally increased so that it may show tip stallpropagation towards root chord. Tip stall will be preventedby crafting the new wing with an aerodynamic washout.

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18−0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Cd

Cl

Cl

Figure 26 - Sharky baseline gliding ratio (α = 0).

0 5 10 15 20

0

0.02

0.04

0.06

0.08

0.1

Angle of Attack (°)

Cm

Cm

Figure 27 - Sharky moment coefficient to variable α .

0 0.1 0.2 0.3 0.4 0.5 0.6

0

0.02

0.04

0.06

0.08

0.1

Cl

Cm

Cm

Figure 28 - Sharky moment coefficient to variable Cl .

Influence of Moment Coefficient to the Motor Group

Perhaps the most important analysis lies in Sharky momentanalysis since the greater the Cm eventually reaches, moreactive control it will be necessary to drive the MAV to thein-flight equilibrium point. As it was discussed in Section 2.,Sharky motor group configuration is strategically installed sothat it may produce all maneuvers of a motor-glider airplane.Thus, motors M1 − M4 torques could also be employed tocontrol pitching oscillations and moments that might possiblybe intrinsic to Sharky constructive parameters or dynamics.

Figure 31 shows wind tunnel results concerning pitchingmoments for all possible attitude angles and elevon/flappingsets. For all situations, it may be noted that maximumreached pitching moment is Cm ≈±0.015. One may concludethat, due to the small Cm values, a little control effort fromboth elevons and motor groups will be required. From theenergetic perspective, less effort from battery charge wouldbe wasted in Sharky stabilization.

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Figure 29 - Vortex formation along the airfoil as the angleof attack raises.

Figure 30 - Typical tip stall formation in Sharky wing tipsat high angles of agttack.

0.2 0.3 0.4 0.5 0.6 0.7 0.8

−0.015

−0.01

−0.005

0

0.005

0.01

0.015

Cl

Cm

Static Stability Graph

Elevon 0°

Elevon 5°

Elevon 10°

Elevon 15°

Elevon 20°

Figure 31 - Sharky moment analysis in wind tunnel tovariable Cl and elevon deflection.

7. PERSPECTIVES OF APPLICATIONS &MISSIONS

As it was previously discussed in Section 2., in-flight launch-ing perspectives plus V-STOL possibilities allows Sharky toperform a great variety of missions. Consequently, potential

fields of applications which may benefit from MAVs capabil-ities are, but not limited to the following:

• Precision Agriculture - activities like imagery, monitoringand sowing may significantly be improved if MAVs are in-serted in plantation. That may save time, improve the qualityof results and be cheaper than traditional means;

• Urban Surveillance - high manobrability of small scaledUAVs may fit navigation through restricted urban areas, topof buildings and may be easily adapted to the dynamics ofgreat urban centers;

• Wild Life Observation - silent electric MAVs may penetratedense forests and glades in order to capture images and smallsamples where other medium/large UAVs may not be able toaccess;

• Law Enforcement - routine aerial surveillance with MAVsmay restraint criminal activities in determined areas - e. g.,urban centers and neighborhoods;

• Atmospheric Monitoring - a MAV may perfectly be used toget samples in the atmosphere for research purposes - e. g.,ozone density and pollution monitoring;

• Hazardous Environments - a MAV may be deployed overvolcano areas for monitoring and sampling, where the aircraftmay be either expendable (or be later recovered);

• Sea Water Measuring/Collecting - A MAV may be strate-gically deployed overseas in order to acquire samples fromwater to salinity, pollution, microorganisms studies;

• Military/Border Control - Critical areas (like borders andwar zones) may make use of MAVs for monitoring andimagery without the need to put human lives in danger;

• Remote areas Medicine Delivery - Remote areas, likemountains and deep forests may benefit from MAVs whichmay transport medicines, vaccines and bring human samples(urine, blood, etc.) to big cities;

Solar Power Perspectives

Considering the fact that Sharky presents relative good glid-ing ratio, the the possibility of an in-flight launching and thefact that it may extend flight time in comparison to currentMAVs/MAVs, solar panels may recover the MAV fuselage.Sharky presents about 0,8 m2 (8,6 f t2) of exposed area,which may produce an approximate power of 70W . Thatmay be enough to feed small-power devices, e.g. TTL smallhardware, LEDs or even contribute to battery charge in a longterm exposition. Figure 32 shows the conceptual illustrationof Sharky recovered by solar panels.

8. CONCLUSIONS & FUTURE WORKSIn this paper the problem of optimizing the scope of operationof electric flying robots is first addressed. Energy limitationsgrounds the presentation of a novel morphology of MAVwhich aims to broaden the scope, range and quality of mis-sions involving UAVs/MAVs. The design of a hybrid electricflying robot, named Sharky, that mixes quadrotor abilities andmotor-glider features was modeled and evaluated. Projectrequirements for a potential and novel modality of launchingis proposed. The in-flight launching of a flying robot is

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Figure 32 - Sharky recovered by solar panels, being hitby solar light, in flight simulation.

grounded in solid analytical and numeric tools. The resultingplatform is constructed around robust criteria and may bea potential candidate to perform both in-flight and V-STOLdeployments.

Sharky complete mathematical models, both for the airplaneand the quadrotor configurations, are presented. A deepevaluation of lateral and longitudinal stabilities are run inVortex Lattice Method (VLM)/Panel Method software, whichis followed by computational results. Later, a completewind tunnel experimental evaluation is performed in order toextract Sharky aerodynamic characteristics. Finally, quanti-tative and qualitative analysis are outlined.

Perspectives of applications are presented. A wide varietyof mission may be improved and broaden as well as energyissues may be improved or optimized. Future works include acomplete power group analysis, wingtip washout realization,followed by Sharky first flight, which is programmed tohappen in the first half of 2014.

ACKNOWLEDGMENT

Authors gratefully acknowledge the sponsorship of TheBrazilian Government CAPES/FAPESP agencies. Au-thors also would like to thank USP/EESC/Baja andUSP/EESC/Formula automotive teams for the valuable con-tribution on manufacturing our models.

REFERENCES[1] Vijay Kumar and Nathan Michael. “Opportunities and

challenges with autonomous micro aerial vehicles”. TheInternational Journal of Robotics Research, 2012.

[2] Nikolic, J.; Burri, M.; Rehder, J.; Leutenegger, S.;Huerzeler, C.; Siegwart, R., “A UAV system for in-spection of industrial facilities”, Aerospace Conference,2013 IEEE , vol., no., pp.1,8, 2-9 March 2013

[3] Zingg, S.; Scaramuzza, D.; Weiss, S.; Siegwart, R.,“MAV navigation through indoor corridors using opticalflow” Robotics and Automation (ICRA), 2010 IEEEInternational Conference on , vol., no., pp.3361,3368,3-7 May 2010

[4] Austin, R., “Unmanned Aircraft Systems - UAVs Des-gin, Development and Deployment”. Wiley, 2010.

[5] CARLSON D. E.: On Gunther’s stress functions forcouple stresses, Quart. Appl. Math., 25, (1967), 139-146.

[6] Hepperle, M.; “Neue Profile fur Nur Hugelmodelle”.1988.

[7] Bloch, M.; Weiss, S.; Scaramuzza, D.; Siegwart, R.;“Vision based MAV navigation in unknown and un-structured environments”, Robotics and Automation(ICRA), 2010 IEEE International Conference on , vol.,no., pp.21-28, 3-7 May 2010

[8] Etkin, B. , “Dynamics of Flight: Stability and Control”,3rd Edition, Wiley, 1996

[9] Santana, L., Catalano, F. M., Medeiros, M. A. F.,Carmo, M.; “The Update Process and Characterizationof the Sao Paulo University Wind-Tunnel for Aeroa-coustics Testing”. 27th ICAS, Nice France, 2010.

[10] Dobrzynski, W., “Almost 40 Years of Airframe NoiseResearch - What did we achieved?”, 14th AeroacousticsConference, Vancouver, 2008

[11] http://www.esdu.com/

BIOGRAPHY[

Rafael Coronel B. Sampaio receivedthe B.E. degree in computing/electronicengineering and the M.Sc. degree inmechanical engineering, in 2011, fromthe University of Sao Paulo, Sao Carlos,Brazil, where he is currently workingtoward the Ph.D. degree. He is cur-rently the Team Leader of Aerial RobotsTeam (ART) with the Mechatronics Lab-oratory, University of Sao Paulo. He

has authored more than 20 important papers in importantconferences, journals and one chapter of book, involvingrobust control systems for ground and aerial mobile robots.His research interests are designing novel morphologies forUAVs and MAVs, flight dynamics, robust control systems andcontrol laws for aircrafts AFCS, high performance models forcontrol in Hardware/Software-in-the-Loop flight simulation,experimental and computational aerodynamics.

Andre Carmona Hernandes receivedthe B.E. degree in mechatronics engi-neering, in 2009, from the University ofSao Paulo, Sao Carlos, Brazil, where heis currently working toward the PhD de-gree, working on probabilistic reasoningusing Bayesian networks. Since 2013, hehas been working on Aerial Robots Team(ART), Group of Mechatronics, MobileRobots Laboratory, University of Sao

Paulo. His research interests are mobile robots, modeling, de-cision making, and probabilistic reasoning for aerial robots.

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Marcelo Becker received the M.Sc.and D.Sc. degrees in mechanical en-gineering from the State University ofCampinas (UNICAMP), Brazil, in 1997and 2000, respectively. During his D.Sc.studies, he spent eight months as a GuestStudent with the Institute of Robotics,Swiss Federal Institute of Technology,Zurich, Zurich, Switzerland. At thattime, he was involved in research on

obstacle avoidance and map-building procedures for indoormobile robots. From August 2005 to July 2006, he was onsabbatical leave with the Autonomous System LaboratorySwiss Federal Institute of Technology, Lausanne, Lausanne,Switzerland, where he was involved in research on obstacleavoidance for indoor and outdoor mobile robots. From2001 to 2008, he was an Associate Professor with PontificalCatholic University of Minas Gerais, (PUC Minas), BeloHorizonte, Brazil. From 2002 to 2005, he was also a co-Head of the Mechatronics Engineering Department and of theRobotics and Automation Group, PUC Minas. Since 2008, hehas been a Professor with the University of Sao Paulo, SaoCarlos, Brazil. He has authored more than 80 papers in thefields of vehicular dynamics, mechanical design, and mobilerobotics in several conference proceedings and journals. Hisresearch interests focus on mobile robots, inspection robots,vehicular dynamics, design methodologies and tools, andmechanical design applied on robots and mechatronics.

Fernando Catalano Fernando MartiniCatalano received the PhD. degree inaeronautical engineering from CranfieldUniversity in 1993. He is currently FullProfessor at University de Sao Pauloand has published 6 articles in special-ized journals and 56 papers. He alsoholds 6 technical products. He has su-pervised 14 M.Sc., 5 PhD. and 14 under-graduated thesis. From 1994 and 1998

he coordinated 5 research projects in aerospace engineering.His major interests include experimental aerodynamics foraircrafts and vehicles in wind tunnel.

Fabio Zanini is currently working to-ward the degree in aeronautical engi-neering with the University of Sao Paulo,Sao Carlos, Brazil. Since 2012, he hasbeen working on Aerial Robots Team(ART), Group of Mechatronics, MobileRobots Laboratory, University of SaoPaulo. His research interests are ex-perimental and computational aerody-namics, flight dynamics and stability for

autonomous aerial robots.

Joao L. E. Melo is currently workingtoward the degree in aeronautical engi-neering with the University of Sao Paulo,Sao Carlos, Brazil. Since 2013, he hasbeen working on Aerial Robots Team(ART), Group of Mechatronics, MobileRobots Laboratory, University of SaoPaulo. His research interests are com-posite materials of fuselage manufactur-ing for autonomous aerial robots.

Caio Martins is currently working to-ward the degree in aeronautical engi-neering with the University of Sao Paulo,Sao Carlos, Brazil. Since 2013, he hasbeen working on Aerial Robots Team(ART), Group of Mechatronics, MobileRobots Laboratory, University of SaoPaulo. His research interests are aero-dynamics and stability of autonomousaerial robots.

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