A New VTOL Propelled Wing for Flying Cars: Critical Bibliographic Analysis

Abstract

This paper is a preliminary step in the direction of the definition of a radically new wing concept that has been conceived to maximize the lift even at low speeds. It is expected to equip new aerial vehicle concepts that aim to compete against helicopters and tilt rotors. They aim achieving very good performance at very low speed (5 to 30 m/s) by mean of an innovative concept of morphing ducted-fan propelled wing that has been designed to maximize the lift force. This paper presents an effective bibliographic analysis of the problem that is a preliminary necessary step in the direction of the preliminary design of the wing. A preliminary CFD evaluation allows demonstrating that the claimed results are in line with the initial expectations. According to the CFD, results it has been produced a preliminary energetic evaluation of the vehicle in a flying car configuration by EMIPS method. Even if the results are still preliminary, they allow evidencing a good energy efficiency of the vehicle against helicopters.

Full text

Abstract
This paper is a preliminary step in the direction of the denition of a
radically new wing concept that has been conceived to maximize the
lift even at low speeds. It is expected to equip new aerial vehicle
concepts that aim to compete against helicopters and tilt rotors. They
aim achieving very good performance at very low speed (5 to 30 m/s)
by mean of an innovative concept of morphing ducted-fan propelled
wing that has been designed to maximize the lift force. This paper
presents an eective bibliographic analysis of the problem that is a
preliminary necessary step in the direction of the preliminary design of
the wing. A preliminary CFD evaluation allows demonstrating that the
claimed results are in line with the initial expectations. According to
the CFD, results it has been produced a preliminary energetic
evaluation of the vehicle in a ying car conguration by EMIPS
method. Even if the results are still preliminary, they allow evidencing
a good energy eciency of the vehicle against helicopters.
Introduction
Generalities
This paper presents a radically new wing design that aims to equip
radically new aircraft designs such as ying car or other new aircraft
architectures with the aim of emulating the behaviour of helicopters
and tilt rotors with much higher eciency, better performances and
higher safety levels. The specic design has been realized to allow
producing typical manoeuvres including VTOL operations and
hovering by mean of a radically new and simple high-chamber
morphing wing with an embedded ducted fan. It has a dual
conguration: the rst one aims to increase lift by mean of Coandă
eect [1] and super circulation [2] and the other one aims to produce
a vertical thrust by jet deviation. It is derived by a family of possible
congurations, which have been preliminarily originated by the
optimization of the energy balance of a helicopter in ight. By
optimizing this model, it is possible to dene a new vehicle concept
that can do anything that a helicopter can do with mayor energetic
benets. The above analysis identies the possibility of overcoming
the energetic limits of rotary wing aircrafts with respect to other
vehicles [3]. In particular, the future environmental exigencies of
greening aeronautics have focused the attention on possible solutions
that can be electrically propelled [4, 5, 6, 7]. The main characteristics
ore the proposed wing design are the following.
1. distributed electrical propulsion by mean of ducted fan
propellers embedded into the wing [11, 12];
2. acceleration of the uid stream on the upper surface of the wing
by mean of EDF propellers [13] that produces a much higher lift
coecient, with respect to any other aircrafts (up to 9-10);
3. very low stall speed (lower than 10m/s) and consequent increase
of the ight envelope in the low speed domain up to 10÷12 m/s;
4. ight at lower velocity than stall speed by the innovative aps
that can change both the conguration of the aircraft in ight
and the direction of the thrust by mean of Coandă eect [14].
The functional scheme shows clearly the two congurations of the
wing. It can assume a position that produces an increased lift force by
mean of the coupled action of both Coanda eect on the convex
surface of the mobile wing and the attraction eect on the high-speed
stream. This conguration is adequate for high-speed cruise ight. A
second conguration is obtained by mean of an axial rotation of the
rear wing for low speed ight to produce an almost vertical direction
of the thrust. with an almost vertical lift coecient and more
deected thrust, and by mean of uid deection to an almost vertical
direction of thrust for vertical take o and landing (VTOL) and
hovering [15].
A New VTOL Propelled Wing for Flying Cars: Critical
Bibliographic Analysis
2017-01-2144
Published 09/19/2017
Michele Trancossi, Mohammad Hussain, and Sharma Shivesh
Sheeld Hallam Univ.
Jose Pascoa
Universidade Da Beira Interior
CITATION: Trancossi, M., Hussain, M., Shivesh, S., and Pascoa, J., "A New VTOL Propelled Wing for Flying Cars: Critical
Bibliographic Analysis," SAE Technical Paper 2017-01-2144, 2017, doi:10.4271/2017-01-2144.
Copyright © 2017 SAE International
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Figure 1. Architecture of the new high lift propelled wing.
Simplified Energy Balance of Air Vehicles
With the development of aviation technology, helicopter has coupled
eective performances and exibility [16-17] with lower energy
eciency with respect to any other vehicle [18]. The energy
ineciency of helicopters has been demonstrated specically by
Trancossi who has performed an eective comparison of the
energetic performances of dierent vehicles by EMIPS (Exergetic
Material Input per Unit of Service) [19, 20] method.
Trancossi [11] has modied the former assessment method by Dewulf
by considering the mass of the vehicle (whatever is his nature)
divided into the mass of the vehicle and the mass of the payload. In
this way, he analyses the energy eciency of the vehicle and the one
for moving the payload. The results for helicopters have identied
their energetic and exergetic ineciency.
Figure 2. Forces on a helicopter during flight.
Figure 3. Forces on an aircraft during flight.
Helicopter are capable of vertical take o and landing, vertical
movements, forward and reverse ight, and hovering. Having a very
limited aerodynamic lift, they need a much higher thrust also in
vertical direction. The forces that apply to helicopter during dierent
ight conditions are summarily presented into Figure 1. The forces
applied on a helicopter changes in dierent ight conditions [22] and
the equations of ight mechanics of helicopters can be obtained from
Phillis and Venkatesan [23].
(1)
Three dierent conditions can be evidenced: vertical ight (Figure
1.a and b) forward ight (Figure 1.c) and reverse ight (Figure 1.d).
According to gure 2, it is possible to express the equations of ight of
an aircraft [24, 25] that can apply also to tilt rotors in horizontal ight.
(2)
In horizontal ight they become
(2’)
Wood [9] and Zuang [26] have developed helicopters energetic ight
models of a helicopter. From it can be possible to derive the equation
of the energy state of a generic multicopter with n propellers at any
altitude airspeed-RPM combination:
(3)
Equations (2), (2’) and (3) can describe also tilt rotor aircrafts, such
as Boeing Osprey, which allow coupling some of the features of
helicopter and some of the features of aircraft.
Tiltrotors
Tilt rotors are aircrafts, which can tilt their propellers allowing them
to operate with vertical (helicopter mode) or horizontal axis (airplane
mode). Military users use Tilt rotors, even if some civil vehicles are
going to be delivered on the market.
Tilt rotors, such as Boeing Osprey [27], have large tilting propellers
that can assume both vertical axis (helicopter mode) and horizontal
axis (airplane mode). They are mostly used in military eld, but some
civil concepts have been presented. They have problems and
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operative limits [28]: vibrations of drive shafts, coupled wing/shaft
exing, high disc loading generates excessive downwash, instability
when wing angle is between 35° and 80°.
Figure 4. Tilt rotor aircraft configurations during flight
They have also a lower eciency against helicopters in vertical ight
and against aircraft in horizontal ight [29]. In particular, the Phase II
report on Osprey [29] demonstrates that a twin-engine commercial
tiltrotor derived from the military V-22 would be comparable to a
medium-size commuter turboprop and could carry around 40
passengers up to 600 miles. It would be capable of vertical takeo
and landing, but short takeo and landing rolls would improve
payload or range. Tiltrotors could use existing airports, but 40-seat
versions would be too large for many heliports. To compete with
airline shuttle service, passenger cabin noise, vibration, and overall
comfort levels will have to be at least equivalent to that of commuter
aircraft, such as the DeHavilland Dash 8-300. Compared with
turboprop aircraft, a tiltrotor would cost around 40 to 45 % more to
produce and about 14 to 18 % more to operate (over a 200-mile trip).
In addition, they have suered of some operative problems [30] since
vertical landings at unimproved sites produce massive dust clouds
that are ingested into its engines. This is why V-22s rarely stray from
hard surface runways, and prefer rolling take-os to outrun any dust.
This particular problem forced to introduce limits in operations.
Figure 5. Expected development of tilt rotors
Autogyros
Autogyros [31, 32] have a horizontal axis propeller and a free-spinning
rotor actuated by the relative motion in air that sustains the autogiro
[33]. Autogyros had a large success both in civil and military aviation.
Development continued to bring the rotor up to a sucient speed for
takeo. The Pitcairn-Cierva Autogiro solved the problem with a
mechanical power transmission, which can be detached by a clutch.
Figure 6. De la Cierva 1923 autogyro.
A particular architecture of autogiros is Rotodyne [34]. It was a 1950s
compound gyroplane realized by Fairey Aviation for both commercial
and military applications [32]. The Rotodyne has been conceived as
autogyro design propelled by coupled tip jet-powered rotor that
burned a mixture of fuel and compressed air produced by two
wing-mounted turboprops. The rotor has been powered during VTOL
operations, hovering and low-speed translational ight. It was
autorotating during cruise ight in which the necessary power has
been produced by to two propellers applied to the turboprops. The
project was stopped because of huge acoustic problems.
Figure 7. Fairey Rotodyne
Propelled Wings
Another competitor of helicopter is propelled wing architecture.
Propelled wings have been designed with multiple concepts that can
couple also with diused propulsion concepts:
1. Magnus Eect enhancers introduces cylinders propeller into a
wing increasing uid adhesion [35].
2. Jet diusers [36, 37] couple jet propulsion with wings. Jet wing
discharge distributes the jet exhausts using channels inside the
wings and coupled with mobile aps that allow orienting the jet
(Figure 1). Wing-mounted jet-propulsion system [38] develops a
similar concept, by mean of multiple jets inside a wing.
Figure 8. Magnus effect enhancer or propulsion (1941)
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Figure 9. Jet wing discharge propulsion system (1949)
Figure 10. Wing mounted jet propulsion
Figure 11. The patents by Capuani
Figure 12. LEAPTech wing mounted on the testing truck during ground test
activities; NASA SCEPTOR 3D models; comparison between LEAPTech the
much higher lift generated by the present propelled wing concept.
Coandă Effect Enhanced Aircrafts
Capuani [39, 40] has proposed a jet-propelled aircraft in which
propulsion jets are directed over the top surface of the wing (Figure
11). It produces additional lift because of the supercirculation induced
on the wing and the deection of the jets downwards by mean of
Coandă eect, immediately downstream of the wing is provided with
two longitudinal surfaces projecting from said top surface to form a
single surface ejector system.
The results of the former EU FP7 ACHEON (Aerial Coandă High
Eciency Orienting Nozzle) Project [41, 42] has demonstrated that it
is possible to produce a propulsive synthetic jet, which is generated
by two impinging streams, by mean of Coandă eect (Fig.1). The
core of the ACHEON thrust and vector propulsion is a nozzle with
two internal channels, which converge in a single outlet with two
facing Coandă surfaces (3) and (3’).
Figure 13. ACHEON Nozzle concept
Two impinging jets (2) and (2’) generate a synthetic jet that proceeds
straight if the streams have equal momentum, or adheres to the
Coandă surface on the side of the stream with higher momentum.
Control and stability are increased by Dielectric Barrier Discharge
(DBD) installation [43, 44]. In particular, DBD has been
experimented during the project into two dierent functions:
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1. increasing the adhesion with a DBD jet directed in the direction
of the uid stream;
2. Reducing the rigidity and favouring the detachment by mean of
a contrary jet.
The architecture ts with electric propulsion and subsonic aircrafts
(Mach 0-0.5). In particular, it has veried that the deection angle of
the jet (and of the thrust) is a function of both momentums (and
speeds) of the two primitive streams and the geometric conguration
of the nozzle [45, 46]. Trancossi et al. [47, 48] have clearly
demonstrated the advantages of ACHEON in case of application to
STOL aircraft in terms of takeo roll and in case of horizontal ight.
Figure 14. Preliminary conceptual design of the aircraft [30]
Interesting fallout of the ACHEON project has been the preliminary
concept of a new propelled wing conguration [3] and produced an
eective energy model of a drone based on that wing (Fig. 2). The
key advantage of this conguration is an almost perfect emulation of
the behaviour of helicopters by a reversible system. This solution can
be interesting but it is still under development. It require eective
ducted system from inlet to the compressor and then to the outlet with
reasonable pressure losses. Another hypothesis is a reversible
propeller/compressor for propulsion that can be hosted inside the
wing and ensure minimum pressure losses.
Figure 15. Nelson’s propulsion nozzle
Nelson has studied a new aircraft modular design, with a propulsion
system, including an engine, inlet, and exhaust nozzle can be
integrated into the aft body to be at least partially hidden behind the
wing [49]. In one embodiment, the entrance of the inlet can be
positioned beneath the wing, and the exit of the nozzle can be
positioned at or above the wing.
Radelspiel [50] has developed an important variable geometry wing
jet discharge concept that uses tangential blowing of thin wall jets to
overcome the adverse pressure gradients from locally very large ow
turning rates increasing the Coandă eect. It also uses oblique
blowing of air jets to generate longitudinal vortices in the boundary
layer and to provide a convective redistribution of momentum in the
boundary layer with an increase of turbulent momentum transport.
Radelspiel has also produced an important activity on the inuence of
stream-wise vortices on a generic high-lift conguration [51].
Figure 16. Radelspiel’s dual curvature flapped wing [31].
Figure 17. Supercirculation rotary wing by Drăgan
It is also important to cite the huge activity produced on the eciency
of turbo-machineries by Drăgan [52] who has coupled traditional
theoretical research with CFD. In particular, Drăgan has assessed the
robustness of the models of Coandă eect by Roderick [53] and
Benner [54]. Drăgan [55] has also produced a fundamental reference
regarding coupling super circulation with Coandă eect adhesion on
rotary wing propulsion.
Figure 18. NASA LEAPtech wing during tests (NASA Web site).
Some attempts of increasing the lift are connected to diused
propulsion embedded into the trailing of the wing. The most
successful sample in this direction is constituted by the NASA
LEAPtech project [56]. The project is indented to increase the lift
coecient of an aircraft wing by mean of diused electric propulsion.
During preliminary testing on board of a truck, lift coecients CL in
the range 5 - 7 have been achieved (Figure 4).
The integration of a LEAPTech wing into an aircraft will produce
NASA’s SCEPTOR project [58], which will convert a Tecnam into
the X-57. It aim to improve the aerodynamic eciency in cruise by
reaching a better positioning of the cruise point along the drag polar,
reducing the wetted area and increasing the aspect ratio of the wing
[59]. Multiple propellers along the leading edge increases the local
Reynolds number and produce some increase in term of friction drag
together with some disturbances in the lift distribution over the wing.
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Theoretical Background
A New Propelled Wing Concept
The proposed propelled wing concept has been inspired by Nelson’s
nozzle [49], and the studies by Benner [54], Drăgan [52] and
Trancossi’s blowing wing concept [3]. It is based on a dual system
based on an unconventional high lift wing coupled with an electric
ducted fan unit blowing on the top surface of the wing (Fig. 5).
Figure 19. Conceptual schematic of the proposed wing concept (showing in
red) expected effect of Coandă adhesion
Using Benner’s model it can be possible to describe Coandă adhesion
in terms of equilibrium between centrifugal and pressure forces:
(4)
(5)
where, dθ is the innitesimal angular element.
The model of the system can be subdivided into two control volumes
according to Fig. 6. The rst one is dominated by uid deviation by
means of the presence of the interaction of the jet through a surface.
The second one is dominated by the Coandă adhesion caused the
pressure phenomena.
Figure 20. Structure of the fluid dynamic jet
Pressure drop along the jet can be expressed according to Benner [54]
who present a crude but functional model for h/R ratios smaller than
one. He produces a balance between the pressure forces and the
centrifugal forces acting upon a volume of uid.
(6)
Benner equation is based on dierence on pressure only and works
properly only for the condition h/R<1 and does not consider the shear
stress and the external uid attraction. Dragan has veried the
robustness of this formulation, but has also evidenced the necessity of
introducing a correction to allow Benner equation to t better
numerical results. This activity on Benner model integrates with the
models by Trancossi [45,46]. The aim is not the production of any
corrective coecient that can t the results, but the denition of a
robust theoretical model that can t a set of problems that have been
marginally studied. In particular, the proposed area of interest focus
in a large jet that blows almost tangentially on a convex surface. This
preliminary denition of a new wing concept assumes that R is large
some considerations can be done about the uid jet development and
it can be considered that the development of the boundary layer is
similar to the one over a at plate. In particular, it can be assumed
that the thickness δ of the jet is given to two dierent thicknesses: δb
that refers to the boundary layer being caused by shear stress and to
δa that refers to the jet and is caused by the phenomena of uid
attraction from the surrounding free stream.
Considering a preliminary 2D model the following assumptions can
be adopted:
3. The length over the Coandă surface has been indicated with x, x = Rθ
where θ is the generic angle of contact.
4. The Coandă jet considering the eects involved has been
considered as the combination of three eects:
a. the boundary layer eect governed by shear stress;
b. the equilibrium of centrifugal and pressure forces (main
Coandă eect);
c. the attraction of the surrounding slower uid;
5. The three eects can be considered separately and their eects
can be added by superposition. In the core zone of the uid,
over the boundary layer boundary, the velocity is kept at least in
one point equal to the initial velocity of the jet;
6. The jet has an initial constant prole of velocity.
The gauge pressure at the nozzle outlet is zero (i.e., p2 = 0), since air is
discharged to the atmosphere. According to the principle of conservation
of mass, neglecting the uid attraction phenomena, it results:
(4)
By assuming x = θ · R, and assuming, that R is suciently large, it
has preliminary modeled the boundary layer according to the model
which is used for the boundary layer on a at plane. For the boundary
layer term it can be possible to consider the solution by Schlichting
[70] in a turbulent regime:
(5)
(6)
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Skin friction for turbulent ows is given by
(7)
Wall shear stress is another parameter of interest in boundary layers.
It is usually expressed as a function of skin friction dened as:
(8)
and
(9)
The uid attraction phenomena can be modeled by the interaction of
the external uid and the jet. It is consequent of the dierence
between the static pressures of the surrounding uid and the Coandă
jet. It generates a reduction of the average velocity of the uid, but
generates an eective augmentation of the mass ow. This
phenomenon presents more diculties in term of an eective
modeling. It has been preliminarily neglected.
Preliminary Evaluation of the Concept
A coupled study of both helicopters’ ight mechanics and of the
above-cited theoretical and conceptual references has allowed
synthesizing a radically new morphing wing concept according to the
operative schema described in Figure 19. It is composed by a front
propulsive section and a rear bi-sided mobile convex/concave high
camber and low thickness wing prole (Figure 13). It has a dual mode
conguration. It increases the lift when the propulsive uid stream
ows over the convex wing prole by coupled action of high speed on
the top surface and attraction on the surrounding uid. It generates a
vertical thrust by uid deviation on the concave surface of the wing
during takeo, landing, hovering and very low speed operations.
Figure 21. Architecture of the high lift propelled wing.
A.
B.
C.
Figure 22. Preliminary wing design: (A) reference wing, (B) initial wing
design; (C) final modified design
CFD Setup Method
Ansys Fluent 17.1 has been used for preliminary CFD simulations.
They have been performed according to ERCOFTAC guideline [59]
as described by Rizzi [60] and Celik [61], and by referencing Dragan
[55], Schlichting [62], Pngsten [63], and Besagni [64]. The
numerical stability of the grid has been veried in unsteady
conditions through the numerical computation of the grid at dierent
renement levels. It has been found that, when the grid resolved the
viscous sub-layer until y+ value less than 2, it is possible to get the jet
deection angle independent of the grid. Two dierent turbulence
models have been used Spalart Allmaras [65, 66] for preliminary
setup and SST K-ω [67, 68] model. Second order upwind scheme has
been used to discretize the momentum equation and of k and ω
model. Pressure and velocity have been coupled through the PISO
(Pressure-Implicit with Splitting of Operators) method [69]. Pressure
gradient term has been discretized using PRESTO (PREssure
STaggering Option) method [70]. The PRESTO scheme provides
improved pressure interpolation in situations where large body forces
or strong pressure variation are present. Unsteady term has been
discretized using rst order implicit method [71] taking advantage of
unconditionally stable with respect to time step size, which has
assumed Δt =1×10-03 s.
Preliminary CFD Activity
The design has been preliminary veried by mean of preliminary 2D
CFD simulations. A preliminary CFD investigation on a 2D model
has been performed in order to produce a preliminary optimization of
the shape.
The study considers an initial design (Figure 14) which is based on a
high-thickness wing prole that can reach high-lift values. .
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The preliminary wing shape (Figure 22/A) has been initially modied
host a propeller and a second section that can move assuming
dierent positions (Figure 22/B). Both 2D and 3D simulations have
been performed. Final meshes have been generated assuming the
following parameters:
1. lines discretization: 2.5 10-3 m;
2. ination layers: height: 0.25 10-3; expansion factor: 1.1; total
levels: 10; max aspect ratio: 1/5.
A sample of the mesh of the wing is provided in gure 23. In
particular, the following parameters have been reached: max
skewness: 1.54, max aspect ratio: 9.11.
Those preliminary results have produced a huge modication in the
system architecture with the objective of reducing the pressure losses.
From this very preliminary CFD it has been possible to produce a
new architecture (Figure 22/C) with deep modications in the
propeller area, which has been deeply analyzed by 2D simulations
(Figure 24).
Figure 23. Preliminary configuration 3D CFD
Figure 24. Example of the Fluent tri-mesh with boundary layer refinement
Figure 25. An example of CFD solution
The simulations have been performed at dierent airspeeds in the
range Uo=0÷20 m/s and dierent jet speeds Uj=Uo+5÷Uo+30 m/s.
Dierent cases have been evaluated. The reference wing has been
simulated in the same range.
Results have been reported for the conguration in Figure 22/C.
Sample velocity vectors has been presented in Figure 25. The results
have been analytically reported:
1. lift and drag for the reference wing in Figure 18,
2. lift for the propelled wing prole in Figure 19,
3. drag and lift coecients in Figure 28 and 29.
It can be observed that CD and CL appear specically variable and
dependent on the intensity of the Coandă Jet.
The front air intake has the advantage of allowing an eective
reduction of Drag by mean of the front air intake. The results show
clearly the expected lift and drag results.
Figure 26. CL as function of jet speed at different velocities.
Figure 27. Lift results for wing in figure 21/C
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Figure 28. Drag Coefficient Results
Figure 29. CL as function of jet speed at different velocities.
Figure 29 shows clearly that the it is possible to notice the main
problem, which has been identied and regards explicitly the
interaction between the high speed stream and the mobile high
chamber wing prole that has been installed. The optimization of the
mobile wing prole has been considered fundamental for producing a
more eective wing prole.
Analysis of CFD Results
The results appear to be clearly in line with the Coanda eect models,
which have been presented by Roderick and Brenner. In fact, it is
evident the correlation between the angle of attachment and the
geometric parameters of the Coanda surface. This preliminary
theoretical evaluation of the results is being currently analysed
according to rst and second law.
On the other side, the results allow to dene the redesign of the wing
system to correct the defects and improve the limits of the tested
conguration. The redesign activity has been focused on reducing
internal pressure drops caused by the reduction of the exit section and
on a better shaping and kinematic analysis of the moving wing to
improve the uiddynamic behaviour when the wing is used to
produce vertical thrust. A preliminary result of the redesign activity
has shown in Figure 30. This new conguration is currently under
massive CFD testing with the objective of producing a more eective
design that improves radically actual design.
A.
B.
Figure 30. Main measures of the wing
Flying Cars
This vehicle can insert into the segment of the ying cars. Major
competitors appear to be a vehicle, which is currently far from any
optimization and appears like cars with deployable wings. Most of
them are not VTOL and must take o from airports. They do not
present any real operative advantage with respect to an aircraft.
Figure 31. Aeromobil flying car
1. AeroMobil is a car with deployable wings. It is under testing in
ultra-light category (Czech certication). When the nal product
will be available or how much it will cost is not specied. [72]
2. Urban Aeronautics' X-Hawk and Airmule (unmanned) is a
VTOL turbojet [73] powered aircraft announced in 2006 with
a rst ight planned for 2009. It was intended to operate like a
tandem rotor helicopter, with ducted fans rather than exposed
rotors. As of 2015, no ights had been reported.
3. Moller Skycar M400 [74, 75] is a personal VTOL (vertical
takeo and landing) aircraft that act as a tilt rotor with four pairs
of ducted fan propeller moved by Wankel rotary engines.
Skycar would be allowed to y from airports & heliports. They
have proposed an all-electric version.
4. The Xplorair PX200 [76] is a project of single-seater VTOL
aircraft without rotating airfoil, relying on Coandă eect and
Downloaded from SAE International by Michele Trancossi, Monday, September 25, 2017

using an array of small jet engines called "thermoreactors"
embedded within tilt wings' body. A full-scale drone has
scheduled for ight at Paris Air Show 2017.
5. Terrafugia TF-X [77] is an electric hybrid tilt-rotor vehicle that
would be the rst fully autonomous ying car. It has a range of
500 miles (800 km) per ight and batteries are rechargeable by
the engine. Development of TF-X is expected to last 8-12 years
(2021-2025).
6. Macro SkyRider X2R [78] is a project of a ying car which is
lighter than the Moller Skycar.
Figure 32. Xplorair AirMule prototype and XHawk drawing
Figure 33. Moller Skycar prototype
Figure 34. Xplorair PX200
Figure 35. Terrafugia TF-X
Figure 36. Macro SkyRider X2R
Figure 37. Preliminary aircraft architecture
Preliminary Vehicle Definition
The proposed wing is expected to be the key component of a novel
urban all-electric ying vehicle. It is a two-seater (FAA-EASA
Light-Sport aircraft) with a MTOW lower than 600 kg and a price in
line with high-class cars (around 90,000 €). The dimensions (length
and wingspan lower than 7 m) allow operations from large urban
roads for personal transport, emergency, civil protection and police
use. It has the objective of substituting or integrating ground transport
and helicopters. It has an exceptional operative exibility by
performing both VTOL and STOL operations. It can be dened by
using industrial grade battery (the BASF Ovonic NiMH battery that
was installed on the GM EV-1 [79]) with 80 Wh/kg at the cell level,
and a power discharge of 100 W/l.
Downloaded from SAE International by Michele Trancossi, Monday, September 25, 2017

Figure 38. An emotional rendering.
By assuming the preliminary results produced by Hussain [80] and
and Trancossi [81] in terms of performance of the wing it is possible
to produce a vehicle assessment that demonstrate the potential of the
proposed vehicle. In the case of this electric vehicle, because of the
necessity of comparing solution with dierent fuels and propulsion
systems, GHG are evaluated at the 2014 value of EU GHG emission
factor for electric production.
Figure 39. Another preliminary system rendering
Energy consumption and GHG emissions of Blowing urban-craft has
been estimated assuming CFD results and veried according to the
well-known second principle based EMIPS Method [19, 20] as
modied by Trancossi [18].
The evaluations consider a reference mission prole, which has been
shown in Figure 40.
Figure 40. Reference mission profile.
The reference mission prole do not consider take o and landing
operations to allow an eective comparison between aircraft of
dierent nature including aircrafts and helicopters.
Table 1. Comparison against competitors
The results clearly show the excellent energy eciency and low
emissions of the vehicle with respect to the competitors in a speed
regime between 25 and 30 m/s. Encouraging results have been
obtained, even if they are still a preliminary evaluation assessed on
the basis an approximated but well tested method that needs to be
evaluated with a more eective method.
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Contact Information
Dr. Michele Trancossi
Senior Lecturer
Sheeld Hallam University
m.trancossi@shu.ac.uk
m.trancossi@gmail.com
Definitions/Abbreviations
EDF - electric ducted fan
Ω - angular speed (rpm, rad/s)
δ - distance of the rear ailerons from center of mass (m)
δa - boundary layer thickness
δb - stream
ε - thrust angle (deg, rad)
γ - glide angle (deg, rad)
ϕ - pitch angle of helicopter propeller (deg, rad)
ρ - density (kg/m3)
τ - Shear stress (kg/m2)
A - area (m2)
D - drag (N)
I - moment of inertia (kg m2)
L - lift (N)
R - radius of Coandă surface (m)
T - thrust (N)
W - weight
h - Coandă jet thiickness
n - number of propeller
p - pressure (Pa)
u - velocity (m/s)
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