U.S. patent application number 16/194366 was filed with the patent office on 2020-05-21 for double wing aircraft.
The applicant listed for this patent is FARUK DIZDAREVIC DIZDAREVIC. Invention is credited to FARUK DIZDAREVIC, MITHAD DIZDAREVIC.
Application Number | 20200156787 16/194366 |
Document ID | / |
Family ID | 70461530 |
Filed Date | 2020-05-21 |
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United States Patent
Application |
20200156787 |
Kind Code |
A1 |
DIZDAREVIC; FARUK ; et
al. |
May 21, 2020 |
DOUBLE WING AIRCRAFT
Abstract
The present invention is a double wing aircraft with two fixed
wings embodied as either a flying wing configuration or a double
wing configuration having a fuselage with smaller external
dimensions, larger airlifting area, thinner airfoils, and lighter
airframe relative to prior art that altogether is resulting with
lower drag, fuel consumption, harmful emissions, and noise, as well
as higher speed and flight safety, longer range, and shorter runway
when compared to prior art.
Inventors: |
DIZDAREVIC; FARUK; (Anaheim,
CA) ; DIZDAREVIC; MITHAD; (Anaheim, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DIZDAREVIC; FARUK
DIZDAREVIC; MITHAD |
Anaheim
Anaheim |
CA
CA |
US
US |
|
|
Family ID: |
70461530 |
Appl. No.: |
16/194366 |
Filed: |
November 18, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B64C 39/10 20130101;
B64C 39/08 20130101; B64C 3/32 20130101; B64C 3/10 20130101; B64C
2039/105 20130101 |
International
Class: |
B64C 39/08 20060101
B64C039/08; B64C 3/32 20060101 B64C003/32; B64C 3/10 20060101
B64C003/10 |
Claims
1. A double wing aircraft comprising: a. a front wing lifting
surface defined by: i. a low aspect ratio less than 4.5; ii. a high
taper with a taper ratio less than 0.2; b. a rear wing lifting
surface with an area that is 40% to 100% of the front wing lifting
surface area defined by: i. a low aspect ratio less than 56.5; ii.
a high taper with a taper ratio less than 0.2; c. at least one
connecting element joining the front wing and the rear wing; d. an
aircraft gravity center; e. a front wing mean aerodynamic chord
with a leading and trailing edge having a front wing air pressure
center located forward of 35% of the front wing mean aerodynamic
chord in cruise and a rear wing mean aerodynamic chord with a
leading and trailing edge having a rear wing air pressure center
located forward of 35% of the rear wing mean aerodynamic chord in
cruise wherein the rear wing mean aerodynamic chord leading edge is
located aft of the front wing mean aerodynamic chord trailing edge
at a short distance that is less than the length of the front wing
mean aerodynamic chord, the aircraft gravity center is located
forward of the rear wing lifting surface air pressure center and
aft of the front wing lifting surface air pressure center in
cruise; whereby the front wing aspect ratio, the front wing taper
ratio, the rear wing aspect ratio, the rear wing taper ratio, the
ratio between the front wing and rear wing lifting surface areas,
the front wing air pressure center location, the rear wing air
pressure location, and the distance between the front wing mean
aerodynamic chord trailing edge and the rear wing mean aerodynamic
chord leading edge are the mutually supported critical geometric
and aerodynamic variables for the improvement of double wing
aircraft cruise flight efficiency, the aircraft gravity center
location in flight direction is an additional independent variable
that is used in conjunction with other geometric and aerodynamic
variables for additional improvement of double wing aircraft cruise
flight efficiency; the low aspect ratios of the front and rear wing
lifting surfaces for their given respective wing spans result with
increased front and rear wing lifting surface areas due to
elongated wing chords across their respective wing spans, thus
further resulting with increased length of the front and rear wing
mean aerodynamic chords, the elongated front and rear wing chords
result with the reduction of skin friction drag coefficients of the
front and rear wing and additionally allowing for the reduction of
airfoil relative thickness of the front and rear wing across their
respective wing spans; the increased front and rear wing lifting
surface areas require lower cruise lift coefficient that with the
square value thereof decrease induced drag coefficient and together
with reduced airfoil relative thickness exponentially reducing
compression and wave drag coefficient at high subsonic speeds; the
increased front wing lifting surface area with elongated chords
increasing front wing ground effect when the aircraft is flying
close to the ground and thereby preventing rough landing, thus
allowing for the reduction of landing gear weight, the increased
front wing ground effect further reducing takeoff speed, and
consequently reducing either takeoff runway length or engine thrust
and weight; the front wing high taper and the rear wing high taper
shift the respective resultants of front wing and rear wing lifting
forces toward their respective front and rear wing roots, thus
reducing bending momentums across the front and rear wing spans
that allow for the reduction of structural weight of the front and
rear wing; the front wing high taper and the rear wing high taper
increase the rate of elongation of the respective front and rear
wing chord lengths approaching wing roots, thus further increasing
the structural resistance to reduced bending momentums and allowing
for further reduction of airfoil relative thickness approaching
wing roots of the front and rear wing, which wing roots experience
highest bending momentums; the increased front wing lifting surface
area generating higher positive front wing lifting forces in
cruise, the forward shift of the front wing air pressure center
where the resultant of the front wing lifting forces is located
along with the elongated front wing mean aerodynamic chord together
increase the distance of the resultant of the front wing cruise
lifting forces from the gravity center, thus both increased
positive front wing cruise lifting forces and the increased
distance of front wing air pressure center from the gravity center
substantially increasing the positive front wing pitch momentum in
cruise; the forward shift of the rear wing air pressure center
where the resultant of the rear wing lifting forces is located
along with the elongated rear wing mean aerodynamic chord together
with the shorter distance between front wing mean aerodynamic chord
trailing edge and the rear wing mean aerodynamic chord leading edge
shift the rear wing air pressure center and the resultant of the
rear wing cruise lifting forces substantially forward toward the
gravity center, thus the substantially increased positive front
wing cruise pitch momentum and the substantial shift of the
resultant of the rear wing cruise lifting forces forward toward the
gravity center compel the rear wing lifting surface to create
higher rear wing positive cruise lifting forces to establish and
maintain the required static pitch stability of the double wing
aircraft in cruise, the required higher rear wing positive lifting
forces in cruise are obtained by the increase of the ratio between
the rear and front wing lifting surface areas until the rear wing
generate approximately the same cruise lift coefficient as the
front wing; the mutually supported critical geometric and
aerodynamic variables with their suggested numerical values
altogether are simultaneously substantially increasing structural,
lift, and aerodynamic efficiency, thus consequently substantially
increasing the cruise flight efficiency of double wing aircraft
relative to prior art.
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. The double wing aircraft of claim 1, wherein the connecting
element is a fuselage for payload accommodation.
7. (canceled)
8. The double wing aircraft of claim 1, wherein at least two
vertically oriented slender connecting elements are joining the
front and rear wing with the front wing enclosure accommodating
payload.
9-20. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to aircraft with two fixed
wings mutually arranged in flight direction.
BACKGROUND OF THE INVENTION
[0002] Most natural flyers and man-made flying objects are having
only one pair of symmetric wings for lift production that are
attached to a centrally positioned body. The exceptions to this
configuration are related to very rare smaller natural flyers with
two pairs of flapping wings and flying objects with multiple
smaller rotary wings such as helicopters that have insufficient
lift capacity, speed, and range for the current mass-transportation
needs.
[0003] The following configurations of aircraft for mass
transportation have been created so far: [0004] "Tube-and-wing"
aircraft configuration with a pair of wings for lift production and
roll control, fuselage for payload accommodation, and empennage for
pitch and yaw control. [0005] "Tube-and-wing" configuration with
only a vertical tail where wings except for lift production are
used for flight control in pitch and roll directions while vertical
tail for yaw control. [0006] "Canarded tube-and-wing" configuration
where canards are substituting tailplane for pitch control. [0007]
"Tailless flying wing" configuration where a single wing is used
for lift production, payload accommodation, and flight control.
[0008] "Tailed flying wing" configuration where tail surfaces are
assisting a single wing in pitch and yaw flight control. [0009]
"Canarded flying wing" configuration where canards are substituting
the role of tailplane in pitch direction. [0010] Multiple wing
configuration with more than one wing arranged in flight direction
for simultaneous lift production and flight control.
[0011] The first idea of an aircraft having more than one fixed
wing appeared more than 80 years ago in U.S. Pat. No. 2,147,968 of
Feb. 21, 1939. This patent suggested a substitution of empennage
used only for flight control with a fixed rear wing that in
addition to flight control is capable to assist with lift
production in order to increase the lift capacity of aircraft. This
idea has been very attractive, thus initiating many subsequent
patents since then with different solutions for multiple wing
arrangements. However, over the past 80 years, nobody has been able
to develop a realistic aircraft that is competitive with the
current prevailing tube-and-swing configuration with a single wing
and empennage for mass transportation as multiple wing idea
requires more complex flight mechanics relative to the single wing
arrangement with separate surfaces for lift production and pitch
control.
[0012] The initial U.S. Pat. No. 2,147,968 whose idea is similar in
some ways to double wing aircraft as outlined in this application
did not offer any specifics relative to the wing geometry, size,
and gravity center position relative to the wings, as well as any
other aerodynamic feature of the wings that would address how to
achieve lift production on both wings and simultaneously a
sufficient level of flight control and safety of such aircraft.
[0013] The only specific in the initial patent was outlined in
claim 1 as "a rear wing staggered relative to the forward wing by a
distance at least equal to the width of the front wing" with no
specifics as to in which direction "distance" is referred to
whether being horizontal, vertical, diagonal, etc., which is
important for flight mechanics. The confusion in this regard is
further increased with a reference in specification "it is to be
noted that the number and relative position of the front and rear
wing may be varied", which relates to a modification shown in FIG.
8 that reflects an additional vertically coupled front wing with a
rear wing.
[0014] From the standpoint of shape and size of front and rear
wing, only one generic sentence was noted in specification where it
says that "the maneuvering may be insured by means of hinged
ailerons mounted on wings 1 and 2 of which the shapes and
dimensions, as will be understood, are selected in such manner to
ensure the desired lift and stability." The position of gravity
center relative to front and rear wing that is essential for flight
mechanics of a double wing configuration was completely omitted in
claims, specification, and drawings.
[0015] The "double wing aircraft" idea of this patent application
contrary to the above initial patent is revealing geometric
configuration variables related to the mutual size and distance
between front and rear wing, their aspect ratio that is affecting
the wing shapes, and aerodynamic features of both wings as
reflected with the position of their air pressure centers relative
to the position of gravity center in flight direction that are
forcing rear wing to generate a substantial positive lift and high
stability of aircraft in stationary flight conditions by using the
best simultaneous combinations of suggested variables. The
suggested shape of wings as the consequence of low aspect ratio is
resulting with longer chords and lower airfoil thickness, which
along with low lift coefficient due to the large size of both wings
is reducing aerodynamic drag.
[0016] The double wing aircraft idea relative to the initial U.S.
Pat. No. 2,147,968 on the top of the above specific suggested
variables is additionally offering many innovating ideas related to
the specific architectural solutions for connecting front and rear
wing, specific solutions for payload accommodation, as well as
specific accommodation and connections of engines and landing gears
to the airframe.
[0017] All patents related to aircraft that are having more than
one wing based on the initial U.S. Pat. No. 2,147,968 until today
may be sorted in two general groups: [0018] Pure double wing
aircraft without any other planar airlifting surfaces [0019]
Multiple wing configurations with more than two planar airlifting
surfaces
[0020] An efficient aircraft configuration with two or more wings
should generate approximately the same lift coefficient in cruise
on all wings from the standpoint of aerodynamic efficiency while
guaranteeing sufficient flight controls from the standpoint of
flight safety where the term "wing" refers to an airlifting surface
that is providing a positive lift in stationary flight.
[0021] In order to provide for a stable stationary flight, multiple
wing aircraft must have at least two wings, one in front of gravity
center and other behind gravity center with both wings producing
positive lift in order to provide for the static stability in
stationary flight and sufficient flight control in all flight
regimes. An aircraft with more than two planar surfaces from the
standpoint of both aerodynamic and flight control efficiency is
aerodynamically oversized.
[0022] If there is not enough lift in stationary flight, it is more
rational to increase the size of the existing wings as opposed to
adding another wing. If there is insufficient level of flight
control, it is more rational to adjust the mutual size and distance
of existing two wings relative to gravity center than add new
flight control surfaces. For this reason, the patents with more
than two airlifting surfaces will not be addressed further.
[0023] Aircraft configurations with only front and rear wing may be
sorted in three groups formed by: [0024] Transformation of
stabilizing tailplane set behind gravity center into a rear wing
and simultaneously shifting the same forward towards gravity center
while increasing its size. [0025] Transformation of destabilizing
canard set in front of gravity center into a front wing by shifting
the same in aft direction towards the gravity center and increasing
its size. [0026] Formation of a substantial tandem wing
configuration with gravity center between and far away from both
front and rear wing.
[0027] The initial U.S. Pat. No. 2,147,968 and double wing aircraft
of this patent application fall in the first group with a larger
main front wing. Other than shifting a smaller tailplane surface
forward towards gravity center while increasing its size, it is
necessary to additionally shift the front wing airlifting forces in
front of gravity center in stationary flight by either shifting the
gravity center in aft direction behind front wing lifting forces or
shifting the front wing air pressure center forward away from the
gravity center, or doing both simultaneously. During this
transformation, the rear wing lifting forces are staying
substantially behind gravity center with its trailing edge flight
control surfaces far behind the gravity center in order to
guarantee a sufficient level of pitch control.
[0028] The double wing aircraft that belong to the second group as
in U.S. Pat. Nos. 4,030,688 and 8,123,160B2 are formed from a
low-stable canarded aircraft that have a large main rear wing whose
airlifting forces are positioned close to gravity center. An added
small canard that is positioned moderately in front of gravity
center is assisting with static pitch stability in stationary
flight while additionally providing for pitch control in all flight
regimes. The canard size of such aircraft is usually much smaller
than the tailplane size to prevent a higher aircraft natural
destabilization with larger destabilizing canard surfaces that are
positioned in front of gravity center.
[0029] The transformation of canarded aircraft into a double wing
configuration with a front canarded wing starts with the shift of
aircraft gravity center forward away from rear wing air pressure
center towards the canard, while simultaneously shifting the canard
in aft direction towards the shifted gravity center with the
increase of canard size to provide for a static stability of
aircraft with higher positive lift production by the forward
positioned canarded wing. This solution with canarded front wing
and the large main rear wing has greater limitations during
transformation when compared to the first group with tailplane as
the forward shift of gravity center and aft shift of canards are
shifting trailing edge flight control surfaces of the canard very
close to the gravity center, thus making the canard inefficient for
commanded pitch control when the forward shift of gravity center is
making the large rear wing more aerodynamically sluggish for
commanded pitch control of the aircraft, whereby decreasing the
commanded pitch control efficiency and making such aircraft
unsuitable for commercial transportation.
[0030] The third solution with a substantial tandem wing
arrangement as in U.S. Pat. No. 4,390,150 is characterized with a
long distance between front and rear wing, while the gravity center
being positioned far between both wings. In this arrangement, a
large front wing set far in front of gravity center is acting as a
highly destabilizing canard, hence such aircraft are naturally
either low-stable or unstable, thus such arrangement is also not
suitable for commercial transportation.
[0031] The U.S. Pat. No. 8,056,852 of Nov. 15, 2011 called
"Longitudinal Flying Wing Aircraft" reflects a multiple wing
configuration with a large front wing that is adjusted for payload
accommodation and gravity center positioned therein. The front wing
carries a rear vertical reinforcement to which a "V" tail is
connected to as rear stabilizing surfaces. "V" tail stabilizing
surfaces on their upper ends carry integral rear airlifting surface
with engine aerodynamic cover integrated in between. "V" tail with
its high sweepback angle is connected to the aft portion of the
vertical reinforcement of front wing to increase its own
stabilizing function and simultaneously shift rear stabilizing
airlifting surface in aft direction to the highest extent possible,
whereby altogether shifting the aircraft neutral point and gravity
center with positive static margin behind front wing lifting forces
in order to enable rear airlifting surfaces to generate positive
lift in cruise. However, far aft position of rear airlifting
surfaces behind gravity center is increasing its stabilizing role
but decreasing their ability to generate higher positive lift in
cruise.
BRIEF SUMMARY OF INVENTION
[0032] A preferred embodiment of the present invention is a double
wing aircraft with two large fixed wings mutually arranged in
flight direction as a front and rear wing with both having a low
aspect ratio with aircraft gravity center being located within
front wing and between front and rear wing air pressure centers in
stationary flight regime. The double wing idea reflects two
different versions including a double wing aircraft with fuselage
and a double wing as a flying wing aircraft depending on the shape
of connecting elements by which front and rear wing are joined.
With the flying wing version, the payload can be accommodated in
the large front wing only, or in both wings depending on the mutual
size of front and rear wing. Aircraft engines are preferably joined
the rear wing structure and may be integrated within or attached
externally thereto. The double wing aircraft configuration is
allowing for a variety of landing gears attachment methods
including a version with hydrodynamic floats for taking off and
landing on the water.
[0033] These and other aspects of the invention will be better
understood from the following detailed description and
drawings.
[0034] Longitudinal Double Wing aircraft provides for the following
applications and advantages over the prior art: [0035] a) An
opportunity to design a double wing aircraft to generate a positive
lift over more than 90% of its total wetted area in cruise flight
configuration when having an optimal cruise lift coefficient across
both wings, hence providing for a high lift capacity, aerodynamic
efficiency, as well as unmatched range till the present day. [0036]
b) An opportunity to design large commercial double wing aircraft
with significantly smaller outer dimensions including span, length,
and height for easier and safe operations at smaller airports.
[0037] c) An opportunity to design large transport double wing
aircraft requiring a much shorter take-off runway to enable them to
operate on smaller airports. [0038] d) An opportunity to design
long-range double wing aircraft with higher economical cruising
speed to reduce the flight time over long distances. [0039] e) An
opportunity to design commercial double wing aircraft that are
generating much lower level of noise in aircraft cabin and around
airports while reducing environmentally harmful emissions when
compared to present-day aircraft.
[0040] Accordingly, besides the objects and advantages of the prior
art as described above in our patent application, the following
objects and advantages of "Double Wing Aircraft" invention are:
[0041] a) Increasing the space for payload accommodation inside
highly efficient airlifting surface of Front Wing to the highest
degree possible without increase of overall outer aircraft
dimensions while reducing the total wetted area per unit of
payload. [0042] b) The highest possible extension of airfoil chords
of both wings from tips to symmetry plane in order to increase the
total airlifting area and structural resistance, hence reducing
structural weight while elongated chords resulting with thinner
airfoils and therefore altogether resulting with major reduction in
induced, compression, and wave drag at higher cruising speed with a
goal to reduce fuel consumption and increase economical cruising
speed and range.
[0043] Still further objects and advantages will become apparent
from consideration of ensuing description and drawings. Although
description contains many specifics, they should not be construed
as limiting the scope of invention but merely providing
illustrations for some of the presently preferred embodiments of
invention. Therefore, the scope of the invention should be
determined by the appended claims and their legal equivalents
rather than by given examples.
SHORT DESCRIPTION OF DRAWINGS
[0044] FIG. 1 shows the flying wing version of a double wing
aircraft with simple shapes of front and rear wing including the
position of their lifting forces relative to gravity center to
better understand the basic prerequisites needed to design a double
wing aircraft with a positive lift production on both wings in
stationary flight. It further shows geometric and aerodynamic
variables of front and rear wing that the level of positive lift of
rear wing depends upon.
[0045] FIG. 2 shows the fuselage version of double wing aircraft
with front and rear wing being mutually connected by a fuselage
that has payload accommodated therein.
[0046] FIG. 3 shows a flying wing version of double wing aircraft
with approximately the same size of front and rear wing to enable
the accommodation of payload in both wings, which requires a
specific attachment of rear wing landing gears to connecting
elements instead of large wings.
[0047] FIG. 4 shows a double wing aircraft that is using a water
surface for takeoff and landing where landing gears are substituted
by hydrodynamic floats attached to connecting elements between
front and rear wing.
[0048] FIG. 5 shows a flying wing version of a double wing aircraft
that has extended front wing trailing section around symmetry line
between connecting elements in order to increase the payload
capacity while the trailing portion of rear wing central section
around symmetry line is accommodating aircraft engine inside its
aerodynamic contour.
[0049] FIG. 6 shows the exploded planforms of front and rear wing
of aircraft as shown in FIG. 5 to better outline the shapes of
front wing with extended trailing section thereof and the cut-out
leading portion of rear wing central section required for engine
air intake creation.
[0050] FIG. 7 illustrates a modified version of double wing
aircraft from FIG. 5, wherein aircraft engines are attached
externally over the rear wing while the trailing portion of rear
wing central section is aerodynamically restored with the smooth
leading edge instead of engine air intakes.
TABLE-US-00001 REFERENCE NUMERALS IN DRAWINGS 100 Double Wing
Aircraft 110 Line of Symmetry 120 Aircraft Gravity Center 130
Lateral Connecting Elements 140 Fuselage Connecting Element 150
Externally Attached Engines 160 Internally Integrated Engines 162
Engine Fan 164 Engine Air Intake 170 Rear Landing Gears 172 Front
Landing Gears 175 Hydrodynamic Floats 180 Payload Cabin 190 Fin
With Rudder 195 Winglet Fin With Rudder 200 Front Wing 210 Front
Wing Leading Edge 220 Front Wing Trailing Edge 222 Front Wing
Trailing Edge Lateral Segments 224 Front Wing Trailing Edge Central
Segment 226 Front Wing Trailing Edge Farthest Aft Point 230 Front
Wing Mean Aerodynamic Chord 235 Front Wing Mean Aerodynamic Chord
Leading Edge 236 Front Wing Mean Aerodynamic Chord Trailing Edge
240 Front Wing Trailing Section 242 Front Wing Trailing Section
Lateral Elements 252 Front Wing Trailing Section Lateral Ends 260
Front Wing Air Pressure Center 300 Rear Wing 310 Rear Wing Leading
Edge 312 Rear Wing Leading Edge Farthest Forward Point 314 Rear
Wing Leading Edge Lateral Segments 316 Rear Wing Leading Edge
Central Segment 320 Rear Wing Trailing Edge 322 Rear Wing Trailing
Edge Farthest Aft Point 330 Rear Wing Mean Aerodynamic Chord 335
Rear Wing Mean Aerodynamic Chord Leading Edge 336 Rear Wing Mean
Aerodynamic Chord Trailing Edge 340 Rear Wing Central Section 342
Rear Wing Central Section Leading Portion 344 Rear Wing Central
Section Trailing Portion 350 Rear Wing Lateral Sections 352 Rear
Wing Lateral Sections Free Inner Ends 354 Longest Rear Wing Chord
360 Rear Wing Air Pressure Center
DETAILED DESCRIPTION
[0051] The present invention is a double wing aircraft for mass
commercial air transportation with front and rear wing being
mutually arranged in flight direction and embodied as a fuselage or
flying wing version with bulky payload including passengers and
cargo being accommodated inside the fuselage or wing respectively
while a propulsion system is primarily joined the rear wing by
being either attached on the top thereof or integrated within. The
double wing aircraft can be also designed for take-off and landing
over the ground or water as a hydroplane.
[0052] In accordance with the present invention, apparatus and
methods of carrying bulky payload in an efficient double wing
aircraft are presented.
[0053] In the following description, for purposes of explanation
and not limitation, specific details are set forth in order to
provide a more thorough understanding of the present invention.
However, it will be apparent to one skilled in the art that the
present invention may be practiced in other embodiments that depart
from these specific details. In other instances, detailed
descriptions of well-known methods and devices are omitted so as to
not obscure the description of the present invention with
unnecessary detail.
[0054] FIGS. 1A and 1B respectively illustrate a planform and side
view of a flying wing version of double wing aircraft 100 with
payload cabin 180 accommodated inside the contour of lifting
surface of front wing 200 as shown with shaded area in FIG. 1A of
double wing aircraft 100. Gravity center 120 is located within
front wing 200 as shown in FIGS. 1A and 1B. Rear wing 300 and front
wing 200 are mutually set in a tight arrangement in flight
direction so that rear wing leading edge farthest forward point 312
is located behind gravity center 120 and slightly in front of front
wing trailing edge farthest aft point 226. Front wing 200 and rear
wing 300 are mutually connected by two symmetrical lateral
connecting elements 130 that are aerodynamically shaped in flight
direction.
[0055] The shape and size of front wing 200 is defined by the shape
of front wing leading edge 210 and trailing edge 220, as well as
their mutual distance in flight direction that is affecting front
wing aspect ratio, which is recommended to be under 4. The aspect
ratio of front wing 200 in FIG. 1A is approximately 2.1. Smaller
aspect ratio for the same wing span is reflected with longer wing
chords. The shape of front wing 200 is also defined by its taper,
which is recommended to be under 0.2. Higher taper with the same
aspect ratio is resulting with longer wing root chords and
therefore higher structural resistance of wing.
[0056] The shape and size of rear wing 300 that has approximately
the same wing span as front wing 200 is defined with leading edge
310 and trailing edge 320 with aspect ratio being approximately 3.2
as shown in FIG. 1A, which is below the recommended upper size
limit of 5.5 while taper ratio being around 0.18. Low aspect ratio
with high taper of both front wing 200 and rear wing 300 is a
characteristic and important feature of double wing aircraft 100,
especially for front wing 200. The size of rear wing 300 as shown
in FIG. 1A is approximately 66% of the size of front wing 200,
which is within the recommended range between 40% and 100% of the
front wing size.
[0057] The resultant of front wing airlifting forces F.sub.LFW is
positioned at the front wing air pressure center 260 that is
located in front of gravity center 120 while the resultant of rear
wing airlifting forces F.sub.LRW is positioned at the rear wing air
pressure center 360 that is located behind gravity center 120 as
shown in FIG. 1B, which is a prerequisite that both front wing 200
and rear wing 300 are producing positive lift in stationary flight
so that front wing and rear wing pitch momentums M.sub.PFW and
M.sub.PRW respectively around gravity center 120 have to be the
same but with opposite orientation to counter each other and
provide for the static pitch stability necessary for stationary
flight of aircraft as shown in FIG. 1B.
[0058] Front wing air pressure center 260 is in front of 35% of
front wing mean aerodynamic chord 230 from front wing mean
aerodynamic chord leading edge 235. The same applies to rear wing
air pressure center 360 that is in front of 35% of rear wing mean
aerodynamic chord 330 from rear wing mean aerodynamic chord leading
edge 335 as shown in FIG. 1A. The air pressure centers 260 and 360
are changed with the change of attack angles. The suggested
position of air pressure centers in front of 35% of mean
aerodynamic chords 230 and 330 is associated with low attack angles
of both wings in stationary cruise flight when it is necessary to
provide for static pitch stability as reflected in FIG. 1B. Further
shift of air pressure center 260 forward at low cruise attack angle
by adjusting the shape of airfoils of front wing 200 would increase
the distance d.sub.FW of the resultant of front wing airlifting
forces F.sub.LFW from gravity center 120 and consequently increase
front wing pitch momentum, thus requiring the increase of rear wing
lift F.sub.LRW to establish static pitch stability in stationary
flight, whereas further shift of rear wing air pressure center 360
forward by adjusting the shape of airfoils of rear wing 300 would
decrease the distance d.sub.RW of F.sub.LRW from gravity center,
hence requiring additional increase of rear wing positive lift
F.sub.LRW to be able to counter front wing pitch momentum M.sub.PFW
and establish necessary static pitch stability of double wing
aircraft 100.
[0059] The longitudinal positions of air pressure centers 260 and
360 depend on the geometry of local airfoils across the span of
front wing 200 and rear wing 300 respectively. Efficient airfoils
with aft camber that have a high lift coefficient and more shifted
air pressure center in aft direction at low cruise attack angles
are not favorable for front wing 200 of double wing aircraft 100 as
the lift efficiency of rear wing 300 would be lower while a high
lift coefficient of large front wing 200 would generate high
induced, compression, and wave drag. For that reason, double wing
aircraft are using more balanced airfoils with forward shifted air
pressure centers at cruise attack angles with a lower cruise lift
coefficient to reduce major induced, compression, and wave drag of
front wing 200 while the total cruise lift of aircraft would be
restored by a higher lift production of large rear wing 300 by
using similar airfoils as on front wing 200.
[0060] The extremely elongated chords, especially of front wing 200
of flying wing version as shown in FIGS. 1A and 1B are providing
for positive side effects such as substantial reduction of airfoil
relative thickness especially in the large area of bulky payload to
reduce compression and wave drag, increase payload capacity of
flying wing version with longer cabin 180 and decrease cruise lift
coefficient, as well as increase structural resistance to reduce
airframe weight compared to prior art.
[0061] A relatively wide range of recommended geometric and
aerodynamic variables including aspect ratio, mutual size and
distance between front wing 200 and rear wing 300, as well as the
longitudinal position of their air pressure centers is due to their
complimentary use during optimization with different preferential
priorities related to preferred flight performance of double wing
aircraft 100.
[0062] FIGS. 2A and 2B show respective top and side views of a
double wing aircraft 100 where a fuselage for payload accommodation
is used as connecting element 140 between front wing 200 and rear
wing 300. It represents the fuselage version of double wing
aircraft 100. The fuselage version of double wing aircraft 100 as
shown in FIG. 2 is using the same geometric and aerodynamic
variables for optimization of front wing 200 and rear wing 300 as
the aircraft shown in FIG. 1 with similar recommended values in
order to provide for a similar positive lift production of rear
wing 300 and required flight safety in stationary flight of
aircraft as shown in FIG. 2.
[0063] When comparing the double wing aircraft 100 with fuselage as
shown in FIG. 2 with prior art aircraft that have wing and
tailplane connected to the fuselage to which it has superficially
visual likeness, it is apparent upon closer look that there are
differences in the aspect ratio of both wings, the ratio between
the size of front wing 200 and rear wing 300 planar surfaces, their
different mutual position in flight direction, as well as different
positions of air pressure centers 260 and 360 relative to gravity
center 120 in stationary flight, which is similar to the flying
wing version of double wing aircraft 100 in FIG. 1 in order to
enable both wings to generate positive lift in stationary
flight.
[0064] Front wing 200 with much longer chords compared to prior art
is integrated with the bottom of the fuselage 140, thus covering a
wide area of the fuselage's bottom surface, whereby forming a wide
and long integral lower surface of front wing 200 and fuselage 140
close to the ground, thus generating a substantial ground effect
and therefore resulting with much shorter take-off runway when
compared to prior art. Rear wing 300 is connected to the top of
rear portion of fuselage 140 to avoid turbulent airflow behind
front wing 200. High lateral aerodynamic reflection of the large
fuselage and absence of lateral connecting elements 130 in FIG. 1
are requiring additional vertical fin with rudder 190 along
symmetry line 110, similarly as with prior art. An alternative
architectural solution for yaw control of fuselage version is to
have two smaller vertical winglets that act as fins with rudder 195
as shown in view "A" of detail "1" in FIG. 2A. Aircraft engines 150
are connected externally to rear wing 300 over its airlifting
surface.
[0065] The double wing aircraft with fuselage is generally less
efficient than flying wing version of double wing aircraft 100 due
to smaller airlifting area of both front wing 200 and rear wing 300
for the same span that are discontinued by a wide fuselage and due
to an added large parasitic area of fuselage 140, as well as fin
and rudder 190. However, it is more suitable for accommodation of
bulky payload for smaller size aircraft of up to 150 passengers
since flying wing version of double wing aircraft 100 of that size
would require much higher relative thickness of front wing airfoils
in order to provide for a sufficient height of payload cabin, which
would substantially increase compression and wave drag at higher
speeds of the flying wing version when compared to double wing
aircraft with fuselage.
[0066] FIGS. 3A, 3B, and 3C show respective top, side, and front
views of the flying wing version of double wing aircraft 100 with
the size of rear wing 300 being close to the suggested 100% size of
front wing 200 with a tight arrangement in flight direction between
front wing 200 and rear wing 300 that are mutually joined with two
lateral connecting elements 130 and aircraft engines 150 attached
to rear wing 300. Approximately the same size and aspect ratio of
both wings are resulting with approximately the same space inside
the aerodynamic contour of both wings for the accommodation of
payload cabin 180 in order to increase the payload capacity of the
flying wing version of double wing aircraft with substantially
increased lift capacity provided by the increase of the size of
rear wing 300. Such aircraft would be favorable for less bulky or
liquid payload, thereby being suitable for bulk cargo, air
refueling, and firefighting aircraft. Such aircraft would have a
turboprop power plant when used as firefighter or tanker aircraft
for aerial refueling, which fly at lower speeds. Bulk cargo
aircraft that fly at longer distances would preferably have turbo
jet engines.
[0067] Large and heavy rear wing 300 with engines 150 and payload
cabin 180 accommodated inside rear wing 300 are shifting the
gravity center 120 very close to the front wing trailing edge 220,
thus rear landing gears 170 that must be located behind gravity
center would be impossible to attach to front wing 200 for aircraft
shown in FIG. 1. A long distance of rear wing 300 above the ground
would require irrationally very long rear landing gears. For that
reason, the lower structure of two lateral connecting elements 130
that is positioned close above the ground is designed to enable the
attachment of short rear landing gears 170 with a possibility of
their retraction inside the contour of connecting elements during
flight while front wing landing gear 172 is attached to front wing
200 as shown in FIG. 3B similarly to the aircraft shown in FIG.
1.
[0068] FIG. 4 shows architectural solutions similar to the double
wing aircraft 100 as depicted in FIG. 3. The differences relate to
the substitution of landing gears 170 and 172 as shown in FIG. 3
with two hydrodynamically shaped floats 175 that are integrated
with the lower structure of two lateral connecting elements 130 to
enable take-off and landing over the water surface as a hydroplane
as shown in FIG. 4B. Such aircraft would be used for transportation
of low bulky or liquid payload to smaller islands without robust
airport infrastructure.
[0069] FIGS. 5 and 6 show a flying wing version of double wing
aircraft 100 with a specific innovative architecture of front wing
200 and rear wing 300, as well as aircraft engines 160 with fans
162 and air intakes 164 that are integrated with and accommodated
inside trailing portion 344 of rear wing central section 340 as
shown in FIGS. 5A and 5B, as well as cross section view I-I. FIGS.
5A and 5B show respective top and side views pf double wing
aircraft 100 while FIG. 6 shows the exploded view of front wing 200
and rear wing 300 to reflect more clearly the innovative aspects of
both wings in the area of their mutual connection.
[0070] Front wing trailing section 240 about line of symmetry 110
is having two lateral elements 242 as shown in cross-section I-I of
FIG. 5A. Two lateral elements 242 are extending over the airlifting
surface of front wing 200 in order to connect front wing 200 and
rear wing 300 as shown in cross-section I-I and FIG. 5B. The
lateral elements 242 separate front wing trailing edge lateral
segments 222 from front wing trailing edge central segment 224 of
front wing 200, as well as leading edge lateral segments 314 from
leading edge central segment 316 of rear wing 300 as shown in FIG.
6. The lateral elements 242 are extending in aft direction behind
front wing trailing edge lateral segments 222 and central segment
224 as shown in FIGS. 5A and 5B. Front wing trailing section 240 is
bound in aft direction with front wing trailing edge central
segment 224 as shown in FIGS. 5A and 6. The front wing 200 inside
its airlifting surface including trailing section 240 is
accommodating payload cabin 180 about symmetry line 110 as shown in
FIG. 5A.
[0071] Initially short trailing section 240 that is bound by the
central segment 224 as shown with dash lines in FIG. 6 is extended
further in aft direction far behind lateral segments 222 up to
where central segment 224 is reaching a new position as shown with
a solid line in FIG. 6 in order to increase the airlifting area of
front wing 200, the length of airfoil chords between front wing
leading edge 210 and central segment 224, as well as the length of
payload cabin 180 of double wing aircraft 100 as shown in FIG.
5A.
[0072] The rear wing 300 inside the airlifting surface of trailing
portion 344 of rear wing central section 340 is accommodating
aircraft engines 160 about the line of symmetry 110 side-by-side
between front wing lateral elements 242 as shown in cross section
view I-I, as well as FIGS. 5A and 5B. The leading portion 342 of
rear wing central section 340 in front of engine air intakes 164
between lateral elements 242 including rear wing leading edge
central segment 316 are cut out as shown in FIG. 6 to create engine
air intakes 164 that are exposed to free airflow as shown in FIGS.
5A, 5B, and cross section view I-I in FIG. 5A.
[0073] The integration of engines 160 inside the airlifting surface
of trailing portion 344 is eliminating the parasitic drag of engine
pylons while side-by-side mutual position of engines 160 with air
intakes 164 that border each other is substantially increasing the
entry area of air intakes 164 as shown in cross section I-I in FIG.
5A relative to circular air intakes of prior art.
[0074] The deep cut-out of leading portion 342 along with the rear
wing leading edge central segment 316 as shown in FIG. 6 left a
large space in front of engine air intakes 164 and between the rear
wing lateral sections 350 as shown in FIG. 6, which enables a
significant elongation of front wing trailing section 240 in aft
direction behind lateral segments 222 up to where central segment
224 is reaching a position just in front of and below air intakes
164 as shown in FIGS. 5A, 5B, and cross section view I-I of FIG.
5A. Simultaneously, front wing lateral elements 242 are extending
behind central segment 224 and raising up to cover and structurally
connect rear wing lateral section free inner ends 352 as shown in
FIG. 6, as well as FIGS. 5A, 5B, and cross section view I-I of FIG.
5A, thus resulting with insignificant aerodynamic interference
between front wing 200 and rear wing 300 despite a long aft
extension of front wing trailing section 240 between rear wing
lateral sections 350.
[0075] The lateral ends of air intakes 164 as shown in FIG. 5A and
cross section view I-I are aerodynamically blended with inner
surfaces of lateral elements 242 in front of air intakes 164.
Lateral elements 242 that are aerodynamically blended with the
lateral sides of trailing section 240 as shown in cross-section
view I-I of FIG. 5A behind lateral segments 222 as shown in FIGS.
5A and 5B are acting as upward oriented winglets that are
preventing vertical vortices around the lateral ends 252 of
trailing section 240 behind lateral segments 222 as shown in FIG. 6
while lateral elements 242 that are aerodynamically blended with
rear wing lateral sections free inner ends 352 as shown in FIG. 6
are acting as downwardly oriented winglets that are preventing
vertical vortices around rear wing lateral section free inner ends
352 in front of air intakes as shown in FIG. 6 and cross-section
view I-I of FIG. 5A. Additionally, lateral elements 242 that are
set laterally in front of air intakes 164 and front wing trailing
section 240 that is set below air intakes 164 as shown in FIGS. 5A,
5B, as well as cross section view I-I of FIG. 5A are deflecting
free airflow towards the air intakes 164, thus increasing engine
efficiency at higher cruising speeds and simultaneously preventing
the spread of air intake noise towards the ground at lower speeds
during landing.
[0076] The aft extension of trailing section 240 is generating many
positive side effects: [0077] Extension of payload cabin, whereby
increasing the payload capacity of double wing of aircraft as shown
in FIG. 5A without the increase of aircraft outer dimensions, thus
allowing operations of larger aircraft at smaller airports. [0078]
Increasing front wing airlifting area and chord lengths in the area
of bulky payload. The increased lifting area is reducing cruise
lift coefficient while increased chord lengths are reducing airfoil
relative thickness in the large area of bulky payload, thus the
reduced cruise lift coefficient with its square value reducing
induced drag and together with reduced airfoil relative thickness
exponentially reducing compression and wave drag of double wing
aircraft 100 shown in FIG. 5. [0079] Shifting aircraft gravity
center 120 in aft direction towards rear wing 300, thus requiring a
higher positive lift production of rear wing 300 and additionally
reducing cruise lift coefficient by increasing the area of rear
wing 300. [0080] Aft shifted trailing section 240 to which lateral
elements 242 are structurally connected deeply behind rear wing
leading edge farthest forward point 312 below rear wing lateral
sections free inner ends 352 of rear wing 300 to which lateral
elements 242 are structurally connected as shown in FIGS. 5A, 5B,
and cross section view I-I of FIG. 5A are shifting the structural
connection between front wing 200 and rear wing 300 closer to the
lifting forces of rear wing 300, thus reducing the momentums of
rear wing lifting forces that are loading connecting structures of
front wing trailing section 240 and lateral elements 242, as well
as rear wing lateral sections 350 and consequently increasing the
structural efficiency of front wing 200, rear wing 300, and lateral
elements 242 as a connecting structure in the area of their mutual
joint, hence subsequently reducing the airframe weight in that area
of joint of large front and rear wings 200 and 300
respectively.
[0081] FIG. 7 shows the top and a longitudinal cross-section view
I-I in symmetry line of the flying wing version of double wing
aircraft 100 with the same architectural solution of front wing 200
where bulky payload is accommodated but with modified configuration
of rear wing 300 relative to aircraft in FIGS. 5 and 6. The
integrated engines 160 as shown in FIG. 5 are removed from trailing
portion 344 to form a separate engine assembly 150 so that each
engine has their own aerodynamic cover with air intake and pylon
for external attachment thereof to the structure of rear wing 300
as shown in FIG. 7 and cross-section view I-I. The trailing portion
344 is aerodynamically recovered so that air intakes 164 of
aircraft in FIG. 5A are substituted with smooth leading edge 316 of
trailing portion 344 between lateral elements 242 and behind
central segment 224 as shown in the top view of FIG. 7 in order to
avoid aerodynamic interference between trailing section 240 of
front wing 200 and trailing portion 344 of rear wing 300.
[0082] The solution with separate engine assemblies 150 relative to
the solution with integrated engines 160 has positive and negative
aspects.
[0083] The positive aspect is that it is allowing to select the
optimal size, number, and position of engines while the restored
leading edge 316 of trailing portion 344 substantially increasing
the efficiency of trailing portion 344 for lift production, as well
as natural and commanded pitch control and stability of
aircraft.
[0084] The negative side effects of the solution with separate
engines 150 are related to the increased parasitic wetted area and
weight of engine aerodynamic covers and pylons, as well as lower
aerodynamic efficiency of separate engine air intakes and
consequently lower engine fuel efficiency at higher cruising speeds
and altitude relative to air intakes 164 of engines 160 that are
shown in FIG. 5A and associated cross-section view I-I.
* * * * *