AU2020100605B4 - A vtol-capable airplane having angled propulsors - Google Patents

Abstract

A VTOL-CAPABLE AIRPLANE HAVING ANGLED PROPULSORS ABSTRACT The present invention relates to an airplane capable of hyper-short / vertical takeoff and landing (hyper-STOL / VTOL) and having a positive tilt angle applied to the 5 horizontal propulsors (104A, 104B). A positive tilt angle may also be applied to the vertical propulsors (106A, 106B, 106A1, 106A2, 106B1, 106B2). This invention attempts to reduce pitch angle during hovering and vertical flight. Most Illustrative Diagram: FIG. 3

Description

A VTOL-CAPABLE AIRPLANE HAVING ANGLED PROPULSORS FIELD OF INVENTION

The present invention relates to an aircraft capable of hyper-short / vertical takeoff and landing (hyper-STOL / VTOL) having horizontal and vertical propulsors.

BACKGROUND OF INVENTION

Personal aviation and aerial ridesharing such as Uber Air are on the rise globally. In the words of Airborne, "OEMs and startups alike are racing the clock to launch the first electric vertical take-off and landing (eVTOL) aircraft by 2025" [1]. Many of the airframes used to realize eVTOL is largely based on that of a combined fixed wing and multicopter aircraft, also known as a "QuadPlane" [2]. This type of aircraft is known to have the benefit of vertical takeoff and landing, significantly higher cruising speed, and the ability to land vertically at the destination [2]. The design of a QuadPlane is built upon an airplane, but with an addition of at least 4 rotors/propellers for vertical flight [2]. In other words, there are separate propulsions for horizontal cruising flight and vertical flight. So in general, when a QuadPlane is hovering, its horizontal airplane-like propulsion(s) is/are inactive. Likewise, when said QuadPlane is cruising through the air using wing-borne lift in horizontal flight mode, its powerful helicopter-like vertical propulsions are inactive and having zero contribution. This, from our viewpoint, is inefficient and unoptimized. Other well known airframe configurations that enable an airplane to hover and perform vertical flight are those based on tilt-wings and tilt-rotors involving rotatable propulsion units which often are technologically more complex than a QuadPlane [3,4].

We proposed the concept of a fixed-wing aircraft (airplane) having "tandem roto-stabilizer" as an effective solution to overcome the limitation of QuadPlane design by making efficient use of both horizontal and vertical propulsions during hovering and vertical flight (Malaysian Patent Application No. PI 2020000674). During hovering and vertical flight the airplane assumes a nose-up attitude known as 'harrier' with positive pitch angle so that the horizontal propulsor(s) and the vertical propulsors both contribute to lift via resolution of vectors. If both horizontal and vertical propulsions have equal thrust output, said aircraft will typically takeoff or hover with a pitch angle of 45°. An exemplary embodiment of such aircraft is as shown in FIG. 1. However, while such pitch angle is fine for unmanned aircraft applications, it may be a little uncomfortable for manned flight or aircraft that carry passengers.

SUMMARY OF INVENTION

An object of the present invention is therefore an attempt to reduce the takeoff and hovering pitch angle of an airplane equipped with "tandem roto-stabilizer".

In the Malaysian Patent Application No. PI 2020000674, the thrust vectors of the horizontal propulsors are substantially parallel to the longitudinal axis of the aircraft as indicated in FIG. 1. A distinctive feature of the present invention is that the thrust vectors of the horizontal propulsors are angled upward by an amount # during hovering and VTOL resulting in a greater vertical thrust component thereby reducing the pitch angle, p. This is implemented by applying tilt angle # to the horizontal propulsors during hovering and VTOL. Tilt angle r may also be applied to the vertical propulsors to help further reduce the pitch angle during hovering and VTOL.

Embodiments of the airplane in the present invention comprise an airframe, the airframe can be divided into a front section, and a back section. The airframe further comprises at least a pair of wings with ailerons for roll control; at least a pair of horizontal propulsors having a positive tilt angle # with respect to the longitudinal axis of the airplane in the range of 0.5 to 80 during hovering and VTOL; and at least two vertical propulsors which may be divided into fore unit(s) and aft unit(s), at least one fore vertical propulsor is located on the front section of the airframe, at least one aft vertical propulsor is located on the back section of the airframe, wherein the fore and aft vertical propulsors are in substantially lateral symmetrical positions about the longitudinal axis of the aircraft. The airframe in the embodiments may further comprise at least a fuselage. At least one horizontal propulsor may be mounted to each side of the wings wherein the thrust vectors of the horizontal propulsors are substantially parallel to the chord lines of the respective wings and so 0, the angle of incidence of the wings on which the horizontal propulsors are mounted is equal to the tilt angle of the propulsors 4. In other words, in the present invention, it is always true that 0= and vice versa. Also note that, # the tilt angle of the horizontal propulsors (104A, 104B) may remain in the range of 0.5° to 80 during hyper-STOL.

Furthermore, in accordance with the present invention, each wing may have one or more ailerons or elevons for roll control but there should be at least one aileron immersed in strong propeller wash generated by the horizontal propulsors to help ensure effective roll control during vertical flight and hovering. The horizontal propulsors should therefore be mounted in such a way that would enable said ailerons to be exposed to strong air-stream generated by the horizontal propulsors to help ensure adequate roll control in deep wing-stall regimes. For this reason, the horizontal propulsors should be positioned in front of the ailerons.

During hovering and vertical flight, both the horizontal propulsors and the vertical propulsors contribute to lift via resolution of vectors. In accordance with the present invention, having the horizontal propulsors at a tilt angle $ during vertical flight leads to a reduction in the takeoff and hovering pitch angle p, which will particularly benefit manned flight applications.

In preferred embodiments of the present invention, the tilt angle and hence the angle of incidence of the wings on which the horizontal propulsors are mounted is reconfigurable / variable to offer flexibility to meet flight requirements. The change in the angle of incidence however, can be made either manually or automatically, i.e., the angle of incidence of the wings can be manually set and secured in place using nuts and bolts while the airplane is parked inside a hanger or it can be changed while airborne. The airplane in the present invention that is predominantly used for short haul flight, of say 10 km, may have the angle of incidence of the wings manually set and locked to +12. For long-haul flight such as a flight distance of 500 km, the angle of the incidence may be manually configured to +5 while the airplane is on the ground. This makes the airplane adaptable to changing need and offers possibility to prioritize comfort and vertical flight performance over horizontal flight performance or vice versa.

In embodiments of the present invention, the airframe may also comprise at least an aerodynamic surface for pitch stability and control during horizontal flight mode, and examples of which are horizontal stabilizer, inverted V-tail and delta shaped wings, all of which will be exemplified by the various embodiments of the present invention described herein. In the case where horizontal stabilizer is employed, the entire horizontal stabilizer may be used to actuate pitch control or the horizontal stabilizer can have elevators for aerodynamic pitch control depending on the nature of applications. The airplane's forward thrust during horizontal flight mode (cruising flight) is provided by the horizontal propulsors. Additionally, the horizontal propulsors may be based on a variety of drives such as electric motor, turbine engines (including turboprop and turbojet), internal combustion, and solar engine.

The airplane in the present invention is expected to be able to handle wind gust better in VTOL mode compared with a traditional tiltwing aircraft. This is because the vertically tilted wing of a tiltwing aircraft represents a large surface area for crosswinds to push against [5]. The present invention with differential thrust yaw may also have better authority in VTOL mode under windy condition.

All embodiments of the airplane in the present invention are capable of vertical takeoff and landing (VTOL) as well as hyper-short takeoff and landing (hyper-STOL).

Reference will now be made to the drawings wherein like numerals refer to like elements throughout. The proceeding disclosure is provided by way of example and not by way of limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an exemplary airplane comprising two vertical propulsors (or roto-stabilizers) in accordance with the Malaysian Patent Application No. PI 2020000674.

FIG. 2 is a perspective view of an exemplary airplane comprising a pair of horizontal propulsors, each having a fixed tilt angle of +6° in accordance with the present invention.

FIG. 3 is a side view showing an exemplary airplane similar to that in FIG. 2 in hovering attitude with pitch angle p, and with tilt angles $ and r applied to the horizontal and vertical propulsors respectively, as well as the associated forces acting on it in accordance with the present invention.

FIG. 4(a) shows an embodiment of the airplane in the present invention comprising an ellipsoidal fuselage, a pair of upper wings, and a pair of lower wings having an

angle of incidence of 45° during hovering and VTOL.

FIG. 4(b) shows a side view of the embodiment as presented in FIG. 4(a).

FIG. 4(c) is a perspective view of the embodiment shown in FIG. 4(a) and it comprises an inverted V-tail for long-haul flight in accordance with the present invention.

FIG. 4(d) is another perspective view of the embodiment depicted in FIG. 4(a) and it

shows the lower wings having an incidence angle of 45° and the respective ailerons

being deflected 450 upward to affect the resultant thrust vectors of the horizontal propulsors during horizontal flight mode.

FIG. 4(e) is a perspective view of the embodiment depicted in FIG. 4(a) comprising a plurality of lower wings, each further comprising an aileron.

FIG. 5(a) shows an embodiment of the present invention wherein the airframe comprises four vertical propulsors and a pair of horizontal propulsors. The angle of

incidence of the wings is 20.

FIG. 5(b) is a bottom view of the embodiment as depicted in FIG. 5(a).

FIG. 6(a) is a perspective view of an embodiment of the present invention comprising a delta-like wings and an inverted vertical stabilizer.

FIG. 6(b) is a close up view around the front section of the airframe of the embodiment as depicted in FIG. 6(a).

FIG. 6(c) is a side view of the embodiment as depicted in FIG. 6(a).

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention relates to a fixed-wing aircraft (airplane) capable of hyper-short / vertical takeoff and landing (hyper-STOL / VTOL) with reconfigurable trust vectors of the horizontal propulsors and the vertical propulsors.

FIG. 2 is a perspective view of an exemplary airplane in accordance with the present invention. The airplane comprises an airframe (100). The airframe (100) can be divided into a front section, and a back section. Said airframe (100) further comprises at least a fuselage (101), at least a pair of wings (102), the wings (102)

have positive angle of incidence in the range of 0.5 to 80 during hovering and

VTOL; at least a horizontal propulsor (104A, 104B) is mounted on each wing (102); and at least two vertical propulsors (106A, 106B) which may be divided into fore unit(s) and aft unit(s), at least one fore vertical propulsor (106A) is located on the front section of the airframe and in front of the center of gravity (C.G.) of said airplane, at least one aft vertical propulsor (106B) is located on the back section of the airframe (101) and behind the C.G. of said airplane, wherein the fore and aft vertical propulsors are in substantially lateral symmetrical positions about the longitudinal axis of the aircraft as illustrated in FIG. 2. In this exemplary airplane, one horizontal propulsor (104A, 104B) is mounted to each side of the wings wherein the thrust vectors of the horizontal propulsors are substantially parallel to the chord

lines of the respective wings (102), and so this means that $, the tilt angle of the

horizontal propulsors (104A, 104B) is equal to 0, the angle of incidence of the wings

(102). In this embodiment, the angle of incidence is manually fixed at 6 and secured with nuts and bolts to the fuselage (101) while the airplane is at rest on the ground

and # remains 60 while airborne. The airplane's forward thrust during horizontal

flight mode (cruising flight) is provided by the horizontal propulsors (104A, 104B). The horizontal propulsors (104A, 104B) may be based on a variety of drives such as electric motor, turbine engines, internal combustion, and solar engine. Both the vertical propulsors (106A, 106B) are preferably located at substantially equal distance from the C.G. for optimal pitch control performance. Furthermore, the tandem vertical propulsors (106A, 106B) in this example have counter-rotating rotors to cancel out the torque effect and the same principle may apply to the horizontal propulsors (104A, 104B).

Each wing (102) comprises at least an aileron (108) for roll control. The horizontal propulsors (104A, 104B) should be mounted in such a way that would enable said ailerons (108) to be exposed to strong air-stream generated by the horizontal propulsors (104A, 104B) to help ensure adequate roll control in deep wing stall regimes such as hovering, vertical landing and hyper-short takeoff. For this reason, the horizontal propulsors (102A, 102B) should be positioned in front of the ailerons (108) and in this particular example, they are mounted proximate to leading edges of the wings (102).

During hovering and vertical flight, the horizontal propulsors (104A, 104B) and the vertical propulsors (106A, 106B) contribute to lift via resolution of vectors. In accordance with the present invention, having a positive angle of incidence of the wings (102) during vertical flight leads to a reduction in the takeoff and hovering pitch angle, which will be of particularly benefit to manned flight applications. The angle of incidence of the wings (102) is reconfigurable. The change in the angle of incidence can be made either manually while the airplane is on the ground or automatically while the airplane is airborne.

The airframe (100) of this exemplary airplane comprises at least an aerodynamic surface for pitch stability and control during horizontal flight mode in the form of a horizontal stabilizer (110) in canard configuration. In this example, almost the entire horizontal stabilizer (110) is used to actuate pitch control as illustrated in FIG. 2. Use of the horizontal stabilizer (110) for pitch control during cruising flight allows the vertical propulsors (106A, 106B) to be switched off thereby improving efficiency and extending range of travel. Optionally, the airframe (100) may comprise at least one vertical stabilizer (112) which is useful for directional stability during a glide or in case the horizontal propulsors (104A, 104B) are malfunctioning and differential thrust for yaw control is not available. It is possible to have more than one vertical stabilizer (112). The vertical stabilizer(s) (112) may further comprise rudder(s) (114), though simulation suggested that the airplane can still turn satisfactorily using only ailerons without use of rudder (114). FIG. 2 shows at least an aft unit (106B) of the vertical propulsors (106A, 106B) mounted on top of the vertical stabilizer(s) (112). Yaw control during vertical flight mode may be realized using differential thrust of the horizontal propulsors (104A, 104B).

A set of main gears (116) is located on the back section of the airplane, behind the C.G. of said airplane. Main landing gears (116) and nose gear (118) with wheels are useful for hyper-STOL and emergency landing involving ground roll on runway. Given the vertical takeoff and landing (VTOL) capability of the airplane, the main landing gears (116) and nose gear (118) may be equipped with floats for water operation or skis for operating from snow.

The vertical propulsors (106A, 106B) in the present invention can accept either variable or fixed-pitch rotor, however, for mechanical simplicity and to reduce maintenance cost, the rotors of said vertical propulsors (106A, 106B) are preferably fixed-pitch. The same applies to the horizontal propulsors (104A, 104B). This means that each vertical propulsor (106A, 106B) can only exert aerodynamic force in one direction. The vertical propulsors (106A, 106B) having fixed-pitch rotors actuate pitch control of the airplane by differential thrust.

In addition, the tandem vertical propulsors (106A, 106B) can be used to provide partial lift to the airplane during takeoff and landing, helping to reduce forward airspeed, and hence resulting in hyper-short takeoff / landing distance. As mentioned in Malaysian Patent Application No. PI 2018500050, at certain conditions, vertical takeoff and landing are possible without requiring use of tilt-wings or tilt rotors.

Referring now to FIG. 3 which shows an airplane in the present invention performing a hover in order to gain insight into the forces acting on the airplane that make hovering and VTOL flight possible. The airplane is hovering with a pitch angle of p. Each of the horizontal propulsors (104A, 104B) generates a thrust Ti. Each of the vertical propulsors (106A, 106B) generates a thrust of T2. The airplane has an all up-weight (AUW) of W. For ease of illustration, let's consider a scenario in which T2 = Ti. As mentioned, the angle of incidence of the wings (102), 0= $ and the angle of tilt of the vertical propulsors (106A, 106B) is -, measured against a vertical axis of the airplane. Note that said vertical axis is parallel to the yaw axis of the airplane.

Considering the horizontal components of the forces when the airplane is hovering, one obtains

Ti cos(p + #) = T2-sin(p+ ).

Now, considering the vertical components of the forces, one obtains

T. sin(p+ #)+ T2- cos(p + -) = 0.5x W.

In the case of p = 16, $= 40, and -= 180 as illustrated in FIG. 3

-> Ti = T2 = 0.30W.

Taken together, the vector analysis shows that when the pitch angle p is 16° and when the horizontal propulsors (104A, 104B) and the vertical propulsors (106A, 106B) produce the same amount of thrust, i.e. Ti = T2 = 0.30W, stationary hover is attained. Therefore, all embodiments of the airplane in the present invention are capable of vertical takeoff and landing (VTOL) as well as hyper-short takeoff and landing (hyper-STOL). A way to achieve hyper-STOL is simply by increasing the ratio of T1 /T 2 while maintaining pitch angle p and tilt angles $ and r. Note that if an embodiment in the present invention is capable of hovering and VTOL flight, then it is certainly capable of performing hyper-STOL as well.

Had $= 0, and - = 00 as presented in the Malaysian Patent Application No.

PI 2020000674, then the pitch angle p required for a hover will be 45.

Among the notable and interesting results from vector analysis are as follow:

1. $=45° -=45° p= 0° Ti=T 2 =0.3536W

2. $= 45° - = 450 p= 100 Ti = 0.4096W, T2 = 0.2868W

3. $= 120 - = 12° p = 330 Ti = T2 = 0.3536W

4. $=50 0 lC=00 p=2 0 ° Ti=T2 =0.266W

5. $=700 -= 200 p = 50 Ti =0.3287W, T2 = 0.2013W

6. $=80 0 v=0 0 p=50 Ti=T 2 =0.251W

Result-i indicates that when $ and - are both 450, the airplane should be able to perform vertical takeoff and landing with pitch angle of 00, i.e., fuselage in level position and the horizontal propulsors and the vertical propulsors would each generate a thrust that equals approximately 35% of the all-up-weight of the airplane, W. If the takeoff pitch angle p is now increased to 100 as shown in Result-2, then each of the vertical propulsors is only expected to output a thrust of 0.2868 Win order to sustain a stationary hover. On the other hand, each of the horizontal propulsors should output a greater thrust of about 0.4 W. This is an efficient design because apart from providing thrust for vertical flight, the powerful horizontal propulsors can also be used for high speed cruising. Result-5 is yet another interesting result which can be practically implemented.

Result-3 is yet another interesting result because it suggests that an angle of incidence of 12 may be used for both vertical and horizontal flights involving moderate airspeed and therefore the wings (102) can simply be locked in position against the fuselage (101). Analysis shows that for an angle of incidence of 500 and above, the required thrust of each propulsor approaches 0.25 W. Note that in Result-6, $= 80° is about the maximum possible because if $= 90, there will be no contribution of thrust from the horizontal propulsors (104), and without propeller wash over the ailerons (108), there will be no roll control.

FIG. 4(a) is a perspective view of an embodiment of the airplane in accordance with the present invention wherein the airframe (100) comprises a fuselage (101) and the shape of the fuselage (101) is substantially an ellipsoid. The airframe (100) comprises at least a pair of wings (102). In this exemplary airplane, each wing (102) further comprises an upper wing (102U) and a lower wing (102L), wherein the upper wings (102U) are fixed-wing with fixed angle of incidence and they are primarily used for horizontal flight. In accordance with the present invention 0, the angle of incidence of the lower wings (102L) and hence $ the tilt angle of the horizontal propulsors (104A, 104B) is in the range of 0.5° to 80 during hovering and VTOL. In accordance with the present invention, # the tilt angle of the horizontal propulsors (104A, 104B) may remain in the range of 0.5 to 80 during hyper-STOL. In this exemplary airplane however, 0 and hence $ is fixed at 45 during vertical flight and horizontal flight. Each lower wing (102L) comprises at least a horizontal propulsor (104A, 104B), and at least an aileron (108). Furthermore, the wingspan of each lower wing (102L) is nearly the same as the diameter of the rotor of the respective horizontal propulsor (104A, 104B). This is because the primary function of the lower wings (102L) are intended for slow or vertical flights. In accordance with the present invention, the horizontal propulsors (104A, 104B) should be positioned in front of the ailerons (108) and in this particular example, they are mounted proximate to leading edges of the wings (102L). In accordance with the present invention, # the tilt angle of the horizontal propulsors (104A, 104B) is substantially equal to 0 the angle of incidence of the lower wings (102L) on which the horizontal propulsors (104A, 104B) are mounted.

FIG. 4(b) is a side view of the exemplary airplane as shown in FIG. 4(a). The ellipsoidal fuselage (101) comprises a horizontal principal axis (1OIHA). Said ellipsoidal fuselage comprises an upper front section, a lower front section, an upper back section, and a lower back section. The upper front section is separated from the lower front section by the horizontal principal axis (101HA). The exemplary airplane comprises at least one fore vertical propulsor (106A) disposed on the lower front section of the ellipsoidal fuselage (101), and at least one aft vertical propulsor (106B) disposed on the upper back section of the ellipsoidal fuselage (101). The angle of tilt of the vertical propulsors (106A, 106B) - as shown in FIG. 4(b) is 45. The thrust vectors Ti and T2 are also indicated in FIG. 4(b).

With -= 450 and $ = 450, the takeoff pitch angle p is 00. This means that in this configuration, the airplane is able to perform VTOL with the fuselage being substantially level. The airframe (100) also comprises a cockpit windscreen (120). The ellipsoidal fuselage (101) design is attractive in that at least one fore vertical propulsor (106A) can be mounted below the cockpit windscreen (120) and therefore helping to keep the pilot's field of view clear. The embodiment as depicted in FIG. 4(b) is compact and may be suitable for short-haul flights. The fuselage (101) also comprises at least an attachment point (122) on the back section to attach a tail assembly as an option for long-haul flight applications.

FIG. 4(c) is a perspective view of the airplane in a substantially horizontal flight mode with both the fore and aft vertical propulsors (106A, 106B) retracted into the fuselage (101) to improve aerodynamic efficiency. The vertical propulsors (106A, 106B) are housed inside a compartment with a pair of hatch doors (119) that slide sideway. The tail assembly comprises at least one supporting structure (124), an inverted V-Tail (126) that provides combined pitch and yaw function during horizontal flight mode. The inverted V-Tail (126) further comprises control surfaces (128). After making transition to horizontal flight mode, 0 the angle of incidence of the lower wings (102L) may be reduced to, for example, 3 either manually or automatically as shown in FIG. 4(c).

It may be possible to effectively reduce tilt angle of the thrust vector of the horizontal propulsors (104A, 104B) by deflecting the ailerons (108) upward. To improve effectiveness of such deflection, plurality of horizontal propulsors (104A, 104B) on respective lower wings (102L) having smaller rotors than that of a single horizontal propulsor (104A, 104B), as shown in FIG. 4(d). The other possible approach to improve efficiency of this approach is to have each lower wing (102L) further comprising a plurality of lower wings (102L), each of which comprises at least an aileron (108), as shown in FIG. 4(e). Since 0= 450 for this exemplary airplane, the ailerons (108) are being deflection upward by 45 in FIGS. 4(d) and 4(e). Advantage of this approach is that there is no tilting involved for the horizontal propulsors (104A, 104B) and only deflection of the relatively large ailerons (108) are used to control the resultant thrust vectors of the horizontal propulsors (104A, 104B). This technique is expected to be suitable for 0 having a value of 45 or less.

An alternative method to control the airplane's pitch is to use weight-shifting method. Likewise, an alternative method to actuate the airplane's turning (combination of roll plus yaw) during horizontal flight is to use spoilerons on the upper wings (102U) instead of ailerons (108). With abilities to affect pitch, roll and yaw during horizontal flight, the optional tail assembly can be eliminated resulting in a rather compact VTOL airplane suitable for personal aviation that can potential takeoff and land in one's backyard.

FIG. 5(a) shows a perspective view of another embodiment of the airplane in accordance with the present invention. The airframe (100) of said airplane comprises a horizontal stabilizer (110) in tail-aft configuration, and the horizontal stabilizer (110) has elevators (111) for aerodynamic pitch control during level flight. This exemplary airplane comprises four vertical propulsors (106A1, 106A2, 106B1, 106B2) arranged such that they exhibit lateral symmetry except, they are located at a distance away from the longitudinal axis of the airplane, as shown in a bottom view in FIG. 5(b).

Referring back to FIG. 5(a), the fore vertical propulsors (106A1, 106A2) and the aft vertical propulsors (106B1, 106B2) are connected to the respective wings (102) via a supporting structure (130) such that a change in the angle of incidence of the wings (102) affects the tilt angle of the horizontal propulsors (104A, 104B) and the tilt angle of the vertical propulsors (106A1, 106A2, 106B1, 106B2). In other words, change in the tilt angle of the vertical propulsors (106A1, 106A2, 106B1, 106B2), A - = A#= AO.

In FIG. 5(a), - = $= 0 = 200 and thus, the airplane is expected to hover with a pitch angle, p of 25. A unique advantage of this embodiment is that the vertical propulsors (106A1, 106A2, 106B1, 106B2) tilt together with the horizontal propulsors (104A, 104B) whenever the angle of incidence of the wings (102), 0 changes.

At least a set of main gears (116) may be placed substantially behind the aft units of the vertical propulsors (106B1, 106B2) to prevent rotors of the aft units of the vertical propulsors (106B1, 106B2) from ground strike. A safety benefit of this arrangement is that as the airplane pitches upward for takeoff, the rotors of the aft vertical propulsors (106B1, 106B2) move further away from the ground until a certain pitch angle is reached.

Conventional airplanes often require that the main gears be placed close to the airplanes' C.G. to facilitate rotation during takeoff. Yet, the set of main gears (116) can be placed so far behind the airplane's C.G. in this invention is because of the uniqueness offered by the tandem roto-stabilizers in that it provides partial lift to the airplane, making takeoff rotation possible. This holds true for all embodiments of the present invention. Another implication is that, the main landing gears (116) and nose gear (118) are not essential for vertical takeoff and landing, and scheme based on "belly landing" is possible especially for light AUW applications such as small unmanned airplanes.

FIG. 6(a) shows a perspective view of yet another embodiment of the airplane in accordance with the present invention wherein at least a pair of wings is of delta like shape for pitch stability and control. Each wing (102) comprises at least a horizontal propulsor (104A, 104B), and at least an elevon (103). This embodiment is also suitable for high speed applications and thus the horizontal propulsors (104A, 104B) should preferably be of those types capable of propelling the airplane to a high airspeed, for example turbojet, and turbofan. Each horizontal propulsor (104A, 104B) comprises a thrust vectoring nozzle (105) capable of two degrees of freedom to actuate roll and yaw controls during hovering and the substantially vertical takeoff and landing. Among the well-known design variations of delta wings are cropped delta, compound delta, cranked arrow and ogival delta [6]. In this embodiment, at least a vertical stabilizer (112) is mounted on the back section of the airframe (100) and underneath the airframe (100). The airplane also has two vertical stabilizers (112) at respective wingtips.

Similar to the embodiment depicted in FIG. 4, the fuselage (101) of this airplane also comprises a storage compartment (115) as shown in a close up view in FIG. 6(b). In accordance with the present invention, the storage compartments (115) enable the vertical propulsors (106A, 106B) to be retracted to improve aerodynamic efficiency. Each storage compartment (115) has at least a hatch cover (119) that slides in the front-back direction.

FIG. 6(c) shows a side view of the airplane as depicted in FIG. 6(a). It shows the thrust vectoring nozzle (105) belonging to the horizontal propulsor (104A) on the left side of the airplane being rotated downward by 45 with respect to the longitudinal axis of the airplane. This in turn, gives $, the tilt angle of the horizontal propulsor (104A) an effective value of substantially 45 as indicated in FIG. 6(c).

It is anticipated that if the airplane is carrying heavy fuel load or payload such that the airplane's AUW exceeds the total vertical thrust components of the vertical propulsors (106A, 106B) and the horizontal propulsors (104A, 104B), then hyper short takeoff is a more appropriate and efficient option due to contribution of wing borne lift.

The foregoing description of the present invention has been presented for purpose of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable other skilled in the art to utilize the invention in such or other embodiments and with various modifications required by the particular application(s) or use(s) of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.

References:

1. M. Francesco (2020) Is the Urban Air Mobility Industry ready for Take-Off? https://www.airbome.com/urban-air-mobility-the-rise-of-evtol-vehicles/ 2. ArduPilot Dev Team (2019) QuadPlane Overview. https://ardupilot.org/plane/docs/quadplane-overview.html 3. D. Z. Morris (2017) The V-22 Osprey: A Crash Decades in the Making. https://fortune.com/2017/08/05/v22-osprey-crash-australia/ 4. DeVry University (2020) Drones: Description & Thesis. https://www.coursehero.com/file/p2mea4o/There-are-4-types-of-drones majorly-used-namely-Fixed-wing-drone-that-has-long/#/doc/qa 5. Wikipedia (2019) Tiltwing. https://en.wikipedia.org/wiki/Tiltwing 6. Wikipedia (2020) Delta wing. https://en.wikipedia.org/wiki/Delta wing

Claims (3)

CLAIMS:

1. A fixed-wing aircraft capable of hovering, and vertical takeoff and landing (VTOL) while assuming a positive pitch angle (nose-up attitude) such that both horizontal and vertical propulsions contribute to lift via resolution of vector comprising:

a longitudinal axis;

a vertical axis;

a center of gravity;

an airframe (100) comprising a front section and back section;

at least one fore vertical propulsor (106A) located on the front section of the airframe (100), the fore vertical propulsor (106A) generates a thrust vector;

at least one aft vertical propulsor (106B) located on the back section of the airframe (100), the aft vertical propulsor (106B) generates a thrust vector;

at least a pair of wings (102) attached to the airframe (100), the wing (102) comprises a chord line; the wings (102) have an angle of incidence; said angle of incidence is fixed while airborne; and

at least one horizontal propulsor (104A, 104B) attached to at least one wing (102), the horizontal propulsor (104A, 104B) comprises a positive tilt angle with respect to the longitudinal axis; each horizontal propulsor (104A, 104B) generates a thrust vector, the thrust vectors of the horizontal propulsors (104A, 104B) are substantially parallel to the chord lines of the respective wings (102) such that the tilt angle of the horizontal propulsor (104A, 104B) is equal to the angle of incidence of the wings (102), wherein:

said angle of incidence of the wings (102) is reconfigurable when the aircraft is on the ground;

the fore vertical propulsor (106A) and the aft vertical propulsor (106B) have a fixed

tilt angle in the range of 0 to 45 measured against the vertical axis;

the angle of incidence of the wings (102) is in the range of 5 to 650; and

the pitch angle of the fixed-wing aircraft during hovering is 33 when: the thrust vectors of the horizontal propulsors (104A, 104B) and the vertical propulsors (106A, 106B) are of equal magnitude, the angle of incidence of the wings (102) is 12°, and the fixed tilt angle of the vertical propulsors (106A, 106B) is 12°.

2. The aircraft in Claim 1, wherein the airframe (100) comprises a fuselage (101); the shape of the fuselage is substantially an ellipsoid, wherein said ellipsoidal fuselage comprises an upper front section, a lower front section, an upper back section, and a lower back section; wherein at least one fore vertical propulsor (106A) disposed on the lower front section of the ellipsoidal fuselage (101), and further wherein at least one aft vertical propulsor (106B) disposed on the upper back section of the ellipsoidal fuselage (101); wherein each wing (102) further comprises an upper wing (102U) and a lower wing (102L); the upper wings (102U) are fixed-wing with a fixed angle of incidence; each of the lower wing (102L) has an angle of incidence, said angle of incidence is in the range of 0.5° to 80° during hovering and VTOL; each lower wing (102L) comprises at least a horizontal propulsor (104A, 104B), and at least an aileron (108); the horizontal propulsors (104A, 104B) are positioned in front of the ailerons (108), the horizontal propulsors (104A, 104B) are mounted proximate to leading edges of the wings (102L); the tilt angle of the horizontal propulsors (104A, 104B) is equal to the angle of incidence of the lower wings (102L).

3. The aircraft in Claim 2, wherein the wingspan of each lower wing (102L) is nearly the same as the diameter of the rotor of the respective horizontal propulsor (104A, 104B).

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Page 1/13 2020100605 20 Apr 2020

Ground

FIG. 1

Page 2/13 2020100605 20 Apr 2020

106B

100 112 114

106A

108 102

104B C.G.

102

101 110 101 116 118 104A 110

FIG. 2

Page 3/13

100 106A 106B T2 T2 ρ τ τ 101 T1 104A, 104B

φ 112 ρ

ρ C.G.

W

Ground

FIG. 3

Page 4/13 2020100605 20 Apr 2020

100 102U

102U 108

104B 106B

104A

102L 102L

108 120

108

101 106A 116 118

FIG. 4(a)

Page 5/13 2020100605 20 Apr 2020 102U 108

100 T2

106B 104A T1 102L

120 101HA

108 122

106A

101 T2

118 116

FIG. 4(b)

Page 6/13 2020100605 20 Apr 2020

102U

100

108

120 119 126 124

108 128

102U

102L 108 128 124 104A 116 101 118

FIG. 4(c)

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102U 100

108 104B

102U 102L

108

126 106B 104A 128

104A

102L 128 108 106A 101 116

FIG. 4(d)

Page 8/13 2020100605 20 Apr 2020

102U 100 108

106B 126

120 108 104A

104A

108

104A 108

102L 102L 106A 101

FIG. 4(e)

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100 106A2

114 112

108 106A1 104B 130 106B2 104A

101 108 106B1 111 110 118 102 116 130

FIG. 5(a)

Page 10/13 2020100605 20 Apr 2020 Longitudinal axis 100

101 118 106A2 106A1

130

130 108 102

106B2 106B1

110 116

111

FIG. 5(b)

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100 112 106B 103 105 103 116 102

112 106A

102

104A 112 101 118

FIG. 6(a)

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119 102

106A

102

115

118

101 100

FIG. 6(b)

Page 13/13 2020100605 20 Apr 2020

100 112 102 102 T1

 101 105 112 104A

FIG. 6(c)