Method for manufacturing propulsion unit having rim foil, and propulsion unit and flying vehicle manufactured by the same

A method for manufacturing a propulsion unit having a rim foil, which significantly reduces drag during forward flight while protecting a rotor blade from surrounding obstacles, the method including a plate member formation step in which an airfoil-type plate member is formed to have an outline forming an airfoil shape in side view, a rim foil formation step in which a through-hole is formed in the airfoil type plate member to form a rim foil member having an outline forming at least a portion of an airfoil shape in side view, and a rotor blade installation step in which a rotor blade is installed in the through-hole.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a propulsion unit having a rim foil, a propulsion unit manufactured by the same, and a flying vehicle including the propulsion unit. More particularly, the present invention relates to a method for manufacturing a propulsion unit having a rim foil capable of significantly reducing drag during forward flight, a propulsion unit manufactured by the same, and a flying vehicle including the propulsion unit.

BACKGROUND ART

Recently, use of unmanned flying vehicles is rapidly increasing in many applications such as surveillance, reconnaissance, distribution, and leisure activities. In particular, a multi-rotor unmanned flying vehicle is a rotorcraft and is capable of moving in all directions and hovering as well as vertical take-off and landing. In addition, such a multi-rotor unmanned flying vehicle has the advantages of a simple structure and good efficiency, as compared with other flying vehicles such as coaxial rotorcrafts and single-rotor flying vehicles.

However, in the case of a rotorcraft, since a rotor blade thereof is completely exposed to an outside environment, there is a possibility that the rotor blade will be caught on an obstacle such as tree branches, making it difficult to maintain flight. In addition, when the rotorcraft files close to a crowded area, people can be injured by rotational force of the rotor blade. In particular, in design of urban air mobility using large unmanned flying vehicles such as multi-rotor unmanned flying vehicles, it is necessary to consider the danger of a rotor blade exposed to an outside environment, the possibility of a crash in a downtown area, which can cause serious casualties, and difficulty in blocking noise from a tip of the rotor blade.

In order to solve such problems, a rotor blade protection ring or duct covering a rotor blade is additionally disposed to protect the rotor blade from obstacles and to prevent people from being injured by the rotor blade. In addition, such a rotor blade protection ring or duct has the benefit of reducing thrust loss during vertical take-off and landing by guiding the flow of air passing through the rotor blade.

However, since the rotor blade protection ring or duct is designed in consideration of only flow characteristics of air passing through a rotor blade during vertical take-off and landing of a flying vehicle, there is a problem in that drag on the flying vehicle during forward flight can significantly increase.

As a related art of the present invention, there is Korean Patent Laid-open publication No. 2016-0041697 (issued on Apr. 18, 2016).

DISCLOSURE

Technical Problem

Embodiments of the present invention are conceived to solve such problems in the art and it is an object of the present invention to provide a method for manufacturing a propulsion unit having a rim foil which can significantly reduce drag during flight while protecting a rotor blade from surrounding obstacles, a propulsion unit manufactured by the same, and a flying vehicle including the propulsion unit.

Technical Solution

In accordance with one aspect of the present invention, a method for manufacturing a propulsion unit having a rim foil includes: a plate member formation step in which an airfoil-type plate member is formed to have an outline forming an airfoil shape in side view; a rim foil formation step in which a through-hole is formed in the airfoil type plate member to form a rim foil member having an outline forming at least a portion of the airfoil shape in side view; and a rotor blade installation step in which a rotor blade is installed in the through-hole.

A projection area of the airfoil-type plate member in plan view may cover a projection area of the rotor blade and the airfoil-type plate member may be continuously changed in cross-sectional scale parallel to a forward direction.

At least some cross-sections of the rim foil member may include a leading cross-sectional region having a leading edge at a front end thereof and a trailing cross-sectional region having a trailing edge at a rear end thereof.

An empty cross-sectional region, which is a portion of the through-hole in which the rotor blade is installed, may be placed between the leading cross-sectional region and the trailing cross-sectional region.

In the plate member formation step, an airfoil-shaped cross-section of the airfoil-type plate member may be set to have a zero-lift angle of attack of −9 degrees to −5 degrees.

In the rim foil formation step, the through-hole may be formed in a direction perpendicular to a chord line of an airfoil-shaped cross-section of the rim foil member.

In the rotor blade installation step, an axis of rotation of the rotor blade may be placed perpendicular to a chord line of an airfoil-shaped cross-section of the rim foil member such that the chord line is parallel to the rotor blade.

In accordance with another aspect of the present invention, a propulsion unit manufactured by the method set forth above is provided.

In accordance with a further aspect of the present invention, a flying vehicle includes: a body; and the propulsion unit having the rim foil set forth above, the propulsion unit allowing the body to fly.

The flying vehicle may further include: a fixed wing disposed between the body and the rim foil member, wherein the rim foil member and the fixed wing may have the same airfoil-shaped cross section.

The flying vehicle may further include: a passenger capsule coupled to the body, the passenger capsule having a forward thrust rotor blade producing forward thrust.

Advantageous Effects

With the airfoil-type rim having an airfoil-shaped cross section, the propulsion unit according to the present invention can minimize damage to a rotor blade due to surrounding obstacles and related accidents and can significantly increase lift and thrust of a flying vehicle through reduction in drag during flight.

In addition, the propulsion unit according to the present invention can reduce noise through suppression of generation of a vortex around a tip of the rotor blade.

MODE FOR INVENTION

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In description of the embodiments, the same components will be denoted by the same terms and the same reference numerals and redundant description thereof will be omitted.

Embodiments of the present invention provide a method of manufacturing a propulsion unit having a rim foil that can reduce drag during flight while protecting a rotor blade from surrounding obstacles.

Herein, the term “rim foil” refers to a streamlined rim for protection of a rotor blade, which covers the rotor blade to minimize damage to the rotor blade due to surrounding obstacles and related accidents and has an airfoil shape in side view to maximize lift and minimize drag during forward flight.

The term “airfoil” generally refers to a streamlined structure that is designed to maximize lift and minimize drag during motion in a fluid, such as a fixed wing, a rudder, or a cross-section of a rotor blade. The magnitudes of lift and drag on the airfoil depend on a chord line, which is a straight line connecting tips of leading and trailing edges of the air foil. In addition, an angle of attack, which is an angle between the chord line and a direction of a relative airflow, is also known as a key factor in determining the magnitude of lift.

FIG.1is a flowchart of a method for manufacturing a propulsion unit having a rim foil according to one embodiment of the present invention.

Referring toFIG.1, the method of manufacturing a propulsion unit having a rim foil according to this embodiment includes a plate member formation step S110, a rim foil formation step S120, and a rotor blade installation step S130.

FIG.2is a perspective view of an airfoil-type plate member manufactured according to one embodiment of the present invention, andFIG.3shows a plan view (a) of the airfoil-type plate member ofFIG.1, a sectional view taken along line A-A ofFIG.3(a), and a sectional view taken along line B-B ofFIG.3(a).

Referring further toFIG.2andFIG.3, in the plate member formation step S110, an airfoil-type plate member110is formed.

The airfoil-type plate member110according to this embodiment may have an outline forming an airfoil shape in side view.

A projection area of the airfoil-type plate member110in plan view may cover a projection area of a rotor blade130

In addition, the airfoil-type plate member110may be continuously changed in cross-sectional scale parallel to a forward direction.

That is, as shown inFIG.3(a), the airfoil-type plate member110may gradually decrease in airfoil-shaped cross-sectional area111from a center line C1in the forward direction A1toward both ends in a lateral direction A2perpendicular to the forward direction A1.

In addition, the airfoil-type plate member110may be partially cut at both ends thereof in the lateral direction A2perpendicular to the forward direction A1such that both lateral ends of the airfoil-type plate member110have a vertical surface110a.

The airfoil-type plate member110may be solid inside, as shown inFIG.3. However, it will be understood that the present invention is not limited thereto and the airfoil-type plate member110may have An empty portion therein.

The airfoil-type plate member110according to this embodiment may be manufactured by cutting a surface of a plate member such that the plate member has an airfoil shape or by bending a plate member into an airfoil shape. Alternatively, the airfoil-type plate member110may be manufactured by assembling multiple plate members into an airfoil shape.

In the plate member formation step S110according to this embodiment, a zero-lift angle of attack of the airfoil-shaped cross-section111of the airfoil-type plate member110may be set to a negative (−) value.

Sometimes a rotorcraft such as a helicopter flies forward with a body thereof including a rotor blade130slightly tilted with respect to the forward direction A1to obtain thrust.

If the zero-lift angle of attack of the airfoil-shaped cross-section is set to maintain zero degrees, an angle of attack of the airfoil-shaped cross-section is changed to a negative value when the rotorcraft tilts the body thereof with respect to the forward direction during forward flight, causing generation of negative lift (downward force) and increase in drag.

Conversely, if an airfoil having a negative (−) zero-lift angle of attack is designed upon setting of the airfoil-shaped cross-section of the airfoil-type plate member110as in this embodiment, the airfoil-shaped cross-section111can maintain an angle of attack corresponding to a positive (+) lift coefficient even when the rotorcraft flies forward with the body thereof including the rotor blade130tilted with respect to the forward direction A1to obtain thrust. Accordingly, it is possible to further reduce drag due to the shape of the airfoil during forward flight.

According to this embodiment, the zero-lift angle of attack of the airfoil-shaped cross-section111is preferably set within the range of −9 degrees to −5 degrees.

Here, the angle of −9 degrees to −5 degrees may correspond to the maximum angle to which the airfoil-shaped cross-section111can be tilted with respect to the forward direction A1during forward flight.

FIG.4is a graph showing parameters of an airfoil according to one embodiment of the present invention, specifically a ratio of lift to drag (L/D), a lift coefficient (CL), a drag coefficient (CD), and a center of pressure (CP) in % of chord from leading edge depending on the angle of attack (in degrees) of the airfoil.

Referring toFIG.4, the selected airfoil is set to have a zero-lift angle of attack of −9 degrees.

Since the airfoil ofFIG.4has a zero-lift angle of attack of −9 degrees, the airfoil can always have a positive (+) lift coefficient during forward flight so long as the airfoil maintains a tilt angle of less than 9 degrees with respect to the forward direction. Accordingly, if a flying vehicle flies forward with the tilt angle thereof maintained at a value less than 9 degrees, drag due to the cross-sectional shape of the airfoil can be reduced while further increasing lift and thrust.

FIG.5is a perspective view of a rim foil member manufactured according to one embodiment of the present invention, andFIG.6shows a plan view (a) of the rim foil member ofFIG.5, a sectional view (b) taken along line A-A ofFIG.6(a), a sectional view (c) taken along line B-B ofFIG.6(a), and a sectional view (d) taken along line C-C ofFIG.6(a).

After formation of the airfoil-type plate member110is completed, the airfoil-type plate member110is formed into a rim foil member.

Referring further toFIG.5andFIG.6, in the rim foil formation step S120, the rim foil member120is formed from the airfoil-type plate member110.

The rim foil member120according to this embodiment may be formed by forming a through-hole121in the airfoil-type plate member110.

The through-hole121defines an inner diameter of the rim foil member120and is adapted for the rotor blade130to be installed therein. The through-hole121may have a larger diameter than the rotor blade130.

The through-hole121may be formed in a direction perpendicular to the chord line CL of the airfoil-shaped cross-section111. Thus, the through-hole121may guide an airflow passing through the rotor blade130in a downward direction.

The rim foil member120thus manufactured may have an annular shape, and may have an inner diameter D1larger than the diameter of the rotor blade130. In addition, the rim foil member120may have a constant width W along the entire circumference thereof excluding the vertical surface110a.

The rim foil member120may have an outline forming at least a portion of an airfoil shape in side view. At least some cross-sections of the rim foil member120may include a leading cross-sectional region122ahaving a leading edge at a front end thereof and a trailing cross-sectional region122bhaving a trailing edge at a rear end thereof.

That is, with reference to the lateral direction A2perpendicular to the forward direction A1, the rim foil member120may have a central area CA in which the rotor blade130is disposed and a side area SA lying on both lateral sides of the central area CA, as shown inFIG.6(a).

As shown inFIG.6(b)andFIG.6(c), the central area CA of the rim foil member120includes the leading cross-sectional region122ahaving the leading edge at the front end thereof and the trailing cross-sectional region122bhaving the trailing edge at the rear end thereof in cross-section parallel to the forward direction A1.

An empty cross-sectional region122c, which is a portion of the through-hole121, is placed between the leading cross-sectional region122aand the trailing cross-sectional region122b. Here, the empty cross-sectional region122cis a virtual cross-sectional region connecting the leading cross-sectional region122ato the trailing cross-sectional region122b.

An outline encompassing the leading cross-sectional region122a, the hollow cross-sectional region122c, and the trailing cross-sectional region122bforms an airfoil shape122corresponding to the airfoil-shaped cross-section111of the airfoil-type plate member110.

In addition, as shown inFIG.6(d), the side area SA of the rim foil member120may also have an airfoil shape corresponding to the airfoil-shaped cross-section111of the airfoil-type plate member110in cross-section parallel to the forward direction A1, wherein the airfoil shape does not include the empty cross-sectional region122c.

Accordingly, the leading cross-sectional region122aincluding the leading edge LE can reduce drag during forward flight, and the trailing cross-sectional region122bincluding the trailing edge TE can suppress excessive generation of a vortex in a region behind the rim foil during forward flight.

In addition, since the rotor blade130disposed inside the through-hole121is not exposed outside the rim foil member120in side view, it is possible to minimize damage to the rotor blade130due to surrounding obstacles and related accidents during operation of the rotor blade130.

In addition, the rotor blade130placed inside the through-hole121can avoid an airflow guided by the rim foil member120.

Accordingly, the rim foil member120can reduce drag against a relative airflow during forward flight while further increasing lift and thrust.

The rim foil member120may be provided at both lateral ends thereof with the vertical surface110aformed in the plate member formation step S110. The vertical surface110aallows a body or fixed wing of a flying vehicle to be coupled thereto.

After manufacture of the rim foil member120is completed, the rotor blade130is installed.

That is, in the rotor blade installation step S130, the rotor blade130is installed in the through-hole121of the rim foil member120.

FIG.7is a side sectional view illustrating installation of the rotor blade according to one embodiment of the present invention.

Referring further toFIG.7, the rotor blade130may be disposed inside the through-hole121.

Here, an axis of rotation130cof the rotor blade130may be placed perpendicular to the chord line CL of the airfoil cross-section111such that the rotor blade130is parallel to the chord line CL.

In other words, a center line of the through-hole121and the axis of rotation130cof the rotor blade130may be collinear with each other. Accordingly, not only can the rotor blade130be placed with a gap between the rotor blade and the through-hole121minimized, but an airflow passing through the rotor blade130can be guided downwards in a stable and uniform manner by the through-hole121.

In addition, through appropriate regulation and design change of a gap between the inner diameter D1of the through-hole121and a tip of the rotor blade130, generation of a vortex around the tip of the rotor blade130can be controlled, thereby achieving noise reduction.

In addition, since the rotor blade130disposed inside the through-hole121is not exposed outside the rim foil member120in side view, it is possible to minimize damage to the rotor blade130due to surrounding obstacles and related accidents during operation of the rotor blade130.

After positioning of the rotor blade130, a drive unit140may be connected to the axis of rotation130cof the rotor blade130. The drive unit140is configured to rotate the rotor blade130, and may include a motor directly connected to the axis of rotation130cof the rotor blade130.

Next, a flying vehicle according to one embodiment of the present invention will be described.

FIG.8is a perspective view of a flying vehicle according to one embodiment of the present invention, andFIG.9shows an enlarged perspective view (a) and plan view (b) of a propulsion unit ofFIG.8.

Referring toFIG.8andFIG.9, the flying vehicle1000according to this embodiment may include a body200and a propulsion unit100.

The body200may provide a space for storing articles or carrying people. For example, when the flying vehicle is an unmanned flying vehicle, the body200may provide a space for storing a battery, a camera, communication parts, control parts, and the like. In addition, when the flying vehicle is a manned flying vehicle, the body200may provide a space for an engine, communication parts, control parts, a cockpit, a passenger compartment, and the like. The body200may have any suitable shape.

The flying vehicle1000according to this embodiment may further include a passenger capsule300.

The passenger capsule300may be coupled to the body200, and may provide an additional space for carrying cargo or passengers as needed. The passenger capsule300may be detachably coupled to the body200. The passenger capsule300may have any suitable shape.

In addition, the passenger capsule300may be provided with a forward thrust rotor blade310.

With the forward thrust rotor blade310provided to the passenger capsule300, a tilt angle of the flying vehicle1000including the propulsion unit100during forward flight of the flying vehicle1000can be reduced, thereby further increasing lift generated by the propulsion unit100having the rim foil while increasing thrust of the flying vehicle1000.

The propulsion unit100allows the body200to fly by generating an airflow in a downward direction of the body200.

The propulsion unit100may include a rotor blade130, a drive unit140rotating the rotor blade130, and an annular rim foil member120surrounding the rotor blade130. Redundant description of the propulsion unit100having the rim foil will be omitted.

The body200may be connected to one or more propulsion units100, wherein the propulsion units100may be radially arranged from a center of the body200. Although the flying vehicle is illustrated as including six propulsion units100in this embodiment, it will be understood that the present invention is not limited thereto and the flying vehicle may include any suitable number of propulsion units.

The flying vehicle1000according to this embodiment may further include a fixed wing150.

The fixed wing150may be disposed may be disposed between the body200and the propulsion unit100, and may have an airfoil-shaped cross section. Here, the fixed wing150and the rim foil member120may have the same airfoil-shaped cross-section.

The fixed wing150may be coupled at one end thereof to the body200and may be coupled at the other end thereof to the rim foil member120of the propulsion unit100. The fixed wing150can further increase lift of the flying vehicle1000while securing more stable flight.

In addition, the fixed wing150may be provided at the other end thereof with a cantilever-type support beam141to support the rotor blade130and the drive unit140.

The support beam141may have various cables embedded therein to supply power to the drive unit140or to control the propulsion unit100.

In addition, the support beam141may extend from a tip of the fixed wing150to the propulsion unit100without protruding beyond upper and lower surfaces of each of the fixed wing150and the rim foil member120so as to avoid an airflow guided along the surfaces of the fixed wing150and the rim foil member120. That is, a cross-sectional width of the support beam141may be smaller than that of the tip of the fixed wing, at which the support beam141is disposed, and may be smaller than that of a fixed wing coupling portion provided to the rim foil member120.

Alternatively, the support beam141may be disposed under the fixed wing150and the rim foil member120. In this case, the cantilever-type support beam141extending from the fixed wing150can more stably support the propulsion unit100.

The other end of the fixed wing150may be coupled to the vertical surface110a(seeFIG.6) of the rim foil member120. Here, robustness of coupling therebetween can be weakened depending on the dimensions of the fixed wing150and the propulsion unit100.

In order to solve this problem, one end of the rim foil member120coupled to the fixed wing150may be cut to form a coupling surface127. The coupling surface127allows coupling between the fixed wing150and the rim foil member120to be established over a wider area, thereby ensuing stable coupling between the fixed wing150and the propulsion unit100. In addition, the coupling surface127allows a cross-section at a joint between the fixed wing150and the rim foil member120to retain an airfoil shape, thereby increasing lift.

In addition, upon setting of the airfoil shape of the fixed wing150, a zero-lift angle of attack formed between a chord line CL of the airfoil shape and a relative airflow is set to have a negative (−) value. Accordingly, a lift coefficient of the fixed wing150can maintain a positive (+) value even when the flying vehicle1000flies forward with the fixed wing150tilted with respect to the forward direction A1to obtain thrust, whereby drag on the flying vehicle1000during forward flight can be reduced while further increasing lift and thrust.

Although some embodiments have been described herein, it should be understood that various modifications, changes, alterations, and equivalent embodiments can be made by those skilled in the art without departing from the spirit and scope of the invention.

INDUSTRIAL APPLICABILITY

With the airfoil-type rim having an airfoil-shaped cross section, the propulsion unit according to the present invention can minimize damage to a rotor blade due to surrounding obstacles and related accidents during flight, can significantly increase lift and thrust of a flying vehicle through reduction in drag during flight, and can reduce noise through suppression of generation of a vortex around a tip of the rotor blade. Thus, the propulsion unit may be widely used in the aircraft industry, such as drones and vertical take-off and landing flying vehicles.