Patent Application
20200198781
Placing a fan inside a duct can result in a system that produces more thrust for the same power. This increase in thrust is produced because the shape of the duct allows the duct to carry a thrust force. In order to maximize efficiency, ducts typically include an expanding conical diffuser section that serves to slow down the exit velocity, which returns the flow to atmospheric pressure. The diffuser divergence angle is limited by the need to prevent boundary layer separation of the airflow from the duct surface. This limited diffuser angle requires a longer length of the diffuser section to return the airflow to atmospheric pressure.
Aircraft do not generally include ducts around propellers or proprotors because the benefit of the increased thrust/power is often outweighed by the drag caused by the duct and the additional weight of the duct itself. However, if the amount of thrust provided could be sufficiently increased, and/or the size and weight of the duct could be sufficiently reduced, the use of a ducted propeller or proprotor may be justified. Because helicopter tail rotors produce thrust in a direction that is orthogonal to the primary direction of travel, the tail rotor may be placed within the vertical tail section of the helicopter itself, and therefore, ducted tail rotors may not substantially increase the drag of the helicopter in forward flight. However, increasing the thrust produced by a given sized fan would enable the use of smaller, lighter ducted tail rotors. Moreover, in order to limit the drag caused by the width of the vertical tail section during forward flight, helicopters with ducted tail rotors often limit the length of the diffuser section to a less than optimal length. Accordingly, it would be beneficial to have a ducted tail rotor system capable of returning the airflow to atmospheric pressure in a shorter diffuser section.
While the making and using of various embodiments of this disclosure are discussed in detail below, it should be appreciated that this disclosure provides many applicable inventive concepts, which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative and do not limit the scope of this disclosure. In the interest of clarity, not all features of an actual implementation may be described in this disclosure. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another.
In this disclosure, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of this disclosure, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction. In addition, the use of the term “coupled” throughout this disclosure may mean directly or indirectly connected, moreover, “coupled” may also mean permanently or removably connected, unless otherwise stated.
This disclosure divulges a duct for improving the thrust capability of a ducted fan arrangement. Currently, duct exits are limited to a maximum diffuser divergence angle. This maximum diffuser divergence angle is determined by the angle at which airflow through the fan separates from the diffuser surface. The duct divulged in this disclosure allows for a greater divergence angle that permits a shorter duct, resulting in less weight and less drag. The duct may utilize a greater divergence angle because the interior surface of the duct includes an opening that introduces additional airflow along the diffuser surface. This additional airflow energizes the boundary layer, thereby facilitating attachment of the airflow through the fan to the diffuser surface at the greater divergence angle.
Referring to
Duct 114 includes an annular interior surface 124 surrounding rotation axis 120. Interior surface 124 includes a nozzle portion 126 located upstream of tail rotor 112, a diffuser portion 128 located downstream of tail rotor 112, and a cylindrical portion 130 located between nozzle portion 126 and diffuser portion 128. Diffuser portion 128 has a generally frustoconical shape with a divergence angle 132 defined as the angle between diffuser portion 128 and rotation axis 120. Interior surface 124 includes an opening 134 extending around the circumference of duct 114 located proximate the transition from cylindrical portion 130 to diffuser portion 128.
Opening 134 is configured to introduce additional airflow 136 along diffuser portion 128 to energize the boundary layer and facilitate attachment of airflow 122 to diffuser portion 128. Accordingly, additional airflow 136 allows divergence angle 132 to be greater than the maximum functional divergence angle that would be possible for a standard duct surrounding an identical tail rotor 112. This greater divergence angle 132 allows for a greater pressure recovery and a greater efficiency of tail rotor 112, and therefore, greater thrust than would be possible for a standard duct surrounding an identical tail rotor 112. Moreover, it enables a length of duct 114 along rotation axis 120 to be shorter than would otherwise be required to return airflow 122 to atmospheric pressure. Thereby allowing for tail boom 106 to be narrower and lighter than previously possible. Divergence angle 132 may be greater than ten degrees. In addition, divergence angle 132 may vary along a length of diffuser portion 128. For example, divergence angle 132 may increase, or decrease, with distance from tail rotor 112. Interior surface 124 may further include a second opening (not shown) downstream of opening 134 configured for the introduction of additional airflow along diffuser portion 128.
As shown in
Referring to
While the structure of ducts 214 is not shown, it should be understood that it is similar to that of ducts 114 discussed above. That is, each duct 214 includes an opening configured to introduce additional airflow along a diffuser portion to energize the boundary layer and facilitate attachment of the airflow passing by forward-facing propeller 212 to the diffuser portion. For each duct 214, the additional airflow is drawn into an airflow intake 238, located proximate the front end of fuselage 202, and flows through a channel that extends from intake 238, through fuselage 202, to the opening of the respective duct 214. The additional airflow is drawn into the channel and pressurized by a fan located within each channel.
Referring to
While the details of duct 314 are not shown, it should be understood that the structure is similar to that of ducts 114 discussed above. That is, duct 314 includes an opening configured to introduce additional airflow 336 along a diffuser portion to energize the boundary layer and facilitate attachment of airflow 322 passing by tail rotor 312 to the diffuser portion. Additional airflow 336 is drawn into an airflow intake 338, located proximate the tail end of body section 304, and flows through a channel 340, extending through tail boom 306, to the opening of duct 314. Additional airflow 336 is drawn into channel 340 and pressurized by a fan 342 located within channel 340. Helicopter 300 may include pressure sensors within channel 340 to automatically adjust the speed of fan 342, or pitching the blades thereof, to produce the required additional airflow 336 necessary to maintain attachment of the corresponding airflow 322 to the diffuser portion.
Helicopter 300 is also configured to provide anti-torque thrust by utilizing the Coanda effect on tail boom 306. Normally, the downwash from the main rotor of a helicopter flows evenly around the tail boom. However, as shown in
While this disclosure describes devices for increased thrust for use as tail rotors and forward-facing propellers on helicopters, it is not so limited. The disclosed devices may be used with any aircraft including fixed-wing airplanes, rotorcraft with fixed ducted rotors, such as those on a quadcopter, or on ducted tiltrotor aircraft. Moreover, the disclosed devices may also be used with any ducted fan arrangement that may benefit from increased efficiency and decreased size and weight.
At least one embodiment is disclosed, and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, Rl, and an upper limit, Ru, is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=Rl+k*(Ru−Rl), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 95 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention. Also, the phrases “at least one of A, B, and C” and “A and/or B and/or C” should each be interpreted to include only A, only B, only C, or any combination of A, B, and C.
