Patent Application
20210047047
The embodiments disclosed herein relate generally to unmanned aircraft systems (UAS). In specific embodiments, the present invention is directed to UAS having reduced acoustic signatures.
Unmanned aircraft systems (UAS) colloquially known as “drones” have obtained increased importance in the armed forces of many countries due to several desirable characteristics including, for example, (i) high autonomy, range and time on station abilities, (ii) advanced intelligence, surveillance and reconnaissance systems, (iii) adequate flight envelope, reduced observability both acoustically and by radar, and (iv) systems reliability (i.e., reliability of the data links with remotely-based controllers/pilots on which the UAS depend for flight mission accomplishments).
The vast majority of conventional UAS platforms are single engine, pusher propulsive layouts. Although such a conventional solution has several advantages, most notable is that only one propulsion system is required, it has less variables for optimization and decreased reliability as compared to a multi-engine design. For example, the propeller of single engine UAS must be optimized so as to concurrently maximize performance and decrease acoustic signature. Such a design requirement may be quite challenging since conflicting requirements may appear while optimizing the propeller design, e.g., tip speed, chord distribution, activity factor, diameter, and the number of blades, among other parameters.
The single engine design for conventional UAS also reduces the design space for hybrid electric propulsion, since a greater number of hybrid propulsion architectures can be considered for a multi-engine UAS design layout.
Therefore, one significant technical problem which the embodiments describe herein address is to de-couple the design restrictions described above from the aircraft design, thereby enabling a multi-engine propulsion concept for UAS with increased performance and decreased noise signature to be realized, while also enabling the conceptualization of a quieter hybrid-electric propulsion (HEP) architecture. It is therefore towards providing solutions so such a problem that the embodiments described herein are directed.
Generally, the embodiments disclosed herein are directed toward unmanned aircraft having aligned propulsion systems having different performance and/or noise characteristics. More specifically, according to some embodiments, unmanned aircraft are provided having a forward propulsion system comprising a forward engine and a forward tractor propeller and an aft propulsion system comprising an aft engine and an aft pusher propeller. Selected ones of forward and aft propulsion systems will thus be provided to have greater and lesser operational flight performance characteristics and/or greater and lesser noise signature characteristics, respectively, as compared to the other. By way of examples, the forward propulsion system may be provided with the greater operational flight performance and/or non-optimized noise signature characteristics as compared to the aft propulsion system, while conversely the aft propulsion system may be provided with a lesser flight performance and/or decreased noise signature characteristics as compared to the forward propulsion system.
A mode controller is preferably provided so as to allow for the controllably operation of the forward and/or aft engines and the forward tractor and/or aft pusher propellers in order to achieve at least first and second flight performance modes having greater and lesser noise characteristics. For example, the first flight performance mode may comprise a take-off and/or climb flight phase of the unmanned aircraft in which both the forward tractor and aft pusher propellers are in a thrust condition to provide thrust to the unmanned aircraft, while the second flight performance mode may comprise a quiet loiter flight phase of the unmanned aircraft in which the forward tractor propeller is in a feathered condition to provide no thrust to the unmanned aircraft and the aft pusher propeller, optimized for minimum noise signature, is in a thrust condition to provide thrust to the unmanned aircraft.
Thus, the unmanned aircraft may provide a variety of combinations of propulsive systems and propeller types so as to achieve the differential performance/noise characteristics between the forward and aft propulsion systems and thereby attain a variety of in-flight modes where increased flight performance or reduced in flight noise can be selected.
In one embodiment, the unmanned aircraft will include port and starboard fuselage booms and a central mid-wing airfoil joining the fuselage booms. Port and starboard wings are provided so as to extend outwardly from the port and starboard fuselage booms, respectively. A propulsion control pod supported by the central mid-wing airfoil is aligned with a central axis of the unmanned aircraft and includes forward and aft ends housing the forward and aft propulsion systems, respectively. An inverted V-shaped empennage is positioned between an aft portion of the port and starboard fuselage booms so as to provide yaw and pitch control to the aircraft.
These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.
The disclosed embodiments of the present invention will be better and more completely understood by referring to the following detailed description of exemplary non-limiting illustrative embodiments in conjunction with the drawings of which:
Accompanying
The UAS 10 includes an on-board controller 20 operably connected to the on-board systems, including the propulsive systems 12a, 12b, the fuel management systems, flight control servos and the like. An on-board mode controller 20 communicates via data links 22 (e.g., satellite or earth-based communications hubs) to a remote base control station 24 (e.g., a ground-, air- or naval-based control station providing human and/or computer control input to the UAS 10 to allow accomplishment of the flight mission) in order to allow propulsion mode control in a manner described below. As is known, an on-board flight controller (not shown) may also be connected to the control station 24 via the data links 22 to allow an operator to control the flight characteristics and profile of the UAS 10. The mode controller 20 and/or the flight controller may also be pre-programmed to permit autonomous flight of the UAS 10 for a specific airborne mission.
The propulsion systems 12a, 12b can be a variety of engine types and may include thermal engines, e.g., internal combustion in-line engines, rotating or reciprocating piston engines, gas turbine engines or the like. As seen in the embodiment schematically depicted by
In the embodiment of
Those skilled in this art will understand that the noise from the propellers 12a-2, 12b-2 will dominate over the noise of the respective engines 12a-1, 12b-1. Therefore, the propellers 12a-2, 12b-2 represent the on-board equipment where there is a greater opportunity for noise reduction optimization. Those skilled in this art will also understand that propellers optimized for minimum noise characteristics can be quite different from propellers optimized for maximum flight performance characteristics. In order to minimize noise, the propeller must exhibit a decreased airfoil loading by, for example, increasing the number of blades and blade chord or by the activity factor, while also having a decreased rotational speed.
By providing two independently optimized propulsion systems 12a, 12b, the UAS 10 in accordance with the embodiments herein can thus operate in both “maximum performance” and “quiet power” modes when necessary by suitable operational commands issued by the mode controller 20. While in a “maximum performance mode”, both propulsion systems 12a, 12b can thus be commanded to be operational, providing the maximum thrust possible for a given amount of power input. While in “quiet power” mode, however, that one of the engine/propeller combinations 12a-1/12a-2 or 12b-1/12b-2 as the case may be that is designed to be the “maximum performance” engine/propeller combination can be inactivated (e.g., by complete engine shut down and/or by feathering the propeller). While in the “quiet mode”, the UAS 10 may then powered by that one of the propulsion systems 12a or 12b having the engine/propeller combination designated as the “minimum noise” propulsion system thereby taking full advantage of the minimum noise optimization criteria. One possible operational grid that can be commanded by the mode controller 20 whereby the forward propulsion system 12a is provided with the “maximum performance” engine/propeller combination 12a-1/12a-2, while the aft propulsion system 12b is provided with the “minimum noise” engine/propeller combination 12b-1/12b-2 is summarized below in Table 1 over several flight phases of the UAS 10.
Those skilled in the aeronautical arts will recognize that when a propeller is in a thrust condition, then thrust forces are being generated by that propeller to counteract the drag forces associated with the aircraft. Conversely, when a propeller is in a feathered condition, that propeller is providing no thrust forces to counteract the draft forces associated with the aircraft. The pitch of a controllable propeller of the variety employed in the embodiments herein can therefore be selective adjusted to provide the proper propeller angles of attack to develop desired thrust during various flight phases or be feathered to provide no thrust. During propeller feathered conditions, the associate engine may or may not be shut down since operation of the engine will not affect whether or not the propeller is generating thrust. However, in view of increased fuel efficiency (and hence range), it is typically desirable to have the engine shut down when a propeller associated with that engine is in a feathered condition.
An additional optional feature is the installation of a duct around the minimum noise propeller, further decreasing the aircraft acoustic signature. In accordance with the embodiment of
A hybrid propulsion system is shown in accompanying
As is known, an electric motor 50a is much quieter than a comparably powered combustion engine. Thus, with the embodiment provided by
Similar to the all combustion engine embodiment of
As discussed hereinabove, the low acoustic signature of any UAS is very important for its operational mission for which it was designed. The proposed embodiments discussed above therefore aim to reduce the noise signature of the UAS 10 thereby providing valuable acoustic stealth characteristics.
Therefore, while reference is made to a particular embodiment of the invention, various modifications within the skill of those in the art may be envisioned. Therefore, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope thereof.
The present application is related to U.S. Design patent application Ser. No. ______ (Atty. Dkt. BHD-4439-0324) filed concurrently herewith entitled “Design For: Unmanned Aircraft”, the entire contents of which are expressly incorporated hereinto by reference.
