Abstract:
An Unmanned Aerial Vehicle (UAV) for use in military and civilian functions, including a UAV being optimized by utilizing a front and a rearmost engine positioning in addition to an engine operating system for maximum fuel efficiency and performance.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to the U. S. Provisional Application for Patent having the Application Ser. No. 61/751,661, filed Jan. 11, 2013, and entitled “Unmanned Aerial Vehicle.” The above-referenced application is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     This disclosure relates in general to the field of aviation, more specifically an Unmanned Aircraft Vehicle (UAV) design focusing on a weight-balanced front and rearmost engine positioning and an efficient power band engine operation of two separate, center line thrust positioned engines. 
     BACKGROUND 
     An aircraft without a human pilot on board is known as an Unmanned Aerial Vehicle (UAV), otherwise referred to as a drone. UAVs can be controlled either by an electronic computer located within the aircraft itself or remotely by a navigator or pilot located on the ground or elsewhere, separate from the UAV. UAVs are used for a variety of different purposes including, but not limited to, military operations and surveillance. 
     Traditional aviation design focuses on many aspects that create a balance of efficiency and performance. The first aspect that is taken into consideration is the center of gravity (CG). The CG is the point at which weight force, or the entire weight of the aircraft, is considered to be concentrated. The CG affects the stability of the entire aircraft and must be kept within certain bounds in order to maintain safety. 
     To counterbalance the weight force, aircraft generate an opposing force, a lift force, which is generated by the motion of the aircraft as it travels through the air. Another consideration taken into account with aircraft design is the center of lift (CL). The CL is the point at which the lift force is considered to be concentrated. 
     In most existing aircraft, cargo cannot be placed too far forward or backward in the plane, relative to the CG, because it can create instability. Cargo being transported in the aircraft must be placed within a location very close to the CG, referred to as the CG envelope, usually located around the center portion of the aircraft. The CG envelope can be designated by the manufacturer and takes into account the equipment and contents of the aircraft. This can limit space for transportation to a very small area within the craft. 
     SUMMARY 
     The present disclosure relates to an Unmanned Aerial Vehicle (UAV) that incorporates a front and a rearmost engine, along with an engine operating system, for optimal space and energy efficiency. 
     UAVs can be used for a variety of functions including, but not limited to: load droppings, military operations, intelligence gathering, surveillance, and data collection. UAVs can be equipped with sensors of a large variety that will allow for a range of functions to be performed by the aircraft. 
     Limitations often exist with UAVs due to space and fuel consumption concerns. There exists a limited range where the CG of a UAV can be located and still maintain a safe and controlled flight. Additionally, onboard supplies and cargo can only be placed near the CG in order to maintain stability, which often results in a waste of available space and associated efficiency concerns. 
     By utilizing foremost and a rearmost engine arrangement, the aircraft is able to maintain balance and stability during flight while allowing the front and rear spaces of the aircraft to be occupied by onboard equipment, supplies, or cargo needing to be transported or utilized depending on the intended purpose of the flight. While the spaces at the front and tail-end of the aircraft would normally remain empty due to stability concerns, the disclosed engine arrangement allows for maximum space efficiency. 
     It is difficult to achieve optimal fuel efficiency with a single engine. By utilizing two engines for space and balance concerns, fuel efficiency is also able to be maximized through a control system. The system utilizes an approach in which one engine is shut off once the cruise altitude is reached. Depending on the characteristics of the two engines being used, and the optimization point or speed desired, the engine with the best fuel efficiency for a specialized purpose will be solely operating. 
     These and other aspects of the disclosed subject matter, as well as additional novel features, will be apparent from the description provided herein. The intent of this summary is not to be a comprehensive description of the claimed subject matter, but rather to provide a short overview of some of the subject matter&#39;s functionality. Other systems, methods, features and advantages here provided will become apparent to one with skill in the art upon examination of the following FIGURE and detailed description. It is intended that all such additional systems, methods, features and advantages that are included within this description, be within the scope of any claims filed later. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURE 
       The features believed characteristic of the invention will be set forth in the claims. The invention itself, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  shows an embodiment of the disclosed UAV. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to an Unmanned Aerial Vehicle (UAV) employing a fore and rearmost engine positioning as well as an engine operating system in the design. 
     The disclosed UAV has two engines (e.g., a twin-engine configuration), with the first engine installed in the front most extreme of the fuselage  1  and the second engine installed at the rear most extreme of the fuselage  2 . In some embodiments, both engines are installed in the center of the longitudinal axis, with each engine having its own support, independent front engine control  18 , and rear engine control  19 . Each engine may have its own electric generator  16 ,  17  to achieve redundancy both in terms of propulsion and electric generation in order to safely operate the aircraft and its flight control systems, communications, and sensors. 
     The disclosed UAV creates flight stability by balancing a front engine with a rearmost engine to allow the aircraft to utilize a two-engine design for balance with the center of gravity envelope. This embodiment generates symmetry in the weight distribution, with respect to the center of gravity (CG) 6 of the UAV, allowing for the fullest possible utilization of internal volume for the transport of fuel, equipment, payload, etc. 
     In order to maintain pitch stability, a CG 6 must be maintained within certain limits in all types of aircraft. In some embodiments, in order to maintain said CG, the variable useful load due to fuel is distributed with 2 or more tanks equally distanced from the CG 6, one located in the front  3  of the UAV and one located in the rear  4 . As a result, enough space is maintained very near and around the CG 6 position to carry highly variable different payloads and equipment without exceeding weight and balance limitations. Additionally, the available cargo space situated in near proximity to the CG position is ideal for the placement of an automatic pilot  9 . 
     In some embodiments, it is possible to distribute the necessary equipment along the fuselage by utilizing the available space on top of the fuel tanks. Such equipment can include, but not be limited to, batteries  23 , a transponder  24 , satellite communications equipment  25  or radio communications equipment  26 . 
     In some embodiments, in order to install and service the equipment and payload, several access doors may be employed on the top side of the fuselage. The access doors may be located in the front  10 , in the center front  11 , in the center rear  12 , and in the rear  13  of the UAV. The number and position of said access doors may vary according to a multitude of factors such as the size and shape of the UAV. 
     The power requirements for UAVs may vary greatly according to the flight phase. Full power is needed for takeoff, high power is needed for climb, and very low power is needed for cruise flight (loiter mode). Internal combustion engines attain their most efficient fuel consumption, otherwise known as the Specific Fuel Consumption (SFC) or Brake Specific Fuel Consumption (BSFC), within a very specific power band. The SFC can be very high under a high power demand or under a low power demand. In some embodiments, one of the engines may be shut off at the loiter phase without producing any thrust asymmetries, while at the same time obtaining the best SFC possible. 
     In some embodiments, two engines of different types and power characteristics can be used for increased efficiency of the UAV for each mission requirement. For example, in order to maximize endurance, a low power 4 cycle engine can be utilized in the front  1  of the UAV while a high power 2 cycle engine can be utilized at the rear  2  of the UAV. A low power 4 cycle engine with a very favorable SFC may be employed to operate the UAV under loiter conditions. Although the higher power 2 cycle engine has a much higher SFC than a low power 4 cycle engine, it is very light in weight and may be operated for just a few minutes (under the takeoff and climb phases) so the fuel penalty may be negligible. 
     In other embodiments, in order to preserve the power redundancy with one engine shut off, it is possible to install in-flight engine starters. Flight engine starters may be incorporated into the generators  16 ,  17  or separately in such a way that, if the operating engine fails, the engine that had previously been shut off will immediately start. 
     In some embodiments, two engines of different powers and weights may be utilized, which may require a balance. Even though two different types of engines may be used having different power outputs, balance can maintained due to the similarity in weight of a high power 2 cycle engine and a lower power 4 cycle engine. Any small weight differences that remain may be balanced with strategic placement along the fuselage of equipment and sensors. 
     In order to maintain a CG within the required limits, in some embodiments it may be necessary to keep the fuel levels of the engine(s) employed at an almost equal level in order to maintain balance. In other embodiments, a fuel management system may be required in which the fuel from each tank is routed through fuel lines  14 ,  15  to a central distribution fuel tank  22 . The central distribution fuel tank may send the fuel to a front engine via its fuel line  7  and to a rear engine via a separate fuel line  8 . Any imperfections in fuel levels may be corrected by alternating which fuel tank is selected for use using valve selector mechanisms or by a fuel transfer pump system between the main tanks. A weight balancing fine tuning mechanism allows for the reduction of the horizontal stabilizer down force to its minimum value, reducing the unwanted trim drag produced. 
     In some embodiments, the main landing gear  20  and the directional control landing gear  21  may be located in the front of the UAV and may or may not be retractable, depending on the priorities of the particular purpose being performed by the UAV. In other embodiments, the main landing gear  20  and the directional control landing gear  21  may also be eliminated if another system is preferred such as a dolly or catapult takeoff system. The UAV may then be landed with the assistance of a parachute, captured in a net or line, or landed on its belly. 
     While the invention has been described with respect to a limited number of embodiments, the specific features of one embodiment should not necessarily be attributed to other embodiments of the invention; however, in some embodiments features could be removed and/or combined with one or more features of the other embodiments to create additional embodiments. No single embodiment is representative of all aspects of the inventions. Moreover, variations and modifications therefrom exist. For example, the invention described herein may comprise other algorithms or pieces. Various steps may also be added to further enhance one or more properties of said pieces. In addition, some embodiments of the methods described herein consist of or consist essentially of the enumerated steps. The claims to be appended later are intended to cover all such variations and modifications as falling within the scope of the invention.