Abstract:
A propulsion system for miniature vehicles, such as model airplanes, having multiple direct-current motors arranged radially about a central axis of the propulsion system that drive a propeller system.

Description:
FIELD OF THE INVENTION 
   This invention relates to a propulsion system for miniature vehicles. More particularly, the invention relates to an electric-powered propulsion system for miniature vehicles such as aircraft. 
   BACKGROUND OF THE INVENTION 
   The popularity of the radio-control hobby, as it applies to miniature or model aircraft, cars, boats and miniature military vehicles, has seen dramatic growth in recent years. Advancements in electric power technology, such as the increase in power-to-weight ratio of electric motors and batteries, have encouraged interest in the hobby for all age groups. 
   Today&#39;s radio-controlled models are less expensive and can be purchased almost ready-to-fly. They are typically made of molded foam in attractive colors with motors and control equipment pre-installed. 
   An important factor in the use of electric propulsion is the extreme quietness of the units. Noise pollution is almost non-existent so electric models can be flown at almost any park, school ground or ball field. 
   Most recently the challenges of electric flight have diminished to the point that it has become a common form of propulsion for all types of miniature aircraft. 
   All electric, radio-controlled models utilize a single motor or multiple single motor configurations. No electric powered multiple radial type motor is currently available. 
   It is the intent of this invention to provide a propulsion system that can be used on model airplanes. 
   It is a further intent of this invention to provide a propulsion system that allows a scale-like, electric motor to power models of World War I and II vintage aircraft. There are many examples of these aircraft such as English Sopwith Camels, German Fokker Tri-planes and a vast selection of United States bi-plane trainers, fighter planes and civilian aircraft. All of the above examples sold to the public at this time use single motor configurations. 
   It is the intent of this invention to offer an electric radial propulsion system that is powerful and offers the additional advantage of scale-like appearance and sound. 
   It is a further intent of this invention to provide a multiple-cylinder, electric, radial motor propulsion system that is configured to power miniature vehicles, such as model planes, at a scale-like speed that is safe, quiet, durable and economical to operate and that enhances the appearance of any scale-type model by more closely duplicating the original full-scale round-looking type of engine. 
   SUMMARY OF THE INVENTION 
   This invention is a propulsion system for use in a miniature vehicle having a motor assembly comprised of a plurality of direct current motors operating together and arranged radially from a central axis of the motor assembly 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
       FIG. 1   a  is a frontal view of the propulsion system of the present invention, as mounted on one type of a miniature aircraft, with the propeller cutaway. 
       FIG. 1   b  is a side view of the propulsion system of  FIG. 1   a  installed on a different type of a miniature aircraft, with the propeller in place. 
       FIG. 2  is a partially-exploded side view of the propulsion system showing the propeller assembly, the motor assembly and the drive shaft of the present invention. 
       FIG. 3  is a front view of the motor assembly of the present invention along lines A-A′ of  FIG. 2 . 
       FIG. 4  is a rear view of the motor assembly of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawings, it is noted that like reference characters designate like or similar parts throughout the drawings. The figures, or drawings, are not intended to be to scale. For example, purely for the sake of greater clarity in the drawings, wall thicknesses and spacings are not dimensioned as they actually exist in the assembled embodiments. 
     FIG. 1   a  is a frontal view of a propulsion system  100  of a preferred embodiment mounted on a miniature aircraft  102   a .  FIG. 1   b  is a side view of propulsion system  100  mounted on the front of the aircraft  102   b  by attaching the propulsion system  100  to a firewall  104  in the aircraft  102   b.    
   The propulsion system  100  of the preferred embodiment includes the elements shown in  FIG. 2 . The details of the preferred embodiment are discussed below and include a motor assembly  106  and a propeller assembly  108  connected together with a drive shaft  110 . 
   As shown in the front view in  FIG. 3 , the motor assembly  106  of the preferred embodiment utilizes five, small, approximately 3-7 volt direct current electric motors  112  configured in a symmetrical pattern that is radially disbursed from the drive shaft  110  which is the axis of the motor assembly  106 . The motors must be configured properly for the voltage, weight, torque and amperage specifications of the desired unit. The five-unit embodiment is meant by way of example and is not intended to limit the scope of the invention. 
   This radial motor configuration emulates the advantage of the fly-wheel effect produced by a large propeller (not shown). This effect is what develops the maximum power of the motor assembly  106  and allows the aircraft  102   a  and  102   b  to fly. This phenomenon also is evident in full-scale aircraft designed with radial engines (not shown). Conversely, increasing the voltage and RPM has little effect on power output and only serves to use more energy. 
   The dimensions of the individual motors  112  in this preferred embodiment are approximately 1⅜″ long by 1″ wide with about a ⅜″ long by 2 mm diameter motor shaft  114 . The top and bottom of the individual motors  112  are approximately flat which makes the height of the motors  112  approximately ¾″. Cylindrical motors (not shown) of approximately the same size and power requirements also can be used. All dimensions are meant by way of example and are not meant to limit the scope of the invention 
   As shown in  FIGS. 2 ,  3  and  4 , each DC motor  112  has approximately a ½ inch diameter, 45-degree pinion gear  116  pressed onto the respective motor  112 . All of the pinion gears  116  mate to a main gear  118 . The main gear  118  is about 1½ inches in diameter. The final gear ratio (pinion to main gear) is 3:1 and turns a 14-inch diameter by 10-inch pitch propeller  120  approximately 2300 RPM. This produces about 12.9 ounces of thrust at a 3.9 ampere draw from a 12-volt flight battery (not shown). This 3:1 ratio is critical to the proper rotational speed of the propeller  120 , which is targeted for optimum flight time and power. 
   The main gear  118  and the pinion gears  116  can be made of nylon, plastic or other light-weight, non-conductive material. Only a slight amount of lubricant (not shown) is required for the main gear  118  and the pinion gears  116 . Typically, one small drop is sufficient for every ten flights. 
   As illustrated in  FIG. 2 ,  FIG. 3 , and  FIG. 4 , the 45-degree configuration of the main gear  118  and the pinion gears  116  allows the motors  112  to be mounted flat and in a radial arrangement around the main gear  118 , with the motor shafts  114  of the motors  112  positioned perpendicular to the drive shaft  110 . This mounting configuration replicates a full-scale aircraft engine (not shown). Additionally, having the main gear  118  mounted forward of the pinion gears  116  provides a way to easily adjust the pinion-to-main gear clearance. The clearance is set by simply sliding the propeller assembly  108  and the main gear  118  forward and off the pinion gears  116  and inserting a strip of material of known thickness, such as a common business card, to set the clearance at the desired depth of 0.005-0.008 inches. Proper gear spacing is important to reduce drag. 
   The gear clearance is locked in place by a thrust collar  122  at the distal end  124  of the drive shaft  110 . The thrust collar  122  is pinned to the drive shaft  110  by a set screw  148  and rides on a thrust washer  126 . It serves to secure the drive shaft  110  to a front mounting plate  128  and a rear mounting plate  130 . The rear mounting plate  130  has equally-spaced mounting holes  140  ( FIG. 4 ) around the edge of the plate  130  to allow screws (not shown) to pass through the rear mounting plate  130  to mount the propulsion system  100  to the firewall  104  in the aircraft  102   a  or  102   b.    
   In the preferred embodiment, the front mounting plate  128  ( FIG. 3  and  FIG. 4 ) is designed in a star configuration and allows airflow around the motors  112  to facilitate cooling. As shown in  FIG. 2 , the rear mounting plate  130  is separated from the front mounting plate  128  by 2 inch plate supports (spacers)  132 . This separation or clearance between the front mounting plate  128  and the rear mounting plate  130  increases cooling by providing additional airflow space around the motors  112  and provides space for the separation of drive shaft bearings  134 . This space between the front mounting plate  128  and the rear mounting plate  130  strengthens the entire motor assembly  106  and separates the drive shaft bearings  134  for precise alignment of the drive shaft  110 . 
   The front mounting plate  128  and the rear mounting plate  130  can be made of plywood or molded from plastic or other light-weight, non-conductive, rigid and durable material. 
   The dimensions of the drive shaft  110  are approximately ¼ inch by 3 inches. The drive shaft  110  can be made of nylon, plastic or other durable, light-weight, non-conductive material. The propeller  120  is mounted at the proximal end  136  of the drive shaft  110  and is secured to a propeller hub  144  by a spinner nut  138  (¼ inch by twenty-eight threads per inch). The spinner nut  138  can be made of plastic, aluminum or other similarly featured material. Propellers  120  are commonly available and are frequently made of wood or molded plastic. 
   The propeller hub  144  is positioned on the drive shaft  110  between the propeller  120  and the main gear  118  and rotates in synchronization with the propeller  120 . The propeller hub  144  is pinned to the drive shaft  110  by a pin  146 . 
   All wiring (not shown) is pre-installed to each motor terminal and can be color-coded for positive and negative polarity. An electrical connector can be soldered to the end of the motor wires for connecting to an electronic throttle control device (not shown) provided by the kit manufacturer or consumer. 
   The propulsion system  100  can be easily installed on many ready made and quick-assembly kits for miniature aircraft  102   a  and/or  102   b  for example as shown in  FIG. 1 . Short screws (not shown) are used to connect the propulsion system  100  to the aircraft firewall  104 . The flight transmitter (not shown) sends commands to the electronic throttle control device (not shown) that controls the throttle on/off and power setting of the propulsion system  100 . 
   The flight batteries (not shown) are quick charged from a 12-volt field battery (not shown) or automobile batteries (not shown) on site. Many 800 milliamp flights can be made during the normal flying session. 
   Flight duration with a typical 30-inch span bi-plane ( FIG. 1   a ) with 400-500 square inches of wing area, weighing 28 ounces, will typically last about 20-30 minutes. However, exact flying time depends on the amount of aerobatics performed and throttle setting, wind speeds and other factors. The motors  112  also can be wired in parallel (not shown) for more power but less flight time. 
   It is anticipated that those skilled in the art of motors will recognize various other ways of practicing the invention and other uses of the invention. While the invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention, as set forth in the following claims.