Background Art Model planes for amusement or education are generally classified based on the type of power source they use. Different types of model planes include a powerless type, a rubber powered type, and an electric-powered type. The powerless model plane can fly without a separate power source, but using natural wind forces. The powerless model plane is simple and convenient since no power source is used. However, due to the same reason, i. e. , since no power source is used, the powerless model plane should be launched on a hill when the wind is rising. Further, the powerless model plane cannot fly for long. The rubber powered model plane uses an elastic cord and a propeller rotated by elastic forces generated by the elastic cord. The rubber powered model plane cannot fly for long either.

The electric-powered model plane typically includes a body having wings, an electric motor mounted on the body, a propeller connected with the electric motor, and a battery for supplying electric power to the electric motor. To reduce capacity of the electric motor which should be mounted on the body, the body and the wings are usually made of light materials, such as wood or plastic, rather than heavy metals. Further, usually a rechargeable battery, such as a rechargeable NiCd battery, is used as the battery. In comparison with the other types, the electric-powered type model plane has advantages in that the weight and the size o the body having wings

can be reduced and the power source, i. e. , the battery, can be easily recharged after flights.

However, a conventional electric-powered model plane has problems in that the flight is greatly affected by the weather, particularly in a case where the wind velocity is 6 m/sec or faster.

Further, the flight path and other performance values vary according to the initial launching conditions. In addition, in the event that the flight continues due to natural wind forces even after the power source stops supplying power, the electric-powered model plane can fly too far from the launching location and is frequently lost. Further, due to a low capacity of the battery, the flight speed is low, and since the weight of the body and the wings should be minimized for improving flight performance, the structure of the conventional electric-powered model plane is very weak and easily breakable.

Disclosure of the Invention The present invention provides an electric-powered model plane having excellent flight stability without being significantly affected by the initial launching and weather conditions. Also, the possibility of losing the model plane is reduced in comparison with conventional electric-powered model planes.

Further, the present invention provides an electric-powered model plane having a high flight speed and a sufficiently strong structure.

An electric-powered model plane according to the present invention includes a body; a rechargeable battery that is accommodated in a front lower section of the body and has an exposed terminal for recharging the battery; an electric motor that is electrically connected to the rechargeable battery and is mounted at a rear section of the body, which is located higher than the centroid of the entire model plane ; a propeller that is connected to a pivot of the electric motor; a tail boom that has one end connected with the rear

edge of the body and extends rearwards in the longitudinal direction of the body; and wings, including a main wing which is connected with both sides of the body and has an airfoil shape, wherein the maximum camber of the main wing is located within a 1/4 range from the front edge of the main wing with respect to a straight reference line connecting the front edge and the rear edge of the main wing, and tail wings that are connected with the other end of the tail boom.

In order to ensure flight stability of the model plane by making a portion of backwash produced by the propeller flow through the tail wings, it is preferable that the centerline of the pivot of the electric motor is parallel to the straight reference line.

Further, it is preferable that the centerline of the pivot of the electric motor and the axis of the tail boom form an angle of 3 degrees.

The tail wings are preferably comprised of a horizontal tail wing and a vertical tail wing, and the horizontal tail wing preferably has a horizontal control section formed at a part of the rear thereof, which can be tilted upward and downward, to ensure flight stability of the model plane.

Further, in order to prevent loss of the model plane, the vertical tail wing is preferably attached to the left side of the tail boom when viewed from the rear, and has a vertical control section formed at a part of the rear thereof, which can be titled leftward and rightward.

Additionally, in order to reduce the weight while sufficiently strengthening the structure of the model plane, it is preferable that the body and the wings are made of Styrofoam, and the battery is a condenser.

Brief Description of the Drawings FIG. 1 is a perspective view of an electric-powered model plane according to a preferred embodiment of the present invention;

FIG. 2 is a bottom view of FIG. 1 in which a section has been cut through the body of the model plane ; FIG. 3 is a front view of FIG. 1; FIG. 4 is a cross-sectional view of FIG. 1 taken along line IV-IV ; FIG. 5 is a cross-sectional view of the propeller of the model plane shown in FIG. 1; FIG. 6 is a cross-sectional view of the main wing of the model plane shown in FIG. 1; FIG. 7 is a perspective view of the tail wings of the model plane shown in FIG. 1; FIG. 8 shows the status which the condenser of the model plane shown in FIG. 1 is being charged; and FIGS. 9 and 10 show flight modes of the model plane shown in FIG.

1.

Best mode for carrying out the Invention A preferred embodiment of the present invention will now be described with reference to the attached drawings.

FIG. 1 is a perspective view, FIG. 2 a bottom view, FIG. 3 a front view, and FIG. 4 is a cross-sectional view of an electric-powered model plane according to a preferred embodiment of the present invention, respectively. As shown in FIGS. 1 through 4, the electric-powered model plane 1 according to a preferred embodiment of the present invention includes a streamlined body 10, a rechargeable battery 20 that is accommodated in a front lower section of the body 10, an electric motor 30 that is electrically connected with the rechargeable battery 20 and is mounted at a rear section of the body 30, a power switch 23 that is mounted at a side section of the rechargeable battery 20 and projects from the body 10, a propeller 40 that is connected to a pivot of the electric motor 30, a tail boom 50 that has one end connected with the rear edge of the body 10 and is extended

backwardly in the longitudinal direction of the body 10, and wings 60 that are connected with the body 10 and the tail boom 50. The wings 60 are comprised of a main wing 61 that is connected with both sides of the body 10 and produces lift and tail wings 63 that are connected with the other end of the tail boom 50. The tail wings 63 are comprised of a vertical tail wing 65 for ensuring stability in the vertical direction and a horizontal tail wing 67 for ensuring stability in the horizontal direction. Connections between the body 10 and the main wing 61, the tail boom 50, the rechargeable battery 20, and the electric motor, as well as connections between the tail boom 50 and the vertical and the horizontal tail wings 65 and 67 are made using an adhesive such as an adhesive from the acetic vinyl resin group.

Any kind of rechargeable battery can be used as the battery 20 insofar as it is light and has a large capacity. However, in this embodiment, a recently commercialized light-weight, large-capacity condenser is used as the battery 20 in consideration of weight and driving forces. Such a condenser has an advantage in that initial output power is very good. The condenser 20 has a diameter of 10 mm, a length of 30 mm. It has a regulated voltage of 2.3 V and a capacity of 10 F, and weighs 3.5 g. The condenser 20 is accommodated in a front lower section of the body 10 such that a recharging terminal 21 thereof is outwardly exposed. An electrode of the condenser 20 is used as the recharging terminal 21, and a recharging electrode 71 of a recharging device 70 to be described later is connected to the recharging terminal 21 to recharge the condenser 20. As described above, the condenser 20 is accommodated in the front lower section of the body 10. Since the relatively heavy condenser 20 is placed at the lower section of the centroid of the model plane 1, the model plane 1 has very good static and dynamic stability.

The electric motor 30 is electrically connected to the condenser 20. Further, the electric motor 30 is connected with a rear upper section of the body 10 and a central section of the main wing 61 such that the centerline of the pivot 31 thereof is parallel to a straight reference line 62 drawn from the front edge to the rear edge of the main wing 61, as shown in FIG. 6. Specifically, the electric motor 30 is connected at a position about 17mm higher than the centroid of the model plane 1.

The power switch 23 is mounted at and projected from a side section of the body 1 10. Power is connected and disconnected from the condenser 20 to the electric motor 30 through the power switch 23. The power switch 23 is a toggle type push on/off switch having a regulated capacity of more than 120 mA and is connected to an electrode, i. e. , the charging terminal 21 of the condenser 20. In regard to the operation of the power switch 23, when the power switch 23 is in the on state and is pushed once, the on state is changed to the off state during which the power supply from the condenser 20 to the electric motor 30 is disconnected, and the off state is kept unless the power switch 23 is pushed once more. If the power switch 23 is pushed once more in the off state, then the power switch 23 is pulled out and the off state is changed to the on state during which power is supplied from the condenser 20 to the electric motor 30. Therefore, in order to recharge the condenser 20, the power switch 23 is in the off state to disconnect the supply of power to the electric motor 30. After completing the recharge of the condenser 20, if the model plane 1 is thrown and launched while pushing the power switch 23 with a finger, the power switch 23 is toggled out immediately after the model plane 1 leaves the user's hand to start supplying power from the condenser 20 to the electric motor 30, and accordingly, the propeller 40 begins to rotate to produce a driving force.

FIG. 5 is a cross-sectional view of the propeller of the model plane shown in FIG. 1. Referring to FIG. 5 together with FIG. 3, the propeller 40 has a diameter D of 60 mm and a pitch P ranging 40 to 50 mm and produces a relatively high driving force of 3.5 gf at a flight speed of 6 m/sec and 9500 rpm. The propeller 40 is mounted at the rear of the body 10 to function as a pusher. Since the thrust line of the propeller 40 is identical to the centerline of the pivot 31 of the electric motor 30, which is shown in FIG. 6, and is located 17 mm above the centroid of the model plane 1, a pitching-down moment, which lowers the front edge of the model plane 1, is produced when power is supplied. The pitching-down moment offsets a pitching-up moment produced by the main wing 61 of the model plane 1 when the model plane 1 is accelerated so that the pitching moment during powered flight can be balanced and the flight stability of the model plane 1 can be improved.

The tail boom 50 has a length of about 135 mm. The tail boom 50 is connected at a rear section of the body 10, which is 35 mm below the straight reference line 62 of the main wing 61, and is extended rearward in the longitudinal direction of the body 10. The tail boom 50 and the reference line 62 of the main wing 61 form an angle of 3 degrees. The tail boom 50 is made of light materials such as wood, and resin is coated thereon to improve the strength in comparison with the weight.

The wings 60 are comprised of the main wing 61 and the tail wings 63 spaced apart from the main wing 61 by a predetermined distance and connected with the tail boom 50. The tail wings 63 are comprised of a vertical tail wing 65 and a horizontal tail wing 67.

FIG. 6 is a cross-sectional view of the main wing of the model plane shown in FIG. 1. Referring to FIG. 6 together with FIG. 3, the main wing 61 has a length (not shown) of 320 mm, a width (not shown) of 60mm and a dihedral A1 of 8 degrees, and is shaped by molding

Styrofoam to have a constant thickness. The maximum camber C of the main wing 61 is 5 to 8 % of the length L of the straight reference line 62 and is located at a distance X of 15 to 22 % from the front edge to provide excellent stall recovery characteristics. The wing shape having the maximum camber C located at the position X forward the aerodynamic center of the wing shape which is 25% of the length L of the straight reference line 62 has a great pitching-down moment characteristic to reduce the pitching angle during a stall.

In a case where a speed of the model plane 1 greatly increases, the pitching-down moment greatly decreases to increase the pitching angle of the model plane 1. Therefore, the excellent stall recovery characteristic due to the shape of the main wing 61 increases flight stability of the model plane 1 to cope with launching postures and inadequate inclination of a horizontal control section 68 of the horizontal tail wing 67 to be described later.

More specifically, in regard to launching postures, if the model plane 1 is launched with a large pitching angle, rapid recovery from the stall and thus normal flight can be achieved. Further, if the model plane 1 is launched with a small pitching angle, increases in lift and in pitching angle can be achieved due to a rapid increase in speed so that the model plane 1 can rise again before contacting the ground. Similarly, if the horizontal control section 68 of the horizontal tail wing 67 is excessively inclined upward, i. e. , if the model plane 1 has a large upward pitching moment at the time of launching, recovery from the stall can be made without loss of altitude due to a rapid stall as with typical model planes. If the horizontal control section 68 of the horizontal tail wing 67 is excessively inclined downward, i. e. , if the model plane 1 has a large downward pitching moment at the time of launching, the lift greatly increases when the model plane 1 is accelerated due to loss of

altitude, and therefore, a sudden crash into the ground can be prevented. Further, in an environment of strong air current, if the pitching angle of the model plane 1 is large, the stall phenomenon may occur since the pitching-down moment of the main wing 61 decreases due to an increase in the air flowspeed over the main wing 61. However, rapid recovery from the stall is possible due to the shape of the main wing 61. Because of the repeated stall and recovery from the stall during flight, rising in altitude can be prevented, and accordingly, loss of the model plane 1 due to a sudden rise in altitude with a strong air current can be prevented.

FIG. 7 is a perspective view of the tail wings of the model plane shown in FIG. 1. As shown in FIG. 7, the tail wings 63 are comprised of a vertical tail wing 65 and a horizontal tail wing 67.

The vertical tail wing 65 is attached to the left side of the tail boom 50 when viewed from the rear, and has a vertical control section 66 formed at a part of the rear thereof, which can be titled leftward and rightward. Since the vertical tail wing 65 is attached to the left side of the tail boom 50 when viewed from the rear, a roll motion moment produced by the vertical tail wing 65 can offset the roll motion moment of the model plane 1 due to the propeller 40 and directional motion stability can be improved by allowing the model plane 1 to turn around without flying far away considering the possibility of losing the model plan. The horizontal tail wing 67 has a horizontal control section 68 formed at a part of the rear thereof, which can be titled upward and downward, and a fine groove is formed at the tilting portion of the horizontal control section 68 to allow the horizontal control section 68 to be tilted conveniently. If the horizontal control section 68 is tilted upward, i. e. , the horizontal control section 68 is directed upward, since the pivot 31 of the electric motor 30 is declined at about 3 degrees with respect to the tail boom 50, backwash of the propeller 40 can flow over a portion of the horizontal

tail wing 67 and a pitching moment to raise the pitching posture of the model plane 1 can be produced from the horizontal tail wing 67 due to the backwash. Therefore, the pitching moment produced during flight can be adequately adjusted using the horizontal control section 68 of the horizontal tail wing 67. The vertical and horizontal tail wings 65 and 67 are made of Styrofoam and molded flat.

As described above, since the electric motor 30 and the propeller 40 are placed above the centroid of the model plane 1, adequate adjustment of the horizontal control section 68 of the horizontal tail wing 67 ensures balance of the pitching moment during horizontal or smoothly rising flight in a powered condition and more stable flight.

In this case, if the power is exhausted, balance of the pitching moment of the model plane 1 is achieved during descending flight with a fall angle A2 of about 12 degrees. Accordingly, the model plane 1 having no power is less affected by air currents and quickly returns to the ground so that loss of the model plane 1 can be prevented.

A method of using and the electric-powered model plane according to a preferred embodiment will now be described.

FIG. 8 shows the status which the condenser of the model plane shown in FIG. 1 is charged. As shown in FIG. 8, the condenser 20 is recharged when the recharging terminal 21 exposed to the outside of the model plane 1 is connected to the recharging electrode 71 of the recharging device 70. At this instant, if the power switch 23 is not switched off, the propeller 40 rotates since the power is supplied to the electric motor 30 when the recharging of the condenser 20 starts. Therefore, it is desirable to recharge the condenser 20 after switching off the power switch 23. After completing the recharge of the condenser 20, if the model plane 1 is thrown and launched and simultaneously the power switch 23 is pushed by a user's finger, the power switch 23 is toggled out immediately after the model plane 1

leaves the user's hand to start supplying power from the condenser 20 to the electric motor 30, and accordingly, the propeller 40 begins to rotate to produce a driving force.

FIGS. 9 and 10 show flight modes of the model plane shown in FIG. 1. In a powered flight mode as shown in FIG. 9, the propeller produces a downward pitching moment since the propeller 40 is rotated by the electric motor 30 placed above the centroid of the entire model plane 1 and the horizontal tail wing 67 causes an upward pitching moment due to the backwash from the propeller 40.

Since the downward and the upward pitching moments offset each other, the model plane 1 can fly with balanced pitching moments.

When the power is exhausted, i. e. , when the driving force becomes weak due to insufficient torque of the electric motor, the model plane 1 starts to drop at an angle of about 12 degrees as shown in FIG. 10.

Specifically, when the model plane 1 drops while the power is exhausted, since the backwash of the propeller 40 becomes weak, the upward pitching moment caused by the horizontal tail wing 67 decreases faster than the decrease of the downward pitching moment due to the driving force of the electric motor 30.

Accordingly, the pitching moments are balanced when the model plane 1 drops at an angle of about 12 degrees and the model plane stably flies back down. Consequently, the model plane 1 returns to the ground fast with less affects due to air currents, and the possibility of losing the model plane 1 can be reduced.

As described above, since the main wing 61 is shaped to rapidly recover from a stall and the electric motor 30 and the propeller 40 are placed above the centroid of the entire model plane 1, the model plane 1 according to the present invention has excellent flight stability without being significantly affected by the launching postures and weather conditions, and the possibility of losing the model plane 1 can be considerably reduced in comparison with conventional model

planes. Further, since the light-weight condenser 20 having a large capacity, the wings 60 and the body 10 made of Styrofoam, and the tail boom 50 made of light materials are used, the model plane 1 according to the present invention can fly fast and still have sufficient structural strength.

While a light-weight condenser having a large capacity is used as the battery 20 in the above-described embodiment, any kind of rechargeable batteries can be used insofar as they are light and have a large capacity. Further, while an electrode of the condenser 20 is used as the recharging terminal 20 in the preferred embodiment described above, it is also possible to expose a recharging cord having an end on which a recharging terminal 21 is formed and another end connected with the electrode of the condenser 30.

In addition, while the horizontal control section 68 of the horizontal tail wing 67 is tilted upward and the electric motor 30 is mounted such that the centerline of the pivot 31 thereof is parallel to the straight reference line 62 of the main wing 61 in the above-described embodiment, it is also possible to tilt the horizontal control section 68 downward and mount the electric motor 30 so that the centerline of the pivot 31 is not parallel to the straight reference line 62 of the main wing 61 insofar as the model plane 1 can fly with a balanced pitching moment during the powered fight mode.

Industrial Applicability As described above, according to the present invention, there is provided an electric-powered model plane having excellent flight stability without being significantly affected by the launching postures and weather conditions, and the possibility of losing the model plans can be considerably reduced in comparison with conventional model planes.

Further, the model plane according to the present invention can fly

fast and has sufficient structural strength due to the use of a light condenser having a large capacity, wings and a body made of Styrofoam, and a tail boom made of light materials.