BACKGROUND Gliding is a popular sport which requires a tow plane or similar powered craft to tow a glider (being an unpowered craft) into the air and to a sufficient height'so that the glider can then glide on its own in a safe manner.

Typical current towing methods include attaching a flexible cable of the like to a rear end of a tow plane and the other end to a forward end of the towed craft.

A problem with this arrangement is that the, towed plane is very sensitive to the relative height of the towed craft relative to the tow plane. If, for example, the towed craft rises too high relative to the tow plane, it is possible for the towed craft to exert a significant pitching force on the tow plane which can be dangerous.

It is an object of the present invention to address or at least ameliorate some of the above disadvantages.

BRIEF DESCRIPTION OF INVENTION Accordingly, in one broad form of the inventor, there is provided a towing mechanism for linking a towing plane

to a towed craft ; said towing mechanism including a tow line attachment point affixed to said towing plane in an area proximate to the thrust line and pitch center line of said towing plane, Preferably said tow line attachment point is affixed to the fuselage of said towing plane.

Preferably said tow line attachment point is affixed to the wing of said towing plane.

Preferably wherein said tow line attachment point is adapted to permit relative vertical and horizontal movement of said towed craft relative to said tow plane.

Accordingly, in a further broad form of the invention, there is provided, a towing mechanism for linking a towing plane to a towed craft ; said towing mechanism allowing said towed craft to rise substantially above said towing plane with minimal affect on the pitch of said towing plane.

Accordingly, in a further broad form of the invention, there is provided, a towing mechanism for linking an ultra- light towing plane to a towed craft ; said towing mechanism including a frame pivotally attached to the wings of said ultra-light towing plane.

Preferably said frame is substantially in the form of a"V"and wherein the outer ends of said"V"are pivotally retained in brackets affixed to said wings.

Preferably said pivot axes of said brackets are coaxial and proximate to the center of pitch of said ultra- light towing plane.

Preferably said brackets are attached to said. wings at the pressure centers of said wings.

Preferably said brackets are supported by structural members attached to compression struts in said wings.

Preferably said structural members are braced by wire ropes tensioned between said structural members and the front spars of said wings.

Preferably said. frame is provided with a tow line attachment fitting at the base of said"V".

Preferably said frame is supported in a substantially horizontal position when said ultra-light towing plane is at rest.

Accordingly, in a further broad form of the invention, there is provided a method of towing an un-powered flying craft so as to render said un-powered flying craft airborne and independent of said tow plane ; said method including the steps of : (a) providing a towing mechanism on a tow plane ; said mechanism including a point of attachment for a tow line proximate to the thrust line and the pitch center line of said tow plane, (b) connecting said un-powered craft to said tow line,

(c) accelerating said tow plane to a first ground speed at which said un-powered craft becomes airborne, (d) increasing said, ground speed from said first ground speed until said un-powered craft has climbed to a height where the angle of said tow line to the horizontal plane attains a maximum value, (e) increasing said ground speed to cause said tow plane to take off.

Preferably said point of attachment is effected by a shaped towing frame ; said frame pivotally attached at its outer ends to brackets affixed to the wings of said tow plane.

Preferably said brackets are attached to said wings along a line defined by the pressure centers of said wings.

Preferably said brackets are attached to said wings at the pressure centers of said wings.

Preferably said frame and said tow line lie substantially in a common plane while said un-powered flying craft is airborne and attached to said tow line.

BRIEF DESCRIPTION OF DRAWINGS Embodiments of the present invention will now be described with reference to the accompanying drawings wherein:-

Fig 1 is a perspective view of a towing aircraft provided with a towing apparatus in accordance with a first preferred embodiment of the present invention Fig 2 is'a side view of the apparatus of Fig 1 showing a further step in the towing method of a first embodiment, Fig 3 is a perspective view of a towing aircraft in accordance with a further preferred embodiment of the present invention Fig 3A shows detail of the wing attachment5, Fig 4 is a side view of the arrangement of Fig 3 in a further towing step and Fig 5 is a side section view of the wing of the towing aircraft of Fig 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS A desirable feature in the towing arrangements for the launching of un-powered craft by a towing aircraft, is for the effective attachment point of the tow line on the towing aircraft to lie as near as possible to the thrust line and center. of pitch of the towing aircraft, where the thrust line is generally taken as lying through the axis of the propeller and the center of pitch is the line joining the pressure centers (or centers of lift) of the wings.

With reference to figure 1, in a first preferred embodiment of the present invention a single engined puller propeller towing plane 10 for the launching of un-powered

craft 11, such as gliders and para-gliders for example, is provided with a tow line 16 attachment point 12, Attachment point 12 is situated at a point on the fuselage 13 lying approximately on the line joining the pressure centers 14 of the wings 15 and in the longitudinal mid plane.

An un-powered craft 11 such as a glider or para-glider when under tow becomes airborne at a lower ground speed than that of the towing plane 10, and the position of the tow line 16 attachment point 1. 2 allows the towed un-powered craft 11, once airborne, to rapidly assume a position well above the towing plane 10 whilst the towing plane 10 is still traveling over the ground 17 as illustrated in figure 2.

The greater the angle a which the tow line 16 makes with the horizontal plane 18, the greater the upward tension provided by the towed un-powered craft 11 on the towing plane 10, thereby effectively lowering the take-off. speed along the ground of the towing plane 10, Conversely, the downward tension on the tow line 16 from the towing plane 10 improves the stability of the towed un-powered craft 11 whilst still attached to the tow line 16.

With reference to figure 3, in a second preferred embodiment of the present invention, a single engine, pusher propeller towing plane 110, is provided with a towing frame 120. Towing frame 120 comprises light tubular elements 121 and 122 arranged so as to approximate a"V"

form wherein the outer ends 123 and 124 of the"V"are attached to each wing 125 and 126 respectively of towing plane 110.

Outer ends 123 and 124 are pivotally retained in brackets 127 and 128 respectively as shown in the enlargement of figure 3A and arranged so that the pivot axes 129 and 130 of the brackets 127 and 128 are coaxial.

Preferably, the point of attachment of brackets 127 and 128 on wings 125 and 126 is at the pressure center of each wing.

The height of the'V"that is the distance from the line joining outer ends 123 and 124 to the base 131 of towing frame 120, is such as to leave a gap between base 131 and rudder 135 of towing plane 110.

The base 131 of the towing frame 120 is provided with a towing fitting 132 adapted for the attachment or a tow line 133 as commonly used in the art. Towing frame 120 iß so arranged, that when towing plane 110 is stationary on the ground prior to take-off, towing frame 120 lies in a generally horizontal plane.

In at least one particular preferred embodiment the towing plane is an ultra-light and it is the wire bracing (not shown) between the wings and the tail of the ultra- light which may act as a support for towing frame 20 when the ultra-light is at rest prior to use for towing. The tow

line 135 may then lie along either side of the rudder 136 of towing plane 110.

In a preferred embodiment of an ultra-light towing plane and with reference to figure 5, each of brackets 127 and 128 is supported by added structural member 140 attached to an existing compression strut 141 and guyed for lateral support by two wire ropes 142 and 143 (only one of which is visible in figure 5) from the main wing spar 144.

In use, in this embodiment of the invention, an un- powered craft 111 becoming airborne before the towing plane 110 becomes airborne, immediately causes towing frame 120 to pivot upwardly about the pivot axes 129 and 130, thus allowing towing plane 120 to maintain its optimum pre take- off and post take-off trajectory. Because towing frame 120 is free to pivot'upwardly, it and the tow line 135 lie practically in the one plane and the un-powered craft 111 is effectively towed from the two attachment points on the wings of the towing plane.

It will be understood that in this preferred embodiment the effective point of attachment of the un- powered craft is the mid point between the two brackets and is thus the equivalent of the attachment point as described in for the first embodiment above. Thus the interaction of the towing plane and towed un-powered craft through the tow line and towing frame is as previously described for the first embodiment above.

In practice it has been found that the forward speed of the towing plane necessary to achieve lift-off is significantly reduced and the rate of climb of the towed craft is increased. Thus for example where a typical ground speed of a conventionally configured towing aircraft at the point of lift-off may be of the order of 30 mph, the towing arrangement of the present invention allows lift-off at approximately 20 mph.

Since the tow line is not attached to the end of the towing plane, the angled upward drag on a tow line of an un-powered towed craft flying at a higher altitude to that to the towing plane has no significant affect on the pitch of the towing plane thereby significantly adding to the safety of the towing operation.

When the un-powered towed craft releases the tow line, the commonly used drag parachute incorporated in the line creates sufficient drag on the line to ensure that the towing frame is allowed to return gradually to its at-rest position.

The above describes only some embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope and spirit of the present invention.