GB2261864A - Propulsion by self aligning foil - Google Patents

Abstract

Propulsion is achieved using one or more foils each mounted on a shaft about which they are free to rotate. The design of the foils and their mountings ensures that they are self aligning to adopt a constant angle of attack. This provides a high lift, low drag, efficient means of propulsion. A single hydrofoil f, mounted on a bent shaft s, which oscillates about a nearly horizontal axis at the stern of a boat, Fig 1. provides a sculling action, and can be controlled to provide efficient steering and propulsion, forward or backward, with one hand. Multiple foils, mounted to form a screw propeller or turbine, provide an automatic variation of pitch without complex control mechanisms, applicable where the cost of fully optimal control is not warranted. As well as propelling craft through air and water, fluid can be pumped, or energy extracted with good efficiency in a range of conditions. In a further embodiment two pivoting, self adjusting foils replace the two fixed blades of a kayak paddle. <IMAGE>

Description

PROPULSION BY SELF ALIGNING FOIL This invention relates to the propulsion of craft by the oscillation and rotation of a suitably mounted blade or foil, which is self aligning as described below.

An example of the application of this technique is the propulsion of a small boat by a hydrofoil which oscillates from side to side at the stern, Fig 1. The foil, f, is free to rotate on a nearly vertical tubular shaft ,s, which itself oscillates about a pin bearing,p, fixed perpendicularly to the shaft above the waterline. The shaft is bent forward over the bearing and extended to provide a handle ,h, within reach of a boatman sitting comfortably near the centre of the boat. A side to side motion of the handle ,Mh, produces an opposite side to side motion of the foil, Mf, Fig 2.

This device will thus appear similar to a tiller, as normally used to steer a boat However, in this case, the side to side motion of the tiller propels the boat forward. To make the necessary conversion of side to side force into a forward acting force on the beats transom the foil must generate a force, L, perpendicular to it's direction of motion relative to the water,V, Fig 3. Such forces, usually referred to as "lift" even when not acting vertically, are generated by suitably designed oil sections , as used for keels and rudders.

There will also be a component of force ,D opposing the foil' r 5 motion through the water, usually referred to as "drag", which is, in this case, best minimized This is in contrast to many other less efficient propulsive system such as ors, paddle wheels and flapping plates, in which the drag provides the major driving force.

The increased efficiency is combined with greater convenience 1. The boatman sits facing to one side, either port or starboard at his or her choice. This makes it easy to see forward. in contrast to the situation when using oars.

2. There are no projections sideways, making it easier to manoeuvre through narrow gaps, especially in marinas and other congested areas. It is possible to manoeuvre close to high sided quays etc, with one hand free to grasp a ladder or bollard.

3. The device can easily be taken off and carried for extra security.

4 The device is as easy to use as an outboard motor but generates no pollution and is cheap and simple to make. It is also iess sensitie to clogging with weed or breakage in the event of cell vision with underwater obstacles.

Optimisation of the lift force L requires the foil angle to be controlled. The important "angle of attacks , is the angle between the direction of motion of the foil relative to the water ,V and the plane defined by the foil leading edge ,1, and trailing edge, t, Fig 3. A suitable foil freely pivoted on a shaft running parallel to the leading edge can be shown to automatically adopt an angle a which gives a near optimum lift and a good lift/drag ratio. In this example, the foil pivots on its support shaft, and maintains z constant despite variations in the direction of motion of the shaft and the speed of the vessel through the water. This foil section must be symmetrical to operate well when moving in either direction.The shaft centre line thus lies in the same plane as the leading and trailing edges.

For small angles @ the combined lift and drag force can be considered to act through a fixed centre of effort (C. E.

Fig 3). The position of the pivot line (the shaft centre) with respect to the C.E. is crucial to achieve the desired automatic adjustment of angle of attack If the pivot line were coincident with the C.E., the foil would be "balanced", and stable over a range @ -Z 10 If the pivot line is fixed between the C.E and the leading edge as in a typical rudder, the resultant moment maintains @ = Oc unless displaced by an external force on the tiller.However, if the pivot line is between the C.E. and the trailing edge, offset by distance .-, the foil is unstable at f. = OJ and it rotates to increase @ and L until the foil starts to "stall".As this occurs the drag D increases and the C.E. moves toward the trailing edge until @ becomes stable. The angle at which stahility is achieved depends on the details of the foil design, but is near : =10ç.

This freely pivoting foil design has potential applicability to many other areas of fluid mechanics. As a further example, such pivoting foils can be substituted for the fixed blades of a screw propeller or turbine. This provides an automatic pitch adjustment in a very simple way. A nearly optimal lift force will then be maintained over a range of vessel speeds or shaft rotation speeds. The drag will be greater than that of an ideally controlled variable pitch system, but the simplicity should result in reduced costs, appropriate for small craft operating in sea and air. Pumps and fluid power generators (e.g. windmills) which need to operate in variable conditions are also likely to benefit from this invention.

Another embodiment of the invention is as kayak paddles in which two pivoting foils replace the two fixed blades.

These paddles are best used in a sideways sweeping action similar to existing fixed foil paddles, but the self aligning properties of the pivoting foils ensures an optimum lift force in use.

Steering of a boat driven by the system shown in Fig 1.

can be achieved by controlling the arc over which the shaft pivots on the pin bearing. If the average position of the handle is not central, the average forward force will act to one side of the centre line, and the boat will turn. In this simple unrestricted system, the foil can be made buoyant, so that the inclination of the shaft to the vertical ensures that it starts in the position shown in Fig 1, and that the foil produces a forward acting force when operated.

To turn tighter corners, some additional control of foil angle is required. By limiting the free rotation of the foil on the shaft the foil is forced to stall in one direction. The resultant drag will rapidly cause the boat to turn, whilst retaining forward drive on the opposite stroke. A rotatable pair of limit stops ,m, will provide this featre, Fig 4.

If now the stops are rotated through 180 , the foil will act in the reverse sense and the boat will move backward. Full control is thus achieved.

To make this operation more convenient, the limit stops ,m, can be mounted on a control rod ,r, which passes up through the hollow main shaft. An vindicating lever ,i, can then be used to turn the rod and to indicate the current control setting. Yet mor convenience can be provided by a separate tubular handle shaft, slid over the forward extension of the main shaft and allowed to rotate on it. A bevel gear or other suitable mechanism can then be used to turn the control rod and control indicator. flotation of the handle will then control direction of motion of the boat, both forward, backward and when turning.

Alternatively, the limit stop can be a rod which slides through the support shaft to one side or the other. This intercepts a block mounted on the end of the foil to limit the rotation. A similar rod near the handle can be connected by wire links to provide control. It is then easy to operate the sliding stop whilst roving. Once again this will limit the range of rotation of the foil in one direction to ensure a high drag force, and consequent steering force.

In this case a separate limit stop is required to determine if forward or backward motion is to occur. This stop can also be made controllable from the handle. A simpler version would require the device to be lifted into the boat before resetting for ths other direction.

To allow the device to be used in shallow water, a third pivot can be provided, by hinging the block in which the shaft bearing pin rotates, about a line parallel to the top of the transom. The handle can then be lowered, raising the foil and reducing its depth in the water.

Claims (9)

1 A means of propulsion for boats which uses a hydrofoil oscillated from side to side at the stern, the foil being allowed to rotate about the shaft on which it is mounted in such a way as to ensure that it aligns itself to give a substantially constant angle of attack and to provide a large lift force and small drag force

2. A foil propulsion system as claimed in Claim 1 wherein the oscillatory motion is achieved by a shaft pivoting about a nearly horizontal axis perpendicular to the top edge of the transom, bent above the pivot point and controlled by a side to side motion of a handle mounted on the end of the shaft at a convenient inboard position.

3. A foil propulsion system as claimed in Claims 1 or Claim 2 wherein the shaft support block is itself allowed to pivot about a horizontal axis parallel to the top edge of the transom.

4. A foil propulsion system as claimed in any preceding claim, wherein the angle through which the foil can rotate on it's mounting shaft may be limited by mechanical means to enforce a fully stalled condition when moving in one direction but not the other, thereby steering the boat.

5. A foil propulsion system as claimed in any preceding claim wherein the angle through which the foil can rotate on it's mounting shaft is limited to ensure that the direction of the propulsive forces is controlled, either forward or backward.

6. A propulsion system using a screw propeller or turbine wherein the blades comprise self adjusting foils, pivoting on shafts projecting from the central boss, mounted in a position which ensures that each foil aligns itself at a substantially constant angle of attack to produce a large lift force and small drag force.

7. A foil propulsion system as claimed in Claim 6, used to move craft on or in any fluid, especially water and air.

8. A foil propulsion system as claimed in Claim 6, used to pump fluid.

9. A foil propulsion system as claimed in claim 1, used to rotate a shaft connected-to a generator, thus extracting energy from a moving fluid, and converting it to another form of energy, such as electricity.

9 A foil propulsion system as claimed in Claim 6, used to rotate a shaft connected to a generator, thus extracting energy from a moving fluid, and converting it to another form of energy, such as electricity.

10 A propulsion system for boats such as canoes and kayaks ,wherein two self adjusting foils are mounted each end of a paddle shaft held across the boat so that each foil is used in turn to propel the boat by a sideways sweeping action.

Amendments to the claims have been filed as follows 1 A means of propulsion or energy conversion, which use one or mor symmetric section foils immersed in g fluid, each mounted on a cylindrical shaft whose This liss in the plane of symmetry of the foil; where the foil Is free to rotate about the shaft over a range of angles which includes the desired operational angles.A suitably mourted, self aligning foil requires no additional mechanical constraints to achieve a substantially constant, non-zero angle of attack between the direction of it's motion relative to the fluid and it's plane of symmetry. Lift forces are then developed orthogonal to the direction of potion of the foil relative to the fluid, which are much larger than the drag forces par allel @ to the direction of.

motion.

2. A means of propulsion for watercraft using a self aligning foil as claimed in claim 1. Forward motion of the craft is achieved by oscillatory motion of the shaft in a direction substantially crthogonal both to it's axis and to the motion of the craft.

3. A foil propulsion system as claimed in claim 2 wherein the oscillatory motion of the part of the shaft supporting the foil is achieved by use of a pivot bearing near the centre of the shaft. A pivot pin fixed to the craft can then be used as a fulcrum. A handle, mounted on the @pp@site end of the shaft to that used to support the foil, can then be used to provide the required cscillatory motion of the shaft 4. A foil propulsion system asclaimed in claim 3 wherein the shaft is hent in are @r more places. This sl@ows the fixed pivet bearing and @perator's handle to be conveniently placed with the foil well immersed in the water.The bent shaft geometry can then be designed to achieve the desired mechanical adv@ntage of foil motion to handle mation.

5. A foil propulsion system as claimed in any preceding claim wherein additional mechanical means may be applied by the user to limit the rotation of the foil on the shaft to a defined range of angles. By this means the user can inhibit the self allg@ing action in one or more directions to provide steering and control of the forward or backward notion of the craft.

6. A propulsion system using a screw propeller or turbine wherein the blades comprise self adjusting symmetric foils as described in claim 1, mo@nted on shafts projecting from a central boss.

7. A foil propulsion system as described in claim 6, used to propel craft in or on any fluid, especially water and air.

8. A foil propulsion system as claimed in claim 1, used to pump fluid.