Hand-held sail
United States Patent 3924870
A small hand-held and hand-controllable sail may be used by an ice skater or the like for propulsion. The sail includes a spar arrangement for supporting the sail in a suitable aerodynamic configuration which is operative when the sail is held to leeward of the skater. The spars are arranged so that when held by the skater, the center of effort of the sail is disposed behind the location where the skater holds the structure so that it has a natural tendency to head up into the wind. The angle of incidence of the sail is controlled by means of a control stick connected to the forward end of the spar arrangement. The control stick extends aft and on the windward side and is operated by the user's other hand. The attitude of the sail about a horizontal axis is also controlled through the control stick by means of cables which extend from the stick to the opposite spars. The various parts of the device are easily disassembled for compact, lightweight storage and handling.
US Patent References:
Folding skate sail
Sprinkle - May 1932 - 1859178
Sail control device
Melges - December 1952 - 2620760
Sails and rigging of boats
Duerr - January 1955 - 2699136
Sail for skater
Bowman - May 1957 - 2793870
SKATE SAIL
Goldberg - October 1973 - 3768823
Folding skate sail
Sprinkle - May 1932 - 1859178
Sail control device
Melges - December 1952 - 2620760
Sails and rigging of boats
Duerr - January 1955 - 2699136
Sail for skater
Bowman - May 1957 - 2793870
SKATE SAIL
Goldberg - October 1973 - 3768823
Inventors:
Spivack, Mayer (Watertown, MA)
Kern Jr., Fred R. (Lexington, MA)
Kern Jr., Fred R. (Lexington, MA)
Application Number:
05/393989
Publication Date:
12/09/1975
Filing Date:
09/04/1973
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
114/102.110
International Classes:
A63C3/00; B63B35/79; B63H9/06; B63B35/73; B63H9/00; A63C3/00
Field of Search:
280/11.37S 244/153R 9/31A,31D,31R 114/102,103,39
Other References:
"Sails by Watts" Yachting Magazine, January 1963, pg. 41..
Primary Examiner:
Friaglia, Leo
Assistant Examiner:
Smith, Milton L.
Attorney, Agent or Firm:
Bookstein, Arthur Z.
Claims:
Having thus described the invention, what we desire to claim and secure by Letters Patent is
1. A hand-held aerodynamic propulsion device comprising:
2. A device as defined in claim 1 wherein said first grippable means is located forwardly of the center of effort of said sail.
3. A device as defined in claim 1 wherein said sail is substantially symmetrical about a central chordal line.
4. A device as defined in claim 3 wherein said second grippable means is connected to said frame at a point along said line of symmetry.
5. A device as defined in claim 4 further comprising:
6. A device as defined in claim 5 further comprising:
7. A device as defined in claim 5 wherein said cross piece is bowed away from said sail on the windward side thereof.
8. A device as defined in claim 3 further comprising:
9. A device as defined in claim 3 further comprising:
10. A device as defined in claim 9 further comprising each of said indicia having two perpendicular axes of symmetry.
11. A device as defined in claim 1 further comprising:
12. A device as defined in claim 1 further comprising:
13. A hand-held aerodynamic propulsion device comprising:
14. A device as defined in claim 13 wherein said second grippable means is pivoted to said apex region.
15. A device as defined in claim 14 wherein there are only two of said spars, said spars being arranged to diverge rearwardly from said apex.
16. A device as defined in claim 14 wherein said second grippable means is elongate and further comprises:
17. A device as defined in claim 13 further comprising:
18. A device as defined in claim 17 wherein said means for securing said collars comprises:
19. A device as defined in claim 18 further comprising:
20. An aerodynamic propulsion device comprising:
21. A device as defined in claim 20 further comprising:
22. A hand-held aerodynamic propulsion device comprising:
23. An aerodynamic propulsion device comprising:
24. A device as defined in claim 23 further comprising:
25. An aerodynamic propulsion device comprising:
26. An aerodynamic propulsion device as defined in claim 25 further comprising:
27. An aerodynamic propulsion device as defined in claim 25 further comprising:
1. A hand-held aerodynamic propulsion device comprising:
2. A device as defined in claim 1 wherein said first grippable means is located forwardly of the center of effort of said sail.
3. A device as defined in claim 1 wherein said sail is substantially symmetrical about a central chordal line.
4. A device as defined in claim 3 wherein said second grippable means is connected to said frame at a point along said line of symmetry.
5. A device as defined in claim 4 further comprising:
6. A device as defined in claim 5 further comprising:
7. A device as defined in claim 5 wherein said cross piece is bowed away from said sail on the windward side thereof.
8. A device as defined in claim 3 further comprising:
9. A device as defined in claim 3 further comprising:
10. A device as defined in claim 9 further comprising each of said indicia having two perpendicular axes of symmetry.
11. A device as defined in claim 1 further comprising:
12. A device as defined in claim 1 further comprising:
13. A hand-held aerodynamic propulsion device comprising:
14. A device as defined in claim 13 wherein said second grippable means is pivoted to said apex region.
15. A device as defined in claim 14 wherein there are only two of said spars, said spars being arranged to diverge rearwardly from said apex.
16. A device as defined in claim 14 wherein said second grippable means is elongate and further comprises:
17. A device as defined in claim 13 further comprising:
18. A device as defined in claim 17 wherein said means for securing said collars comprises:
19. A device as defined in claim 18 further comprising:
20. An aerodynamic propulsion device comprising:
21. A device as defined in claim 20 further comprising:
22. A hand-held aerodynamic propulsion device comprising:
23. An aerodynamic propulsion device comprising:
24. A device as defined in claim 23 further comprising:
25. An aerodynamic propulsion device comprising:
26. An aerodynamic propulsion device as defined in claim 25 further comprising:
27. An aerodynamic propulsion device as defined in claim 25 further comprising:
Description:
BACKGROUND OF THE INVENTION
Our invention relates to improvements in hand-held sail propulsion devices, which may be used by ice skaters and the like. A number of devices have been proposed and employed in the prior art to utilize the wind to propel a skater. While these devices have been characterized as "sails" they have typically functioned more like a kite in which the air flow is turbulent or "separated" on the leeward side of the sail rather than as a true sail in that the air flow is laminar or "attached". They are held to the windward side of the skater who leans, with his back and shoulder against the leeward side of the sail. As a result, these prior sails have had relatively low L/D (lift to drag) ratios. The prior sails present a number of inherent difficulties. For example, they are large, heavy and awkward to handl. Because of this, they afford little means to control their attitude and/or operation. Because they are held on the windward side of the skater, their large size tends to obstruct the skater's vision. In addition, strong gusts of wind may tend to blow the skater over should he be unable to lean into the sail with sufficient strength. Also, because of the relatively poor aerodynamic characteristics of the prior devices, the range of skating directions is somewhat limited because of the relative inability to sail close to the wind. It is among the primary objects of our invention to provide an improved sail device which eliminates or minimizes the foregoing problems.
SUMMARY OF THE INVENTION
Our invention may be embodied in a sail which is approximately one-half the size of the prior devices which have been called skating sails. The sail includes a leading edge, or edges, which are maintained sufficiently rigid by suitable spars. The spars are connected by a crossbow which is secured, at its ends, to the spars. The crossbow and spars are arranged so that the center of effort of the sail is aft of the crossbow and also so that when in use, the crossbow is disposed in a somewhat vertical attitude. The skater holds the crossbow in one hand generally near its midportion with the sail to the skater's leeward side. With his other hand the skater grips a control stick which is secured to the spar arrangement at the forward or luff region of the sail. The control stick is used to control the angle of incidence and pitch of the sail to the relative wind and also, by cables which extend from the stick to the spars to control the angle which the sail makes with the vertical. The sail pattern and spars are arranged to support the sail so that when filled with wind it will define an airfoil shape which is adapted to maintain substantially laminar, unseparated flow on its leeward surface. The various parts of the sail and its supporting structure can be disassembled easily for compact storage.
It is among the objects of the invention to provide an improved hand-held sailing device which is held to the leeward of the user.
Another object of the invention is to provide a sail of the type described which is substantially smaller, lighter in weight and is much less awkward to handle than previous devices.
Another object of the invention is to provide an improved sail which utilizes the aerodynamic principles of an airfoil and which displays a relatively high lift to drag ratio.
A further object of the invention is to provide a sail of the type described which is considerably safer to use than prior devices.
A further object of the invention is to provide a sail of the type described which provides the user with substantially increased control over the attitude and operation of the sail.
Still another object of the invention is to provide a sail of the type described which allows the user to sense and feel the wind force and direction more accurately to therefore enable him to trim the sail more accurately.
A further object of the invention is to provide a sail of the type described which is much lighter and provides the user with substantially improved visibility than did the previous sails.
DESCRIPTION OF THE DRAWINGS
The foregoing and other objects and advantages of our invention will be understood more fully from the following detailed description thereof, with reference to the accompanying drawings wherein:
FIG. 1 is an illustration of the device as seen from the windward, operator's side;
FIG. 2 is an illustration of the device as seen from the front with its various parts shown in an operating configuration;
FIG. 3 is an illustration of the device as seen from the rear;
FIG. 4 is an illustration of the device as seen from above in FIG. 3;
FIG. 5 is an enlarged illustration of one type of apex joint usable with the invention;
FIG. 6 is n enlarged illustration of one of the sliding collars;
FIG. 7 is an illustration of a modified form of apex joint;
FIG. 8 is an illustration of the device as seen from the windward side showing a modified forward control member;
FIG. 9 is an illustration of the arrangement shown in FIG. 8 as viewed in plan; and
FIG. 10 is an illustration of some further modifications which may be incorporated into the device including a unique identification system and the manner in which streamers may be employed on the leeward surface of the sail.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in the drawings, our invention includes a sail 10 which may be made by using conventional sail making techniques. In the illustrative embodiment, the sail 10 is of generally triangular shape having an apex region 12 at its forward and a leach 14 which defines its rear edge. In the illustrative embodiment, the leading aerodynamic edges of the sail 10 defined a swept-back luff indicated at 16 and 16'. The sail 10 is designed so that when presented to the wind at a positive angle of incidence, the sail 10 will fill to define a suitably selected airfoil shape. The luff regions 16, 16' of the sail are supported by a pair of luff spars 18, 18' which are connected to each other at the forward end of the device at an apex joint indicated generally by the reference character 20. The spars 18, 18' diverge rearwardly from the apex joint 20 and are retained in sleeves 22, 22' formed at the luff region 16, 16' of the sail. The sleeves 22, 22' may be formed with their rearward ends closed with the sail and sleeves 22, 22' being drawn tightly over the spars 18, 18' by means of an apex line 24 suitably secured, as through a metal grommet, to the apex region 12 of the sail 10 which can be fastened firmly to an eyebolt 38 at the apex joint. The sleeves 22, 22' may be closed at their rear ends, as shown, or may be open and used in conjunction with outhauls to draw the sail tightly to the rear end of the spars.
In the illustrative embodiment the spars 18, 18' are maintained in a fixed angular relation to each other and are made rigid by a crossbow 26 which is secured, at its ends, by means of C-shaped collars 28, 28' to the spars 18, 18' respectively. The crossbow is bowed away from the sail 10 in an arcuate shape and serves as a handle by which the user may grip the bow 26. Usually, the bow 26 will be gripped at or near its midportion although it should be noted that one of the features of the invention is that the position where the user holds the crossbow can be varied to vary the attitude of the sail from a vertical plane should he desire this. For example, the user may grip the crossbow 26 slightly above its midportion which will cause the sail to assume an inclined attitude to the vertical in which a portion of the aerodynamic lift will be directed upwardly. The user may adjust the location of his grip so that the magnitude of the upwardly directed lift component substantially is equal to the weight of the device so that it may be self-supporting thus reducing fatigue of the user's arms.
As shown in FIG. 6, each of the C-shaped collars 28 defines an opening 30 through which the sail 10 extends. Each of the collars also includes a trunnion 32 which receives its associated end of the crossbow 26. Each end of the crossbow 26 has a hole formed therethrough to enable an eyebolt 34 to be passed through the aligned holes in the crossbow 26 and trunnion 32 to pivotally secure each end of the bow 26 to its associated collar 28, 28'. The crossbow 26 and the spars 18, 18' are secured in the operative configuration shown by a tension line 36 which is secured at each end to the eyebolts 34, 34' and which passes through eyebolt 38 at the apex joint 20. The line 36 preferably includes a detachable clip 40 at one end which facilitates easy assembly and disassembly in a manner described more fully below. The line 36 should be of a length so that it may restrain the collars 28, 28' and crossbow 26 from sliding along the spars 18, 18' rearwardly beyond a predetermined position. In this regard it may be noted that when in use, the aerodynamic forces acting on the sail tend to cause the spars to swing inwardly toward each other and the extent to which such inward swinging motion may occur is limited by precluding the spars 18, 18' from sliding forwardly through the collars beyond a predetermined point, as determined by the length of the line 36.
The invention also includes means for controlling the attitude of the sail by controlling the relative position of the apex 12 of the sail. For this purpose, a control stick 42 is located on the windward side of the sail and extends rearwardly from the apex joint 20. The control stick 42 may be pivotally mounted to the apex joint 20 and includes a pair of torque control lines 44, 44', each of which extends from near the midportion of the stick 42 to one of the C collars 28, 28'. The torque control lines 44, 44' are of substantially the same length and should be sufficiently long to enable the user to hold and manipulate the end of the stick 42 comfortably when the stick 42 is swung away from the sail to draw the lines 44, 44' taut. By holding the bow in one hand and the end of the stick 42 in the other, the sail can be manipulated to vary its attitude in relation to the apparent wind. The angle of incidence to the relative wind can be varied by manipulating cooperatively the bow 26 and stick 42 as can be the pitch of the sail. The angle which the sail makes with the vertical (the roll angle) also can be varied and controlled by manipulating the stock 42 to draw one of the lines 44, 44' taut and then urging the stick downwardly or upwardly depending on whether the roll angle is to be increased or decreased.
FIG. 5 shows one type of apex joint 20 which may be employed in the invention. It includes a bolt 46 which serves as a pivot and which is passed through a suitable opening in the forward ends of the spars 18, 18'. The end of the bolt 46 is rotatably secured to a fitting 48 which, in turn, is pivoted at 50 to the forward end of the control stick. Suitable spacers or washers 52 are located between the spars 18, 18' and about the bolt 46. This arrangement permits the spars 18, 18' to be pivoted with respect to each other in a substantially vertical plane and also permits substantially universal movement of the control stick 42. FIG. 7 shows another type of apex joint, shown as 20' which is made from a single piece of molded flexible plastic or rubber hose having spar sockets 54 and a control stick socket 56. The apex joint 20' should be made from a material which is sufficiently flexible to enable the control stick socket 56 to be flexed to the various possible configurations of the stick 42. It may include an eyebolt 38' for the same purpose as eyebolt 38 previously described.
FIGS. 8 and 9 show a modified form of a control stick arrangement which may be employed. As shown, it includes a control bar 60 which may be of V or U-shaped configuration shown having a pair of arms 62 which may be secured at their ends to spars 18, 18' as by suitable fasteners such as bolts 64 with appropriate quick disconnectable fasteners such as wing nuts or the like. An end of each of the arms 62 thus is secured to one of the spars 18, 18' in a rigid connection. The control bar 60 extends outwardly from the spars at an angle such as that suggested in FIG. 9. In use, the operator holds the control bar 60 at or near its bight 66 with one of his hands. Because the control bar 60 is secured rigidly to the spars 18, 18' there is no need to employ torque control lines 44, 44' as with the previous embodiment. In some instances it may be desirable to connect the ends of the arms 62 to the spars 18, 18' to enable the bight 66 end of the control bar 60 to be swung about a generally vertical axis to enable the control bar 60 to be folded toward the plane of the said for storage or to enable the user to vary the horizontal distance between the control bar 60 and the cross bar 26 as he may desire.
In use, the sail is held to the leeward of the skater and, as shown in FIG. 1, would be held with the crossbow 26 in the user's right hand, the end of the control stick 42 in his left. Holding the sail in that manner would allow the skater to skate on a port tack. Should he wish to sail on the opposite side of the wind he can raise the sail over his head to his other side and then switch hands so that the crossbow 26 is held in his left hand and the control stick 42 held in his right. He can then skate on a starboard tack. Because the center of effort of the sail is located aft of the bow, the sail will tend to head up into the wind during such switching of tacks and will develop relatively little, if any, lift which otherwise might tend to pull the sail from the skater's hands. It may be noted further that it is preferred to hold the sail in an attitude in which it is at a slight angle to the vertical. As described above, holding the sail at a slight angle or roll directs a small component of the lifting force upwardly so that the weight of the sail is supported by aerodynamic lift. This reduces the weight of the sail which the skater must support and minimizes fatigue of his arms. The horizontally directed lift component must, of course, be resisted by the skater and it may be desirable in some instances for the skater to lean away slightly from the sail, to windward.
The sail provides a number of advantages over the "kite-type" of sails previously employed. Because the sail is held to leeward of the skater, it is significantly safer in that any sharp gusts of wind which cannot be resisted by the skater will not tend to blow him over. Instead, he can either spill the wind from the sail by releasing the stick 42 or, if the wind gust is sufficiently strong he can simply release the sail completely. A further advantage of our device is that because the sail is held to leeward, the airfoil surface is unobstructed by the skater which promotes laminar non-separated flow over the airfoil shape of the sail. The relative efficiency between our sail and those previously proposed is apparent from the fact that our sail can develop a propulsive force equal to prior skate sails having at least double the sail area. By providing a sail having a high lift to drag ratio, the sail can be made much smaller and the ease with which it can be manipulated and controlled is enhanced greatly.
A further aspect of the invention relates to the compact and easily storable nature of the sail. It can be easily brokendown and folded for simple storage. This may be done by unfastening one end of the line 36. The C collars 28, 28' can slide along their respective spars 18, 18' while the spars are folded toward each other. For example, the collar 28 would slide toward the apex joint 20 and the collar 28' would slide away from the apex joint 20. When folded, the line 36 can be wrapped about the sail structure to furl it into a lightweight, compact, easily storable package.
The invention may include further features such as the provision of visually distinguishable indicia on the opposite upper and lower end of the sail to enable others to determine at a glance, and from a distance, whether the skater is on a port or starboard tack. For example, the indicia may comprise different colors on the opposite ends of the sail or may include streamers or the like. Alternatively, one of the ends may be marked with P to indicate that when that end of the sail is up the skater is on a port tack. Similarly, the other end of the sail may be marked with a S to indicate that the skater is on a starboard tack.
Still another aspect of the invention relates to a unique system by which the sail may be provided with symmetrical identification symbols which will appear substantially the same whether the sail is held on a port or starboard tack. FIG. 10 shows a sail having such identification markings from which it may be seen that each of the symbols is symmetrical both about a horizontal and vertiical axis. The symbols may include various combinations of numbers, letters, geometric figures or other symbols which are symmetrical both about horizontal and vertical axes and define a palindrome. In addition, the symbols preferably are arranged on the sail so that they substantially lie along the axis of symmetry of the sail. While the foregoing arrangement is preferred, there are some symbols which, while not perfectly symmetrical about both horizontal and vertical axes, are symmetrical about one axis and will be readily identifiable and if presented inverted. For example, the symbol delta (Δ) would not present precisely the same appearance on both port and starboard tacks although it would be readily identifiable in either case. It is important, however, in any event, that whatever the symbols selected, they are arranged in a palendromic configuration.
While the significantly reduced size of the sail minimizes the obstruction to the user's view, the obstruction may be reduced still further by fabricating the sail from a transparent material such as a suitable plastic sheet or the like. In addition, when the sail is made from a transparent material or has transparent windows, it may be desirable to secure lightweight streamers, some times called "woolies" to the leeward surface of the sail at various locations to provide the skater with an indication of the character of the airflow over the leeward surface of the sail. The skater can determine whether the airflow over the leeward surface is substantially laminar or whether it has separated and become turbulent. The woolies 68 are made from light-weight material such as yarn and can be located by tape or the like as desired along the surface of the sail. It may be noted that because separation over airfoils typically tends to begin near the trailing edge of the airfoil, it would be desirable to at least include some woolies 68 approximately one-third of the chordal distance from the trailing edge.
Still another feature of the invention may relate to the inclusion of a line, suggested in phantom by the reference character 50 in FIG. 1 to enable the camber of the sail to be varied. The line 50 may be secured to the rear ends of the spars 18, 18' and may be adjustable length to draw the ends of the spars slightly toward each other. This will tend to reduce the camber of the sail and may provide better control in higher winds.
The foregoing description of the invention relates primarily to a sail structure which is generally triangular in shape having an apex at its forward end and rearwardly divergent spars which form a swept-back configuration. The invention may be utilized in other sail shapes having suitably supported leading edges or leading edge. In this regard it is not strictly necessary to have the apex swept-back configuration shown. The sail structure should, however, be symmetrical so that it presents substantially the same configuration to the wind whether on a port or starboard tack.
It may be noted further that the arrangement for connecting the crossbow with the spars may be modified from that previously described by eliminating the C-shaped collars 28, 28', and instead simply securing the ends of the crossbow 26 to the spars 18, 18' with a simple through-bolt connection. This would also eliminate the requirement for the line 36. While the originally described embodiment is preferred because it increases somewhat the versatility of the sail structure, the more simplified technique for securing the crossbow 26 to the spars may be preferred because of its lesser cost.
It should be understood that the foregoing description of the invention has been intended to be merely illustrative thereof and that other embodiments and modifications may be apparent without departing from its spirit.
Our invention relates to improvements in hand-held sail propulsion devices, which may be used by ice skaters and the like. A number of devices have been proposed and employed in the prior art to utilize the wind to propel a skater. While these devices have been characterized as "sails" they have typically functioned more like a kite in which the air flow is turbulent or "separated" on the leeward side of the sail rather than as a true sail in that the air flow is laminar or "attached". They are held to the windward side of the skater who leans, with his back and shoulder against the leeward side of the sail. As a result, these prior sails have had relatively low L/D (lift to drag) ratios. The prior sails present a number of inherent difficulties. For example, they are large, heavy and awkward to handl. Because of this, they afford little means to control their attitude and/or operation. Because they are held on the windward side of the skater, their large size tends to obstruct the skater's vision. In addition, strong gusts of wind may tend to blow the skater over should he be unable to lean into the sail with sufficient strength. Also, because of the relatively poor aerodynamic characteristics of the prior devices, the range of skating directions is somewhat limited because of the relative inability to sail close to the wind. It is among the primary objects of our invention to provide an improved sail device which eliminates or minimizes the foregoing problems.
SUMMARY OF THE INVENTION
Our invention may be embodied in a sail which is approximately one-half the size of the prior devices which have been called skating sails. The sail includes a leading edge, or edges, which are maintained sufficiently rigid by suitable spars. The spars are connected by a crossbow which is secured, at its ends, to the spars. The crossbow and spars are arranged so that the center of effort of the sail is aft of the crossbow and also so that when in use, the crossbow is disposed in a somewhat vertical attitude. The skater holds the crossbow in one hand generally near its midportion with the sail to the skater's leeward side. With his other hand the skater grips a control stick which is secured to the spar arrangement at the forward or luff region of the sail. The control stick is used to control the angle of incidence and pitch of the sail to the relative wind and also, by cables which extend from the stick to the spars to control the angle which the sail makes with the vertical. The sail pattern and spars are arranged to support the sail so that when filled with wind it will define an airfoil shape which is adapted to maintain substantially laminar, unseparated flow on its leeward surface. The various parts of the sail and its supporting structure can be disassembled easily for compact storage.
It is among the objects of the invention to provide an improved hand-held sailing device which is held to the leeward of the user.
Another object of the invention is to provide a sail of the type described which is substantially smaller, lighter in weight and is much less awkward to handle than previous devices.
Another object of the invention is to provide an improved sail which utilizes the aerodynamic principles of an airfoil and which displays a relatively high lift to drag ratio.
A further object of the invention is to provide a sail of the type described which is considerably safer to use than prior devices.
A further object of the invention is to provide a sail of the type described which provides the user with substantially increased control over the attitude and operation of the sail.
Still another object of the invention is to provide a sail of the type described which allows the user to sense and feel the wind force and direction more accurately to therefore enable him to trim the sail more accurately.
A further object of the invention is to provide a sail of the type described which is much lighter and provides the user with substantially improved visibility than did the previous sails.
DESCRIPTION OF THE DRAWINGS
The foregoing and other objects and advantages of our invention will be understood more fully from the following detailed description thereof, with reference to the accompanying drawings wherein:
FIG. 1 is an illustration of the device as seen from the windward, operator's side;
FIG. 2 is an illustration of the device as seen from the front with its various parts shown in an operating configuration;
FIG. 3 is an illustration of the device as seen from the rear;
FIG. 4 is an illustration of the device as seen from above in FIG. 3;
FIG. 5 is an enlarged illustration of one type of apex joint usable with the invention;
FIG. 6 is n enlarged illustration of one of the sliding collars;
FIG. 7 is an illustration of a modified form of apex joint;
FIG. 8 is an illustration of the device as seen from the windward side showing a modified forward control member;
FIG. 9 is an illustration of the arrangement shown in FIG. 8 as viewed in plan; and
FIG. 10 is an illustration of some further modifications which may be incorporated into the device including a unique identification system and the manner in which streamers may be employed on the leeward surface of the sail.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in the drawings, our invention includes a sail 10 which may be made by using conventional sail making techniques. In the illustrative embodiment, the sail 10 is of generally triangular shape having an apex region 12 at its forward and a leach 14 which defines its rear edge. In the illustrative embodiment, the leading aerodynamic edges of the sail 10 defined a swept-back luff indicated at 16 and 16'. The sail 10 is designed so that when presented to the wind at a positive angle of incidence, the sail 10 will fill to define a suitably selected airfoil shape. The luff regions 16, 16' of the sail are supported by a pair of luff spars 18, 18' which are connected to each other at the forward end of the device at an apex joint indicated generally by the reference character 20. The spars 18, 18' diverge rearwardly from the apex joint 20 and are retained in sleeves 22, 22' formed at the luff region 16, 16' of the sail. The sleeves 22, 22' may be formed with their rearward ends closed with the sail and sleeves 22, 22' being drawn tightly over the spars 18, 18' by means of an apex line 24 suitably secured, as through a metal grommet, to the apex region 12 of the sail 10 which can be fastened firmly to an eyebolt 38 at the apex joint. The sleeves 22, 22' may be closed at their rear ends, as shown, or may be open and used in conjunction with outhauls to draw the sail tightly to the rear end of the spars.
In the illustrative embodiment the spars 18, 18' are maintained in a fixed angular relation to each other and are made rigid by a crossbow 26 which is secured, at its ends, by means of C-shaped collars 28, 28' to the spars 18, 18' respectively. The crossbow is bowed away from the sail 10 in an arcuate shape and serves as a handle by which the user may grip the bow 26. Usually, the bow 26 will be gripped at or near its midportion although it should be noted that one of the features of the invention is that the position where the user holds the crossbow can be varied to vary the attitude of the sail from a vertical plane should he desire this. For example, the user may grip the crossbow 26 slightly above its midportion which will cause the sail to assume an inclined attitude to the vertical in which a portion of the aerodynamic lift will be directed upwardly. The user may adjust the location of his grip so that the magnitude of the upwardly directed lift component substantially is equal to the weight of the device so that it may be self-supporting thus reducing fatigue of the user's arms.
As shown in FIG. 6, each of the C-shaped collars 28 defines an opening 30 through which the sail 10 extends. Each of the collars also includes a trunnion 32 which receives its associated end of the crossbow 26. Each end of the crossbow 26 has a hole formed therethrough to enable an eyebolt 34 to be passed through the aligned holes in the crossbow 26 and trunnion 32 to pivotally secure each end of the bow 26 to its associated collar 28, 28'. The crossbow 26 and the spars 18, 18' are secured in the operative configuration shown by a tension line 36 which is secured at each end to the eyebolts 34, 34' and which passes through eyebolt 38 at the apex joint 20. The line 36 preferably includes a detachable clip 40 at one end which facilitates easy assembly and disassembly in a manner described more fully below. The line 36 should be of a length so that it may restrain the collars 28, 28' and crossbow 26 from sliding along the spars 18, 18' rearwardly beyond a predetermined position. In this regard it may be noted that when in use, the aerodynamic forces acting on the sail tend to cause the spars to swing inwardly toward each other and the extent to which such inward swinging motion may occur is limited by precluding the spars 18, 18' from sliding forwardly through the collars beyond a predetermined point, as determined by the length of the line 36.
The invention also includes means for controlling the attitude of the sail by controlling the relative position of the apex 12 of the sail. For this purpose, a control stick 42 is located on the windward side of the sail and extends rearwardly from the apex joint 20. The control stick 42 may be pivotally mounted to the apex joint 20 and includes a pair of torque control lines 44, 44', each of which extends from near the midportion of the stick 42 to one of the C collars 28, 28'. The torque control lines 44, 44' are of substantially the same length and should be sufficiently long to enable the user to hold and manipulate the end of the stick 42 comfortably when the stick 42 is swung away from the sail to draw the lines 44, 44' taut. By holding the bow in one hand and the end of the stick 42 in the other, the sail can be manipulated to vary its attitude in relation to the apparent wind. The angle of incidence to the relative wind can be varied by manipulating cooperatively the bow 26 and stick 42 as can be the pitch of the sail. The angle which the sail makes with the vertical (the roll angle) also can be varied and controlled by manipulating the stock 42 to draw one of the lines 44, 44' taut and then urging the stick downwardly or upwardly depending on whether the roll angle is to be increased or decreased.
FIG. 5 shows one type of apex joint 20 which may be employed in the invention. It includes a bolt 46 which serves as a pivot and which is passed through a suitable opening in the forward ends of the spars 18, 18'. The end of the bolt 46 is rotatably secured to a fitting 48 which, in turn, is pivoted at 50 to the forward end of the control stick. Suitable spacers or washers 52 are located between the spars 18, 18' and about the bolt 46. This arrangement permits the spars 18, 18' to be pivoted with respect to each other in a substantially vertical plane and also permits substantially universal movement of the control stick 42. FIG. 7 shows another type of apex joint, shown as 20' which is made from a single piece of molded flexible plastic or rubber hose having spar sockets 54 and a control stick socket 56. The apex joint 20' should be made from a material which is sufficiently flexible to enable the control stick socket 56 to be flexed to the various possible configurations of the stick 42. It may include an eyebolt 38' for the same purpose as eyebolt 38 previously described.
FIGS. 8 and 9 show a modified form of a control stick arrangement which may be employed. As shown, it includes a control bar 60 which may be of V or U-shaped configuration shown having a pair of arms 62 which may be secured at their ends to spars 18, 18' as by suitable fasteners such as bolts 64 with appropriate quick disconnectable fasteners such as wing nuts or the like. An end of each of the arms 62 thus is secured to one of the spars 18, 18' in a rigid connection. The control bar 60 extends outwardly from the spars at an angle such as that suggested in FIG. 9. In use, the operator holds the control bar 60 at or near its bight 66 with one of his hands. Because the control bar 60 is secured rigidly to the spars 18, 18' there is no need to employ torque control lines 44, 44' as with the previous embodiment. In some instances it may be desirable to connect the ends of the arms 62 to the spars 18, 18' to enable the bight 66 end of the control bar 60 to be swung about a generally vertical axis to enable the control bar 60 to be folded toward the plane of the said for storage or to enable the user to vary the horizontal distance between the control bar 60 and the cross bar 26 as he may desire.
In use, the sail is held to the leeward of the skater and, as shown in FIG. 1, would be held with the crossbow 26 in the user's right hand, the end of the control stick 42 in his left. Holding the sail in that manner would allow the skater to skate on a port tack. Should he wish to sail on the opposite side of the wind he can raise the sail over his head to his other side and then switch hands so that the crossbow 26 is held in his left hand and the control stick 42 held in his right. He can then skate on a starboard tack. Because the center of effort of the sail is located aft of the bow, the sail will tend to head up into the wind during such switching of tacks and will develop relatively little, if any, lift which otherwise might tend to pull the sail from the skater's hands. It may be noted further that it is preferred to hold the sail in an attitude in which it is at a slight angle to the vertical. As described above, holding the sail at a slight angle or roll directs a small component of the lifting force upwardly so that the weight of the sail is supported by aerodynamic lift. This reduces the weight of the sail which the skater must support and minimizes fatigue of his arms. The horizontally directed lift component must, of course, be resisted by the skater and it may be desirable in some instances for the skater to lean away slightly from the sail, to windward.
The sail provides a number of advantages over the "kite-type" of sails previously employed. Because the sail is held to leeward of the skater, it is significantly safer in that any sharp gusts of wind which cannot be resisted by the skater will not tend to blow him over. Instead, he can either spill the wind from the sail by releasing the stick 42 or, if the wind gust is sufficiently strong he can simply release the sail completely. A further advantage of our device is that because the sail is held to leeward, the airfoil surface is unobstructed by the skater which promotes laminar non-separated flow over the airfoil shape of the sail. The relative efficiency between our sail and those previously proposed is apparent from the fact that our sail can develop a propulsive force equal to prior skate sails having at least double the sail area. By providing a sail having a high lift to drag ratio, the sail can be made much smaller and the ease with which it can be manipulated and controlled is enhanced greatly.
A further aspect of the invention relates to the compact and easily storable nature of the sail. It can be easily brokendown and folded for simple storage. This may be done by unfastening one end of the line 36. The C collars 28, 28' can slide along their respective spars 18, 18' while the spars are folded toward each other. For example, the collar 28 would slide toward the apex joint 20 and the collar 28' would slide away from the apex joint 20. When folded, the line 36 can be wrapped about the sail structure to furl it into a lightweight, compact, easily storable package.
The invention may include further features such as the provision of visually distinguishable indicia on the opposite upper and lower end of the sail to enable others to determine at a glance, and from a distance, whether the skater is on a port or starboard tack. For example, the indicia may comprise different colors on the opposite ends of the sail or may include streamers or the like. Alternatively, one of the ends may be marked with P to indicate that when that end of the sail is up the skater is on a port tack. Similarly, the other end of the sail may be marked with a S to indicate that the skater is on a starboard tack.
Still another aspect of the invention relates to a unique system by which the sail may be provided with symmetrical identification symbols which will appear substantially the same whether the sail is held on a port or starboard tack. FIG. 10 shows a sail having such identification markings from which it may be seen that each of the symbols is symmetrical both about a horizontal and vertiical axis. The symbols may include various combinations of numbers, letters, geometric figures or other symbols which are symmetrical both about horizontal and vertical axes and define a palindrome. In addition, the symbols preferably are arranged on the sail so that they substantially lie along the axis of symmetry of the sail. While the foregoing arrangement is preferred, there are some symbols which, while not perfectly symmetrical about both horizontal and vertical axes, are symmetrical about one axis and will be readily identifiable and if presented inverted. For example, the symbol delta (Δ) would not present precisely the same appearance on both port and starboard tacks although it would be readily identifiable in either case. It is important, however, in any event, that whatever the symbols selected, they are arranged in a palendromic configuration.
While the significantly reduced size of the sail minimizes the obstruction to the user's view, the obstruction may be reduced still further by fabricating the sail from a transparent material such as a suitable plastic sheet or the like. In addition, when the sail is made from a transparent material or has transparent windows, it may be desirable to secure lightweight streamers, some times called "woolies" to the leeward surface of the sail at various locations to provide the skater with an indication of the character of the airflow over the leeward surface of the sail. The skater can determine whether the airflow over the leeward surface is substantially laminar or whether it has separated and become turbulent. The woolies 68 are made from light-weight material such as yarn and can be located by tape or the like as desired along the surface of the sail. It may be noted that because separation over airfoils typically tends to begin near the trailing edge of the airfoil, it would be desirable to at least include some woolies 68 approximately one-third of the chordal distance from the trailing edge.
Still another feature of the invention may relate to the inclusion of a line, suggested in phantom by the reference character 50 in FIG. 1 to enable the camber of the sail to be varied. The line 50 may be secured to the rear ends of the spars 18, 18' and may be adjustable length to draw the ends of the spars slightly toward each other. This will tend to reduce the camber of the sail and may provide better control in higher winds.
The foregoing description of the invention relates primarily to a sail structure which is generally triangular in shape having an apex at its forward end and rearwardly divergent spars which form a swept-back configuration. The invention may be utilized in other sail shapes having suitably supported leading edges or leading edge. In this regard it is not strictly necessary to have the apex swept-back configuration shown. The sail structure should, however, be symmetrical so that it presents substantially the same configuration to the wind whether on a port or starboard tack.
It may be noted further that the arrangement for connecting the crossbow with the spars may be modified from that previously described by eliminating the C-shaped collars 28, 28', and instead simply securing the ends of the crossbow 26 to the spars 18, 18' with a simple through-bolt connection. This would also eliminate the requirement for the line 36. While the originally described embodiment is preferred because it increases somewhat the versatility of the sail structure, the more simplified technique for securing the crossbow 26 to the spars may be preferred because of its lesser cost.
It should be understood that the foregoing description of the invention has been intended to be merely illustrative thereof and that other embodiments and modifications may be apparent without departing from its spirit.