Wind turbine device
A hybrid blade wind turbine device formed of at least a pair of straight outer airfoil blades, and a pair of inner helical wing blades, as supported for rotation within a safety protective cage structure, which wind turbine can be mounted in the vertical, horizontal, or other aligned operational positions. The inner helical half wing blades, being preferably somewhat shorter than the length of the outer airfoil blades, act to “regularize” the swirling wind regime flowing through the hybrid wind turbine, so as to maximize the efficiency of the outer airfoil blades. The helical half wing blades can be formed of individual segmented vane segments to provide improved operational capabilities for the overall hybrid wind turbine. To best harness annualized available wind conditions, the hybrid wind turbine can be customized, through modification of the number of vane segments, the selection of the specific shape of the outer airfoil blades, and the specific operational positioning of the outer airfoil blades. Alternatively, the helical halfwing blades can be formed as generally smooth-walled blades.
This patent application is a divisional of prior U.S. patent application Ser. No. 11/529,854, filed Sep. 29, 2006, still pending, and which is a divisional of prior U.S. patent application Ser. No. 10/629,370, filed Jul. 29, 2003, now U.S. Pat. No. 7,132,760.
II. FIELD OF THE INVENTIONThis invention relates to wind turbine devices, and more particularly to a universal-axis wind turbine device having a combination of multiple blade designs and a surrounding safety cage structure.
III. BACKGROUND OF THE INVENTIONVarious known designs of wind turbine structures include the common propeller blade type turbine, the so-called Darrieus blade type turbine, and the so-called Savonius blade type turbine.
Several Savonius or “S”-rotor blade designs are known, including those typified in Canadian Patent No. 1,236,030, EPO Publication No. 0040193 B1, French No. 961,999, German No. 187865, Japanese Publication No. 60-090992, Swedish No. 65,940, WIPO No. WO/99/04164, and U.S. Pat. Nos. 1,697,574 and 4,293,274. Each of those various Savonius-type blade designs have inherent limitations, including the limitation of noise during operation, excessive vibration during operation, a tendency to “run away” during elevated wind speed operations and often excessive drag created during rotation of the leeward or non-wind-gathering portion of the blade's movement.
Further, various Darrieus-type turbine blade designs are disclosed in U.S. Pat. Nos. 1,835,018, 2,020,900, 4,112,311, 4,204,805 and 4,334,823. However, these Darrieus-type designs also have inherent deficiencies, including that only the middle one-third of their blade length (at least for curved Darrieus blade versions) efficiently creates power; that the farther the distance from a curved blade to its axis of rotation, the greater the likelihood, especially in large scale power generation units, of a Darrieus type unit going into harmonic vibration and self-destructing; that all such Darrieus-blade type units are not self-starting, but need assistance in starting; and that in many wind conditions they can, on a periodic basis, use up more energy than they actually produce. Without proper controls and/or mechanical braking systems, Darrieus type units (like Savonius units) have been known to “run away” during elevated wind speed conditions.
Further yet, there have been attempts at combining a bucket-shaped Savonius-type drag blade system with a Darrieus-type curved lift blade system, as found in U.S. Pat. No. 3,918,839, and in Tanzawa, et al., “Dynamic Characteristics of the self-controlled Darrieus-Savonius Hybrid Wind Turbine System,” Proceedings of the CSPE-JSME-ASME International Conference on Power Engineering, Vol. 1, (1995), pp. 115-121 (“Tanzawa”). Yet in U.S. Pat. No. 3,918,839, significant difficulties arose relative to the operational, i.e., rotational, stability of the unit at high wind speeds. In Tanzawa, the addition of a Savonius bucket rotor to start the Darrieus rotor resulted in a reduction in the total turbine power and high braking torque at higher rotational rates. There were also the above-noted inherent problems present in all separate Darrieus and Savonius-type blade systems.
Most available wind turbine designs have problems of excessive noise and vibration, often self-destruct in high wind conditions, some require separate start-up, braking or stopping mechanisms, and many are not considered safe, readily insurable or building-code permitted, at least not for use in congested urban settings.
Thus, there has been an ongoing need for a wind turbine design that can be successfully incorporated into various building and tower structures, that produces minimal noise and vibration during operation, is capable of starting up and operating in each of low speed, steady, gusty, and high speed wind conditions, has a built-in self-regulation via an inherent structural geometry against over-speeding runaway conditions, is formed of blade designs that operate in essentially all wind conditions and produce moderate drag during full rotational operation, which is easy to manufacture and ship, and which can be housed in a safe operating package for use in crowded urban settings.
IV. SUMMARY OF THE INVENTIONThe present invention comprises in one form a hybrid wind turbine formed of both an inner helical screw-type blade design, with the individual helical blades formed of flexible segmented vane members operable as an air valve to allow air to pass between them when in their leeward (non-wind-gathering) position relative to the wind so as to reduce blade drag, and at least a pair of outer generally straight airfoil blades, which are of greater overall length than the inner helical blades. The entire hybrid blade combination is mounted for rotation within a protective cage structure to prevent unwanted entry of humans, birds and other objects in the blade path, and to help with secure, low vibration mounting, safety and insurability for urban settings.
The inner segmented helical screw-type S blades permit early start up of the hybrid turbine at low wind speeds. They also act as wind brakes at unduly high wind speeds to prevent runaway conditions. The outer airfoil blades enable the hybrid wind turbine to achieve high rotational speeds and resultant high energy production efficiencies at upper wind speeds. Together the helical and airfoil blades help maximize harvesting of wind energy. The present hybrid wind turbine operates with minimal noise and vibration, particularly since the segmented helical vane members operate at a rotational (varying torque) rate that does not exceed the speed of the wind by more than three and a half times and with a varying profile that always presents generally the same overall blade area to the wind. (This is in distinct contrast to standard “non-twisted” “S” rotors which, in essence, offer a alternating high- or wide- and then a low- or narrow-profile to the wind as they rotate.) This acts to substantially eliminate the “banging” noise and harmful action, especially in the support bearings, as found in many non-helical, non-twisted prior art Savonius-type turbine blades. The segmented helical screw blades, formed into two helical half wing blades, can be selectively formed with different numbers, and hence widths, of elongated vane segments, and with different spacing between such vane segments, depending upon the operational height at which the hybrid wind turbine will be mounted, and also upon the average annual wind speed available at that operational height. Additionally, both the cross-sectional shape of the outer airfoils, and their operational distance from the inner helical blades, can be altered for the same reasons. The inner helical blades can be alternatively formed as generally smooth-walled blades, i.e., formed via an edge-abutting or slightly overlapping series of flat panel segments but that in either case do not have edge separation during rotational operation.
The present hybrid wind turbine is of universal axis such that it can be mounted horizontally, vertically, or at any other near vertical or angular operational orientation as desired, and as specific mounting surface conditions may require. It can be used in urban settings, such as a single generation point with minimal transmission loss, such as for a so-called “zero energy” building. The overall shape of the present hybrid wind turbine can be cylindrical, conical, frustro-conical, or other shape. Further, a belt-drive or direct-drive type permanent magnet alternator, a belt-drive or direct-drive type generator, or alternatively, a belt-drive or direct-drive type air motor can be used to harness and convert the wind-generated power from the hybrid wind turbine.
The means by which the foregoing and other aspects of the present invention are accomplished and the manner of their accomplishment will be readily understood from the following specification upon reference to the accompanying drawings, in which:
Having reference to the drawings, wherein like reference numerals indicate corresponding elements, there is shown in
The cage 22 comprises a pair of generally concave hub ends 28a, 28b, each comprising a rigid outer support ring member 30. There is also a similar central cage support ring member 32. Each of hub ends 28a, 28b has a central journal hub 34 and outwardly-extending support arms 36 connected to ring 30. The helically twisted inner turbine blades may be journaled for rotation about a common axis and having an outer diameter 31 (
Safety cage 22 also comprises a series of elongated tie members 42, all of which are rigidly affixed, such as by threaded fasteners or welding, to the respective end and central support ring members 30, 32. Although omitted from
Preferably, the elongated airfoil blades 26a, 26b are formed as straight length blades, of a symmetrical cross section, with ends 25 that extend beyond the length of the inner helical blades 24a, 24b. Further, the overall length of the airfoil blades 26a, 26b is preferably with the range of some 105% to 150% greater than the overall length of the helical blades 24a, 24b, and more preferably, some 120% greater. This allows a substantial percentage of the available wind energy, especially at higher wind speeds, to be harnessed by the more efficient airfoil blades 26a, 26b. Advantageously, the somewhat shorter length of the helical blades (vs. larger airfoil blades) allows for use of concave-shaped hub ends 28a, 28b, which in turn allows room to house an associated energy transformation, power conversion and/or power generation unit, namely, for example a direct drive permanent magnet alternator 35 which may be attached directly to an electrical circuit (not shown), may be attached to a battery 37 for electrical storage, or the like. It will be appreciated by one of ordinary skill in the art that any suitable generator may be used as the alternator 35, including, for example, a belt-drive or direct-drive type permanent magnet alternator, a belt-drive or direct-drive type generator, or alternatively, a belt-drive or direct-drive type air motor.
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The attachment of the respective vane segments to a tubular support frame 70 will now be described. The support frame may be formed of tubular metal, plastic, or similar material. As depicted in
During rotation of the hybrid wind turbine formed with a segmented blade assembly, the separation distance SD can vary greatly depending on the material used for each respective vane segment, the running width W of each vane segment, the flexibility present in a given vane segment between its fixed longitudinal edge 66 and its free edge 72, and the given wind speeds (i.e., air pressure) being encountered by the wind turbine at any given moment.
For example, prototype units were made in accordance with the present invention, where the overall blade length for airfoil blades 26a, 26b was approximately 9.5 feet, the overall length of the helical half wings 62a, 62b was approximately 8 feet, the diameter of joined helical half wings (designated as DH in
It will be appreciated by one of ordinary skill in the art that even though specific examples of measurements are giving in illustrated embodiment above, various modifications in the dimensions of the components may be made without deviating from the teachings of the present invention. For example, the diameter of the outer airfoil blades 26a, 26b may be in the range of approximately 4 to 24 inches greater than that of the outermost edge of the inner half wing blades 24a, 24b, the length of the turbine mast 38 may be in the range of approximately 8 to 10 feet, the length of each half wing blade 24a, 24b may be in the range of approximately 6 to 9 feet, and the length of each airfoil blade 26a, 26b may be in the range of approximately 9.5 to 11.5 feet. Similarly, the half wing blades 24a, 24b may have a thickness in the range of approximately 0.03 to 0.25 inches, each vane segment 58a, 58b, 58c, 58d, 58e, 58f may have a width in the range of approximately 3 to I 1 inches, the diameter of the half wing blades 24a, 24b may be in the range of approximately 24 to 50 inches, and the cross sectional thickness of each airfoil blade 24a, 24b may be in the range of approximately 0.5 to 1.5 inches.
Thus, the segmentation-type combination turbine blade assemblies 54 and 60 have distinct advantages over the smooth surface-type blade assembly 23 (where the helical half wings are formed of only a generally smooth surface, or of edge-abutting flat panel sections creating a generally smooth surface, and without any segmentations and without otherwise having separate flexible vane segments with free-floating edges). For example, the elongated segmentation of the helical half wings in the present invention, which is the preferred embodiment, results in a substantial reduction in the air drag, contrary to what was previously present with Savonius type blade systems, including the twisted S-type helical versions thereof. By way of explanation, as the rear or leeward side of a non-segmented Savonius blade rotates into position against the wind, i.e., after just being in a wind gathering mode, it enters a non-gathering wind position. In that condition, the blade's concave back side presents a substantial drag against performance.
However, with the present invention's preferred segmentation structure, oncoming swirling wind is allowed to simply filter through air slots present in the back side of the cascading, overlapping, and segmented helical vane segments (e.g., vane segments 64a, 64b, 64c). This occurs due to the presence of the air slots provided via segmentation distances SD. (To visualize, this is not unlike the slots formed among and between the edges of a series of Venetian blinds as helically twisted 180° from end-to-end.) This allows one vane segment to create a vacuum effect to lift the free edge of the next adjacent vane. For example, it has been noted that at start up and at lower speed rotations, the respective vanes of the helically twisted blades of the present hybrid wind turbine 20, formed as having vane segments, tend to close on one another as they take in air, and then slightly open on the backside or leeward side of a cycle, i.e., the non-wind gathering side, to create elongated air slots and thereby reduce air drag by letting air through. However, as described above, when at full rotational speeds and particularly with very flexible vane material (e.g., rubber sheeting), the separation distances SD created between vane segments essentially stay constant throughout the full rotational cycle, i.e., during both the wind gathering and non-wind gathering cycle portions. In effect, the presence of the vane segments in the helical half wings helps substantially overcome the prior art problem of so-called “blade profile differentiation”, as was common with most Savonius blade systems. Thus, the segmented vane structure helps substantially increase the performance capability for the respective helical half wing portions of the segmented combination blade assemblies 54, 60, particularly in high speed winds, e.g., over 45 mph.
Then, during high operational, i.e., higher wind speed, conditions, the vane segments, even when in their wind-gathering condition, have the tendency to “open up”. This allows yet even more wind to flow through the air slots formed by the segmentation distances SD. This, in turn, results in allowing the segmented helical half wings to rotate even faster than they normally would, because they are under the rotational influence of the much higher operational speed airfoil blades 26a, 26b. Thus, the normally slower inner Savonius-type turbine blades have the tendency to get out of their own way, i.e., to increase overall hybrid turbine performance and efficiencies at higher wind speeds.
Then, further still, in extremely high rotational speed conditions, the vane segments actually act as an “airbrake”, relative to the airfoil blades, helping to prevent runaway conditions when operational safety might otherwise be of concern for the turbine 20. That is, under extreme wind conditions, the segmented helical half wings, even though the vane segments thereof are opened up with air slots, tend to continuously brake or slow down the otherwise excessively freely-rotating outer airfoil blades 26a, 26b, to keep the entire hybrid blade assembly 23 from over-speeding.
It has been found that in normal operation, the more segmented (i.e., more individual vane segments) the helical half wings are, the less efficient they are. This is because with such a segmented hybrid turbine, it takes more wind at start up to commence turbine rotation. However, once reaching higher operational speeds, the presence of the extra number of vane segments helps the inner helical turbine blades to, in effect, get out of their own way, thereby helping minimize their own drag effect on the more efficient outer airfoil blades. Thus, it will be appreciated that the choice of individual vane segmentation will depend on the projected operating conditions of the hybrid turbine. For example, in places with traditionally lower wind speeds, a smaller number, for example two vane segments with one air slot per helical half wing, segments may be utilized, while at locations with traditionally higher wind speeds, a greater number of segments may be utilized.
Further yet, it has been noted in smoke-type testing that the segmented helical vanes tend to, in effect, “standardize” the turbulent air within any given gusty wind regime blowing through them, which has the result of greatly assisting the outer airfoil blades' performance. That is, as believed and understood, the segmented twisted vanes tend to organize (or perhaps better stated as “regularize”) the wind currents before they reach the respective outer straight airfoil blades. This has the effect of yet further increasing the efficiency of the hybrid wind turbine 20, as especially noted along the outer ends thereof, i.e., by maximizing the efficiency of the outer airfoil blades via standardizing the amount and flow pattern of wind currents that reach them.
Still further, it has been found via testing that by using straight length blades, rather than curved length blades, for airfoils 26a, 26b, when in combination with the inner helical blades 56a, 56b (or 62a, 62b), the overall efficiency and operational speed of the present hybrid wind turbine, in any given speed wind, is greatly improved. As to the form of attachment for the respective outer straight airfoil blades 26a, 26b, those blades, as preferably formed of a suitable extruded aluminum material, are welded via welds 75 into the end of the respective metal support struts 46, 48, 50 (see, for example,
Such a selected change in the radial positioning for the respective outer straight airfoil blades is quite advantageous. This is because the positioning of the outer airfoil blades 26a, 26b, can be customized for a given installation, all depending upon the expected available wind conditions and regimes. For example, when winds are normally of generally higher speeds, the airfoil blades are formed to have a smaller operating diameter. But when installed where wind conditions are normally of only modest speeds, the airfoil blades 26a, 26b can be positioned at a more outermost position. This approach recognizes that, while airfoil blades in the outermost positions can supply more angular momentum to the hybrid wind turbine, they can also tend to increase chances for unwanted vibration for the overall hybrid wind turbine.
Preferably, the smooth surface helical half wings 24a, 24b of combination blade assembly 23 (per
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In operation, the helical halfwing blades of the present hybrid turbine blade invention (whether of smooth-walled or vane segment type) commence rotation quickly, i.e., with as little as 4 to 6 mph wind. Thus, the inner helical half wing blades 24a, 24b quickly start the overall hybrid wind turbine 20 into rotation. Thereafter, the straight airfoil blades 26a, 26b begin rotating, again as initially powered by the helical blades, and then at higher wind speeds they start harnessing wind and generating power at their much higher efficiency level, i.e. at their higher blade-tip-velocity-to-wind velocity ratio.
Through testing it has been found that there is an optimum ratio of the width WT (see
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It will be appreciated that the two hybrid wind turbines 20-1 and 20-2 may be combined in a number of different ways, and in a number of different configurations. While it is preferable that the turbine mast of each hybrid wind turbine 20-1 and 20-2 be mounted so as to operate separately and independently, it will be understood that the two masts may be joined so as to form a combined, elongated central mast. Similarly, the various components associated with the hybrid wind turbines 20-1 and 20-2, may be combined or separated as desired, including having a single alternator, a single battery, or the like.
From the foregoing, it is believed that those skilled in the art will readily appreciate the unique features and advantages of the present invention over previous types and designs of wind turbines and blades therefore. Further, it is to be understood that while the present invention has been described in relation to particular preferred and alternate embodiments as set forth in the accompanying drawings and as above-described, the same nevertheless is susceptible to change, variation and substitution of equivalents without the pressure from the spirit and scope of this invention. It is therefore intended that the present invention be unrestricted by the foregoing description and drawings, except as may appear in the following appended claims.
Claims
1-89. (canceled)
90. A method of overcoming blade profile differentiation in a helical wind turbine blade having a windward side and a leeward side, comprising the steps of:
- forming a rotatably supported helically twisted blade to comprise a plurality of flexible elongated vane segments, wherein each vane segment has a fixed edge and a free edge, and the free edge of one segment at least one of partially overlaps and substantially abuts the fixed edge of the next adjacent vane segment; and
- raising the free edge of at least one vane segment up from the fixed edge of the next adjacent vane segment during rotation of the rotatably supported helically twisted blade, thereby providing an air valve opening to reduce air drag when the leeward side surfaces of the helically twisted blade are being periodically presented against the wind.
91. The method of claim 90, wherein during rotation, the free edge of each vane segment is adapted to rise up from the fixed edge of the next adjacent vane segment by a variable separation distance in the range of between approximately ⅛″ to ¾″.
92. The method of claim 91, wherein during rotational operation, the variable separation distance between the radially-outermost mounted vane segments is greater than the variable separation distance between the radially-innermost mounted vane segments.
93. The method of claim 90, further comprising the step of mounting the helically twisted blade to a substantially vertically aligned rotatable turbine mast.
94. The method of claim 90, further comprising the step of converting rotational energy of the rotatably supported helically twisted blade into electrical energy.
95. The method of claim 94, further comprising the step of converting rotational energy of the rotatably supported helically twisted blade into electrical energy utilizing one of a direct drive permanent magnet alternator, a belt drive permanent magnet alternator, a direct drive generator, a belt drive generator, a direct drive air motor and a belt drive air motor.
96. The method of claim 90, wherein the helically twisted blade is twisted from one end to the other end, through a twist rotation of one of approximately 45°, 90°, 180°, and 270°.
97. The method of claim 90, further comprising the step of mounting a plurality of substantially straight airfoil blades fixed for rotation with the helically twisted blade and rotatably supported therewith.
98. The method of claim 97, wherein the airfoil blades are longer than the helically twisted blade.
99. The method of claim 97, further comprising the step of converting rotational energy of the rotatably supported helically twisted blade and airfoil blades into electrical energy.
100. The method of claim 97, wherein the converting step comprises utilizing one of a direct drive permanent magnet alternator, a belt drive permanent magnet alternator, a direct drive generator, a belt drive generator, a direct drive air motor and a belt drive air motor.
101. The method of claim 97, wherein the helically twisted blade is twisted from one end to the other end, through a twist rotation of one of approximately 45°, 90°, 180°, and 270°.
102. The method of claim 90, further comprising the steps of lowering the free edges of the respective vane segments towards the respective fixed edges of adjacent vane segments when the leeward side is in position of taking in air, and raising the free edges up from adjacent fixed edges of adjacent vane segments as an air valve when the windward side is in position of being forced against wind, thereby creating reduced air drag by letting air flow from the leeward side through the separation air slots as formed between the respective raised free edges and fixed edges of the vane segments.
103. A wind turbine apparatus for harvesting wind energy, comprising:
- a helical blade journaled for rotation;
- the helical blade being separated into a plurality of lengthwise blade segments, each blade segment having a radially inward fixed edge, and a radially outward free edge, the respective free edges being adapted, during wind turbine operation, to rise up through a separation distance away from the respective fixed edges, the free edges thereby moving from a normal rest position to a full operating position.
104. The apparatus of claim 102, further comprising a turbine mast journaled for rotation and wherein the helical blade is carried by the turbine mast;
105. The apparatus of claim 102, wherein the free edge of a given blade segment radially overlaps the fixed edge of the next adjacent blade segment.
106. The apparatus of claim 102, and an aerodynamically shaped nose element mounted on the fixed edge of the respective blade segments so as to help reduce air drag.
107. The apparatus of claim 102, and at least a pair of airfoil blades fixed with and located radially outward of the helical blade.
108. The apparatus of claim 107, wherein the overall length of the airfoil blades is in the range of approximately 105% to 150% of the overall length of the helical blade.
109. The apparatus of claim 107, wherein two airfoil blades are carried by the turbine mast at diametrically opposed positions.
110. The apparatus of claim 107, wherein a plurality of airfoil blades are carried by the turbine mast at circumferentially symmetrical positions.
111. The apparatus of claim 107, wherein the airfoil blades are substantially straight.
112. The apparatus of claim 107, wherein the airfoil blades are radially positionally adjustable relative to the helical blade, to thereby help maximize wind harvesting depending upon the local wind conditions and the mounting height of the wind turbine apparatus.
113. The apparatus of claim 107, and a protective cage enclosing the helical blade and airfoil blades.
114. The apparatus of claim 102, wherein the helical blade is mounted in one of substantially horizontal, vertical, and angular alignment.
115-122. (canceled)
123. A method of maximizing wind energy harvesting by a wind turbine while minimizing air drag and over-speed conditions, comprising the steps of:
- mounting a helically twisted blade supported for rotation;
- mounting a plurality of substantially straight airfoil blades for rotation, wherein the substantially straight airfoil blades are mounted radially outwardly of the helically twisted blade and rotate with the helically twisted blade;
- wherein the helically twisted blade is adapted to operate in low wind speed conditions to start the rotation of the airfoil blades,
- wherein the airfoil blades and the helically twisted blade cooperate in mid-range wind speed conditions to rotate both the airfoil blades and the helically twisted blade,
- and wherein the helically twisted blade is adapted to operate in high speed conditions to produce an air drag to prevent the over-speed rotation of the airfoil blades and the helically twisted blade.
124. The method of claim 123, wherein the helically twisted blade comprises a plurality of flexible elongated vane segments, wherein each vane segment has a fixed edge and a free edge, and wherein in low speed conditions the free edge of at least one vane segment at least one of partially overlaps and substantially abuts the fixed edge of the next adjacent vane segment, to thereby assist in starting the rotation of the airfoil blades.
125. The method of claim 124, wherein in mid-range wind speed conditions the free edge of at least one vane segment variably raises away from the fixed edge of the next adjacent vane segment thereby providing an air valve opening to reduce air drag when the leeward side surfaces of the helically twisted blade are being periodically presented against the wind.
126. The method of claim 124, wherein in high speed conditions the free edge of at least one vane segment raises away from the fixed edge of the next adjacent vane segment thereby providing air drag to help prevent the over-speed rotation of the airfoil blades.
127. The method of claim 124, wherein during rotation, the free edge of each vane segment is adapted to rise up from the fixed edge of the next adjacent vane segment by a variable separation distance in the range of between approximately ⅛″ to ¾″.
128. The method of claim 124, wherein during rotational operation, the variable separation distance between the radially-outermost mounted vane segments is greater than the variable separation distance between the radially-innermost mounted vane segments.
129. The method of claim 123, further comprising the step of converting rotational energy of the rotatably supported helically twisted blade and airfoil blade into electrical energy.
130. The method of claim 129, further comprising the step of converting rotational energy of the rotatably supported helically twisted blade into electrical energy utilizing one of a direct drive permanent magnet alternator, a belt drive permanent magnet alternator, a direct drive generator, a belt drive generator, a direct drive air motor and a belt drive air motor.
131. The method of claim 123, wherein the helically twisted blade is twisted from one end to the other end, through a twist rotation of one of approximately 45°, 90°, 180°, and 270°.
Type: Application
Filed: Feb 19, 2008
Publication Date: Nov 6, 2008
Inventor: William S. Becker (Northbrook, IL)
Application Number: 12/070,677
International Classification: F03D 7/00 (20060101); F03B 15/06 (20060101);