GB2507773A - Continuous ring airfoil for turbine or propeller - Google Patents

Abstract

A wind turbine or propeller comprises a continuous band with an airfoil profile that follows wavy or annular coil (garter spring) shape. When the band rotates about its axis the airfoil presents a largely common angle of attack to the fluid flow. The pressure and suction surfaces of the airfoil swap sides of the band through a generally symmetrical transition across the peaks and troughs of the wave or radial minima and maxima of the spiral. The chord, band path, airfoil section and angle may vary around the path of the band to enhance its ability to entrain more fluid and expel it more judiciously in order to increase its effectiveness as a generator or propeller. The band can be retained about a central hub by spokes, cables or pylons 22or the tops of the waves can be connected to an external ring (figures 4-7).

Description

CONTIINDOUS BAND PROPELLER

The invcntion is a low turbulence fluid acceleration or dccelcration dcvicc.

FIELD OF THE INVENTTON

The present invention relates to a device which when rotated accelerates the ambieni Iluid medium as ii ii. were a propeller, hul which exhibits superior Iluid dynamics in avoiding tip vortex turbulence, duct wall turbulence and hub spin losses. As such it can also he driven by the movement of surrounding fluid in the manner of a kinetic energy reclaiming turbine.

BACKGROUND OF TIlE INVENTION

There are a grcat many embodimenis of propellers, impcllcrs and Uc likc performing a myriad of fluid pumping, blowing or energy reclaiming tasks, however all exhibit some disadvanlage in particular applications. Generally a rolating device either accelerates the fluid using centripetal force in the manner of a radial blower or uses Bernoulli's law to generate a pressure differential over an airfoil as demonstrated by a conventional propeller, in the first case centripetal blowers tend to be better at generating higher pressures, hut because of their commensurately high speed of rotation they create a lol 0!' Lurhulenee and hence noise and inefficiency. Conventiona' propellers are more efficient, hut suffer from tip vortices where high pressure air on the underside of the blade Lakes a shorL cut around Lhe tip Lo the low-er pressure air above it. In addition whereas the outer region of the blade sweeps a relatively large area, the inner region is less effective and tends to be inhibited by the large twist and angle of attack required to keep pace with the axial Iluid velocity and so is parlicularly compromised by changes in fluid or rotation speed.

Recently there have been a number ol innovations proposing propeUers that Form loops or twists to avoid the imposition of an external blade tip. 1hesc have been particLilarly developed br the wind lurhine industry, exhihiled by HAWT embodiments like the Loopwing', Gedayc', and Wind Wandlcr'. All of these continue thcir wing solution up to the hub or huh axis. As such they still exhibit the high angle of attack slirring clUed Ihat causes an axia' vortex and can operale ebicien1ly al only one specilic wind specdlrotation speed condition. Some also have significant axial depth thereby being unsuitable for mounting in the conventional manner of a propeller supported at one end and inslead require a frame with a long axis being supported at hoih ends.

It is also very desirable Ihal parlicularly lurhines and Lo a lesser exlenL propellers cntrain as much fluid flow as possible within as small a diametcr rotor as possiblc. thc concept of entrainment caused by a forward facing elliptical blade in the case of a generaLor is laughi by US Patent 6302652 Lhat proposes the same with elliptical bbrward swept blades, however that embodiment is difficult to build as centripetal force tends to hex the blades whereas this invenLion supports ihe lips by heing pan of Ihe conlinuous band.

OBJECTS OF THE TNVENTION

A principal object of this invention, therefore, is to provide an improved means to LransaLe shall rolalion mb axial fluid flow and the reverse.

Another object of the invcntion is to achicvc such translation with rcduccd Lurhulence and thereby enjoy less noise and improved efficiency.

Another object of thc invention is to offer a swap out upgrade to convcntional impellers or blade arrays with a more efficient and compact solution.

Slill anoiher object of the invention is to enable a fan to achieve a greater movcmcnt of air with less encrgy and with less noisc in a smaller diamcter.

A further object of the invention is to extract a greater proportion of kinetic energy from a moving fluid siream than currenily possible by entraining as much peripheral flow as possible.

Another objeci of the invenbion is to provide br an aubomalic pitch adjustment system for gcnerator cmbodimcnts.

A still further object of the invention is to enable such improved efficiency at low cosi and with a high degree of durability.

SUMMARY

This invention considers two ways of forming a continuous band that can bc profiled like an airfoil and used to force an axial fluid flow when rotated about it's axis.

Or similarly bc forced to rotate by an axial flow in the manncr of a generator. And all is achieved with a smaller diameter hand than the equivalent conventional propeller and wilhouL otherwise requiring a diffuser with il's site and encumbrance.

One lollow-s a wave (15) wiLh a radially inclined amplitude around a circular perimeter as shown in Fig. with peaks (17) and troughs (16) such that most elements of Ihe hand cooperate in accelerating a local fluid when the hand is caused Lo roLale about it's axis. this is bccausc thc band's airfoil has an angle of attack that is maintained relative lo the flow direclion even as the hand lollows iCs peripheral wave paLh. The other as shown in rcscmbles a strctchcd gartcr spring as shown in Fig. S in that the wavc is likc a coil who's axis substantially follows the circumference of a circle moving between maxima (20) and minima (2i). The difFerence between the Iwo is Ihat the Former is csscntially flat as shown in Fig. 5 -although a degree of thrcc dimcnsional twist can be added to facilitate a range of operating conditions as shown in Fig. 6 and to an even grealer extenl in Fig. 7 -while ihe garLer spring variant is nalurally three dimensional and so has dcpth that can be employed to enhance fluid entrainment which is particularly relevanl when considering turhine raLher Ihat propeller apphcalions. This garter spring form similarly scts it's airfoil to maintain a reasonably constant angle of attack to thc prevalent axial direction as the hand follows it's path.

The maximum viable angle of atlack varies in accordance with Ihe airfoil's proNe and local Reynolds number. As the chord reduces so does the Reynolds number. When acting as a propeller ihe angle of allack is an incremental addition to the setling angle required to accommodatc thc axial speed of thc flow through the rotating band, or when acting as a turbine it is subtracted. The setting angle is inversely proportional to the radial offset, increasing as it approachcs thc spin axis in the manner of a screw thread.

In order to ensure the hand accelerates/decelerates all of the fluid within it's spin area, as well as being effecled by the nd setting angle and Lhe raLio of local hand speed to wind speed, ihe chord must also vary proporlional to the degree of angular displacement between adi acent hand members of common radial offset. The further band elements have Lo Iravel the greaLer the chord has to be (being equivalent to having fewer Nades).

With conventional straight blades the speed ratio is constant for a given blade radius just as the angle between successive blades is constant, how-ever with Lhe wavy hand Lhis ratio is only constant at the single radial offset (5) where the angular displacement between hand elements is equal. At other radial offsets (4) and (6) alternate band blade elements have a different angular olisel in the dockwise direction Lo the anti-clockwise direction even as the total angle between waves or coils remains constant and equal to 361) degrees divided by the integer number of waves or coils in one circumference.

At the peaks and the Lroughs of the band waves the airibil morphs as shown in Fig. 3 such that the lower substantially flat surface (1) becomes the upper substantially curved surface (3) and vice versa, transitioning through a point where it's section is symmetrical (2). this ensures that the airfoil always shows it's curved upper surface facing the spin direction with the leading edge towards the flow when acting like a Lurhine being driven by Lhe flow and conversely facing opposite to the spin direction wiLh the leading edge away from the flow when acting like a propeller in causing the flow as in Fig. 3. Note that a different airfoil set-up is required to optimize performance br each condition as in order to work both as a propeller and a turbine the airfoil would need to be symmetrical about it's chord mid point normal such that the leading edge is the same shape as the trailing edge.

Wilh respeci lo the firsi wave' embodiment Ihe waves have Ihus far been described as occurring substantially in the radial plane perpendicular to the spin axis, but particLilarly at high tip speed ratios where the airfoil's combined angle o1 allack and sctting angle is small the transition through the symmetrical scction would leave thc chord very shori, compromising the band's effectiveness al preventing the lormalion ol tip vorticcs. This condition can be mitigatcd by introducing an axial offset to the path of the wave ahead of and behind the transition point such that viewed in a radial direction it lorms an "S" with it's centre being draw-n towards a more axial direction as show in Figs 6 and 7. In ordcr to maintain the flow of the wave's path the axial offset occurs in thc same direction ahead of both the wave's peak and trough, and then again in the reverse direction behind the peak and the trough.

When acting as a propeller, if the band is spinning anti-clockwisc from the front propefling fluid backwards, and the "S' loop at the peak slaris rearward and ends lbrward thcn a radial component of thc airfoil's lift vector tcnds to entrain fluid inwards on thc trailing side of the loop (furthest forward) rather than lust propel it axially. Similarly the how is enirained on the trailing side of Ihe Irough. Conversely when acling as a Lurhine hut with the same spin and flow direction, fluid tends to he entrained inwards ahead of Ihe wave peaks as ii does from in Iront of the iroughs. These elTecis are beneficial as in thc casc of the propeller they cooperate with thc natural reduction in flow cross sectional area as the fluid accelerates, increasing the propellers effective diameter beyond the band's diameter. In the case of a turbine it acts like a virtual venturi and countcracts the tendency for fluid to be deflected out of the turbine's path by the pressure rise in front of Ihe hand. These effects are dependeni on Lhe axial depth of the band.

The second spring' style of band with it's natural depth and enhanced flow entrainment improves Ihe effectiveness of the turbine al ingesling additional Iluid by cntraining external flow as shown in Fig. 1 (7) thercby incrcasing the reserves of kinetic energy the turbine can tap. In effect the increased flow concentrales ahead of Ihe band increasing the forward pressure.

On the exhaust side of the band (8) the opposite effect is achieved. Just as in front of the band the how is entrained inwards, behind the hand Ihe how is pushed radially outwards. us is again very helpful as in expanding the flow volume its pressure is reduced. The extracted power comes from the difference between the high pressure in Iront of the band and the low pressure hehind it, so reducing the exhaust pressure increases this differential and hence also the power.

A forward how Ibeusing cone and a rear how expanding diffuser is another mcthod of achieving this result, but by integrating thc actions of a diffuser within thc blade structure a more compact and efficient solution is achieved. The wavy blades in ehiect become a dynamic cone and diffuser, operating over a larger how seclion because of their sweep area and the improved flow control.

Parameters can be adjustcd to vary the degree of entrainment. The chord of thc hand can he increased such that a greater proportion of the blade is brought into use for radial cntrainment as shown on Fig. 1 where the band chord changcs between (9) -thin and (10) -wide. The concave part then does more work than the convex part therefore iniroducing a bias that favors entrainment.

1! used as a lurhine and Ihe transition poini is retarded lo Ihe Irailing side of ihe peaks and troughs then again the balance of lift vectors favors entrainment, or the airfoil usd1 can he adjusled such Ihal the angle of aLlack or genera] lilt effectiveness is increased in thc appropriatc entrainment region.

The spring' hand can also he biased in curvature such Ihal the coi] is nol round hut favors in the casc of a turbinc thc maintenance of the concavc curvature of thc backward facing portion (10) while the forward convex facing portion is flattened (9).

The hack concave curvature lacing mb the flow creales Ihe]ow radial pressure that cntrains flow whercas thc forward curvaturc facing into the flow would otherwisc servc to dispel flow radially. Consequently favoring the concave over the convex increases the net enirainmeni. In al] cases the converse app]ies when working as a propeller as shown in Fig. 2 wherc thc flow (11) is entrained by thc convex bladc portion (13) with thc concave blade porLion (14) thinned and Ilaitened]eaving Lhe flow to he exhausted largdy axially (12).

Many a]bernative emhodimenLs of Lhe hand's configuration are viable. Variations in the integer number of waves or coils per rev can be accommodated. The fewer the waves or coils, the grealer Lhe amplilude or coil diameler ihat can he supported wilhout unduly pinching the rate of curvature. Increases in amplitudc or coil diamcter arc appropriate where there is a preference for a higher speed ratio, which can then he balanccd by a smaller chord band and vice versa as shown in Fig 11 and from the back in Fig. 12.

The hand can he retained either internally or externafly. internal would he the most common preference where a series of spokes e.g. (22) can he employed to couple the undersides of the troughs to the huh. These spokes can he rigid like pylons or flexible like cables. in thc casc of spokes, if 2 spokes are uscd at the bottom of each trough it is desirable that they are arranged in pairs with a common vertex at the trough low point with the spokcs connecting to the hub at an anglc such that the torque component of the axial thrust on the turhine is equal and opposite to the torque generated by the band blade.

in the case of a propeller the spin can he powered from a simple core huh or similarly in thc case of a turbine, energy can be cxtractcd by a gcnerator at thc hub. Fig. 9 shows a 7 lobe band generator supported via spokes to a central hub. Fig. 10 shows two oF such turbines being connected together and pivoted at their combined C of (3 by a suitable tower for scrvicc as a wind turbine.

Particularly in the embodiment of a fan it may bc dcsirable for safety and aesthetics for the band to he driven externally, thereby leaving a completely empty core.

To Facilitate this a hoop (19) is deployed circumferential to the hand with pylon like connections connecting the hoop inwards to the peaks of the waves as shown in Fig. 4.

This hoop is then pinched between rollers with at least one of them powered thereby acting as a friction drive to spin the band by driving thc hoop tangentially. Other embodiments see the hoop attracted magnetically to the driven member, or coupling and bcing driven through the use of a magnctic gcar rather than friction.

The chord of ihe hand can he increased as can the huh diameler Favoring marine applications as in Figs 17. The hand diameter will he smaller than the equivalent propefler being an advantage in shallow water and where ihe propeller ads below ihe bottom of the hull. A further advantage for marine applications is thc natural weed shedding capability. The screw thread' Form of ihe band pushes hack any enirained weed or lines that might otherwise tightcn around thc shaft. This can be cnhanccd by a furthcr variation introduces a hias to the hand such that the wave assumes a saw tooth form as shown in Fig iS, with the peaks displaced to one side so they do nol lie centrally hetween thc troughs. The objcct hcing to vary thc rakc of thc blade to improve the airfoil effectiveness or weed shedding ability in the case of a marine propeller.

The band has bccn described as comprising of an airfoil profile following it's path wilh surface curvature transitions occurring al the peaks and the troughs, hui in addition aerodynamic dcviccs can be employed to further rcducc the band's drag, incrcase the lift without flow separation and reduce the trailing edge turbulence.

Biomimelics leaches thai the luhercks on the kading edges on humpback whale flippers can be mimicked on aero and hydro dynamic surfaces to reduce drag and increase the angle of atlack ihal can he sustained withoul the wing stalling. A Canadian company called Whalepower Corporation havc developed various embodiments of this concept but their main US Patent 6431498 is limited in it's scope by prior art. A further cmbodiment is herewith proposcd for thc lcading edgcs of thc band which promiscs significant benefits. The simulated tuhercle features extend passed the point of maximum ihickness on ihe hand's upper surface and blend mb bhe irailing edge.

DRAWINGS

the prescnt invention can best be undcrstood in conjunction with the accompanying drawing, in which: Fig.1 illustrates the hypothetical flow lines of a fluid through a garter spring type band blade configured as a generator; Fig. 2 illustrates the hypothetical flow lines of a Iluid through a garter spring type band blade configured as a propeller; Fig. 3 shows a full face view of a band blade with a radially inclined amplitude conligured as a propeller and idenlilies the morphing airloil section that occurs at a representative peak; Fig. 4 shows a similar hand blade mounled hy relaining an externally connecled ring to a driving mechanism in the manncr of a fan embodiment; Fig. 5 shows a side view of such a band, revealing it's thin profile: Fig. 6 shows a variani of such a hand wiLh a degree of twist imposed al the peaks and troughs; Fig. 7 shows a Further variant with a higher degree ol Iwisi imposed; Fig. 8 shows a generator configured garter spring type band with 9 orbits; Fig. 9 shows a generator configured garter spring type band with 7 orbits and retained to a hub by virtue of spokc pairs emanating from the troughs; Fig. 10 shows two of such band blades configured as turbines connected to a common masi to provide service as a wind turbine: Fig. I I shows a garler spring Lype hand with 5 orhils arranged as a generator connected to a hub; Fig. 12 shows Lhe same generalor eonhgured garter spring type hand 1mm Ihe rear; Fig. 13 shows a 7 orhil propeller configured garter spring Lype hand connecied Lo a hub; Fig. 14 shows the same 7 orbit hand from the rear; Fig. IS shows a 5 orhil propeller configured garter spring Lype hand connecied Lo a hub; Fig. 16 shows a propefler configured wide chord 5 wave hand attached to a huh with pylons: Fig. 17 shows a similar 5 wavc band connected to a largc hub in the manner of a marine propeller; Fig. 1 S shows a propcller configured asymmetric 5 wavc band in the manner of a saw tooth connected to a hub with pylons.

In the drawings, preferred embodiments of the invention are illustrated by way of example, it being express'y understood thai ihe descripLion and drawings are only br Lhe purposc of illustration and preferrcd designs, and are not intended as a definition of the limits of the invention.

PREFERRED EMBODIMENT(S) OF TIlE INVENTION Fig. 3 shows a wave hand blade configured as a propeller. This has 9 waves, although other numbers are possible, it heing preferred to have an odd number of waves in order Lo mitigaLe any weighL and balance issues. In Fig. 4 an embodimeni of Ihis type of band blade is shown (23) with 7 waves with the purpose of acting as a fan.

The band hiade is held hy shorl pylons to a circumscribing peripheral ring 09). Tn this case the ring has small magnets embedded in it with such magnets aligned axially with alternating forward facing polarities. In the drive assembly (18), two disks are conlained in a sealed box with a closed slol between them. The discs are driven hy an electric motor such that when the ring is inserted into the drive cavity they overlap the ring and consequently can force its rotation when they themselves rotate. By this means Ihe blade is caused Lu rotate.

Further rollers offset to either side of the drive point constrain the ring to roll about a fixed virtual axis.

Ic blade chord is set as appropriate for the spacing between successive blade elements of similar radial offset. Consequently as shown on Fig. 3 (4), when spinning clockwise the blade has a greater chord at (I) Ihan at (3). Only al Ihe mid radial oliseL (5) is the chord the same on both sides of the wave. Similarly at (6) the chord is greater on Ihe left Lhan on the right of the (sough.

The angle of attack is calculated to match the anticipated flow speed at a given rpm, the helix angle being set as appropriate for the radial offset. To this setting angle is added the angle of attack for a near optimum lift/drag ratio as suitable for the chosen airfoil such that flow separation does not occur over a significant part of the upper airfoil surface which would result in a staB and a signilicanL drop in the liii Lo drag ratio.

The area in Ihe eenLre of Ihe hand where no blades operate is neverLhdess a very useful space. Firstly it avoids that region where the blades angle would he so severe that Ihe hlades would act more as paddles and generate a vortex rather Ihan axial how.

Secondly it then provides for air to be entrained through it by the Venturi effect of the circumscribing how. In accordance wiLh Bernoufli's principle this reduces Ihe how speed but increases the flow volume, such additional volume not having been subject to any blade interaction is of a particularly smooth flow which is desirable for fan ventilation.

The wave nalure of Ihe band significantly reduces turbulence by avoiding the tip vortices that are the product of open ended propellers. The result is again a less turbulent flow with much less noise generation.

The hand is lightweight and smooth edged, and with it's peripheral ring sale Lo the touch. This obviates the need for external protective cages as required for impeller based fans, resulting in a more elegant and efficient product solution.

The band also has limited depth, so in the embodiment of a wall mounted unit as shown in Fig. 4 it can be folded back against the wall when not in use, thereby being no more obtrusive than a piclure frame.

In anoiher embodiment as shown in Fig. 10 two garter spring slyle Lurhines as shown in close up in Fig. 9 are mounted together by a horizontal member (24) such that they can share a common slewing and tilting pivot point. The advantage of mounting two turbines side be side is that they create a natural slewing torque as the wind veers to either side. The turbine that is most upwind creates a wind shadow over the turbine most down wind, and Lhe resulting higher ihrusl on Lhe upwind Lurhine causes ii to slew around unlil both turbines axes are normal to the wind direction. Furthermore ii lilt about the horizontal axis connecting the turbines (24) is permitted then the turbines will also he able to slew around this i1 the wind approaches from a lower or high aspect as may occur if mounted on a hillside or on an escarpment or roof Because the spring has depth, it can generate it's own how shadow when mounted individually rather than in a pair as previously described. the shadow reduces thc thrust on the downwind portion of the blade assisting in providing a torque to slew the blade hack to the optimum flow normal condition. This effect can he encouraged by permitting thc spring axis of rotation to veer relative to the hub axis, however because of the impact of gyroscopie precession it is most beneficially used to augment the usual slewing axis.

the turbines will perform as pcr the flow simulation shown in Fig. 1 where thc arger concave blade member (ID) causes additional flow to he entrained from the forward direction (7) thereby reducing the amount of flow that would otherwise blow around the turbine as a result of it acting as a pressure dam as with a conventional wind turbine. The flow being exhausted from the turbine will he turned towards a blade normal direction (8) and as such will he caused to expand by the increasing cross sectional area.

This reduces the pressure as per Bernoufli's principle, increasing the pressure differential between the front and the back of the turbine and hence increasing the energy that can be extracted by the blade band.

lb increase the effectiveness of this process, the convex part of the band (9) is flattened backwards to reduce the otherwise compensating opposite effect and it's chord is reduced with the same result.

The absence of any blade lips which wouki otherwise cause lip vorlices makes Ihe turbine operate more quietly and consequently also more efficiently.

The centra' area Ihal is not swept by any blades has coflaleral advanlages. Tt enables more of the entry flow to be entrained by the concave blade format where it does more good by conlrihuling useful addiliona flow where the blades work al Iheir best efficiency. It avoids the generation of a strong core vortex caused by the excessive pitch angle, large blade chord and low tangential velocity near the hub. It also avoids the slagnalion zone that lypically occurs behind ihe huh Ihat compromises Ihe exhausl flow by increasing the rearward pressure reducing the pressure differential from which power can he extracted.

A variation of the spokes arrangement creates an automatic pitch control system powered by the ceniripelal and axial lorces acling on the turbine. The spring blade is mouldcd using materials with some flexibility, enabling it to both compress and expand.

In use a dynamic balance is effected between the centripetal force tending to increase ihe garler springs diameter and axial ihrusl acting on Ihe whole band blade tending to fold the spokes backwards and reduce it. This balance is translated into a balance in the selling angle as strelching the spring reduces ii while compressing it increases it. In addition, when thc springs diameter reduces in order to maintain it's angular momentum its rate of rotation increases, .iust as increasing the diameter slows the rpm down. [his change in rpm in the manncr of a figure skater pulling in her arms to increase her spin rate can occur very quickly as the net rotational kinetic energy stays the same.

A gust will therefore reduce the spring's diameler so increasing the setling angle and torque and also the rotational speed so that more power can he extracted, just as a lull will increase the diameter, reducing the selling angle and drag and also the speed so cnabling more ready freewhccling without unduly loosing rotational momentum. fhc solution is superior lo an aulo piich thaI merdy rolales a conventional hade ahoul it's axis as it adjusts thc bladc twist as wcll as the setting anglc. it also reacts quickly to increase or slow the rate of spin. Changing the rate of spin is easier to translate into changing the power oulput Ihan merely changing the Lorque.

Differcnt mcans can be employcd to cffcct the compression of the spring with increasing axial thrust, for example a simple crank lever with pivoted pylons arranged such thai thrust loads pull the pylons inwards or inclined ramps thai move a carriage supporting the spokes or pylons in towards thc axis when displaced under increasing Lhrust load.

A furthcr embodiment employs thc torque acting on the band when driven by thc flow to effect a similar reduction in the spring hand's diameter, either separately or in conjunclion wiLh the axial Lhrust driven means.

More coils to the spring would also increases the ease with which the spring can he compressed or extended.

Other arrangements of wave or orbit numbers and permutations of design bias offsets and mounting options would be obvious to those skilled in thc art and arc thus considered in the scope of the present invention. l

Claims (13)

1. Whal is claimed is: I. A hand with an airfoil profile that foflows a continuous path like a wave substantially in the plane of a virlual disc moving around the circumference between it and a common radial offset such that when the band rotates about the disc's axis the airthil presents a largely common angle of attack to the fluid flow when moving heiween it's amplitude peaks and iroughs made possible by the fact thai al both the peaks and the troughs the upper surface and lower surfaces of the airfoil morph through a largely symmetrical transition to swap sides on the band.And where: a. The angle of aliack of the chosen airfoil is added lo ihe appropriate airfoil setting angle in the case of a propeller with the leading edge and upper surface of the airfoil facing away from the induced flow direelion.b. the angle of attack is subtracted from the appropriate airfoil setting angle in the ease of a generator with the leading edge and lower surface of the airfoil facing the flow direction.
2. 2. A band with an airfoil profile that follows a continuous path like a garter spring with it's axis moving around the circumference of a virtual disc such when the band rolales aboul the disc's axis the airfoil presenis a largely common angle of attack to the fluid flow even as it moves around it's path between it's radial maxima and minima made possible by the fact that at both the maxima and minima the upper surface and lower surfaces of the airfoil morph through a largely symmetrical iransilion Lo swap sides on the band.And where: a. The angle of attack of the chosen airthil is added to the appropriate airfoil setling angle in the case of a propeller wiih the leading edge and upper surface of the airfoil facing away from the induced flow direction.b. The angle of aLiack is subtracted from the appropriate airfoil setting angle in the case of a generator with the leading edge and lower surface of the airfoil facing the flow direction.
3. 3. A band as in Claim 1 where the width of the band representing the chord of the airfoil varies to account for the angular displacement between successive band elements ol' similar radial oliset such Lhat where the displacemeni is large Ihe chord is commensurately large and vice versa.
4. 4. A band as in Claim 1 where at the peaks of the waves the band is twisted about a radial direction due to an axial displacement of the band towards the flow direciion ahead oF the peaks and Lroughs and an axial displacemeni away from the flow direction behind the peaks and troughs.
5. 5. A hand as in Claim 1 where the holloms of the troughs are connected lo a ceniral hub by spokes or cables or pylons or the tops of the peaks are connected to an external ring.
6. 6. A hand as in Claim 2 where the radial minima of the coils are connected to a central hub by spokes or cables or pylons or the radial maxima of the coils are connected to an external ring.
7. 7. A hand as in Claim 2 where when acting as a generalor the rear concave part of the coil when facing into the wind has an enhanced chord and the forward convex part a reduced chord and when acting as a propeller the convex part is enhanced and the concave pan reduced.
8. S. A hand as in Claim 2 where when acting as a generator the rear concave part of the coil when facing mb the wind shows a full radial or elliptical curvalure while the forward convex part is significantly flattened and when acting as a propeller the convex part retains a high curvature while the concave part is flattened.
9. 9. A hand as in Claim 2 where when acting as a generalor the forward convex part of the coil when facing into the wind has an airfoil of a form and at an angle set to do tess work compared to the concave part and vice versa when acting as a propeller.
10. 10. A hand as in Claims I and 2 where the peaks of the waves or tops of the coils do not lie centrally hetween successive waves or oops hut are offset to one side generating a saw tooth' form where one side has a greater ramp angle than the other.
11. 11. A hand as in Claim 2 where the means by which the radial minima of the ganler spring are attached to the hub is permitted to extend radially when centripetal force stretches the garter spring thereby causing the outside diameter to increase.
12. 12. A band as in Claim 2 and/or Claim 11 where the means by which the radial minima of the garter spring are attached to the huh results in a reduction in the radial length of such means when the axial lhrusl loading increases thereby pulling the spring inwards causing the outside diameter of the garter spring to reduce such reaction overwhelming any unhalanced centripetal forces acting in the opposibe dineclion.
13. 13. A band as in Claim 2 and/or Claim it where the means by winch the radial minima of the spring are attached to the huh results in a reduction in the radial length of such means when Ihe lorque loading on the spring blade increases thereby pulling the spring inwards causing the outside diameter of the garter spring to reduce such reaction overwhe'ming any unbalanced centripetal forces acling in Ihe opposite direction.