GB2341355A

GB2341355A - Cars of very low fuel consumption

Info

Publication number: GB2341355A
Application number: GB9819838A
Authority: GB
Inventors: Brian Stapleton Stratford
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-09-12
Filing date: 1998-09-12
Publication date: 2000-03-15
Anticipated expiration: 2018-09-12
Also published as: WO2000015485A1; GB9819838D0; AU5874199A; GB2341355B

Abstract

A car has cabin boat-tailing almost entirely on the sidewalls 2, 3. The boat-tailing is sufficient for streamlined airflow to pass between the cabin, given some indentation, and the fairings 25, 26 which cover the rear wheels and suspension. The deeper indentation such as 28, 30 is below the boot floor. Correspondingly the roof "diverges", i.e. the centreline 4, 5 rises substantially and continuously, or nearly so, for the full length of the car from the windscreen rearwards. These features are combined <I>interdependently</I> with a structural shell, having only one routine entrance 6 for people rearwardly of the front seats and additionally a simplified axisymmetric retractable tail-cone 1. The low weight of the shell-based car justifies the slim fairings 25, 26; the tail-cone 1 eliminates the bluff base drag and provides the aerodynamic improvement of the car.

Description

CARS OF VERY LOW FUEL CONSUMPTION This invention relates to cars of very

low fuel consumption.

In some forms of the invention, such as in the main example described, three technical items are combined inierdependently. Each item could be considered to be from a separate technical subject, so that the total discussion is laid out as follows:- Part I Aerodynamic aspects of sidewall boat-tailing - and a summary of the total proposals;

Part H A lightweight car, Part III Retractable tail-cones.

The claims follow immediately after Part III.

Part I AerodyLlarnic aspects of sidewall boat-tailing - and a sununM of the total proposals.

Introduction

A well known feature of aeroplanes and birds is that their streamlining is not only around their wings and bodies, but it is also fiffly around their feather-edged trailing edges, on both their wings and bodies. Fish, basically, have the.same feature. If, however, instead of the thin, fully streamlined, feather-edged, trailing edges, there were an area of bluff base, the fish, the bird and the aeroplane would be pulled back by the wake flows behind the bluff base: these wake flows mix violently with the mainstream flow, the mainstream flow is around the wake, it flows at high speed rearwards in the opposite direction from the wake, and in the mixing it therefore "puns" strongly rearwards on the wake flow and, so, on the base.

Modem cars are becoming progressively more streamlined as they gradually reduce drag and fuel consumption. Nevertheless there is still a significant area of bluff base. Removal of the bluff base component of drag could in principle reduce the total aerodynamic drag to a small proportion of current conventional values. At steady high speed there would then be a large reduction in fuel consumption. In a broad sense, therefore, the objective in Part I of the present proposals has been to provide cars with fiffly streamlined flow, including over feather-edged trailing edges.

The objective in Part I, in more detail Obstacles discouraging the removal of blufihess drag may be shown to include the preferred wide seating arrangement of the passenger cabin, the preferred rear access to substantial luggage space, combined with length limitations for parking, garaging and urban driving, as well as the widths of the wheel spacing needed for stability. In addition cost and weight contribute, in that a very long sleek car could have less aerodynamic drag than a short bluff car, but would tend to be both more expensive, and heavier, with the heaviness causing higher fuel consumption.

In order to try to meet the above situation a retractable tail-cone, extendable and retractable while the car is moving, is discussed in Part Ill. However, as mentioned in Part III, there may possibly be problems in applying the tail-cone to a conventional high performance car. The most natural shape for a tail-cone for a conventional car seems to be close to twodimensional. The two-dimensional shape, it is felt, could perhaps introduce aero-elastic excitation, the construction could tend to be expensive and heavy in order to obtain sufficient strength and stiffness in a retractable device, the low energy "boundary layer" flow on the narrowing side-walls may be difficult to diiTuse, and there could be a tendency for the tail-cone to "swing" sideways, even if it were rigid, if the car turned rather sharply at speed. While in practice it may perhaps be found that none of these problems apply, or that if they do apply they may be readily solved, Part III points out that a tail-cone with an axisymmetric geometry would seem less likely to have such problems. The present proposal is therefore put forward partly to allow a high performance car to be adapted to an axisymmetric retractable tail-cone.

The second reason for the present proposal is to provide a design for a car which is slim within its own length, Le. a streamlined car streamlined everywhere including at and around its own thin trailing edge.

A third reason for the proposal is that it fits very well with the Part H proposals for low weight.

The first step in the aerodMarm c proposal The first step is that, on a car intended for ordinary purposes, aerodynamic "boat-tailing" of the cabin is almost entirely on the cabin side-walls, with the cabin substantially narrower, over its full height, at the rear of the car proper than it is at the driver's seat. In addition, wings cover any wheels and suspension that would otherwise become uncovered to the airflow, with the wings and undersurface being designed aerodynamically for reasonably streamlined flow in conjunction with the cabin.

In all the discussion the wheel and overall envelope planform of the car itself, without tailcone, is taken to be substantially conventional, in order to maintain ride quality and stability, as well as the usual ease of parking, garaging and urban driving.

"Boat-tailing' is a term sometimes used for the aerodynamic tapering, or the gradual decrease, of the cross-sectional area of a body towards the trailing edge. Conventionally on a car, or, more specifically, on a car which has a substantial amount of boat-tailing, the boat-tailing is carried out on the roof. Small amounts of boat-tailing are often carried out on the sidewall, but ordinarily to a smaller degree than is achieved in various current conventional cars by shaping the roof and rear window. The present proposal would be for the boat-tailing on the cabin of the car to be substantial and for almost all of it to be carried out on the sidewalls.

Despite the problems introduced by boat-tailing on the sidewalls there could be aerodynamic advantages additional to its present association with axisymmetric tail-cones. There is an advantage aerodynamically, at least in a fundamental sense, in that the full flow relevant to the analysis for a car includes the reflection in the ground, as in Figure 1. For this total flow, of car plus reflection, the plane of the ground becomes just a plane of symmetry. Consequently the relevant, fundamental, thickness aspect ratio for the flow may be related to twice the height of the car, divided by the width, rather than just the height to width ratio. That tends to make the width of the car become the "thickness" of the threedimensional body being analysed and twice the height become the "span". Then, rather than boat-tailing on the height, the width could be the more fundamental dimension aerodynarnicaNy for the application of boattailing.

The treatment of the roof has to take the sidewall boat-tailing into account. With sidewall boat-tailing the width of the roof decreases in its approach to the trailing edge, so tending to narrow and thicken the roof boundary layer, and it does so in conjunction with the edge flows at the sides of the roof and the difflusion in the region. Such a situation could tend to produce various undesirable three-dimensional flows and a core or cores of high loss flow opposing the diffusion. It is therefore suggested that the central meridional line of the roof rises rearwards, diagrammatically as shown by the upper broken line of Figure 2 - where the lower broken line represents the roof of a conventional car. Simultaneously there is a change in roof section shape, such that the roof leads to a tail fin, also as in Figure 2. The result is that each semi-span of the boundary layer which had approached on the roof is rotated to some extent with the local roof, in a controfied process, as the air moves rearwards, so that it crosses the trailing edge distributed, although in an imperfect manner, respectively on each side of the upper part of the tail fin. Such an arrangement could be more efficient than maintaining either a horizontal roof, or a downward sloping boat-tailing roof, if the sidewalls of the cabin are specified as the main walls for the cabin boat-tailing. It may be noticed in Figure 2 that corners are introduced at the base of the tail fin. The situation will be discussed briefly, and modified, at the end of Part 1, so allowing the corners to be eliminated, as well as smoother distributions of thickness achieved along the---span-,with "span" used for the type of geometry as in Figure 1.

From the above reasoning the present main proposal, of substantial boattailing on the sidewalls, is made almost exclusive, in the sense of almost all of the cabin boat-tailing being specified as being on the side walls. The side view of all such cars would tend, therefore, with appropriate qualifications, to be characterised by the rising fine and tail fin general appearance of the upper broken line of Figure 2.

The preceding discussion describes the general direction in which the aerodynamic design is taken. However in Figure 2, an additional, local, modification has been adopted, indirectly for structural reasons. The structural arrangements include the rear near side doorway to the rear seats, for a 4 seat car, becoming the routine access for all the seats. The internal access between the doorway and seats has been eased by various modifications, including adding headroom. That has influenced somewhat the roof shape shown in Figure 2. In that Figure the roof has been domed, slightly, even more than would have been suggested for aerodynamic reasons, at about the fore and aft position of the rear seat entrance, as well as slightly forward of that position. That modification will be discussed further in Part II. Another qualification on the above rather general discussion is that the change of section for the roof, especially given the blend, where necessary, with an axisymmetric tailcone, makes it more difficult to distinguish between roof and sidewall boat-tailing, although the objective remains as described.

The under surface of the car is not formally affected by the above arguments on boattailing. The under surface is taken to be derived from the various low loss requirements, such as for streamlining and for aerodynamic matching with the rest of the car, as well as from the more general space requirements.

Three intMretations of the proposal for sidewall boat-tailing.

In all of the present discussion the maximum cabin width is taken to be at a fore and aft position in the vicinity of the driving scat. The roof line broadly is taken as just discussed. The bonnet for simplicity is taken, very broadly, to be conventional, as is the planform of the wheels, with the sizing of the overall planform of the car (without tail-cone) being taken in the range of the middle to large sizes of the European market. Wing coverage, full streamlining, and full benefits of wing-body interaction are taken to be adopted as is found reasonable. The cabin sidewall boat-tailing is then used in the region to the rear of the position of maximum cabin width. It is assumed that the boat-tailing is used to the greatest reasonable degree possible, after allowance for unfavourable wing-body and wing-body junction effects, for transition shapes needed on the approach to the trailing edge, and for reasonable stability in side wind.

With the above general specification three representative interpretations of sidewall boattailing are suggested, linked to the value of the maximum cabin width adopted at about the fore and aft position of the driving seat.

The first interpretation is for the maximum cabin width to equal either the full width of the car, exclusive of mirrors, or almost the Rill width. That, in the particular version discussed here, gives a 4 seat cabin. The second interpretation is for a 2 seat cabin in the style of a small aeroplane, i.e. with the seats in line fore and aft, with a maximum cabin width equal to about half the width of the car. The third interpretation is intermediate between the first two, with the maximum cabin width equal to about three quarters of the width of the car. In this third interpretation, of the three quarters width, the seating is arranged primarily for one to two people in total, but is able to accommodate up to four on occasions. Each of the near side seats would perhaps be set back slightly behind the offside seats in order to allow plenty of -elbow space". In addition, say, the backs of the near side seats may fold down for conversion of the area to "office space" or supplementary luggage space.

The 4 seat cabin of the first interpretation would be adapted to an axisymmetric tail-cone, extendable and retractable while the car is moving, as will be discussed in the example.

The 2 seat interpretation is a car where the side wall boat-tailing gives essentially zero width of bluff base, at the trailing edge, achieved within the length of the car itself It therefore does not have a tailcone.

The car of intermediate width, to take four people on occasions, can be adapted to a small axisymmetric tail-cone. Alternatively it could be adapted to cones of other shape, given that only a small size would be required. Another possibility would be to accept a compromise:- of a reduced area of bluff base, without tail-cone. Such a compromise could be an easy way of providing rear area for bumper, registration plate and lights - in conjunction with a reasonably good aerodynamic performance. The more perfect aerodynamics of the other proposals can be more difficult to accommodate in such respects.

The 2 seat car, by itself, would have eliminated the bluff base component of drag, so that, if carefully designed, its total aerodynamic drag should be very very much less than for conventional cars. The same conclusion on drag holds for the other two cars, provided they are used in conjunction with their extendable and retractable tail-cones. The car of intermediate width cabin would have a significantly reduced drag compared with conventional, even without tail-cones.

Now a small fuel consumption, overall, requires preferably that the weight of the car should be low, as well as its aerodynamic drag. Consequently all the configurations discussed are suggested for use in conjunction with light weight designs, in particular with the proposals of Part H. Part II is introduced as its proposals appear to be complementary to those of Part 1 for the narrower cabin widths, while for the full width 4 seat cabin the two Parts appear to be interdependent.

For the narrower two cabin widths the wings between the front and rear wheels can slope downwards towards the rear, rather slowly, behind the front wheel fairings, in order to achieve streamline flow. The flow in the region is complex. Air can be brought down by the well rounded edge curve of the windscreen in a favourable wing body interference. Then, with the air meeting from each forward direction, the airflow would be designed to leave the rearward facing surface of the wing as nearly as possible as a rearward, steady and low loss flow, as determined by a three-dimensional nodal shape built into the surface of the wing. Such a rearward sloping wing will be found to fit the Part H requirements. It would give the additional areas of permanently fixed sidewalls in the positions that are most important for achieving low stress. It would also allow a convenient means of access to the cabin, when used in conjunction with firm step positions, handholds, and other items discussed in Part II.

Consequently the narrower two cabin widths seem to be suitable both for low drag and low weight.

The wider, 4 seat, cabin will be discussed in an example.

Consequently, as a result of the discussion so far, and of the example which follows, and according to the present invention, there is provided a car for ordinary purposes, with aerodynamic "boat-tailing" of the cabin almost entirely on the sidewalls of the cabin, and with the cabin substantially narrower, over its full height, at the rear of the car proper than it is at the driver's seat - and with the rear part of the cabin sufficiently narrow that, at least with some indentations, a streamlined airflow passage can be, and in fact is, formed between the cabin and each of the wings which cover the rear wheels and suspension and with the centre of the roof rising substantially, and continuously (or nearly so), particularly in comparison with a current conventional high performance car, for the full length of the car proper, from the windscreen rearwards.

Example

A specific embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings, in which:

Figure 2 is a side view, and Figure 3 is a plan view, and in which both Figures are schematic illustrations of a 4 seat car according to the present invention.

Example summaU Both diagrams show the 4 seat slim car with its retractable axisymmetric tail-cone I in its extended position, as for medium and high speed travel.

Within the car itself the boat-tafling is provided by the cabin sidewalls 2, 3 in Figure 3. Some airflow bypasses the rear wing fairings 25, 26, as indicated by the broken lines 27 to 30 of Figure 3, with the deep indentation being at a level below the floor of the boot. The roof in Figure 2 follows a generally rising line 4, (particularly in comparison with the current conventional lower broken line,) as well as a change of section, to the central and vertical tail fin 5. Fully streamlined flow is achieved over the whole car and tail-cone, in conjunction with nominaUy zero area of bluff base. Consequently the drag is very low.

Suitable arrangements allow routine access for all seats through only a single doorway, i.e. the near side doorway 6 in Figure 2. The doorway 6 is at the conventional fore and aft position to serve the rear seats, in a 4 seat car, and at a slightly raised level. Permanently fixed, and structural, cabin sidewal1s, of low stress, then reach up to the window line 7, in figure 2, on both sides of the cabin, other than for the single access doorway 6 on the near side. Moreover the windows are fixed, they are of a material of some significant structural ability, and are carefully bonded, or welded, into position, in order to provide secondary structure and so create a structural sheU, as discussed in Part II. Furthermore, the total load is limited to 400 kg, with any trailer limited to 100 kg out of the 400 kg, and additionally there is a trailer speed limit of 50 mph. Consequently the stressing is very low, so that very much more than usual of the car is in existing fight weight materials of reasonably low manufactured cost.

Optimisation gives a virtuous circle with very low drag, low total weight, small size components, easier strean-dining (particularly of the fairings at the rear wheels and suspension), low first costs, low maintenance costs, and a very low fuel consumption, as well as low external noise and improved crashwortliiness, all in comparison with conventional cars.

Exaniple - further detail The tail-cone is manufactured in a material woven from robust plastic thread, of substantially nonstretch properties at ordinary stress levels, and sealed by spray. The tail-cone is extended, while the car is moving, by applying internal air pressure; it is retracted, by tough, highly elastic, "bungee" type cords, when the pressure is released. Extension and retraction are both automatic once authorised by the driver. Various warnings apply both for the driver and for the following traffic. The tail-cone is mounted on the concave side of a light weight dished circular rear door, which is held, automatically, after closure, at several positions around the circumference, and which can be reversed, for security, by rotation at its spherical hinge.

The rear wheels have been moved aft relative to the rear seats, in comparison with the conventional layout, in order to ease the geometry, but a moderate distance has been retained between the rear wheels and the rear of the car to give distance for that part of the streamlinirig. The conventional layout taken as a datum for the present example has been chosen as one of the longer "estate" cars for the European market, in order to obtain a generous spacing between the rear seats and the rear of the car. Additionally, the wheels and suspension have been taken to be slimmer than conventional; that has been justified on the basis of all the factors claimed to give a reduction in the total, all-up, weight of car plus maximum load.

The flow velocities in the rear bypass regions of the wing-to-cabin body junction, represented by the lines 27 to 30, are kept low, as far as is reasonably possible, by local diff-usion just upstream. Reacceleration occurs as sharply as possible at the exit from the region, in order to keep a good flow on all surfaces. Such treatment needs a substantial flow area in the bypass. Consequently, the suspension is set as low as is mechanically acceptable, in order to lower the floor of the bypass passages. Similarly the suspension is set as much as possible into the width of wheel.

The tail-cone, also, is positioned as low as is mechanically acceptable and is given a slight downwards inclination, again as much as is mechanically acceptable. That helps to keep a good streamlined flow on the undersurfaces in that region, probably as well as in the bypass channels for the rear wheels and suspension. It also allows as good a rear view as possible for the driver.

In order to secure the above low positions for the tail-cone and bypass channels, one option with the present example of the car has its hydraulic rear dampers adapted to contain a substantial active, quasisteady, component of lift, for clearing urban, and other, bumps which occur at low speed. This option effectively converts the rear dampers to act additionally as lifting rams. It allows the prime low drag configuration to be designed as is required, for high speed, with low positions for the car and suspension, and with only small movements of the suspension. It could also give a low car position when stationary, for boarding and loading. Ilie arrangement would probably be appropriate in all options.

7he windscreen is well rounded at its sides. This feature continues up to and along the edges of the forward part of the roof, to the degree that is practicable, in order to try to reduce undesirable separating cross flows during side winds, in turn in order to reduce the side wind loads on the forward region of the cabin. The well rounded edges also ease the change of section to the rear fin and retractable tail-cone, and strengthen the structural shell.

Figure 4 shows that M a conventional car the sidewalls of the passenger cabin already have a strong curvature. In Figure 4, items 8 and 9 show the relevant sidewalls, in the transverse vertical cross section, and at the fore and aft Position of the driver. Consequently, on the proposed car, the sidewalls, after boattailing, and with the additional rounding of the corners at the edge of the roof as just discussed, blends fhirly readily with the pure circle, 10, M Figure 4, diagrammatically as required at the trailing edge of the car proper in order to match the axisymmetric, retractable tail-cone.

Acute corners at the rear between the wings and the cabin body are avoided, as far as possible, by sloping and curving upwards towards the body the floors of the passages between the body and the rear wheel fairings. In addition, a slight slope of the floors upwards towards the rear, for a given tail-cone position, reduces the exit areas of the passages and therefore economises in the flow required in the passages.

A very small horizontal tail plane at the rear of the tail-cone could help to dampen vertical vibration.

The sidewall boat-tailing of the cabin should improve the view from the side mirrors, therefore giving some compensation for the blockage of view from the tail-cone. However, two high internal mirrors may perhaps allow external mirrors to be unnecessary, given generous windows along the sidewalls. In the example, the central region of the windscreen has been moved forwards and upwards, slightly, in order both to facilitate the accommodation of two high internal mirrors and to improve the streamlining.

The rear bumper, lights and registration would all be as streamlined as is reasonably possible.

Ilie fuel tank is limited in size to give an ordinary maximum distance between fuel stops of 400 miles, or 640 km, in order to ease streamlining and the fire safbty of the light-weight structure. Fire safiAy is treated according to the best practice, by the use of fire bulkheads, detectors, extinguishers, waniings, the best possible choice of the positioning of the fuel tank, a careful choice of manufacturing materials and any other appropriate techniques.

In the example as described above, difficulties could be caused by the comers at the base of the fin. Consequently, in a modification, the fin trailing edge is given a near triangular section with generous base radii, while a matching fairing is built on to the otherwise axisymmetric tailcone. The fairing would be constructed from pressurised longitudinal tubes and a sheet covering, with the inter-spaces connected to a low pressure position on the car. Problem would be avoided by the small size of the fairing. Mechanical connection would be entirely to the main tail-cone, but without affecting the basically axisymmetric nature of the main cone.

Part H A lightweightt car Introduction

In many small aeroplanes of very high performance the pilot entered by climbing over the sidewall of the fuselage and then down into the cockpit. Most, or all, of the height of the sidewall alongside his cockpit could therefore be permanently fixed - and was so - and formed an integral and very important part of the structure of the aircraft.

In contrast, the ordinary modem car is designed more to suit our personal convenience. Each of the structural sidewalls which are on the aircraft are replaced, on the car, by one or more extremely large holes - the doorways through which we enter and leave the car. As a result the stress loads have to be transmitted, or redirected, around the holes (other than for the load parts which can go through the doors), the local loads are magnified, and an elegant steel structure is the usual result. The arrangement has obvious advantages and, by now, a century of global design and development has made this type of car so successful that it has become a part of our life. Recently, however, circumstances have perhaps become such that there is need for a change. The change, arguably, that is required would be to reduce the weight of the car in order to reduce its fuel consumption. Such a change, if large enough, and if combined with a substantially reduced aerodynamic drag, would make the car much more acceptable in its influence on resource conservation, on atmospheric pollution, on the possible atmospheric "greenhouse effect", and indeed on global strategic priorities. Consequently various possibilities which could provide such a weight reduction could perhaps become acceptable where, before, they were not.

The present proposal is concerned initially with emulating the many, small, very high performance aircraft in an "ordinary purpose" car, in order to reduce the weight of the car.

In fact it is found that a series of changes, which start from the above arguments, seems to give the most natural response to the structural requirements. The structural shaping which results then seems best accommodated by using it in conjunction with the aerodynamic proposals of Parts I and HL The present Rroposal The present proposal, in the first instance, is that in an ordinary purpose car there would be a substantial area of fixed structural sidewall on each side of the cabin additional to the area which is conventional in current ordinary purpose cars, and without additional cut- outs of comparable stress significance being made elsewhere, but that adequate access for the driver and passengers would nevertheless be arranged accordingly. The increased area of structural sidewall would be expected to lead, as a first step if necessary, towards reduced maximum stresses and a reduction in the weight of the car, possibly with the construction employing substantially greater use of existing light weight materials of reasonably low manufactured cost. Animproved crashworthiness could also be built in to the arrangements in order to improve the acceptability of the changes to potential customers.

The argument One of the more important considerations in determining the strength needed in a car is the load line during a front impact. The impact would be transmitted to the cabin by the structure and mass that are under the bonnet, so that, for efficient use of the structure available, the ideal sidewall structure for the forward part of the cabin would stretch from the car's lower edge up to about the top of the bonnet. To the rear of that position the top of the sidewall structure could decrease in height, as the requirement for stiffening gradually decreased, and as the impulse carried by the sidewall were both gradually redistributed and gradually decreased. Towards the rear, however, other directions of impact and other types of loading could take effect. Consequently a tentative shape for the upper edge of the sidewalls, taking an optimum based on structural considerations only, could be rather like line 11 in Figure 5. For comparison, line 12 represents the window line, i.e. the fine obtained by following and joining the lower edge of the windows of conventional cars, while line 13 represents the upper edge of the conventional fixed structural wall, or sill. For lines 11 and 13 the lower edge of the sidewalls is at the lower edge of the car, at the line 32. Also, for line 11 and in all the present discussion, structural framework for the windows and roof is taken to run above the upper edges discussed, in whatever manner is appropriate.

Now access would not be obvious if line 11 were used for the sidewalls. If instead, therefore, a fine were considered lower than fine 11, the structural requirements could be argued to be that the sidewalls should provide adequate stilfening, and should be able to transmit to other areas, very gradually, much of the impulse which the sidewall itself receives during the front impact. Consequently one could make a first proposal for a line 14, say, for the upper edge of a compromise side wall. A side wall which extended the full length of the passenger acconunodation, and from the lower edge of the car up to line 14, on both sides of the cabin, should meet, reasonably, the main structural requirements just suggested, while not being so difficult for access as for line 11. In addition, the doors with line 14 could carry the now conventional anti-intrusion bars. A fine something like fine 14 could therefore be a fairly good compromise solution. It would eliminate a significant stress concentration during front impact; also the front impact loading would pass through it in a much more direct manner than conventionally. There are, however, other possibilities, and for these, other considerations need to be taken into account.

Firstly, one might judge that the near side region of the car would be less vulnerable in front impact than would be the ofiEside, the offside being the closer to oncoming vehicles. Secondly, the front passenger scat would be less frequently occupied than the driver's seat. Thirdly, access to and from the car is less of a hazard, particularly to passing pedal cyclists, when carried out from the near side than from the offside. Fourthly, a very large amount of stiffening from one side wall could, to some extent, stiffen and stabilise the complete width of the car rather than only the part local to the side wall considered. And fifthly, line 14 is only a compromise - the function for which it was introduced - and a line that stayed higher for longer would be better.

From all of the above considerations a second possible proposal is as follows to provide routine access from the near side of the car only (with high level emergency exits on the offside as appropriate), to make the offside wall of the cabin a permanently fixed structural wall all the way from the lower edge of the car up to the window line 12, to make the near side wall of the cabin a permanently fixed structural wall up to the line 14, to provide anti-intrusion bars in the near side doors, and then to make near side access reasonably easy over line 14.

For this second proposal, as above, the access arrangements would include tipping seats on the near side, with the near side front seat more easy to slide than is conventional and being controllable both from all the seats and from standing just outside the car, the arrangement would also include generous firm areas with good grip for stepping as appropriate, and likewise generous handholds, the seats on the near side would have firm, and long, folding armrests to ease changing between standing and sitting, the upper edge of the fixed wall, i.e. at line 14, would be made smooth and would be kept clean by a generous overlap of the doors down over line 14, the floor would be kept reasonably free of controls and fixings, sufficiently for the driver and the rear offside passenger to be able readily to swing across to and from their seats, and the upper edge of the tipped seats would be "perchable" (half sitting). Finally, it would be arranged that the driver and passengers could be standing upright, if they so wished, during much of the entry or exit. To that end the floor and the lower part of the side wall structure would be built slightly wider than conventional to provide a permanent surface at about the level of the conventional sill and extending just fully over to the near side limit of the car width. A double foot-hold, or two foot-holds, at each entry, each giving direct support for almost the whole of each foot, (as on stairs in a house), would then be provided by putting two to four holes in the web of the girder type structure constituting the near side fixed structural sidewall. Correspondingly, the top of each of the two doors would extend, as an indentation, very slightly into the plane of the roof As the top of the doors and the roof edge are conventionally already well inset into the width of the car, the very slight indentation would be enough to allow the person to stand comfortably upright, with their feet securely in the two footholds or double foothold per doorway just described. Entry and exit should then be reasonably easy - although potential customers would still need to be consulted. The indentation into the roof from the tops of the doors would seem possible while allowing a reasonably smooth line for the frame carrying the windscreen and roof. The emergency exits to compensate the lack of offside doors could be arranged in the roof and through the offside windows.

Given that the addition to the cabin of a substantial area of fixed structural sidewall, particularly in the forward area, can allow a large reduction in stress, and given that, in principle, there may be various ways of making such a change, it is now required to consider the effects on the weight of the car.

The simpler and, probably, at first, the more readily acceptable proposal of the two so far discussed is the first arrangement, using the compromise line 14 on both sides of the cabin, with access modified ordy slightly and available on both sides of the car. With that proposal, however, the number of doors has not altered, their size is not greatly reduced, and it may be that, for a four seat car, the local redesigns of the structure would not save much weight. On the other hand if the second proposal were adopted, with access restricted to be on only the near side of the car, with say line 14 on the near side and line 12, i.e. the window line, used for the upper edge of the fixed structural wall on the offside, then 2 less doors and 2 less doorway fi-ames would be required, giving some saving in weight, although there would be load bearing wall in their place. The second proposal therefore gives some weight saving as well as a reduction in stress. Consequently the second proposal is examined further.

Now in Part 1 the aerodynamic proposals which are put forward in order to achieve low aerodynamic drag lead to a centre line roof line which rises in the rearward direction. Moreover, it would seem possible to adjust those aerodynamic proposals, and to combine them into the present discussion, in a manner that would achieve locally an even higher roof than in the aerodynamic proposals, and considerably higher than would otherwise seem reasonable in a high performance car, and to do so both on and near the centre line, and at the fore and aft position which would be required for a door that leads directly to the rear seats. The additional height could then be used as a rather dome shaped addition of headroom, for the purpose of creating, and justifying, in total, only a single routine entry for all the seats, with the entry being from the near side only, and from the more rearward position that directly serves the rear seats of a 4 seat car, ie at a position where the stresses are lower than at the front of the cabin. Furthermore, again for aerodynamic reasons, the 4 sear "slim ca?' of Part 1 has a small local area of wing. This local area of wing is ideally situated to act as a step for the single entry being considered. The 4 seat slim car also has a cabin which is already slightly contracted on width at the position of the single entry being considered, particularly at the roo sufficiently to allow a person to stand upright on the wing without requiring an indentation of the door into the roof and probably without requiring holes for footholds in the sidewafl. The 4 seat slim car aerodynamic proposal therefore seems to fit perfectly if used in conjunction with the present structural proposals.

The joint proposal is therefore for a single routine entry on the near side, instead of two entries from the near side, and stifi with no routine entry on the offside. The single routine entry would be at the conventional position that directly serves the rear seats of a 4 seat car. The floor would be kept as low as is acceptable in the required regions, without compromising the height of the near side fixed structural wall at the cut-out. There is then a saving of 3 doors and 3 doorway fi-ames compared with conventional, there is an excellent structural wall up to the window fine on the presumed more vulnerable offside, and a wall better than line 14 on the near side. The near side wall could reach to the window fine other than for the single entry discussed - given that the doorway has a suitable reinforcement frame - and the single routine entry could have a reasonably high level for its threshold. Access is discussed in the example. Additional emergency exits could be considered appropriate, perhaps through the roof or offside windows.

The above arrangement could give a useful reduction in both weight and stress.

Given that in the proposal just discussed the cabin construction would consist mostly of primary structural wall up to the window line 12, i.e. a structural wall which is integral with the rest of the structure of the car, including the cabin floor, with the whole being of fairly low stress, it is now suggested that the part of the cabin above line 12, i.e. the windows and roof, should be used either as "secondary structur&', or as a combination of primary and secondary structure, to convert the whole of the passenger cabin into a shell, a shell which is entirely joined up, and which is fairly close to being a completely closed envelope. In principle the windows and roof could be manufactured from mainly a single item of material and then joined very securely, by electrothermal welding, to the lower part of the cabin. An alternative technique is described in the example below.

The term "secondary structure" is used above to indicate material which is not itself highly stressed, but which nevertheless helps to retain the general shape of the car so that the main structure can be effective. The stress in the transparencies would be very very low.

Example, continued from Part I A specific embodiment of the present invention will now continue to be described briefly, by way of example only, with reference to the accompanying drawings, where:- Figure 2 is a schematic illustration of a car in side view, and Figure 3 is the corresponding illustration in plan view, with both illustrations having been used in the discussion of Part I.

Example, general summ In Figures 2 and 3 the car is for ordinary purposes, such as to be a family car or mainly for personal commuting. The routine access for the driver and passengers is made through one doorway only, positioned at 6 in Figure 2, on the near side. The modifications for access are discussed below. The doorway is at about the fore and aft position of the doors serving the rear seats in a conventional 4 seat car, and at a threshold height slightly higher than for the conventional doorway. Permanently fixed structural sidewalls are used up to the window fine 7 joining the lower edge of the windows - on the offside of the passenger cabin, and up to line 7 except for the cut-out for the doorway 6, which has a suitable reinforcement frame, on the near side. These fixed structural sidewalls are part of the main structure of the car and are joined integrally with that main structure, including with the floor of the cabin. They greatly reduce the maximum stress levels. The reinforcement for the doorway includes a rib sloping downwards rather like the forward parts of the discussion lines 11 and 14 of Figure 5.

The upper part of the car, i.e. above the window line 7, is a combination of primary structure and secondary structure. As such, this upper part of the car converts the total structure of the cabin into a single shell, a shell which is a fairly complete envelope, and which is fully joined up. The roo together with the mullions between the windows, is primary structure, and has a similar construction to the primary structure below line 7. The windows are nonopening and are secondary structure. They are constructed in a reasonably robust material; in addition, they are bonded, or welded, to the main structure at all peripheries, as well as being continuous across the mullions where practicable. The bonds are wide, with both materials at the bonds being suitably tapered on thickness to reduce the stress concentrations in the bond at the edges of the materials. The windows are protected, on at least their outside surface, against abrasion and ultra violet degradation by bonding to them a thin layer of glass, rather as for laminated glass.

With the above arrangements the main cut-outs in the structural shell are the main entry 6, the rear luggage access, probably circular or nearly so, a circular emergency exit above the driver, and a second emergency exit not yet determined. For such a shell the applied loading given by the use of the car is very light, especially after optimisation of the total car. Consequently a low weight construction and structure and a low weight car would be expected.

In the car of the diagram the above proposals are used in conjunction with proposals for very low aerodynamic drag, as given in Part I. The two sets of proposals complement each other. In particular, (i) the aerodynamic features make the critical, structural, single routine entry practicable, as discussed earlier in the text, while (ii) the mechanical features give low weight, and therefore slim wheels and suspension, so making the critical, rear, streamlining practicable.

(iii) The two sets of proposals therefore seem reasonably described as:

"interdependent'.

Optimisation of the total car, as mentioned in Part 1, gives a virtuous circle of very low stress loading, small Ughtweight components, much easier streamlining, in particular at the important fairings for the shin rear wheels and suspension, low total weight, low external noise, low cost, very low drag, very low fuel consumption, and improved crashworthiness, all in comparison with a conventional car.

Example, some detail The fin 5, at the rear of the roof line, is primarily for aerodynamic purposes. Structurally it is a local feature external to the more smoothly rounded structural shell. However, as a prominent second skin it provides added support in a rollover.

In the example the main structure is constructed of a robust existing lightweight material, about the most robust, and tough, such material available, of reasonably low manufactured cost, in the form of single or double sheets, ribbed, with the ribs positioned along the most important lines of force, as well as elsewhere in some positions to prevent vibration. The more important ribs, including around the main cut-outs, are reinforced with galvarused steel. In the more important areas, which include all the areas with steel reinforcement, the sheets are double and are joined by electrothennal welding across the ribs, to form a deep girder double skin construction suitably enclosing the steel.

Me use of the additional area of fixed structural sidewalls particularly at the front and lower region of the cabin, in comparison with conventional cars, and the consequent replacing of the stress concentration by direct compressive loading during front impact, should make the potential high strain of lightweight materials much more acceptable than it would be in a conventional type of design in that general area.

Three roof lines are shown in Figure 2. The lower broken line represents the roof for a conventional car. The upper broken line shows diagrammatically the roof which would have been used for the aerodynamic design of Part I had there been no special structural requirement. The actual roof line 4 then shows the dome-like-shaped headroom space added to ease the single routine entry required structumlly - and also to facilitate high level internal mirrors. A somewhat greater domed effect should be possible without undue compromise of the aerodynamics.

The higher roof 4 just discussed, as allowed by the aerodynamic design of Part 1, provides a further structural advantage, in that the structural shell is brought significantly above the level of the top of the cut-out for the doorway 6. The floor level in the central region is as low as is mechanically acceptable, In order to achieve both maximum shell strength and maximum head room.

And another advantage of the high aerodynamic roof is that a roll-bar type structure should fit in an ideal manner inunediately to the rear of the single routine doorway: - the roll-bar type structure would occupy space and height not required for headroom, the aerodynamic change of roof section discussed in Part I would fit the roll-bar structure, as would the rear reinforcing for the single main entry 6.

Figure 3 shows a diagrammatic view looking downwards at a horizontal cross-section of the car taken at the height where the cabin width is greatest, i.e. slightly higher than the top of the wheel arches. The broken lines show passages for airflow, at a height mostly below the floor of the boot. The lower surface at entry to these passages form wings, on which one position is shown pinpointed at the dot and circles 15, 16 in Figure 3 and, in Figure 2, at the dot 17 representing the same position, and irrimediately under the doorway 6. Consequently on the near side the wing is ideally placed for assisting routine extemal access to the doorway.

The internal modifications for the single routine doorway include features previously discussed in the text, as well as others:- various handholds, the back of the near side front seat tipping forward, a wider space between the central supports of the front seats, and the floor between those supports flat, clear and low. The last of these features means that the conventional deep stiffening along the floor centre-line is lost. That is justified by several items:- the smaller and lighter engine and gearbox, built as far forward as is reasonably possible, into the front of a fidl conventional-sized engine compartment under the bonnet, with a correspondingly modified bulkhead and crumple zone across the front of the cabin, in order to provide additional crumple space, and in order to control the crumple more effectively, between engine and cabin during front impact and by the general shell structure of the cabin, with its double skinned girder construction and galvanised steel reinforcement where necessary.

7he increased sill level of the single routine doorway, relative to conventional, seems to give an aerodynamic advantage, in that loads from the rear can be taken more directly than is conventional. Consequently, the wall thicknesses can probably be decreased, to advantage, in the bypass passages between the cabin and the rear wheel fairings.

Ile driver and passengers would be compensated for their inability to open the windows by their having an individual control for their air conditioning rather as on aircraft - with a rather more powerful flow and control for the driver.

The low external noise claimed for the car may not be apparent inside the cabin as the lightweight wall would absorb less noise than conventionally.

With a structure largely in existing lightweight material, it might be considered appropriate to put a small number of ski-type runners, of tough galvanised steel, well inset into the floor, in a way that would allow thern to reach and project externally without breaking the integrity of the floor, M order to give some protection should there ever be contact with the ground.

Some further possibilities are now mentioned.

Bolted "stable doors" The strains in the shell structure, at least for crash situations, would tend to be large when constructed of existing lightweight materials of reasonably low manufactured cost. Consequently, if the single routine entry were, say, of a "stable door" type arrangement then multiple bolts in say one half could act as part of the structure, during crash situations, even though the clearance at the bolts would be made large enough to allow thern to be used freely in everyday routine. The bolts could ordinarily be operated manually, or by a local or driver's control, with indicators accordingly, and could have a manual over-ride on a suitably long handle.

Such an arrangement could ease the stressing of the shell. Other doors might also have the dual purpose bolting.

Narrower cabins Part 1 discusses various cabins, including narrow cabins with quite wide wings. These may be seen to fit very well with the requirements of Part Il.

High speed stabilisers Potentially the cars of the present proposals could be both very fast and very light. Ilie high speed could make additional control desirable relative to that of conventional cars, while both the lightness and the high speed could increase the effectiveness of aerodynamic controls compared with conventional controls acting through wheel friction. Consequently cars according to the present proposals may be fitted with variable aerodynamic control surfaces appropriately linked to the existing brakes and steering. They may also have aerodynamic surfaces to augment stability in sidewinds - perhaps additional to the stability provided by the sort of roof shaping discussed for Figure 2. Some of the control or stabilising surfaces may themselves need to be stabilised against sidewinds, perhaps by mounting thern to obtain weathercock stability, with ailerons or flaps for the control function and possibly heavy damping for the stability.

Other types ofpower The discussion so far has implicitly been for cars with conventional types of power and conventional types of engine. The principles may be read across, however, with adaptation where required, to other types of power, such as man power, wind power, or some combination of say man, wind, battery, fuel cell, solar and conventional engine. The term "man powe?' is used to include any combination of one or more people providing the power.

With these other types of power it could be appropriate to put more emphasis on lightness and perhaps less on crashwortliffiess, more as for a conventional pedal cycle. Such matters would be influenced by the availability of roads and other arm fl= of other types of traffic. One advantage of, say, man powered vehicles of the present type would be that they could be much faster than ordinary pedal cycles, while not losing stability from the sidewind forces on the large aerodynanuc fairings, because of the stabilising Wide wheel base. In addition they would not require the "rider" to make long preparation for weather, provided efficiently controlled ventilation were arranged - preferably with flow control available by streamlined variation of the area of the outlet flow jet strewn. Also luggage and cleanliness could be easy, and perhaps security. On the other hand, in comparison with conventional cars, exercise would be provided for the rider, along with lower pollution, less use of resources, and lower costs. Miere could also be less use of conventional roads, if supplementary roads of light construction were provided for man-powered vehicles. However, in mixed traffic, supplementary power may be required on man-powered vehicles m order to maintain traffic speed, on appropriate roads.

Part M Retractable tail-cones The PM2sal The proposal is for a retractable tail-cone for road vehicles.

The tafl-cone is extended while the vehicle is travelling at low speed, prior to travel at medium and high speed. It remains extended at moderate and high speeds, but is retracted and stowed in the rear of the vehicle for low speed urban driving and for parking and garaging.

The arrangement provides a very large reduction m the medium and high speed drag. Consequently there is a very large reduction in the fuel consumption at steady medium and high speed.

Stability may need close consideration, both for the tail-cone and for the vehicle.

Although called a "cone", the geometry is thought of as any suitable tapering shape.

Some detailed considerations Road users close behind a vehicle which has a tail-cone would have an early claim on the attention of the designer. Ilieir safety would probably require the cone to be made entirely from flexible materials. In addition, there would be clear warning on the back of the vehicle, both in general, and, just prior to the extension of the cone.

Dashboard indication would keep the driver informed as to whether the tail-cone were extended or retracted. Extension and retraction could both in principle be automatic and be dependent on say time at speed. However, until experience were gained on the use of tail-cones in real situations, it would probably be preferable to require the driver to make a positive movement within his controls in order to authorise the system to take action either way.

In most of the remainder of the discussion the vehicle will for simplicity be taken to be a car.

In order to keep the length of the cone to a minimum it would be preferable to design the car for the best known aerodynamics consistent with the purposes of the car. One might for example design a conventional saloon car, or a "hatch", to have reasonably good streamline flow right down over its rear window, so that the retractable tail-cone would need to cover only the rear area below the window and would be short accordingly. An "estate", however, may be considered by the car designer to require almost the whole height of the vehicle to be available for loads, as well as for loading at the rear, so that use of the simplest "square" shape for the upper and side surfaces of the rear of the car could cause the tail-cone to be long. Compromises would probably then be appropriate, in that some careful curving of the surfaces of the estate car close to the rear could much improve the total geometry without significant loss of space or height. Additionally, some truncation of the tail-cone at its rear end may considerably reduce its length while still leaving it with an overall advantageous performance.

Of the two examples just mentioned the estate, with its essentially full height at the rear of the car proper, would require a transparency m the tail-cone if internal rear vision were required. On the other hand, the particular saloon, or hatch, with its excellent aerodynamic designarranged to give at least reasonably good streamline flow over the rear window, that would not require the transparency M the retractable cone. Consequently the tail-cone would be much easier to design, both for its not requiring a transparency and for its shorter length.

The rear shaping of some current cars does not achieve a good compromise between a large "boot", for rear storage, a clear rear view downwards through the rear window, and a streamlined external flow over the rear window. That could cause detailed problems in the present preferred proposals. With that situation m mind as a possible qualification, the present preferred shaping for a car within the broad pattern of current conventional cars, but intended for use with a tail-cone, would be to reduce the maximum, curvature at the top of the windscreen, in comparison with many current cars, very slightly raise the fore and aft middle of the roof and increase its fore and aft curvatures, then come down more steeply behind the rear passengers, in comparison with several current designs, to a steeper rear window, and, then, take the window through a smooth inflection, and to a lower level, into a more shallow angled final surface. The columns at the sides of the rear window would also be kept narrow. With such shaping, the tail-cone would start at a fairly low level, it would not need to be long, it would not need a transparency, the overall aerodynan-dc drag of the car with tail-cone should be capable of being made very low, and the mechanical and aeroelastic design of the cone may perhaps be much simplified compared with a cone designed for a more arbitrary arrangement.

From the above discussion one may conclude that, while any tail-cone which gives a fairly slow taper rate could probably improve the flow at the rear of a vehicle, and reduce the drag accordingly, it would probably be more satisfactory to design the tail-cone to suit the geometry and aerodynamics for any particular type of vehicle, rather as discussed for various types of circumstances. It would probably be even more satisfactory, as suggested above, to design the car and the tail-cone in conjunction with each other, in order that the steady adynamics, the mechanics, and the structural stability were all satisfactory.

During the course of designing the above aerodynamic flows it may be found helpful to use some suitable form of optimum boundary layer flow, or, perhaps, to include some suitable form of boundary layer control, all as used by those skilled in the art for the present three-dimensional situation. Similarly, special techniques could be appropriate for the three-dimensional main flow, Le. outside the boundary layer.

The rear wheels of the car may be best moved rearward slightly, In order the better to hold the loads caused by the tail-cone. However, for cars already well capable of accepting the loading from large trailers, it may be that the loads from a moderate tail-cone could be found to be easily within the existing capabilities.

One necessity with a tail-cone would be to consider the tendency, when the car turned, for the rear of the cone to move sideways, geometrically, relative to a line of traffic, even if all the design were mechanically rigid. Ths effect would be as a result of the overhang from the rear wheels. An arrangement having a sideways converging taper would help the situation, with rear lights positioned accordingly. A rearward movement of the rear wheels would also help In that respect, by reducing the overhang. A more complicated alternative, perhaps worth consideration, for a very large cone on a vehicle with a very large area of bluff base, would be to mount the cone on a trailer, with a flexible streamlined joint between the vehicle and the cone, and to make perhaps only the rear part of the cone retractable.

In principle a tail-cone could reduce the aerodynamic drag at high speed to a small fraction of conventional values for cars.

One problem with a tail-cone could be the possibility of aeroelastic instztbilities caused by vortex shedding at the trailing edge. Should such instabilities be encountered, those skilled in the art would probably be able to suggest possible cures. One approach could be to decorrelate the vortex shedding along the trailing edge, perhaps by varying the thickness, by large amounts, along the span.

Another problem with a two-dimensional shape of tail-cone could be that on the end walls there could be a significant component of boundary layer thickening caused by the reducing depth of the end walls. In addition, there could be undesirable three-dimensional flows induced near the edges of the end walls. The mechanical construction could also be of some complexity.

A different approach to the design, for vehicles of suitable shape, could be to use tail-cones entirely of purely circular and co-axial crosssections, i.e. axisymmetric tail-cones. These might be expected to have advantages of simplicity and cheapness, stiffness, possible freedom from vortex shedding, and suitable clearances for other traffic when turning. Parts I and 11 give some discussion of cars especially designed for axisymmetric, tail-cones.

Examples

Specific embodiments of the present proposals will now be described by way of example only, with reference to the accompanying drawings, in which:

Figure 6 is a schematic illustration of a car with a quasi twodimensional tail-cone in its high speed operating position; Figure 2 is a schematic illustration in side view of a car especially designed for its axisymmetric tail-cone; and Figure 3 is a schematic illustration in plan view of a car especially designed for its axisymmetric tail-cone.

In the example of Figure 6, the car itself is closely similar to a conventional car, but nevertheless the whole of the car, together writh the tail-cone 38, has been designed aerodynamically as a single Unlit, in order to achieve smooth strean-dine flow over the whole surface, and with only a small area of bluff base. In particular, the design provides streamline flow over the rear window within the length of the car itself, so that the tail-cone starts behind the rear window and does not contain a transparency.

The general shape of the tail-cone, which is quasi two-dimensional, is illustrated in Figure 6.

The tail-cone surface starts at plane 18. Most of the reduction in the cross-sectional area of the cone is provided by the upper surface. The under surface is smooth and rises only slowly. The sides of the tail-cone over the lower region are reasonably flat and parallel, so that the full span of the car is available at the rear, in particular for the rear lighting. The sides in the upper region of the tail-cone follow as a continuation of the broadly rounded sweep of the car surfaces conventionally present from some distance upstream. The lower corners of the cone are also rounded, but less so than the upper corners.

When the car is being driven at low speed, or when it is parked or garaged, the tail-cone is retracted and stowed in the box-like space 19 between planes 18 and 20. The subsequent extension process is just the reverse of retraction. Either process would take place automatically once it has been authorised by the driver - provided there is no over-ride in operation. However, there could, for example, be an over-ride to prevent extension if the car were stationary. There could also be an over-ride in order to prevent either extension or retraction being started if the speed at authorisation exceeded say 45 mph.

Re structure of the tail-cone m Figure 6 is based on 2 circular cones. The cones are truncated, manufactured from high strength flexible plastic sheet, and pressurised. At their larger, forward end they are anchored to the car at plane 20, while at the rear they are fixed to the rear "base plate", with one circular cone fairly close to each end of the "plate". The "plate", while being nominally rigid, relies for its sfiffiess on the inflation of a mesh tubes of the flexible plastic sheet. The physical surface and the required physical external shape of the tail-cone is obtained by building on to the base plate and on to the circular cones a structure formed from further high strength plastic sheeting, together with appropriate internal air pressures, positive or negative relative to ambient, to hold the whole structure reasonably firmly.

In order to make the system retractable each circular cone has 3 or more cables attached to an "anchorage", which is itself rigidly attached to the base plate and positioned a short distance upstream of it. These cables run to positions, at large diameter and equally spaced around the circumference, just inside their respective circular cone at its front face - or, at least, within the pressurised space associated with the circular cone so that there is no leakage when the cables move. The cables may now be supposed to pass over a pulley type system, and then the cables in each circular cone unite. The uniting of the cables, together with the symmetry of their layout, are critical to the simplicity and effectiveness of this particular mechanism for controlling a retractable tail-cone, as, given these features, if the united cables are now moved by some suitable means of actuation, all the cables move by accurately the same amount. It will now be seen that such actuation, given the symmetry of the actuation system, and accompanied by controlled bleed of the air pressurisation, causes the retractable tail-cone to retract, and to do so along an accurately and fim-dy controlled reversible and repeatable straight path, and with the correct orientation at all positions. Now under partial pressurisation the larger diameter regions of the circular cone, i.e. at the front, will remain open, while the smaller diameter as at the rear will collapse. Consequently the circular cones and the tail-cone as a whole will retract progressively, starting from the rear base plate and moving forward. That arrangement should give greater stability, compared with retraction working progressively in the opposite sense.

The extension process is obtained by following the various stages of retraction in reverse, and M reverse order. Substantially full extension occurs when both of the circular cones are extended to substantially their full length by their internal air pressure. At that position the cables, nominally, all come on to their stops. The stiffness and strength of the whole assembly is then increased by increasing substantially the air pressure. The actual, final, adjustment of the cable stops is arranged such that at maximum pressure the loading is shared suitably between the cables and the high strength plastic sheeting.

]be last part of the retraction process is to close the box 19, for security and for good appearance. Two plates are hinged to the car and effectively form part of the outer surface of the tail- cone when in its operating position. The later stages of the retraction of the tail-cone then actuates the plates to a partially closed position. Suitable link mechanisms, together with pneumatic or electromagnetic rams, inside box 19, can then complete the closure. Further operation of suitable pneumatic or electromagnetic bolts also inside box 19 then locks the whole arrangement into place. Box 19 itself is mounted on the door which gives access to the rear luggage space, with the door suitably strengthened and balanced.

Operation of the above retracting mechanism in either direction, i.e. as a retraction or as an extension, is thought of as being authorised specifically by the driver of the car and would be intended to be carried out and completed below some specified speed, perhaps 50 mph. A starting speed for the operation may then be limited to say 40 to 45 mph. If the car accelerated to above the 50 mph during the operation of the mechanism there could be a suitable over-ride, perhaps ensuring that the shorter route were taken to an end position, if that seemed appropriate.

When the tail-cone is not strongly truncated it is likely to be fairly slender m its general proportions. Consequently the operating cones could also then be fairly slender. On the other hand the loading on the tailcone during operation of the extending and retracting mechanism could be considerable, unless the specified maximum car speed for the operation were rather low. Consequently it would probably be found very desirable for the operating circular cones to have as large a diameter as the tailcone shape makes reasonably possible. One method for achieving some increase in diameter relative to the nominal maximum would be to compromise the optimised aerodynamics slightly by allowing the operating cones to bulge, slightly, through the aerodynamically specified surfaces. Some compensation aerodynamically could be obtained by sinking inwards the remainder of the span at the appropriate axial positions. Such a result could be obtained "automatically", on the upper surface of the tail-cone, by joining between the two operating cones by a single high strength plastic sheet, for the upper surface, and applying a suitable sub-ambient pressure under that upper surface.

The second example of the retractable tail-conc has essentially the same geometry as the first and air operation is used rather as before. However, the tail-cone is manufactured from woven sheets, woven from tough plastic thread, and sealed against the air pressure by plastic sprayed on to the surface. The woven plastic under pressure then provides all the stiffness, so that retraction is by a mesh of the very elastic and robust "bungee" cords fixed to the woven plastic at suitable positions.

The third example of a retractable tail-cone is the axisymmetric version shown in Figures 2 and 3, where the tail-cone is represented by the chain dotted lines, item 1. Those Figures are discussed in Parts I and II of the present proposals.

A fourth example is constructed of an artificial "rubber" "stretch" material, with extension and retraction by air inflation and deflation. Such an arrangement could be particularly suited to small tailcones. A further such simplifying variant could have the fully extended size of the tail-cone determined by the air pressure.

CLAlMS 1. A car for ordinary purposes, with aerodynamic "boat-tailing" of the cabin almost entirely on the sidewalls of the cabin, and with the cabin substantially narrower, over its full height, at the rear of the car proper than it is at the driver's seat - and with the rear part of the cabin sufficiently narrow that, at least with some indentations, a streamlined airflow passage can be, and in fact is, formed between the cabin and each of the wings which cover the rear wheels and suspension and with the centre of the roof rising substantially, and continuously (or nearly so), particularly in comparison with a current conventional high performance car, for the full length of the car proper, from the windscreen rearwards.

2. A car as claimed in claim 1, wherein the overall width and length of the car, when measured exclusive of any retractable tail-cone, are in about the conventional range for cars.

3. A car as claimed in any preceding claim, wherein the wings and cabin are designed aerodynamically, both for reasonably streamlined flow, and for a substantially smaller than conventional total area of bluff base, the bluff base including any bluff rear window.

4. A car as claimed in any preceding claim, wherein the cabin and wings are designed aerodynamically reasonably in conjunction with each other.

5. A car as claimed in any preceding claim, wherein favourable interactions between the cabin and wings are built into the aerodynamic design.

6. A car as claimed in any preceding claim, wherein the undersurface is designed aerodynamically for reasonably streamlined flow and reasonably in conjunction with the remainder of the car.

7. A car as claimed in any preceding claim, including claim 2, wherein the car is primarily a 2 scat car with the seats positioned "smaH aeroplane style" in line fore and aft, and wherein the boat-tailing on the sidewalls within the length of the car itself (together with the streamlining of the wings) gives essentially zero area of bluff base at the trailing edge, or a very much reduced area of bluff base in comparison with conventional cars, and wherein the aerodynamic drag has been reduced to a very small value compared with conventional cars.

8. A car as claimed in claim 5, wherein air flow is drawn down behind the part of the wing covering each front wheel, including from the region where the flow is approaching the windscreen, and wherein a nodal line "shape" is used on the sloping rearward facing surface of the wing such that the flow drawn down from in front of the windscreen is caused to leave the surface at, and from one side of, the nodal line, while flow approaching from the other side of the nodal line also leaves at the nodal line, the design being arranged such that the two flows unite steadily at the nodal line with but little or no vorticity-sourced dissipation between then at each position along the line.

Claims

9. A car as claimed in any preceding claim, wherein, together with the

general rise in the central mendian of the roof line that is continuing, substantially, all the way to the trailing edge,(e.g. see the last part of Claim 1) - accepting, broadly, the compromise for headroom at the single routine entry - there is an accompanying change of section in the roof, with the intention such that each half of a horizontal span of the low energy, or "boundary layee', flow, approaching from the front part of the roof, could "rotate" in a controlled process, following the 'crotation" of the local part of the roof, as it passes along the change in section, and correspondingly could cross the trailing edge spread along a substantial length correspondingly of each side of the upper part of a central vertical tail-fin type of geometry.

10. A car as claimed in any preceding cWR wherein atail-cone can be extended while the car is moving at low or medium speed, for use as the rear part of the total car at medium and high speed, in order to reduce the aerodynamic drag, possibly to very small values; and wherein the tailcone can be retracted, while the car is moving, for ease of urban travelling at lower speeds, as well as for ease of parking and garaging; "td-cone" being taken singular or plural and of any suitable shape.

11. A car as claimed in claim 10, wherein a substantial retractable tailcone has essentially only purely circular and co-axial cross-sections, Le it is basically axisymmetric, for ease of manufacture, ease of retraction and extension, and simplicity and efficiency of steady use; "essentially" and "basically" not precluding smaH non-axisyminetric additions which do not substantially negate the advantages of being axisymmetric.

12. A car as claimed in either of the claims 10 and 11, wherein the shaping and boat-tailing of the cabin and car is controlled to match the requirements of the retractable tail-cone, mechanically, aerodynamically, aeroelastically, and with respect to convenient manufacture, within the total context of the design of the car.

13. A car as claimed in any of the claims 10 to 12, wherein one or more of the tail-cones is constructed of an artificial "rubber" "stretch" material, with extension and retraction by air inflation and deflation.

14. A car as claimed in any of claims 10 to 13, wherein the fully extended size of the tail-cone is determined by the air pressure.

- A car as claimed in any of claims 10 to 13, wherein the fully extended size of the tail-cone when pressurised is determined by flexible nonstretch material longitudinally and circumferentially fastened at intervals to the stretch material or woven into it and suitably sealed by spray.

16. A car as claimed in any of claims 10 to 12, wherein one or more of the tail-cones is constructed of strong, tough, and essentially "nonstretch", flexible sheet material, with extension, strength and stifFness provided by air inflation, and with retraction by a combination of deflation and the action of very elastic, strong, and tough, cords, such as "bungee cords", the cords being in a mesh suitably fixed to the cone and to the car.

17. A car as claimed in claim 16, wherein the sheet material of the tailcone is, for extra toughness, a woven material and woven from suitably strong and tough thread, with the whole made airtight by suitable spray treatment.

18. A car as claimed in any preceding claim, wherein the claimed low drag features are used in conjunction with structural features of low weight possibly including: - (a) additional areas of fixed structural sidewalls for the cabin, particularly at the front and lower parts of the sidewalls, suitably fixed permanently to the other structure of the car, including to the floor of the cabin; (b) only a single routine access doorway for people, with that doorway on the near side and at a fore and aft position giving direct access to the rear seats (of a 4 seat car), and with features internal to the cabin such as additional handholds, and adequate clear and low level floor space, in order to ease internal transfer to and from all the seats; (c) non-opening windows, manufactured in a reasonably robust material, and suitably bonded or welded at all peripheries, or integral, to form a very low stress (or "secondary") part of the main structure; (d) a main structure based on a fully joined up and almost fully closed structural shell; (e) loading Emits on the car made rather lower than conventional; and wherein the low drag and low weight features operate, possibly interdependently, in allowing the use of any of the following: - (i) shmmer than conventional rear wheels and suspension, in order to make it possible to achieve the streamlining and bypass airflow needed at the rear fairings in the present aerodynamic type of design, wffile yet maintaining the general proportions needed in creating a popular 4 scat high performance car; (ii) dome-like-shaped additional headroom at the centre of the roof, opposite the single routine doorway, as well as just forward of that position, in order to ease people's internal transfer between the doorway and all the seats, probably without undue compromise to the aerodynamics of the already rising central roof line.

(iii) the formation of a step to assist external access to the single routine doorway, making use of the area of wing created to improve the aerodynamic entry to the rear airflow bypass passage; (iv) the positioning of the single routine doorway and door to take advantage of the external step and wing area, and of the reduction of the cabin and roof width at that position, all as given by the sidewall aerodynamic boat-tailing, in order to make it easy to stand upright on the step as a helpful intermediate position when a person uses the single routine doorway; (v) to use the high central area of the cabin roof, as allowed aerodynamically, to strengthen the structural shell, given the cut-out of the single routine doorway; (vi) to use the various access improvements, in particular those facilitated by the aerodynamics, to allow a threshold to the single routine doorway somewhat higher than that for the doorways of a conventional car, in order to improve the structural shell at the cut-out; (vii) to use the high central area of the cabin roof, as allowed aerodynamically, partly for the provision of anti-roll-damage reinforcement, possibly based partly on the reinforcement around the single routine entry; (viii) (With a narrower, say 2 seat small-aeroplane-type cabin, to use a streamlined, rearward sloping, Wing, between the ftont and rear wheel fairings, to provide the structural sidewalls of claim 18(a), as well as a converuent and easy access for steps to the cabin); (ix) to obtain the mutual gains more ordinarily obtained when combining structural lightening, aerodynamic drag reduction and overall re-optin- dsation, gains such as the reduction of component weight and volume, and the ease of streamlining, together with the virtuous circles of assessment feedback.

19. A car as claimed in any preceding claim, wherein the dampers of the rear suspension are adapted to be able to give also a quasi-steady component of lift, in order to raise the car for low speed driving over a bumpy surface, and, while the car is moving, lower the car for high speed driving on smooth surfaces, in order to be able to design the prime high speed low drag configuration, particularly of the rear airflow bypass passages, for a low position of the suspension and car and for only small movements of the suspension, and possibly wherein the same damper adaptation is arranged to be able to lower the car when stationary for easing of loading and unloading of people and luggage.

20. A car as claimed in any preceding clairn, wherein the components of the rear suspension are set as low as is acceptable, and as inset into the wheel hub as is acceptable, in order to give as clear and large a passage as is reasonable for the bypass airflow.

21. A car as claimed in any preceding claim, wherein the engine and gearbox, which are smaller than conventional because of the low weight and low drag of the car, are built into the front of a conventional sized engine compartment under the bonnet, and the crumple zone and front bulkhead of the cabin redesigned accordingly, in order to control more effectively the crumple between engine and cabin during a front impact.

22. A car as claimed in any preceding claim, wherein the single routine doorway may have a "stable" door, with one of the two halves being suitably bolted to be easily opened for routine use, but to form part of the structure during the large strains of crash situations, in order that the total shell structure may then be more completely closed: possibly also with other doors bolted for two uses rather similarly.

23. A car as claimed in any preceding claim, wherein stabilisers and variable aerodynamic controls are added appropriate to cars of light weight and high speed.

24. A car as claimed in any preceding claim, wherein appropriate modifications have been made to allow the car to be "man-powered", with one or more people providing the power, including for use on roads or other areas fi-ce of various other types of traffic, in order to use one or more aerodynamic fairings to reduce drag to very low values, in order to allow easy high speed, and to give easy protection against the weather, all while remaining stable in sidewinds because of the widely spaced wheels; and rather similarly ",Mnd-powered", or some combination of man, wind, battery, fuel cell, solar and conventional engine powered; all at very low weight.

25. A car for ordinary purposes substantially as described herein, particularly with reference to Figures 2 and 3 of the accompanying drawing.

-Z Li Amendments to the claims have been filed as follows A car with all of the following features:- (a) routine access for people to sit in any seat in the front row of seats of the car provided as a space between a driver's seat and a front passenger seat, with at least one doorway allowing people to reach that space from outside the car, with that doorway in line with a row of seats more rearward than the front row of seats and there being no routine direct entrance from outside the car for people to sit in any seat in the front row of seats, whether the routine direct entrance is a door and doorway or otherwise; (b) the cabin of the car in plan view tapers inwards towards the rear in the region behind the front row of seats; and (c) one or more retractable tail-cones are fitted at the rear of the car proper.

2. A car as claimed in claim 1, wherein there is only one doorway giving people routine entrance from outside to sit in the car, with that doorway on the near side.

3. A car as claimed in claim 2, wherein the route for routine access to the front seats is provided with suitable head room, by forming a suitable dome-like space on and near the centre-line of the roof of the car.

4. A car as claimed in claim 3, wherein the windows are non-opening and are a fixed part of the structure, other than for the requirements of exit.

5. A car as claimed in claim 4, wherein the structure is essentially a joined up and closed "shell", other than for the one, only, doorway of claim 2, for the doorway to the boot, and for one or more emergency exits.

6. A car as claimed in any preceding claim, wherein there is an air passageway between the cabin and each of the rear wings covering the rear wheels and suspension.

7. A car as claimed in claim 6, wherein, with the taper of claim 1,(b), together with the forward lower surface of the passageway of claim 6, there is provided, within the width of the car, an entrance step to the slightly recessed, or set back, routine access doorway.

8. A car as claimed in any preceding claim, wherein, one or more doors may be "stable" doors, i.e. operable in two parts, and where one or more of the doors or parts of doors may be held by multiple bolts of moderate clearance suitably designed and controlled so that in routine use the bolts operate "freely", but in the large strain of a crash the structural strength is near-continuous through the bolted joints.

9. A car as claimed in any preceding claim, wherein the centre-line of the roof rises, overall, when going rearwards, from the top of the windscreen to the top of a fin-like shape at the rear of the car proper.

10. A car as claimed in any preceding claim, wherein the main tail-cone is basically axisymmetric, "basically axisymmetric" being taken not to exclude small non-axisymmetric attachments.

11. A car substantially as described herein, particularly with reference to Figures 2 and 3 of the accompanying drawing.

P.6 correspondingly could cross the trailing edge spread along a substantial length correspondingly of each side of the upper part of a central vertical tail-fin type of geometry.

10. A car as claimed in any preceding claim, wherein a tail-cone can be extended while the car is moving at low or medium speed, for use as the rear part of the total car at medium and high speed, in order to reduce the aerodynamic drag, possibly to very small values; and wherein the tailcone can be retracted, while the car is moving, for ease of urban travelling at lower speeds, as well as for ease of parking and garaging; "tail-cone" being taken singular or plural and of any suitable shape.

11. A car as claimed in claim 10, wherein a substantial retractable tailcone has essentially only purely circular and co-axial cross-sections, Le it is basically axisymmetric, for ease of manufacture, ease of retraction and extension, and simplicity and efficiency of steady use; &'essentially" and "basically" not precluding small non-axisymmetric additions which do not substantially negate the advantages of being axisymmetric.

12. A car as claimed in either of the claims 10 and 11, wherein the shaping and boat-tailing of the cabin and car is controlled to match the requirements of the retractable tail-cone, mechanically, aerodynamically, aeroelastically, and with respect to convenient manufacture, within the total context of the design of the car.

13. A car as claimed in any of the claims 10 to 12, wherein one or more of the tail-cones is constructed of an artificial "rubber" "stretch" material, with extension and retraction by air inflation and deflation.

14. A car as claimed in any of claims 10 to 13, wherein the fully extended size of the tail-cone is determined by the air pressure.

15. A car as claimed in any of claims 10 to 13, wherein the fully extended size of the tail-cone when pressurised is detern-dned by flexible non-stretch material longitudinally and circumferentially fastened at intervals to the stretch material or woven into it and suitably sealed by spray.

16. A car as claimed in any of claims 10 to 12, wherein one or more of the tail-cones is constructed of strong, tough, and essentially "nonstretch", flexible sheet material, with extension, strength and stiffness provided by air inflation, and with retraction by a combination of deflation and the action of very elastic, strong, and tough, cords, such as "bungee cords", the cords being in a mesh suitably fixed to the cone and to the car.

17. A car as claimed in claim 16, wherein the sheet material of the tailcone is, for extra toughness, a woven material and woven from suitably strong and tough thread, with the whole made airtight by suitable spray treatment.

18. A car as claimed in any preceding claim, wherein the claimed low drag features are used in conjunction with structural features of low weight, possibly including:- (a) additional areas of fixed structural sidewalls for the cabin, particularly at the front and lower parts of the sidewalls, suitably fixed permanently to the other structure of the car, including to the floor of the cabin; (b) only a single routine access doorway for people, with that doorway on the near side and at a fore and aft position giving direct access to the rear seats (of a 4 seat car), and with features internal to the cabin such as additional handholds, and adequate clear and low level floor space, in order to ease internal transfer to and from all the seats; (c) non-opening windows, manufactured in a reasonably robust material, and suitably bonded or welded at all peripheries, or integral, to form a very low stress (or "secondary") part of the main structure; (d) a main structure based on a fully joined up and almost fully closed structural shell; (e) loading Emits on the car made rather lower than conventional, and wherein the low drag and low weight features operate, possibly interdependently, in allowing the use of any of the following:- (i) slimmer than conventional rear wheels and suspension, in order to make it possible to achieve the streamlining and bypass airflow needed at the rear fairings in the present aerodynarnic type of design, while yet maintaining the general proportions needed in creating a popular 4 seat high performance car; (ii) dome-like-shaped additional headroom at the centre of the roof, opposite the single routine doorway, as well as just forward of that position, in order to ease people's internal transfer between the doorway and all the seats, probably without undue compromise to the aerodynamics of the already rising central roof line; (Iii) the formation of a step to assist external access to the single routine doorway, making use of the area of wing created to improve the aerodynamic entry to the rear airflow bypass passage; (iv) the positioning of the single routine doorway and door to take advantage of the external step and wing area, and of the reduction of the cabin and roof width at that position, all as given by the sidewall aerodynamic boat-tailing, in order to make it easy to stand upright on the step as a helpful intermediate position when a person uses the single routine doorway; (v) to use the high central area of the cabin roof, as allowed aerodynamically, to strengthen the structural shell, given the cut-out of the single routine doorway; (vi) to use the various access improvements, in particular those facilitated by the aerodynamics, to allow a threshold to the single routine doorway somewhat higher than that for the doorways of a conventional car, in order to improve the structural shell at the cut-out; (vii) to use the high central area of the cabin roof, as allowed aerodynamically, partly for the provision of anti-roll-damage reinforcement, possibly based partly on the reinforcement around the single routine entry; (viii) (with a narrower, say 2 seat small-aeroplane-type cabin, to use a streamlined, rearward sloping, wing, between the front and rear wheel fairings, to provide the structural sidewalls of claim 18(a), as well as a convenient and easy access for steps to the cabin); (1x) to obtain the mutual gains more ordinarily obtained when combining structural lightening, aerodynamic drag reduction and overall re- optimisation, gains such as the reduction of component weight and volume, and the ease of streamlining, together with the virtuous circles of assessment feedback.

19. A car as claimed in any preceding claim, wherein the dampers of the rear suspension are adapted to be able to give also a quasi-steady component of lift, in order to raise the car for low speed driving over a bumpy surface, and, while the car is moving, lower the car for high speed driving on smooth surfaces, in order to be able to design the prime high speed low drag configuration, particularly of the rear airflow bypass passages, for a low position of the suspension and car and for only small movements of the suspension, and possibly wherein the same damper adaptation is arranged to be able to lower the car when stationary for easing of loading and unloading of people and luggage.

20. A car as claimed in any preceding clairn, wherein the components of the rear suspension are set as low as is acceptable, and as inset into the wheel hub as is acceptable, in order to give as clear and large a passage as is reasonable for the bypass airflow.

21. A car as claimed in any preceding claim, wherein the engine and gearbox, which are smaller than conventional because of the low weight and low drag of the car, are built into the front of a conventional sized engine compartment under the bonnet, and the crumple zone and front bulkhead of the cabin redesigned accordingly, in order to control more effectively the crumple between engine and cabin during a front impact.

22. A car as claimed in any preceding claim, wherein the single routine doorway may have a "stable" door, with one of the two halves being suitably bolted to be easily opened for routine use, but to form part of the structure during the large strains of crash situations, in order that the total shell structure may then be more completely closed: possibly also with other doors bolted for two uses rather similarly.

23. A car as claimed in any preceding claim, wherein stabilisers and variable aerodynamic controls are added appropriate to cars of light weight and high speed.

24. A car as claimed in any preceding claim, wherein appropriate modifications have been made to allow the car to be "man-powered", with one or more people providing the power, including for use on roads or other areas free of various other types of traffic, in order to use one or more aerodynarffic fairings to reduce drag to very low values, in order to allow easy high speed, and to give easy protection against the weather, all while remaining stable in sidewinds because of the widely spaced wheels; and rather similarly "windpowered", or some combination of man, wind, battery, fuel cell, solar and conventional engine powered; all at very low weight.

25. A car for ordinary purposes substantially as described herein, particularly with reference to Figures 2 and 3 of the accompanying drawing.