The present invention relates to vehicle airflow control apparatus, for example such apparatus for land vehicles such as motor cars.

A motor car has to function as a product of good engineering while in most cases also being aesthetically pleasing. There is often a conflict of interest between designers and aerodynamicists when deciding on the form of the vehicle. With high speed motor cars, such as those capable of exceeding 200 or even 300 kilometres per hour, lift can be generated in the region of the rear "axle" area and such fast motor cars require a low co-efficient of lift to prevent them from losing grip in corners and so as to avoid undesirable driving characteristics.

It is also desirable for a motor car to have relatively low drag so that it is economical and/or can travel faster with a motor/engine providing a given power to the power train.

One aerodynamic device used is a rear "flip". Some of the earliest effective motor cars to use these devices were the Ferrari 250 GTO, and the Aston Martin DP214 and DP215 racing cars which in the year 1963 where the first motor cars ever to be officially timed at over 300 kph on the very long Mulsanne Straight at Le Mans. More recently, boot lid flips have become relatively common among production cars and are included on, for example, the Aston Martin DBS, BMW Z4 and Mercedes Benz SLK55 AMG models.

Another aerodynamic device is a deployable spoiler such as used on the Bugatti Veyron Super Sport at the rear of the vehicle. Another known aerodynamic device is a fixed wing at the rear of the vehicle such as used on the Aston Martin V12 Zagato and Mercedes Benz C63 AMG Black Series models. Another aerodynamic device is a Gurney flap which is an element which may be fixed to the top trailing edge of a wing on a racing car and has been used since the 1970s.

FR-A-2885343 discloses the use of blowing slots on an MPV or hatchback with a flat roof. EP-A- 150691 1 shows air blown out near a rear windscreen of a hatchback. EP-A-1907267 shows a motor car having a horizontal opening for air which has passed a cooling duct. EP-A-1048556 shows an apparatus for emitting air up next to and behind a substantially vertical drop surface behind a substantially horizontal boot lid - a rather unsightly arrangement due to the exterior nature of the apparatus. EP-A-0467523 discloses air passageways inclined upwards and with baffles disposes in the passageways.

While some of these devices can be useful to greater or lesser extents from an aerodynamic performance perspective, they do not always fit in with the objects which vehicle designers may be attempting to achieve from an aesthetic perspective on some projects. Some vehicle designers may desire very clean lines for the shape of their vehicles, at least when the vehicles are on display or stationary and without a substantial and/or complex arrangements. It is very challenging to engineer a vehicle which is capable of very high speed with good vehicle response and stability across the road speed range during straight line and cornering manoeuvres while also meeting vehicle aesthetic design objectives.

The present invention aims to alleviate at least to a certain extent the problems of the prior art.

A first aspect of the present invention provides a vehicle airflow control apparatus comprising an airflow blowing arrangement located at or in a vehicle body upper surface for reducing lift away from the vehicle body surface when the vehicle is in forward motion, the air blowing arrangement being behind or within a downwardly sloping area of upper vehicle body work.

The downwardly sloping area of vehicle body work may slope down at a slope angle which is at over 5 degrees to the horizontal. The slope angle may be from 5 to approximately 60 degrees, preferably from about 10 to 40 degrees, for example within 15 to 30 degrees, one example being substantially 20 degrees.

According to a second aspect of the present invention there is provided a vehicle airflow control apparatus comprising an airflow blowing arrangement located at or in a vehicle body surface for reducing lift away from the vehicle body surface when the vehicle is in forward motion, the blowing arrangement and vehicle body surface being arranged and configured to decrease lift and/or drag when a vehicle to which the apparatus is fitted is travelling forwards at a Reynolds number above 2 x 10 ⁶ or above 3 x 10 ⁶ . A third aspect of the present invention comprises a vehicle airflow control apparatus comprising an airflow blowing arrangement located at or in a vehicle body surface for reducing lift away from the vehicle body surface when the vehicle is in forward motion, the blowing arrangement including a slot extending across the vehicle body surface, the slot having a length in the intended longitudinal direction of motion of the apparatus of between 2 and 10mm.

A further aspect of the present invention comprises a vehicle airflow control apparatus comprising an airflow blowing arrangement located at or in a vehicle body surface for reducing lift away from the vehicle body surface when the vehicle is in forward motion, the air blowing arrangement and vehicle body surface being configured such that at least one lateral position and at least one airflow speed for the apparatus the airflow blown out from the blowing arrangement towards free stream airflow is sufficient to move a pressure point at a rear of the vehicle body surface forwards relative to its position with the blowing arrangement blocked or inactive (a) forwards over 10cm, typically over 25cm, in some examples over 40cms such as 40 to 50cm forwards or (b) forwards over 5% of the wheel base length of a vehicle to which the apparatus is to be fitted, typically over 10% or 15%, such as between 15 and 20% forwards. The pressure point may be (although is not necessarily) a point at which pressure equals or is greater than free stream pressure.

A further aspect of the invention comprises a vehicle airflow control apparatus for a land vehicle comprising a vehicle body surface and a surface member which is arranged to extend generally away from the vehicle body surface and extend laterally thereacross in relation to intended free stream flow, the surface member be positionable with portions of its surface substantially perpendicular to adjacent portions of the vehicle body surface, the surface member being movable from a first position to a second position in which the surface member protrudes further from the vehicle body surface than it does in the first position. In the first position, the surface member may be flush or sub-flush with the vehicle body surface. The surface member may be arranged to act as a Gurney flap.

A further aspect of the invention comprises a vehicle airflow control apparatus comprising a vehicle body surface and a surface member which is arranged to extend generally away from the vehicle body surface and extend laterally thereacross in relation to intended free stream flow, and a blowing arrangement in the vicinity of the surface member for blowing air into passing airflow. The blowing arrangement may be formed with an air exit aperture within the surface member. The exit aperture may comprise at least one slot. The surface member may be arranged to operate as a Gurney flap. The features of the above aspects of the invention have been found in testing to provide improved vehicle response and stability across vehicle road speed range during straight line and cornering manoeuvres. At the same time, the blowing arrangement can be very unobtrusive and can simply consist in some embodiments of one or more apertures or slots in the vehicle body surface and can therefore enable aerodynamicists to engineer vehicles which may be capable of very high speeds with good vehicle control while still meeting the aesthetic objectives of vehicle designers.

A number of preferred features which may be incorporated when carrying out any of the above aspects of the invention will now be discussed. The blowing aperture may be adapted to blow flow out into free stream or at least nearby passing flow and to create an obstruction to flow travelling over the vehicle body surface and to create a high pressure region upstream of an exit from the blowing arrangement. The blowing arrangement may comprise a duct leading to at least one outlet aperture or exit. The blowing arrangement may be arranged to jet flow in a direction substantially perpendicular to flow passing the vehicle body surface. However, the jet flow direction may be in other embodiments in any other direction but especially in the longitudinal and vertical plane of the vehicle to which the apparatus is fitted. The blowing arrangement may be arranged to provide the jet flow such that substantially all of the flow from an exit of the blowing arrangement is ejected from the exit in substantially the same overall direction. The blowing arrangement may comprise an array of blowing elements extending substantially laterally across the vehicle body surface. The array may include at least one elongate slot. The array may comprise a plurality of said slots such as 2, 3, or 4 said slots, which are substantially aligned and are arranged one next to the other across the vehicle body surface, such as comprising aligned left, centre and right slots. Each slot may have a width laterally which is substantially longer than its length longitudinally in the intended direction of motion of the apparatus. The vehicle body surface is preferably an A-surface. In some embodiments one or more perforated panels areas with a series of small perforations may be used in addition to or as an alternative to one or more slots, if desired. The vehicle body surface preferably comprises an upper body surface. The vehicle body surface may include a roof portion and/or a rear window portion of an occupant space for a vehicle, the roof portion and/or rear window portion lying in front of the blowing arrangement. The vehicle body surface may comprise or include a boot lid or deck lid such as a rear boot lid or deck lid. When the vehicle body surface includes a boot lid or deck lid portion, the blowing arrangement may be formed at least partly or fully in the said boot lid or deck lid portion. The boot lid or deck lid portion may be arranged to cover a rear enclosure of a vehicle, such as an enclosure for luggage and/or vehicle motor/engine components.

When the blowing arrangement includes at least one blowing slot, each slot may have a length in the longitudinal direction of flow of between about 2 to 8mm, some examples being about 3 and about 5mm.

The vehicle body surface may be connected to a rear drop down surface located below a rear edge of the vehicle body surface. The drop down surface may be overhung, thereby extending downwardly and forwardly from the rear edge of the vehicle body surface. The blowing arrangement may have a rearmost portion which is located about 0.5 to 100mm from the rear edge of the vehicle body surface, more typically within about 3 to 50mm some examples being about 35mm and about 10mm, such as about 7mm or 5mm from the rear edge. The drop down surface and vehicle body surface may be oriented (in at least one vertical section in a longitudinal plane) substantially perpendicular to one another, the rear edge of the vehicle body surface (which is the edge between them) having a radius which is less than 10cm, preferably less than 5cm, about 1 , about 2 or about 3cm being some examples. The blowing arrangement may include a duct leading to an exit aperture thereof, the duct preferably curving gradually towards the aperture. The duct may have a duct supply portion running directly towards or within about 20 degrees of directly towards the exit aperture, the duct supply portion having a flow length which is over 5 times the length (in the flow direction inside the duct) of the exit aperture/slot length (in the free stream flow direction) of the blowing apparatus, the flow length of the duct portion for example being 5 to 10 times or about 10 to 15 times this length. This has been found advantageously to increase the performance of the blowing arrangement.

In some preferred embodiments, the blowing arrangement and/or vehicle body surface and a vehicle structure in front of the blowing arrangement may be configured such that with at least one speed flow near the vehicle body surface is substantially attached and/or lacking in substantial vortices or turbulence. The blowing arrangements thus blow out into such flow.

In some embodiments, the blowing arrangement may include a Gurney or surface member arranged to extend generally away from the vehicle body surface and extending laterally across the vehicle body surface, the surface member preferably having a front part positioned upstream of a flow exit aperture or exit slot of the blowing arrangement.

The said aperture or slot of the blowing arrangement may be positioned within the surface member.

The surface member may be positionable with portions of its surface substantially perpendicular to adjacent portions of the vehicle body surface. The surface member may be retractable within and/or below the vehicle body surface. A control may be provided for retracting the surface member. The surface member may be retractable in response to a signal indicative of stationary vehicle, engine off or travelling at low speed. The surface member may be extendable out from the vehicle body surface in response to a signal indicative of vehicle motion or travelling at high speed or in response to a driver input such as a push button. A cover member may be provided for moving over and covering the surface member and/or the blowing arrangement when the surface member is retracted. The cover member may be arranged to move to a position in which it is substantially aligned with the vehicle body surface such that with a vehicle to which the apparatus is fitted stationary there is no or is substantially no prominence within the region of the airflow control apparatus and a high level of design aesthetics or a design objective for little or no prominence may be achieved.

The said aperture or slot of the blowing arrangement may be formed in a moveable vehicle body surface section. . The vehicle body surface section may comprise a surface extending across the width of the vehicle.

The moveable vehicle body surface section may be substantially perpendicular to the surface member.

The moveable vehicle body surface section may be positionable with portions of its surface substantially aligned with adjacent portions of the vehicle body surface. The vehicle body surface section may be raised above the adjacent vehicle body surface. The surface member, which may comprise part of the vehicle body surface section, may then face upstream of the vehicle. The blowing arrangement may comprise two laterally extending slots. Each sot may be fluidly connected to a separate respective air inlet, for example, provided on a respective side of the vehicle.

A heating arrangement may be provided for the blowing arrangement. Thus, ice, snow or other precipitation may be prevented from blocking the blowing arrangement and adversely affecting performance.

The blowing arrangement may include an air inlet for supplying the airflow to an exit portion of the flow control apparatus at the vehicle body surface. The air inlet may comprise at least one aperture located in the region of a rear quarter light window of a vehicle. The air inlet may otherwise comprise another type of simple A-surface intake, such as a side pod, scoop or discontinuous shut line arrangement. Alternatively, the air inlet may comprise an under floor scoop underneath a vehicle such as a car to which the air flow control apparatus is to be fitted, or a powered air feed inlet such as involving a compressor, turbine or another form of electromechanical or mechanical system.

The blowing arrangement may be configured to decrease lift and/or drag when a vehicle to which it is fitted is operating at a Reynolds number above 2 x 10 ⁶ or above 3 x 10 ⁶ for example, above 10 x 10 ⁶ , 12 x 10 ⁶ or 15 x 10 ⁶ being other examples, between 2 x 10 ⁶ and 35 x 10 ⁶ being considered achievable, between 3 x 10 ⁶ and 30 x 10 ⁶ being quite typical and some examples of successful application being operation at 3.39 x 10 ⁶ , 16.9 x 10 ⁶ and 25.44 x 10 ⁶ . In the calculation of Reynolds number in this specification, the characteristic length is the longitudinal length of the vehicle.

A further aspect of the present invention comprises a vehicle including a vehicle airflow control apparatus as set out in any one of the preceding aspects of the invention. The vehicle may comprise a land vehicle. The land vehicle may comprise a motor car. The motor car may be capable of operation in excess of 200 kph or even in excess of 250 or 300 kph, operation at up to or over about 450 to 500 kph being envisaged in some motor car arrangements. The vehicle may, for example, comprise a fastback, GT, saloon, estate, hatchback, SUV or convertible. The present invention has been found through testing to enable the provision of a motor car capable of operating at high speeds and at relatively high Reynolds numbers with good vehicle response and stability across the full speed range during straight line and cornering manoeuvres. Measurements have showed an increase in surface pressure on the vehicle body surface (when it is deck lid) up stream of the blowing arrangement of approximately 900Pa. This translates into a very significant reduction in aerodynamic lift at the rear of the vehicle and can also be associated with a reduction of drag, thus improving efficiency while providing good high speed handling.

The blowing arrangement may emit air into passing air flow with a speed higher than free stream air speed. The present invention may be carried out in various ways and embodiments of preferred vehicle airflow control apparatus is in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a view of pressure distribution on a vehicle body without a blowing arrangement active; Figure 2 is a similar pressure distribution example but with a blowing arrangement active;

Figure 3 shows a CFD depiction of the flow caused by the blowing arrangement of Figure 2, with air jetted out from the A-surface to create an obstacle for the passing air over the boot/deck lid surface; Figure 4 shows a preferred embodiment of a vehicle as in Figures 2 and 3 and including the preferred blowing arrangement;

Figure 5 is a view showing part of a blowing slot of the blowing apparatus;

Figure 6 schematically shows a blowing duct as it approaches the airflow exit at a slot from the flow blowing arrangement;

Figure 7 shows a modified airflow control apparatus having a surface extending generally away from a vehicle body surface, the surface member being in an extended position thereof;

Figure 8 shows the apparatus of Figure 7 with the surface member retracted and covered by a cover;

Figures 9A and 9B show an A-surface air inlet for use with the devices of Figures 1 to 8;

Figure 10 shows an arrangement similar to that shown in Figure 4 for air blowing slot of the preferred airflow blowing arrangement and including three separate but aligned slots in a boot or deck lid instead of one long one;

Figure 1 1 shows a cross-section of a modified airflow control apparatus comprising a deployable spoiler with a blowing slot provided in an upper surface thereof; and

Figure 12 shows a plan view of the airflow apparatus of Figure 1 1 . Figure 1 shows a 44.44 m/s CFD simulation taken along a central vertical plane of a motor car having a front wind screen 12, roof 14 and boot or deck lid 16 and a rear drop down surface 18. The figure also shows a powertrain component 20, torque tube 22, transaxle/differential 24 with rear wheel axis generally at point 26, as well as fuel tank 28. Figure 1 shows that there is a positive downward pressure compared to free stream of about 400 Pa at a lower part 30 of the front windscreen 12, a negative (lift) pressure of about 400 to 600 Pa at upper point 32 of the roof 14 and lift pressure all of the way along from the upper point 32 to rear edge 35 which is between the boot lid 16 and rear drop down surface 18, the pressure at the edge 35 being a negative (lift) pressure of about 300 to 400 Pa.

Figure 2 is a similar view in which the motor car 10 has been modified to include a blowing slot 34 as shown in Figures 2 to 12.

The blowing slot 34 is fed from an inlet 36 which in this example is an A-surface inlet 36 located at a rear corner 38 of rear quarter light area 40 of the car 10. The inlet 36 is connected to the blowing slot 34 by a duct 42 part of which is shown in Figure 6. When the vehicle is in forward motion, as shown in Figure 4, a stream 44 of air passively (i.e. without the use of compressor etc.,) enters into the inlet 38 and is fed by the duct 42 to the slot 34 where the stream 44 emerges as a jet 46 which as shown in Figures 3 and 4 extends across the full width of the blowing slot 34 and is directed substantially vertically into the passing airflow 48, although the angle of the jet 46 may be varied, for example so as to be perpendicular to the adjacent body surface 16/boot lid surface 16.

As shown in Figure 2, which shows flow at the same speed (44.44 m/s) and Reynolds number (about 8.5 x 10 ⁶ ) as that in Figure 1 , the blowing slot 34 results in a high pressure area 50 in front of the blowing slot 34 where the pressure is up to about 500 or 600 Pa above free stream air pressure and the pressure in this area is therefore up to about 900 Pa higher than the same place in Figure 1 . The place 62 at which the pressure returns to positive or at least zero (gauge pressure compared to free stream) on the boot lid 16 is approximately 40 to 50cm in front of rear edge 34 - and this is with a motor car having a wheelbase of about 2.8 metres. Therefore, negative lifting pressure is no longer present for this relatively long distance at the rear of the motor car 10.

Accordingly even with the large back light angle (alpha) between the horizontal/free stream airflow direction and the adjacent angle of the boot lid 16 (which is marked 65 in Figure 1 as well as "alpha" and is substantially 20 degrees), and despite the curved roof profile at the point 32, the blowing slot 34 enables the motor car 10 to be engineered which does not involve significant lift near the rear of the vehicle which will be taken up mainly by the rear wheels on the axis 26. The blowing slot 34 thus has reduced the negative pressure on the upper surface of the motor car 10 and therefore lift. In place of the negative pressure on the boot 16, there is now a high pressure region (at about 400 to 500 Pa or so above free stream) for at least approximately 10cm or more in front of the blowing slot 34 which creates down force. The blowing slot 34 creates an obstruction for the flow travelling over the surface of the boot 16 creating a high pressure region up stream of the exit 34 from the duct 42. The blowing slot therefore jets fast moving air into the flow vertically and/or substantially perpendicular to the adjacent A-surface, creating the aerodynamic effect of a flip, but without changing the back light angle and without having to have a flip or spoiler.

Figure 3 shows a close up of the effect of the air 46 coming out from the blowing slot 34 into the free stream or adjacent airstream. The fast air coming out from the duct forces air to slow down and travel over the top of the jet 46 of air. The exit geometry at the blowing slot has a significant effect on efficiency and a blowing slot width in the direction of flow of both 3mm with a 2mm radius on the edges and larger 5mm slot have been tested, with the 5mm width slot surprisingly performing better than the initially calculated best size of 3mm. The larger 5mm slot increases the mass flow of the duct and ultimately the effect that the blowing slot 34 has on lift and drag reduction. Thus, in Figure 5, the distance D, which is the longitudinal size of the slot along the airflow direction, is substantially 5mm. A slot larger than 5mm could be provided in other embodiments but may not be acceptable from an aesthetic point of view in all cases. As shown in Figure 6, the duct 42 which is a generally hollow element is in the region of the blowing slot 34 angled up towards the blowing slot 34. For a distance E, which is approximately 75mm, the direction of flow in the duct 42 is substantially directly towards the slot 34 and is within about 10 or 20 degrees or so from being directly towards the slot 34. The inventors have found that the sooner the duct 42 curves upwards to face the surface of the boot lid 16 normal from its original path, i.e. the path 66 from the inlet 36 which is shown in Figure 6, the more powerful the blowing slot 34 is, i.e. the longer the air had pointed up at the underside of the boot or deck lid 16, the better the performance of the blowing slot 34.

The distance X shown in Figure 6 of the blowing slot 34 to the rear or trailing edge 35 of the deck lid surface 16 is important and the lesser this distance the more powerful and effective the blowing slot 34 is in many embodiments. The distance X is substantially exaggerated in Figure 6 since as can be seen in Figures 3, 4 and 5, the trailing edge of the blowing slot is approximately 5 to 10mm from the edge 34. As shown in Figure 3, the edge 35 between the boot lid surface 16 and the overhung drop down surface 18 has a relatively small radius which is in some embodiments about or less than 20mm. Directly after the blowing slot 34 is a low pressure region of separated flow which can in some embodiments generate a concentrated lift force and to minimise this effect, the blowing slot 34 is normally positioned as close to the trailing edge 35 of the deck lid 16 as possible.

It is notable that the entire upper surface of the motor car at the central section of Figure 2 from the windscreen 12 and over the roof top 14 and past the deck lid 16 to the rear edge 35 is non-concave - all of the way along, it is convex or substantially flat. For about a first quarter of horizontal distance back from the leading lower edge of windscreen 12 to rear edge 35, this central section is substantially flat or slightly convex, for about a middle two quarters the section is convex and for about a last quarter the section is slightly concave or substantially flat and sloped down at about 15 to 25 degrees more specifically at about 20 degrees to horizontal. The width of the blowing slot 34 across the motor car 10 provides linear performance sensitivity, i.e. as the slot increases in width (assuming an increasing mass flow to maintain exit velocity), the lift linearly reduces with the drag. In the real world, where the mass flow stays relatively constant, the lift and drag continue to decrease with increasing slot width to a point where the exit velocity becomes very low (approximately equal to or less than 0.2 times the velocity of the free stream flow).

As shown in Figure 7, a surface member 70 or "Gurney" - type member may be positioned upstream of the blowing slot 34 exit and it has been found that this may cause more flow to be drawn through the duct 42. As shown in Figure 8, the blowing slot 34 may be sealed when it is not needed, i.e. while the motor car 10 is stationary, has the engine off or is travelling at low speed. Instead of the orientation in Figure 7, in which the surface member 70 is deployed and extends from the A- surface/boot lid 16 of the motor car 10 with the cover panel 72 moved out of the way in the X (longitudinal) and Z(vertical) directions, as shown in Figures 8, the Gurney member or surface member 70 is retracted below the height of the boot lid surface 16 and the cover member 72 is slid along and moved down such that its upper surface is aligned with the upper surface of the boot lid 16 and a rear most panel element 16A just in front of the edge 35 which leads down to the rear drop surface 18. As can be seen in Figure 7, the blowing slot 34 is essentially a gap in the middle of the surface member 70 where the blowing slot air is released as the jet 46, part of which is shown in Figure 7. The configuration shown in Figure 8, with the cover panel 72 folded back into A-surface of the motor car 10, the Gurney member or surface member 70 is hidden. This advantageously allows the arrangement to meet a design objective for clean lines which may be set in some circumstances yet still provide a good aerodynamic system.

A mechanism or other movement means (not shown) is provided for moving the member 70 and other arrangements may be used in other embodiments to seal the duct when the vehicle is stationary and/or deployed.

To form the inlet 36, the side glass of the rear quarter light 40 has been rolled inboard to reveal an opening comprising the inlet 36. The inlet 36 in other embodiments may be replaced while still providing the same type or similar blowing slot 34 in which the air is controlled/forced to react with the free stream upon leaving the duct 42. Other possible intake method includes simple A-surface intakes, such as side pod, scoop, discontinuous shut lines etc, and under floor scoop, similar to that shown in Figure 4 but underneath the motor car end/not on an A-surface, or a powered air feed, such as involving a compressor, turbine or other electro-mechanical system.

The blowing arrangements of the embodiments described herein have a working range where the effects of the device are measurable from 40 to 200 mph, although this range can be extended to well above 200 mph because the effects of the blowing slot increase with vehicle speed and this has been shown both with CFD and on test drives. It is considered therefore that the blowing arrangements described in the present application can be used on motor cars at the speeds up to equal to or in excess of 260 or 300 mph for road vehicle applications. In aerospace applications, higher speeds are envisaged. With the Reynolds number as calculated by multiplying the wheel base length of the vehicle which is 2.803 meters by the density of air at 15°C which is 1 .225 kg per cubic meter and multiplying by the velocity of the free stream air in meters per second, and then dividing by the viscosity of the air at 15°C which is 1 .81 x 10 ^~5 kg per meter per second, the arrangements in the present application operate at 40 miles per hour at a Reynolds number of 3.39 x 10 ⁶ at 200 miles per hour of 16.96 x 10 ⁶ and at 300 miles per hour of 25.44 x 10 ⁶ . CFD analysis so far has shown that the blowing arrangement designs in the present application have the following performance capabilities on a vehicle as shown in Figures 2, 3 and 4, although the values will change dependent upon the application of the blowing slot and the specific vehicle geometry. With an arrangement as shown and described with reference to Figures 2 to 6, the drag reduction as C _d is 10 and rear axle lift reduction is C _L r is 35. For the arrangement shown in Figures 7 and 8 the drag reduction C _d is 4 and rear axle lift reduction C _L r is 50. These are very useful reductions in drag and lift suitable for improved economy, stability and road handling. Physical tests have been performed using first an unmodified vehicle 10 similar to that shown with reference to Figure 1 , second with the vehicle 10 modified to have a blowing arrangement as described with reference to Figures 2 to 6 and third with the vehicle 10 modified to have an arrangement similar to that in Figures 7 and 8 with a deployed surface member or Gurney member 70 as shown in Figure 7.

The motor vehicle was instrumented to provide data along with drive evaluation and measurements included surface pressures, vehicle ride height, suspension displacement, lateral accelerations and vehicle speed. A series of tests were carried out and the test procedures explored vehicle response and stability across the full vehicle road speed range during straight line and cornering manoeuvres. The tests also evaluated various failure modes, operation with one or both side windows open, in yaw and with one side inlet 36 blocked.

The test measurements showed an increase in surface pressure on the deck lid upstream of the blowing slot 34 of approximately 900 Pa translating to a significant reduction in aerodynamic lift acting at the rear of the vehicle.

The professional test driver noted the following information and it must be noted here that the unmodified vehicle 10 compared to average road vehicles is already exceptionally fast with highly superior and safe vehicle handling, so the results are comparative only.

UNMODIFIED MOTOR CAR

Compared to the modified vehicle 10, vehicle stability at 200 kph and 250 kph sine sweep manoeuvre had a smaller under steer limit. The car 10 slid from the rear. MOTOR CAR MODIFIED AS IN FIGURES 2 TO 6

The vehicle stability was improved during 200 kph and 250 kph sine sweep manoeuvring. There was some understeer at the limit and the car slid from the rear. The rear lift appeared to be reduced, giving the rear tyres more capability at the limit. MOTOR CAR MODIFIED WITH BURN SLOT AS SHOWN IN FIGURE 7 Vehicle stability was improved at 200 kph and 250 kph sine sweep. There was understeer at the limit. The car slid from the rear when provoked. The rear lift appeared to be significantly reduced giving the rear tyres more capacity and capability at the limit. Failure modes have been considered and can be dealt with by failure controller outputs as follows. Failure modes of ice packing, detected with pressure measuring equipment, can be handled by a failure controller output consisting of a transmission of a heating signal to a heater means (not shown) for the duct 42, a driver warning signal and/or speed limiter signal. Failure of the Gurney or surface member 70 failing to deploy be handled by a failure controller output comprising a driver warning and/or a speed limiter signal. A failure of the Gurney or surface member 70 failing to stow can be handled with a driver warning. A failure mode of one or more windows at the side of the vehicle being lowered can be handled by no action being necessary. A failure mode of a duct 42 leaking can be handled by a failure controller output consisting of a driver warning. Figure 10 shows a modification in which the blowing slot 30 of Figure 4 is replaced by three blowing slots 34 which are placed in line across the boot lid 16.

In other embodiments, the blowing slot may instead of a length of 5mm in the flow direction of freestream flow have a length from 2mm to 8mm. The width of the blowing slot across the motor car may be chosen for the application and in some embodiments 30 cm in length over a rear haunch panel 80 may be used and in others a width of around 1 .5 meters across the span of the rear of the motor car can be used. The simulations in Figures 1 and 2 are run at 44.4 meters per second. At this speed, the air exiting the duct was 50 meters per second. The exit angle from the duct can also be varied and the range of plus to minus 60° relative to normal to the surface of the boot lid 16 has a desirable effect. The larger the velocity exit, the steeper the angle that can be used. The main operating window is between 45° aiming upstream from normal to 30° downstream from normal.

Figure 1 1 shows a cross-section of a modified airflow control apparatus comprising a moveable vehicle body surface section shown generally at 720 with a blowing slot 340 provided in an upper surface thereof. Here, not cover is provided. This arrangement is a variation of the arrangement shown in Figure 7.

In Figure 1 1 , a surface member 700 or "Gurney" - type member may be positioned upstream of the blowing slot 340 exit. In contrast to Figure 7, the surface member 700 joins an upper surface 721 , 722 of the body surface section 720. In the embodiment, the surface member 700 is generally perpendicular to the upper surface 721 , 722 of the body surface section 720.

The upper surface 721 , 721 of the body surface section 720 and surface member 700 may be retracted such that the surface 721 , 722 of the body surface section, or at least portions thereof, is in substantial alignment with an adjacent upper surface 160 of the body of the vehicle. The body surface section 720 and surface member 700 can be deployed, for example above a predetermined vehicle speed or air mass flow measurement, by extending the gurney or surface member 700 from the A- surface/boot lid 160 of the motor car. The body surface section 720 and surface member 700 can be raised above the adjacent vehicle body surface. The surface member 700, which may comprise part of the vehicle body surface section 720, may then face upstream of the vehicle to act as a Gurney-type flap.

When in the deployed, raised state, the surface member 700 is located against an inner surface edge 161 which extends below the upper surface 160 of the vehicle. The inner surface edge 161 joins a swan-neck like profile surface 162 which forms a channel 163 in which the surface member 700 can be received when in a retracted state.

The blowing slot 340 comprises front and rear surfaces 422, 421 , which extend into duct 420, which duct is fluidly coupled to an inlet such as the inlet 36 shown in Figure 2.

When the body surface section 720 is deployed and retracted, the front and rear surfaces 422, 421 of the blowing slot 430 increasingly or decreasing overlap with corresponding surfaces 426, 427 of the duct 420. Between the corresponding surfaces 426, 427 of the duct 420, sealing elements 424a, b and 423a, b are provided, to provide a seal between the surfaces and prevent leakage of air in duct 420 into the interior surfaces of the body surface section 720.

When in a retracted position, the rear surface 722 of the body surface section 720 extends over the trailing edge 350 of the deck lid, overlapping, with an obtusely profiled lip 723, partially over the rear drop down surface 180.

Air flow in the duct is represented by arrow 660. An air-guide 425 may be provided in the duct 420 to prevent stagnation of air in a square recess 428 in the duct formed to receive the rear surface 421 of the blowing slot 340 when the body surface section 720 is retracted. A drain (not shown) may be provided in the duct 660 to drain liquid which may collect in the duct 420.

The longitudinal depth b of the blowing slot 340, in the embodiment, is of the order of 13.5 mm. A depth of 2 to 10 mm is also contemplated. When extended, the surface member 700 has a height a of around 40 mm. The overall depth of the body surface section is around 55 mm. The blowing slot 340 is located preferably as near to the edge of the surface member 700 as possible. The surface member is positioned as near as possible to the drop line 180 of the vehicle. The radius between the surface member 700 and the front body surface section surface 721 is made as sharp as possible, although is a minimum of 2.5 mm to comply with legal requirements. The exact dimensions can be chosen to provide suitable aerodynamic performance. The effect of the blowing slot and surface member 700 is generally the same as described in relation to the embodiment of Figures 7 and 8. The leading face provided by the surface member 700 serves to create a high pressure region that acts on the vehicle's boot and a low pressure bubble behind itself which can help suck more air out from the air inlet in the side of the vehicle.

The deployable body surface section 720 provides a smooth vehicle body profile when retracted. Similarly to the embodiment of Figure 7, the deployable surface member provides an additional means of down force should, for example, the blowing slot become blocked, for example, by snow. The duct may be provided with filters or grates of the like to prevent the ingress of air-borne objects in the duct. Warm air, for example, from cooling of the engine, may also be directed through the duct to prevent freezing of mechanisms.

When the body surface section 720 is retracted, the arrangement can meet design objective for clean lines which may be set in some circumstances yet still provide a good aerodynamic system.

Figure 12 shows a plan view of the arrangement shown in Figure 1 1 . The body surface section 720 is shown retracted.

The blowing slot comprises two blowing slot sections 345a, 345b, each of which extends approximately half way across the lateral width of the body surface section. Each blowing slot 345a, 345b is fed with air from a respective inlet on each side of the vehicle, for example, the inlet 36 shown in Figure 2.

A mechanism or other movement means (not shown) is provided for moving the body surface section 720 and surface member 700. Actuators 345a, 345b may be provided at either side of the body surface section 720. These actuators can include, but are not limited to, hydraulic, pneumatic or other mechanical means.

Various changes can be made to the embodiments described without departing from the invention.