Abstract: The invention relates to a module, comprising: —at least one, preferably only one, tangential turbomachine (28-1; 28-2) comprising a bladed wheel (32-1; 32-2) and a motor (33-1; 33-2) for rotationally driving the bladed wheel (32-1; 32-2), —a frame (30-1; 30-2) forming an opening (60-1; 60-2), preferably only one opening, —a shut-off means (62-1; 62-2) designed to selectively shut off the opening (60-1; 60-2), the shut-off means (62-1; 62-2) having at least two regions which, in contact in a position of the shut-off means (62-1; 62-2) in which the opening (60-1; 60-2) is left free, are at a distance apart in a position in which they shut off the opening (60-1; 60-2).

Abstract: A heat exchange module includes at least a first heat exchanger and a ventilation device intended to generate a flow of air. The ventilation device includes at least one cross-flow fan for setting in motion an air flow and a guide means that includes at least one air guiding element for guiding the air set in motion by the cross-flow fan. The first heat exchanger and the ventilation device are positioned relative to one another in such a way that the air flow set in motion by the ventilation device is fed into the heat exchanger and, when the fan is in operation, this air is drawn in by the cross-flow fan passes through the heat exchanger before entering the cross-flow fan.

Abstract: The invention relates to a cooling module (22) for a motor vehicle (10), comprising: —at least one heat exchanger (301-303) delimiting a surface, referred to as the working surface, —at least one first tangential-flow turbomachine (28-1) and a second tangential-flow turbomachine (28-2), each of said turbomachines (28-1, 28-2) being capable of creating an air flow in contact with said working surface, each of said turbomachines comprising a rotor rotating about an axis and a volute for housing the rotor, comprising an air guiding portion and an air outlet outside the turbomachine, said turbomachines (28-1, 28-2) being arranged such that the air outlet of the first turbomachine (28-1) is arranged opposite the guiding portion of the second turbomachine (28-2).

Abstract: An air-cooled internal combustion engine including a crankshaft rotating about a crankshaft axis, a first cylinder having a first cylinder head, a second cylinder having a second cylinder head, and a blower assembly. The blower assembly includes a blower housing, a first fan, and a second fan. The first fan is positioned proximate the first cylinder and the second fan is positioned proximate the second cylinder.

Abstract: A control system for controlling a work machine includes an engine for producing power to propel the work machine during a normal operating mode, a cooling system for cooling at least the engine during the normal operating mode, and a controller for controlling the cleaning system during the normal operating mode and a clean operating mode. During the normal operating mode, the engine is running and the controller operably controls a cooling fan of the cooling system to rotate in a first rotational direction to produce a first air flow in a first direction. During the clean operating mode, the engine is not running and the controller operably controls the cooling fan to rotate in a second rotational direction to produce a second air flow in a second direction. The first rotational direction is opposite the second rotational direction, and the first direction is opposite the second direction.

Abstract: A method of making a modular fan includes positioning a mounting pad of a blade between two plates of a center hub assembly, aligning the blade such that the mounting pad is located radially inward of an outer edge of at least one of the two plates, and spacing the outer edge of the at least one of the two plates from the blade at the outer edge.

Abstract: Disclosed is a chainsaw capable of introducing outside air into a body casing by rotation of a cooling fan to adequately cool a control unit provided inside the body casing. The chainsaw is configured to cool a control unit provided inside a body casing by a cooling fan being rotated under driving of an electric motor, wherein a handle comprises a base portion through which the handle (30) is attached to the body casing, and a grip formed to extend from the base portion in such a manner as to be grippable by a worker; and an air inlet is formed in a counter wall of the body casing opposed to the base portion of the handle, and wherein the base portion is attached to the counter wall of the body casing to cover the air inlet in an air introduceable state.

Abstract: An engine includes a crankcase with cylinders and fins on outer circumferences of the cylinders. A crank shaft penetrates the crankcase. A cooling fan is provided on an outer side of the crankcase and arranged coaxially with the crank shaft. A first cover covers an outer side of the cylinders and the crankcase, and the cooling fan. A second cover capable of being detached from/attached to the first cover. The first cover includes a first opening facing the cooling fan, and second openings facing the fins. The second cover includes an air inlet facing the first opening, and attached to the first cover to cover the first opening and the second openings.

Abstract: A gas turbine engine has a nose cone, a fan for delivering air into a bypass duct as bypass flow, and into a core engine to be delivered to a compressor. The nose cone includes a vent to receive air and deliver the air across a heat exchanger, which receives a fluid to be cooled. The air from the vents is delivered to an outlet downstream of the heat exchanger, such that a majority of the air being delivered to the outlet becomes part of the bypass flow.

Abstract: In one possible implementation, a motor is provided including a rotor and a stator. Front cooling fins are thermally coupled to a front of the stator, and rear cooling fins are thermally coupled to a rear portion of the stator. The winding is between the front and rear cooling fins.

Abstract: An apparatus including a fixed part, a rotary support configured to be driven in rotation relative to the fixed part, at least one item of electrical equipment carried by the rotary support, and a power supply device configured to supply electrical energy to the electrical equipment. The power supply device includes an asynchronous machine including a stator fixed to the fixed part and a rotor carried by the rotary support, and an excitation device. The stator includes an electrical circuit including at least one switch configured to switch between an open state in which the electrical circuit is open and a closed state in which the electrical circuit is closed. The rotor includes at least one winding connected to the electrical equipment. The excitation device is configured to provide a reactive current to the electrical circuit of the stator or to the winding of the rotor.

Abstract: A nose cone assembly for a gas turbine engine and method of circulating air in a gas turbine engine are disclosed. The nose cone assembly includes a nose cone having an aperture communicating air to an interior space of the nose cone and a discharge member communicating the air out of the nose cone.

Abstract: An apparatus includes a substrate having one or more fastener apertures that extend therethrough. Each fastener aperture has a centerline and includes first and second circular segmented regions and a central channeled region. Each circular segmented region has a diameter and a segment length that extends along the centerline, wherein the segment length is greater than one-half the diameter. The central channeled region extends along the centerline between the first and the second circular segmented regions. The central channeled region has a height that is less than the diameter of the first and the second circular segmented regions.

Abstract: An apparatus or system includes a component that generates or transfers noise having a frequency within a noise frequency range. The component may include a boundary. The apparatus or system may be an engine in some examples. The engine may additionally include a micro-perforated sheet positioned a distance from the boundary. The micro-perforated sheet may include a plurality of micro-perforated holes, and may be configured to absorb sound within an absorption frequency range based on parameters of the micro-perforated sheet. The parameters may include the distance from the boundary and dimensions of the micro-perforated holes, and may be set such that the absorption frequency range overlaps the noise frequency range.

Abstract: A work vehicle includes a vehicle body, a guiding pipe, a first heating section, and a second heating section. The vehicle body has a partition wall that partitions a space in an inner section into a first region and a second region. The guiding pipe is configured to guide a reducing agent. The guiding pipe has a first pipe section and a second pipe section. The first pipe section is positioned inside the first region. The second pipe section is positioned in the second region. The first heating section heats the first pipe section. The second heating section heats the second pipe section and adjusts the temperature independently from the first heating section.

Abstract: A vision system for a vehicle includes a camera having an imager and a lens. The camera is disposed at an exterior portion of a vehicle and has a field of view exterior of the vehicle. An air flow element has an inlet port and an outlet port, with the outlet port configured to direct air flow in front of the lens to direct debris away from the lens. The outlet port is configured to direct air flow at a velocity that is greater than a velocity of air flow that is flowing into the inlet port. The inlet port may have an inlet area that is substantially greater than an outlet area of the outlet port. The system may include an air flow generating device for generating or enhancing air flow through the air flow device.

Abstract: A cooling device for use with an engine is provided. The cooling device includes a flow control portion that includes a base and an opening defined therein. The flow control portion also includes a plurality of blades that extend from at least a portion of the base. The cooling device also includes a grid portion having an opening defined therein, said grid portion opening is substantially concentrically aligned with the base opening. An attachment portion is configured to couple the cooling device to at least one rotatable component of the engine. Each of the flow control portion, the grid portion, and the attachment portion are formed integrally together such that the cooling device is a single component.

Abstract: A cooling device for use with an engine is provided. The cooling device includes a flow control portion that includes a base and an opening defined therein. The flow control portion also includes a plurality of blades that extend from at least a portion of the base. The cooling device also includes a grid portion having an opening defined therein, said grid portion opening is substantially concentrically aligned with the base opening. An attachment portion is configured to couple the cooling device to at least one rotatable component of the engine. Each of the flow control portion, the grid portion, and the attachment portion are formed integrally together such that the cooling device is a single component.

Abstract: A power tool has an internal combustion engine with a cylinder. An injection valve supplies fuel to the internal combustion engine. A fuel pump conveys fuel from a fuel tank to the injection valve. A fan wheel is provided that is driven by the internal combustion engine. The cylinder is arranged in a first cooling zone of the power tool and the fan wheel conveys cooling air through the first cooling zone. The fuel pump is arranged in a second cooling zone of the power tool. Between the first cooling zone and the second cooling zone a buffer zone is arranged. The buffer zone is separated by at least one first partition from the first cooling zone and by at least one second petition from the second cooling zone.

Abstract: A chassis for mounting a set of operating components of a power head of a surgical instrument is disclosed. The power head has a housing enabling access to an interior volume of the power head encompassed by the housing. The set of operating components have a proper configuration for alignment when mounted within the interior volume encompassed by the housing. The chassis is configured to provide the proper configuration for alignment of either an original or replacement set of operating components mounted on the chassis if the chassis and set of operating components are mounted within the interior volume of the housing. The chassis may be formed from metal and the housing formed from a polymer. The chassis may be configured to ground at least one electrical component.

Abstract: A heat dissipation type starting fly wheel of a model vehicle gasoline engine includes a main body formed with a through hole in the center and having its outer circumferential side annularly provided with a protruding ring, which has one side fixed thereon with a plurality of blades. Thus, when driven to rotate, the main body and the protruding ring will produce an effect of a fly wheel, and when rotated, the blades on the protruding ring will disturb air to form air convection, able to attain an object of enhancing heat dissipation efficacy of the model vehicle gasoline engine.

Abstract: A debris passage for a cooling box of a work vehicle. Airflow is provided into the cooling box from the exterior environment. A plurality of heat exchangers transfer heat into the airflow. The debris passage is defined between opposing heat exchangers to permit debris to pass from the airflow to the exterior of the cooling box. In one embodiment, the debris passage is underneath an air mover and is substantially vertical.

Abstract: In an internal combustion engine (2) of a portable handheld work apparatus, the cylinder (3) is provided with cooling ribs (4, 4?). A cooling airflow is generated by the fan wheel (13) and is guided over the cooling ribs. A carburetor (9) is temperaturized as required by the heated cooling air. A control of the cooling airflow to the carburetor (9) takes place in that an opening (11), which passes the heated cooling air, is selectively closed or opened via a closure element (12). In order to obtain improved cooling of the cylinder during summer operation as well as during winter operation, the closure element (12) is provided with at least one air guide wall which extends essentially transversely to the cooling airflow and causes this cooling air to be partially backed up and deflected.

Abstract: An engine tool comprises an engine, a housing retaining the engine, a top cover provided above the housing, and an air cleaner room provided at the housing. The engine tool is structured in such a way that external air introduced in the air cleaner room or the housing flows through a space formed between the housing and the top cover. The engine tool further comprises a handle part which is grabbed by a user and which is provided above the top cover. External air flows through a space formed between an area of the top cover where the handle part is provided and the housing. The engine tool still further comprises an air inlet for introducing external air provided at a front part of the engine tool.

Abstract: A cooling apparatus of an engine includes a cooling fan, a fan housing, and a shroud guiding cooling air from the fan housing to the outer circumferential surface of an engine body portion. Further, a cooling air passage passing throughout in a cylinder head from one side surface of the cylinder head to the other side surface thereof is formed in the cylinder head, and a narrowed or throttle guide portion which guides the cooling air from the interior of the fan housing to an inlet opening of the one side surface of the cooling air passage is formed in the shroud.

Abstract: A motor driven implement having an internal combustion engine having at least one cylinder and at least one carburettor, which is disposed in a carburettor chamber, which is separated by an intermediate wall from an engine compartment, wherein a fan wheel is further provided by which means air from the engine compartment can be introduced through an engine compartment opening in the intermediate wall into the carburettor chamber. A warm air opening is provided in the intermediate wall, through which the air heated over the cylinder can be introduced into the carburettor chamber and wherein an adjusting element is provided which can be brought into a summer position in which the engine compartment opening is open and the warm air opening is closed and which can be brought into a winter position in which the engine compartment opening is closed and the warm air opening is open.

Abstract: A hand-held work apparatus includes an engine housing (200). An internal combustion engine (202) is arranged in the engine housing (200) and includes a cylinder (204) and a crankshaft. A fan wheel (214) is driven directly or indirectly by the crank shaft, such that the fan wheel (214) rotates about an axis A. A fan housing (216) surrounds and cooperates with the fan wheel (214). A combustion air inlet (224) is located radially outside of the fan wheel (214) for leading air to the internal combustion engine (202). Further, the combustion air inlet (224) includes a combustion air inlet port (226) and a combustion air duct (228). The combustion air inlet port (226) is provided with a first edge (230), which first edge (230) is located radially adjacent to the periphery (220) of the fan wheel (214).

Abstract: An air-cooled internal combustion engine includes an engine block, a blower assembly including a blower housing and a fan, and a static cover. The static cover includes multiple air intake openings and is configured to prevent user access to a moving component of the engine. The blower housing is configured to at least partially direct air to the engine block. The fan is configured to move air into the blower assembly through the air intake openings when rotating in a first direction in a cooling mode and to move air out of the blower assembly through the air intake openings when rotating in an opposite second direction in a debris-removal mode.

Abstract: In an engine including a cooling fan provided at one end of a drive shaft to cool the engine, a muffler is attached such that a longitudinal direction thereof coincide with a direction of gravity, and a muffler accommodating chamber is formed by a muffler cover. A portion of cooling air generated by the cooling fan is introduced into the muffler accommodating chamber so as to cool the muffler. At the muffler accommodating chamber, a cooling air outlet is provided at an upper end of a cooling passage, such that the waste heat of the muffler is discharged from the cooling air outlet to the outside during the stop of the engine. A cooling air inlet is disposed below the cooling air outlet such that the cooling air flows from the lower side to the upper side of the muffler.

Abstract: A cooling fan includes: a hub; a plurality of cooling vanes provided along an outer circumference of the hub; and an annular connector for connecting the cooling vanes. The hub is provided with a through hole that axially penetrates the hub. A first cover on a case for covering an outward side of the cooling fan is provided with a first outer-air intake. A second cover for partitioning between the cooling fan and a crankcase and for covering an inward side of the cooling fan is provided with a second outer-air intake. With this arrangement, even when one outer-air intake (for instance, the first outer-air intake) adjacent to where the cooling vanes are provided is clogged by a large amount of dust generated during operations, the cooling vanes can breathe from the non-clogged other outer-air intake (for instance, the second outer-air intake) through the through hole, thereby restraining reduction in air flow.

Abstract: A cylinder cooling apparatus for an air-cooled engine is equipped with a cooling fan provided on one end section of a crankshaft; a pair of pushrod insertion holes for air intake and exhaust valves formed in a cylinder outer circumferential wall section; a fan shroud for covering the cooling fan and for covering the cylinder outer circumferential wall section in which the pushrod insertion holes are formed; a cutout ventilating section formed in the cylinder outer circumferential wall section between the pair of pushrod insertion holes; and tunnel-shaped ventilating holes formed in the cylinder outer circumferential wall section between the pushrod insertion hole disposed on the side of the cooling fan and a cylinder bore and extending from the cylinder outer circumferential wall section on the side of the cooling fan to the cutout ventilating section.

Abstract: An air cooling system provides cooling air within an engine bay of a vehicle. The vehicle includes a radiator and a cooling fan, the cooling fan is operable to force air to flow through the radiator, and the cooling fan is also operable to blow air within a blow zone away from the cooling fan and into the engine bay. The air cooling system includes a duct having a first end that defines an inlet, a second end that defines an outlet, and a sidewall that extends between the first end and the second end. The duct is operable to be mounted to the vehicle with the second end and the outlet disposed within the downstream blow zone such that air exiting the outlet is blown by the cooling fan toward the engine bay.

Abstract: A rotating screen, for use with a centrifugal fan of an engine, includes a hub having a rotational axis and a plurality of blades extending radially outwardly from the hub. Each of the blades includes a root adjacent the hub, a tip, a leading edge extending between the root and the tip, and a trailing edge extending between the root and the tip. The blades also include an airfoil shape. The rotating screen also includes a band concentric with the hub and interconnecting the tips of the respective blades.

Abstract: A blower system for an engine includes a base of a blower scroll coupled to an engine crankcase. The base has a bottom wall with an opening sized to accommodate an end of a crankshaft. The base also has a sidewall extending away from the crankcase. The blower system further includes a blower housing fastened to the base, without the use of threaded fasteners. Together the blower housing and the base form a chamber having an inlet and an outlet. Also, the blower system includes a fan within the chamber. The fan is driven by the crankshaft and is designed to direct a flow of air through the outlet of the chamber.

Abstract: An exhaust fan chamber is defined with a belt cover and a fan cover provided over the belt cover, and an exhaust fan is accommodated in the exhaust fan chamber. The fan cover has an air intake port for sucking air within an engine cover into the exhaust fan chamber and an exhaust outlet port for discharging air within the exhaust fan chamber to outside of the exhaust fan chamber. The exhaust outlet port is in communication with an exhaust opening formed in an upper portion of the engine cover so that the air discharged through the exhaust outlet port is discharged to outside of the engine cover through the exhaust opening.

Abstract: An air bearing for a ram air fan includes a shaft having a first end portion that defines a cap end, a second end portion that defines a thrust shaft receiving end, and an intermediate portion extending between the first and second end portions. The cap end includes a cap pilot bore and the thrust shaft receiving end includes a thrust shaft pilot section. The thrust shaft pilot section has an outer diameter of between about 1.6032-inches (about 40.7212 mm) and about 1.6002-inches (about 40.6450 mm).

Abstract: A rotating screen, for use with a centrifugal fan of an engine, includes a hub having a rotational axis and a plurality of blades extending radially outwardly from the hub. Each of the blades includes a root adjacent the hub, a tip, a leading edge extending between the root and the tip, and a trailing edge extending between the root and the tip. The blades also include an airfoil shape. The rotating screen also includes a band concentric with the hub and interconnecting the tips of the respective blades.

Abstract: A centrifugal fan for use with an engine includes a hub defining a rotational axis, a plurality of blades arranged about the rotational axis, and a screen coupled to the hub and blades for co-rotation therewith. The hub, the blades, and the screen are integrally formed as a single piece.

Abstract: A reduced size four-stroke engine and a working machine using the same are provided. A fuel tank is disposed in the space below a carburetor and an engine base is integrally formed with a fuel tank. By this means, the fuel tank is disposed in the space below the carburetor, and therefore the oil tank is not required to be disposed below the oil tank, so that it is possible to reduce the size.

Abstract: An apparatus and method for facilitating coupling of a fan and a flywheel, as well as an internal combustion engine and other applications for such apparatus and method are described herein. In one example embodiment, an apparatus for facilitating coupling of a fan and a flywheel includes a plurality of protrusions formed on the fan, wherein each of the protrusions defines a respective hole therewithin, a plurality of receiving structures formed in the flywheel, and a plurality of pins. The receiving structures are positioned so that, when the fan is axially aligned with and adjacent to the flywheel, the protrusions are respectively received by the receiving structures. Further, when the pins are inserted into the holes, portions of the protrusions expand outwardly so that interference is created between surfaces of the protrusions and the receiving structures, whereby due to the interference the fan and flywheel are rotationally coupled.

Abstract: A device is provided for a piece of equipment with an internal combustion engine having a crank case and a combustion space, wherein an air cooling stream is present for cooling the internal combustion engine. The device, on the one hand, is effective for cleaning of the intake air, and on the other hand, a thermal separation between tank and crank case is achieved in a simple manner. The device includes at least one recess, which is constructed open or closed, and is arranged in the crank case, and is separated from an interior of the crank case and forms air cushions.

Abstract: A power tool has an internal combustion engine with an injection valve through which fuel is supplied to the internal combustion engine; a crankcase; and a crankshaft arranged in the crankcase so as to be rotatable about an axis of rotation. A fan wheel housing is provided and a fan wheel is arranged in the fan wheel housing and conveys cooling air to the internal combustion engine. In the fan wheel housing a connecting opening is formed. The injection valve is arranged in a cooling area, wherein cooling air is supplied by the fan wheel through the connecting opening to the cooling area.

Abstract: A power tool has an internal combustion engine with a cylinder. An injection valve supplies fuel to the internal combustion engine. A fuel pump conveys fuel from a fuel tank to the injection valve. A fan wheel is provided that is driven by the internal combustion engine. The cylinder is arranged in a first cooling zone of the power tool and the fan wheel conveys cooling air through the first cooling zone. The fuel pump is arranged in a second cooling zone of the power tool. Between the first cooling zone and the second cooling zone a buffer zone is arranged. The buffer zone is separated by at least one first partition from the first cooling zone and by at least one second petition from the second cooling zone.

Abstract: A fan drive system is provided that is hydraulically controlled having an electrical failure mode wherein midrange operation of the fan drive system is maintained. Accordingly, in the failure mode, a fan drive system hydraulic relief valve is not closed thereby ensuring a degree of operation of the fan drive system even during periods of electrical failure.

Abstract: In a device for providing clean combustion air for an internal combustion engine of a working tool, provision is made for a cyclone filter into which ambient air contaminated with impurities can be sucked. A partial air flow contaminated with impurities can be extracted by suction from the cyclone filter, a partial air flow substantially freed from impurities is branched off from the cyclone filter and supplied to the internal combustion engine as combustion air. A fan which provides a flow of cooling air against the internal combustion engine, is at least partially accommodated in a housing. Provision is made in the housing for at least one suction bore, which leads into the housing and provision is made in the area of the suction bore for a flow element for creating a low pressure. The partial air flow contaminated with impurities is connected to the suction bore.

Abstract: The invention relates to a portable, hand-held work apparatus such as a chain saw, a cut-off machine, a brush cutter or the like with an air cooled combustion engine. A cooling air blower (4) which includes a cooling air spiral (6) and a fan wheel (5), moves a cooling air flow (13) for cooling the combustion engine. Further a combustion air channel (30) leads from the cooling air blower (4) to the combustion engine (2) and branches off from an air output window (20) provided in the base (14) of the cooling air spiral (6). The diverting device (21) includes a guide wall (22) which extends into the cooling air spiral (6) between the fan wheel (5) and the air output window (20). In order to divert a large volume of combustion air (19) with minimal disruption to the cooling air flow, the pass-through cross-section of the air output window (20) tapers in the direction of the diverted combustion air (19) from a first pass-through area (29) to a second pass-through area (31).

Abstract: An air-cooled general-purpose engine includes: a cooling fan fixed to one end portion, protruding outward from one end wall of an engine main body, of a crankshaft; and a shroud which is mounted to the engine main body, and which defines a cooling-air path between the shroud and the one end wall, the cooling-air path guiding a cooling air blown under pressure from the cooling fan. The air-cooled general-purpose engine includes: an oil pump which pumps up an oil from an oil reservoir; and an oil-supply path which is formed in the one end wall, facing the cooling-air path, of the engine main body, and configured to guide the oil discharged from the oil pump to a valve operating chamber in a head portion of the engine main body, and a jet for jetting the oil is provided in an opening of the oil-supply path, the opening being open to the valve operating chamber.

Abstract: A blower system for an engine includes a base of a blower scroll coupled to an engine crankcase. The base has a bottom wall with an opening sized to accommodate an end of a crankshaft. The base also has a sidewall extending away from the crankcase. The blower system further includes a blower housing fastened to the base, without the use of threaded fasteners. Together the blower housing and the base form a chamber having an inlet and an outlet. Also, the blower system includes a fan within the chamber. The fan is driven by the crankshaft and is designed to direct a flow of air through the outlet of the chamber.

Abstract: An arrangement for cleaning of intake air for an air-cooled internal combustion engine of a motor-driven tool, such as a chain saw. The arrangement includes an air conductor surrounding a fan wheel arranged to propel intake air around an axis of the fan wheel. An inner wall of the air conductor is arranged for guiding air propelled by the fan wheel. An air nozzle for cleaning of intake air is arranged on the inner wall of the air conductor radially close to said fan wheel. The air nozzle serves as a passage way for providing cleaned intake air from the fan wheel to the engine of the motor-driven tool, wherein the air nozzle and the air conductor are manufactured in one piece.

Abstract: A cooling fan (10) for a vehicle engine (50), having a fan casing (60) and a fan rotor (12) which is movable axially relative to the fan casing during operation. There is an actuator (20) for moving the fan rotor (12) to positions which represent various degrees of protrusion (a) from an end of the fan casing (60) in order to optimise the fan's suction capacity and efficiency on the basis of current operating parameters such as fan speed and vehicle velocity.