BACKGROUND OF THE INVENTION

The present invention relates to an electric engine, for example for use in aircraft propulsion.

Fuel-burning gas turbine engines (commonly called“jet engines”) are well known as a means of aircraft propulsion. In recent decades improvements have been made with regard to efficiency and noise reduction, but environmental concerns still remain.

The civil and defence aerospace sectors have driven developments in“more electric engines”, aimed at making step changes in functionality and reliability while achieving reductions in cost and weight. Many of these developments however relate to increased use of electrical components and sub-systems within gas turbine engine architectures, rather than replacement of these fuel- burning engines by electrical powerplants.

An example of an electrical propulsion system is the electric ducted fan (EDF), which is commonly used in model aircraft and which may be suitable for use in small passenger aircraft. An EDF typically comprises a fan mounted within a cylindrical shroud or duct. The blades of the fan are mounted on a shaft which extends from a brushless electric motor mounted centrally in the duct. Fixed stator vanes may be provided behind the thrust-producing fan, for straightening out the rotational airflow received from the fan. The electrical architecture of the EDF offers advantages over the gas turbine engine in terms of simplicity of construction. On the other hand the EDF has some drawbacks, for example that the shrouded fan tends to be less efficient than a conventional open propeller at lower thrust levels, for example as used at cruise speeds.

In view of the foregoing discussion there is a need for an electrical engine or powerplant which will alleviate at least to some extent the problems of the prior art. SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided an electric engine comprising: an inner casing; an outer casing which is positioned around the inner casing; a rotor comprising a plurality of rotor blades, the rotor being located between the inner and outer casings and being rotatable about an axis of the inner casing; a stator comprising a plurality of stator vanes, the stator being located between the inner and outer casings and being located axially downstream of the rotor such that the rotor and stator together form an axial compressor; and a field winding which is positioned around the rotor, wherein the rotor comprises at least one permanent magnet and the field winding is operable to cause the rotor to rotate, thereby to cause the rotor blades to move air to the stator vanes so as to increase the pressure of the air, and wherein: an annular flow passage is formed between the inner and outer casings and is located axially downstream of the compressor; the inner casing comprises an axially-extending duct having open upstream and downstream ends; and the outer casing comprises a flow deflection surface which is located axially downstream of the annular flow passage and of the downstream end of the duct and immediately adjacent to the downstream end of the duct, such that in use compressed air expelled from the compressor is caused to flow through the annular flow passage and over the flow deflection surface, such as to generate a low pressure region of the compressed air which causes duct air to be drawn from the upstream end of the duct and out through the downstream end thereof, thereby to generate propulsive thrust.

The rotor and the field winding together comprise a brushless permanent magnet electric motor, while the rotor and stator together comprise an axial compressor. Thus the rotor itself forms the moving component of the electric motor that drives it, and also serves as part of the axial compressor. This“dual- function rotor” aspect reduces the number of engine components and thereby the weight and complexity of the engine. Since the field winding is positioned around the rotor and causes the rotor to turn, then different from a conventional gas turbine engine (“jet engine”) there is no requirement for a turbine-driven centre shaft (and associated gearbox) to drive the compressor rotors. Instead the rotor blades are located outside (radially of) the stationary inner housing. This further reduces weight and complexity.

The provision of the axially-extending through-duct and the flow deflection surface enable the engine to provide more propulsive thrust for the same electricity consumed, as will be described in more detail later herein.

The electric engine may comprise a controller configured to vary a supply of electrical current to the field winding in order to vary the rotational speed of the rotor.

The electric engine may comprise a power source for providing electrical current to the field winding.

The stator may comprise an outer ring and an inner ring which is concentric with the outer ring, the stator vanes extending between the inner and outer rings, the outer ring being fixedly attached to the outer casing and the inner ring being fixedly attached to the inner casing.

The rotor may comprise an outer ring and an inner ring which is concentric with the outer ring, the rotor blades extending between the inner and outer rings, the outer ring comprising the at least one permanent magnet and being received in a circumferential groove which is formed in the outer casing, the field winding being located in the circumferential groove such as to circumferentially surround the outer ring.

The field winding may comprise a plurality of field coils.

The rotor may comprise a single permanent magnet. The rotor may comprise a plurality of permanent magnets. The electric engine may comprise: a plurality of the rotors and a plurality of the stators, each one of the stators being located axially downstream of a respective one of the rotors such as to form a plurality of axial compressor stages; and a plurality of field windings, each one of the field windings being positioned around a respective one of the rotors.

The controller may be configured to vary the electrical current to each one of the field windings individually in order to vary the rotational speeds of the rotors independently of each other.

Any one of the compressor stages may differ in size from any of the other compressor stages. The compressor stages may progressively reduce in size in the downstream axial direction.

The flow deflection surface of the outer casing may comprise an annular lip which protrudes towards the axis of the inner casing. The annular lip may comprise a curve. The annular lip may comprise at least one flat face. The annular lip may extend continuously around the circumference of the outer casing. The annular lip may extend discontinuously around the circumference of the outer casing such as to provide a plurality of discrete flow deflection surfaces.

The surface of the outer casing may define: a convergent portion having a flow area which decreases in the downstream axial direction from the annular flow passage to the flow deflection surface; and a divergent portion having a flow area which increases in the downstream axial direction from the flow deflection surface to a downstream end of the outer casing.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example, with reference to the accompanying figures in which: Figures 1 and 2 show simplified cutaway views of an electric engine assembly according to an embodiment of the invention;

Figure 3 shows components of the electric engine; and

Figures 4a and 4b show simplified cross-sectional views of casings of the electric engine including fluid paths therein.

DETAILED DESCRIPTION

Referring to Figures 1 to 3, an electric engine assembly 100 (or electric powerplant) in accordance with an embodiment of the invention comprises a housing or inner casing 102 which has a longitudinal axis X-X’ and is arranged concentrically with an outer housing or casing 104 which circumferentially surrounds (or encircles) the inner casing 102 such as to form an annulus 106 between the inner casing 102 and the outer casing 104. In this exemplary embodiment the inner casing 102 is substantially tubular such as to comprise a central duct 102a which is open at both ends.

The inner casing 102 is supported within the outer casing 104 by a plurality of compressor stators S1 , S2, S3 which are axially spaced from one another along the longitudinal axis X-X’. An inner ring S1 a, S2a, S3a (only S3a being labelled in the figures) of each one of the stators S1 , S2, S3 is fixedly secured to the exterior surface of the inner casing 102 and an outer ring S1 b, S2b, S3b of each one of the stators S1 , S2, S3 is fixedly secured to an interior surface of the outer casing 104. Thus each one of the stators S1 , S2, S3 is located in the annulus 106 between the inner casing 102 and the outer casing 104 and is in fixed relationship with both the inner casing 102 and the outer casing 104.

Each one of the stators S1 , S2, S3 comprises a plurality of fixed vanes (or blades) S1 c, S2c, S3c (only S3c being labelled in the figures) which extend radially (i.e. normal to the longitudinal axis X-X’) between the inner ring S1a, S2a, S3a and the outer ring S1 b, S2b, S3b of the stator S1 , S2, S3. The vanes S1c, S2c, S3c are of aerofoil shape, as is conventional in compressor stators. In this exemplary embodiment the vanes S1 c, S2c, S3c are formed initially as separate components which are subsequently attached to the inner and outer rings S1 a, S2a, S3a; S1 b, S2b, S3b. Alternatively the vanes S1 c, S2c, S3c may be formed integrally with the inner and outer rings S1a, S2a, S3a; S1 b, S2b, S3b.

The electric engine assembly 100 further comprises a plurality of compressor rotors R1 , R2, R3 which are axially spaced from one another along the longitudinal axis X-X’. For the sake of clarity of the drawings, only the front-most rotor R1 is included in Figures 1 and 2. Each one of the rotors R1 , R2, R3 is located in front (i.e. axially upstream) of a respective one of the stators S1 , S2, S3, such that the rotors R1 , R2, R3 and stators S1 , S2, S3 alternate in the downstream direction.

An inner ring R1 a, R2a, R3a of each one of the rotors R1 , R2, R3 is mounted to the exterior surface of the inner casing 102 by means of a roller bearing (not shown in the figures) such as to be rotatable about the longitudinal axis X-X’. Alternatively a different type of bearing or frictionless surface may be used to enable the rotors R1 , R2, R3 to rotate. An outer ring R1 b, R2b, R3b of each one of the rotors R1 , R2, R3 is received in a respective circumferential groove (or slot) 104a, 104b, 104c (only 104b and 104c being labelled in the figures) which is provided in the interior surface of the outer casing 104. With regard to each rotor R1 , R2, R3 a clearance gap exists between the outer ring R1 b, R2b, R3b and the side walls of the circumferential groove 104a, 104b, 104c, so that the rotor R1 , R2, R3 is free to turn in the groove 104a, 104b, 104c.

The outer ring R1 b, R2b, R3b of each one of the rotors R1 , R2, R3 comprises a permanent electric magnet. In this exemplary embodiment the entire outer ring R1 b, R2b, R3b is formed as a permanent magnet. Alternatively the outer ring R1 b, R2b, R3b may comprise a plurality of discrete (individual) permanent magnets which may be spaced equidistant around the circumference of the outer ring R1 b, R2b, R3b.

Each one of the rotors R1 , R2, R3 comprises a plurality of blades R1 c, R2c, R3c (only R1c being labelled in the figures) which extend radially (i.e. normal to the longitudinal axis X-X’) between the inner ring R1 a, R2a, R3a and the outer ring R1 b, R2b, R3b of the rotor R1 , R2, R3. The blades R1 c, R2c, R3c are of aerofoil shape, as is conventional in compressor rotors. In this exemplary embodiment the blades R1 c, R2c, R3c are formed initially as separate components which are subsequently attached to the inner and outer rings R1a, R2a, R3a; R1 b, R2b, R3b. Alternatively the blades R1c, R2c, R3c may be formed integrally with the inner and outer rings R1 a, R2a, R3a; R1 b, R2b, R3b.

Thus each one of the rotors R1 , R2, R3 is located in the annulus 106 between the inner casing 102 and the outer casing 104 and is rotatable with respect to the inner casing 102 and the outer casing 104. Furthermore in this exemplary embodiment each one of the rotors R1 , R2, R3 is in abutment with one or two of the stators S1 , S2, S3.

The rotors R1 , R2, R3 and the stators S1 , S2, S3 are thus arranged in rotor- stator pairs R1 , S1 ; R2, S2; R3, S3 along the longitudinal axis X-X’ of the electric engine 100, the vanes S1 c, S2c, S3c of each one of the stators S1 , S2, S3 being located immediately adjacent (axially downstream) to the blades R1 c, R2c, R3c of a respective one of the rotors R1 , R2, R3. Also the blades R1 c, R2c, R3c of each one of the rotors R1 , R2, R3 and the vanes S1 c, S2c, S3c of each one of the stators S1 , S2, S3 are aligned in the opposite direction to each other. Each rotor-stator pair R1 , S1 ; R2, S2; R3, S3 thus provides a single compressor stage of the electric engine assembly 100, as will be described in more detail later herein.

In this exemplary embodiment the rotors R1 , R2, R3 (excluding the permanent magnet parts) and their blades R1 c, R2c, R3c and the stators S1 , S2, S3 and their vanes S1c, S2c, S3c are constructed from aluminium alloy. Alternative suitable materials include, but are not limited to, metal or metal alloys including titanium alloys and steel, plastics, and ceramics.

The electric engine assembly 100 further comprises a plurality of field windings (or electrical stators) FW1 , FW2, FW3. For the sake of clarity of the drawings, only the front-most field winding FW1 is included in Figures 1 and 2. In this exemplary embodiment each one of the field windings FW1 , FW2, FW3 comprises a plurality of field coils FC which are fixedly secured in a respective one of the circumferential grooves 104a, 104b, 104c in the interior surface of the outer casing 104. Accordingly each one of the field windings FW1 , FW2, FW3 comprises a ring of field coils FC which circumferentially (or peripherally) surrounds (or encircles) the outer ring R1 b, R2b, R3b of a respective one of the rotors R1 , R2, R3. With regard to each rotor R1 , R2, R3 a clearance gap exists between the outer ring R1 b, R2b, R3b of the rotor R1 , R2, R3 and the surrounding ring of field coils FC. In other words, the ring of field coils FC of each one of the field windings FW1 , FW2, FW3 is radially spaced from the outer ring R1 b, R2b, R3b of the respective rotor R1 , R2, R3, so that the rotor R1 , R2, R3 is free to turn.

Thus the respective rotors R1 , R2, R3 and field windings FW1 , FW2, FW3 are arranged in rotor-field winding pairs, each pair R1 , FW1 ; R2, FW2; R3, FW3 comprising a brushless permanent magnet electric motor. The field coils FC of each one of the field windings FW1 , FW2, FW3 are controllable by electronic switching circuitry (not shown in the figures). In this exemplary embodiment electrical power is provided by an electric generator (not shown in the figures) which may be powered by diesel or petrol, for example. Alternatively electrical power may be provided by a battery or solar cells. Other appropriate sources of electrical power may be apparent to the skilled person and all of these are within the scope of the claimed invention.

Figure 4a shows a simplified cross-sectional view of the inner and outer casings 102, 104. For the sake of clarity of the drawing, the rotors R1 , R2, R3, stators S1 , S2, S3 and field windings FW1 , FW2, FW3 are omitted. As can be seen in the figure, the inner diameter of the outer casing 104 varies in the axial direction from the front to the rear (from left to right in the sense of Figure 4a). Accordingly the cross-sectional area of the annulus 106 between the inner casing 102 and the outer casing 104 also varies in the axial direction.

The outer casing 104 is locally thickened around the rear portion of the inner casing 102, such that a narrow, slit-like annular aperture or passage 108 is formed between the inner surface of the outer casing 104 and the outer surface of the inner casing 102. The (axially upstream) portion of the inner surface of the outer casing 104 which leads to the annular passage 108 is curved or contoured such that the cross-sectional area of the annulus 106 gradually reduces (converges) in the downstream axial direction.

Rearward (axially downstream) of the rear edge of the inner casing 102 the outer casing 104 is thicker still, such as to form a constriction or neck 1 10 at which the inner diameter of the outer casing 104 is at its smallest. The neck 1 10 is located immediately adjacent (axially downstream) to the annular passage 108. The portion of the inner surface of the outer casing 104 which defines the neck 110 is a flow guiding or deflection surface 112. In this exemplary embodiment the flow deflection surface 112 comprises a continuous, convexly-curved annular lip which protrudes inwardly towards the longitudinal axis X-X’ of the inner casing 102. Alternatively the flow deflection surface 1 12 may comprise one or more generally flat surfaces, for example arranged in a step, or a combination of curved portions and flat portions. Various geometrical arrangements of the flow deflection surface 1 12 may be apparent to the skilled person and all of these are within the scope of the claimed invention, provided that they provide the flow deflection function, which will be described in more detail later herein.

Rearward of the neck 110 the outer casing 104 is reduced in thickness and is curved or contoured, such that the inner diameter of the outer casing 104 gradually increases (diverges) in the downstream axial direction to the rear edge of the outer casing 104.

Thus rearward (axially downstream) of the inner casing 102 and the annular passage 108 there is a chamber 114 which is defined by the inner surface of the outer casing 104. The chamber 114 comprises a convergent portion or nozzle, which is located axially upstream of the neck 110 and which is in fluid communication with the central duct 102a of the inner casing 102 as well as with the annular passage 108, and a divergent portion, which is located axially downstream of the neck 1 10 and extends to the rear edge of the outer casing The operation of the electric engine assembly 100 will now be described, in particular in the context of use in an aircraft.

Electric current is provided to the electric engine assembly 100 by a power source onboard the aircraft, for example batteries, an electric generator, solar power, or other appropriate means. DC current is supplied to the field coils FC of each one of the field windings FW1 , FW2, FW3. The field coils FC are controlled, preferably by the pilot of the aircraft using the electronic switching circuitry, to create magnetic fields. Since the outer ring R1 b, R2b, R3b of each one of the rotors R1 , R2, R3 comprises a permanent magnet, which is circumferentially surrounded by the field coils FC of a respective one of the field windings FW1 , FW2, FW3, the rotors R1 , R2, R3 are caused to rotate. The current supply may be controlled so as to vary the rotational speed of the rotors R1 , R2, R3, independently if preferred, in order to obtain the desired thrust for the phase of flight.

Referring now also to Figure 4b, during aircraft flight a flow F of air enters the front of the electric engine assembly 100. The airflow F passes into the annulus 106 between the inner casing 102 and the outer casing 104 and enters the rotor R1 of the first compressor stage R1 , S1. Energy is imparted to the air by the blades R1 c of the rotating rotor R1 , which exert a torque on the air and accelerate the airflow F. The air is then passed to the stator S1 , where the fixed vanes S1 c (which are aligned in the opposite direction to the blades R1 c of the rotor R1 ) slow the air and convert the kinetic energy of the circumferential component of the airflow F into static pressure. Thus a rise in the static pressure of the air is achieved by the first compressor stage R1 , S1. The fixed vanes S1 c further direct the airflow F axially downstream toward the second compressor stage R2, S2.

The airflow F then passes through the second compressor stage R2, S2 and subsequently through the third compressor stage R3, S3, the static pressure of the air being increased in each of the second and third compressor stages R2, S2; R3, S3 in the manner described hereinabove with respect to the first compressor stage R1 , S1.

After exiting from the stator S3 of the third compressor stage R3, S3, the compressed airflow F continues through the annulus 106 and is directed by the curved inner surface of the outer casing 104 to the annular aperture or passage 108 at the rear portion of the inner casing 102. The airflow F passes through the passage 108 and over the flow deflection surface 112 which defines the neck 110.

The airflow F is guided by the flow deflection surface 1 12 and becomes attached to the deflection surface 1 12, entraining surrounding air in the region of the neck 110 and creating a region of low pressure in the airflow F at the deflection surface 1 12. This low pressure region has the effect of drawing in more air FD from the front of the electric engine assembly 100, through the central duct 102a of the inner casing 102, thus adding to the airflow F at the neck 1 10. That is, additional air FD is rapidly induced into the region of the neck 1 10, via the central duct 102a, due to the region of low pressure in the compressed airflow F which is caused by the airflow F being guided along the flow deflection surface 112 and becoming attached thereto. Thus the compressed airflow F is augmented or“amplified” by outside air FD which enters through the duct, due to the presence of the flow deflection surface 1 12, thereby increasing the propulsive thrust of the engine.

The flow deflection surface 112 exploits the well-known Coanda effect, which may be summarised as the tendency of a jet of fluid (any liquid or gas, including air) emerging from an orifice to follow an adjacent flat or curved surface and to entrain fluid from the surroundings so that a region of lower pressure develops. The flow deflection surface 1 12 may therefore alternatively be called a“Coanda surface” or a“flow guiding surface” or a“flow attachment surface”.

Having emerged from the neck 1 10 the total (“amplified”) airflow F + FD passes through the divergent portion of the outer casing 104 to the rear edge thereof, the gradually curved surfaces in this region ensuring generally laminar (non- turbulent) flow. Axially downstream of the rear edge of the outer casing 104, the total airflow F + FD leaving the electric engine assembly 100 is joined by air from outside of the engine. The high velocity and volume of the rearward total airflow F + FD provides an“augmented” thrust force in the direction of travel of the aircraft.

As has been explained herein above, locating the field winding(s) around the outside of the rotor(s) advantageously eliminates the need for a turbine-driven centre shaft to drive the compressor rotor(s). In the above-described embodiment the absence of a centre shaft is exploited by the provision of the axially-extending through-duct, in conjunction with the flow deflection surface, to make use of the Coanda effect in order to augment the propulsive thrust of the engine. The inclusion of the through-duct (and the flow deflection surface), and thereby the provision of augmented thrust, is made possible by the specific arrangement of the rotor(s) and field winding(s), which provides a space for the through-duct where a shaft would conventionally be located.

It will be understood that the invention has been described in relation to its preferred embodiments and may be modified in many different ways without departing from the scope of the invention as defined by the accompanying claims.

While the figures show an electric engine assembly comprising three compressor stages (i.e. three pairs of rotors and stators), the electric engine assembly may comprise fewer compressor stages, even a single compressor stage. On the other hand, it will be understood that it is desirable to have multiple compressor stages with each stage providing a relatively small pressure increase. In this way the rate of deceleration, or diffusion, of the airflow through each of the rotor blades and stator vanes is limited so as to avoid losses due to flow separation and subsequent blade stall. Although the pressure ratio of each stage is relatively small, there is an overall increase in pressure across each stage. Accordingly the electric engine assembly may comprise any number of compressor stages, as may be appropriate for optimised compressor efficiency and/or performance. The size (diameter) of any one of the compressor stages (and its rotor blades and stator vanes) may differ from the size of any of the other compressor stages (and its rotor blades and stator vanes), as may be appropriate for optimised compressor efficiency and/or performance. For example, the size of the compressor stages may reduce in the downstream axial direction, such that the largest compressor stage is toward the front and the smallest compressor stage is toward the rear of the electric engine assembly. In this way the axial velocity of the air passing through the engine may be maintained at a near constant level, as is typically desirable in compressor stages in conventional gas turbine engines.

In an embodiment, an additional stator is positioned behind (axially downstream of) the rear-most stator, without a rotor interspersed between the two stators. The additional stator comprises fixed outlet guide vanes which serve to finally straighten out the flow of air in operation.

In an embodiment, fixed inlet guide vanes are provided in front (axially upstream of) the front-most rotor, to optimally direct the incoming air flow to the front-most rotor.

In an embodiment, the inner and outer stator rings are omitted and the respective ends of the fixed stator vanes are simply attached to the exterior surface of the inner casing and the interior surface of the outer casing.

While the figures depict cylinder-shaped field coils with their cores arranged radially, alternative configurations (e.g. horseshoe-shaped field coils) may provide the same function and all of these are within the scope of the claimed invention.

While the figures show the inner and outer housings as solid structures, it will be understood that the housings may be differently configured (e.g. to include hollow portions) for optimised strength and weight. With regard to use of the electric engine assembly in an aircraft, the shape of the chamber downstream of the flow deflection surface will be designed for optimally smooth airflow and to maximise the thrust, and it may be different from that as illustrated in the drawings. Similarly, the shape of the outer and inner casings and the central duct will be optimised for smooth airflow and may be different from the drawings.

In view of the foregoing description it will be seen that the claimed invention offers numerous advantages. One of these is that the main components of the engine double up in functionality. The rotors also perform the function of the moving component of electric motors, and the stators are also used to hold the inner and outer casings in position.

In electric ducted fans (EDFs) and conventional gas turbine compressors, the blades of the rotors are only attached at their inner ends and each blade thus needs a substantial secure fastening to cope with the centrifugal force it has to endure at high rotational speeds. Conversely in the present invention the blades may be attached to both their ends, thus forming a strong box structure together with the inner and outer rings.

In the invention many field coils may be used thus providing more efficiency and more accurate speed control, and since a separate coil ring can be used for each rotor the field coils can be made smaller to minimise the size of the outer casing.

The engine according to the invention can effectively accommodate a large number of rotors and stators, depending on requirements, by simply increasing the engine’s front-to-rear length, thus allowing expansion to more thrust capability within the same engine housing circumference, with resultant weight- saving and compactness benefits.

If the engine is mounted in a nacelle outside the aircraft fuselage then an additional Coanda slit and Coanda surface, both positioned annularly on the outside of the outer housing and to its rear, may be used to create even more entrainment of surrounding air that will smoothly join the stream of air exiting the engine, to further augment the total thrust.

Because the rotors are housed between an inner and an outer duct, there is more insulation against the noise from their rotation and so the engine may have a lower acoustic signature compared to a conventional centre-shaft engine.

By having a lower frontal area than a conventional centre-shaft engine, the inventive engine has less possibility of bird ingestion in flight, and the consequential damage.

When used in a multi-engined aircraft where the engine is not required during some phases of flight, there is less drag when it is then not in operation, due to its lower frontal area.

The drawings illustratively show the blades in the rotors being similarly aligned for the rotors to all rotate in the same direction within the engine. As with most propeller-driven aircraft, a torque is then created that results in the engine itself (and the aircraft it is attached to) having a tendency to rotate in the direction opposite to that of the rotors. If the engine is used for horizontal thrust the aircraft then exhibits a tendency to roll, or if it is used for vertical thrust, to yaw, especially at high power settings.

This unwanted rolling or yawing can be cancelled out in the inventive engine by the engine having an even number of rotors, each contra-rotating and with blades orientated in the opposite direction to the rotor adjacent to it. When such contra-rotating rotors are used, the oppositely aligned fixed vanes of the interspersed stators may not be required. The stators would then instead be replaced by radially arranged supports (with sufficient space between them to allow for the axial air flow from rotor to rotor) to still be able to perform the function of holding together the inner and outer casings.

While the electric engine assembly and its operation have been described herein with regard to use in an aircraft, it will be understood that the invention may find utility in a variety of applications other than aviation, including, but not limited to, propulsion for land or sea vehicles, and domestic heating and cooling.