WO2023067339A1

WO2023067339A1 - A vtol aerial vehicle

Info

Publication number: WO2023067339A1
Application number: PCT/GB2022/052670
Authority: WO
Inventors: Matthew DENTON; Antony QUINN
Original assignee: Maverick Aviation Ltd
Priority date: 2021-10-21
Filing date: 2022-10-19
Publication date: 2023-04-27
Also published as: GB2614228A8; GB2614228B; GB202115069D0; GB2614228A

Abstract

A VTOL aerial vehicle (10) is disclosed, comprising: an airframe (12); one or more arms (202) coupled to the airframe (12) at a pivot (206); and three or more propulsion units, each mounted on a gimbal (16) having a gimbal axis, and each gimbal (16) coupled to one of the one or more arms (202). Each arm (202) is configured to pivot between an unfolded position and a folded position with respect to the airframe (12).

Description

A VTOL AERIAL VEHICLE

TECHNICAL FIELD

The present invention relates to a VTOL aerial vehicle.

BACKGROUND

VTOL (vertical take-off and landing) aerial vehicles can be used to deliver a payload from point to point, for aerial photography, or as a mode of personal transport, for example.

Where a VTOL aerial vehicle is used to deliver a payload, the vehicle needs to have sufficient upward thrust to take-off with the payload (beyond just lifting itself) as well as handling well in the air and allowing directional flying. Adding a payload may unbalance the vehicle and an unstable vehicle could result in damage to the payload and/or the vehicle - for example if the vehicle is so unstable it crashes. Other factors may unbalance the vehicle in flight, for example blowing wind.

This is a particular problem if the payload is a delicate or expensive item, or a person. VTOL aerial vehicles can be used by search and rescue teams, for example, where land vehicles and other airborne vehicles are not suitable or will not get to the site of the emergency quickly enough. The person operating the VTOL aerial vehicle should be given a safe and comfortable flight experience.

Many VTOL aerial vehicles (e.g. unmanned drones) employ electrical motors driving fixed pitch propellers, and achieve control by adjustment of motor speed. Electrical motors have relatively high response speed, which facilitates this approach. However, electrical motors require electrical power, which tends to limit endurance and/or payload capability. Existing VTOL aerial vehicles for single person transportation (e.g. jetpacks) may employ gas turbine engines, which respond relatively slowly. Typically, VTOL single person aerial vehicles are not straightforward to operate, limiting their safety and usefulness.

The present disclosure seeks to provide an alternative VTOL aerial vehicle with improved stability and directional flight. The present disclosure also seeks to provide a VTOL aerial vehicle that is user-friendly to those without extensive (or any) pilot training - for example a member of the emergency services.

SUMMARY

A first aspect of the present invention provides a VTOL aerial vehicle, comprising: an airframe; three or more propulsion units coupled to the airframe; a single axis gimbal for each propulsion unit, each single axis gimbal configured to vary the orientation of the respective propulsion unit with respect to the airframe by rotation of the propulsion unit about a gimbal axis; wherein at least one of the gimbal axes is at an angle of at least 10 degrees to at least one other of the gimbal axes.

Having the gimbal axes at angles to each other means that rotation of the propulsion units about their respective gimbal axes will couple into a yaw moment, enabling control over roll, pitch and yaw by rotation of the propulsion units about their respective gimbal axes. The single axis gimbals may be lighter and stiffer than two axis gimbals, with less backlash and slop in control. This may facilitate a lower cost and more controllable vehicle.

The aerial vehicle may be able to lift substantially greater payloads than any current electric UAV of the same size. In addition, the aerial vehicle may be substantially easier to use than any current personal mobility aerial vehicles.

The airframe may have a square, rectangular or circular plan, for example. The airframe may be another shape suitable to receive propulsion units. The airframe may be U-shaped or substantially U-shaped, with straight edges, with two sides and a back side, with an open front. The airframe may be formed from metal such as aluminium or aluminium alloys, or from composites. The airframe may be dimensioned to fit into a large-sized case (which may be around 740mm in height and have a capacity of around 117 litres).

The airframe may include a platform suitable to receive a payload. The airframe may define an opening suitable to receive a payload - for example, the payload may be placed in the opening and fixed to the airframe (e.g. by straps etc). The opening may be defined within the U-shaped airframe, for example, having an open front side. The airframe may include a harness for receiving a payload - the payload may be a person and the harness may be configured to receive part of the person’s body. The back side of the U-shaped airframe may be arranged adjacent the person’s back for flight.

The aerial vehicle comprises three or more propulsion units, and preferably at least four propulsion units. A minimum of three propulsion units provides desired stability and drivability of the aerial vehicle.

The propulsion units may be arranged to provide upward thrust for vertical take-off. Each propulsion unit may be rotatable on the single axis gimbal. Each propulsion unit may have a body, which may have a gimbal extending into the body.

Each of the gimbal axes may be parallel to a plane of the airframe. The plane of the airframe may include each of the gimbals. The airframe may define a longitudinal axis which corresponds with the vertical direction of take-off. The plane of the airframe may be perpendicular to that longitudinal axis. The angle between one of the gimbal axes and another of the gimbal axes may be 40 degrees, 60 degrees or 90 degrees for example. Two or more of the gimbal axes may be substantially parallel - for example, those single axis gimbals may be arranged on generally opposing sides of the airframe. For example, in an embodiment with a rectangular airframe and a propulsion unit in each corner, diagonally opposite gimbals may have parallel gimbal axes.

Rotation of each propulsion unit on its gimbal may adjust the vertical component of thrust from the propulsion unit. This may be used to generate pitch, roll and yaw moments for attitude adjustment. For example, a vertical thrust component on a port side may be reduced by rotation of one or more propulsion units on the port side about their respective gimbal axes, resulting in a change in roll attitude. Similarly, a vertical thrust component on a forward side may be reduced by rotation of one or more propulsion units on the forward side about their respective gimbal axes, resulting in a change in pitch attitude.

A second aspect of the present invention provides a VTOL aerial vehicle, comprising: an airframe; one or more arms rotatably coupled to the airframe; three or more propulsion units, each mounted on a gimbal having a gimbal axis, and each gimbal coupled to one of the one or more arms, wherein each arm is configured to pivot between an unfolded position and a folded position with respect to the airframe.

In the unfolded position the one or more arms may project from the airframe such that the volume of the vehicle is greater than in the folded position. In the unfolded position, the vehicle may be configured to be flown by an on-board passenger. In the folded position the VTOL aerial vehicle may be configured to be flown as a drone.

Each of the one or more arms may rotate at least 70 degrees between the folded and unfolded positions (for example, approximately 90 degrees).

Each of the one or more arms may be at least 30cm long.

Each arm may comprise a propulsion unit at least 20cm from the pivot.

Each arm may comprise a proximal propulsion unit and a distal propulsion unit, the proximal propulsion unit closer to the pivot than the distal propulsion unit.

The distal propulsion unit and the proximal unit may be on opposite sides of the pivot. The proximal propulsion unit may be at a distance of less than 20cm from the pivot, and the distal propulsion unit may be at a distance of more than 20cm from the pivot.

In the unfolded position the arm may be at an angle of 70-110 degrees to the airframe. In the folded position, the arm may be at an angle of less than 20 degrees to the airframe.

The vehicle may comprise a single axis gimbal for each propulsion unit, each single axis gimbal configured to vary the orientation of the respective propulsion unit with respect to the arm to which the gimbal is coupled by rotation of the propulsion unit about a gimbal axis. At least one of the gimbal axes may be at an angle of at least 10 degrees to at least one other of the gimbal axes when the arm is in the unfolded position. The airframe may include a platform suitable to receive a payload. The arms in the unfolded position may define an opening suitable to receive a payload - for example, the payload may be placed in the opening and fixed to the airframe (e.g. by straps etc). The airframe may include a harness for receiving a payload - the payload may be a person and the harness may be configured to receive part of the person’s body. The airframe may be arranged adjacent the person’s back for flight.

The propulsion units may be arranged to provide upward thrust for vertical take-off (with the arms in the unfolded position). Each propulsion unit may be rotatable on the single axis gimbal. Each propulsion unit may have a body, which may have a gimbal extending into the body.

Rotation of each propulsion unit on its gimbal may adjust the vertical component of thrust from the propulsion unit. This may be used to generate pitch, roll and yaw moments for attitude adjustment. For example, a vertical thrust component on a port side may be reduced by rotation of one or more propulsion units on the port side about their respective gimbal axes, resulting in a change in roll attitude. Similarly, a vertical thrust component on a forward side may be reduced by rotation of one or more propulsion units on the forward side about their respective gimbal axes, resulting in a change in pitch attitude. The following features are applicable to both the first and second aspect.

Each propulsion unit may comprise a longitudinal axis. The longitudinal axis of each propulsion unit may be generally perpendicular to the gimbal axis of the gimbal associated with the propulsion unit. For each propulsion unit, a direction towards the centre of thrust may be defined by a line between the longitudinal axis and the centre of thrust. The centre of thrust may be defined as a central point between the propulsion units (e.g. about which there is nominally no net moment from the propulsion units, with the propulsion units at equal thrust and a neutral position).

The gimbal axis may be offset from perpendicular to the direction towards the centre of thrust by a non-zero amount, for example at least 1 degree, or at least 5 degrees, gimbal axis may be offset from perpendicular to the direction towards the centre of thrust by at least 15 degrees. This may enable generation of a yaw moment by rotation of the propulsion units about their gimbal axes. In some embodiments, rotation of all the propulsion units by the same amount about their gimbal axes may not generate a yaw moment. In some embodiments, relative rotations of different propulsion units (e.g. those on different diagonals of a rectangular airframe) about their gimbal axes may produce a yaw moment.

Each gimbal axis may be offset by between 5 and 30 degrees or between 5 and 40 degrees from perpendicular to the direction towards the centre of thrust. Each gimbal axis may be offset by less than 45 degrees from perpendicular to the direction towards the centre of thrust. These offsets enable adjustment of yaw moment, but result in an appropriate amount of coupling between the different attitude axes. Very strong coupling between the different axes may result in difficulties in control. It has been found that a relatively small offset from perpendicular to the centre of thrust provides a relatively optimal compromise between yaw control and stability.

Each propulsion unit may have a neutral position in which the longitudinal axis of the propulsion unit is tilted towards the centre of thrust. The neutral position may be the position of the propulsion unit when the vehicle is not in operation - or not flying.

The thrust vector from each propulsion unit may be tilted by at least 5 degrees or at least 10 degrees towards the centre of thrust in the neutral position. For example, may be tilted by 10 degrees, 20 degrees or 30 degrees. In this way, the exhaust end of the propulsion units is tilted away from the payload (which may be a person), improving safety as the exhaust may be hot. The thrust vector from each propulsion unit may not be tilted towards the centre of thrust in a neutral position and may align with the longitudinal axis of the airframe - the payload may be protected from the exhaust end of the propulsion units by a distance between the payload and the propulsion unit such that tilting is not required, or the propulsion unit may comprise a head shield for example. Even with a non-zero tilt in the neutral position, the propulsion unit may comprise a heat shield.

Each gimbal and corresponding propulsion unit may be configured to allow at least +- 15 degrees of rotation of the propulsion unit about the gimbal axis. For example, each gimbal and corresponding propulsion unit may be configured to allow at least +-30 degrees of rotation of the propulsion unit about the gimbal axis.

The propulsion unit may comprise a gas turbine engine and the turbine may rotate about a shaft that lies along the longitudinal axis of the propulsion unit. The gimbal control may be particularly suitable for embodiments with gas turbine engines. In other embodiments each propulsion unit may comprise an electric ducted fan engine.

Each gimbal may comprise an actuator configured to rotate the corresponding propulsion unit about the gimbal axis in response to a control signal. Two or more actuators may be associated with a single gimbal - for example, a pair of actuators arranged on the gimbal axis, which may increase redundancy.

The actuator may comprise a motor to drive rotation. Each actuator may comprise an electric servomotor, or a linkage and linear actuator, for example.

The vehicle may comprise four propulsion units. Stability may be easier to achieve with an even number of propulsion units versus an odd number of propulsion units.

The airframe may define four corners, and a propulsion unit may be arranged on the airframe at each corner.. This may be safer where the vehicle is used to transport a person, who should not get too close to the propulsion units. Furthermore, disposing propulsion units at corners of an airframe may maximise spacing between propulsion units, increasing roll and pitch moments from changes in vertical thrust components (due to rotations about the gimbal axes).

The airframe may comprise a mount at each corner for coupling each propulsion unit to the airframe. Each mount may include a single axis gimbal, wherein a pair of mounts may be connected to and extend a length from a first edge of the airframe in a first direction and wherein another pair of mounts may be connected to and extend a length from a second edge of the airframe, opposite to the first edge, in a second, opposite direction.

The mounts may house the actuators, or the actuators may be arranged on the mounts, for example in an actuator housing on the mount.

For example, the airframe may have two opposing sides that - in use - are either side of the payload (which may be a person). The mounts may extend away from these sides such that the propulsion units are offset away from the payload or person - or the centre of thrust of the airframe. To improve stability, it may be preferable that a pair of propulsion units extend away from the same side of the airframe. The pair of mounts may extend away from one another as well as away from the same side of the airframe - spacing the propulsion units and improving balance further. The mounts extending away from the payload may also allow the vehicle to accommodate a larger payload (than if the propulsion units were mounted directly on the airframe, for example, and thus closer to the centre of thrust of the airframe).

The propulsion units may be evenly distributed around a perimeter of the airframe. This may assist in improving balance.

The airframe may be configured to fly with at least one failed propulsion unit. One or more propulsion units may be provided as ‘back-up’ propulsion units and may not provide any thrust in normal flight conditions. The vehicle may be configured so that in the event a ‘main’ propulsion unit fails - causing a reduction in thrust - a back-up propulsion unit will start providing thrust to balance the vehicle. The back-up propulsion unit(s) may be controlled by manual or automatic control in order to start providing thrust. The vehicle may comprise an additional, fixed propulsion unit that is not gimbal controlled and that is configured to provide vertical thrust for additional lift capacity. The flight control computer may be configured to include the additional thrust and its direction in determining the positions of the other moving propulsion units.

The vehicle may further comprise one or more sensors that are one or more of: an IMU (inertial measurement unit), a gyroscope, an accelerometer, a magnetometer, a LIDAR (laser imaging, detection and ranging) system, a barometer, an optical sensor and a range finder.

The vehicle may further comprise a flight control computer, configured to receive control inputs and determine control outputs in dependence on the control inputs.

One or more of the sensors may obtain sensor data during flight and transmit sensor data to the flight control computer. One or more of the sensors may transmit sensor data to a remote device - for example a laptop or tablet - so that an operator can monitor the aerial vehicle remotely.

Increased or decreased wind speeds, change of terrain (for example where the aerial vehicle is close to buildings or a wooded area) or different types of payload (human or living, or non-living items) may affect the aerial vehicle in flight. For example, a person flying with the aerial vehicle may swing their legs or otherwise move and affect (i.e. alter) the centre of thrust of the aerial vehicle; the aerial vehicle may be diverted or thrown off balance. The sensors may be used to monitor factors affecting the aerial vehicle in flight. The flight control computer may use sensor data to counteract effects of such factors and so maintain stability and intended flight path of the aerial vehicle.

The sensors may obtain data automatically during flight or may be triggered by a pilot. The pilot may be the person flying in the vehicle. The pilot may fly the vehicle via a remote control - for example, from the ground.

The control inputs may comprise inputs from the pilot. The flight control computer may comprise a fly-by-wire system that determines control outputs in dependence on both the control inputs and sensor data from the one or more sensors. The flight controller may be configured to fly the vehicle autonomously without a pilot.

The flight control computer may be configured to control vehicle pitch, roll and yaw by rotating the propulsion units about their respective gimbal axes. The flight control computer may be communicatively coupled to each actuator to adjust the orientation of the propulsion units. The actuators may be individually controllable such that adjustments may be made to individual propulsion units.

The flight control computer may be configured with an inner control loop in which vehicle attitude is controlled using rotation of the propulsion units about their gimbal axes, and an outer control loop in which vehicle attitude is controlled by varying a magnitude of thrust from each propulsion unit, wherein the inner control loop may be configured to act faster than the outer control loop.

The inner control loop may additionally control vehicle attitude by varying a magnitude of thrust from each propulsion unit.

The outer control loop may be configured to vary a magnitude of thrust from each propulsion unit more slowly than the inner control loop. The outer control loop may be configured to vary a magnitude of thrust from each propulsion unit to stabilise an uneven load, for example. In this way, gimbal rotations becoming saturated due to an uneven load may be avoided and the inner control loop may be used for flight stability.

The aerial vehicle may be a UAV (unmanned aerial vehicle). For example, the aerial vehicle may be a drone. The drone may be configured to carry a payload and/or may include an onboard camera or other equipment for which stability is important.

The aerial vehicle may be a personal aerial mobility system and the payload may be a person. The personal aerial mobility system may be a jetpack. The payload may be more than one person. The propulsion units may be generally aligned with the person’s shoulders in use, for example, or generally aligned with the person’s waist. For the propulsion units to be arranged at (or generally at) waist height of the person rather than shoulder height, the airframe may be arranged at or generally at the person’s waist height. A benefit of arranging the airframe and the propulsion units generally at waist height is that the person has a fuller range of arm motion compared with having the airframe and propulsion units generally at shoulder height, with a reduced risk of burning.

The airframe may comprise a harness to allow the person to wear the personal aerial mobility system. The harness may be configured to receive the person’s torso, for example, or the person’s shoulders and/or chest and/or may fit under their arms and/or legs. The harness may fit over the person’s shoulders - for example, where the airframe is arranged at waist height in use. The airframe may comprise a seat. The harness and/or seat may be arranged on the airframe spaced from the propulsion units so that the person does not physically contact the propulsion units - otherwise, the person could accidentally change the orientation of the propulsion units on the gimbals, for example, affecting flight, which is not a desirable effect.

The aerial vehicle may be configured to adjust the orientation of the propulsion units and/or the thrust of the propulsion units in response to movement of the person that changes the centre of gravity of the aerial vehicle. The aerial vehicle may be configured to adjust the orientation of the propulsion units and/or the thrust of the propulsion units automatically in response to movement of the person that changes the centre of gravity of the aerial vehicle.

The flight control computer may be configured to control the propulsion units for automatic take-off, automatic landing and steady hover.

The person may use their body weight to change direction in flight, moving relative to the thrust vectors. Arranging the airframe and propulsion units generally at waist height may allow greater ease of moving their own centre of gravity relative to the thrust vectors and therefore provides the ability to control directional flight using body weight shift only. In the aspect having one or more arms, the one or more arms may be coupled to the airframe at an angle 6_r, which is a fixed roll angle between 70 and 90 degrees from a longitudinal axis of the airframe.

In the unfolded position the one or more arms may project from the airframe at an angle of 90 degrees from a longitudinal axis of the airframe and in the folded position the one or more arms may lie parallel to the longitudinal axis of the airframe.

The one or more arms may comprise a locking mechanism configured to lock the one or more arms in (i) the unfolded position, (ii) the folded position and/or (iii) a position between the unfolded and folded positions with respect to the airframe.

The one or more arms may comprise a retractable stand, configured to project from one of the one or more arms in order to support the vehicle and configured to retract into the arm to be hidden for flight.

The vehicle may comprise a shoulder harness configured to fit over a passengers shoulders to protect the passenger in flight and to allow the passenger to carry the vehicle on their shoulders. The vehicle may comprise a pair of arms, one arranged either side of the shoulder harness at a height on the vehicle level with a bottom end of the shoulder harness, wherein the shoulder harness is configured to extend to waist height of a passenger in use.

In a combination of both aspects, the vehicle of the first aspect may further comprise one or more arms rotatably coupled to the airframe, wherein the propulsion units are coupled to one of the one or more arms, wherein each arm is configured to pivot between an unfolded position and a folded position with respect to the airframe, wherein in the unfolded position the one or more arms project from the airframe such that the volume of the vehicle is greater than in the folded position and the vehicle is configured to be flown by an on-board passenger, and wherein in the folded position a volume of the vehicle is smaller than in the unfolded position and the VTOL aerial vehicle is configured to be flown as a drone.

DETAILED DESCRIPTION Examples, which should not be construed as limiting, are shown in the figures, in which:

Figure 1 shows a plan view of a VTOL aerial vehicle;

Figure 2 shows a schematic diagram of the aerial vehicle;

Figure 3 shows a side view of a propulsion unit;

Figure 4 shows a top view of a propulsion unit and a mount;

Figure 5 shows sensors and a flight control computer;

Figure 6 shows a flight control computer;

Figure 7 shows a person wearing the aerial vehicle;

Figure 8 shows a side view of the person wearing the aerial vehicle of Figure 6;

Figure 9 shows a person wearing the aerial vehicle;

Figure 10 shows a side view of the person wearing the aerial vehicle of Figure 8;

Figure 1 1 shows a person wearing the aerial vehicle;

Figure 12 shows a schematic diagram of example elements of the aerial vehicle;

Figure 13 shows a schematic diagram of an example vectored turbine unit.

Figure 14 shows a front view of a VTOL aerial vehicle in a folded position and including the harness;

Figure 15 shows a front view of the VTOL aerial vehicle of Figure 14 and not including the harness;

Figure 16 shows a side view of the VTOL aerial vehicle of Figure 14;

Figure 17 shows a side view of the propulsion units and arm of Figure 16, not including the harness;

Figure 18 shows two propulsion units on an arm of any of Figures 14-17;

Figure 19 shows a front view of the VTOL aerial vehicle of Figure 14 in an unfolded position (including the harness);

Figure 20 shows a side view of the VTOL aerial vehicle of Figure 19; and

Figures 21 (a), (b) and (c) are a front view, a perspective view and a side view of a person wearing the VTOL aerial vehicle of Figure 19, in an unfolded position.

Embodiments of the present invention are described by way of example below.

Figure 1 shows a VTOL aerial vehicle 10 including an airframe 12. The airframe 12 shown has a rectangular plan; however, any suitable shaped airframe 12 may be provided. The depicted airframe 12 has four corners 22 and sides - with pairs of opposite sides 32, 42. Propulsion units 14 are shown arranged at corners 22 of the airframe 12.

The aerial vehicle 10 may comprise onboard LiPo (lithium polymer) or Lithium Ion batteries to provide a power source, for example, or another type of battery or source of electrical power. The aerial vehicle 10 may be rechargeable - for example including rechargeable batteries.

Each propulsion unit 14 may comprise its own power source - for example within a housing of the propulsion unit 14.

Each propulsion unit 14 may comprise a turbine. Each propulsion unit 14 may include a brushless starter motor and at least one fuel pump. The or each fuel pump may comprise an air trap to eliminate air bubbles that may get into the fuel supply. The fuel may be kerosene - for example Jet-Al - or diesel, or any suitable liquid or gaseous propellant fuel.

The aerial vehicle 10 may comprise a fuel tank 70 (shown in figure 7, for example) arranged on the airframe 12. The fuel tank 70 may include a puncture resistant fuel bladder or vented hard tank. The fuel tank 70 may have a capacity of 15-25 litres, for example 20 litres. The fuel tank 70 may include a lightweight composite shell (which may be formed from the same material as the airframe 12). The fuel tank 70 may be arranged in a space between two propulsion units 14 - for example, where a person is the intended payload, the fuel tank 70 may be arranged adjacent the person’s back in use.

Each propulsion unit 14 is arranged on a gimbal 16. The gimbal 16 may be attached to the propulsion unit 14 such that the propulsion unit 14 is rotatable on the gimbal 16. As shown in figure 1, the gimbal 16 may be coupled about opposing sides of the propulsion unit 14. One side of the gimbal 16 may be driven. The other side of the gimbal 16 may be configured to rotate freely or substantially freely. In some embodiments both sides of the gimbal 16 may be driven.

The gimbal 16 is a single-axis gimbal 16, allowing rotation of the propulsion unit 16 about a single axis. In some embodiments, the aerial vehicle 10 may comprise fixed propulsion units, or propulsion units mounted on multi-axis gimbals in addition to the at least three propulsion units 14 mounted on single axis gimbals 16. Multi-axis gimbals may increase technical complexity as well as the weight of the aerial vehicle 10. It is desirable for an aerial vehicle 10 to be as easily portable as possible. Reduced technical complexity versus a vehicle with multi-axis gimbals (which may require multiple actuators) may improve robustness of the aerial vehicle 10.

The gimbal 16 may be supported on a mount 20. Each mount 20 projects from the airframe 12. Each mount 20 supports and houses an actuator 18. Each mount 20 may be relatively simple to detach from the airframe 12 - for example, removably attached by screws or the like. Each propulsion unit 14 may therefore be easy to repair and/or replace.

In some embodiments, one or more of the mounts 20 may be compactable for easy and safe storage, as described in more detail below.

Figure 2 shows the airframe 12 including four propulsion units 14 according to an example. Fore, Aft, Port and Starboard directions are shown. Each gimbal 16 of figure 1 has a gimbal axis 160. Figure 2 shows gimbal axes 160. Each gimbal axis has an offset angle from an axis perpendicular to a longitudinal axis 120 of the airframe 12. The top-left propulsion unit 14 is marked with the axis 120’ to illustrate the offset. Angle 0 in Figure 2 is equal to ( 180-30) degrees and the offset of the gimbal axes 160 from axis 120’ is 30 degrees.

When using a single axis gimbal mechanism 16 the optimum angle of the gimbal location rotated about the longitudinal axis 120 of the airframe 12 (vertical direction of take-off) would be 45 degrees from the plane of the airframe 12 (perpendicular to longitudinal axis 120). This should give an equal control over pitch and roll control when gimbaling the thrusters about their axis. However, in this arrangement yaw control would not be possible.

To overcome this issue, moving the gimbal offset angle away from 45 degrees brings back yaw control. The airframe 12 may be configured to move predominantly in a forward direction (shown in figure 2 by the arrow on axis 120’), the gimbal angle can be favoured to give better pitch control over roll control. In the case of the example of figure 2, the gimbal angle would be rotated so that it would be closer to perpendicular with the plane fore to aft axis. In this example, the offset angle is 30 degrees.

Figure 3 shows one propulsion unit 14 and gimbal 16 in more detail. The propulsion unit 14 and gimbal 16 may be associated with a single actuator 18. The actuator 18 may be operably coupled to the gimbal 16 in order to drive rotation. The actuator 18 may comprise a power source or otherwise receive power, for example from a power source of the aerial vehicle 10.

Each propulsion unit 14 and gimbal 16 may be associated with a single actuator 18 - this may facilitate independent control of each propulsion unit 14.

Figure 3 shows three axes - the longitudinal axis 140 of the propulsion unit 14, the gimbal axis 160 of the gimbal 16 and the longitudinal axis 120 of the airframe 12 (which is not shown). The longitudinal axis 120 of the airframe 12 is also the vertical axis when the aerial vehicle 10 is taking off vertically, as above.

The propulsion unit 14 is shown in figure 3 at an ‘offset’ angle, i.e. the longitudinal axis 140 of the propulsion unit 14 is not aligned with the longitudinal axis 120 of the airframe 12. As set out above, the propulsion unit 14 may have a neutral position in which the axes 120, 140 are not aligned.

The mount 18 comprises a fluid connector for receiving a fluid conduit configured to carry a fuel supply to the propulsion unit 14. A flexible pipe connects the fluid connector to the propulsion unit. The flexible pipe accommodates rotation of the propulsion unit while maintaining connection to the fuel supply.

Figure 4 shows a top view of the propulsion unit 14 shown in figure 2. Figure 4 also shows the mount 20. The mount 20 may house the actuator 18 and/or the actuator 18 may be mounted on the mount 20, and the gimbal 16 may be mounted on the mount 20. The mount 20 may comprise a cover to protect electrical elements housed therein, but in figure 3 the interior of the mount 20 is visible. The mount 20 may define a recess 24 such that the propulsion unit 14 can rotate without hitting the mount 20. The gimbal 16 may be arranged adjacent the recess 24. Each side of the gimbal 16 is arranged on opposing sides of the recess 24.

As the propulsion units 14 can be rotated such that the direction of thrust changes, for safety reasons the aerial vehicle 10 may comprise a laser on one or more of the propulsion units 14 to indicate on the ground the direction of the exhaust - which may be hot and therefore dangerous. The laser may be configured to produce a beam parallel with the longitudinal axis 140 of the propulsion unit 14.

Figure 5 shows a simplified diagram of a sensor system 400 of the aerial vehicle 10 and a flight control computer 500 in communication with the sensor system 400.

The sensor system 400 may comprise one or more of an IMU (inertial measurement unit) 402, a gyroscope 404, an accelerometer 406, a magnetometer 408, a LIDAR (laser imaging, detection and ranging) system 410, a barometer 412, an optical sensor 414 and a range finder 416. The sensor system 400 may comprise other additional sensors.

For example, the sensor system 400 may comprise a fuel level sensor to detect the fuel level of the aerial vehicle 10. The sensor system 400 may comprise a heat sensor adjacent the exhaust end of the propulsion unit 14 to monitor whether output heat could be damaging to the payload (which may be a person) and/or monitor the health and performance of the propulsion unit 14. The sensor system 400 may comprise an altitude sensor, and the flight control computer 500 may be configured to reduce altitude if the altitude exceeds a threshold (sensed by the altitude sensor), to protect the payload (which may be a person) from falling from a non-survivable height.

The sensor system 400 may obtain sensor data during flight (for example during takeoff and/or landing). The sensors in the system 400 may be configured to obtain sensor data periodically (e.g. at least every 100ms), or when triggered by the flight control computer 500 for example.

The flight control computer 500 may receive sensor data from one or more of the sensors in the system 400. The flight control computer 500 may control one or more of the actuators 18 accordingly. The flight control computer 500 may control the actuators 18 to adjust the orientation of the propulsion units 14 based on the sensor data. This may stabilise the aerial vehicle 12.

Control of flight by adjustment of the orientation of the propulsion units 14 may enable the propulsion units to operate at a relatively constant thrust level, which may provide optimal efficiency. This may be more energy efficient than a control regime in which changes in thrust from different propulsion units are used to control flight (which may consume energy). Embodiments may consequently have improved energy efficiency (e.g. fuel economy).

The flight control computer 500 may be configured to control the propulsion units 14 - for example, the thrust produced.

Figure 6 shows the flight control computer 500. The flight control computer 500 may comprise an inner control loop 502 and an outer control loop 504. A control software programme may implement the inner and outer loops 502, 504.

The inner control loop 502 may be configured to control the attitude of the aerial vehicle 12 by adjusting the orientation of one or more of the propulsion units 14. For example, the inner control loop 502 may control one or more of the actuators 18. The inner control loop 502 may further be configured to vary a magnitude of thrust from one or more of the propulsion units 14.

The outer control loop 504 may be configured to control the attitude of the aerial vehicle 12 by varying a magnitude of thrust from one or more of the propulsion units 14 (e.g. by controlling a fuel pump). The outer control loop 504 may be used to automatically trim the vehicle, so as to compensate for an offset payload, for example.

The inner control loop 502 may be configured to act faster than the outer control loop 504 such that user inputs requesting changes to the vehicle attitude are primarily effected by changing the orientation of one or more of the propulsion units 14. This provides a quick response - for example, in emergencies where evasive action may be required. The vehicle attitude may be adjusted using a combination of the inner control loop 502 and outer control loop 504 to adjust both orientation and thrust of one or more of the propulsion units 14.

The flight control computer 500 may configured to land the aerial vehicle 10 safely, automatically, if the fuel level sensor of the sensor system 400 indicates that the fuel level has dropped below a threshold.

The flight control computer 500 may include a GPS (global positioning system) and may automatically generate control inputs to fly the aerial vehicle 10 based on a destination. The flight control computer 500 may be configured to determine a flight path based on the destination. The flight control computer 500 may adjust the orientation of the propulsion units 14 and/or thrust of the propulsion units 14 to reach the destination. The flight control computer 500 may be configured to run beyond visual line of sight (BVLOS) operations, which may use the GPS.

The flight control computer 500 may be configured to respond to a collision avoidance and detection system, either LIDAR, SONAR, optical, infra-red, or other sensor.

The flight control computer 500 may be configured to control one or more back-up propulsion units 14 which are normally ‘off’ during flight (i.e. produce a comparatively low level of thrust compared with a propulsion unit 14 being used for flight). The flight control computer 500 may be configured to identify failure of a propulsion unit 14 and automatically control a back-up propulsion unit 14 to begin producing a greater amount of thrust. The low level of thrust may be rapidly increased where the back-up propulsion unit is needed to account for loss of thrust from a failed propulsion unit 14. The flight control computer 500 may be configured to orient the back-up propulsion unit 14 such that once the back-up propulsion unit 14 starts producing a greater amount of thrust, the orientation of the back-up propulsion unit 14 and thrust magnitude balance the propulsion unit 14 that has now failed - restoring stability.

Figures 7 and 8 show a person 62 wearing the aerial vehicle 10. The airframe 12 may comprise a harness 64, as shown. Figures 7 and 8 illustrate an example in which the propulsion units 14 are substantially at shoulder level in use. As described above, the aerial vehicle 10 may be worn differently - for example, the person’s arms may not be below the propulsion units 14 as shown but may be above the propulsion units 14 - for example as in the embodiment of figure 21, described below.

Figure 8 shows three propulsion units 14 on the person’s right side. The aerial vehicle 10 may comprise three, four, five, six or more propulsion units 14 that may be evenly spread around the perimeter of the airframe 12 to balance the propulsion units 14. In the example shown in figures 7 and 8, there is a space between the front two propulsion units 14 where propulsion units 14 to the side of the person 62 are closer together. This may allow the person 62 to get into the aerial vehicle 10 by holding onto the airframe 12 between the front two propulsion units 14, for example, and may improve comfort for the person and allow them to see where they are going. The harness 64 may be attached to the airframe 12 between the front two propulsion units, for example.

The aerial vehicle 10 may include an on-board flight controller 506 that allows the pilot to control the flight control computer 500, the actuator(s) 18 and/or the propulsion units 14. The on-board flight controller 506 may comprise a joystick that allows the pilot to adjust the attitude of the aerial vehicle 10, as shown in figures 8, 9 and 10. The joystick may be a thumb operated joystick, for example. The on-board flight controller 506 may comprise one or more buttons, switches or an interface that allows the pilot to adjust the attitude of the aerial vehicle 10. The on-board flight controller 506 may comprise an altitude adjustment switch with a climb position, hover position and a descend position, to allow the pilot to adjust altitude. The onboard flight controller 506 may alternatively comprise buttons to increment altitude by a present amount for each press, and which cause a fixed altitude velocity when held down.

The onboard flight controller 506 may comprise three or more proportional controls (e.g. two two axis joysticks), and one or more mode select buttons. In an embodiment a flight mode may be provided in which a first joystick is be configured to command absolute pitch and roll angles, and a second joystick is configured to command yaw velocity and altitude velocity. In an alternative flight mode a first joystick may be configured to command forward ground velocity on one axis, and turn rate on the other axis, and a second joystick may be configured to command altitude velocity on a first axis and lateral ground velocity on a second axis. The turn rate command may be configured to act differently based on forward velocity, for example to cause a banked turn when forward velocity is above a threshold value, and to cause a pure yaw when forward velocity is below the threshold value. Figure 1 1 shows the aerial vehicle 10 with the onboard flight controller 506 comprising two joysticks, for example.

The flight control computer 500 receives sensor data from the sensor system 400 and commands from the on-board flight controller 506, and determined appropriate control commands to achieve either what is commanded by the pilot or required by a flight plan or automatic flight control mode.

The flight control computer 500 may have two main operating modes - pilot control and autonomous control. In pilot control mode, the flight control computer 500 determines control signals required to produce what is commanded by the pilot. In autonomous control mode, the flight control computer 500 may determine the required control signals based on a flight plan or objective (e.g. vertical take-off to a specific altitude, or vertical landing from any altitude). The flight control computer 500 may be programmed to approximate the position of the pilot’s feet in order to safely control touchdown during an automated or manual landing manoeuvre.

The flight control computer 500 may switch between pilot control and autonomous control modes automatically based on a condition sensed by one or more of the sensors of the sensor system 400. For example, one of the sensors of the sensor system 400 may determine that the aerial vehicle 10 has exceeded a threshold velocity or fallen below a threshold velocity and may switch modes accordingly. This may enhance safety, by providing automatic control overrides in the event a dangerous condition exists.

It may be the case that the sensor system 400 fails and/or the flight control computer 500 simultaneously fails. The aerial vehicle 10 may comprise an override system configured to take direct control of the propulsion units 14 and/or the actuators 18 - by-passing the flight control computer 500 - giving the pilot control of the pitch, roll and yaw rates and/or thrust of the aerial vehicle 10.

The flight control computer 500 may be configured to perform auto-take-off, autolanding or steady hover operations. The flight control computer 500 may be configured to adjust the orientation of one or more of the propulsion units 14 and/or the thrust of one or more of the propulsion units 14 to take-off or land without a pilot’s manual control. The flight control computer 500 may be configured to adjust the orientation of one or more of the propulsion units 14 and/or the thrust of one or more of the propulsion units 14 to hover in place without a pilot’s control.

The flight control computer 500 may be configured to process commands from the pilot and adjust the attitude of the aerial vehicle 10 accordingly, by adjusting one or both of the thrust and orientation of one or propulsion units 14. For example, the onboard flight controller 506 may allow the pilot to indicate they wish to change direction of flight, and the flight control computer 500 may adjust both the yaw velocity and absolute roll of the aerial vehicle 10 accordingly, in order to achieve a banked turn (rather than just pure yaw).

Figure 9 shows a person 62 wearing the aerial vehicle 10, including the airframe 12. Part of the on-board flight controller 506 may be arranged on the airframe 12 or on a rigid arm or cable 122 extending from the airframe 12, to allow easy access by the pilot. The on-board flight controller 506 may comprise two joysticks as shown in figure 1 1, or two interfaces/sets of buttons, arranged either side of where a pilot would be positioned in the aerial vehicle 10, to allow control by the pilot with two hands. In figures 9, 10 and 1 1, parts of the on-board flight controller 506 are shown on cables 122 of the airframe 12 and accessible to the person’s hands. The cables 122 or another part of the airframe 12 may include handles without parts of the on-board flight controller 506 included, merely for the person’s comfort and safety and reducing the likelihood of the person moving their limbs (and altering the centre of thrust of the vehicle 10, affecting stability of the vehicle 10).

Alternatively, the aerial vehicle 10 may be configured to carry a payload 60 other than a person 62. In that case, there may not be any on-board flight controller 506. The aerial vehicle 10 may be operated by a remote pilot and/or on autopilot based on the sensor system 400.

In some cases, the payload 60 may be a person 62 who is unconscious and unable to operate the on-board flight controller 506. Again, the on-board flight controller 506 may therefore be disabled and the aerial vehicle 10 may be flown by remote control of the flight control computer 500, by autopilot or based on the sensor system 400. The harness 64 may include hooks, carabiners or other attachment mechanism for attaching a payload 60 other than a person 62 to the aerial vehicle 10 via the harness 64.

The harness 64 may be a full-body webbing harness 64, for example. More than one harness 64 may be provided where the aerial vehicle 10 is to be used for search and rescue or similar first-aid uses (where the aerial vehicle 10 may need to transport a professional such as a first responder as well as an injured person). As above, only the injured person (for example unconscious person) may be transported. The airframe 12 may comprise one or more hooks, carabiners or other mechanisms to attach a person 62 and/or harness 64 to the airframe 12. A removable harness 64 may allow quick extraction of a casualty from the aerial vehicle 10.

The aerial vehicle 10 may be low in weight versus other known VTOL aircraft and therefore easier to transport for emergency services and the like.

The aerial vehicle 10 may be configured as jetpack with harness 64 but remotely operated as a drone; making it suitable as an emergency personnel recovery for military operations or any other high-risk environments such as offshore energy installations, maritime platforms etc. i.e. it flies to you autonomously (or via remote control), but you fly it out in jetpack mode (or remote controlled).

The comparative simplicity of control may be desirable to emergency services or other people who are not trained pilots but need or want to use a personal aerial mobility system.

The aerial vehicle 10 does not require any ground-based infrastructure to take-off and land, in contrast with other VTOL aircraft.

The flight control computer 500 may be configured to receive control signals from a remote device. For safety reasons, to avoid a third-party undesirably remotely controlling the aerial vehicle 10, the flight control computer 500 may require authentication before a remote device is able to supply control signals. Figure 12 shows an example block diagram for the aerial vehicle 10, with part positioned in ways that are broadly representative of an embodiment. The fuel tank 70 is shown between two sets of propulsion units 14, on the port and starboard side of the aerial vehicle 10. An example sensor system 400 is shown, including two IMUs, a GPS and a range finder.

The aerial vehicle 10 of figure 12 shows two batteries. The aerial vehicle 10 may comprise multiple power sources as described above. The aerial vehicle 10 may comprise a power distribution unit as shown, to distribute power to the propulsion units 14 and/or actuators 18 and/or sensor system 400 and/or flight control computer 500 and/or other powered elements of the aerial vehicle 10. Figure 12 shows power being delivered to the flight control computer 500, for example.

Figure 13 shows a diagram of an example propulsion unit 14. The propulsion unit 14 may comprise an engine control unit and engine control interface, as shown and/or may be controlled by the flight control computer 500. The propulsion unit 14 may comprise a fuel pump configured to receive and pump fuel from the fuel tank 70. The propulsion unit 14 may comprise a turbine as above.

The propulsion unit 14 may comprise a vectored nozzle as above. Figure 11 shows a pair of actuators 18 - a first actuator 18 may be provided to actuate the propulsion unit 14 and a second actuator 18 may optionally be provided to actuate the same propulsion unit 14.

Figure 14 shows an embodiment of the VTOL aerial vehicle 10 in which the propulsion units 14 are arranged generally at waist height of a person 62, in use. The harness 64 may comprise parts to be worn over the person’s shoulders, for example a shoulder harness. The harness 64 may comprise parts to be worn on the person’s chest. The harness 64 may be convenient for the person 62 to hold onto in flight, for their comfort and safety, similar to harnesses 64 common in rollercoasters. The harness 64 may be padded for comfort. The airframe 12 may include padding arranged behind the passenger 62 in use, for comfort and safety of their back. The harness 64 may comprise a waist belt. The waist belt and other parts of the harness 64 may be flexible enough to allow the person to move their body, shifting their weight to steer the aerial vehicle 10. By way of the harness 64, the person may be able to carry the weight of the aerial vehicle 10 easily on the ground, for example if ground manoeuvres are required while still wearing the vehicle 10 or before take-off. The harness may further comprise leg straps (not shown in Figure 14, but along the lines shown in Figure 1 1).

One or more of the mounts 20 of the aerial vehicle 10 may normally be configured projecting from the airframe 12 as described above but may comprise a pivot such as a hinge or may otherwise be moveable from their projected position to be folded away.

One or more of the mounts 20 may be rotatably attached to the airframe 12 such that the mount 20 can be rotated away from the projected position and into a folded position. The folded position may be at around 90 degrees from the projected position or at another angle, making the aerial vehicle 10 more compact. The smaller form- factor may render the aerial vehicle 10 easier to transport (for example, for emergency services who travel with the aerial vehicle 10). Folding the propulsion units 14 inwards may move the centre of mass closer to the centre of the airframe 12 for easier manoeuvring of the airframe 12.

Figure 14 shows an embodiment of the aerial vehicle 10 in which mounts 20 comprise arms 202 rotatably connected to the airframe 12 to allow the mounts 20 to be folded closer into the airframe 12 for storage. The figure shows the arms 202 in a folded position. In the example shown, the airframe 12 comprises two arms 202, each arm 202 comprising two mounts 20, and the airframe 12 comprises four propulsion units 14. Any suitable number of arms 202, mounts 20 and propulsion units 14 may be provided - for example, three propulsion units 14 on three mounts 20 on two arms 202, or four propulsion units 14, each on a mount 20, each of which is on an arm 202 (i.e. four arms 202 in total). In the earlier figures, six propulsion units 14 are included on the airframe; the airframe 12 may include two arms 202 each having three propulsion units 14, in accordance with earlier examples. As long as the payload is not made unstable, unsafe or uncomfortable (for a person) then any suitable combination of arms 202, mounts 20 and propulsion units 14 may be used.

The arm 202 may be formed from metal such as aluminium or aluminium alloys, or from composites. The arm 202 may be rotatably connected to the airframe 12 and the connection may be via a pivot 206, for example a hinge. The arm 202 may comprise multiple segments rotatably attached to one another - for example via a pivot which may be a fold pivot or hinge - such that the arm 202 itself can be folded, as well as being rotatable towards the airframe 12.

The arm 202 may be rotatably connected to the airframe 12 at a position adjacent the person’s back, in use - shown clearly in figure 21. The arm 202 may swing forwards from the person’s back towards the person’s front, such that the arm 202 sits alongside the person 62 at generally waist height. Figure 15 shows the rear of the VTOL aerial vehicle 10 and indicates the location of the pivots 206 for the example having two arms 202. The arms 202 are shown comprising mounts 208 for the pivots 206 to attach to the airframe 12. The arms 202 may be rotatable with respect to the mounts 208.

The arm(s) 202 and/or mount(s) 208 may include locking pins or another locking mechanism to prevent unwanted pivoting of the arm(s) 202 with respect to the mount(s) 208 in flight, or when the airframe 12 is folded up for storage or transit for example. The arm(s) 202 may be lockable in the unfolded position or in the folded position. One or more locking pins or other locking mechanisms may be provided to lock the arm(s) 202 in a position between the unfolded and folded positions, for example if the passenger 62 chooses to fly with the arm(s) 202 at an angle different from the unfolded and folded positions.

Figure 15 shows ‘v’, a folded width of half of the aerial vehicle 10. The folded half width may be in the range 350mm to 530mm. The folded half width may be in the range 370mm to 480mm.

The mounts 208 (for example, the aerial vehicle 10 may comprise one mount 208 per arm 202) may be removably attached to the airframe 12. Figure 15 shows the mounts 208 attached to the rear of the airframe 12 and shows the airframe 12 including structural element comprising a pair of bars across the rear of the airframe 12, to which the mounts 208 are attached. The bars may be formed from metal such as aluminium or aluminium alloys, or from composites, and may be strong enough to support the arms 202 accordingly. An arm 202 may comprise a strut 204 configured to support the arm 202, as shown in figure 14. The strut 204 may connect a propulsion unit 14 on the arm 202 to other parts of the airframe 12. For example, the strut 204 may be configured to supply power or fuel, for example via a channel in the strut 204, to elements of the aerial vehicle 10 that are arranged on the arm 202, for example configured to supply fuel to a propulsion unit 14. An arm 202 may define a channel for supplying fuel to a propulsion unit 14. The or each channel (in the arm 202 or strut 204) may be in fluid communication with the fuel tank 70. The fuel tank 70 may be as described with reference to the previous embodiments and is more clearly shown in figures 16 and 20.

The arms 202 being rotatably connected to the airframe 12 may allow the space for receiving a person 62 to be adjusted based on the space required for the person to fly using the aerial vehicle 10 comfortably. The arms 202 may be fixable in position between the projected position as shown in figure 1 and the folded position to prevent the arms 202 from moving during a flight. For example, the arms 202 may include clips, holes and pins or another suitable fixing mechanism to prevent the position of the arms 202 from changing once adjusted as desired. This may also be useful for storage purposes, to prevent the arms 202 from unfolding in transit.

Figure 16 shows the aerial vehicle 10 with an arm 202 in a folded position. The arm 202 is shown at 90 degrees or substantially 90 degrees from the position of the arms 202 in figure 21, which is an unfolded position ready for flight. The airframe 12 may comprise a stand 124. The stand 124 may be configured to support the aerial vehicle 10 if it is set down on a surface, such as the ground. The stand 124 is shown in figure 16 as having a generally semi-circular shape, extending from the front to the rear of the aerial vehicle 10; however, the stand 124 may extend in another direction, such as 90 degrees to the stand 124 shown, in order to support the vehicle 10. The stand 124 may have another shape, including feet for example.

The stand 124 may be arranged on an arm 202. For example, each arm 202 may comprise a stand 124. As shown in figure 16, the stand 124 may be connected adjacent a propulsion unit 14 at the end of an arm 202, such that when the arm 202 is rotated into the folded position the stand 124 is placed in a position to support the aerial vehicle 10. As with the rest of the airframe 12, the stand may be formed from metal such as aluminium or aluminium alloys, or from composites. The stand 124 may be rotatably attached to the arm 202 or airframe 12 in order to be folded away during flight. The stand 124 may be removable to be stored for flight.

The stand 124 may be retractable, as shown in figures 20 and 21 in which the stand 124 has been retracted for flight. The stand 124 may include separately retractable parts - in the depicted example, the stand 124 comprises two parts that retract into the arm 202. The arm 202 may define one or more recesses to receive the retractable stand 124. This may protect a human passenger 62 from injury due to the stand 124 in flight. The stand 124 may not be needed during storage or transit, for example, and retracting the stand 124 reduces the folded volume of the aerial vehicle 10.

Figure 17 shows the arm 202 of figure 16, without the harness 64, for reference.

Figure 18 shows two propulsion units 14 on an arm 202. One of the propulsion units 14 is arranged further from the centre of the airframe 12 than the other propulsion unit 14. In one example, the aerial vehicle 10 may comprise a pair of arms 202 and each arm 202 may diverge from the centre of the airframe 12. Propulsion units 14 on the arms 202 may therefore also diverge from the centre of the airframe 12.

The arm(s) 202 may include a controller as part of the on-board flight controller 506. For example, the joystick discussed above may be arranged on an arm 202. The arms 202 diverging from the centre of the airframe 12 - and from the harness 64, for example - may place the controller from the on-board flight controller 506 in easy reach of the passenger’s 62 hands.

The arm(s) 202 diverging may allow for a passenger 62 to position their body in the harness 64 without bumping into the arms 202 and potentially displacing them, for example, or injuring themselves.

As shown in figure 18, the arm(s) 202 may be attached to the airframe 12 at an angle 0_r, providing a fixed roll angle. 0_r may be between 70 and 90 degrees from the longitudinal axis 120 of the airframe 12 (which is vertical at take-off). For example, the angle 0_r may be 80 degrees, which gives the propulsion units 14 an additional roll angle of 10 degrees with respect to gravity when the airframe 12 is oriented in a vertical position. Any propulsion units 14 that are not on a gimbal 16 (i.e. are not pivotally mounted but are fixed) may also have an additional roll angle of 10 degrees with respect to gravity when the airframe 12 is oriented in a vertical position. This additional roll angle may keep the hot exhaust from the propulsion units 14 pointing away from the passenger 62 with only a minimal loss in thrust efficiency (currently less than 2%).

This additional roll angle gives a greater range of travel for vectoring turbines at their outer mechanical limit due to the added fixed roll angle, while their inner limit is reduced, thrust is only reduced at the inner limit by a minimal amount (currently less than 2%).

When the airframe 12 is folded (i.e. when the mounts 20 or arm(s) 202 are in the folded position), with a fixed roll angle less than 90 degrees, for example 80 degrees, the overall volume required by the airframe 12 is reduced.

The propulsion unit(s) 14 may be rotatable on its respective gimbal 16 as described above. The gimbal 16 may be a single-axis gimbal or may be a two or three axis gimbal 16, for example.

The aerial vehicle 10 may be operable with the mounts 20 in the folded position, for example when the arms 202 are towards the airframe 12. This may be preferable where the VTOL aerial vehicle 10 does not have a passenger 62, either where the payload is an inanimate object or where the passenger 62 is finished with their flight and the aerial vehicle 10 is to be delivered elsewhere (without a payload). For example, the aerial vehicle 10 may be flown as a drone (under the control of a flight computer). The airframe 12 may be oriented such that its longitudinal axis 120 runs parallel to the ground (at around 90 degrees from its orientation at take-off with a passenger 62 as described above) to be flown as a drone by a remote pilot.

The remote control may comprise a controller with a wireless link, with a control interface comprising two joysticks (e.g. thumbsticks) and optionally one or more buttons and/or switches. Figure 19 shows the airframe 12 with the example two arms 202 in the unfolded position. As clear from figure 18, front propulsion units 14 are arranged further out from the centre of the airframe 12 than rear propulsion units 14.

Figure 20 shows the airframe 12 of figure 19 from the side, showing how the arm 202 projects at substantially 90 degrees from the longitudinal axis 120 of the airframe 12 when unfolded.

Figures 21(a), (b) and (c) show a passenger 62 wearing the VTOL aerial vehicle 10, with their arms at the height of the arms 202 of the airframe 12. As shown, the propulsion units 14 are arranged generally at waist height rather than the shoulder height example shown in figure 7 for example. The arms 202 may be arranged level or substantially level with a bottom end of the shoulder harness, for example. The shoulder harness may end at generally waist height of the passenger such that the propulsion units 14 on the arms 202 are arranged below the passenger’s shoulders. Having the propulsion units 14 at this height in the unfolded position may protect the passenger’s face from hot emissions from the propulsion units 14 in flight. They may fly the aerial vehicle 10 with their hands and arms level with the arms 202 and this may be most comfortable if the arms 202 are at waist height in use.

As shown in figures 21(a), (b) and (c), the propulsion units 14 may be arranged such that in their neutral position the exhaust end points away from the passenger 62. The passenger’s hands and arms are higher than the exhaust ends of the propulsion units 14 so in this arrangement the passenger 62 does not need to worry about burning their hands or arms while steering the aerial vehicle 10.

Figures 21(a), (b) and (c) show part of the on-board controller 506 in the passenger’s hands, which may be joysticks or other hand-held controls. A cable 210 may communicatively couple the hand-held controls to a propulsion unit 14 allowing the passenger 62 to control the aerial vehicle 10 as discussed above. The cable 210 may also provide a handle for the passenger 62, convenient for their hands.

Although specific examples have been described, these are not intended to limit the scope of the invention, which should be determined with reference to the accompanying claims.

Claims

1. A VTOL aerial vehicle, comprising: an airframe; one or more arms coupled to the airframe at a pivot; three or more propulsion units, each mounted on a gimbal having a gimbal axis, and each gimbal coupled to one of the one or more arms, wherein each arm is configured to pivot between an unfolded position and a folded position with respect to the airframe.

2. The vehicle of claim 1, wherein in the unfolded position the one or more arms project from the airframe such that the volume of the vehicle is greater than in the folded position.

3. The vehicle of claim 2, wherein the vehicle is configured to be flown by an onboard pilot in the unfolded position.

4. The vehicle of claim 3, wherein the vehicle is configured to position the propulsion units at waist height when in the unfolded position, with the airframe on the passenger’s back.

5. The vehicle of any preceding claim, wherein in the folded position the VTOL aerial vehicle is configured to be flown as a drone.

6. The vehicle of any preceding claim, wherein the one or more arms rotates at least 70 degrees between the folded and unfolded positions.

7. The vehicle of any preceding claim, wherein each arm comprises a propulsion unit at least 20cm from the pivot.

8. The vehicle of claim 7, wherein each arm comprises a proximal propulsion unit and a distal propulsion unit, the proximal propulsion unit closer to the pivot than the distal propulsion unit.

9. The vehicle of claim 8, wherein the distal propulsion unit and proximal propulsion units are on opposite sides of the pivot.

10. The vehicle of any preceding claim, wherein each gimbal is a single axis gimbal, each single axis gimbal configured to vary the orientation of the respective propulsion unit with respect to the arm to which the gimbal is coupled by rotation of the propulsion unit about a gimbal axis.

1 1. The vehicle of any preceding claim, wherein: each propulsion unit comprises a longitudinal axis, for each propulsion unit: a direction towards the centre of thrust is defined by a line between the longitudinal axis and the centre of thrust, and the gimbal axis is offset from perpendicular to the direction towards the centre of thrust by at least 5 degrees.

12. The vehicle of claim 1 1, wherein each gimbal axis is offset by between 5 and 30 degrees from perpendicular to the direction towards the centre of mass.

13. The vehicle of any preceding claim, wherein each propulsion unit has a neutral position in which the longitudinal axis of the propulsion unit is tilted towards the centre of thrust.

14. The vehicle of claim 13 wherein the longitudinal axis of each propulsion unit is tilted by at least 10 degrees towards the centre of mass in the neutral position.

15. The vehicle of any preceding claim, wherein each gimbal and corresponding propulsion unit is configured to allow at least +-15 degrees of rotation of the propulsion unit about the gimbal axis.

16. The vehicle of any preceding claim, wherein the airframe is configured to fly with at least one failed propulsion unit.

17. The vehicle of any preceding claim, further comprising one or more sensors that are one or more of: an IMU (inertial measurement unit), a gyroscope, an accelerometer, a magnetometer, a LIDAR (laser imaging, detection and ranging) system, a barometer, an optical sensor and a range finder.

18. The vehicle of claim 17, further comprising a flight control computer, configured to receive control inputs and determine control outputs in dependence on the control inputs.

19. The vehicle of claim 18, wherein the flight control computer comprises a fly- by-wire system that determines control outputs in dependence on both the control inputs and sensor data from the one or more sensors.

20. The vehicle of claim 19, wherein the flight control computer is configured to control vehicle pitch, roll and yaw by rotating the propulsion units about their respective gimbal axes.

21. The vehicle of claim 20, wherein the flight control computer is configured with: an inner control loop in which vehicle attitude is controlled using rotation of the propulsion units about their gimbal axis, and an outer control loop in which vehicle attitude is controlled by varying a magnitude of thrust from each propulsion unit; wherein the inner control loop acts faster than the outer control loop.

22. The vehicle of any preceding claim, wherein the aerial vehicle is a UAV, and/or a personal aerial mobility system wherein the payload is a person.

23. The vehicle of any preceding claim, further comprising an additional, fixed propulsion unit that is not gimbal controlled and that is configured to provide vertical thrust for additional lift capacity.

24. The vehicle of any preceding claim, wherein the one or more arms are coupled to the airframe at an angle 0_r, which is a fixed roll angle between 70 and 90 degrees from a longitudinal axis of the airframe.

25. The vehicle of any preceding claim, wherein the one or more arms comprises a locking mechanism configured to lock the one or more arms in (i) the unfolded position, (ii) the folded position and/or (iii) a position between the unfolded and folded positions with respect to the airframe.

26. The vehicle of any preceding claim, wherein the one or more arms comprises a retractable stand, configured to project from one of the one or more arms in order to support the vehicle and configured to retract into the arm to be hidden for flight.