GB2516620A

GB2516620A - Lighter Than Air Drone

Info

Publication number: GB2516620A
Application number: GB1310728.9A
Authority: GB
Inventors: Dennis Majoe
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-06-17
Filing date: 2013-06-17
Publication date: 2015-02-04
Also published as: GB201310728D0

Abstract

A surveillance air drone that achieves lift through the use of lighter than air components due to the containment of lighter than air gases. The drone preferably has a tubular fuselage 4, a rudder 3 and two perpendicular arms. The first perpendicular arm is attached at either end to aerofoils 5, 6 that are arranged to exert a rotational force on the fuselage about its longitudinal axis. The second perpendicular arm is attached at either end to frames 7, 8 shaped to produce low aerodynamic drag and which comprise a series of bladed vanes arranged so that they produce an accelerating force parallel to the longitudinal axis of the fuselage in the opposite direction to the rudder.

Description

Lighter Than Air Drone This invention relates to an airborne surveillance drone.

In order to provide surveillance using cameras at altitudes drones are commonly available based on remote controlled planes or helicopters. However these airborne devices must use great amounts of energy to stay afloat in the air and therefore have limited usage times as the energy source runs out after a short time. In addition they make a great deal of noise.

An alternative to powered drones is the use of balloons filled with lighter than air gases, such as weather balloons.

However these balloons are blown away at the speed of the wind and cannot maintain their position over a point on land without using a great deal of energy to act against the forces of the wind.

To overcome this, the present invention proposes a drone that achieves lift through the use of lighter than air components due to the containment of lighter than air gases. The invention incorporates aerodynamic structures which allow it to remain stationary relative to the ground despite a prevailing wind and to achieve this using zero or comparatively small amounts of power.

Preferably, the drone has one or more aerofoil structures generating lift forces orthogonal to the direction of wind flow, as a result of the air flow rate differences between the convex and concave aerofoil main surfaces, where the aerofoil structures are arranged such that in the presence of the ambient wind flow the overall drone assembly moves.

Preferably, the drone has one or more angled bladed vane structures with which an exchange of momentum occurs as the drone and structures moves through the air.

The angled bladed vane structures are preferably arranged such that the interaction of the bladed vanes and the air results in forces on the drone in an opposite direction to the wind.

In this arrangement four main forces must be considered; the drag force of the wind on the structures pushing the drone with the wind in a backwards direction, the aerofoil effect forces moving the drone orthogonal to the wind direction, the drag forces associated to moving that part of the overall structure comprising the bladed vanes and finally the forces created by the bladed vanes pushing the drone in an opposite direction to the wind in a forwards direction. Provided the forces pushing the drone forward into the wind are significant then they will act to reduce significantly the effect of the drag forces of the wind pushing the drone backwards.

If the forces balance each other out then the drone will arrive at a stationary position despite the forces of the prevailing wind.

To achieve this, the structures should be designed to have very low front facing drag coefficients while at the same time having powerful aerofoil lift forces resulting in significant blade vane velocity.

One arrangement of the aerofoil structure could be to move the drone sideways and to pull with it the laded vane structures so as to perform a tacking manoeuvre similar to sailing boats. However this will result in high stress on the structures and will not provide a stationary surveillance platform relative to the ground.

Preferably the forces derived from the aerofoil structures cause the drone to rotate around the drone's major axis rather than to move the drone from side to side. By rotating the entire drone around its major axis, continuously in one rotation sense, the aerofoil and bladed vane structures effectively maintain a constant and infinitely long tacking manoeuvre without the need to change tack.

Preferably, the drone has an axial fuselage and tail section which under the forces of wind on the tail and fuselage, forces the aerofoil and bladed vane structures to face the prevailing wind.

Preferably the aerofoil structures and fuselage and rudder sections are hollow.

Preferably the bladed vane structure has a very small cross section area facing the wind and multiple bladed vanes set at an angle such as 45 degrees along its width. The point first contacting the wind flow should be curve shaped similar to the front point of an aerofoil and the opposite end should be tapered. Such a structure will have very low drag due to the low cross sectional area and the aerodynamic front nose and tapered trailing edge. Howeverthe multiple angled bladed vanes will approximate a large and angled continuous surface area.

Preferably all these components are made from light plastic films and filled with a lighter than air gas such that the drone may lift off the ground without any power required.

Preferably, the drone has a computer to compute the location and movement of the drone in a desired direction by actuating the tail rudder angle and aerofoil and screw rotation rates.

Preferable the drone includes surveillance devices and this equipment is gimballed so that it maintains a clear and constant view of the earth.

Preferably the drone also includes very low power light weight motor and propeller to provide additional thrust when necessary.

An example of the invention will now be described by referring to the accompanying drawings: Figure 1 shows a drone comprising two curved aerofoil structures and two bladed vane structures mounted to an axial fuselage with end rudder section.

Figure 2 shows a hollow aerofoil cross section into which lighter than air gas may be placed.

Figure 3 shows detail of the bladed vane structure.

The drone assembly 1 includes a front face 2 and a rear end 3.

The rear section at 3 includes a rudder section which acts to present the front face 2 towards the prevailing wind.

As the total mass of the drone is lighter than air at ground level pressure, the assembly floats in the air at an altitude and its axis 4 is assumed to be horizontal and the prevailing wind is assumed to blow horizontally striking the front face 2.

Aerofoils 5 and 6 are positioned at an optimal angle of attack with opposite facing lift surfaces. Figure 2 shows the cross section of the hollow aerofoil made by stretching plastic films over a light weight frame.

Multiple bladed vanes are set within thin assemblies forming structures 7 and 8. Figure 3 shows how the structures 7 and 8 are formed from multiple bladed vanes set at an angle in a plane. This arrangement is preferable instead of a single surface bladed vane. A single bladed vane would provide a large surface area onto which wind based drag forces could act. However multiple vanes are preferably combined into an assembly with a low surface area facing the prevailing wind, while maintaining a large surface area of bladed vanes facing the direction orthogonal to the wind direction. In order to further reduce drag, the thin assemblies have a curved nose edge facing the wind and a tapered trailing edge. This further reduces the effect of drag along the assembly width.

Assuming the assembly is at first static floating in the still air then the assembly remains in a static position. As a prevailing wind begins to strike the front face 2 a small amount of backward motion will be experienced due to the drag forces acting on the frontal surfaces of 5, 6, 7 and 8. However as the lift on aerofoils 5 and 6 begins to form, the assembly starts to rotate around the axis 4.

The rotation occurs because of the lift forces generated on the aerofoils 5 and 6. The phenomenon of lift generated by curved and tapered aerofoils is well known.

Due to the rotation of the drone, the multiple bladed vanes of assemblies 7 and 8 are also rotated through the air and air flows in between the bladed vanes. The exchange in momentum results in forces that, in sum, act in a normal direction to the surface of the bladed vanes. These aggregated forces may be resolved into two force components. The first is a drag component that acts so as to counter the assembly rotation. The second is a forward force that acts to push the structures and drone forward along the axis 4 and in the direction of 2.

The assembly rotates up to a maximum speed at which time the rotation drag on the bladed vanes balances the aerofoil lift.

Provided the forward forces created by the bladed vane structures are significant compared to the overall frontal drag forces, the assembly will not accelerate backwards with the full force of the prevailing wind but with some other significantly lower force.

The validity of the invention may be explained as follows.

The aerofoil sections provide a lift force which causes the rotational moment force.

The overall assembly is subject to the forces of the prevailing wind at the time. The invention preferably includes a tail section that positions the front face of the assembly to face the wind. The wind creates a drag force acting on this front face.

The drag force is given by the equation D = (Cdff * Aff * .5 * Ro * VA2) + (Cdfs * Asf * .5 * Ro * VA2) Where Cdff is the drag coefficient for the aerofoil facing direction 2 and Aff is the related cross frontal surface area of the aerofoil.

Where Cdfs is the drag coefficient for the bladed vane structure facing direction 2 and Asf is the related cross frontal surface area of the bladed vane structure.

Ro is the density of the air, and V is the velocity of the prevailing wind.

Assuming the drone is stationary to start and a prevailing wind with velocity V begins to blow then the lift force on the aerofoil will be given by Lf = Cf * Atf * .5 * Ro * VA2 Where CIf is the lift coefficient of the aerofoil, Atf is the area of the foils top surface This lift force will cause a rotational movement of the assembly about the central axis. The assembly will begin to rotate and will accelerate until the lift force is equally balanced by the drag forces of the rotating assembly.

The balancing equation may be described as occurring when the rotational lift forces dependent on speed of prevailing wind equal the total drag on the surfaces of the aerofoil and the bladed vane structure dependent on rotational speed. The equation for this is CIf * Atf * .5 * Ro * VA2 = (Cdtf * Atf * .5 * Ro * Vr"2) -i-(Cdts * Ats * .5 * Ro * Vr"2) Where yr is the velocity of the rotating surfaces, Atf is the surface area on the top surface of the aerofoil, Ats is the surface area on the top surface of the bladed vane structure, Cdtf is the drag coefficient of the top surface of the foil, Cdts is the drag coefficient of the top surface of the bladed vane structure.

This leads to the relationship Vr=V * SQRT( CIf * Atf/(Cdtf * Atf + Cdts * Ats)) The blades are set at a pitch of 45 degrees. Therefore when moving at speed Vr, the bladed vane structure may generate a forward force approximately half that of the drag at yr.

Therefore the forward drive of the bladed vane structure may be approximated as Forward drive, Ffwd = 0.5 * (Cdts * Ats * .5 * Ro * VrA2) Ffwd = 0.25 * Ro * Cdts * Ats * V"2 * (CIf * Atf/ (Cdtf * Atf + Cdts * Ats)) Then this forward drive must at least be equal to the total frontal face drag D to ensure the assembly does not move backwards. If the Ffwd force is greater than the drag the assembly will move forward into the prevailing wind. We already had that D = (Cdff * Aff * .5 * Ro * V"2) 4-(Cdfs * Asf * .5 * Ro * V"2) So for no movement backwards or for forward movement Ffwd >= D, Ffwd >= (Cdff * Aff * .5 * Ro * V"2) + (Cdfs * Asf * .5 * Ro * V"2) Which leads to the equation 0.25 * Ro * Cdts * Ats * VA2 * (CIf * Atf/ (Cdtf * Atf + Cdts * Ats)) >= (Cdff * Aff * .5 * Ro * VA2) + (Cdfs * Asf * .5 * Ro * VA2) Or Cdts * Ats * CIf * Atf I (Cdtf * Atf 4-Cdts * Ats) = 2 * (Cdff * Aff -i-Cdfs * Asf) This equation shows that the assembly can achieve zero motion even in the face of a prevailing wind dependent purely on the area of the top and front surfaces and drag and lift coefficients of the aerofoil and the bladed vane structure. It is air density and wind speed independent.

Typical figures for the drag and lift coefficients may be entered into this equation.

Cdts is the drag for a rectangular surface e.g. 1.0 Cdtf is the drag for a rectangular surface e.g. 1.0 CIf is the lift for an aerofoil which we can suggest as 1.0 Cdff is the drag of an aerofoil front face which is around 0.1 Cdfs is the drag of a rectangular surface 1.0 Ats*Atf/(Atf + Ats) = 0.2A11 + 2.0 * Asf Preferably we assume the area Ats and Atf are equal and we set them to 1.0 Preferably we assume the frontal areas are 0.1.

With these values the left hand side of the equation comes to 0.5 while the right hand side of the equation comes to 0.22, therefore this set of values of drag and lift and area ratios satisfy the condition that the assembly will either remain stationary or move forward into the prevailing wind.

However the principle of conservation of energy provides an upper limit to the above explanation.

If the drone were to be rotated by an external applied rotation force in still air and as a result of this the bladed vane structure forward forces caused the drone to be accelerated forward to a velocity V, then even if the externally applied rotation force were then removed the above argument implies that with a relative forward velocity and apparent air flow of V. the aerofoils would act to maintain the forward force, via rotation of the drone, and thereby allow the drone to carry on forward without the need for any apparent energy source.

Since energy conversion is not perfect the best case scenario is that the drone's forward force Ffwd reaches a value slightly less than the total backward drag force.

In addition one should consider that the above is only true if one assumes the air trapped in the bladed vanes is stationary. In reality the air around the blades is moving at different speeds from V down to stationary.

If air molecules are travelling at V and with the blades at an angle of 45 degrees one can show that simplistically, the blades should be turning at a speed Vr similar in size to the wind speed V in order to create the necessary forces. In order for yr to be close in size to V, from the following equation Vr=V * SQRT( CIf * Atf/(Cdtf * Atf + Cdts * Ats)) it can be seen that the product Cdts*Ats must be very small and CIf very high to ensure Vr is similar in size to V. Therefore the size of the bladed vanes must be optimised to provide the highest forward force but lowest rotational drag and the aerofoils must be optimised to provide the necessary lift coefficient at the best angle of attack.

Therefore In reality the drone will drift backwards to a degree, and this drift could be matched by on board low power motor driven propellers.

In a preferred embodiment, the bladed vane structure section consists of plastic film ribbons stretched across a carbon fibre frame.

The aerofoils and fuselage comprise a carbon fibre frame and plastic film (typically biaxially-oriented polyethylene terephthalate polyester film) the internal volume of which is filled with helium or another lighterthan air gas.

In a preferred embodiment the drone would require to lift a payload of for example 300 grams comprising the bladed vane assembly, navigation computer and navigation sensors, camera, wireless communications, batteries, DC motor and propeller for use in emergency still air conditions and the plastic film.

The aerofoils and fuselage would offer the main internally free volume. With helium as the lighter than air gas, a volume of approximately 300 litres is required to lift the 300 grams.

Given the fuselage has a cross sectional area radius of 10 cm and the aerofoils have a similar cross sectional area, then the total fuselage length would be 4 metres and each of the two aerofoil sections would be 2 meters long by approximately 0.5 meters wide. Given these dimensions and the state of the art carbon fibre structures known today, one can practically implement a viable assembly.

Using the above mentioned plastic film the flight time could be in the region of 5 days, limited only due to helium leakages.

The invention was evaluated using a smaller model of the drone. Non lighter than air components were used, however the same assembly of aerofoils and bladed vane structurewas made as in figure 1. No rear section was implemented.

The aerofoils were based on NACAS4O9 profile set at an angle of attack of 10 degrees.

The assembly was held with axis 4 vertical and the front face pointing upwards. The assembly was held in the vertical with a needle shaft and balanced so it could rotate freely in the horizontal plane. The whole assembly was then placed on a highly sensitive weighing scale. A smooth air flow was generated using an air multiplier fan blowing air down onto the front face. The weight of assembly measured by the scale was monitored with the scale reading zeroed under static conditions.

In a first recording the assembly was rigged such that any rotation was blocked. As expected when the initial air flow began the scale indicated an increase in weight to a maximum figure. This is considered to be an approximate figure for the total drag force although it is known that such a static test is not truly representative of the dynamic drag figure.

In a second recording as the air flow was started the assembly was allowed to rotate freely.

As the rotation speed increased the measured weight fell in a series of oscillations to less than half the maximum recorded weight of the first recording. The experiment strongly suggests that the energy in the prevailing wind may be utilised to drive a bladed vane airscrew which generates sufficient forward force to overcome a large fraction of frontal drag forces. The oscillations and lack of greater performance is explained by the fact that the forces across the bladed vanes are not necessarily always balanced and the slightest imbalance upsets the delicate testing arrangement to act as a see saw on the needle pivot.

This would not occur in an airborne version where the long fuselage acts as a stabilising force and the energy available from aerofoil action would be fully available to increase the speed of the bladed vane air screw and thus gain higher forward forces.

Claims

Claims 1 An air craft comprising a first structure with an aerofoil effect which makes the craft body move in response to wind blowing in one direction and a second structure with a propeller effect moved by the craft body to produce thrust in said direction.
2 A craft as in claim 1 where the craft body rotates under the aerofoil effect in the presence of the wind blowing in one direction and the thrust in said direction is created by angled blades rotating with the body.
3 A craft as in Claim 2 in which the aerofoil and angled blade structures are shaped and dimensioned such that wind drag force experienced by the aerofoil and angled blades structures when facing the wind are opposed to a large degree by the propeller forces created by the rotation of the angled blades such that any further navigation of the craft may be carried out with propelling devices operating at very low power consumption.
4 A craft as in Claim 3 comprising light weight components including the aerofoil structure, the propeller structure comprising angled blades, a body fuselage to which the first and second structures are attached, a rudder end section of the fuselage which acts to manoeuvre the craft and point the two structures to face into the wind.
A craft as in claim 4 in which the angled blade structure comprises multiple parallel bladed vanes, where the individual vane length is at least ten times or more the vane width, where the blades are set at an angle relative to the structures largest surface, that are offset from each other by their width with their longitudinal centres set within a plane with one width edge having a symmetric aerofoil shaped nose in length cross section and the opposite width edge shaped with a symmetric aerofoil shaped tapered end.
6 A craft as in the above claims which includes a navigation computer, navigation sensors, motor driven propellers, surveillance sensors and battery that together can navigate the craft.