Annular airborne vehicle

#This patent application is a U.S. Nationalization of international patent application no. PCT/GB2008/001329, filed Apr. 16, 2008, which claims priority to United Kingdom application no. GB0707512.0, filed Apr. 18, 2007, all of which applications are expressly incorporated herein by reference in their entireties.

#The present invention relates to an annular airborne vehicle—that is, a vehicle having an outer wing-body which defines a wing-body axis and appears substantially annular when viewed along the wing-body axis, the interior of the annulus defining a duct which is open at both ends.

#It is well understood that aircraft should be designed for minimal drag and mass characteristics, while maximising lift and aeroelastic characteristics so that fundamental aircraft design parameters may be adapted to achieve specific goals including better lift to drag ratios, better fuel efficiency, longer endurance and higher payload capacities, for example.

#Various embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

#FIG. 1a is a front view of a first propelled vehicle;

#FIG. 1b is a cross-section of the right-hand side of the vehicle taken along the wing-body axis and along a line A-A in FIG. 1;

#Referring to FIGS. 1a and 1b, an airborne vehicle 1 has an outer wing-body 2 which is evolved from a laminar flow aerofoil profile (shown in FIG. 1b) as a body of revolution around a wing-body axis 3. Thus the outer wing-body 2 appears annular when viewed along the wing-body axis as shown in FIG. 1a. An inner wall 4 of the annulus defines a duct 5 which is open fore and aft so that air flows through the duct as the vehicle moves through the air, generating aerodynamic lift by differential fluid flow across upper and lower aerofoil surfaces, which in this example arises whenever the axis of the annulus maintains an angle of incidence to its trajectory.

#As shown in FIG. 1b, the aerofoil profile tapers outwardly gradually from a narrow nose end 6 to a widest point 7, then tapers inwardly more rapidly to a tail end 8. In this particular embodiment the widest point 7 is positioned approximately two-thirds of the distance between the nose and tail ends. The particular aerofoil section as described has symmetrical upper and lower surfaces which in this example provides for low minimum drag under cruising conditions, and may be modified in variants of this and other vehicles so as to modify the coefficients of lift, drag and pitch moment to suit the particular mission envelope and associated fluid flow regime as determined by the relevant range of Reynolds numbers.

#A pair of propulsors 9, 10 are mounted symmetrically on opposite sides of a vertical plane containing the wing-body axis 3. In this particular embodiment the propulsors are shown as ducted electric fan motors comprising propellers (or impellers) 11, 12 which are mounted on L-shaped support shafts 13, 14 which in turn are mounted to the wing-body in line with the widest point 7 as shown in FIG. 1b. The propellers are mounted within shrouds 15, 16 in such a way that their efficiency is increased within a proportion of the motor operating envelope. Each I,-shaped shaft is pivotally mounted to the wing-body so that it can rotate independently of the other shaft by 360 degrees relative to the wing-body about an axis parallel to the pitch axis of the vehicle, thus providing thrust-vectored propulsion. Both the shroud and L-shaped shaft have an aerofoil section using a ratio between chord length and height similar to that described for the outer wing-body, where the optimal relationship between height and chord is once again determined by the relative fluid flow regime as described by the relevant Reynolds number for these elements. Thus for example the propulsors 9, 10 can be rotated between the co-directed configuration shown in FIGS. 1a and 1b, in which they provide a thrust force to propel the vehicle forward and along the wing-body axis, to a contra-directed configuration (not shown) in which they cause the vehicle to roll continuously around the wing-body axis.