AIRFRAME CONFIGURATIONS FOR GROUND EFFECT VEHICLES

Abstract: An airframe for a ground effect aircraft or other hybrid aerodynamic vehicle comprising a wing and stabilising surfaces mounted behind and outboard of the tips of the said wing.

Description: AIRFRAME CONFIGURATIONS FOR GROUND EFFECT VEHICLES This invention relates to aircraft and other hybrid aerodynamic vehicles which operate in ground effect. A class of vehicles using the wing-in-ground (WIG) effect is well known. These vehicles fly at altitudes comparable to their wing chord and achieve high power or flight efficiency by using the interference between the wing and the surface_over which they are flying. Examples of this type of vehicle are the "Xtreme Explorer" and the Russian Ekranoplan. These WIG vehicles are known to be inherently unstable in pitch when operating in ground effect because of adverse movement of the centre of pressure as the vehicle approaches the surface. Various solutions have been proposed to address the problem of pitch instability in WIG vehicles. For example some solutions measure pressure beneath various parts of the vehicle structure and use measured pressure differentials to adjust aerodynamic surfaces on the vehicle via active control loops. The disadvantages of the known solutions are complexity, reliability, cost of maintenance and environmental vulnerability. It is an object of our invention to overcome the above disadvantages and to provide airframe configurations for WIG vehicles inherently stable by virtue primarily of the shape of those vehicles. According to the present invention an airframe comprises a wing and pitch stabilising surfaces mounted behind and outboard of the tips of the said wing. The stabilising surfaces may be mounted on booms extending rearwardly from the tips of the wing. The stabilising surfaces may be mounted so as to be in the same plane or above or below the plane of the wing and may be mounted so as to be horizontal or inclined to the horizontal to provide desirable lateral stability and control characteristics. The wing may be fitted with wing tip end plates or vertical surfaces at the wing tips to enhance aerodynamic efficiency. An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings of which Figure 1 is a plan elevation view of a wing-in- ground effect vehicle, Figure 2 is a side elevation view of the WIG vehicle shown in Figure 1 , and Figure 3 is a front elevation view of the WIG vehicle shown in Figure 1 and 2. In the drawings a wing-in-ground effect (WIG) vehicle 1 comprises a fuselage 2 having a seaplane hull shaped lower profile 4, and forward crew compartment with windows 6 and twin gas turbine engines 8 mounted in its upper surface. Attached to the fuselage 2 at mid-section is a wing 10 having a relatively low span to chord ratio. At the ends of the wing i.e. the wing tips, are wing tip end plates or vertical surfaces 12 which blend into float members 14 at their lower ends. Extending rearwardly from the tips of the wing 10 are twin booms 16 which are faired into the wing tip end plates 12 at their upper surfaces. At the rearward end of the booms 16 are vertical fins 18 each carrying lateral control surfaces or rudders 20. Extending horizontally from the ends of the booms 16 are pitch stabilising surfaces 22 each carrying an elevator control surface 24. It will be seen that the horizontal stabilising surfaces 22 are thus mounted behind and outboard of the tips of the wing 10 and moreover that in this example the plane of the stabilising surfaces is above that of the wing 10. The WIG vehicle we have shown in the drawings operates on water. In operation it accelerates on the surface of the water until flying speed is achieved. The pilot then brings the vehicle to a height at which the wing 10 is operating with the benefits of the wing-in-ground effect. Because of the location of the pitch stabilising surfaces 22 i.e. behind and outboard of the tips of the wing 10 these surfaces 22 are in the upward-going part of the wing tip vortices indicated by arrows "V" and thus experience an airflow with an upward component. If the vehicle descends towards the surface the strength of the vortices "V" will reduce due to ground effect, resulting in a reduced upward component of the airflow over the stabilising surfaces. Thus reducing altitude in ground effect will result in an increasing nose up pitching moment and vice versa. In fact the vehicle is inherently stable in the pitch plane in ground effect and very little control by the pilot using the elevators 24 will be required to keep the vehicle flying straight and level at the WIG height above the sea or ground surface. Flaps 25, ailerons 26 and other aerodynamic control devices may be fitted for lift enhancement, attitude control and manoeuvring purposes. Many other variations of the airframe configuration shown in the drawings will now suggest themselves to those skilled in the art. For example the vehicle need not be waterborne but could carry an undercarriage. The vehicle need not have wing tip end plates but could instead have a large span wing with relatively narrow chord. The craft may be capable of conventional flight at higher altitudes

Claims: CLAIMS 1. An airframe for a ground effect aircraft or other hybrid aerodynamic vehicle comprising a wing and stabilising surfaces mounted behind and outboard of the tips of the said wing. 2. An airframe as claimed in claim 1 and wherein the stabilising surfaces are mounted on booms extending rearwardly from the tips of the wing. 3. An airframe as claimed in claim 1 or claim 2 in which the stabilising surfaces are mounted so as to be above, below, or in the plane of the wing. 4. An airframe as claimed in any one of the preceding claims and wherein the stabilising surfaces are horizontal or inclined to the horizontal. 5. An airframe as claimed in any one of the preceding claims and wherein the wing has wing tip end plates or vertical surfaces mounted at the wing tips. 6. An airframe substantially as hereinbefore described and with reference to Figures 1 , 2 and 3 of the accompanying drawings.

Inventors: FELLOWS JEFFREY KEITH, STONE JOHN WILLIAM, FELLOWS, JEFFREY, KEITH, STONE, JOHN, WILLIAM
Applicants: BRITISH AEROSPACE, FELLOWS JEFFREY KEITH, STONE JOHN WILLIAM, BRITISH AEROSPACE PUBLIC LIMITED COMPANY, FELLOWS, JEFFREY, KEITH, STONE, JOHN, WILLIAM
Application year: 1999
Main classification: B60V1
IPC codes: B60V1