The present invention relates generally to a structural support and, more particularly, to a rib for buttressing the enclosing sections and upper deck floor of an aircraft pressure cabin.
There are primarily two types of aircraft configurations: the more common (conventional) configuration which includes a tail section comprised of vertical and horizontal stabilizers located at the aft end of a tubular fuselage; and the tailless configuration. As to the latter, there are two sub-types: a first type which has no central body, commonly known as a "flying wing," and a second type having a central body which is blended into laterally extending wings.
FIG. 1 is a schematic drawing of aircraft 20, a generic example of a conventional aircraft having a tubular fuselage and tail section. Aircraft 20 includes tubular fuselage 21, wing 23, horizontal stabilizer 25, and vertical stabilizer 27. When loaded, aircraft 20 has center of gravity 29. Horizontal stabilizer 25 controls the rotation of aircraft 20 about the pitch axis passing through center of gravity 29.
The vector L represents the lift generated by wing 23. The additional lift generated by fuselage 21 is small in comparison to L, and will be ignored for the limited purpose of this brief discussion. The vector l represents the lift generated by horizontal stabilizer 25. Generally, in normal flight, L acts in the upward, or positive direction, while l acts in the opposite, or negative direction. L has a magnitude much larger that that of l. The angle of attack of aircraft 20 is controlled and stabilized by the pitch moments about center of gravity 29 generated by L and l.
The presence of horizontal stabilizer 25 causes a significant increase in the drag for aircraft 20 in comparison to what the drag would be in the absence of the two aforementioned control elements.
Another drawback inherent to aircraft 20 is the weight of fuselage 21, which serves to provide a pitch moment arm of sufficient length to allow the pitch rotation of aircraft 20 to be controlled by the lift l generated by horizontal stabilizer 25.
Also, in order to sustain flight, L must have a magnitude sufficient to lift the weight of the entire aircraft, including wing 23, fuselage 21, horizontal stabilizer 25 and vertical stabilizer 27. L must thus exceed the weight of wing 23. As a consequence, wing 23 will be subjected to a resultant upward force equal to L minus the weight of wing 23. This resultant force subjects wing 23 to a distributed bending moment, with the maximum moment occurring at the wing root where wing 23 joins fuselage 21.
Wing 23 must be designed to withstand the bending moments induced by the distributed wing lift and weight forces, for the whole prescribed range of flight and ground load conditions. The strengthening of wing 23 also typically takes up additional volume that might otherwise be utilized to carry fuel. Both of the foregoing factors reduce the range of aircraft 20.
The foregoing drawbacks inherent to the conventional aircraft configuration exemplified by aircraft 20 have caused aeronautical engineers to consider tailless designs. A perspective view of tailless aircraft 30, a generic example of a tailless aircraft, is shown in FIG. 2. Aircraft 30 includes main wing section 31, deflectable reflexes 33, deflectable flaps 35, wing tip 37, and center of gravity 39.
FIG. 3 provides a side view of wing tip 37, and shows reflex 33 with particularity. Generally, in normal flight, main wing section 31 generates upward, or positive, lift vector L, whereas each reflex 33 generates a lift vector l acting in the opposite, or negative, direction. The flight of tailless aircraft 30 is controlled and stabilized by the appropriate deflections of reflexes 33 and flaps 35.
As may be discerned by cursory inspection of FIG. 3, tailless aircraft 30 has no horizontal stabilizer projecting into the ambient airstream. Moreover, since the flight of aircraft 30 is controlled and stabilized without a horizontal stabilizer, it does not require the moment arm to this stabilizer otherwise provided by a fuselage. The absence of a horizontal stabilizer and a fuselage lowers the drag coefficient and weight of tailless aircraft 30 in comparison to aircraft 20. Wing section 31 also weighs less than wing 23 of aircraft 20 because it need not be designed to withstand the moment generated by having to lift a fuselage in addition to its own weight.
Although the foregoing advantages inherent to tailless aircraft are widely recognized, modern commercial airliners nonetheless have continued to be developed and produced using designs which incorporate tubular fuselages and tail sections. The reason apparently derives not from comparative performance analyses, but rather from commercial realities confronting airlines and the designers and builders of commercial airliners.
More particularly, modern commercial airliners are typically designed and built as one model in a family of derivative configurations. For conventional aircraft exemplified by aircraft 20, each model varies primarily in the length of its tubular fuselage, with the various family members sharing a similar wing and avionics. By using different members of a manufacturer's family of airliners, the airline company's pilots, mechanics, and other support personnel need only acquire detailed knowledge of one model in the family. They are subsequently able to fly, maintain and repair another model in the same family with substantially less instruction and training than would be required to acquire proficiency with a completely new and unfamiliar aircraft.
The primary means of creating a new model from an existing aircraft is by inserting a hollow axial plug having the identical diameter of the original fuselage, into the fuselage. This increases the length and thus the size of the original aircraft, and avoids the significant investment necessary to develop a completely new model. An airline company will select a model based on the predicted passenger load and the length of the route the aircraft is to service.
Despite offering excellent aerodynamic efficiency, no manufacturer has ventured to produce a tailless base model because of the difficulty and expense which would be entailed to develop variants to satisfy the desires of the airline companies. More particularly, as the "flying wing" type of tailless aircraft obviously does not have a fuselage whose length can be readily changed, this design cannot be easily modified to alter its load carrying capacity. The blended wing-body type of tailless aircraft has a central body which could be modified, but this design has a drawback which has impeded its commercial viability.
More particularly, the pressure cabin enclosed by the body of a blended wing-body aircraft is not cylindrical like that formed by fuselage 21 of conventional aircraft 20, but rather has top and bottom body sections which are flat or gently curved. At altitude, the pressure cabin is subjected to a force caused by the pressure differential between the pressure cabin and the ambient atmosphere, as well as dynamic forces caused by aircraft maneuvers. In a conventional cylindrical pressure cabin, this pressure force is directed radially outwards and creates a tensile force in the cabin's cylindrical shell. In the non-cylindrical body sections of the blended wing-body pressure cabin, the pressure forces are reacted largely by bending of the shell between rib supports.
As a consequence, the pressure cabin body sections for a blended wing-body aircraft would have an increased weight compared with that for a conventional cylindrical shell. The shell would suffer lateral deflections that would increase drag and, with such cyclic deflection occurring on every flight, deleteriously affect the structural integrity of the aircraft body.
To provide an attractive interior layout with adequate space for passengers and their carry-on luggage, it is necessary to space the supporting ribs widely apart. This increases the weight of the pressurized shell and the deformations of the structure.
The foregoing characteristics inherent to the configuration of tailless aircraft have impeded the development of an airliner having a tailless design in spite of its having an aerodynamic efficiency greater than conventional designs having a tubular fuselage and tail section.
Based on the foregoing, it can be appreciated that there presently exists a need for a supporting rib which overcomes the above described disadvantages and shortcomings of the structural supports of the prior art. The present invention constitutes a rib which fulfills this need in the art and, in so doing, facilitates the design of a commercially viable blended wing-body aircraft.