Aeronautics and astronautics – Aircraft structure – Load accommodation
Reexamination Certificate
1999-07-15
2001-07-10
Swiatek, Robert P. (Department: 3644)
Aeronautics and astronautics
Aircraft structure
Load accommodation
C254S08900R
Reexamination Certificate
active
06257522
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the modification or conversion of passenger carrying aircraft to freight carrying aircraft and, more particularly, to a method of supporting such an aircraft without damage while major structural components, particularly floor-beams, are being removed and replaced.
When aircraft are converted for freight carriage, stronger structural components are sometimes required as a result of the extra weight imposed by the cargo. This is accomplished by reinforcing some structural components and removing some of the weaker components and replacing them with stronger components. The quantity of structural components that may be removed concurrently is limited to prevent significant deformation of the aircraft. The greater the amount of work that may be accomplished concurrently, the quicker the aircraft may be put back into revenue generating service. The aircraft is supported, usually with jacks and cradles, in an attempt to minimize deformation.
The floor structure, which may consist of floor-beams, floor panels, seat tracks, intercostals, hard point fittings, cargo handling equipment, and hydraulic and electrical standoffs, often represents a significant quantity of the structural items that must be removed and replaced with stronger components. Replacement is usually limited to every other floor-beam at a time. This requires that each floor-beam be carefully located to ensure a flat level floor. The remaining floor structure is then located and installed. This installation is accomplished by mechanics working in confined quarters beneath the floor-beams or lying on top of the floor-beams. This difficult process is labor intensive and contributes significantly to the down time required to modify the aircraft. Small errors in locating parts often compound and result in re-assembly fit problems requiring unique repairs for each occurrence. This decreases the quality of the product and adds to the down time and the expense associated with the aircraft modification. Minor movement of the fuselage can also compound into re-assembly fit problems.
In the time period after the floor beams are installed and prior to the installation of the rest of the floor structure, the floor beams are unstable thus presenting hazardous conditions to individuals working inside the aircraft. In addition, dropped tools and parts represent a hazard to mechanics and other people working below the floor beams. Drill shavings, created while installing floor structure components, fall into the lower lobes of the aircraft. Cleaning up these drill shavings, in the confined area of the lower lobes is difficult and time consuming.
BRIEF SUMMARY OF THE INVENTION
According to an aspect of the invention, a method of supporting the aircraft with jacks is improved such that the internal fuselage shear and bending stresses are minimized resulting in minimum aircraft deformation during modification. This allows for the disassembly of additional structure concurrently with minimum deformation to the aircraft. Measurements are made at strategic locations in areas where major disassembly will occur, particularly laterally across the fuselage in the vicinity of the floor-beams that are to be removed.
The aircraft is weighed and panel weights are developed in a manner typical of the industry. A mathematical model representing the load distribution of the fuselage is created from the panel loads. The support, or jack, locations are then superimposed on the mathematical model, representing reactions to the load distribution. The reactions are manipulated to minimize internal shear and bending moment stresses internal to the fuselage. The sum of the reactions must closely balance the weight of the fuselage. In addition the CG of the jacks must closely approximate the CG of the fuselage. The amount of load at any support location must be low enough to preclude any localized deformation of or damage to the fuselage. Once the required jack loads are determined, the aircraft is jacked on the three main jacks. The remaining jacks are located as determined above and then loaded simultaneously to their proper loads. All jacks are then locked in place and the modification work (including floor-beam removal) begins.
The required jacking scheme will vary from one type of aircraft to another. Even within a family of airplanes the weight and CG may vary enough to change the support scheme. The amount of structural disassembly and the location of the disassembly will also change the support scheme.
Sound engineering judgement is required in developing the mathematical model and in choosing and locating the supports. Consideration is given to representing heavy components as point loads on the model, subtracting them from the panel weights. Knowledge of the aircraft's design philosophy, and physical characteristics are important in determining the maximum allowable shear and bending moment, usually expressed as a percentage of ultimate design shear and bending moment, allowed that will prevent significant or catastrophic failure. Specific knowledge of aircraft components is required to determine how much, if any, deformation of the fuselage is acceptable.
In accordance with an aspect of this invention, the floor structure is built into a floor-beam complex prior to aircraft modification beginning. This allows for more sophisticated tooling to be utilized when locating and installing floor structure components, improving the quality of the product while decreasing the required number of unique repairs. The flatness of the floor is particularly enhanced. This method also allows for a safer and more convenient work environment. The risk of mechanics and other individuals falling due to unstable beams is eliminated. Dropped parts and tools no longer put mechanics or other individuals at risk to injury. The drill shavings associated with the floor-beam complex no longer fall into the constricted lower lobes of the aircraft, thus greatly decreasing the time previously expended in clean up activity. Furthermore, all work accomplished prior to the beginning of the aircraft modification, decreases aircraft down time and contributes to the aircraft beginning revenue-producing flights more quickly.
The size and quantity of complexes built vary depending on the nature of the modification, the size of the opening in the fuselage through which the complex is loaded, and the particular aircraft being modified. The floor-beam complex may require additional splices, beyond those on a conventional floor structure, to accommodate handling and installation. The locations of these splices vary dependent upon component geometry, manufacturing considerations, and the size of the floor beam complex. The splices are predrilled and become locating tools upon installation on the complex. Some components, such as floor panels, may require temporary removal from the complex to provide access to these splices.
Another aspect of this invention is the special tool utilized in loading the floor complexes. The geometry of the tool may vary dependent upon the size of the floor complexes, the geometry of the aircraft fuselage, and the size of the opening in the fuselage through which the complexes are loaded. The tool includes a strong back that attaches to the floor complex, typically to hard points and seat tracks. It is important for the strong back to be sufficiently rigid to prevent the complex from twisting and becoming damaged during its transport and that sufficient attachment points be provided to preclude localized damage to the floor structure. The strong back is attached to the c-shaped member of the tool by a gimbal capable of two degrees of rotation. This allows the complex to be tilted between the horizontal and vertical planes and rotated about the gimbal. Counter weights are utilized to balance the strong back and floor structure. A crane or some similar device is utilized to lift the tool and the attached floor complex. The c-shaped tool must be of sufficient size to preclude it from striking the aircraft
Burden Arthur W.
Chappell Bruce A.
Friend John D.
Hime David B.
Johnson Daniel J.
Gardner Conrad O.
Swiatek Robert P.
The Boeing Company
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