Aeronautics and astronautics – Landing gear – Retractable
Reexamination Certificate
2000-06-06
2001-12-11
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Landing gear
Retractable
C244S1020SL, C188S371000
Reexamination Certificate
active
06328259
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to aircraft landing gear assemblies and, more particularly, to a landing gear assembly including a variable load shear collar.
BACKGROUND OF THE INVENTION
All modern aircraft employ some type of landing gear assembly for supporting the aircraft fuselage above the ground when the aircraft is not in flight. Virtually all landing gear assemblies include some type of shock absorption system. These shock absorption systems are not only necessary for normal landings, but are also critical for hard and/or crash landings.
The landing gear in a rotorcraft, such as a helicopter, must be able to protect the airframe and mission equipment during hard landings. Further, the landing gear must be able to increase the survivability of the rotorcraft occupants during crash impacts. This is accomplished by designing the landing gear to absorb a significant part of the impact energy during the hard or crash landing.
Rotorcraft landing gears are calibrated in terms of sink speed. Military rotorcraft are required to function in vertical sink speed ranges from 10 ft/sec for normal landings to 42 ft/sec for crash landings. In order to provide protection to the airframe, mission equipment package, and occupants over this wide range of impact sink speeds, landing gear having multiple-stage shock struts have been utilized.
A common multiple-stage shock strut employs a first-stage nitrogen-oil type oleo. The first stage functions in landing sink speeds up to the reserve energy condition of about 12 ft/sec. During such low landing sink speeds, the second-stage is static. However, during landing sink speeds that exceed the reserve energy condition, including crash conditions, the second-stage of the shock strut is activated.
One way to activate the second-stage involves the controlled mechanical failure of design features within the shock strut such as an internal diaphragm, shear pin, or shear collar. Prior to the controlled mechanical failure, the second-stage is static and does not stroke. However, upon the controlled mechanical failure, the second-stage of the shock strut strokes and absorbs the landing force. While most shock strut second-stages include a stroking piston similar to the first stage, some landing gear shock strut second-stage designs consist entirely of mechanical devices such as crushable tubes.
The major limitation of current military rotorcraft landing gear is that each shock strut assembly is designed for a specific aircraft gross weight. The landing gear performance degrades when it is employed in an aircraft having a higher gross weight. This may result in increased airframe and mission equipment package damage during hard and/or crash landings. Therefore, derivative or second generation rotorcraft having increased gross weights require the redesign and requalification testing of suitable landing gear. Unfortunately, redesigning and requalifying landing gear is expensive and time-consuming.
In view of the foregoing, it would be desirable to provide a landing gear assembly including a variable force activation device for enabling it to be employed on aircraft having different gross weights. As such, the same landing gear could be used for a family of aircraft designs without requiring landing gear redesign or requalification.
SUMMARY OF THE INVENTION
The above and other objects are provided by a multiple stage shock strut having a first and second-stage. The first-stage is separated from the second-stage by a variable-load shear collar. Upon the application of a pre-selected force to the shear collar by the first-stage, the shear collar experiences a controlled mechanical failure. This activates the second-stage of the shock strut. Advantageously, the shear collar includes an adjustment mechanism which enables variation of the force required for causing the mechanical failure. As such, the shock strut may be employed on different aircraft having different gross weights.
In a preferred embodiment of the present invention, the multiple stage shock strut includes a housing having a first and second piston axially disposed therein. An annular shear collar is rotatably coupled about the housing and includes an inner radial wall, an outer radial wall and a plurality of axially spaced apart shear flanges radially extending from the inner radial wall. The second piston includes a plurality of axially spaced apart force transmitting flanges radially extending therefrom which abuttingly engage the plurality of shear flanges. The degree to which the force transmitting flanges engage the shear flanges corresponds to a circumferential orientation of the shear collar relative to the second piston. The amount of abutting engagement dictates the amount of force required to shear the shear flanges, thereby allowing the second piston to stroke.
To change the circumferential orientation of the shear collar, a flange is provided radially extending from the outer radial wall. The flange includes a plurality of index holes circumferentially spaced apart along the flange. An index pin is selectively inserted through a preselected index hole to rotatably align the shear collar relative to the second piston. Preferably, the plurality of shear flanges and the plurality of force transmitting flanges are interrupted along the inner radial wall and the second piston such that the shear collar can be rotated to completely disengage the shear flanges from the force transmitting flanges.
REFERENCES:
patent: 3538785 (1970-11-01), Grancon
patent: 3697108 (1972-10-01), Diener
patent: 3716208 (1973-02-01), Fagan et al.
patent: 3763740 (1973-10-01), Fletcher et al.
patent: 3997133 (1976-12-01), Fagen
patent: 4361212 (1982-11-01), Bolang et al.
patent: 4759430 (1988-07-01), Kalin
patent: 4823923 (1989-04-01), Moyer
patent: 5090755 (1992-02-01), Garnweidner
patent: 5294077 (1994-03-01), Derrien
patent: 5337976 (1994-08-01), Derrien
patent: 5547148 (1996-08-01), Del Monte et al.
patent: 5927646 (1999-07-01), Sandy et al.
patent: 6062355 (2000-05-01), Nohr et al.
Dinh Tien
Harness & Dickey & Pierce P.L.C.
Jordan Charles T.
The Boeing Company
LandOfFree
Variable-load shear collar for helicopter landing gear shock... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Variable-load shear collar for helicopter landing gear shock..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Variable-load shear collar for helicopter landing gear shock... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2566134