Fluid reaction surfaces (i.e. – impellers) – Removable auxiliary attachment to work surface
Reexamination Certificate
2003-05-09
2004-12-28
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Removable auxiliary attachment to work surface
C416S22300B, C416S24400R
Reexamination Certificate
active
06835045
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the art of aircraft cover methods and apparatuses, and more particularly to covers for helicopter rotors.
BACKGROUND OF THE INVENTION
Modern civilian and military helicopters utilize, nearly exclusively, composite blades. Typical composite blades utilize a Nomex honeycomb core with bonded glass skin, such as one or more layers of fiber reinforced plastic, forming the aft fairing portion of the blade. For further reinforcement, Kevlar, carbon or glass fibers are used. The Nomex core is oriented with the open lines of the cells bonded to the top and bottom skins. D-shaped spars, comprising a glass lay-up with a titanium erosion strip, provides structural support within the blades. The spars are bonded together by epoxy or other adhesive material.
Civilian and military helicopters deployed in warm regions, particularly in desert regions, are subjected to the adverse effects of prolonged exposure to direct sunlight. While most helicopters have been designed to operate in extreme temperature conditions, for example, modern day helicopters have been designed to operate in temperature conditions exceeding 130° F., it generally inadvisable to subject the helicopter to extreme temperature conditions for prolonged periods of time. Specifically, high temperatures resulting from absorbing the sun's infrared rays cause bonding deterioration and delamination of helicopter rotor blade components. Debonding is the disintegration of the epoxy or other adhesive materials between spar connections, and delamination is the peeling of layers of the composite skin forming the outer surface of the rotor blade. Both problems contribute to premature rotor blade failure, particularly when under the high wind sheer and vibrations inherent with helicopter operation.
In addition to the ultraviolet effects of the sun, erosion, poor repairs and repeated high cyclical loading exasperates the problem causing minute openings in the skins. The problem is further perpetuated because, in an outdoor environment, helicopters blades are normally tied down placing the top skins of the blades under constant tension and further weakening deteriorated areas of the rotor blade.
Still further, a rotor blade sitting outside in the sun can easily reach 180° F. When heated, the air inside the NOMEX honeycomb core expands and leaks out through any fissures in the skin. Upon cooling, the pressure within the honeycomb core will decrease, and air will be pulled back into the blade, along with any moisture present near the surface of the blade, including rain water, condensation and humidity.
Over time, deterioration of the bonding between the spar connections and delamination of the composite layers not only lead to direct failure of the rotor blades, but also indirectly lead to failure of the blade by allowing water to accumulate and store in the blade's core cavities. Upon significant water accumulation, the track and balance of the rotor blades can become upset, causing operational problems.
Replacement and/or repair of the rotor blades is expensive, time consuming, and requires the highly skilled technician. A replacement blade for a typical military helicopter costs in the neighborhood of between $85,000 and $105,000.
It is known in the art to apply a cover over the rotor hub and rotor blades of a helicopter to provide a shield which mitigates the adverse effects of direct sunlight. For proper function of the cover, it is necessary to consider not only the ability of the cover to reduce aircraft related temperatures, but also other factors such as weight, costs, transportability, ease of installation and removal, resistance to contaminates/chemicals, moisture resistance/breathability, and detectability such as whether detectable infrared signals are created and the degree of glint.
A conventional solution to minimize the effects of excessive exposure to direct sunlight is to house aircraft in containment shelters that shield the aircraft from incident sunlight. However, shelters, either permanent or temporary, often are not practical, interfering with the practical use of the aircraft. For example, aircraft may be deployed in a rapid response condition to underdeveloped locations where contaminate shelters are not readily available. In similar matter, aircraft may be temporarily deployed to satellite locations for limited time durations which make erection of containment facilities non-cost effective. Such shelters are also easily detected by satellite reconnaissance.
Another conventional approach is to drape a canvas cover over the rotor hub and rotor blades of helicopters to provide a shield against direct sunlight. Such canvas covers are difficult to deploy, being bulky and weighty, and often require as many as ten personnel to lift, position, and secure the canvas cover in the proper position. Further, canvas material has a tendency to snag or catch on equipment discontinuities and/or obstructions in the rotor hub area and along the rotor blade, making deployment time consuming. Also, canvas made of non-porous material, tends to maintain moisture and may be moved from proper position by wind conditions or prop wash from adjacent helicopters or aircraft. Most importantly, significant temperature reduction is not achieved through use of a canvas cover.
In response to the unsatisfactory results of conventional covers, the military has sought out new cover configurations and materials to reduce the intense and destructive heat loads presently encountered by aircraft, and to satisfy the other above-listed considerations. These covers failed to provide a complete solution as briefly discussed below:
One such approach is a highly reflective cover comprised of an outer aluminum foil surface bonded to a tight-knit fiberglass fabric inside surface. Although good temperature reduction can be achieved, the cover is very detectable. First, the highly reflective external surface provides tremendous glint. Second, the smooth aluminum foil outer surface sharply reflects infrared signals. Clearly, a cover which enhances the detectability of a covered aircraft is not well suited for military operations. As a further consideration, the aluminum foil is not durable and will debond from the fiberglass inside surface through use and exposure to heat build-up.
Another cover formed of a light weight, highly formable camouflaged material. This cover configuration is largely ineffective in obviating heat build-up, and in some cases may actually contribute to heat build-up.
A further cover is formed of a polyester duck cloth with an optional liner such as a multi-layered quilt with polyester fiber fill and polyester/cotton on either side of a Mylar film. Only moderate temperature reduction was achieved and the bulky cover requires personnel standing on ladders to install.
Additionally, it is important to protect the helicopter, in general, from exposure to the sun's infrared rays and from the accompanying heat build-up. Unprotected aircraft systems, components, and enclosures can deteriorate from the heat build-up resulting in an increased failure rate of the equipment. Heat build-up is particularly problematic in the cockpit area and tends to degrade avionics equipment and reduces the readiness response of the aircraft (while cooling systems are utilized to bring the avionics equipment within operating ranges). High temperatures also create a cockpit environment that is not conducive to maximum pilot efficiency and performance. Likewise, heat radiating from the helicopter causes discomfort for ground and air crew personnel, diminishing their ability to perform duties.
Accordingly what is needed is for an aircraft cover, and particularly a helicopter rotor blade cover, which protects the rotor blade from the adverse effects from prolonged exposure to direct sunlight, and the associated heat build-up. Additionally needed is for the cover to have minimal detectability, with indistinguishable infrared signature and de minimis glint. Further needed is for the cover to be light wei
Barbee Brent W.
Hough E. Andrew
Everman Gregory R.
Look Edward K.
McAleenan James M.
Miller, Everman & Bernard, PLLC
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