Fastener with recessed head and head insert

Details Fastener with recessed head and head insert Fastener with recessed head and head insert

2000-04-18

2001-10-16

Saether, Flemming (Department: 3627)

Expanded, threaded, driven, headed, tool-deformed, or locked-thr

Headed fastener element with nut, washer, securing means or cap

Cap over the head

C411S377000, C411S403000, C411S510000

Reexamination Certificate

active

06302630

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention is generally related to mechanical fasteners, and more particularly to fasteners for low radar signature or stealth aircraft, vehicles and weapons.
BACKGROUND OF THE INVENTION
Military aircraft and vehicles such as tanks and ships typically have access panels that are attached with fasteners. Nuts may be permanently affixed to interior panels, for example, to receive the threaded shaft of the fasteners. In many military applications, detection of the vehicle by radar is undesirable, and an effort has been made to design aircraft, ships and land vehicles, with substantially smooth exterior contours which may be coated with special films to reduce radar signatures and thus inhibit detection.
A problem with stealth aircraft and vehicles is that the presence of screws and other fasteners on the exterior surface contributes to the radar signature. Typically a recessed screw head is used to install doors and panels. This involves countersinking the hole in the surface the screw enters and using a chamfered screw head to fit within the countersunk hole so that the head of the screw is flush with the surface. However, even the use of recessed screws is detectable in the signature of the vehicle.
The recessed exterior screws and fasteners on stealth aircraft and vehicles must be covered to reduce the radar signature. Special coatings are typically used to decrease radar detection of a vehicle. When applied to the fasteners, the coatings fill in the driving engagement mechanisms, and thus the fasteners are not easily accessible by service personnel when needed for repair or maintenance. The head and recess of the fastener must then be scraped to remove the debris, which is time-consuming.
One prior art method involves using an aero-smoothing caulk to cover the heads of fasteners to decrease radar detection. The aero-smoothing caulk must be removed prior to accessing the fastener, and then must be reinstalled following maintenance. This is disadvantageous because the caulk or putty is difficult and time-consuming to remove. Another prior art solution involves bonding donut-shaped plastic attachments on the surface of the fastener heads. This method creates an expensive fastener that is easily damaged and must therefore be replaced frequently.
What is needed is a fastening device for stealth aircraft, vehicles and weapons absent these problems of the prior art.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a fastener with a recessed insert that fits within and is retained by the fastener head. The insert covers the fastener head to reduce the signature of the aircraft or vehicle. The engagement portion of the fastener head recess may be accessed through an aperture in the insert to allow removing and installing the fasteners. The insert is easily snapped in and out of the fastener head, requiring no special tools to install or replace the inserts.
In one embodiment, disclosed is a fastening device with a recessed insert. The fastener has a head at one end and a threaded shaft at the opposing end. The fastener head includes a recessed engagement portion and a concentric counter-bored section thereabout. The counter-bored section has a greater diameter than the engagement portion and extends into the fastener head less than the depth of the engagement recess. The counter-bored section securely receives the insert. The insert is made of a different material than the fastener and has a retainer mechanism such as threads adapted to secure to the counterbored section of the fastener head. The head of the insert advantageously has a circular opening in the center thereof for permitting insertion of the fastener activation tool.
Also disclosed is an insert for a fastener having a recessed fastener engagement portion, preferably being a concentric counter-bored section. The fastener counter-bored section has a greater diameter than the recess and extends into the fastener head less than the engagement recess. The insert includes a hollow shaft adapted to be securely retained within the fastener counter-bored section, and has a head coupled to the shaft. The insert head has a circular opening in the center thereof for permitting access to the fastener engagement portion therethrough.
Further disclosed is a method of reducing the radar signature of a vehicle, including the steps of installing one or more fasteners on the exterior surface of the vehicle, the fasteners having a head comprising an engagement recess preferably comprising a larger concentric counter-bored section. The method also includes the step of installing an insert into the fastener counter-bored section. The insert has a head with a diameter substantially equal to the diameter of the fastener head. The insert head has an aperture for permitting access to the fastener engagement recess and is made of a different material than the fastener.
Advantages of the invention include reducing the radar signature of an aircraft or vehicle. The fastening device may be removed and installed via the aperture in the insert without removing the insert, resulting in cost and labor savings. The insert is easily snapped into place within the fastener recess using finger pressure. Special tools, materials or adhesives are not needed for installation or removal of the insert, as in prior art methods. If damaged, the insert is easily removed and replaced without replacement of the fastener. The recessed insert allows quick restoration of aircraft surface integrity after maintenance.


REFERENCES:
patent: 2627778 (1953-02-01), Hodell
patent: 3405595 (1968-10-01), Peterson
patent: 3885492 (1975-05-01), Gutshall
patent: 4452556 (1984-06-01), Nelson
patent: 4884929 (1989-12-01), Smith
patent: 5391028 (1995-02-01), Charles
patent: 5536124 (1996-07-01), Silva
patent: 5603472 (1997-02-01), Hutter
patent: 5795116 (1998-08-01), Frank

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