Patent Description:
Aircraft structures employ stringers as stiffening elements for skin panels and other integrated structural elements. Stringers increase the bending strength of a panel and may extend for significant runs along interior panel surfaces. Stringers may have various cross sections but may have a hat section which provides an interior duct or channel. This duct may be employed for secondary purposes such as using the stringer as a conduit for venting fuel and fuel vapors from wing fuel tanks and surge tanks. This approach is particularly applicable for a fuel tank cross-venting system. The duct must be dammed at fuel tank boundaries to separate the tanks and at interfaces with other system tubes to direct the vent airflow.

In composite construction, stringers are typically bonded to the skin or other panel with flanges extending from a base portion of the hat section. To accommodate venting, one or more apertures are formed in the hat section to direct the fuel or fuel vapors out of and into desired fuel transfer conduits or tanks. To seal the stringer at the aperture to prevent fuel or vapors from continuing through the stringer beyond the apertures, vent dams in the stringer are required. Fabrication techniques for the bonded stringers typically require that the vent dam be inserted into the stringer after bonding to the skin. The size and shape of the apertures is desirably minimized to maintain structural strength of the stringer and avoid stress risers. A cap may be installed over the aperture with fittings to engage the fuel/vent conduit. The attaching conduit is typically substantially orthogonal to the stringer duct and reduction of turbulence and pressure drop in fuel flowing into or out of the stringer is also desirable.

Inserting the vent dam through the aperture and then sealing the dam can be challenging to provide the desired change in flow direction of the fuel or vapor. Multi-piece dams have been employed to allow a collapsed or piecemeal insertion through the aperture and assembly inside the stringer duct. However, such dams require joining fasteners and create added complexity and parts count. Additionally, such joining fasteners may require electrical grounding further increasing fabrication complexity.

The document <CIT> states, in accordance with its abstract, a vent dam for use in a vent stringer in a fuel vent system. The vent dam is configured to mount to and within the vent stringer The vent dam has a contoured guiding surface for guiding fuel flow into and out of an interior of the vent stringer, wherein the vent dam, the vent stringer, and a tube attached to the vent stringer are in fluid communication with one or more fuel tanks. The vent dam further has one or more side flanges extending from the contoured guiding surface for providing attachment of the vent dam to one or more interior portions of the vent stringer, wherein the contoured guiding surface and the one or more side flanges are formed as one piece.

According to the present disclosure, a device, a system, and a method as defined in the independent claims <NUM> and <NUM> are provided. Further embodiments of the claimed invention are defined in the dependent claims. Although the claimed invention is only defined by the claims, the below embodiments, examples, and aspects are present for aiding in understanding the background and advantages of the claimed invention.

The features, functions, and advantages that have been discussed can be achieved independently in various implementations of the present disclosure or may be combined in yet other implementations, further details of which can be seen with reference to the following description and drawings.

The implementations and methods described herein provide a single piece vent dam insert sized to be received into an aperture in a stringer. The vent dam insert has lateral flanges which are offset along a longitudinal axis of the stringer when in the seated condition. The offset of the lateral flanges provides a reduced dimension orthogonal to a lateral hypotenuse of the trailing edge of the first lateral flange and a leading edge of the second lateral flange allowing the insert to be rotated from a final sealed orientation and received through the aperture.

Referring to the drawings, <FIG> shows a fuel vent system <NUM> for an aircraft <NUM>. As seen in <FIG> and <FIG>, the fuel vent system <NUM> includes a vent stringer <NUM>. The vent stringer <NUM> has a duct <NUM> with a curved trapezoidal cross section forming an internal periphery <NUM> and a longitudinal axis <NUM>. A normal axis <NUM> is perpendicular to the longitudinal axis <NUM>. An aperture <NUM> is defined through the vent stringer <NUM> and, in some implementations, is an oval in shape. A single piece insert <NUM> is received in the duct <NUM> as a vent dam.

Referring to <FIG>, the single piece insert <NUM> has a first lateral flange <NUM> and a second lateral flange <NUM>. The duct <NUM> has opposing first and second interior lateral surfaces <NUM>, <NUM> as a portion of the internal periphery <NUM>. The first lateral flange <NUM> and the second lateral flange <NUM> are configured to engage the first and second interior lateral surfaces <NUM>, <NUM> of the duct <NUM> with an insert axis <NUM> aligned with the longitudinal axis <NUM> in a seated position. The first and second lateral flanges are offset longitudinally along the insert axis and joined with a curved wall <NUM> having a curvature <NUM>. The curvature <NUM> is shaped to be received, with the insert oriented in a rotated position at an insertion angle <NUM> rotated about the normal axis <NUM> perpendicular to the longitudinal axis, in the aperture <NUM> in the vent stringer <NUM>.

Referring again to <FIG>, an aircraft skin <NUM> can include the vent stringer <NUM>. The implementation in the example shown is a composite multilayer laminated structure which employs webs <NUM> extending laterally from the vent stringer <NUM> providing a base laminated onto the skin <NUM>. The vent stringer <NUM> acts as a structural element resisting bending loads in the skin <NUM>. However, the vent stringer <NUM> additionally provides the interior duct <NUM> which may be employed, as in the implementations disclosed herein, in a fuel vent system for transfer of fuel or fuel vapor between fuel conduits or tanks, such as surge tanks. As seen in <FIG>, a cap <NUM>, extending over the stringer <NUM> to cover the aperture <NUM> and sealed to the stringer and webs <NUM>, may be employed for interconnection to other conduits. The vent dam insert <NUM> (visible in <FIG>) is placed in the duct <NUM> to seal the duct diverting flow from the duct <NUM> into the cap <NUM> and any connected conduit or plumbing for routing elsewhere in the aircraft structure.

As seen in <FIG> and <FIG>, the single piece insert <NUM> has a first lateral flange <NUM> and a second lateral flange <NUM>. The first lateral flange <NUM> and the second lateral flange <NUM> are configured to engage the opposing interior lateral surfaces <NUM>, <NUM> of the duct <NUM>. The insert <NUM> engages the internal periphery <NUM> of the duct <NUM> in the vent stringer <NUM> in sealing contact in a seated position. The first and second lateral flanges <NUM>, <NUM> are offset longitudinally along the longitudinal axis <NUM> of the duct <NUM> and a coaxial longitudinal axis <NUM> of the insert <NUM> and are joined with a curved wall <NUM>. The wall <NUM> has a curvature <NUM> discussed in greater detail subsequently.

For the example implementation shown in <FIG>, the insert <NUM> has a trailing edge <NUM> of the first lateral flange <NUM> and a leading edge <NUM> of the second lateral flange <NUM> which are oriented on a lateral hypotenuse <NUM> perpendicular to the normal axis <NUM>. The offset of the first and second lateral flanges <NUM>, <NUM> and the curvature <NUM> of the wall <NUM> are configured to allow the insert <NUM> to be rotated to an insertion angle <NUM> as shown in <FIG> and inserted into the aperture <NUM>. This allows the aperture <NUM> to have a minimized minor axis perpendicular to the longitudinal axis <NUM>. The hypotenuse <NUM> has a relative angle <NUM> with respect to the first and second lateral flanges <NUM>, <NUM> of not less than <NUM>°.

The component of the hypotenuse <NUM> perpendicular to the longitudinal axis <NUM> of the insert has a planar length <NUM> less than a planar width <NUM> between the opposing interior lateral surfaces at the aperture as represented in <FIG>. The planar length <NUM> of the perpendicular component of hypotenuse <NUM> is less than the planar width <NUM> of the opposing interior lateral surfaces of the duct at all incremental lengths perpendicular to normal axis <NUM> as the lengths of planar length <NUM> and planar width <NUM> will vary along normal axis <NUM>.

The curvature <NUM>, which may have varying shapes as subsequently described, is limited as shown in <FIG> as curvature <NUM>'. Curvature <NUM>' may be composed of three segments limited in extent to be received within the duct <NUM>. A first segment A cannot exceed an extrapolation of the first lateral flange <NUM> beyond trailing edge <NUM> to a tangent of a second segment B limited by a semicircle of radius <NUM> equal to or less than planar width <NUM> and commencing perpendicular to the longitudinal axis <NUM>. The semicircle of segment B extends over an arc <NUM> equal to or greater than the insertion angle <NUM>. For the implementation shown, the arc <NUM> has a termination at a tangent point <NUM> on the first interior lateral surface <NUM>. A third segment C extends from the termination of segment B at arc <NUM> to an extrapolation of the second lateral flange <NUM> to an intersection point D. Segment C may be parallel to the first lateral interior surface <NUM> of the duct <NUM> (seen in <FIG>).

As seen in <FIG> and <FIG> for the example implementation, the duct <NUM> of the vent stringer <NUM> has an arcuate trapezoidal cross section having an arcuate top with a substantially flat bottom <NUM> in the duct <NUM>. Alternative geometric shapes for the stringer and duct may be employed with flat or curved surfaces. The insert is also substantially trapezoidal in cross section with the first and second lateral flanges <NUM>, <NUM> of the insert <NUM> extending from a flat base <NUM> received on the flat bottom <NUM> of the duct <NUM> to a curved top <NUM> received in an arch <NUM> forming the arcuate top of the duct <NUM>. For the example implementation, the curved top <NUM> (and arch <NUM>) have a chord length <NUM> shorter than a bottom width <NUM>. The first and second lateral flanges <NUM>, <NUM> are received in sealing engagement with the interior lateral surfaces <NUM>, <NUM> of the duct and the insert <NUM> as whole when seated may provide sealing contact with the internal periphery <NUM> created by the opposing internal lateral surfaces <NUM>, <NUM>, flat bottom <NUM>, and arch <NUM>.

Referring in particular to <FIG> and <FIG>, to accommodate insertion of the vent dam insert <NUM> into the aperture <NUM>, a perpendicular distance from a connecting line <NUM>, which extends from the leading edge <NUM> of the second lateral flange to a forward termination <NUM> of the first lateral flange, to the curvature <NUM> of the curved wall <NUM> is less than a clearing distance <NUM> (denoted generally in <FIG> as an arrow perpendicular with respect to a major axis <NUM> of the aperture) to a peripheral edge <NUM> of the aperture along the entire length of connecting line <NUM> with the normal axis <NUM> of the insert <NUM> substantially at a center <NUM> of the aperture. The major axis <NUM> of the aperture is parallel to the duct longitudinal axis <NUM>. Within that clearing distance <NUM>, the curvature <NUM> may be shaped to accommodate flow requirements and may be a simple symmetrical arc or a complex or asymmetric curve. When oriented in a rotated position at the insertion angle <NUM>, the insert <NUM> can be received into the aperture <NUM>. Shaping of the insert <NUM> with the hypotenuse of the lateral flanges and curvature of the wall to be received within the clearing distance <NUM> also allows the aperture to be formed with a minor axis <NUM> less than the bottom width <NUM> of the duct.

Once inserted into the aperture <NUM> with the base <NUM> against the bottom <NUM> of the duct, the insert <NUM> is counter rotated about the normal axis <NUM> through the insertion angle <NUM> to align the insert longitudinal axis <NUM> of the duct <NUM> with the longitudinal axis <NUM> as seen in <FIG>. The asymmetric shape of the curvature <NUM> in the example implementation provides additional relief to avoid interference during rotation of the insert <NUM> and provide clearance for fastener installation, as will be described subsequently. The insert <NUM> is then translated to an engaged position proximate an end of the aperture <NUM> as seen in <FIG>. A cross sectional periphery of the insert is in sealing contact with an internal surface of the duct in the seated position as seen in <FIG>.

To properly position the vent dam insert <NUM> with regard to the aperture to achieve desired performance with respect to diverting flow into the cap <NUM>, a positioning ledge <NUM> extending from a top surface <NUM> of the curved top <NUM> of the insert <NUM>, best seen in <FIG>, engages the arch <NUM> of the duct <NUM> with an edge <NUM> configured to engage an end periphery <NUM> of the aperture <NUM> as seen in <FIG>. Positioning ledge <NUM> additionally prevents the insert <NUM> from being pushed too far into the duct <NUM> beyond the aperture <NUM> to avoid difficulty in bringing the insert back towards the aperture. Additionally, mating shaping of the edge <NUM> and end periphery <NUM> of the aperture also forces the insert longitudinal axis <NUM> to be aligned with duct longitudinal axis <NUM>. The combined curvatures of the edge <NUM> and end periphery <NUM> control <NUM> degrees of freedom for rotational and longitudinal orientation of the insert in the duct. To assist in translating the insert <NUM> a tab <NUM> extends from the positioning ledge <NUM> which may be grasped to assist in moving the insert. The tab <NUM> may additionally be employed as an index received in a mating recess in the cap <NUM> to assist in positioning the cap over the aperture <NUM>. The positioning ledge <NUM> and tab <NUM> assist in the installation of the insert <NUM> but may be eliminated in alternative implementations.

In the example implementation, fasteners <NUM> are employed as seen in <FIG> to secure the insert <NUM> in the seated position in the duct <NUM>. A first fastener is inserted through the first offset flange <NUM> into a first of the opposing lateral interior surfaces <NUM> of the duct <NUM> and a second fastener is inserted through the second offset flange <NUM> into the second of the opposing lateral surfaces <NUM>. The offset flanges <NUM>, <NUM> allow enhanced access for insertion of the fasteners. Additionally, the complex asymmetric curvature <NUM> of the wall <NUM> allows additional clearance for access. In example implementations the fasteners may be protruding head, sleeved fasteners. While one fastener in each of the first and second lateral flanges is shown in the example implementation, multiple fasteners may be employed with vertical and/or longitudinal spacing. In alternative implementations adhesive bonding of the insert <NUM> in the duct <NUM> may alleviate the need for any additional mechanical fasteners.

To assure a seal of the insert <NUM> in the duct <NUM>, a fillet seal <NUM> is applied around a forward peripheral edge <NUM> of the insert <NUM> as seen in <FIG>. The fillet seal <NUM> such as a urethane or silicon seal is applied in a liquid or malleable form and then cured. In exemplary implementations a polysulfide sealant may be employed.

<FIG> and <FIG> show an alternative implementation of the vent dam insert <NUM> in a stringer <NUM> having a differently shaped aperture <NUM>. The variation of curvature of the curved wall from the first example implementation allowable based on the shape of the aperture <NUM> is shown. However, the longitudinally offset lateral flanges <NUM> and <NUM> are maintained. As in the first implementation, the perpendicular distance from the connecting line <NUM> to the curvature <NUM> of the curved wall <NUM> remains less than the clearing distance <NUM> to the peripheral edge <NUM> of the aperture <NUM> along the entire length of connecting line <NUM>. With the normal axis <NUM> of the insert substantially at a center <NUM> of the aperture the insert <NUM> is received into the aperture when rotated to the insertion angle <NUM> and then rotated into sealing engagement with the insert longitudinal axis <NUM> parallel to the duct longitudinal axis <NUM> and translated to an end periphery <NUM> of the aperture. As in the first example implementation a positioning ledge <NUM> is employed.

A method <NUM> for sealing a vent stringer employing the implementations described herein is shown in <FIG>. A vent dam insert is rotated to an insertion angle, step <NUM>. The vent dam insert is inserted into an aperture in a vent stringer, step <NUM>. The vent dam insert is counter rotated through the insertion angle to align an insert axis with a longitudinal axis of a duct in the vent stringer step <NUM>. The vent dam insert is then translated longitudinally along the longitudinal axis into a seated position by sliding the vent dam insert in the duct, step <NUM>. As a portion of seating the vent dam insert, a positioning ledge is engaged with an end periphery of the aperture, step <NUM>. Fasteners may be installed through first and second offset flanges of the vent dam insert into opposing interior surfaces of the duct, step <NUM> A seal is applied around the peripheral edge of the vent dam insert to seal the insert in the duct in the vent stringer, step <NUM>. A cap is installed over the aperture, step <NUM>, to capture flow diverted by the vent dam insert from the duct through the aperture.

Claim 1:
A dam (<NUM>) for use with an aircraft vent stringer (<NUM>) having a duct (<NUM>), the duct (<NUM>) having a curved trapezoidal cross section, a longitudinal axis (<NUM>) and an aperture (<NUM>), the dam (<NUM>) comprising:
a single piece insert (<NUM>) for rotated installation through the aperture, the insert (<NUM>) having a trapezoidal cross section and having a first lateral flange (<NUM>) and a second lateral flange (<NUM>) configured to engage opposing interior lateral surfaces (<NUM>, <NUM>) of the duct (<NUM>), wherein the first and second lateral flanges (<NUM>, <NUM>) extend from a flat base (<NUM>) of the insert (<NUM>) receivable on a flat bottom (<NUM>) of the duct (<NUM>) to a curved top (<NUM>) of the insert (<NUM>),
the insert (<NUM>) configured to engage the duct (<NUM>) in sealing contact in the seated position,
the first and second lateral flanges (<NUM>, <NUM>)
being offset longitudinally along a longitudinal axis (<NUM>) of the insert (<NUM>), which is, in the seated position, coaxially aligned with the longitudinal axis (<NUM>) of the duct (<NUM>), and
joined with a curved wall (<NUM>) having a curvature (<NUM>) shaped to be received, with the insert (<NUM>) oriented in a rotated position at an insertion angle (<NUM>) rotated about a normal axis (<NUM>) of the insert (<NUM>) perpendicular to the flat base (<NUM>) of the insert (<NUM>) and perpendicular to the longitudinal axis (<NUM>) of the duct (<NUM>), in an aperture (<NUM>) in the duct (<NUM>).