EP2555972A1

EP2555972A1 - Connecting element and fastening arrangement for seat rails in an aircraft

Info

Publication number: EP2555972A1
Application number: EP11725606A
Authority: EP
Inventors: Stefan Bräutigam
Original assignee: Premium Aerotec GmbH
Current assignee: Premium Aerotec GmbH
Priority date: 2010-04-09
Filing date: 2011-04-07
Publication date: 2013-02-13
Also published as: BR112012025808A2; DE102010014301A1; US20130216300A1; WO2011124215A1; RU2012147514A; CA2795307A1; US8998137B2

Abstract

A fastening arrangement for connecting two structural elements (1, 2) extending at an angle from each other, especially in a lightweight construction, is disclosed. The first structural element (1) has a recess (10) into which the second structural element engages at least in part. A fastening section (32) of a first leg (30) of the first connecting element (3) that is designed as an angle rests on the first structural element (1) on one side of the recess (10), the first connecting element (3) being connected to the first structural element (1). A fastening section (38) of a second leg (36) of the first connecting element (3) rests against the second structural element (2), the first connecting element (3) being connected to the second structural element (2). In a first direction (z) running parallel to the bending edge (35) between the first (30) and the second (36) leg, the second leg (36) is longer than the fastening section (32) of the first leg (30), an extension part (38') of the fastening section (38) of the second leg (36) projecting beyond the fastening section (32) of the first leg (10) in said direction (z), the extension part (38') having a free end (37). The first leg (30) includes at least one supporting section (34) extending from the fastening section (32) of the first leg (30) to the extension part (39) of the second leg (36). A second connecting element (4) designed as an angle is provided on the side of the second structural element (2) facing away from the first connecting element (3). The second connecting element (4) is connected to both the first structural element (1) and the second structural element (2). The first connecting element (3) includes a third leg (39) that is connected to the first leg (30) and the second leg (36).

Description

CONNECTING ELEMENT AND FASTENING ARRANGEMENT FOR SEAT RAILS IN A PLANE

TECHNICAL AREA

The present invention relates to a connecting element with at least three legs arranged at an angle to one another and one

Mounting arrangement with such a connecting element.

Such fasteners and mounting arrangements are

0 especially in lightweight constructions, for example in aircraft construction,

used. An exemplary application is the connection of seat rails with cross members of a floor in an aircraft. In the same way, other rails, for example guide or lashing rails in a cargo hold of an aircraft with corresponding cross members

5 connected.

STATE OF THE ART

In the prior art there is for the connection of floors in

0 aircraft common carrier structures (seat rails in aircraft longitudinal direction and floor cross member in aircraft transverse direction) in

Essentially two alternative connection concepts, wherein the seat rails and the cross member are formed as a double-T-beam or C-beam: 5 a) The seat rails extend above the floor cross member. Of the

Lower flange of a seat rail is connected to the upper flange of a cross member by screws or rivets. Disadvantage of this type of attachment of the seat rail is the relatively large height required for this floor structure.

0 The seat rail is partially disengaged in the connection area to the cross member, that is provided with a lower recess, in which engages the cross member. Due to this recess, however, the seat rail is significantly weakened in its stability, so that it can only transmit low lateral forces and normal forces. To compensate for this weakening connecting elements must be provided in a complex manner, which are able to transmit the transverse and normal forces, which are introduced via the seats and the load located thereon in the seat rail, over the notched area away. Even if the significant bending moments occur in the seat rail in the middle between two cross members, so the bending moments in the notched area do not decrease to zero, so that the upper flange of the seat rail is usually not able, together with the Sitzschienenkrone, the occurring there To transmit moments. It is also a transmission of relatively small bending moments by the

Connection elements or by a the bridged area bridging connection element required.

There have been different concepts in the past

Connection elements and connection elements developed. In one of these concepts, the floor cross member in the area of the connection of a seat rail is provided locally with a breakthrough, through the one

Connecting element is guided. This connecting element is then firmly connected on both sides of the recess with the seat rail, riveted, for example. In this way, a structure is created in which the seat rail and the cross member pass through each other.

In particular, when floor cross members are designed extremely weight-saving, it can in the connection concept a) in the field of

Connection of a seat rail to the cross member and the consequent

Introduction of the force in the cross member to a Flanschaufbiegung of Cross member come, causing local strength problems occur in the cross member.

In particular, when floor cross members made of anisotropic materials, for example carbon fiber composite material (CFRP), created, the problem of Flanschaufbiegung occur. The main burdens of

Floor crossbeams occur in the y- / z-plane. Therefore, cross beams made of anisotropic materials are mainly equipped with rigidities that withstand this load. Locally in the region of the connection of the seat rail, however, occurs a bending of the cross member upper belt around a transverse axis (y-axis). To absorb this effect, angles can be added to reinforce the area on the cross member, or the cross member component is provided with local stiffnesses that can withstand these loads. For both

Solutions require additional work steps, which increases manufacturing costs. In addition, the structural weight of these local reinforcements must be taken into account.

Another problem is that weight-optimized lightweight cross members tend to tilt in areas where a belt is subjected to compressive loading. Since the upper straps are usually supported laterally by the seat rail connections, especially the unsupported lower belt is at risk of tipping over. In this case, the lower belt deviates forward or backward (in the aircraft longitudinal direction). In order to use therefore weight-optimized cross member in the floor of an aircraft, often additional elements are installed in the aircraft floor, which counteract this tilting effect. These elements also represent additional weight and increase installation costs.

From DE 201 14 953 U1 a connecting element is known which has a

Base body in the form of an equilateral triangle, at the edges of each a triangular fastening strap is arranged by means of material bridges. The connecting line of the respective material bridges forms a bent edge. This connecting element is after bending the fastening tabs to a corner connector for a frame. The individual fastening straps are in each case connected to the base body only via the material bridges. A connection of the fastening tabs directly below each other is not provided.

From DE 34 42 550 C1 a cross-sectionally C-shaped connection shoe for also C-shaped sheet metal profiles is known. This connection shoe has at one end from the middle profile section down, so in the direction of the two lateral legs, bent end face tab. The C-shaped profile body of the connecting element is inserted into a C-shaped profile element. Another C-shaped profile element can then be set at right angles to the first profile element dull in front of this, wherein the connection shoe engages with its protruding from the first profile element section in the second profile element and wherein the vertically bent tab of the

Connection shoe against the central profile portion of the second profile element comes to rest flat. There are no dedicated mounting portions provided in which the connection shoe with the profile elements through

Fastener would be firmly connected.

From DE 103 29 017 B4 is a support structure of rectangular

Hollow profiles known which are interconnected by means of external or internal connecting elements. The hollow sections are set against each other, but do not penetrate each other.

From DE 38 38 220 C2 a connection between posts and bars for facades is known to be used in the cross bar of two sides in a partially recessed post and a kind

Dowel mechanism can be connected to the post. PRESENTATION OF THE INVENTION

Object of the present invention is a generic

Specify connecting element, which can be connected to the connection of two angularly arranged structural elements with these to allow low height sufficient and effective lateral and normal force transmission and bending moment transmission, even if the structural elements at least partially pass through, and thereby to prevent Flanschaufbiegung and tilting of the one structural element in the longitudinal direction of the other structural element.

The object directed to the connecting element is achieved by a

Connecting element with the features of claim 1.

Advantageous embodiments of the connecting element are in the

Subclaims 2 to 6 specified.

The fastening arrangement according to the invention for connecting two structural elements arranged at an angle to one another has a connecting element according to the invention and is provided in particular for a lightweight construction. The first structural element has a recess into which the second structural element at least partially engages, wherein a first,

According configured according to the invention fastener with a first

Attachment portion of a first leg rests on one side of the recess on the first structural element and is connected thereto. The first connection element lies with a fastening section of a second

Leg on the second structural element and is connected thereto. An angle formed as a second connecting element is on the first of the

Connecting element facing away from the second structural element

intended. The second connecting element is both with the first

Structural element, as well as connected to the second structural element. ADVANTAGES

In a preferred embodiment, the support portion is connected thereto over a range of more than half the extension of the extension portion in the first direction. Preferably, the support portion extends to the free end of the extension part. As a result of these measures, the tilting moments occurring in a second structural element connected to the connecting element around the transverse axis are each reliable from the first

Supported legs of the first connecting element and in one with the

Introduced connecting element connected first structural element.

In another advantageous embodiment, the support portion is connected to the attachment portion over a range of more than half the extent of the attachment portion of the first leg in a second direction that is perpendicular to the crease edge and in the x-z plane of the attachment portion of the first leg. Preferably, this connection extends over substantially the entire extent of the attachment portion in the second direction. By this design measure, the forces generated by the tilting forces occurring in the second structural element are introduced optimally and particularly effectively from the support section into the fastening section and from there into the first structural element.

In a further preferred embodiment, the third leg is integrally connected to the first leg and the second leg. This integral design of the first connecting element as a corner angle in the form of a

Kofferecke creates a particularly stable connection part.

The third leg extends in a plane which is preferably perpendicular to the planes of the first leg and the second leg. It is also advantageous if the support portion is formed so that an edge remote from the attachment portion of the support portion from the free end of the first leg to the free end of the extension part of

Fixing portion of the second leg runs. Preferably, this edge is straight; but it can also be curved, for example. The thereby caused beveling of the support section causes a

Material savings and thus a weight reduction of this component. In a particularly preferred embodiment, the three legs of the connecting element are integrally formed with each other, wherein the

Connecting element is preferably made as a forged part or as a casting. As a result, in particular when using titanium as a very lightweight material, time-consuming and expensive machining in the production of the connecting element can be minimized or even avoided.

The directed to the mounting assembly part of the object is achieved by the fastening arrangement specified in claim 7. The provision of the first connecting element and the second

Connecting element, both of which are connected to both the first structural element, as well as with the second structural element, which can be done for example by riveting, screwing and / or gluing, spares the customary in the prior art attachment of the notched portion of the first

Structural element bridging and through an opening in the second

Structural element passing through the connection element. As a result, it is not necessary in the second structural element an opening at this point

provide, whereby the second structural element is not weakened here. The support section on the first leg supports the tilting forces possibly occurring in the second structural element at this point and introduces them into the first structural element, so that in conjunction with the prior art described deflection of the lower flange of the second structural element in the x direction is prevented. The third leg extends in a plane which is preferably perpendicular to the planes of the first leg and the second leg. This third leg, together with the second leg of the first connecting element, acts as an angle reinforcement of the second structural element, which reliably prevents the flange bending described in connection with the prior art in this area.

The inventive solution creates a firm connection between the first structural element and the second structural element which, without providing an additional connecting element, bridges the recess in the first structural element. Furthermore, by the first

Connecting element created a reinforcement of the second structural element in the region of the junction with the first structural element. The first connecting element thus fulfills three tasks in the assembled state, namely: together with the second connecting part, a stiffening of the first structural element in the region of the recess;

a prevention of Flanschaufbiegung of the second structural element and

- A tilt support for preventing the tilting of the second

Structure element around a transverse axis.

Further preferred and advantageous design features of

Mounting arrangement according to the invention are the subject of

Subclaims 8 to 12.

In a preferred development, the third leg is connected to the second structural element, preferably to an upper flange of the second structural element, and cooperates with the second leg of the first structural element

Connecting element as an angle reinforcement of the second structural element, whereby the Flanschaufbiegung described in connection with the prior art in this area is prevented even more reliable.

In a further optimized embodiment of the invention

Fastening arrangement is a, preferably designed as a corner angle, third connecting element provided on the side facing away from the first connecting element side of the first structural element, wherein the third connecting element is connected to both the first structural element, and with the second structural element. As a result, a firm connection between the first and the second structural element is produced on the side facing away from the first connecting element side of the first structural element. Also the third

Connecting element may, like the first connecting element, be provided with a third leg, which is connected to the upper flange of the second structural element.

A still further improved embodiment of the fastening arrangement is characterized in that a fourth connecting element designed as an angle or as a corner angle is mounted on the second connecting element

side facing away from the first structural element is provided and that the fourth connecting element is connected to both the first structural element, as well as with the second structural element. In this way, a further firm connection between the first and the second structural element is provided. In an advantageous embodiment, the second is or are

Connecting element and / or the third connecting element and / or the fourth connecting element formed in the same manner as the first connecting element and connected to the two structural elements. A preferred application of the fastening arrangement according to the invention is characterized in that the first structural element is a seat rail and the second structural element is a cross member of a floor or false floor in an aircraft. Instead of a seat rail, the first structural element but also another guide rail or

Mounting rail, for example, in a cargo hold of an aircraft, be.

Preferred embodiments of the invention with additional

Design details and other advantages are below

Reference to the accompanying drawings described and explained.

BRIEF DESCRIPTION OF THE DRAWINGS

1 shows a perspective view of a connection section between a first structural element and a second structural element with a fastening arrangement according to the invention;

Fig. 2 is a view of the mounting arrangement of FIG. 1 in the direction of

Arrow II; and

Fig. 3 is a view of the mounting arrangement of Figure 1 in the direction of

Arrow III.

PRESENTATION OF PREFERRED EMBODIMENTS

In Fig. 1, the intersection of two intersecting structural elements 1, 2 is shown in a perspective view.

In the example shown, the first structural element 1 is the seat rail of a floor in a passenger plane. This seat rail is designed as a double-T Carrier with a horizontal lower flange 11, a horizontally extending upper flange 12 and a extending between the lower flange 11 and the upper flange 12 vertical rail 14 is formed. On the side facing away from the vertical rail 14 upper side of the upper flange 12, the seat rail crown 13 is arranged in the in known manner corresponding

Engagement elements on the underside of a seat slidably and arrested are added. The trained as a seat rail first structural element 1 extends in the aircraft longitudinal direction x. Transverse to the seat rail extending as a floor cross member formed second structural elements 2, which are supported on the fuselage structure of the aircraft and serve themselves as a support for the seat rails, ie for the first structural elements 1. The second structural elements 2 thus run in the aircraft transverse direction y. In cross-section, the second structural elements can either also be designed as a double-T-carrier, or they can, as shown in Fig. 1, a C-shaped cross-sectional shape, ie the shape of a lying on the side U. Such a second structural element 2 is provided with a lower flange 20, an upper flange 22 and a vertical rail 24 which extends between the lower flange 20 and the upper flange 22.

In the connecting region of the trained as a seat rail first

Structural element 1 with the formed as a floor crossmember second structural element 2 penetrates the floor cross member, the seat rail, which is provided on its underside with a recess 10. In the region of the recess 10, the lower flange 11 and the vertical rail 14 of the first structural element 1 are interrupted and form a gap through which the second structural element 2 can pass. The seat rail rests with its upper flange 12 on the upper flange 22 of the second structural element 2 designed as a floor cross member. The upper flange 12 and the upper flange 22 are connected by rivets 70 firmly in this area. Of course, other connecting means, such as Screws are used, and the two straps 12, 22 may alternatively or additionally be glued together. These alternative or additional types of connection (for example, screws or gluing) may alternatively or additionally also be mentioned for the others in this description

Rivet connections may be provided.

As can be seen in FIG. 1 and in the side view of FIG. 2, a first connecting element 3 designed as a corner connector such as a suitcase corner is provided between the first structural element 1 and the second structural element 2 and connected thereto in the manner described below.

The first connecting element 3 has a first leg 30 which extends in the xz plane, the z-direction corresponding to the aircraft vertical axis, and which abuts with a fastening portion 32 at least partially on the vertical rail 14 of the first structural element 1 and with this connected via rivets 71.

With a lying in the y-z plane second leg 36 is the first

Connecting element 3 on the vertical rail 24 of the second structural element 2 and is fixedly connected thereto via rivets 72. The second leg 36 extends in the direction of the buckling edge 35 between the first leg 30 and the second leg 36 direction z further down, as provided with the rivets 71 mounting portion 32 of the first leg 30. The first leg 30 is below the mounting portion 32 with one

Provided support portion 34 which also extends in the xz plane and has an approximately triangular shape, wherein one edge of the triangle is formed by a part of the bending edge 35. A free edge 33 of the support portion 34 extends from a free end 31 of the first leg 30 to the lower free end 37 of the second leg 36. The attachment portion 38 of the second leg 36 is thus longer in the z-direction than the attachment portion 32 of the first leg 30 and thus has in its lower portion an extension portion 38 'which also has rivets 72' with the vertical rail 24 of the second Structural element 2 is connected.

A third leg 39 of the first connecting element 3 extends in the xy plane and abuts on the upper flange 22 of the second structural element 2 from below. There he is firmly connected via rivets 73 with the upper belt 22. In this way, the first connecting element 3 acts as a reinforcement of the upper belt 22 of the second structural element 2 and thus prevents a Flanschaufbiegung of

Obergurts 22 in this area. The upper leg 39 of the first

Connecting element 3 is connected to the first leg 30 and the second

Leg 36 integrally connected.

On the side facing away from the first connecting element 3 side of the second structural element 2, a second connecting element 4 is provided, which is formed as an angle. A first leg 40 of this second

Connecting element 4 extends in the x-z plane and abuts against the vertical rail 14 of the first structural element 1 and is connected thereto via rivets 74. A second leg 42 of the second connecting element 4 is located in the y-z plane and is located on that of the first connecting element 3rd

remote from the rear side of the vertical rail 24 of the second structural element 2. The rivet connections 72, which connect the upper part of the fixing portion 38 of the first connecting element 3 to the second structural element 2, also penetrate the second leg 42 of the second connecting element 4 and likewise connect it to the second structural element. In this way, a solid and continuous connection of the first leg 40 of the second connecting element 4 via the second leg 42, the vertical rail 24 of the second structural element 2, the second leg 36 of the first connecting element 3 and the first leg 30 is formed, which Recess 10 in the first structural element 1 bridged and so on

Force fit for transmitting the forces extending in the first structural element 1 over the recess 10 away forms. FIG. 3 shows the connecting elements 5, 6 located opposite to FIG. 2 on the rear side of the first structural element 1.

A third connecting element 5 is provided on the side facing away from the first connecting element 3 side of the first structural element 1. This third connecting element 5 is likewise provided as a corner angle with a first leg 50, a second leg 56 and a third leg 59. It corresponds in construction in a mirror-image manner to the first connecting element 3, but is not necessarily with a support portion, such as

Support portion 34 of the first connecting element 3, provided. This may be provided, has been omitted in the example but for weight saving reasons in the third connecting element 5. The third connecting element 5 is by means of the rivets 71, the first leg 32 of the first

Connect connecting element 3 with the first structural element 1 and also penetrate the first leg 50 of the third connecting element 5, fixedly connected to the first structural element 1 and the first connecting element 3. In the region of the recess 10 of the first structural element 1, the first connecting element 3 and the third connecting element 5 are connected directly to one another via rivets 75. The second leg 56 of the third connecting element 5 extends in the y-z plane, abuts against the vertical rail 24 of the second structural element 2 and is fixedly connected thereto via rivets 76.

The third leg 59 of the third connecting element 5 extends in the xy plane and abuts on the upper flange 22 of the second structural element 2 from below. The third leg 59 and the upper flange 22 are fixed to each other via rivets 77 connected. Again, the second leg 56 and the third leg 59 of the third connecting element act as a reinforcement for the upper flange 22 and prevent there a Flanschaufbiegung. A fourth connecting element 6 is provided on the rear side of the vertical rail 24 of the second structural element 2 applied by the third connecting element 5. This fourth connecting element 6 is mirror-inverted to the second connecting element 4 also designed as an angle profile. A first leg 60 of the fourth connecting element 6 bears against the vertical rail 14 of the first structural element and is there via the rivets 74, which is the second

Connect connecting element 4 with the first structural element 1 and which penetrate the first leg 60 of the fourth connecting element 6, with both the first structural element 1, and with the second connecting element 4 firmly connected.

The second leg 62, which extends in the yz plane, bears against the rear side of the vertical rail 24 of the second structural element 2 and is fixed by the rivets 76 provided there with both the second structural element 2 and the third connecting element 5 connected. In this way, a continuous frictional connection is created on this side of the first structural element, which bridges the recess 10 in the first structural element 1.

While trained as a corner angle first and third

Connecting elements are formed as forgings or castings, preferably made of titanium, the second and the fourth connecting element are simple angles that only need to be sawn out of an angle profile. As a result, expensive production costs are saved, especially in the case when these angle profiles are made of titanium, which is preferred for weight reasons. Reference signs in the claims, the description and the drawings are only for the better understanding of the invention and are not intended to limit the scope.

LIST OF REFERENCE NUMBERS

1 first structural element

2 second structural element

3 first connection element

4 second connecting element

5 third connecting element

6 fourth connection element

10 recess

11 lower chord

12 upper strap

13 seat rail crown

14 vertical rail

20 bottom strap

22 upper strap

24 vertical rail

30 first leg

31 free end of 30

32 attachment section

33 edge

34 support section

35 bending edge

36 second leg

37 free end of 39

38 attachment section

38 'extension part

39 third leg

40 first leg 42 second leg

50 first leg

56 second leg

59 third leg

60 first leg

62 second leg

70 rivets

71 rivets

72 rivets

74 rivets

75 rivets

76 rivets

77 Rivets z first direction / vertical direction x second direction / aircraft longitudinal direction y transverse aircraft direction

Claims

claims

Connecting element (3) with at least three legs (30, 36, 39) arranged at an angle to one another,

with one between a first leg (30) and a second one

Leg (36) located buckling edge (35);

wherein the first leg (30) has a first attachment portion (32);

characterized,

the second leg (36) has a second attachment portion (38);

the first limb (30) has at least one support section (34) adjoining the first attachment section (32) in a first direction (z) parallel to the bending edge (35) and connected to the second limb (36),

in that the second leg (36) in the first direction (z), forming an extension part (38 ') having a free end (37) which adjoins the second attachment portion (38), has a larger one

Has extension as the first attachment portion (32) of the first leg (30); and

a third leg (39) is provided which is connected to the first leg (30) and the second leg (36).

2. Connecting element according to claim 1,

characterized,

in that the support section (34) is connected to it over a region of more than half the extension of the extension part (38 ') in the first direction (z) and that the support section (34) preferably extends to the free end (37) of the Extension part (38 ') extends.

Connecting element according to claim 1 or 2, characterized,

in that the support portion (34) extends over a range of more than half the extent of the first attachment portion (32) of the first leg (30) in a second direction (x) perpendicular to the crease edge (35) and in the xz plane of the first attachment portion (32) of the first

Leg (30) extends, with the first attachment portion (32), preferably over substantially the entire extent of the first attachment portion (32) in the second direction (x) is connected thereto.

Connecting element according to one of the preceding claims,

characterized,

in that the first leg (30), the second leg (36) and the third leg (39) are formed integrally with one another, preferably as a forged part or as a cast part.

Connecting element according to one of the preceding claims,

characterized,

in that one edge (33) of the support section (34) facing away from the first attachment section (32) extends from the free end (31) of the first leg (30) to the free end (37) of the extension section (38 ') of the second

Fixing portion (38) of the second leg (36), preferably straight, extends.

Connecting element according to one of the preceding claims,

characterized,

that the three legs (30, 36, 39) are arranged at right angles to each other.

Fastening arrangement for connecting two structural elements (1, 2) arranged at an angle to one another, in particular in one Lightweight construction, with a connecting element (3) according to one of the preceding claims,

wherein the first structural element (1) has a recess (10) into which the second structural element (2) at least partially engages; wherein a first, according to one of the preceding claims formed connecting element (3) with the first

Attachment portion (32) of the first leg (30) on one side of the recess (10) against the first structural element (1) and is connected thereto;

wherein the first connecting element (3) with the second

Attachment portion (38) of a second leg (36) on the second

Structural element (2) rests and is connected thereto;

wherein a second connecting element (4) designed as an angle is provided on the side of the second structural element (2) remote from the first connecting element (3);

wherein the second connecting element (4) with both the first

Structural element (1), as well as with the second structural element (2) is connected.

Fastening arrangement according to claim 7,

characterized,

the third leg (39) is connected to the second structural element (2).

Fastening arrangement according to claim 7 or 8,

characterized,

that one, preferably designed as a corner angle, third

Connecting element (5) on the side facing away from the first connecting element (3) side of the first structural element (1) is provided and in that the third connecting element (5) is connected both to the first structural element (1) and to the second structural element (2).

Fastening arrangement according to one of claims 7 to 9,

characterized,

in that a fourth connecting element (6) designed as an angle is provided on the side of the first structural element (1) facing away from the second connecting element (4), and

in that the fourth connecting element (6) is connected both to the first structural element (1) and to the second structural element (2).

11. Fastening arrangement according to one of claims 7 to 10,

characterized,

that the second connecting element (4) and / or the third

Connecting element (5) and / or the fourth connecting element (6) in the same manner as the first connecting element (1) is formed and connected to the two structural elements (1, 2) is or are.

12. Fastening arrangement according to one of the preceding claims,

characterized,

in that the first structural element (1) is a seat rail and the second

Structural element (2) are a cross member of a floor or false floor in an aircraft.