Fabric attaching cap strip for aircraft

June 13, 1939. c. de ganahl 2,161,802

FABRIC ATTACHING CAP STRIP FOR AIRCRAFT

Filed May 25, 1937

<img file="US2161802A_D0001.tif" />

Patented June 13, 1939

2,161,802

UNITED STATES PATENT OFFICE

2,161,802

FABRIC ATTACHING CAP STRIP FOR AIRCRAFT

Carl de Ganahl, Bristol, Pa., assignor to Fleetwings, Inc., Bristol, Pa., a corporation of Delaware

Application May 25, 1937, Serial No. 144,594

Claims. (Cl. 244—132)

This invention relates to aircraft.

In aircraft wings it has been difficult in the past to proportion the strength of the rib structures to the varying stress demands of the wing 5 structure. Similarly, in attaching fabric to wings and analogous structures in the prior art, objectionable knots and stitches were used that were hard to apply and which enhanced frictional effects to increase the drag of the craft.

It is among the objects of this invention: to provide a tail rib construction of a tapered closed cap section; to provide means for stitching or securing fabric to a wing without interrupting the smooth external appearance of the fabric; to 15 provide a tail rig construction of varying strength in a simple and economical manner; to provide a tapered cap strip section from stainless steel which can be spot welded into shape with a minimum of expense; and many other objects and advantages as will become more apparent as the description proceeds.

In the accompanying drawing:

Fig. 1 represents a transverse vertical section of a wing according to one form of the invention, 25 Fig. 2 represents a fragmentary elevation of a portion of the tapered, closed cap section of the invention,

Fig. 3 represents a fragmentary detached perspective of the closed tapered section of Figs. 1 30 and 2,

Fig. 4 represents a transverse section through the closed cap strip of the Invention taken on line 4—4 of Fig. 1 showing a fragmentary section of fabrics attached thereto,

Fig. 5 represents a similar section on line 5—5 of Fig. 1, and

Fig. 6 represents a fragmentary enlarged section of the cap strip to show the construction.

Although obviously capable of use in other 40 connections, and with different types of wings, etc., the invention can be well understood from the aircraft wing disclosure of. Fig. 1. In that illustration a wing 10 is shown comprising the metal entering edge section II, terminating at 45 the rear in a vertical spar or shear web 12. The box like construction of the entering edge portion is of no particular moment in connection with the instant invention, except to note that it carries the greater part of the load, and has 50 preferably a metal skin.

Suitably secured to the spar 12 are the tail ribs 13 comprising struts or web members 14 secured to the top and bottom cap strip 15. Preferably, although not necessarily, the struts are coni structed in accordance with the disclosure of ap plication Ser. No. 5,191 of Roy A. Miller. The normal load decreases toward the trailing edge 16 so that it is highly desirable to have the rib cap strip sections taper from the connection with the spar 12 toward the trailing edge to de- 5 crease the weight and strength of the parts, as a function of the decrease in the normal load.

Referring to Fig. 3, there is disclosed a cap strip 17 comprising a member having a lower surface or bottom 18, side walls 20 and 21, defin- 10 ing an open slot, trough or channel, which merge into the substantially planar integral wings or faces 22 and 23 perpendicular to the respective side walls, by means of substantially rounded corners 19 and having curled edges 24. Curved 15 corners 19 and edges 24 each are disposed so as to minimize fraying and wear of subsequently attached fabrics. The cap strip extends substantially full length of the tail rib or as far as desired, and is preferably of the same size 20 throughout. As will be discussed later herein the cap strip may be given a slight curvature to shape the ribs as desired.

At suitably spaced intervals the substantially U or staple-shaped pins 25, comprising the spaced 25 parallel legs 26 and transverse bar 27, are inserted in the trough and spot welded into position. The transverse pins are reinforcements for the cap strip assembly, and as will later be discussed, form rigid stitching points for the attach- 30 ment of a fabric cover for the ribs.

The entire cap strip assembly is comprised of the cap strip 17, either with or without the transverse pins or staples 25, with the U-shaped tapering depth member or channel section 30. This is 35 of the simplest of formations, comprising an initially flat strip of metal having non-parallel and convergent side edges 31 and 32, which may if desired be non-linear so as to facilitate the imparting of a suitable curvature to the cap strip. 40 The edges are brought toward each other symmetrically by bends about the center 36 of the strip to form a channel member haring spaced, substantially parallel legs 33 and 34 arranged to straddle and engage the outer surfaces of walls 45 20 and 21 of the cap strip, until the edges 31 and 32 substantially abut the under surfaces of the cap strip wings 22 and 23. If edges 31 and 32 are given a slight curvature, it will be understood that abutment thereof against wings 22 and 23 50 will require a curvature of the cap strip which may be permanently set if the channel and cap strip are anchored together in this position. The depth member is easily spot welded or riveted in place by the welds, or the like, 35, as by bring2,161,802 ing the welding contact electrodes against the outer surfaces, while holding a removable copper electrode of the same thickness as the slot in the trough of the cap strip to simultaneously spot 5 weld each leg 33 and 34 to the cap strip side walls 20 and 21. If desired this rigid attachment mfght be by way of overlapping spots, or seam welding, with rolling electrodes or the like, or one side wall might be welded at a time.

j₀ It is to be observed that the initial strip from which the depth or channel members are formed is provided with convergent, non-parallel edges, - at least in the preferred construction, so that when bent about the center of the strip, the col1J umn is therefore tapering in its longitudinal extent, as will be obvious.

Thus, as shown in Fig. 4, the entire cap strip ^!! column or section will be of considerable depth because of the space between the bottom wall 18 „₀ of the cap strip and the curved rear wall portion 36 of the depth member, while-the section shown in Fig. 5 is of decreased weight, depth andstrength as the curved wall 36 integral with that of Fig. 4, is closer to bottom surfaces 18 of the cap strip. .,- Thus in a simple and highly economical construction a tapering cap section is provided for the tail ribs, which is capable of easy association with the closed section or other struts 14, in any desired manner.

_;!0 The tail ribs including the cap strip sections described, with the open troughs or slots presenting outwardly, form an excellent bearing and attaching framework for fabric skins or wing covers. The fabric, such as linen or the like, in a continuous sheet 31 extending over several ribs, is, for safety, provided preferably with an internal tape of fabric 38 aligned with individual ribs, of such width as to extend laterally beyond the curled edges 24 of the cap strip wings, and of 40 such length as to cover the entire cap strip. The tapes may be stitched to the wing fabric, or secured by “dope”, or in any other desired manner. The fabric and attached tape, if used, is then stretched over the ribs, upon which it is supported ₄₆ by the flat areas of wings 22 and 23 of the cap strips, between the curved non-chafing edges 19 and 24 thereof, and in certain cases upon the transverse reinforcing members 25 as well, depending upon the dispositions thereof. Usually 5Q and preferably the transverse reinforcements 25 have the upper surface of bar 27 just below the level of the planar wings 22 and 23, in order to minimize contact of the fabric therewith, as if it is slightly higher, it tends to indent the fabric 55 with the cross bars. This is usually undesirable, although it will be governed by necessities as to supporting areas.

With the fabric and tape, if used, on the ribs, suitable flexible stitches or metallic clips 40 ap50 plied by any suitable stitching or stapling mechanism or by manual means (not shown), are passed through the fabric, and tape, and about cross bars 27 of the reinforcements 25. The stitches are suitably tied, secured or knotted on θ5 top of the fabric. This stitching at each, or at selected cross bars, securely ties the fabric to the cap strips, in an efficient, and economical manner, without the creation of raised knots, and the like, and is facilitated by the clearance afforded 70 below the cross bars 27 by the depth of slot 9 of the cap strip.

If desired a second tape 4i may be stretched over the fabric and the stitching to cover same to finish the surface and free it from the frictional 73 effects of the small knots of stitches 40. This is not usually necessary however, as the structure shown causes the fabric and knots to be slightly indented instead of protuberant as might occur if the cross bar 27 was exactly in the plane of wings 22 and 23, instead of slightly out of this β plane as shown. Tape or strip 41 may be “doped” into position, or otherwise secured.