Par 2-7 Page 2-46 overlapped and doped seams on the longerons or other wide fabric-forming structur es in accordance with the aircraft Vne speed. (Reference paragraph 2-7 b.)
Holes in Fabric. Never cut any holes in the fabric for inspection panels, spar fittings, or drain grommets; or attach the fabric to the airframe with rib lacing screws, rivets, clips, or rib stitch cord until the fabric has been semi-tauted and stabilized with several coats of dope.
REINFORCING TAPE.
Reinforcing tape should be securely bonded to the fabric surface with dope before cord lacing or installation of hardware. Where multiple attachments are in close proximity, such as on a wing rib, continuous reinforcing tape should be installed, extending at least 1 inch past the last attachment at each end. Random or wide spacing, such as on fuselage stringers or empennage surfaces, may be reinforced with 2-inch lengths of reinforcing tape centered on the attachment location.
Reinforcing tapes should be of the appropriate width for hardware attachment such as screws, rivets, wire clips, etc., which pierce the center of the tape.
Reinforcing tape under cord lacing should be the same width as the rib to which the fabric is laced and may be comprised of multiple widths positioned side-by-side to achieve the required width.
When the aircraft Vne speed is over 250 mph, anti-tear strips, cut from the same quality fabric used to cover the aircraft, are recommended for use under reinforcing tape on the entire top surface of the wing and on the portion of the wing’s bottom surface in the propeller slipstream. The propeller slipstream is considered to be the propeller diameter plus one outboard rib. The anti-tear strip should be installed completely around the wing, beginning and ending at the trailing edge in the propeller slipstream, and installed from the trailing edge over the leading edge and back under to the front spar on the balance of the ribs. Anti-tear strips should extend 1/2 inch past the wing rib cap edges and be thoroughly bonded to the fabric with dope before the reinforcing tape is installed.
(See figure 2-3.)
FIGURE 2-3. Exploded side view of rib.
Par 2-10 Page 2-47 LACING.
Fabric should be attached to aircraft components to prevent ballooning due to aerodynamic forces, in the identical manner and locations as used by the original aircraft manufacturer. Any deviation from the original method(s) of attachment, such as screws, rivets, wire clips, lacing cord, etc., are considered a major alteration and in conflict with the aircraft type design data.
Obtain FAA approval on any deviation.
NOTE: When the type of rib lace knot used by the original aircraft manufacturer is not known, the modified seine knot shown in figure 2-4 through figure 2-9c will be used.
FIGURE 2-4. Standard external modified seine knot used for single and double rib lacing.
During the installation of lacing cord through a wing or any other component, special attention should be given to avoid interference with the routing of any control cable, bellcrank, or any other movable item. To prevent chafing and cutting of the lacing cord, control cables or any other movable items should be tensioned or positioned to their normal alignment before rib lacing and checked afterwards to ensure adequate clearance.
When a lace cord will be chafed by a moving component, a blindstitch may be made around the top and bottom rib caps as illustrated in figure 2-11.
Stationary structures interfering with needle routing may be circumvented by aligning the needle forward or aft adjacent to the rib cap. Pull the needle through the wing and then return through the same hole and exit at the desired adjacent location.
NOTE: The first lace on a wing rib should be spaced from the leading edge fairing no more than 1/2 the required lace spacing for the balance of the rib.
Both surfaces of fabric covering on wings and control surfaces must be securely fast ened to the ribs by lacing cord or any other method originally approved for the aircraft. Care must be taken to insure that all sharp edges against which the lacing cord may bear are protected by tape in order to prevent abrasion of the cord. Separate lengths of lacing cord may be joined by the splice knot shown in figure 2-10 or tied off. The first loop is tied with a square knot as illustrated in figure 2-5 and figure 2-9a, and the knot secured with a half hitch on each side afte r the lacing is pulled tight around the rib. The needle is then routed through the wing and around the rib cap at the
SECOND STITCH OF STANDARD LACING (SINGLE (SHOWN) OR DOUBLE)
HALF HITCH AROUND STITCH LOOPS C
WITH LEAD A BEFORE PROCEEDING TO
SECOND STITCH
LOCK SQUARE KNOT WITH HALF HITCH LEAD A AROUND STITCH LOOPS C WITH END B.
CUT OFF SURPLUS OF END B.
AFT -FINISHED FIRST KNOT.
CAPSTRIP 2- TIE SQUARE KNOT
ON CAPSTRIP WITH LEAD A AND END B.
REINFORCING TAPE (same width as the rib).
• LEAD A END B
STITCH LOOPS C
CAPSTRIP START OF
FIRST KNOT S = NORMAL STITCH SPACING
SCHEMATIC REPRESENTS LACING AROUND ENTIRE RIB.
\ TIE SQUARE KNOT ON FIRST STEP OF S/2 CENTER OF CAPSTRIP
STARTING STITCH
LEADING EDGE FAIRING FIGURE 2-5. Starting stitch for rib lacing.
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Modified Seine Knot , Single Loop lacing Aft Reinforcing Tape (should be same width as the rib) Capstrip Capstrip S Reinforcing tape (Same width as Rib Cap) Schematic represents lacing around entire rib.
Starting stitch S = Normal stitch spacing Wing Leading Edge Fairing FIGURE 2-6. Standard single-loop lacing.
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- Pull No. 4
COMPLETED KNOT Edge of capstrip Pul No. 4 - 10 lb.
to complete knot Edge of capstrip Pull No. 3 pull snug OPERATION NO. 2
- Direction of lacing Pull No. 2 - 5 1b.
to tighten stitch Stitch loops around capstrip Pull No. 1 - 10 lb. From preceding to tighten loops stitch OPERATION NO. 1 FIGURE 2-7. Standard knot for double-loop lacing.
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- Moditied Seine Knot Double loop lacing
• Reinforcing Tape (Same width as rib)
- Capstrip Capstnp - S Reinforcing tape (Same width as Rib Cap) Schematic represents lacing around entire nib.
Starting stitch S = NORMAL STITCH SPACING Wing Leading Edge Fairing FIGURE 2-8. Standard double-loop lacing (optional).
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Square Knot Half Hitch Step 1. Tie a square knot by passing the short Step 2. Secure the tight square knot with a end of the cord thru the fold-back loop, half hitch at each side.
as illustrated.
Step 3. Route the needle back thru the right hand hole and exit at the next pre-punched lacing location.
Step 4. Route the needle back thru the exit hole and thru the opposite fabric surface leaving approximately a 3" loop around a finger on the top surface.
FIGURE 2-9a. Alternate sequence to tie a modified seine knot for rib lacing.
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Step 5. As the needle is returned thru the top surface on the Step 6. The needle tip is routed under cord section "B" to opposite side of the rib cap the loop is rotated to hook and pull cord section "A" aft.
position cord section "A" to the forward side of the needle, then the needle is pulled thru.
Step 7. The needle tip is then routed over the top of cord Step 8. The needle tip is then routed over cord section "D" section "A" and under cord section "B." and passed thru the lacing while holding cord section "D" perpendicular to the surface to avoid cord entanglement.
FIGURE 2-9b. Alternate sequence to tie a modified seine knot for rib lacing.
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Step 9. Pull cord section “D” perpendicular to the fabric surface to remove all slack in the cord back to the last rib lacing knot while working the loose knot to the right side. Do not pull cord section “E.”
Step 10. After all slack is removed by pulling cord section “D,” switch hands and place a thumbnail on the loose knot formed on the right-hand side, then secure the knot by pulling firmly perpendicular to the fabric surface on cord section “E.”
Step 11. After completing all lacing in the same sequence, the end is secured with a half hitch after the modified seine knot. The knot is pulled to the inside by routing the needle thru the wing before cutting the cord to leave the end inside.
FIGURE 2-9c. Alternate sequence to tie a modified seine knot for rib lacing.
Par 2-10 Page 2-55 next rib lace location with the cord and knot remaining on top of the fabric surface as illustrated in figure 2-5, figure 2-6, and figure 2-8. An alternate method is to route the needle under the fabric and out through the next lace location, then back down through the wing as illustrated in figure 2-9a through figure 2-9c. A modified seine knot is then tied as illustrated in figure 2-4 through figure 2-9c.
Rotate each lace loop to place the knot at the side of the rib cap to reduce the protrusion and aerodynamic interference before moving to the next lace location, or the cord routed under the fabric to the next lace location as illustrated in figure 2-9a through figure 2-9c.
The end cord is then cut off leaving a minimum of 1/4 inch stub. Lacing tension should be uniform.
Repeated pulling of long lengths of lacing cord may remove wax coating from the cord and cause fraying. Convenient lengths of rib lacing cord may be used to lace long or thick ribs. The end of each length is tied off with a half hitch as illustrated in figure 2-9c, or if needed, separate lengths of lacing cord may be joined by using the splice knot illustrated in figure 2-10.
Lacing is installed through other components, where applicable, in the same manner as a wing. Single, wide space lace attachments, usually used on empennage surfaces, are tied with a square knot and half hitch on each side, the same as a starting wing rib lace illustrated in figure 2-9a, steps 1 and 2. The lace may be rotated to place the knot under the fabric before cutting the cord.
Blind lacing on a fuselage, wing rib caps above and below a fuel tank, and any other component, when used by the original aircraft manufacturer, should be reinstalled in the same location and spacing as installed by the original aircraft manufacturer. The lace cord is routed around the stringer, rib cap, or other structure using an appropriate length, single or double pointed, curved needle as illustrated in figure 2-11. Blind laces are tied with a square knot, then pulled tight and secured with a half hitch at each side. The lace may be rotated to place the knot under the fabric surface before cutting the cord.
The splice knot is made by crossing the ends of the cord, and making four complete wraps with the small end of the free piece around the end of t he standing piece. The end is then doubled back through the formed loop. The other free end is wrapped and doubled back. The long ends of the cords are then pulled until the knot is tight. The short ends are cut close to the knot. This finishes the splice knot.
FIGURE 2-10. Splice knot.
STITCH SPACING.
Rib lace spacing on wings, formerly referred to as stitch spacing, should be no greater than the spacing used by the original aircra ft manufacturer. When the original spacing cannot be determined the maximum spacing illustrated in figure 2-12 should be used on the wings and wing control surfaces.
Route the needle adjacent to the rib cap at opposite sides.
Return the needle thru the exit hole and thru a third hole opposite the first entry hole.
Complete the square knot with Tie a square knot by a half hitch at each side. passing the short end of the cord thru the foldback loop,as illustrated.
Secure the tight square knot Route the needle back through the with a half hitch at each side. fabric and pull the knot inside before cutting the cord.
FIGURE 2-11. Blindstitch lacing - square knot secured with half hitches.
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F IGURE 2-12. Fabric attachment spacing.
When the lace spacing on the empennage surfaces and fuselage, where so incorporat ed by the original aircraft manufacturer, cannot be determined, a maximum spacing equal to two times the spacing shown in figure 2-12 for the slipstream area on the wings may be used.
The installations of fabric attachments such as screws, rivets, wire clips, and rib lacing should be delayed until the fabric is stabilized and pulled taut with dope. This action is delaye d to avoid pulling wing ribs and other structures out of alignment or tearing the fabric at attachment points as the fabric becomes taut.
All lacing should be installed adjacent to the structure to which the fabric is being laced, to avoid tearing the fabric and/or creating slack in the cord loop when a load is applied. Where plastic washers were used by the aircraft manufacturer to provide increased pull-through resistance, under the heads of rivets or screws, the same diameter aluminum washer may be used as replacement. Aluminum washers are used because th ey are not affected by solvents found in adhesives or dopes, nor do they become brittle because of age or cold weather.
FASTENERS. Several light aircraft designs employ screws, rivets, or single-wire metal clips to secure the fabric to the wing.
Screws holding the old fabric can be removed after spinning a small sharpened tube around each screw or using a razor blade to cut a nd peel away the finishing tape. Care must be taken not to mark or scribe the underlying metal or wood structure. Blind rivets through ribs can be removed by drilling in the center to undercut the head.
Single-wire clips may be removed without damage to the rib by inserting a wide, thin screwdriver blade under the clip and carefully twisti ng. Apply a lifting force at the clip end to pull it up through the hole.