Dope & FabricRefresher

Presented by:Prof. Tim LeBaron

Vincennes UniversityIA Renewal Seminar

February 1999

Nomenclature Bias Bleaching Calendaring Fill (Woof) Mercerizing Selvage Sizing Thread count Warp Weight

Material Selection Marked along the selvage edge Minimum requirements

Must meet or exceed TCDS Vne < 160 MPH, AND Wing loading < 9 lb/ft2

MUST USE GRADE A OR BETTER

STC Stits Poly Fiber Ceconite

Razorback No STC, uses AC 20-44!!!

Covering Methods

Envelope Already sewn for your aircraft Slide on like a sock, attach to frame.

Blanket Individual strips are sewn together and

cover is then attached to frame

Covering Methods

Should not have any seams where rib stitching may occur

Fabrics

Organic Grade A Mercerized 80 lb/in

Means a 1” strip must be able to support 80 pounds in tension without breaking

Deterioration FAA says 70% strength for airworthy

80 * .7 = 56 lb/in

Fabrics

Organic Intermediate grade

Wing loading no more than 9 lb/ft AND Speed less than 160 MPH

65 lb/in test strength new No Longer Available, the data may be

necessary for determining the original strength for recovering. Linen fits in this category

Fabrics

Inorganic Advantages

Resist deterioration by ultraviolet rays Resist microorganism attack better

Disadvantage More careful following of process is required to

ensure correct final product

Fabrics

Inorganic Common NamesPolyester Fabrics (DACRON Base)

Stits Poly Fiber Ceconite

Fiberglass Razorback

Extremely resistant to attack

Tapes

Surface Tape AKA finishing tape Same material, usually “pinked” for better

adhesion qualities Used for:

Opening reinforcement Rib attach cover steamlining

Reinforcing

Tapes

Surface Tape AKA finishing tape Same material, usually “pinked” for better

adhesion qualities Can get separate rolls Used for:

Opening reinforcement Rib attach cover streamlining

Tapes

Reinforcing Much larger Warp thread than Fill Thread Synthetic – must check to see if there is

special tape to be used Use:

Inter rib bracing (under fabric cover) Over fabric on ribs to prevent lacing cord from

cutting through

Tapes Anti Tear Strips

If Vne is > 250 MPH

Bonded to fabric Under reinforcing tape on entire top of the wing

From trailing edge around to behind spar

Under slipstream components on bottom of wing Slipstream = one propeller width plus one rib From trailing edge around leading edge and back to

training edge

Threads

Thread – you knowCord – heaver than thread. Used for

more strength (Rib stitching).

NOTE: When using inorganic fabrics, use the same material as is being installed

on aircraft.

Threads

Machine thread – obvious Tensile strength = 5 lb per strand “White, silk-finish, no. 16, four cord cotton

thread with a Z twist” (Z twist signifies a left twist)

1 lb for 5000 yards

Threads Hand sewing thread

Tensile strength = 14 lb per single strand “unbleached, cotton, silk finished, no. 8, four cord

thread” 1 lb for 1650 yards

Twist Z = left twist S = right twist Importance?

Right handed should stitch from right to left, using left twist, so thread will not untwist

Left handed is all opposite should use right twist thread

Threads

silk finished Has been “sized” to produce a hard, glazed

surface to prevent threat form fraying or weakening

Lacing Cord

AKA rib-stitching cord or rib lacing cordTensile Strength = 40 lb for single or 80

lb for doubleShould be waxed before use to

“lubricate” it Can be done by hand

Waxed cords

Used for attaching Chafing Strips 4 – 5 ply, double twisted and waxed. Chafing Strips

Leather, neoprene, Teflon, polyethylene Used where a cable or control passes through

the fabric.

RIB Stitching

Determined from old coverOr Figure 2-12, p. 2-21 in AC 34-13.1B

NOTE: Different spacing for in the slipstream and out of the slipstream

First and last stitches have ½ stitch spacing

NOTE

When using any “system”you must use all the components of the system for

correct installation.

DO NOT MIX AND MATCH THE SYSTEMS!!

Dope Function: Seals, tautens, and protects the

airplane fabric covering. A colloidal solution of cellulose acetate

butyrate or cellulose nitrates; Other solutions have been developed for

inorganic fabrics

NOTE: If using on inorganic, use NON-Tautening dopes!

Dope

Nitrate Nitrocellulose combined with plasticizers

and thinners. HIGHLY FLAMMABLE in both liquid and

dry states!

Advantage – lower cost, easier to apply, better adhesion.

Dope

Butyrate Cellulose acetate butyrate with plasticizers

and thinners. More fire resistant Provides greater shrinkage of the fabric. Care must be taken not to warp the

structure of the aircraft

Dope

Synthetic Proprietary names (Poly-Fill, Poly- Spray,

etc) are being used on trade name fabrics. Must be followed exactly for correct

protection and strength.

Dope Additives

Fungicidal Prevents microbes from weakening the

fabric Zinc dimethyldithiocarbonate (white powder) Copper naphthonate (bleeds some on light

colors) VERY THIN FIRST COAT to ensure the fabric is

encapsulated

Dope Additives

Aluminum Powders (silver dope) After all the tapes, inspection rings, etc.

have been added Aluminum oxide settles to form an

aluminum layer to reflect ultraviolet rays. Different from pigmented silver dope!

Rejuvenator Thin dopelike finish with powerful solvents. Softens and penetrates the old dope and tries

to replace some of the placticizers and solvents that have evaporated and oxidized.

Should use the special stuff, but THINNED BUTYATE can do the job.

Can extend life of cover, but must check the underneath material.

Solvents

Nitrate Nitrate Dope or Lacquer thinner

Butyrate Cellulose butyrate dope thinner

Acetone Should not be used as a thinner, but can

be cleaner for brushes and guns.

Solvents

Blushing Weakens and “fades” the applied dope,

making the finish weak and useless. Caused by solvents evaporating too fast

and introducing moisture into the materials.

Retarders

Slow drying thinner used to slow the drying time of the dope. Used when HUMIDITY IS HIGH

Process

Table 4-1, P. 96 Maintenance & Repair

Testing & Inspection Based on tensile strength

Seyboth Tested Penetrates the fabric ALL HOLES MUST BE REPAIRED!

Maule Tester Normally does not penetrate the fabric

With these testers, the fabric is tested on the airframe

Tested perpendicular to the fabric being tested

Testing and Inspection

Most accurate test Actual removal of a strip and destructively

tested. From weakest area 1” wide and several inches long Put in tester and pull until tears

Must meet the 70% rule

Repairs

Tears Remove all dope appx 2” past damage Baseball stitch Apply surface tape over repair Finish with original dope to original levels

“V” Tear Same but start at apex (bottom of v) to

ensure all is in place

Repairs

Doped Vne < 150 MPH Remove damaged area Dope on patch (up to 16” in any direction) Up to 8” hole needs 2” overlap, 8-16” hole

needs ¼ the longest distance of damage 12” hole = 3” overlap

Repairs Sewn- in

Vne > 150 MPH and less than 16” damage Damage removed, patch cut to fill the hole,

and sewn in using baseball stitch. Surface patch now cut to cover the sewn in

one If within 1” of a structure member (rib, stringer,

etc.) must extend 3” beyond Reinforcing tape, Rib stitched, surface tape and

then refinished to original

Repairs

Doped on panel