Airframe chapter 5 fabric covering

What type of knot is used for locking the stitches that are used for rib lacing on a fabric-covered aircraft wing?

A modified seine knot.

What is a tie-off knot?

A standard, modified seine knot used on all stitches except the starting stitch.

Where are drainage grommets located on a fabric-covered aircraft wing?

At the lowest point in each bay. It is customary to install a grommet on each side of a wing rib, on the underside of the wing, at the trailing edge.

Should a sewed seam in the fabric used to cover an aircraft wing run spanwise or chordwise?

Both spanwise and chordwise seams are permissible, but chordwise seams are preferred.

How would you determine the correct spacing for stitching if the original spacing was unknown?

Consult the chart in AC-43.13-1B

What two types of organic fibers are used for covering aircraft?

Cotton and linen.

What type of material is used for inter-rib bracing in a fabric-covered aircraft wing?

Cotton reinforcing tape.

What is the minimum strength to which aircraft fabric is allowed to deteriorate before it is considered to be unairworthy?

Fabric can deteriorate to 70% of the strength of the fabric that is required for the aircraft.

How is polyester synthetic fabric shrunk on an aircraft structure?

It is shrunk with heat from an iron or from a heated blower.

What is the purpose of the selvage edge on a roll of fabric?

It prevents the fabric from unraveling.

Where would you use suface tape?

Over rib stitching and sewed seams, over lapped edges, around corners, and along leading and trailing edges.

Why is the surface tape used on the trailing edge of the control surfaces of some airplanes notched?

Since the edges of this tape face into the wind, it is possible that it could start to lift and form a very effective spoiler. If the tape is notched, it will tear off at a notch.

What identification marking is found on the selvage edge, and in which direction is the warp applied?

The FAA-PMA stamp is found on the delvage edge and the warp is applied parallel to the line of flight.

What is the preferred seam used for machine-sewing pieces of aircraft fabric together?

The French fell seam.

How would you determine the strength requirements for fabric used to re-cover an aircraft?

The fabric must be of at least the quality and strength of the fabric used by the orginal manufacturer.

What determines the spacing of the rib lacing stitches on a fabric-covered aircraft wing?

The never-exceed speed of the aircraft.

How wide should the surface tape be that is used to cover the trailing edge of an aircraft wing?

Three inches wide

Where are anti-tear strips used?

Under wing rib stitching when the never-exceed speed is greater than 250 mph.

What is meant by warp, weft, and bias?

Warp is the direction along the length of the fabric, weft is the direction across the the fabric at right angles to the warp, and bias is a direction at a 45 degree angle to the warp and weft.

What type of rib lacing cord is recommended for attaching cotton fabric to an aircraft structure?

Waxed linen cord.

What type of hand-sewing stitch is used when sewing in a panel of new fabric on an aircraft fabric-covered wing?

A baseball stitch, locked every eight to ten stitches.

When is the finishing tape applied to a fabric-covered wing when it is being recovered?

After the second coat of dope has dried and the nap of the fabric has been sanded off.

What is the principal advantage of the envelope method for covering wings?

Almost all the seams are machine-sewed by envelope supplier.

What is an antitear strip, and when are they required on a fabric-covered aircraft?

An antitear strip is a strip of the same type of fabric as is used for covering the wings. It is laid over the rib between the reinforcing tape and the fabric. An antitear strip is required for aircraft that have a never-exceed speed in excess of 250 miles per hour.

How is the strength of the fabric on an aircraft structure determined?

An approximate strength test can be made with an FAA-approved fabric punch tester, but the only way to know for sure that the fabric has sufficient strength is by pull-testing a one-inch-wide sample of the fabric.

Why are some portions of the structure of an aircraft dope proofed before they are covered with fabric?

Dope proofing keeps the fabric from sticking to the structure when the first coat of dope is applied. The fabric normally sags enough to touch the structure before it begins to pull taut.

Which of the several types of fabric is unaffected by moisture and mildew?

Fiberglass

What types of synthetic fibers are used for covering aircraft?

Fiberglass and heat-shrinkable polyester fibers.

What is the recommended type of repair to a fabric-covered aircraft surface when it has an L-shaped tear with each of the legs of the tear more than 14 inches long?

If the never-exceed speed of the aircraft is less than 150 miles per hour, a doped-on repair can be made.

What paperwork must be completed if an aircraft that was originally covered with Grade-A cotton fabric is re-covered using a synthetic fabric?

The covering must be done according to a Supplemental Type Certificate, and a Form 337 must be executed, stating that all materials and processes complied with the requirements of the STC.

How are the fabric type and strength requirements determined for fabric-covered aircraft?

The original manufacturer determines the fabric type, and the strenght requirements are a function of the never-exceed speed and wing loading.

What is the purpose of the reinforcing tape that is used between the fabric and the rib lacing on an aircraft wing?

The reinforcing tape keeps the rib lacing cord from pulling through the fabric.

When are drainage grommets applied when an aircraft is being re-covered?

They are laid into the third coat of dope, at the same time the surface tape is applied.

How should a structure that will be covered with doped fabric be prepared following inspection and prior to covering?

Treat it with a protective coating of paint or varnish as appropriate.

How should the edges of drainage, inspection, and ventilation holes be reinforced?

With plastic, aluminum, or brass grommets.

Fabric is considered unairworthy when it has deteriorated to what percentage of its original strength?

Less than 70%

Aircraft covering fabrics are made of material from what two sources?

Organic materials and synthetic materials.

Name three common types of machine-sewed seams.

Plain overlap, folded-fell, and French-fell.

What are the principle methods used to test the condition of fabric?

Punch testers such as the maule or seybolt tester, and laboratory pull-testing.

What is the function or purpose of reinforcing tape?

Reinforcing tape is used between the fabric and the rib stitching to prevent the lacing cord from cuting through the fabric.