Fabric covering is cotton or linen stretched over the airframe and tautened with coats of dope, a cellulose lacquer that shrinks as it dries; the carrier specifies 3-4 coats of tautening dope followed by 2-3 of protective finish. The fabric must be attached mechanically to the ribs and not just glued, because suction on the top surface tries to lift it off, and the dope’s solvent is flammable and toxic. The corpus holds no method for making dope, so a substitute finish must be tested on a small frame before it goes on a wing.
Part of Aerodynamics and Flight
The cloth skin of a light aircraft, how it is attached and tightened, and the failure modes it creates.
The Skin Has Two Jobs, And Neither Is Strength Of The Wing
The fabric holds the aerofoil shape between ribs and carries the air pressure into them. It adds torsional stiffness to the wing (Wing Twist), but it is not a main load path. Its biggest hazard is coming off: the top surface is under suction (Pressure Distribution), so the cloth pulls away from the ribs and a patch that lifts changes the section and the stall.
What You Need
- Cotton or linen cloth of even weave, free of weak patches. The corpus has Flax Processing for linen fibre, and nothing on weaving to aircraft-cloth standards.
- Dope: the carrier names nitrate or butyrate cellulose lacquer. The corpus has no article on making cellulose lacquers, and nitrate dope is highly flammable. Shellac is an existing finish, and its suitability as a tautener is untested.
- Waxed linen thread and needles for rib stitching, and fabric panels cut with the carrier’s 5 cm overlaps.
- A sealed, dust-free, ventilated space.
Method: Cover, Attach, Tauten
Step 1: Prepare the wood. Sand every edge round, because the carrier warns any sharp edge wears through the fabric, and seal the wood.
Step 2: Lay the cloth without tension. Attach it at the edges and ribs and stretch it only lightly.
Step 3: Stitch to every rib. A stitch passes through the cloth and around the rib, so the cloth cannot lift. Glue alone is not an attachment.
Step 4: Apply tautening coats. The carrier gives 3-4 coats with full drying between each. The cloth shrinks and goes tight.
Step 5: Check the frame. Shrinkage loads the frame; light structures can twist or bow. Measure after each coat.
Step 6: Apply finishing coats. Protect against sunlight and moisture; the carrier gives 2-3.
Step 7: Weigh. The carrier expects the covering to add no more than 1-2 kg per square metre.
If Dope Is Not Available
Without dope a finish must tighten the cloth, seal it, stay flexible, not attack the cloth, survive sun and water, and stay attached under suction. A candidate is shellac or an oil-based varnish; none has aircraft data in the corpus. Make a test panel stretched over a small frame, finish it, leave it in weather, load it with air pressure (a fan, or a vacuum on a boxed frame) and watch for slack, cracks and lifting. If it fails the test, it fails on the wing.
Common Mistakes
- Glue-only attachment — it lifts first at the leading edge.
- Over-tightening a flimsy structure — rib warping and twist.
- Leaving gaps at the trailing edge — flutter of loose fabric starts there.
- Skipping the weather test — sun cracks the finish and the cloth sags.
Safety
Dope vapour burns and poisons
The solvents are flammable, and the vapour is heavier than air and settles in low spots. No flames, sparks, pilot lights or smoking, ventilate strongly, wear respiratory protection, and keep the doped parts away from heat. Fabric treated with some dopes burns fast; keep an extinguishing means to hand.
What’s Next
- Learn next: Landing Gear, the other part that takes ground loads
- Combine with: Boundary Layer, why surface finish matters