Aircraft fabric covering
Encyclopedia
Aircraft fabric covering is a term used for both the material used and the process of covering aircraft open structures. It is also used for reinforcing closed plywood
structures, the de Havilland Mosquito
being an example of this technique.
Early aircraft used organic materials such as cotton
and cellulose
dope
, modern fabric-covered designs usually use synthetic materials such as Nylon
and butyrate
dope for adhesive, this method is often used in the restoration of older types that were originally covered using traditional methods.
s such as George Cayley
and Otto Lillienthal used cotton-covered flying surfaces for their manned glider designs. The Wright brothers
also used cotton to cover their Wright Flyer
. Weak fabric-covered structure allowed wing warping
, an early form of roll
control.
. The German aircraft designer Hugo Junkers
is considered one of the pioneers of metal aircraft; his designs started the move away from fabric covering.
The highly flammable mixture of fabric, dope and hydrogen
gas was a factor in the demise of the Hindenburg
airship
.
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By the World War II era many aircraft designs were using metal monocoque
structures due to their higher operating airspeed
s, although fabric-covered control surfaces were still used on early mark Spitfires
and other types. Many transports, bombers and trainers still used fabric, although the flammable nitrate dope was replaced with butyrate dope instead, which burns less readily. The Mosquito
is an example of a fabric-covered (Madapolam
) plywood aircraft. The Vickers Wellington
used fabric over a geodesic airframe which offered good combat damage resistance.
An interesting case of ingenuity under wartime adversity was the Colditz Cock
glider. This homebuilt aircraft, intended as a means of escape, employed prison bedding as its covering material; homemade glue and dope made from boiled millet
were also used by the prisoners in its construction.
, known by the trade-name Dacron or Ceconite. This new fabric could be glued to the airframe instead of sewn and then heat-shrunk to fit. Grade A cotton would typically last six to seven years when the aircraft was stored outside, whereas Ceconite, which does not rot like cotton, can last over 20 years.
Early attempts to use these modern fabrics with butyrate dope proved that the dope did not adhere at all and peeled off in sheets. Nitrate dope was resurrected as the initial system of choice instead, although it was supplanted by new materials too.
One fabric system, developed by Ray Stits in the USA and FAA-approved
in 1965, is marketed under the brand name Poly-Fiber. This uses three weights of Dacron fabric sold as by the brand name Ceconite, plus fabric glue for attaching to the airframe (Poly-Tak), fabric preparation sealer resin (Poly-Brush) and paint (Poly-Tone). This system is not dope and instead uses vinyl
-based chemicals. Ceconite 101 is a certified 3.5 oz/yd² (119 g/m²) fabric while Ceconite 102 is a 3.16 oz/yd² (107 g/m²) fabric. There is also an uncertified light Ceconite of 1.87 oz/yd² (63 g/m²) intended for ultralight aircraft. This method requires physical attachment of the fabric to the airframe in the form of rib-stitching, rivets or capstrips, which are then usually covered with fabric tapes.
In addition to Poly-Fiber, a number of other companies produce covering processes for certified
and homebuilt aircraft
. Randolph Products and Certified Coatings Products both make butyrate
and nitrate
-based dopes for use with Dacron fabric.
Superflite and Air-Tech systems use a similar fabric, but the finishes are polyurethane
-based products with flex agents added. These finishes produce very high gloss results.
Falconar Avia of Edmonton, Alberta, Canada
developed the Hipec system in 1964 for use with Dacron fabric. It uses a special Hipec Sun Barrier that adheres fabric directly to the aircraft structure in one step, eliminating the need for the riveting, rib-stitching and taping used in traditional fabric processes. The final paint is then applied over the sun barrier to complete the process.
Newer systems were developed and distributed by Stewart Systems of Cashmere, Washington
and Blue River (Ceconite 7600). These two systems use the same certified dacron materials as other systems, but do not use high volatile organic compounds, using water as a carrier instead, making them safer to use and less environmentally damaging.
Many ultralight aircraft are covered with pre-sewn envelopes of 3.9 oz Dacron that are simply screwed, bolted or laced into place. These are produced in a wide variety of colours and patterns and are commonly flown untreated or with an anti-ultraviolet radiation finish to resist sun damage.
. Once the aircraft structure is prepared by sanding the material is applied using dope as an adhesive. Rib-stitching is used on faster aircraft types and especially on undercambered
airfoils to ensure that the fabric follows the aircraft structure. The distance between stitches is reduced in areas affected by the propeller wash. The covering would then be treated with tautening dope to remove wrinkles and increase structural strength, finish coats often containing aluminium powder would serve to protect the surface from ultra-violet light. Large fabric panels of the World War I era aircraft were often laced together through eyelets
to ease access to the internal structure for maintenance. Some disadvantages compared to modern methods are the relatively short service life of the covering due to biological effects such as mildew
and the labour required to achieve the end result.
or heat gun
, once the covering is tight rib-stitching is again used for heavier or faster aircraft. Cosmetic finish coats are usually applied. A side effect of using modern covering materials on wooden structured aircraft is that due to the much longer life the structure remains covered and un-inspected for much longer time periods, this has resulted in special periodic inspections being mandated by aviation regulatory bodies.
With both methods of covering it is normal for the aircraft to be re-weighed after renewal of the fabric to determine any change in mass and centre of gravity.
Plywood
Plywood is a type of manufactured timber made from thin sheets of wood veneer. It is one of the most widely used wood products. It is flexible, inexpensive, workable, re-usable, and can usually be locally manufactured...
structures, the de Havilland Mosquito
De Havilland Mosquito
The de Havilland DH.98 Mosquito was a British multi-role combat aircraft that served during the Second World War and the postwar era. It was known affectionately as the "Mossie" to its crews and was also nicknamed "The Wooden Wonder"...
being an example of this technique.
Early aircraft used organic materials such as cotton
Cotton
Cotton is a soft, fluffy staple fiber that grows in a boll, or protective capsule, around the seeds of cotton plants of the genus Gossypium. The fiber is almost pure cellulose. The botanical purpose of cotton fiber is to aid in seed dispersal....
and cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
dope
Aircraft dope
thumb|right|[[United Kingdom military aircraft serials|2699]] a [[World War I]] [[Royal Aircraft Factory B.E.2]] finished in a clear dopeAircraft dope is a plasticised lacquer that is applied to fabric-covered aircraft...
, modern fabric-covered designs usually use synthetic materials such as Nylon
Nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...
and butyrate
Butyrate
Butyrate is the traditional name for the conjugate base of butanoic acid . The formula of the butanoate ion is C4H7O2-. The archaic name is used as part of the name of butyrates or butanoates, or esters and salts of butyric acid, a short chain fatty acid...
dope for adhesive, this method is often used in the restoration of older types that were originally covered using traditional methods.
Purpose/requirements
The purposes of the fabric covering of an aircraft are:- To provide a light airproof skin for lifting and control surfaces.
- To provide structural strength to otherwise weak structures.
- To cover other non-lifting parts of an aircraft to reduce drag, sometimes forming a fairing.
- To protect the structure from the elements.
Early use
Pioneering aviatorAviator
An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...
s such as George Cayley
George Cayley
Sir George Cayley, 6th Baronet was a prolific English engineer and one of the most important people in the history of aeronautics. Many consider him the first true scientific aerial investigator and the first person to understand the underlying principles and forces of flight...
and Otto Lillienthal used cotton-covered flying surfaces for their manned glider designs. The Wright brothers
Wright brothers
The Wright brothers, Orville and Wilbur , were two Americans credited with inventing and building the world's first successful airplane and making the first controlled, powered and sustained heavier-than-air human flight, on December 17, 1903...
also used cotton to cover their Wright Flyer
Wright Flyer
The Wright Flyer was the first powered aircraft, designed and built by the Wright brothers. They flew it four times on December 17, 1903 near the Kill Devil Hills, about four miles south of Kitty Hawk, North Carolina, U.S.The U.S...
. Weak fabric-covered structure allowed wing warping
Wing warping
Wing warping was an early system for lateral control of a fixed-wing aircraft. The technique, used and patented by the Wright brothers, consisted of a system of pulleys and cables to twist the trailing edges of the wings in opposite directions...
, an early form of roll
Flight dynamics
Flight dynamics is the science of air vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are the angles of rotation in three dimensions about the vehicle's center of mass, known as pitch, roll and yaw .Aerospace engineers develop control systems for...
control.
WWI/Post WWI
The air wars of World War I were mainly fought with fabric-covered biplanes that were vulnerable to fire due to the flammable properties of the Grade A cotton covering and nitrate dope. National insignia painted on the fabric were often cut from downed aircraft and used as war trophiesWar trophy
In ancient Greece and Rome, military victories were commemorated with a display of captured arms and standards. A trophy was originally a war memorial assembled from such items on a battlefield. The Roman triumph also displayed these items as well as cultural objects, which later came to be...
. The German aircraft designer Hugo Junkers
Hugo Junkers
Hugo Junkers was an innovative German engineer, as his many patents in varied areas show...
is considered one of the pioneers of metal aircraft; his designs started the move away from fabric covering.
The highly flammable mixture of fabric, dope and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas was a factor in the demise of the Hindenburg
Hindenburg disaster
The Hindenburg disaster took place on Thursday, May 6, 1937, as the German passenger airship LZ 129 Hindenburg caught fire and was destroyed during its attempt to dock with its mooring mast at the Lakehurst Naval Air Station, which is located adjacent to the borough of Lakehurst, New Jersey...
airship
Airship
An airship or dirigible is a type of aerostat or "lighter-than-air aircraft" that can be steered and propelled through the air using rudders and propellers or other thrust mechanisms...
.
WWII
Monocoque
Monocoque is a construction technique that supports structural load by using an object's external skin, as opposed to using an internal frame or truss that is then covered with a non-load-bearing skin or coachwork...
structures due to their higher operating airspeed
Airspeed
Airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are: indicated airspeed , calibrated airspeed , true airspeed , equivalent airspeed and density airspeed....
s, although fabric-covered control surfaces were still used on early mark Spitfires
Supermarine Spitfire
The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and many other Allied countries throughout the Second World War. The Spitfire continued to be used as a front line fighter and in secondary roles into the 1950s...
and other types. Many transports, bombers and trainers still used fabric, although the flammable nitrate dope was replaced with butyrate dope instead, which burns less readily. The Mosquito
De Havilland Mosquito
The de Havilland DH.98 Mosquito was a British multi-role combat aircraft that served during the Second World War and the postwar era. It was known affectionately as the "Mossie" to its crews and was also nicknamed "The Wooden Wonder"...
is an example of a fabric-covered (Madapolam
Madapolam
Madapolam is a soft cotton fabric manufactured from fine yarns with a dense pick laid out in linen weave. Linen weave is the simplest and thickest interlaced, reversible basic weave, in which the appearance of the face and back of the woven fabric is the same. Its smallest repeat is 2/2, where two...
) plywood aircraft. The Vickers Wellington
Vickers Wellington
The Vickers Wellington was a British twin-engine, long range medium bomber designed in the mid-1930s at Brooklands in Weybridge, Surrey, by Vickers-Armstrongs' Chief Designer, R. K. Pierson. It was widely used as a night bomber in the early years of the Second World War, before being displaced as a...
used fabric over a geodesic airframe which offered good combat damage resistance.
An interesting case of ingenuity under wartime adversity was the Colditz Cock
Colditz Cock
|-See also:-External links:*****...
glider. This homebuilt aircraft, intended as a means of escape, employed prison bedding as its covering material; homemade glue and dope made from boiled millet
Millet
The millets are a group of small-seeded species of cereal crops or grains, widely grown around the world for food and fodder. They do not form a taxonomic group, but rather a functional or agronomic one. Their essential similarities are that they are small-seeded grasses grown in difficult...
were also used by the prisoners in its construction.
Introduction of modern materials
With the development of modern synthetic materials following World War II, cotton fabrics were replaced in civil aircraft applications by Polyethylene terephthalatePolyethylene terephthalate
Polyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...
, known by the trade-name Dacron or Ceconite. This new fabric could be glued to the airframe instead of sewn and then heat-shrunk to fit. Grade A cotton would typically last six to seven years when the aircraft was stored outside, whereas Ceconite, which does not rot like cotton, can last over 20 years.
One fabric system, developed by Ray Stits in the USA and FAA-approved
Supplemental Type Certificate
A Supplemental Type Certificate is an FAA approved major modification or repair to an existing type certified aircraft, engine or propeller. As it adds to the existing type certificate, it is deemed 'supplemental'.-Purpose:...
in 1965, is marketed under the brand name Poly-Fiber. This uses three weights of Dacron fabric sold as by the brand name Ceconite, plus fabric glue for attaching to the airframe (Poly-Tak), fabric preparation sealer resin (Poly-Brush) and paint (Poly-Tone). This system is not dope and instead uses vinyl
Vinyl
A vinyl compound is any organic compound that contains a vinyl group ,which are derivatives of ethene, CH2=CH2, with one hydrogen atom replaced with some other group...
-based chemicals. Ceconite 101 is a certified 3.5 oz/yd² (119 g/m²) fabric while Ceconite 102 is a 3.16 oz/yd² (107 g/m²) fabric. There is also an uncertified light Ceconite of 1.87 oz/yd² (63 g/m²) intended for ultralight aircraft. This method requires physical attachment of the fabric to the airframe in the form of rib-stitching, rivets or capstrips, which are then usually covered with fabric tapes.
In addition to Poly-Fiber, a number of other companies produce covering processes for certified
Type certificate
A Type Certificate, is awarded by aviation regulating bodies to aerospace manufacturers after it has been established that the particular design of a civil aircraft, engine, or propeller has fulfilled the regulating bodies' current prevailing airworthiness requirements for the safe conduct of...
and homebuilt aircraft
Homebuilt aircraft
Also known as amateur-built aircraft or kit planes, homebuilt aircraft are constructed by persons for whom this is not a professional activity. These aircraft may be constructed from "scratch," from plans, or from assembly kits.-Overview:...
. Randolph Products and Certified Coatings Products both make butyrate
Butyrate
Butyrate is the traditional name for the conjugate base of butanoic acid . The formula of the butanoate ion is C4H7O2-. The archaic name is used as part of the name of butyrates or butanoates, or esters and salts of butyric acid, a short chain fatty acid...
and nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
-based dopes for use with Dacron fabric.
Superflite and Air-Tech systems use a similar fabric, but the finishes are polyurethane
Polyurethane
A polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...
-based products with flex agents added. These finishes produce very high gloss results.
Falconar Avia of Edmonton, Alberta, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
developed the Hipec system in 1964 for use with Dacron fabric. It uses a special Hipec Sun Barrier that adheres fabric directly to the aircraft structure in one step, eliminating the need for the riveting, rib-stitching and taping used in traditional fabric processes. The final paint is then applied over the sun barrier to complete the process.
Newer systems were developed and distributed by Stewart Systems of Cashmere, Washington
Cashmere, Washington
Cashmere is a city in Chelan County, Washington, United States. It is part of the Wenatchee–East Wenatchee Metropolitan Statistical Area. The population was 3,060 at the 2010 census.-Early people:...
and Blue River (Ceconite 7600). These two systems use the same certified dacron materials as other systems, but do not use high volatile organic compounds, using water as a carrier instead, making them safer to use and less environmentally damaging.
Many ultralight aircraft are covered with pre-sewn envelopes of 3.9 oz Dacron that are simply screwed, bolted or laced into place. These are produced in a wide variety of colours and patterns and are commonly flown untreated or with an anti-ultraviolet radiation finish to resist sun damage.
Traditional methods
Traditional covering methods use organic materials, such as cottonCotton
Cotton is a soft, fluffy staple fiber that grows in a boll, or protective capsule, around the seeds of cotton plants of the genus Gossypium. The fiber is almost pure cellulose. The botanical purpose of cotton fiber is to aid in seed dispersal....
. Once the aircraft structure is prepared by sanding the material is applied using dope as an adhesive. Rib-stitching is used on faster aircraft types and especially on undercambered
Camber (aerodynamics)
Camber, in aeronautics and aeronautical engineering, is the asymmetry between the top and the bottom surfaces of an aerofoil. An aerofoil that is not cambered is called a symmetric aerofoil...
airfoils to ensure that the fabric follows the aircraft structure. The distance between stitches is reduced in areas affected by the propeller wash. The covering would then be treated with tautening dope to remove wrinkles and increase structural strength, finish coats often containing aluminium powder would serve to protect the surface from ultra-violet light. Large fabric panels of the World War I era aircraft were often laced together through eyelets
Grommet
thumb|right|250px|Some rubber grommets.A grommet is a ring inserted into a hole through thin material, such as fabric. Grommets are generally flared or collared on each side to keep them in place, and are often made of metal, plastic, or rubber. They may be used to prevent tearing or abrasion of...
to ease access to the internal structure for maintenance. Some disadvantages compared to modern methods are the relatively short service life of the covering due to biological effects such as mildew
Mildew
Mildew refers to certain kinds of molds or fungi.In Old English, it meant honeydew , and later came to mean mildew in the modern sense of mold or fungus....
and the labour required to achieve the end result.
Modern methods
Modern covering methods follow the traditional method with minor differences. Synthetic materials are used, covering is adhered to the structure using dedicated glues. The shrinking process is achieved by applying an electric ironIroning
Ironing is the use of a heated tool to remove wrinkles from fabric. The heating is commonly done to a temperature of 180-220 °Celsius, depending on the fabric. Ironing works by loosening the bonds between the long-chain polymer molecules in the fibers of the material...
or heat gun
Heat gun
A heat gun is a device used to emit a stream of hot air. They are superficially similar in shape and construction to a hair dryer, though they run at much higher temperatures...
, once the covering is tight rib-stitching is again used for heavier or faster aircraft. Cosmetic finish coats are usually applied. A side effect of using modern covering materials on wooden structured aircraft is that due to the much longer life the structure remains covered and un-inspected for much longer time periods, this has resulted in special periodic inspections being mandated by aviation regulatory bodies.
With both methods of covering it is normal for the aircraft to be re-weighed after renewal of the fabric to determine any change in mass and centre of gravity.