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Machine sewing thread must have a tensile strength of five pounds per strand and weigh about one
pound per five thousand yards. It is technically described as white, silk-finish, No. 16 four-cord thread
with a left or Z twist.
Hand sewing thread must have a tensile strength of fourteen pounds per strand and weigh one pound per
1650 yards.
Lacing cord is used to attach fabric to the structure of the airplane. It should have a minimum tensile
strength of forty pounds single or eighty pounds double. Bee's wax should be used to lightly coat the cord
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before use by drawing the cord across a piece of wax.
Waxed cord is used to attach leather chafing strips (made of russet strap leather) on parts of the
structure that may be subject to rubbing by moving parts such as brace wires and structural tubing.
Chafing strips protect against wear and abrasion and the cord holding them in place must be double-twist
and waxed.
Leather
Russet strap leather is used for reinforcing where structural parts or controls must pass through the fabric
skin. Horsehide, which is thinner, may be substituted in areas of lesser wear.
Miscellaneous
Tacks are used during construction to temporarily hold fabric in place, but only rustproof tacks, made of
brass, tinned iron or Monel, should be used for permanently attaching fabric to wood.
Where holes are necessary for drainage, inspection or lacing, grommets are used to reinforce the fabric.
Seaplane or marine grommets are shaped to create suction to enhance drainage or ventilation when
necessary.
Dope
In order to make aircraft fabric airtight and weatherproof, dope is applied. Dope also causes the fabric
to tighten, removing wrinkles. Caution should be exercised here, as too much tightening can damage
underlying structures. Clear and pigmented dopes each have their separate purposes. Modern dope is
often pigmented with powdered aluminum to provide protection from sunlight. Aluminum is unknown in
the seventeenth century. Until powdered aluminum becomes available, you'll have to live without it and
plan extra inspection, maintenance and repair to compensate. Final coats of dope are mixed with color
pigments to achieve any desired appearance and also provide some protection from sunlight.
Nitrocellulose dope is made by adding glycol sebacate, ethyl acetate, butyl acetate or butyl alcohol to a
solution of nitrocellulose. Ethyl alcohol or benzol can be used to thin the dope to desired consistency. The
main drawback of nitrocellulose dope is extreme flammability. Once ignited, it burns too fast for fire
fighting to be practical, especially in an aircraft aloft. Adding aluminum, when available, only exacerbates
the problem. For reference, the crash of the Hindenburg is now attributed to its having been coated with
nitrocellulose dope pigmented with aluminum and iron oxide a combination better known in modern
times as "rocket fuel."
Cellulose acetate butyrate (CAB) dope is more resistant to fire than nitrocellulose and penetrates better
as well. On the down side, it has a stronger tautening effect, which can damage fabric or structure if care
is not taken. It can be applied over nitrocellulose dope.
If you want to know about the chemicals that make dope. I haven't a clue and never did. It's not in my
textbooks. As I said at the outset, I'm a mechanic. I know how to maintain and repair airplanes using
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mostly off-the-shelf materials. Dope is something I ordered from a parts catalog.
Modern aircraft coatings also include fiberglass and assorted other plastics, but down-timers are going
to have a hard enough time making the traditional dopes without worrying about up-time synthetics.
Construction and Repair
Vocabulary
As with most technical specialties, there is a broad nomenclature for wooden aircraft. It doesn't exist to
keep nonexperts at bay, but rather to precisely specify things that must be so specified and don't exist in
any other context. So, we must deal with spars, stringers, bulkheads, ribs, formers, longerons and leading
edge strips, all of which have definitions unique to wooden airplanes (as opposed to boats and ships). [ Pobierz całość w formacie PDF ]