Building the flying machine: strong joints, silk cords, no iron
Resistant members, the single-tie wing tendon a, and the finger-joint attachments
Leonardo argues that the flying machine should climb high with the wind's help as its safeguard, provided its members are strongly built to resist the fury of a descent: its joints of strong 'maschereccio' and its tendons of very tough raw-silk cords, and emphatically no ironwork, which soon snaps at its bends or wears out (text 1). He then specifies the tendon 'a' that extends the wing, which must be of thick maschereccio and doubled outside as within so the wing cannot be forced shut if the machine overturns (text 2). A final note keys the attachment points: a b c are where the tendons of the three finger-joints of the wing fasten, and d is where the mover of the lever a d drives the wing (text 3). A large drawing of the curved, jointed wing-frame fills the right side.
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Strong members, silk cords, and no iron
The machine's members must be of great resistance to withstand the fury and impetus of a descent, its joints of strong maschereccio and its tendons of very strong raw-silk cords. Leonardo warns against using ironwork, which soon breaks at its bends or wears out.
The wing-extending tendon a, doubled for safety
The tendon a, which extends the wing, should be of thick maschereccio so that if the machine turns upside down it can overcome the fury of the air that would force the wing shut and cause the machine's ruin. To be safer still, the same sinew-work is duplicated outside exactly as within.
Attachment points a b c d of the finger-joints and lever
The points a b c are where the tendons of the three joints of the wing's fingers are fastened; d is where the mover of the lever a d sits, which drives the wing. This keys the drawn wing-frame to its working parts.