23. Spar or Wing Bars.—The longitudinal members of the interior wing framework.
24. Rib (Wing).—The members of the interior wing framework transverse to the spars.
25. The Longerons or Longitudinals.—The fore and aft or lengthwise members of the framing of the fuselage, usually continuous across a number of points of support.
26. Engine (Right and Left Hand).—In the ordinary tractor machine, when viewed from the pilot’s seat a right-handed engine revolves clockwise and right-handed.
27. Propeller.—
28. Pitch (Propeller).—The distance forward that the propeller would travel in one revolution, if there were no slip, that is, if it were moving in a thread cut at the same inclination as the blade. Pitch angle refers to the angle of inclination of the propeller blade.
29. Slip.—Slip is the difference between the actual travel forward of a screw propeller in one revolution and its pitch.
30. Dope.—A general term applied to the material used in treating the cloth surface of airplane members to increase strength, produce tautness, and act as a filler to maintain air and moisture tightness. Usually of the cellulose type.
31. Controls.—Since there are three axes or main directions about which an airplane may turn or rotate it follows that three controlling devices are required. These are: (1) the elevator for pitching; (2) the rudder for steering or yawing; (3) the ailerons for lateral, rolling or banking control.
The term controls is a general term used to distinguish the means provided for operating the devices used to control speed, direction of flight and attitude of the aircraft.