THE RIGGING OF AIRPLANES
=Object.=—The object of this chapter is to teach the elementary
principles of correct rigging. It is not expected that the student
will become an expert mechanic, but with this treatment as a basis and
through practice he will be able to judge whether or not a machine is
correctly and safely rigged. In other words, he will not have to depend
on someone else’s judgment as to whether panels, wires, controls,
struts, etc., of a machine are in good order, but he will be able to
observe understandingly that they are. If the engine goes wrong he can
land, if the rigging goes wrong he is in great difficulty. Moreover, if
the rigging is wrong, speed is lessened and the stability is uncertain.
The first thing to be learned in rigging is a knowledge of the peculiar
terms which have come into use in aeronautics defining different parts
of the machines. Our present list of terms is derived, partly from
French, partly from English, and partly from American terms. Thus
different names may refer to the same part.
NOMENCLATURE
=1. Tractor.=—An airplane that is pulled through the air by a propeller
situated in front of the machine, is called a tractor.
=2. Pusher.=—If the propeller is back of the main lifting planes the
machine is called a pusher.
=3. Fuselage= or =Body=.—The main body of the airplane in which
the pilot sits and to which the landing gear, motor, controls, and
sustaining surfaces are fixed. A small body, especially in pusher types
of machines, is called a Nacelle.
=4. Cockpit.=—The openings and space in the fuselage where pilot or
observer sits.
=5. Stream-line Body.=—The shape of a body or part which permits a
regular flow of air around and along it with the least resistance, in
other words with minimum, obstruction and eddying.
=6. Fairing.=—Building up a member or part of the plane with a false
piece that it may have a stream-line body.
=7. Wings, Planes, Panels.=—The main supporting surfaces of an airplane
are called wings, although the terms planes and panels are probably
as frequently used and even preferred by many. The term panel refers
properly to a section of the wings with the included struts and wires.
The small panel directly above the body is called the engine section
panel or the center panel, while the panels to the right and left of
the body or fuselage are called the main panels. The main panels are
the right and left panels as seen from the seat. Each main panel may
be subdivided into the inner wing bay, the outer wing bay, and the
overhang.
=8. Landing Gear, Chassis or Undercarriage.=—The wheels and the struts
and wires by which they are attached to the fuselage.
=9. Horizontal Stabilizer or Horizontal Fin.=—The horizontal fixed tail
plane.
=10. Vertical Stabilizer or Vertical Fin.=—The small vertical fixed
plane in front of the rudder.
=11. Rudder.=—The hinged surface used to control the direction of the
aircraft in the horizontal plane. As with a boat, for steering or
“yawing” or changing its direction of travel.
=12. Elevator or Flap; Flippers.=—A hinged horizontal surface for
controlling the airplane up and down, usually attached to the fixed
tail plane; for pitching the machine or “nosing up” and “nosing down.”
=13. Tail or “Empennages.”=—A general name sometimes applied to the
tail surfaces of a machine.
=14. Mast or Cabane.=—The small vertical strut on top of the upper
plane used for bracing the overhang.
=15. Ailerons.=—Movable auxiliary surfaces used for the control of
rolling or banking motion. Other definitions are that they are for the
lateral control or for maintaining equilibrium. When they are a part of
the upper plane they are sometimes called wing flaps.
=16. Landing Wires or Ground Wires (Single).=—The single wires which
support the weight of the panels when landing or on the ground.
=17. Flying Wires, or Load Wires (Double).=—The wires which support the
body or fuselage from the planes when in flight.
=18. Drift Wires.=—The horizontal wires which lead from the nose of the
fuselage to the wings and thus keep them from collapsing backward. For
the same reason the wings have interior drift wires.
=19. Diagonal Wires.=—Any inclined bracing wires.
=20. Skids.=—(_a_) _Tail Skid._—The flexible support under the tail of
the machine.
(_b_) _Wing Skid._—The protection under the outer edge of the lower
wing.
(_c_) _Chassis Skids._—Skids sometimes placed in front of the landing
gear.
=21. Horns, or Control Braces.=—The steel struts on the controls to
which the control wires are attached.
=22. Struts; Wing Struts.=—The vertical members of the wing trusses of
a biplane, used to take pressure or compression, whereas the wires of
the trusses are used to take pull or tension. There are also fuselage
struts and chassis struts.
=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.
=32. Cotter Pins.=—Must be on every nut.
=33. Castelled Nuts.=—Admit cotter pins.
=34. Turnbuckles.=—Must be well and evenly threaded and locked with
safety wires.
=35. Safety Wires.=—For locking turnbuckles and hinge pins.
=36. Shackle and Pin.=—
=37. Hinge Connections.=—
=38. Leading Edge or Entering Edge.=—The front edge of a plane.
=39. Trailing Edge.=—The rear edge of a plane.
=40. Stagger.=—The horizontal distance that the entering edge of the
upper wing of a biplane is ahead of the entering edge of the lower wing.
=41. Dihedral Angle.=—A term used to denote that the wings are arranged
to incline slightly upward from the body toward their tips. The angle
made with the horizontal by this inclination of the wing is called the
dihedral angle.
=42. Angle of Incidence.=—The angle at which a wing is inclined to the
line of flight.
=43. Decalage.=—Difference in angle of incidence between any two
distinct aerofoils on an airplane.
=44. Chord.=—Distance between the entering edge and trailing edge of a
wing measured on a straight line touching front and rear bottom points
of a wing.
=45. Camber.=—The depth of the curve given to a sustaining surface such
as a wing. Thus it will be observed that the planes are not straight
in cross-section but are concave slightly upward. The depth of this
concavity is the camber. Another way of expressing this is that camber
is the greatest distance between the surface of a wing and its chord
line.
=46. Gap.=—The distance between the lower and upper wings of a biplane.
=47. Spread.=—The distance over all from one wing tip to the other wing
tip.
=48. Aerofoil.=—A general name applied to any wing or lifting surface
of an airplane.
=49. Deadhead Resistance.=—Each part of an airplane against which the
wind strikes offers a resistance against being moved through the air.
This is called the _deadhead resistance_ or the _parasite resistance_.
It is for the purpose of lessening this resistance that the parts of a
machine are stream-lined. Remember that force or power must be applied
to overcome this resistance and the lessening of such resistance
decreases the power necessary. A parallel illustration is to think of
the power necessary to push a board sideways through water.
=50. Drift.=—When the air strikes the inclined wing of an airplane its
force has two components. One part called the _lift_ (see 52) acts up
and tends to lift the machine. The other part, called _drift_, tends to
push the machine backward. This drift must also be overcome by applying
power enough to drive the machine forward.
=51. Total Resistance.=—Sometimes called _drag_. (49) Deadhead
resistance added to (50) drift, gives the total forces opposing the
forward movement of the airplane. This is called the total resistance
and is overcome by the _thrust_ of the propeller.
=52. Lift.=—(See 50). The upward or vertical part of the air pressure
acting against the wings, and which is utilized to lift or support the
airplane.
=53. Center of Gravity.=—The point of balance of an airplane which may
be otherwise defined as the point through which the mass of an airplane
acts. If the weight is too far forward the machine is nose-heavy.
If the weight is too far behind the center of lift the machine is
tail-heavy.
=54. Aspect Ratio.=—The ratio of span to chord of a wing or any other
aerofoil.
=55. Gliding Angle (Volplane).=—The angle made to the horizontal by
the flight path of an airplane with the engine shut off; _e.g._, an
airplane is 1000 ft. high, when its engine fails. Suppose its gliding
angle is 1 in 6. Therefore, in still air it can glide 6000 ft. forward.
The general term glide refers to flying without power.
=56. The Angle of Best Climb.=—The steepest angle at which an airplane
can climb.
=57. Stability.=—The property of an airplane to maintain its direction
and to return easily to its equilibrium or balance with a minimum of
oscillation. This is sometimes called dynamical stability. An airplane
may have (first) inherent stability, which is the stability due to
the arrangement and disposition of its fixed parts. It may also have
stability with regard to any one of the three directions in which it
may move. These are named as follows: (1) directional stability, with
reference to the vertical axis; (2) lateral stability with reference to
the longitudinal (or fore and aft) axis; (3) longitudinal stability,
stability with reference to the lateral (or thwartship) axis.
=58. Flying Position.=—Refers to the position of the fuselage when
flying. With the Curtiss JN-4 machines in this position the top
longerons are horizontal and level both ways. The engine bearers are
also level, and the wings have an angle of incidence of 2°.
=59. Capacity.=—The weight an airplane will carry in excess of the
dead load (dead load includes structure power plant and essential
accessories).
=60. Flight Path.=—The path of the center of gravity of an aircraft
with reference to the air.
=61. Stalling.=—A term describing the condition of an airplane which
from any cause has lost the relative speed necessary for support and
controlling, and referring particularly to angles of incidence greater
than the critical angle.
=62. Sweepback.=—The horizontal angle (if any) that the leading edge of
a machine makes with the crosswise or lateral axis of an airplane.
=63. Nose Dive or Vol-pique.=—A dangerously steep descent, head on.