TM 1-410. Technical Manual, Airplane Structures 1941: Section 1 - General

SECTION I: GENERAL

1. General.-The subject of aircraft structures is an exceptionally broad one and no attempt is made in this manual to cover the entire field. It is, however, intended to present sufficient subject matter that the student will be familiar enough with structural details of service airplanes used by the Air Corps to be able to perform properly the inspec tion and maintenance of this equipment. In addition, it was found necessary to include certain information, for example, Air Corps designations, insignia, approved methods of handling, cleaning and lubricating airplanes, etc., which is not generally classified under aircraft structures, but is so closely allied with the main subject matter that it can be presented logically in this manual.

2. Air Corps designation of airplanes.-a. The various types of airplanes used by the Air Corps are determined by their particular tactical and operative employment, for example, bombardment, combat, training, etc. The model of any particular type is governed by specific characteristics of the airplane and identifies the manufacturer. Furthermore, there may be a series of a particular model which provides for minor modifications resulting from engineering improvements but not necessitating a change in the specific characteristics, tactical use, or manufacture of the airplane. When airplanes perform more than one function, the primary one determines the type designation.

b. The types, models, and series of airplanes used by the Air Corps are designated by a combination of letters and figures. These designations consist of

(1) Letter or letters indicating type.

(2) Number indicating model.

(3) Letter suffix indicating the series of the model.

Present types of Army Air Corps airplanes and their respective designations are given in the following table, several of which are shown in figures I to 7, inclusive.

FIGURE 1.-Cargo airplane.

FIGURE 2-Bombardment airplane.

FIGURE 3.-Pursuit airplane.

FIGURE 4-Observation airplane.

FIGURE 5-Basic training airplane.

FIGURE 6.-Attack (light bombardment) airplane.

FIGURE 7.-Observation (amphibian).

c. Airplanes of experimental, service test, limited procurement, and obsolete status are prefixed as follows:

(1) Experimental, X.

(2) Service test and limited procurement, Y.

(3) Obsolete, Z.

3. Principal structural units.-a. The principal structural units of an airplane consist of fuselage, nacelle, engine mount, wings, stabilizers, control surfaces, and landing gear. Figure 8 shows the location of these units on a single-engine airplane and in some cases the details of their structure.

b. The fuselage is the main structure (or body) of the airplane to which the wings and tail units are attached. In the case of single-engine airplanes it houses the crew, passengers, cargo, power plant, etc. On multiengine airplanes however the power plants are mounted on nacelles which are separate units similar in design and construction to the fuselage and attached to the wing structure.

c. Engine mounts are used to attach the power plant to the airplane. On most single-engine airplanes they are mounted on the front end or nose of the fuselage, and on multiengine airplanes they are attached to, or incorporated with, the nacelle structure.

d. The wings constitute the main lifting and supporting surface of the airplane in flight and are designated as right and left. The right and left sides of an airplane are relative to the right and left hand of the pilot seated in the cockpit.

e. Stabilizers are airfoils whose primary purpose is to increase stability of the airplane. They are mounted at the rear end of the fuselage and consist of the vertical fin or fins and the horizontal stabilizer.

f. Control surfaces are movable airfoils by means of which the airplane is controlled in flight. They are hinged auxiliary surfaces and consist of ailerons, elevators, rudders, tabs, and flaps. The control mechanism is the means by which the control surfaces are actuated.

g. Landing gears are the structures which support the airplane while on the ground or water. They incorporate shock-absorbing devices to reduce the shock of landing and taxying and are often retractable in flight. They may be any one of several general types, for example, float, ski, wheel, or a combination float and wheel, or ski and wheel.

4. Definitions and nomenclature-a. The axes and motions of the airplane are described relative to the center of gravity which is the point at which total weight of the airplane is assumed to be concentrated.

FIGURE 9.-Axis and fundamental motions of airplane.

(1) Axes.-The three principal axes of the airplane shown in figure 9 are

(a) Longitudinal (X) axis which is a line parallel to the fuselage axis or thrust line.

(b) Lateral (Y) axis which is a horizontal line through the center of gravity perpendicular to the longitudinal axis.

(c) Vertical (Z) axis which is a line through the center of gravity perpendicular to the other two axes.

(2) Motions.-The three fundamental motions of an airplane as shown in figure 9 are pitching, rolling or banking, and yawing.

(a) Pitching is the angular motion about the lateral axis.

(b) Rolling or banking is the angular motion about the longitudinal axis.

(c) Yawing is the angular motion about the vertical axis.

b. The following definitions of aeronautical terms and nomenclature of airplane parts are presented to serve as a reference for the student and only those items have been included which are necessary for a proper understanding of the material used in this manual.

Accelerometer.-Instrument that measures accelerations of an aircraft in a defined direction.

Aerodynamics.-Branch of dynamics that treats of motion of air and other gaseous fluids and of forces acting on solids in motion relative to such fluids.

Aeronautics.-Science and art of flight.

Aileron.-A hinged or movable portion of an airplane wing, primary function of which is to impress a rolling motion on the airplane. It is usually part of the trailing edge of a wing.

External.-Separate airfoil mounted clear of wing surfaces but usually attached to them and deflected for lateral control.

Frise.-Aileron having nose portion projecting ahead of hinge axis, the lower surface being in line with the lower surface of the wing. When trailing edge of aileron is raised, the nose portion protrudes below lower surf ace of the wing, increasing drag.

Slotted.-Aileron having a nose and axis arrangement somewhat similar to a Frise aileron but having a smooth air passage between nose portion of aileron and wing for the purpose of maintaining a smooth air flow over upper surface of the aileron when its trailing edge is deflected downward.

Upper Surface.-Split flap forming rear upper surface of a wing, deflected for lateral control.

Aircraft.-Any weight-carrying device designed to be supported by the air either by buoyancy or by dynamic action.

Airfoil.-Any surface such as wing, aileron, or rudder, designed to obtain reaction from the air through which it moves.

Airfoil section.-Cross section of an airfoil parallel to the plane of symmetry or to a specified reference plane.

Airplane.-Mechanically driven fixed-wing aircraft, heavier than air, which is supported by dynamic reaction of air against its wings.

Air speed.-Speed of an aircraft relative to the air.

Air speed head.-Instrument which in combination with a gage is used to measure the speed of aircraft relative to the air. It usually consists of a pitot static tube or a pitot venturi tube.

Altimeter.-Instrument that measures elevation of an aircraft above a given datum plane.

Altitude:

Absolute.-Height of an aircraft above the earth.

Pressure.-Altitude corresponding to a given pressure in a standard atmosphere.

Amphibian.-Airplane designed to rise from and alight on either land or water.

Angle:

Dihedral.-Acute angle between a line perpendicular to the plane of symmetry and the projection of the wing axis on a plane perpendicular to the longitudinal axis of the airplane. If the wing axis is not approximately a straight line, the angle is measured from the projection of a line joining the intersection of the wing axis with the plane, of symmetry and the aerodynamic center of the half-wing on either side of the plane of symmetry.

Drift.-Horizontal angle between the longitudinal axis of an aircraft and its path relative to the ground.

Flight path.-Angle between the flight path of the aircraft and the horizontal.

Gliding.-Angle between the flight path during a glide and a horizontal axis fixed relative to the air.

Landing.-Acute angle between the wing chord and the horizontal when airplane is resting on level ground in its normal position; also called "ground angle."

Minimum gliding.-Acute angle between the horizontal and the most nearly horizontal path along which an airplane can descend steadily in still air when the propeller is producing no thrust.

Rudder.-Acute angle between the rudder and the plane of symmetry of the aircraft. It is positive when the trailing edge has moved to the left with reference to the normal position of the pilot.

Angle of attack.-Acute angle between a reference line in a body and the line of relative wind direction projected on a plane containing the reference line and parallel to the plane of symmetry.

Critical.-Angle of attack at which flow about an airfoil changes abruptly as shown by corresponding abrupt changes in lift and drag.

Angle of incidence.-Acute angle between plane of the wing chord and the longitudinal axis of the airplane. The angle is positive when leading edge is higher than trailing edge.

Artificial horizon.-A device that indicates attitude of an aircraft with respect to the true horizon. A substitute for a natural horizon such as a liquid level, pendulum, or gyroscope, incorporated in a navigating instrument.

Atmosphere:

Altimeter calibration standard.-Standard atmosphere used in calibrating aeronautic instruments. The standard now in use in the United States is completely defined in National Advisory Committee for Aeronautics Report No. 246.

Standard.-Arbitrary atmosphere used in comparing performance of aircraft. Standard atmosphere in use in the United States at present represents very nearly average conditions found at latitude 40° and is completely defined in National Advisory Committee for Aeronautics Report No. 218.

Attitude.-Position of an aircraft as determined by inclination of its axes to some frame of reference. If not otherwise specified, this frame of reference is fixed to the earth.

Attitude of flight.-Inclination of the three principal airplane axes to the relative wind.

Automatic pilot.-Automatic control mechanism for keeping an aircraft in level flight and on a set course. Sometimes called "gyro pilot," "mechanical pilot," or "robot pilot."

Bank.-Position of an airplane when its lateral axis is inclined to the horizontal. A right bank is the position with the lateral axis inclined downward to the right.

Bank.-To incline tin airplane laterally, that is, to rotate it about its longitudinal axis.

Blade element.-A portion of a propeller blade contained between the surfaces of two cylinders coaxial with the propeller cutting the propeller blades.

Blade face.-Surface of a propeller blade that corresponds to the lower surface of an airfoil. Sometimes called "thrust. face." or "driving face."

Blade section.-Cross section of a propeller blade made at any point by a plane parallel to the axis of rotation of the propeller and tangent at the centroid of the section to an arc drawn with axis of rotation as its center.

Blade width ratio.-The ratio of chord of a propeller blade section to diameter of propeller.

Mean blade width ratio.-Ratio of mean blade width to diameter of propeller.

Blast gate (supercharger).-Device for controlling pressure in nozzle box of a turbo supercharger by discharging into free atmosphere a portion of the exhaust gases that would otherwise pass through the turbine wheel.

Boost.-To supply an engine with more air or mixture than it normally would induct at sea level.

Boost control, automatic.-Automatic regulator of boost pressure.

Bump.--Sudden acceleration of an aircraft caused by a region of unstable atmosphere characterized by marked local vertical components in air currents.

Cabane.-Arrangement of struts used for bracing on an aircraft.

Cable control.-Line of wire or stranded cable leading from control levers to control surfaces or interconnecting control surfaces.

Camber.-Rise of curve of airfoil section, usually expressed as ratio of departure of the curve from a straight line joining extremities of the curve to the length of this straight line. "Upper camber" refers to the upper surface; "lower camber" to the lower surface; and "mean camber" to the mean line of the section. Camber is positive when departure is upward, and negative when it is downward.

Ceiling.-Height of lower level of a bank of clouds above the ground.

Absolute.-Maximum height above sea level at which a given airplane would be able to maintain horizontal flight under standard air conditions.

Service.-Height above sea level under standard air conditions at which a given airplane is unable to climb f aster than a small specified rate (100 feet per minute in the United States and England). This specified rate may differ in different countries.

Cellule (or cell).-In an airplane, the entire structure of the wings and wing trussing of the whole airplane on one side of fuselage, or between fuselages or nacelles where there are, more than one.

Center section.-Central panel of a wing; in the case of a continuous wing or any wing having no central panel, the limits of center section are arbitrarily defined by location of points of attachment to cabane struts or fuselage.

Chord.-Arbitrary datum line from which ordinates and angles of an airfoil are measured. It is usually the straight line tangent to the lower surface at two points, the straight line joining the ends of the mean line, or the straight line between the leading and trailing edges.

Cockpit.-Open space in an airplane for accommodation of pilots or passengers. When completely enclosed, such a space usually is called a cabin.

Compass, card (or card magnetic).-Magnetic compass in which magnets are attached to a pivoted card on which directions are marked.

Compression ratio.-Ratio of volume of gas in an engine cylinder at beginning of compression stroke to its volume at end of stroke.

Control column.-Lever having a rotatable wheel mounted at its upper end for operating longitudinal and lateral control surf aces of an airplane. This type of control is called "wheel control."

Control servo.-Control devised to reinforce pilot's effort by an aerodynamic or mechanical relay.

Controllability.-Quality of an aircraft that determines ease of operating its controls and/or effectiveness of displacement of controls in producing change in its attitude in flight.

Controls.-General term applied to means provided to enable pilot to control speed, direction of flight, attitude, power, etc., of an aircraft.

Control stick.-Vertical lever by means of which longitudinal and lateral control surfaces of an airplane, are operated. The elevator is operated by a fore and aft movement of the stick; the ailerons by a side-to-side movement.

Control surface.-Movable airfoil designed to be rotated or otherwise moved by pilot in order to change attitude of aircraft.

Cowling.-Removable covering.

Cockpit.-Cowling placed around a cockpit.

Engine.-Removable covering placed around all or part of an airplane engine.

Decalage.-Difference between the angular settings of the wings of a biplane or multiplane. The decalage is measured by the acute angle between the chords in a plane parallel to the plane of symmetry. The decalage is considered positive if the upper wing is set at the larger angle.

Directional gyro.-Gyroscopic instrument for indicating direction, containing a free gyroscope which holds its position in azimuth and thus indicates angular deviation from the course,

Displacement, engine.-Total volume swept by the pistons of all the cylinders during one complete stroke of each piston.

Dive.-Steep descent, with or without power, in which the air speed is greater than the maximum speed in horizontal flight.

Dope.-Liquid material applied to the fabric surfaces of airplanes to increase their strength, to produce tautness by shrinking, and to act as a filler for maintaining airtightness.

Drag.-Component of the total air force on a body parallel to the relative wind.

Induced.-That part of drag induced by lift.

Parasite.-That portion of drag of an aircraft exclusive of induced drag of wings.

Drag strut.-Fore and aft compression member of the internal bracing system of an aircraft.

Elevator.-Movable auxiliary airfoil, the function of which is to impress a pitching moment on the aircraft. It is usually hinged to the stabilizer.

Emergency flotation gear.-Device attached to a landplane to provide buoyancy in case of an emergency landing on water.

Engine:

Compression ignition.-Type in which fuel is sprayed into the cylinder and ignited by heat of compression of air charge.

Double row radial.-Engine having two rows of cylinders arranged radially around a common crankshaft. Corresponding front and rear cylinders may or may not be in line.

Left hand.-Engine whose propeller shaft to an observer facing propeller from engine end of shaft, rotates in a counterclockwise direction.

Right hand.-Engine whose propeller shaft, to an observer facing propeller from engine end of shaft, rotates in a clockwise direction.

Supercharged.-Engine with a compressor for increasing air or mixture charge taken into cylinder beyond that inducted normally at the existing atmospheric pressure.

Dry weight.-Weight of an engine exclusive of fuel, oil, and liquid coolant.

Weight per horsepower.-Dry weight of an engine divided by rated horsepower.

Exhaust collector ring.-Circular duct into which exhaust gases from the cylinders of a radial engine are discharged.

Factor of safety.-Ratio of the ultimate load to, any applied load. This term usually refers to the probable minimum factor of safety which is the ratio of ultimate load to probable maximum applied load.

Fairing.-Auxiliary member or structure whose primary function is to reduce the drag of part to which it is fitted.

Fin.-Fixed or adjustable airfoil attached to an aircraft approximately parallel to plane of symmetry to afford directional stability; for example, tail fin, skid fin, etc.

Fitting.-Generic term for any small part used in structure. If without qualification, a metal part is usually understood.

Flap.-Hinged or pivoted airfoil forming the portion of an airfoil, used to vary the effective camber.

Split.-Hinged plate forming rear upper or lower portion of an airfoil. Lower portion may be deflected downward to give increased lift and drag; upper portion may be raised over a portion of wing for the purpose of lateral control (example, upper surface aileron).

Flare:

Parachute.-Pyrotechnic device attached to a parachute and designed to illuminate a large area when released from an aircraft at an altitude.

Signal.-Pyrotechnic signaling device of distinctive color and characteristics.

Flight path.-Flight path of the center of gravity of an aircraft with reference to the earth, or with reference to a frame, fixed relative to the air.

Float.-Completely enclosed watertight structure attached to an aircraft to give it buoyancy and stability when in contact with water.

Inboard stabilizing.-Stabilizing float placed relatively close to the main float or hull.

Outboard - (or wing tip) stabilizing.-Stabilizing float placed relatively far out from main float or hull, usually at or very near the tip of the wing.

Single.-Single central float fitted under a seaplane and usually requiring two stabilizing floats to give adequate stability and complete the float system.

Stabilizing (or side).-Float used in addition to a single float or hull and intended to provide lateral stability while seaplane or flying boat is at rest on water.

Flow:

Streamline.-Fluid flow in which the streamlines, except those very near a body and in a narrow wake, do not change with time.

Turbulent.-Any part of a fluid flow in which velocity at a given point varies more or less rapidly in magnitude and direction with time.

Flutter.-Oscillation of definite period but unstable character set up in any part of an aircraft by a momentary disturbance, and maintained by a combination of aerodynamic, inertial, and elastic characteristics of the, member itself (example, buffeting.)

Fuselage.-Body of approximately streamline form to which wings and tail unit of an airplane are attached.

Gap.-Distance separating two adjacent wings of a multiplane.

Glide.-To descend at normal angle of attack with little or no thrust.

Ground loop.-Uncontrollable violent turn of an airplane while taxying or during the landing or take-off run.

Gyro horizon.-Gyroscopic instrument that indicates lateral and longitudinal attitude of the airplane by simulating the natural horizon.

Horn.-Short lever attached to a control surface of an aircraft to which the operating wire or rod is connected.

Horsepower of engine, rated.-Average horsepower developed by a given type of engine at the rated speed when operating at full throttle, or at a specified altitude or manifold pressure.

Impact pressure.-Pressure acting at the forward stagnation point of a body such as a pitot tube placed in an air current. Impact pressure may be measured from an arbitrary datum pressure.

Inclinometer.-Instrument that measures the attitude of an aircraft with respect to the horizontal.

Induction system, rotary.-Carburetor induction system used on radial engines in which a rotary fan assists in distributing the fuel charge to the cylinders.

Inflow.-Flow of air into a propeller.

Instability, spiral.-Type of instability inherent in certain airplanes which becomes evident when airplane assumes too great a bank and sideslips; bank continues to increase and radius of turn to decrease.

Instrument flying.-Art of controlling an aircraft solely by use of instruments; sometimes called "blind flying."

Landing.-Act of terminating flight in which the aircraft is made to descend, lose flying speed, establish contact with the ground, and finally come to rest.

Glide.-Landing in which a steady glide is maintained to the landing surface without the usual leveling off before contact.

Normal (or three-point).-Landing in which a path tangential to landing surface and loss in flying speed are attained approximately at instant of contact.

Pancake.-Landing in which leveling off process is carried out several feet above the ground, as a result of which the airplane settles rapidly on a steep flight path in a normal attitude.

Landing area, effective.-That portion of landing area with approaches clear within allowable safe climbing and gliding angle available for take-off and landing of aircraft.

Landing field.-Any area of land designed for take-off and landing of aircraft. It may or may not be part of an airport.

Landing gear.-Understructure which supports weight of an aircraft when in contact with land or water and which usually contains a mechanism for reducing shock of landing. Also called "undercarriage."

Retractable.-Type of landing gear which may be withdrawn into body or wings of an airplane while it is in flight in order to reduce parasite drag.

Landing strip.-Narrow and comparatively long area forming part of land-plane airport or of intermediate or auxiliary field which is suitable for the landing and take-off under ordinary weather conditions.

Leading edge.-Foremost, edge of an airfoil or propeller blade.

Level off.-To make the flight path of an airplane horizontal after a climb, glide, or dive.

Lift, dynamic.-Component of the total aerodynamic force on a body perpendicular to the relative wind.

Lift-drag ratio.-Ratio of lift to drag of any body.

Light:

Anchor.-Light or group of clear lights carried on an aircraft to indicate its position at night while at anchor.

Approach.-Light, usually green, designed to indicate a favorable direction of approach for landing.

Blinker.-Flashing light giving more than 20 flashes per minute.

Boundary.-Any one of the lights designed to indicate limits of landing area of airport or landing field.

Course.-Light projected along course of an airway so as to be visible chiefly from points on or near the airway.

Fixed-Light which is constant in luminous intensity with respect to both time and direction.

Flashing.-Light which is intermittent as viewed from a single direction.

Identification.-Group of lights, clear and colored, carried on rear part of an airplane for identification at night.

Landing direction.-Light designed to indicate either by itself or in conjunction with other lights the direction in which landings are to be made.

Landing.-Light carried by an aircraft to illuminate the ground while landing.

Obstruction.-Red light designed to indicate position and height of an object hazardous to operation of aircraft.

Position.-Any one of a group of lights, red, green, and clear, used aboard an aircraft to indicate its position and direction of motion.

Load:

Full.-Weight empty plus useful load; also called gross weight.

Pay.-That part of useful load from which revenue is derived, that is, passengers and freight.

Useful.-Crew and passengers, oil and fuel, ballast other than emergency, ordnance, and portable equipment.

Loading:

Power.-Gross weight of airplane divided by the rated horsepower of the engine computed for air of standard density, unless otherwise stated.

Wing.-Gross weight of airplane divided by the wing area.

Longeron.-Principal longitudinal member of framing of airplane fuselage or nacelle, usually continuous across a number of points of support.

Loop.-Maneuver executed in such a manner that the airplane follows a closed curve approximately in a vertical plane.

Inverted normal.-Loop starting from inverted flight and passing successively through a dive, normal flight, climb, and back to inverted flight.

Inverted outside.-Outside loop starting from inverted flight and passing successively through a climb, normal flight, dive, and back to inverted flight.

Normal.-Loop starting from normal flight and passing successively through a climb, inverted flight, dive, and back to normal flight.

Outside.-Loop starting from normal flight and passing successively through a dive, inverted flight, climb, and back to normal flight, pilot being on outside of flight path.

Loop, radio.-Specified number of turns of wire located in wings or wound around fuselage of an airplane. Small portable loops on a rectangular f rame are also used.

Maneuver:

To operate aircraft in a skillful manner so as to cause it to perform evolutions out of the ordinary.

To perform tactical or acrobatic evolutions with aircraft.

Maneuverability.-That quality in aircraft which determines rate at which its altitude and direction of flight can be changed.

Marker, circle.-Circular band marking approximate center of landing area or intersection of principal landing strips on airport or landing field.

Mean line (of airfoil profile).-Intermediate line between upper and lower contours of profile.

Mixture control, altitude.-Device on carburetor for regulating weight proportions of air and fuel supplied to engine at different altitudes.

Monoplane.-Airplane with but one main supporting surface, sometimes divided into two parts by fuselage.

High wing.-Monoplane in which the wing is located at or near top of fuselage.

Low wing.-Monoplane in which wing is located at or near bottom of f uselage.

Midwing.-Monoplane in which the wing is located approximately midway between top and bottom of fuselage.

Parasol.-Monoplane in which the wing is above fuselage.

Multiplane.-Airplane with two or more main supporting surface's placed one above another.

Nacelle.-Inclosed shelter for personnel or for a power plant. A nacelle is usually shorter than a fuselage, and does not carry the tail unit.

Nose down.-To depress nose of airplane in flight.

Nose heavy.-Condition of airplane in which nose tends to sink when longitudinal control is released in any given attitude of normal flight.

Nose over.-Colloquial expression referring to accidental turning over of an airplane on its nose when landing.

Nose up.-To elevate nose of airplane in flight.

Octant.-Variation of aircraft sextant which measures angles up to 90°. Its artificial horizon is usually the bubble type.

Oleo gear.-Type of oil-damping device that depends on flow of oil through an orifice for its shock-absorbing effect in a landing gear.

Over-all length.-Distance from extreme front to extreme rear of aircraft, including propeller and tail unit.

Overhang:

One-half the difference in span of any two main supporting surfaces of an airplane. Overhang is positive when the upper of the two main supporting surfaces has the larger span.

Distance from outer strut attachment to tip of a wing.

Overshoot.-To fly beyond a designated mark or area such as a landing field, while attempting to land on the mark or within the area.

Panel (airplane).-Portion of airplane wing constructed separately from rest of wing to which it is attached.

Parachute.-Umbrella-like device used to retard descent of a falling body by offering resistance to its motion through the air.

Pilot.-Small auxiliary parachute attached to apex of main parachute, designed to pull latter out of its pack when rip cord is pulled.

Harness.-Combination of straps, buckles, and fastenings used to attach parachute to the wearer.

Pack.-Parachute and its container.

Rigger.-Person who packs, repairs, and inspects parachutes.

Pilot.-One who operates the controls of an aircraft in flight.

Pitch.-A ngular displacement about an axis parallel to the lateral axis of an aircraft.

Pitching.-Angular motion about lateral axis.

Pitch (or pitching) indicator.-Instrument for indicating existence and approximate magnitude of angular velocity about lateral axis of aircraft.

Pitch of propeller:

Effective.-Distance aircraft advances along its flight path for one revolution of propeller.

Geometrical.-Distance an element of a propeller would advance in one revolution if it were moving along a helix having an angle equal to its blade angle.

Pitot static tube.-Parallel or coaxial combination of a pitot and a static tube. Difference between impact pressure and static pressure is a function of velocity of flow past the tube.

Pitot tube.-Cylindrical tube with an open end pointed upstream used in measuring impact pressure.

Pitot venturi tube.-Combination of a pitot and a venturi tube.