Page:Dictionary of aviation.djvu/195

 DICTIONARY OF AVIATION 171

pitch-angle 'pit$,3erjg9l n. the angle of pitch, as of the blades of an aerial propeller.

pitching 'pit$irj n. the forward downward plunging of an airship; the alternate rising and falling of bow and stern; plunging lengthwise : distinguisht from rolling.

pit-gage 'pi^geeds n. [also spelt piUgauge] a rain^gage ar- ranged in a pit or saucer^ike cavity in the ground.

plane pteen n.

1. a surface or superficies such that every straight line joining any two points in it lies wholly in it; a surface whose intersection with any other like surface is a straight line; often, a horizontal plane; a level.

2. [also, sometimes, spelt 'plane'} a material surface ap- proximately of this nature; also, a thin flat structure pre- senting such surface or surfaces to the air; a plane aero- foil; an aeroplane.

articulated plane, a sustaining^plane in a flymg^machine articulated or jointed in such a manner as to make possible the reduction or increase of the supporting^area according to the speed of the machine.

falling plane, an aeroplane or aerofoil which is falling freely thru the air or other fluid, as in aerodynamic ex- perimentation.

following plane, a plane or aerofoil which fellows, or is attacht at the rear of the other planes or parts of a kite or flying^machine ; one of the hinder supporting^planes among several which are placed tandem, compare leading plane.

horizontal plane, an aeroplane or aerofoil which is in a horizontal position in the air or other fluid, as in aerody- namic experiments : distinguisht from inclined aeroplane.

leading plane, a plane or aerofoil which leads.

main plane, see mainfplane.

normal plane, a plane or aeroplane whose surface is normal, or at right angles to, the line of the direction of its t^anslatqry motion thru the air.

oblique plane, a plane or aeroplane whose surface is oblique or inclined to the line of the direction of its tjans- latory motion thru the air; a slanting plane or aeroplane.

superposed plane, an aeroplane or aerofoil which is placed above another, as the upper of the two planes of a biplane flying^machine or kite ; one of a series of such planes.

trochoidal plane, a plane the center of which moves in a circular path at a uniform speed while the plane is kept normal to the surface of a tjochoidal wave the period of which is equal to the time occupied by the center of the plane in making one revolution.

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