=Turnbuckle=--A form of wire-tightener, consisting of a barrel into each end of which is screwed an eyebolt. Wires are attached to the eyebolts and the required degree of tension is secured by means of rotating the barrel.

=Thrust, Propeller=--See "Air-Screw."

=Undercarriage=--That part of an aeroplane beneath the _fuselage_ or _nacelle_, and intended to support the aeroplane when at rest, and to absorb the shock of alighting.

=Velocity=--Rate of displacement; speed.

=Volplane=--A gliding descent.

=Weight=--Is a measure of the force of the Earth's attraction (gravity) upon a body. The standard unit of weight in this country is 1 lb., and is the force of the Earth's attraction on a piece of platinum called _the standard pound_, deposited with the Board of Trade in London. At the centre of the Earth a body will be attracted with equal force in every direction. It will therefore have no weight, though its ma.s.s is unchanged. Gravity, of which weight is a measure, decreases with increase of alt.i.tude.

=Web= (_of a rib_)--That vertical part of a rib which prevents it from bending upwards. [37_a_]

=Warp, to=--To distort a surface in order to vary its angle of incidence.

To vary the angle of incidence of a controlling surface.

=Wash=--The disturbance of air produced by the flight of an aeroplane.

=Wash-in=--An increasing angle of incidence of a surface towards its wing-tip. [38]

=Wash-out=--A decreasing angle of incidence of a surface towards its wing-tip. [39]

=Wing-tip=--The right or left-hand extremity of a surface. [40]

=Wire=--A wire is, in Aeronautics, always known by the name of its function.

=Wire, Lift or Flying=--A wire opposed to the direction of lift, and used to prevent a surface from collapsing upward during flight. [41]

=Wire, Anti-lift or Landing=--A wire opposed to the direction of gravity, and used to sustain a surface when it is at rest. [42]

=Wire, Drift=--A wire opposed to the direction of drift, and used to prevent a surface from collapsing backwards during flight.

=Wire, Anti-drift=--A wire opposed to the tension of a drift wire, and used to prevent such tension from distorting the framework. [44]

=Wire, Incidence=--A wire running from the top of an interplane strut to the bottom of the interplane strut in front of or behind it. It maintains the "stagger" and a.s.sists in maintaining the angle of incidence. Sometimes termed "stagger wire." [45]

=Wire, Bracing=--Any wire holding together the framework of any part of an aeroplane. It is not, however, usually applied to the wires described above unless the function performed includes a function additional to those described above. Thus, a lift wire, while strictly speaking a bracing wire, is not usually described as one unless it performs the additional function of bracing some well-defined part such as the undercarriage. It will then be said to be an "undercarriage bracing lift wire." It might, perhaps, be acting as a drift wire also, in which case it will then be described as an "undercarriage bracing lift-drift wire." It should always be stated whether a bracing wire is (1) top, (2) bottom, (3) cross, or (4) side. If a "side bracing wire," then it should be stated whether right- or left-hand.

=Wire, Internal Bracing=--A bracing wire (usually drift or anti-drift) within a surface.

=Wire, Top Bracing=--A bracing wire, approximately horizontal and situated between the top longerons of fuselage, between top tail booms, or at the top of similar construction. [46]

=Wire, Bottom Bracing=--Ditto, subst.i.tuting "bottom" for "top." [47]

=Wire, Side Bracing=--A bracing wire crossing diagonally a side bay of fuselage, tail boom bay, undercarriage side bay or centre-section side bay. This term is not usually used with reference to incidence wires, although they cross diagonally the side bays of the cell. It should be stated whether right- or left-hand. [48]

=Wire, Cross Bracing=--A bracing wire, the position of which is diagonal from right to left when viewing it from the front of an aeroplane. [49]

=Wire, Control Bracing=--A wire preventing distortion of a controlling surface. [50]

=Wire, Control=--A wire connecting a controlling surface with the pilot's control lever, wheel, or rudder-bar. [51]

=Wire, Aileron Gap=--A wire connecting top and bottom ailerons. [52]

=Wire, Aileron Balance=--A wire connecting the right- and left-hand top ailerons. Sometimes termed the "aileron compensating wire." [53]

=Wire, Snaking=--A wire, usually of soft metal, wound spirally or tied round another wire, and attached at each end to the framework. Used to prevent the wire round which it is "snaked" from becoming, in the event of its displacement, entangled with the propeller.

=Wire, Locking=--A wire used to prevent a turnbuckle barrel or other fitting from losing its adjustment.

=Wing=--Strictly speaking, a wing is one of the surfaces of an ornithopter. The term is, however, often applied to the lifting surface of an aeroplane when such surface is divided into two parts, one being the left-hand "wing," and the other the right-hand "wing."

=Wind-Tunnel=--A large tube used for experimenting with surfaces and models, and through which a current of air is made to flow by artificial means.

=Work=--Force displacement.

=Wind-Screen=--A small transparent screen mounted in front of the pilot to protect his face from the air pressure.

Types of Aeroplanes.

[Ill.u.s.tration: Plate I.]

The first machine to fly--of which there is anything like authentic record--was the Ader "Avion," after which the more notable advances were made as shown above.

[Ill.u.s.tration: Plate II.]

The Henri Farman was the first widely used aeroplane. Above are shown the chief steps in its development.

[Ill.u.s.tration: Plate III.]

THE AVRO.--The aeroplane designed and built by Mr. A. V. Roe was the first successful heavier-than-air flying machine built by a British subject. Mr. Roe's progress may be followed in the picture, from his early "canard" biplane, through various triplanes, with 35 J.A.P. and 35 h.p. Green engines, to his successful tractor biplane with the same 35 h.p. Green, thence through the "totally enclosed" biplane 1912, with 60 h.p. Green, to the biplane 1913-14, with 80 h.p. Gnome.

[Ill.u.s.tration: Plate IV.]

THE SOPWITH LAND-GOING BIPLANES.--The earliest was a pair of Wright planes with a fuselage added. Next was the famous tractor with 80 h.p.

Gnome. Then the "tabloid" of 1913, which set a completely new fashion in aeroplane design. From this developed the Gordon-Bennett racer shown over date 1914. The gun-carrier was produced about the same time, and the later tractor biplane in a development of the famous 80 h.p. but with 100 h.p. monosoupape Gnome.

[Ill.u.s.tration: Plate V.]