Aeroplanes - Early history of Flying.  Pages 1 2 3 4                                                           Home


Any alteration in the angle of the surface causes this centre of pressure to move forwards when the angle is re-
duced or speed increased, backwards when speed falls or the resistance is augmented. At the same time the
centre of gravity of the system remains fixed.  It is this constant shifting of the centre of pressure which forms
the chief obstacle to stability in flight; for perfect stability the centres of gravity and pressure should always coin-
cide.  In order to re-establish equilibrium between the two, the aeroplane is provided with a tail or other supple-
mentary stability surfaces.  Thus, nowadays, stability  is established by altering the centre of pressure (a method
introduced by Chanute and the Brothers Wright) instead of the former dangerous method of altering the centre
of gravity (Lilienthal, etc).

                                                               
Images. 1)Wilbur Wright. 2) Orville Wright 3)One of the first flights, 120 feet in 12 seconds, 10:35 a.m.;
Kitty Hawk, North Carolina. Orville Wright at the controls of the machine, lying prone on the lower wing with
hips in the cradle which operated the wing-warping mechanism. Wilbur Wright running alongside to balance
the machine, has just released his hold on the forward upright of the right wing. The starting rail, the wing-rest,
a coil box, and other items needed for flight preparation are visible behind the machine.

The curve or camber of aeroplane surfaces is usually parabolic, the leading edge being relatively thick and blunt,
and tapering gradually off the trailing edge to ensure an even flow of air.  In some cases the leading edge is inclined
at a distinct negative angle (Phillips, Hargrave, Dunne, and in many birds' wings).  The depth of the curve is in
inverse proportion to the size of the carrying surface.
Monoplanes consequently have a deeper curve than biplanes; and the general tendency in modern design is to
reduce both curvature and angle of incidence.

Flanders monoplane.
A Flanders monoplane undertaking experiments at Farnborough and Brooklands was the first service aircraft with
radio in United Kingdom. The aircraft was fitted with a Marconi 6V battery-operated tuned-spark transmitter.

The greatest pressure, and therefore the chief lifting-force, being situated near the forward edge, whereas the rear
portion does comparatively little word, aeroplanes must consequently possess their greatest dimension transver-
sely to the direction of flight.  In practice, the span of aeroplane surfaces compared to their fore-and-aft dimension
is about 6 to 1.In order to prevent too great a span, which would lead to constructional difficulties, F.H. Wenham
first proposed, in 1866, to use two or more surfaces superposed at suitable distances. This has lead later experi-
menters to build biplanes, triplanes, and multiplanes, as distinguised from the monoplane or single-surface
aeroplane.

Image. Bleriot monoplane.

An important consideration in aeroplane design is the position of the centre of gravity.  In the earliest designs the
centre of gravity was placed as low as pollible, with a view to producing stability on the pendulum principle.
This method has been gradually abandoned in favour of the sounder principle of disposing the centre of gravity
approximately in the same plane as the centre of thrust and in the line of resistance.  Some designers, in fact,
place the centre of gravity above the centre of resistance (Esnault-Pelterie, etc).
A low centre of gravity has an injurious effect while the aeroplane is describing a turning movement - i.e. when
the machine is 'banked'.

For the maintenance of stability supplementary surfaces are carried.  For preserving longitudinal stability a tail
is added, consisting of one or more fixed horizontal surfaces.  In order to obtain sufficient leverage for counter-
acting injurious alterations in the centre of pressure on the main planes, this tail must be situated as far as
possible from the main surfaces (some machines, such as the early Wright type, were not provided  with a tail,
but in their case the forward elevator, carried well out to the front, fulfilled the same functions.)  For maintaining
lateral stability threee devices arre employed.  (1) The main surfaces are raised at the lateral extremities, forming
a dihedral angle.  First proposed by Cayley and lter adopted by Langley, this method has since been rejected
as unsatisfactory. (2) By 'warping' the rear extremity of the main surfaces - i.e. by twisting them so that one is
raised while the other is depressed (first practically employed by the Brothers Wright). (3) A modification of
(2), in which small balancing planes or flaps are employed.  This device, first utilized by Blériot and Farman, has
since come into general use.  Steering to right and left is effected by means of an ordinary vertical rudder, usually
carried on the tail, and often assisted in its action by the operation of the above methods of control.  Steering in
the vertical plane is effected by means of a horizontal rudder or elevator, fitted either to the tail or carried in front
of the main surfaces.  There is a growing tendency to carry two elevators, one in front and one in the rear, working
in conjunction (Maxim, Farman, later Wright type).

The aeroplane may be started into the air by two different methods.  In the former, due to the Wrights, the machine,
provided with runners or skids, is shot along a temporary rail by the action of a heavy weight caused to fall from
a tower or derrick.  The second method, originating in France, is to run the machine on wheels along the ground
until it has gained sufficient velocity to rise, which is often accomplished within less than 100ft.  For landing,
the majority of aeroplanes are provided, in addition to wheels, with skids to take the shock.

Forward motion is obtained by one or more propellers driven by an internal combustion motor.  In the majority of
monoplanes the propeller revolves in front of the carrying surface; in the greater number of biplanes in the rear,
its position being determined by structural consideration.  Twin propellers arre more rarely used.

Occasionally metal is employed in the construction of propellers; more often wood.  The diameter varies from
6 to 8ft., the number of revolutions from 600 to 1,500 per minute.  The motive power varies from 20 to 100 H.P.,
the average being somewhere near 50 H.P., but there seems little room for doubt that this average will be very
considerably reduced as time goes on.  An aeroplane designed to carry a single passenger is obviously
highly overpowered with an engine developing more than 20 H.P.,  at the same time, for large machines carrying
a greater number of passengers, 100 H.P.,  is not excessive.  Powerful engines will undoubtedly be employed,
since any increase in speed above the average required an excess of power beyound all proportion to the
results attained.

With the exception of the driving mechanism, wood is the chief material employed in aeroplane construction,
the tougher and lighter varieties only being used.  Spruce, hickory, and ash are perhaps the most frequent
materials for the framework.  Weight for weight, the best qualities of these woods are undoubtedly greatly
superior in strength to the finest metals, besides being more suitable in other respects for aeroplance
construction.  Practically all the woodwork employed is of fusiform section, with a blunt entering edge
tapering towards the rear.

The framework of the main planes usually consists of two or more main transverse spars, on which the
longitudinal curved ribs are built up.  The planes are double-surfaced: fabric being tightly stretched over the
upper as well as the lower surface, the upper surface as a rule having the greater camber.  Great care is
taken to make both surfaces as smooth as possible, since any irregularity sets up great resistance.

In a biplane the upper and lower planes are connected by means of vertical struts, strongly cross-braced with
piano wire; the whole skeleton forming a fairly rigid girder.  The body, or fuselage, is built in the same fashion,
and forms a rigid trussed girder on which the tail and steering surfaces are mounted on a chassis, or carriage,
rolling on pneumatic-tyred wheels protected by skids.  The fabric for covering the surfaces is usually
rubberproofed to render it impervious to air, and to protect it from moisture.  Generally, the body is also covered
in with fabric so as the diminish air-resistance to the lowest possible degree. Modern design tends as far as
possible to eliminate wires in construction, since their vibration, in flight, produces enormous head-resistance.
In this particular the bi-plane suffers from a disadvantage compared to the monoplane, in which the only wires
employed are those used to stay the wings, and even for this purpose steel ribbons are often substituted.