The existing autogiro, although it may not resemble the more developed
types which will eventually appear, is the most successful moving-wing
flying-machine yet produced. Señor de la Cierva’s work was described
by an aeronautical engineer as being of secondary importance only
to that of the Wright brothers. That first flush of enthusiasm may
be over, but there seems little doubt that future generations will
regard Señor de la Cierva as the inventor of moving-wing flight. And
I believe that there will be a fierce battle, more prolonged and more
vigorous than has ever been fought between two machines, the battle
between moving-wing flight and fixed-wing flight. The struggle between
reciprocating engine and turbine, broad gauge and narrow gauge,
lighter-than-air and heavier-than-air, water-cooling and air-cooling
will be as nothing compared with the imminent struggle between
fixed-wing and moving-wing.
The autogiro obtains lift from a _free_, four-bladed windmill. Each
blade of the windmill is a wing and is articulated at the root so
that its tip can rise and fall. The autogiro is drawn forward by an
ordinary aero-engine and airscrew which are entirely separated from the
windmill. As the machine is drawn through the air the relative wind,
blowing on the blades or wings, rotates the windmill and it lifts the
machine. The wings rise and fall, and this beating motion gives the
machine a measure of stability.
To exert lift a wing must move through the air.
The moving-wing aircraft derives lift from wings which can move through
the air even though the body of the machine be stationary or nearly
stationary. In the fixed-wing aeroplane both body and wings must move
if the wings are to exert lift.
[Illustration:
Fig. 1.—Diagrammatic representation of moving-wing and fixed-wing
flight. The wings of both machines have travelled equal distances
AA and BB but the body of the moving wing machine has remained
stationary relative to the ground.
]
The difference between moving-wing and fixed-wing aircraft is so
important to this discussion that I shall venture to describe it again
in different words. A fixed-wing aircraft is like a bird with its wings
paralysed or in splints. A moving-wing aircraft is like a bird having
the full use of all its faculties. (Fig. 1).
Perhaps the most important advantage which the moving-wing aircraft has
over the fixed-wing aircraft is that it can virtually land on one spot.
The conventional aeroplane must move forward in still air if it is to
keep up; it must still move forward while landing, and afterwards allow
its impetus to be dissipated during a run along the ground.
In addition to this ability to land on a spot, the moving wing aircraft
is less likely to become uncontrollable while it is in the air. The
fixed-wing aircraft must become uncontrollable in the air if its speed
drops below a certain point. This point was called by airmen “the
stalling speed”. It has needed the mathematician to produce the phrase:
“control of stalled aeroplanes”. In current English a stalled aeroplane
is an aeroplane which is uncontrollable, even if the speed must drop to
zero before this condition arises. If any fixed stalling-_angle_ can be
said to exist outside technical reports, it is the angle at which the
lift of the wings is so reduced that the machine must fall to a nearly
vertical position before recovering.
The moving-wing aircraft in the rudimentary form we know it to-day
could stall, but it would need a major structural failure or violent
and prolonged misuse of the controls to make it do so.
And now one of the weapons which will be used in the battle which I
predict between the two main types of heavier-than-air flying machines
will be recognized. The weapon of the spot-landing.
Taking advantage of its special characteristics, the moving-wing
flying-machine within fifteen years will open hostilities by carrying
passengers into and from the hearts of cities and by running safely
through fog thick enough to stop other transport services. Up till
then the fixed-wing machine with its aerodromes on the outskirts of
cities will have held the field almost unchallenged. But whereas the
fixed-wing aircraft has now had twenty-two years development, the
moving-wing aircraft has had only about three years.
At first, even when it has matured, people will be shy of the
moving-wing machine, and only gradually will it begin to attract
passengers used to the other type.
Travellers will begin to realize that, when they go by fixed-wing
machines, they waste so much time and suffer so much discomfort in the
terminal communications that the advantages of the air-passage are
largely neutralized.
At present the air-traveller going from Paris to London spends one
and a half hours covering the few miles to and from the aerodromes to
the centres of the two cities and only two to two and a half hours
covering the 225 miles of the air-journey. Moreover, he changes
vehicles twice, at Croydon and at Le Bourget, as he does by boat and
train at Dover and at Calais. The aircraft’s ability to fly over land
and sea alike, therefore, has not given the traveller the advantage of
a through-journey. He must taxi from his hôtel in Paris to the place
where the air-company’s car starts, change from car to aeroplane at Le
Bourget, change from aeroplane to car at Croydon, and taxi from the
car’s stopping place to his home. (Fig. 2).
[Illustration:
Fig. 2.—Diagrammatic representation of the advantage in flexibility
of an aircraft capable of making spot landings and so of using small
aerodromes. Alone among vehicles it could provide a through journey
to the centres of cities.
]
The aeroplane dare not risk attempting the journey in thick fog or
heavy snow or hail because, in order to support itself, it must move
forward through the air at a minimum of say 60 miles per hour. At
this speed the pilot, even if aided by a leader-cable, has difficulty
in finding the aerodrome in thick weather; as much difficulty as a
motor-car-driver unable to go slower than 20 miles per hour would have
in crossing London in a dense fog.
If he thinks he catches a glimpse of a landmark, the pilot cannot stop
or slow down and look again to confirm his impression; he must continue
to travel at 60 m.p.h. And if he fail to find the aerodrome he must
endeavour to put down his machine—still travelling at 60 m.p.h.—on
an area of ground which he cannot see clearly and which he does not
know. If a house, ditch, hedge, tree, chimney, shed, road, telegraph
wire, pole, or other obstruction is in the way the result is a serious
accident.
The disadvantages under which the fixed-wing aircraft suffers when
landing and when flying during bad visibility are inherent in the
principle of flight it employs. The moving-wing machine will therefore
concentrate its attack at these very points. Since it is able to fly
slowly, and virtually to hover, it can feel its way through fairly
thick fog. Even if the pilot cannot find the aerodrome, comparatively
little danger attaches to a forced landing on unknown ground, because
the descent can be made vertically or almost vertically and there is
almost no run after touching the ground.
Aerodromes on the roofs of buildings have been foretold with tiresome
persistence. A Frenchman succeeded in landing a fixed-wing aeroplane
on a roof in Paris. Even so I cannot foresee roof-aerodromes for
fixed-wing aircraft, which is the purpose for which former prophets
have foreseen them; but I emphatically can foresee roof-aerodromes for
slow-landing, moving-wing aircraft.
Travellers going by future air-lines will take a taxi from their homes
to Charing Cross, step into a moving-wing machine on a roof-aerodrome,
fly to Paris, land on another roof-aerodrome near the Place de l’Opéra,
and take a taxi to their hotel.
I think it likely that, by the time it reaches maturity, the full
speed of the moving-wing aircraft will be below that of the fixed-wing
aircraft. But it will make up for this disadvantage by offering
travellers the advantages of eliminating terminal communications and
changes of vehicle. Part of the time it loses between Croydon and Le
Bourget it will regain between Croydon and Charing Cross and between Le
Bourget and the Place de l’Opéra. Moreover, on days when, through fog,
the fixed-wing aircraft-service is suspended, the moving-wing aircraft
will still operate.
By these means the moving-wing aircraft will become a formidable
competitor of the fixed-wing aircraft. How will the fixed-wing aircraft
reply to the attack?
It will make a supreme effort to increase its speed to such an extent
that it will offer to travellers a journey taking from door to door
only about two-thirds of the time occupied by the other type. To do
this the time lost in terminal communications by motor-car will, at
first, be partly recovered by extremely high flying speeds. The 250
miles per hour air-express will make its appearance. The wing-loading
of these machines will be high. Dr Rohrbach the German designer,
believes that great advantages accrue through high wing-loadings, and
in lectures and papers he has described at length the reasons for his
belief. In order to get these highly loaded machines off quickly and to
land them within an aerodrome of reasonable size, a form of catapult
launching apparatus and an arrester will be employed.
Catapult-launching has been proved, in England, America, Italy, and
France, to be practicable with fairly large aircraft. There is no
reason to suppose that its development will not continue.
An aircraft-arrester was described by Mr G. H. Dowty in a paper read
before the Institution of Aeronautical Engineers in October 1926.
It consisted in a drum having wound round it a length of cable. The
aeroplane, by some hook and line device similar to that used by Army
co-operation machines in picking up messages, will connect itself to
the end of the cable. The cable will rotate the drum against a brake,
and the aeroplane will be arrested. Mr Dowty calculates that a machine
travelling at 90 m.p.h. could by this means, be brought to a standstill
in 100 yards without an excessive strain being put on the machine’s
structure.
The chances of forced landings in these highly loaded fixed-wing
machines will be reduced to a negligible quantity by big reserves of
power and by providing that power through many engines.
In spite of the acceleration of the fixed-wing services made possible
by the use of these express-aeroplanes, the popularity of the
moving-wing services will continue to grow. The public will count time
well lost against the discomfort of changing twice and motoring long
distances through roads as inadequate for the traffic of that day as
the existing ones are for the traffic of this. They will continue to
take taxis to the Charing Cross roof-aerodrome when they want to travel
by air to Paris, York, Manchester, Glasgow, or Dublin.
The drifting of passengers to the moving-wing services will spur
the supporters of the fixed-wing services to devise another reply.
They will build motor speedways from Croydon reaching into the heart
of London and from all the other big aerodromes into the hearts of
the cities they serve. These speedways will have no side-turnings
or cross-roads. They will be forbidden to pedestrians, bicyclists,
lorries, ’buses, and similar vehicles. They will be hedged in on either
side like railway lines. The flat-footed influence of policeman and
politician will be excluded and along these tracks cars will carry
passengers to and from the aerodromes at 100 miles per hour. Assisted
by these tracks, the great speed of the fixed-wing services will
temporarily prevail, and a fair supply of passengers will be assured
although the moving-wing services will still flourish.
The position at this stage of the battle might be described as a
deadlock. The next stage will perhaps be the most remarkable of all.
It may have been noticed that, unlike most prophets, I have been
exceedingly modest in naming the distances over which these
future services will operate. While discussing the battle between
fixed-wing and moving-wing, instead of speaking of Empire services,
Globe-circling airlines, or non-stop hemispherical flying expresses,
I have spoken of trivial routes like London-Paris and London-Glasgow.
I have not even mentioned London-Karachi, London-Melbourne, or
London-Montreal.
My modesty was only temporarily assumed. I am now about to throw it
off in order to describe what I believe will be the most important
development of the flying machine. This development will begin during
the latter part of the fixed-wing, _v._ moving-wing battle.