The Aeroplane Speaks
by
H. Barber
Part 1 out of 3
Scanned by Charles Keller with OmniPage Professional OCR software
THE AEROPLANE SPEAKS
BY H. BARBER
(CAPTAIN, ROYAL FLYING CORPS)
DEDICATED TO THE SUBALTERN FLYING OFFICER
MOTIVE
The reasons impelling me to write this book, the maiden
effort of my pen, are, firstly, a strong desire to help the
ordinary man to understand the Aeroplane and the joys
and troubles of its Pilot; and, secondly, to produce something
of PRACTICAL assistance to the Pilot and his invaluable assistant
the Rigger. Having had some eight years' experience in
designing, building, and flying aeroplanes, I have hopes
that the practical knowledge I have gained may offset the
disadvantage of a hand more used to managing the ``joy-
stick'' than the dreadful haltings, the many side-slips, the
irregular speed, and, in short, the altogether disconcerting
ways of a pen.
The matter contained in the Prologue appeared in the
Field of May 6th, 13th, 20th, and 27th, 1916, and is now
reprinted by the kind permission of the editor, Sir Theodore
Cook.
I have much pleasure in also acknowledging the kindness
of Mr. C. G. Grey, editor of the Aeroplane, to whom I am
indebted for the valuable illustrations reproduced at the
end of this book.
CONTENTS
PROLOGUE
PART
I. THE ELEMENTARY PRINCIPLES AIR THEIR GRIEVANCES
II. THE PRINCIPLES, HAVING SETTLED THEIR DIFFERENCES, FINISH THE JOB
III. THE GREAT TEST
IV. CROSS COUNTRY
CHAPTER
I. FLIGHT
II. STABILITY AND CONTROL
III. RIGGING
IV. PROPELLERS
V. MAINTENANCE
TYPES OF AEROPLANES
GLOSSARY
THE AEROPLANE SPEAKS
PROLOGUE
PART I
THE ELEMENTARY PRINCIPLES AIR THEIR GRIEVANCES
The Lecture Hall at the Royal Flying Corps School for
Officers was deserted. The pupils had dispersed, and the
Officer Instructor, more fagged than any pupil, was out on
the aerodrome watching the test of a new machine.
Deserted, did I say? But not so. The lecture that day
had been upon the Elementary Principles of Flight, and
they lingered yet. Upon the Blackboard was the illustration
you see in the frontispiece.
``I am the side view of a Surface,'' it said, mimicking
the tones of the lecturer. ``Flight is secured by driving me
through the air at an angle inclined to the direction of
motion.''
``Quite right,'' said the Angle. ``That's me, and I'm
the famous Angle of Incidence.''
``And,'' continued the Surface, ``my action is to deflect
the air downwards, and also, by fleeing from the air behind,
to create a semi-vacuum or rarefied area over most of the
top of my surface.''
``This is where I come in,'' a thick, gruff voice was
heard, and went on: ``I'm the Reaction. You can't have
action without me. I'm a very considerable force, and my
direction is at right-angles to you,'' and he looked heavily
at the Surface. ``Like this,'' said he, picking up the chalk
with his Lift, and drifting to the Blackboard.
``I act in the direction of the arrow R, that is, more or
less, for the direction varies somewhat with the Angle of
Incidence and the curvature of the Surface; and, strange
but true, I'm stronger on the top of the Surface than at
the bottom of it. The Wind Tunnel has proved that by
exhaustive research--and don't forget how quickly I can
grow! As the speed through the air increases my strength
increases more rapidly than you might think--approximately,
as the Square of the Speed; so you see that if the Speed of
the Surface through the air is, for instance, doubled, then
I am a good deal more than doubled. That's because I
am the result of not only the mass of air displaced, but also
the result of the Speed with which the Surface engages
the Air. I am a product of those two factors, and at the
speeds at which Aeroplanes fly to-day, and at the altitudes
and consequent density of air they at present experience,
I increase at about the Square of the Speed.
``Oh, I'm a most complex and interesting personality, I
assure you--in fact, a dual personality, a sort of aeronautical
Dr. Jekyll and Mr. Hyde. There's Lift, my vertical part or
COMPONENT, as those who prefer long words would say; he
always acts vertically upwards, and hates Gravity like poison.
He's the useful and admirable part of me. Then there's Drift,
my horizontal component, sometimes, though rather erroneously,
called Head Resistance; he's a villain of the deepest
dye, and must be overcome before flight can be secured.''
``And I,'' said the Propeller, ``I screw through the air and
produce the Thrust. I thrust the Aeroplane through the air
and overcome the Drift; and the Lift increases with the Speed
and when it equals the Gravity of Weight, then--there you
are--Flight! And nothing mysterious about it at all.''
``I hope you'll excuse me interrupting,'' said a very
beautiful young lady, ``my name is Efficiency, and, while
no doubt, all you have said is quite true, and that, as my
young man the Designer says, `You can make a tea-tray
fly if you slap on Power enough,' I can assure you that I'm
not to be won quite so easily.''
``Well,'' eagerly replied the Lift and the Thrust, ``let's
be friends. Do tell us what we can do to help you to overcome
Gravity and Drift with the least possible Power. That
obviously seems the game to play, for more Power means
heavier engines, and that in a way plays into the hands of
our enemy, Gravity, besides necessitating a larger Surface
or Angle to lift the Weight, and that increases the Drift.''
``Very well,'' from Efficiency, ``I'll do my best, though
I'm so shy, and I've just had such a bad time at the Factory,
and I'm terribly afraid you'll find it awefully dry.''
``Buck up, old dear!'' This from several new-comers,
who had just appeared. ``We'll help you,'' and one of
them, so lean and long that he took up the whole height of
the lecture room, introduced himself.
``I'm the High Aspect Ratio,'' he said, ``and what we
have got to do to help this young lady is to improve the
proportion of Lift to Drift. The more Lift we can get for a
certain area of Surface, the greater the Weight the latter
can carry; and the less the Drift, then the less Thrust and
Power required to overcome it. Now it is a fact that, if
the Surface is shaped to have the greatest possible span,
i.e., distance from wing-tip to wing-tip, it then engages more
air and produces both a maximum Reaction and a better
proportion of Lift to Drift.
``That being so, we can then well afford to lose a little
Reaction by reducing the Angle of Incidence to a degree
giving a still better proportion of Lift to Drift than would
otherwise be the case; for you must understand that the
Lift-Drift Ratio depends very much upon the size of the
Angle of Incidence, which should be as small as possible
within certain limits. So what I say is, make the surface of
Infinite Span with no width or chord, as they call it. That's
all I require, I assure you, to make me quite perfect and of
infinite service to Miss Efficiency.''
``That's not practical politics,'' said the Surface. ``The
way you talk one would think you were drawing L400 a
year at Westminster, and working up a reputation as an
Aeronautical Expert. I must have some depth and chord
to take my Spars and Ribs, and again, I must have a certain
chord to make it possible for my Camber (that's curvature)
to be just right for the Angle of Incidence. If that's not
right the air won't get a nice uniform compression and
downward acceleration from my underside, and the rarefied
`suction' area over the top of me will not be as even and clean
in effect as it might be. That would spoil the Lift-Drift Ratio
more than you can help it. Just thrust that chalk along, will
you? and the Blackboard will show you what I mean.''
``Well,'' said the Aspect Ratio, ``have it your own way,
though I'm sorry to see a pretty young lady like Efficiency
compromised so early in the game.''
``Look here,'' exclaimed a number of Struts, ``we have
got a brilliant idea for improving the Aspect Ratio,'' and
with that they hopped up on to the Spars. ``Now,'' excitedly,
``place another Surface on top of us. Now do you
see? There is double the Surface, and that being so, the
proportion of Weight to Surface area is halved. That's
less burden of work for the Surface, and so the Spars need
not be so strong and so deep, which results in not so thick
a Surface. That means the Chord can be proportionately
decreased without adversely affecting the Camber. With
the Chord decreased, the Span becomes relatively greater,
and so produces a splendid Aspect Ratio, and an excellent
proportion of Lift to Drift.''
``I don't deny that they have rather got me there,''
said the Drift, ``but all the same, don't forget my increase
due to the drift of the Struts and their bracing wires.''
``Yes, I dare say,'' replied the Surface, ``but remember
that my Spars are less deep than before, and consequently I
am not so thick now, and shall for that reason also be able
to go through the air with a less proportion of Drift to Lift.''
``Remember me also, please,'' croaked the Angle of
Incidence. ``Since the Surface has now less weight to carry
for its area, I may be set at a still lesser and finer Angle.
That means less Drift again. We are certainly getting on
splendidly! Show us how it looks now, Blackboard.'' And
the Blackboard obligingly showed them as follows:
``Well, what do you think of that?'' they all cried to the
Drift.
``You think you are very clever,'' sneered the Drift.
``But you are not helping Efficiency as much as you think.
The suction effect on the top of the lower Surface will give
a downward motion to the air above it and the result will
be that the bottom of the top Surface will not secure as good
a Reaction from the air as would otherwise be the case,
and that means loss of Lift; and you can't help matters
by increasing the gap between the surfaces because that
means longer Struts and Wires, and that in itself would
help me, not to speak of increasing the Weight. You see
it's not quite so easy as you thought.''
At this moment a hiccough was heard, and a rather fast
and rakish-looking chap, named Stagger, spoke up. ``How
d'ye do, miss,'' he said politely to Efficiency, with a side
glance out of his wicked old eye. ``I'm a bit of a knut,
and without the slightest trouble I can easily minimize
the disadvantage that old reprobate Drift has been frightening
you with. I just stagger the top Surface a bit forward,
and no longer is that suction effect dead under it. At the
same time I'm sure the top Surface will kindly extend its
Span for such distance as its Spars will support it without
the aid of Struts. Such extension will be quite useful, as
there will be no Surface at all underneath it to interfere
with the Reaction above.'' And the Stagger leaned
forward and picked up the Chalk, and this is the picture
he drew:
Said the Blackboard, ``That's not half bad! It really
begins to look something like the real thing, eh?''
``The real thing, is it?'' grumbled Drift. ``Just consider
that contraption in the light of any one Principle, and I
warrant you will not find one of them applied to perfection.
The whole thing is nothing but a Compromise.'' And he
glared fixedly at poor Efficiency.
``Oh, dear! Oh, dear!'' she cried. ``I'm always getting
into trouble. What WILL the Designer say?''
``Never mind, my dear,'' said the Lift-Drift Ratio,
consolingly. ``You are improving rapidly, and quite useful
enough now to think of doing a job of work.''
``Well, that's good news,'' and Efficiency wiped her eyes
with her Fabric and became almost cheerful. ``Suppose
we think about finishing it now? There will have to be an
Engine and Propeller, won't there? And a body to fix
them in, and tanks for oil and petrol, and a tail, and,'' archly,
``one of those dashing young Pilots, what?''
``Well, we are getting within sight of those interesting
Factors,'' said the Lift-Drift Ratio, ``but first of all we
had better decide upon the Area of the Surfaces, their Angle
of Incidence and Camber. If we are to ascend as quickly
as possible the Aeroplane must be SLOW in order to secure
the best possible Lift-Drift Ratio, for the drift of the struts
wires, body, etc., increases approximately as the square
of the speed, but it carries with it no lift as it does in the
case of the Surface. The less speed then, the less such
drift, and the better the Aeroplane's proportion of lift to
drift; and, being slow, we shall require a LARGE SURFACE in
order to secure a large lift relative to the weight to be carried.
We shall also require a LARGE ANGLE OF INCIDENCE relative to
the horizontal, in order to secure a proper inclination of
the Surface to the direction of motion, for you must remember
that, while we shall fly upon an even keel and with
the propeller thrust horizontal (which is its most efficient
attitude), our flight path, which is our direction of motion,
will be sloping upwards, and it will therefore be necessary
to fix the Surface to the Aeroplane at a very considerable
angle relative to the horizontal Propeller Thrust in order to
secure a proper angle to the upwards direction of motion.
Apart from that, we shall require a larger Angle of Incidence
than in the case of a machine designed purely for speed,
and that means a correspondingly LARGE CAMBER.
``On the other hand, if we are thinking merely of Speed,
then a SMALL SURFACE, just enough to lift the weight off the
ground, will be best, also a SMALL ANGLE to cut the Drift down
and that, of course, means a relatively SMALL CAMBER.
``So you see the essentials for CLIMB or quick ascent and
for SPEED are diametrically opposed. Now which is it to be?''
``Nothing but perfection for me,'' said Efficiency. ``What
I want is Maximum Climb and Maximum Speed for the
Power the Engine produces.''
And each Principle fully agreed with her beautiful
sentiments, but work together they would not.
The Aspect Ratio wanted infinite Span, and hang the
Chord.
The Angle of Incidence would have two Angles and two
Cambers in one, which was manifestly absurd; the Surface
insisted upon no thickness whatever, and would not hear
of such things as Spars and Ribs; and the Thrust objected
to anything at all likely to produce Drift, and very nearly
wiped the whole thing off the Blackboard.
There was, indeed, the makings of a very pretty quarrel
when the Letter arrived. It was about a mile long, and
began to talk at once.
``I'm from the Inventor,'' he said, and hope rose in the
heart of each heated Principle. ``It's really absurdly simple.
All the Pilot has to do is to touch a button, and at his will,
VARY the area of the Surface, the Angle of Incidence,
and the Camber! And there you are--Maximum Climb or
Maximum Speed as required! How does that suit you?''
``That suits us very well,'' said the Surface, ``but, excuse
me asking, how is it done without apparatus increasing the
Drift and the Weight out of all reason? You won't mind
showing us your Calculations, Working Drawings, Stress
Diagrams, etc., will you?''
Said the Letter with dignity, ``I come from an Inventor
so brilliantly clever as to be far above the unimportant
matters you mention. He is no common working man,
sir! He leaves such things to Mechanics. The point is, you
press a button and----''
``Look here,'' said a Strut, rather pointedly, ``where do
you think you are going, anyway?''
``Well,'' from the Letter, ``as a matter of fact, I'm not
addressed yet, but, of course, there's no doubt I shall reach
the very highest quarters and absolutely revolutionize Flight
when I get there.''
Said the Chalk, ``I'll address you, if that's all you want;
now drift along quickly!'' And off went the Letter to The
Technical Editor, ``Daily Mauler,'' London.
And a League was formed, and there were Directors with
Fees, and several out-of-service Tin Hats, and the Man-who-
takes-the-credit, and a fine fat Guinea-pig, and all the rest
of them. And the Inventor paid his Tailor and had a Hair-
Cut, and is now a recognized Press Expert--but he is still
waiting for those Mechanics!
``I'm afraid,'' said the Slide-rule, who had been busy
making those lightning-like automatic calculations for which
he is so famous, ``it's quite impossible to fully satisfy all of
you, and it is perfectly plain to me that we shall have to effect
a Compromise and sacrifice some of the Lift for Speed.''
Thud! What was that?
Efficiency had fainted dead away! The last blow had
been too much for her. And the Principles gathered mournfully
round, but with the aid of the Propeller Slip[[1]] and a
friendly lift from the Surface she was at length revived and
regained a more normal aspect.
[[1]] Propeller Slip: As the propeller screws through the air,
the latter to a certain extent gives back to the thrust of the
propellor blades, just as the shingle on the beach slips back
as you ascend it. Such ``give-back'' is known as ``slip,''
and anyone behind the propellor will feel the slip as a
strong draught of air.
Said the Stagger with a raffish air, ``My dear young lady,
I assure you that from the experiences of a varied career,
I have learned that perfection is impossible, and I am sure
the Designer will be quite satisfied if you become the Most
Efficient Compromise.''
``Well, that sounds so common sense,'' sighed Efficiency,
``I suppose it must be true, and if the Designer is satisfied,
that's all I really care about. Now do let's get on with the job.''
So the Chalk drew a nice long slim body to hold the
Engine and the tanks, etc., with room for the Pilot's and
Passenger's seats, and placed it exactly in the middle of the
Biplane. And he was careful to make its position such that
the Centre of Gravity was a little in advance of the Centre
of Lift, so that when the Engine was not running and there
was consequently no Thrust, the Aeroplane should be ``nose-
heavy'' just to the right degree, and so take up a natural
glide to Earth--and this was to help the Pilot and relieve
him of work and worry, should he find himself in a fog or
a cloud. And so that this tendency to glide downwards
should not be in evidence when the Engine was running and
descent not desired, the Thrust was placed a little below
the Centre of Drift or Resistance. In this way it would in
a measure pull the nose of the Aeroplane up and counterbalance
the ``nose-heavy'' tendency.
And the Engine was so mounted that when the Propeller-
Thrust was horizontal, which is its most efficient position,
the Angle of Incidence and the Area of the surfaces were
just sufficient to give a Lift a little in excess of the Weight.
And the Camber was such that, as far as it was concerned,
the Lift-Drift Ratio should be the best possible for that Angle
of Incidence. And a beautifully simple under-carriage was
added, the outstanding features of which were simplicity,
strength, light-weight, and minimum drift. And, last of
all, there was the Elevator, of which you will hear more
by-and-by. And this is what it looked like then:
And Efficiency, smiling, thought that it was not such a
bad compromise after all and that the Designer might well
be satisfied.
``Now,'' said she, ``there's just one or two points I'm
a bit hazy about. It appears that when the Propeller shaft
is horizontal and so working in its most efficient attitude,
I shall have a Lift from the Surfaces slightly in excess of the
Weight. That means I shall ascend slightly, at the same time
making nearly maximum speed for the power and thrust.
Can't I do better than that?''
``Yes, indeed,'' spoke up the Propeller, ``though it means
that I must assume a most undignified attitude, for helicopters[[2]]
I never approved of. In order to ascend more
quickly the Pilot will deflect the Elevator, which, by the
way, you see hinged to the Tail. By that means he will
force the whole Aeroplane to assume a greater Angle of
Incidence. And with greater Angle, the Lift will increase,
though I'm sorry to say the Drift will increase also. Owing
to the greater Drift, the Speed through the air will lessen,
and I'm afraid that won't be helpful to the Lift; but I shall
now be pointing upwards, and besides overcoming the Drift
in a forward direction I shall be doing my best to haul
the Aeroplane skywards. At a certain angle known as the
Best Climbing Angle, we shall have our Maximum Margin
of Lift, and I'm hoping that may be as much as almost a
thousand feet altitude a minute.''
[[2]] Helicopter. An air-screw revolving upon a vertical axis.
If driven with sufficient power, it will lift vertically,
but having regard to the mechanical difficulties of such construction,
it is a most inefficient way of securing lift compared with the
arrangement of an inclined surface driven by a propeller
revolving about a horizontal axis.
``Then, if the Pilot is green, my chance will come,'' said
the Maximum Angle of Incidence. ``For if the Angle is
increased over the Best Climbing Angle, the Drift will rush
up; and the Speed, and with it the Lift, will, when my
Angle is reached, drop to a point when the latter will be no
more than the Weight. The Margin of Lift will have
entirely disappeared, and there we shall be, staggering
along at my tremendous angle, and only just maintaining
horizontal flight.''
``And then with luck I'll get my chance,'' said the Drift.
``If he is a bit worse than green, he'll perhaps still further
increase the Angle. Then the Drift, largely increasing, the
Speed, and consequently the Lift, will become still less,
i.e., less than the Weight, and then--what price pancakes,[[3]]
eh?''
[[3]] Pancakes: Pilot's slang for stalling an aeroplane
and dropping like a pancake.
``Thank you,'' from Efficiency, ``that was all most
informing. And now will you tell me, please, how the
greatest Speed may be secured?''
``Certainly, now it's my turn,'' piped the Minimum Angle
of Incidence. ``By means of the Elevator, the Pilot places
the Aeroplane at my small Angle, at which the Lift only
just equals the Weight, and, also, at which we shall make
greater speed with no more Drift than before. Then we get
our greatest Speed, just maintaining horizontal flight.''
``Yes; though I'm out of the horizontal and thrusting
downwards,'' grumbled the Propeller, ``and that's not
efficient, though I suppose it's the best we can do until that
Inventor fellow finds his Mechanics.''
``Thank you so much,'' said Efficiency. ``I think I have
now at any rate an idea of the Elementary Principles of
Flight, and I don't know that I care to delve much deeper,
for sums always give me a headache; but isn't there something
about Stability and Control? Don't you think I ought
to have a glimmering of them too?''
``Well, I should smile,'' said a spruce Spar, who had come
all the way from America. ``And that, as the Lecturer
says, `will be the subject of our next lecture,' so be here
again to-morrow, and you will be glad to hear that it will be
distinctly more lively than the subject we have covered
to-day.''
PART II
THE PRINCIPLES, HAVING SETTLED THEIR DIFFERENCES,
FINISH THE JOB
Another day had passed, and the Flight Folk had again
gathered together and were awaiting the arrival of Efficiency
who, as usual, was rather late in making an appearance.
The crowd was larger than ever, and among the newcomers
some of the most important were the three Stabilities,
named Directional, Longitudinal, and Lateral, with
their assistants, the Rudder, Elevator, and Ailerons. There
was Centrifugal Force, too, who would not sit still and
created a most unfavourable impression, and Keel-Surface,
the Dihedral Angle, and several other lesser fry.
``Well,'' said Centrifugal Force, ``I wish this Efficiency
I've heard so much about would get a move on. Sitting
still doesn't agree with me at all. Motion I believe in.
There's nothing like motion--the more the better.''
``We are entirely opposed to that,'' objected the three
Stabilities, all in a breath. ``Unless it's in a perfectly
straight line or a perfect circle. Nothing but perfectly
straight lines or, upon occasion, perfect circles satisfy us,
and we are strongly suspicious of your tendencies.''
``Well, we shall see what we shall see,'' said the Force
darkly. ``But who in the name of blue sky is this?''
And in tripped Efficiency, in a beautifully ``doped''
dress of the latest fashionable shade of khaki-coloured
fabric, a perfectly stream-lined bonnet, and a bewitching
little Morane parasol,[[4]] smiling as usual, and airily exclaiming,
``I'm so sorry I'm late, but you see the Designer's
such a funny man. He objects to skin friction,[[5]] and insisted
upon me changing my fabric for one of a smoother
surface, and that delayed me. Dear me, there are a lot
more of us to-day, aren't there? I think I had better meet
one at a time.'' And turning to Directional Stability, she
politely asked him what he preferred to do.
[[4]] Morane parasol: A type of Morane monoplane in which the
lifting surfaces are raised above the pilot in order to afford
him a good view of the earth.
[[5]] Skin friction is that part of the drift due to the friction
of the air with roughnesses upon the surface of the aeroplane.
``My purpose in life, miss,'' said he, ``is to keep the Aeroplane
on its course, and to achieve that there must be, in
effect, more Keel-Surface behind the Vertical Turning Axis
than there is in front of it.''
Efficiency looking a little puzzled, he added: ``Just like
a weathercock, and by Keel-Surface I mean everything
you can see when you view the Aeroplane from the side of
it--the sides of the body, struts, wires, etc.''
``Oh, now I begin to see light,'' said she: ``but just
exactly how does it work?''
``I'll answer that,'' said Momentum. ``When perhaps
by a gust of air the Aeroplane is blown out of its course
and points in another direction, it doesn't immediately
fly off on that new course. I'm so strong I pull it off the
new course to a certain extent, and towards the direction
of the old course. And so it travels, as long as my strength
lasts, in a more or less sideways position.''
``Then,'' said the Keel-Surface, ``I get a pressure of
air all on one side, and as there is, in effect, most of me
towards the tail, the latter gets pressed sideways, and the
Aeroplane thus tends to assume its first position and course.''
``I see,'' said Efficiency, and, daintily holding the Chalk,
she approached the Blackboard. ``Is this what you mean?''
``Yes, that's right enough,'' said the Keel-Surface, ``and
you might remember, too, that I always make the Aeroplane
nose into the gusts rather than away from them.''
``If that was not the case,'' broke in Lateral Stability,
and affecting the fashionable Flying Corps stammer, ``it
would be a h-h-h-o-r-rible affair! If there were too much
Keel-Surface in front, then that gust would blow the Aeroplane
round the other way a very considerable distance.
And the right-hand Surface being on the outside of the turn
would have more speed, and consequently more Lift, than
the Surface on the other side. That means a greater proportion
of the Lift on that side, and before you could say
Warp to the Ailerons over the Aeroplane would go--probable
result a bad side-slip''
``And what can the Pilot do to save such a situation as
that?'' said Efficiency.
``Well,'' replied Lateral Stability, ``he will try to turn
the Aeroplane sideways and back to an even keel by means
of warping the Ailerons or little wings which are hinged
on to the Wing-tips, and about which you will hear more
later on; but if the side-slip is very bad he may not be able
to right the Aeroplane by means of the Ailerons, and then
the only thing for him to do is to use the Rudder and to turn
the nose of the Aeroplane down and head-on to the direction
of motion. The Aeroplane will then be meeting the air in
the direction it is designed to do so, and the Surfaces and
also the controls (the Rudder, Ailerons, and Elevator) will
be working efficiently; but its attitude relative to the earth
will probably be more or less upside-down, for the action
of turning the Aeroplane's nose down results, as you will
see by the illustration B, in the right wing, which is on the
outside of the circle. travelling through the air with greater
speed than the left-hand wing. More Speed means more
Lift, so that results in overturning the Aeroplane still more;
but now it is, at any rate, meeting the air as it is designed
to meet it, and everything is working properly. It is then
only necessary to warp the Elevator, as shown in illustration
C, in order to bring the Aeroplane into a proper attitude
relative to the earth.''
``Ah!'' said the Rudder, looking wise, ``it's in a case
like that when I become the Elevator and the Elevator
becomes me.''
``That's absurd nonsense,'' said the Blackboard, ``due
to looseness of thought and expression.''
``Well,'' replied the Rudder, ``when 'the Aeroplane is
in position A and I am used, then I depress or ELEVATE the nose
of the machine; and, if the Elevator is used, then it turns
the Aeroplane to right or left, which is normally my function.
Surely our roles have changed one with the other, and I'm
then the Elevator and the Elevator is me!''
Said Lateral Stability to the Rudder, ``That's altogether
the wrong way of looking at it, though I admit''--and
this rather sarcastically--``that the way you put it sounds
rather fine when you are talking of your experiences in
the air to those `interested in aviation' but knowing little
about it; but it won't go down here! You are a Controlling
Surface designed to turn the Aeroplane about its vertical
axis, and the Elevator is a Controlling Surface designed to
turn the Aeroplane about its lateral axis. Those are your
respective jobs, and you can't possibly change them about.
Such talk only leads to confusion, and I hope we shall hear
no more of it.''
``Thanks,'' said Efficiency to Lateral Stability. ``And
now, please, will you explain your duties?''
``My duty is to keep the Aeroplane horizontal from
Wing-tip to Wing-tip. First of all, I sometimes arrange
with the Rigger to wash-out, that is decrease, the Angle
of Incidence on one side of the Aeroplane, and to effect
the reverse condition, if it is not too much trouble, on the
other side.''
``But,'' objected Efficiency, ``the Lift varies with the
Angle of Incidence, and surely such a condition will result in
one side of the Aeroplane lifting more than the other side?'
``That's all right,'' said the Propeller, ``it's meant to
off-set the tendency of the Aeroplane to turn over sideways
in the opposite direction to which I revolve.''
``That's quite clear, though rather unexpected; but how
do you counteract the effect of the gusts when they try to
overturn the Aeroplane sideways?'' said she, turning to
Lateral Stability again.
``Well,'' he replied, rather miserably, ``I'm not nearly
so perfect as the Longitudinal and Directional Stabilities.
The Dihedral Angle--that is, the upward inclination of the
Surfaces towards their wing-tips--does what it can for me,
but, in my opinion, it's a more or less futile effort. The
Blackboard will show you the argument.'' And he at once
showed them two Surfaces, each set at a Dihedral Angle
like this:
``Please imagine,'' said the Blackboard, ``that the top
V is the front view of a Surface flying towards you. Now
if a gust blows it into the position of the lower V you see
that the horizontal equivalent of the Surface on one side
becomes larger, and on the other side it becomes smaller.
That results in more Lift on the lower side and less on the
higher side, and if the V is large enough it should produce
such a difference in the Lift of one side to the other as to
quickly turn the Aeroplane back to its former and normal
position.''
``Yes,'' said the Dihedral Angle, ``that's what would
happen if they would only make me large enough; but
they won't do it because it would too greatly decrease the
horizontal equivalent, and therefore the Lift, and incidentally
it would, as Aeroplanes are built to-day, produce
an excess of Keel Surface above the turning axis, and that
in itself would spoil the Lateral Stability. The Keel Surface
should be equally divided above and below the longitudinal
turning axis (upon which the Aeroplane rolls sideways),
or the side upon which there is an excess will get
blown over by the gusts. It strikes me that my future
isn't very promising, and about my only chance is when
the Junior Draughtsman makes a mistake, as he did the
other day. And just think of it, they call him a Designer
now that he's got a job at the Factory! What did he do?
Why, he calculated the weights wrong and got the Centre
of Gravity too high, and they didn't discover it until the
machine was built. Then all they could do was to give
me a larger Angle. That dropped the bottom of the V
lower down, and as that's the centre of the machine, where
all the Weight is, of course that put the Centre of Gravity
in its right place. But now there is too much Keel Surface
above, and the whole thing's a Bad Compromise, not at all
like Our Efficiency.''
And Efficiency, blushing very prettily at the compliment,
then asked, ``And how does the Centre of Gravity affect
matters?''
``That's easy,'' said Grandfather Gravity. ``I'm so
heavy that if I am too low down I act like a pendulum
and cause the Aeroplane to roll about sideways, and if I
am too high I'm like a stick balanced on your finger, and
then if I'm disturbed, over I go and the Aeroplane with
me; and, in addition to that, there are the tricks I play
with the Aeroplane when it's banked up,[[6]] i.e., tilted sideways
for a turn, and Centrifugal Force sets me going the
way I'm not wanted to go. No; I get on best with Lateral
Stability when my Centre is right on the centre of Drift,
or, at any rate, not much below it.'' And with that he
settled back into the Lecturer's Chair and went sound
asleep again, for he was so very, very old, in fact the father
of all the Principles.
[[6]] Banking: When an aeroplane is turned to the left or
the right the centrifugal force of its momentum causes it to
skid sideways and outwards away from the centre of the turn.
To minimize such action the pilot banks, i.e., tilts, the aeroplane
sideways in order to oppose the underside of the planes to the air.
The aeroplane will not then skid outwards beyond the slight skid
necessary to secure a sufficient pressure of air to balance the
centrifugal force.
And the Blackboard had been busy, and now showed
them a picture of the Aeroplane as far as they knew it, and
you will see that there is a slight Dihedral Angle, and
also, fixed to the tail, a vertical Keel Surface or fin, as
is very often the case in order to ensure the greater effect
of such surface being behind the vertical turning axis.
But Efficiency, growing rather critical with her newly
gained knowledge, cried out: ``But where's the horizontal
Tail Surface? It doesn't look right like that!''
``This is when I have the pleasure of meeting you, my
dear,'' said Longitudinal Stability. ``Here's the Tail Surface,''
he said, ``and in order to help me it must be set IN
EFFECT at a much less Angle of Incidence than the Main Surface.
To explain we must trouble the Blackboard again,'' and
this was his effort:
``I have tried to make that as clear as possible,'' he
said. ``It may appear a bit complicated at first, but if
you will take the trouble to look at it for a minute you will find
it quite simple. A is the normal and proper direction of
motion of the Aeroplane, but, owing to a gust of air, it takes
up the new nose-down position. Owing to Momentum,
however, it does not fly straight along in that direction, but
moves more or less in the direction B, which is the resultant
of the two forces, Momentum and Thrust. And so you will
note that the Angle of Incidence, which is the inclination
of the Surfaces to the Direction of Motion, has decreased,
and of course the Lift decreases with it. You will also see,
and this is the point, that the Tail Surface has lost a higher
proportion of its Angle, and consequently its Lift, than has
the Main Surface. Then, such being the case, the Tail must
fall and the Aeroplane assume its normal position again,
though probably at a slightly lower altitude.''
``I'm afraid I'm very stupid,'' said Efficiency, ``but
please tell me why you lay stress upon the words `IN
EFFECT.' ''
``Ah! I was wondering if you would spot that,'' he
replied. ``And there is a very good reason for it. You see,
in some Aeroplanes the Tail Surface may be actually set
at the same Angle on the machine as the Main Surface, but
owing to the air being deflected downwards by the front
Main Surface it meets the Tail Surface at a lesser angle,
and indeed in some cases at no angle at all. The Tail is then
for its surface getting less Lift than the Main Surface, although
set at the same angle on the machine. It may then be
said to have IN EFFECT a less Angle of Incidence. I'll just
show you on the Blackboard.''
``And now,'' said Efficiency, ``I have only to meet the
Ailerons and the Rudder, haven't I?''
``Here we are,'' replied the Ailerons, or little wings.
``Please hinge us on to the back of the Main Surfaces, one
of us at each Wing-tip, and join us up to the Pilot's joystick
by means of the control cables. When the Pilot wishes to
tilt the Aeroplane sideways, he will move the stick and depress
us upon one side, thus giving us a larger Angle of Incidence
and so creating more Lift on that side of the Aeroplane;
and, by means of a cable connecting us with the Ailerons on
the other side of the Aeroplane, we shall, as we are depressed,
pull them up and give them a reverse or negative Angle of
Incidence, and that side will then get a reverse Lift or downward
thrust, and so we are able to tilt the Aeroplane sideways.
``And we work best when the Angle of Incidence of the
Surface in front of us is very small, for which reason it is
sometimes decreased or washed-out towards the Wing-tips.
The reason of that is that by the time the air reaches us
it has been deflected downwards--the greater the Angle
of Incidence the more it is driven downwards--and in order
for us to secure a Reaction from it, we have to take such a
large Angle of Incidence that we produce a poor proportion
of Lift to Drift; but the smaller the Angle of the Surface in
front of us the less the air is deflected downwards, and
consequently the less Angle is required of us, and the better our
proportion of Lift to Drift, which, of course, makes us much
more effective Controls.''
``Yes,'' said the Lateral and Directional Stabilities in
one voice, ``that's so, and the wash-out helps us also, for
then the Surfaces towards their Wing-tips have less Drift
or `Head-Resistance,' and consequently the gusts will affect
them and us less; but such decreased Angle of Incidence
means decreased Lift as well as Drift, and the Designer does
not always care to pay the price.''
``Well,'' said the Ailerons, ``if it's not done it will mean
more work for the Rudder, and that won't please the Pilot.''
``Whatever do you mean?'' asked Efficiency. ``What
can the Rudder have to do with you?''
``It's like this,'' they replied: ``when we are deflected
downwards we gain a larger Angle of Incidence and also
enter an area of compressed air, and so produce more Drift
than those of us on the other side of the Aeroplane, which
are deflected upwards into an area of rarefied air due to
the SUCTION effect (though that term is not academically
correct) on the top of the Surface. If there is more Drift,
i.e., Resistance, on one side of the Aeroplane than on the other
side, then of course it will turn off its course, and if that
difference in Drift is serious, as it will very likely be if there
is no wash-out, then it will mean a good deal of work for the
Rudder in keeping the Aeroplane on its course, besides
creating extra Drift in doing so.''
``I think, then,'' said Efficiency, ``I should prefer to
have that wash-out,[[7]] and my friend the Designer is so clever
at producing strength of construction for light weight, I'm
pretty sure he won't mind paying the price in Lift. And
now let me see if I can sketch the completed Aeroplane.''
[[7]] An explanation of the way in which the wash-out is combined
with a wash-in to offset propellor torque will be found on p. 82.
``Well, I hope that's all as it should be,'' she concluded,
``for to-morrow the Great Test in the air is due.''
PART III
THE GREAT TEST
It is five o'clock of a fine calm morning, when the Aeroplane
is wheeled out of its shed on to the greensward of the Military
Aerodrome. There is every promise of a good flying day,
and, although the sun has not yet risen, it is light enough to
discern the motionless layer of fleecy clouds some five thousand
feet high, and far, far above that a few filmy mottled streaks
of vapour. Just the kind of morning beloved of pilots.
A brand new, rakish, up-to-date machine it is, of highly
polished, beautifully finished wood, fabric as tight as a
drum, polished metal, and every part so perfectly ``streamlined''
to minimize Drift, which is the resistance of the air
to the passage of the machine, that to the veriest tyro the
remark of the Pilot is obviously justified.
``Clean looking 'bus, looks almost alive and impatient
to be off. Ought to have a turn for speed with those
lines.''
``Yes,'' replies the Flight-Commander, ``it's the latest
of its type and looks a beauty. Give it a good test. A
special report is required on this machine.''
The A.M.'s[[8]] have now placed the Aeroplane in position
facing the gentle air that is just beginning to make itself
evident; the engine Fitter, having made sure of a sufficiency
of oil and petrol in the tanks, is standing by the Propeller;
the Rigger, satisfied with a job well done, is critically ``vetting''
the machine by eye, four A.M.'s are at their posts,
ready to hold the Aeroplane from jumping the blocks which
have been placed in front of the wheels; and the Flight-
Sergeant is awaiting the Pilot's orders.
[[8]] A.M.'s: Air Mechanics.
As the Pilot approaches the Aeroplane the Rigger springs
to attention and reports, ``All correct, sir,'' but the Fitter
does not this morning report the condition of the Engine,
for well he knows that this Pilot always personally looks
after the preliminary engine test. The latter, in leathern
kit, warm flying boots and goggled, climbs into his seat,
and now, even more than before, has the Aeroplane an almost
living appearance, as if straining to be off and away. First
he moves the Controls to see that everything is clear, for
sometimes when the Aeroplane is on the ground the control
lever or ``joy-stick'' is lashed fast to prevent the wind
from blowing the controlling surfaces about and possibly
damaging them.
The air of this early dawn is distinctly chilly, and the
A.M.'s are beginning to stamp their cold feet upon the dewy
grass, but very careful and circumspect is the Pilot, as he
mutters to himself, ``Don't worry and flurry, or you'll die
in a hurry.''
At last he fumbles for his safety belt, but with a start
remembers the Pilot Air Speed Indicator, and, adjusting
it to zero, smiles as he hears the Pilot-head's gruff voice,
``Well, I should think so, twenty miles an hour I was registering.
That's likely to cause a green pilot to stall the Aeroplane.
Pancake, they call it.'' And the Pilot, who is an
old hand and has learned a lot of things in the air that mere
earth-dwellers know nothing about, distinctly heard the
Pilot Tube, whose mouth is open to the air to receive its
pressure, stammer. ``Oh Lor! I've got an earwig already--
hope to goodness the Rigger blows me out when I come
down--and this morning air simply fills me with moisture;
I'll never keep the Liquid steady in the Gauge. I'm not
sure of my rubber connections either.''
``Oh, shut up!'' cry all the Wires in unison, ``haven't
we got our troubles too? We're in the most horrible state
of tension. It's simply murdering our Factor of Safety,
and how we can possibly stand it when we get the Lift only
the Designer knows.''
``That's all right,'' squeak all the little Wire loops,
``we're that accommodating, we're sure to elongate a bit
and so relieve your tension.'' For the whole Aeroplane is
braced together with innumerable wires, many of which
are at their ends bent over in the form of loops in order to
connect with the metal fittings on the spars and elsewhere--
cheap and easy way of making connection.
``Elongate, you little devils, would you?'' fairly shout
the Angles of Incidence, Dihedral and Stagger, amid a chorus
of groans from all parts of the Aeroplane. ``What's going
to happen to us then? How are we going to keep our
adjustments upon which good flying depends?''
``Butt us and screw us,''[[9]] wail the Wires. ``Butt us
and screw us, and death to the Loops. That's what we
sang to the Designer, but he only looked sad and scowled
at the Directors.''
[[9]] Butt means to thicken at the end. Screw means to machine a thread
on the butt-end of the wire, and in this way the wire can make connection
with the desired place by being screwed into a metal fitting,
thus eliminating the disadvantage of the unsatisfactory loop.
``And who on earth are they?'' asked the Loops, trembling
for their troublesome little lives.
``Oh earth indeed,'' sniffed Efficiency, who had not
spoken before, having been rendered rather shy by being
badly compromised in the Drawing Office. ``I'd like to
get some of them up between Heaven and Earth, I would.
I'd give 'em something to think of besides their Debits
and Credits--but all the same the Designer will get his
way in the end. I'm his Best Girl, you know, and if we
could only get rid of the Directors, the little Tin god, and
the Man-who-takes-the-credit, we should be quite happy.''
Then she abruptly subsides, feeling that perhaps the less
said the better until she has made a reputation in the Air.
The matter of that Compromise still rankled, and indeed
it does seem hardly fit that a bold bad Tin god should flirt
with Efficiency. You see there was a little Tin god, and he
said ``Boom, Boom BOOM! Nonsense! It MUST be done,''
and things like that in a very loud voice, and the Designer
tore his hair and was furious, but the Directors, who were
thinking of nothing but Orders and Dividends, had the
whip-hand of HIM, and so there you are, and so poor beautiful
Miss Efficiency was compromised.
All this time the Pilot is carefully buckling his belt and
making himself perfectly easy and comfortable, as all good
pilots do. As he straightens himself up from a careful
inspection of the Deviation Curve[[10]] of the Compass and takes
command of the Controls, the Throttle and the Ignition,
the voices grow fainter and fainter until there is nothing
but a trembling of the Lift and Drift wires to indicate to his
understanding eye their state of tension in expectancy of
the Great Test.
[[10]] Deviation curve: A curved line indicating any errors in the compass.
``Petrol on?'' shouts the Fitter to the Pilot.
``Petrol on,'' replies the Pilot.
``Ignition off?''
``Ignition off.''
Round goes the Propeller, the Engine sucking in the
Petrol Vapour with satisfied gulps. And then--
``Contact?'' from the Fitter.
``Contact,'' says the Pilot.
Now one swing of the Propeller by the Fitter, and the
Engine is awake and working. Slowly at first though, and
in a weak voice demanding, ``Not too much Throttle, please.
I'm very cold and mustn't run fast until my Oil has thinned
and is circulating freely. Three minutes slowly, as you love
me, Pilot.''
Faster and faster turn the Engine and Propeller, and
the Aeroplane, trembling in all its parts, strains to jump
the blocks and be off. Carefully the Pilot listens to what the
Engine Revolution Indicator says. At last, ``Steady
at 1,500 revs. and I'll pick up the rest in the Air.'' Then
does he throttle down the Engine, carefully putting the
lever back to the last notch to make sure that in such position
the Throttle is still sufficiently open for the Engine to continue
working, as otherwise it might lead to him ``losing'' his
Engine in the air when throttling down the power for descent.
Then, giving the official signal, he sees the blocks removed
from the wheels, and the Flight-Sergeant saluting he knows
that all is clear to ascend. One more signal, and all the
A.M.'s run clear of the Aeroplane.
Then gently, gently mind you, with none of the ``crashing
on'' bad Pilots think so fine, he opens the Throttle
and, the Propeller Thrust overcoming its enemy the Drift,
the Aeroplane moves forward.
``Ah!'' says the Wind-screen, ``that's Discipline, that
is. Through my little window I see most things, and don't
I just know that poor discipline always results in poor work
in the air, and don't you forget it.''
``Discipline is it?'' complains the Under-carriage, as
its wheels roll swiftly over the rather rough ground. ``I'm
bump getting it; and bump, bump, all I want, bang, bump,
rattle, too!'' But, as the Lift increases with the Speed,
the complaints of the Under-carriage are stilled, and then,
the friendly Lift becoming greater than the Weight, the
Aeroplane swiftly and easily takes to the air.
Below is left the Earth with all its bumps and troubles.
Up into the clean clear Air moves with incredible speed
and steadiness this triumph of the Designer, the result of
how much mental effort, imagination, trials and errors,
failures and successes, and many a life lost in high
endeavour.
Now is the mighty voice of the Engine heard as he turns
the Propeller nine hundred times a minute. Now does the
Thrust fight the Drift for all it's worth, and the Air Speed
Indicator gasps with delight, ``One hundred miles an hour!''
And now does the burden of work fall upon the Lift and
Drift Wires, and they scream to the Turnbuckles whose
business it is to hold them in tension, ``This is the limit!
the Limit! THE LIMIT! Release us, if only a quarter
turn.'' But the Turnbuckles are locked too fast to turn
their eyes or utter a word. Only the Locking Wires thus:
``Ha! ha! the Rigger knew his job. He knew the trick, and
there's no release here.'' For an expert rigger will always
use the locking wire in such a way as to oppose the slightest
tendency of the turnbuckle to unscrew. The other kind of
rigger will often use the wire in such a way as to allow the
turnbuckle, to the ``eyes'' of which the wires are attached,
to unscrew a quarter of a turn or more, with the result that
the correct adjustment of the wires may be lost; and upon
their fine adjustment much depends.
And the Struts and the Spars groan in compression and
pray to keep straight, for once ``out of truth'' there is, in
addition to possible collapse, the certainty that in bending
they will throw many wires out of adjustment.
And the Fabric's quite mixed in its mind, and ejaculates,
``Now, who would have thought I got more Lift from the
top of the Surface than its bottom?'' And then truculently
to the Distance Pieces, which run from rib to rib, ``Just
keep the Ribs from rolling, will you? or you'll see me strip.
I'm an Irishman, I am, and if my coat comes off---- Yes,
Irish, I said. I used to come from Egypt, but I've got
naturalized since the War began.''
Then the Air Speed Indicator catches the eye of the
Pilot. ``Good enough,'' he says as he gently deflects the
Elevator and points the nose of the Aeroplane upwards in
search of the elusive Best Climbing Angle.
``Ha! ha!'' shouts the Drift, growing stronger with the
increased Angle of Incidence. ``Ha! ha!'' he laughs to
the Thrust. ``Now I've got you. Now who's Master?''
And the Propeller shrieks hysterically, ``Oh! look at
me. I'm a helicopter. That's not fair. Where's Efficiency?''
And she can only sadly reply, ``Yes, indeed, but
you see we're a Compromise.''
And the Drift has hopes of reaching the Maximum Angle
of Incidence and vanquishing the Thrust and the Lift. And
he grows very bold as he strangles the Thrust; but the situation
is saved by the Propeller, who is now bravely helicopting
skywards, somewhat to the chagrin of Efficiency.
``Much ado about nothing,'' quotes the Aeroplane
learnedly. ``Compromise or not, I'm climbing a thousand
feet a minute. Ask the Altimeter. He'll confirm it.''
And so indeed it was. The vacuum box of the Altimeter
was steadily expanding under the decreased pressure of
the rarefied air, and by means of its little levers and its
wonderful chain no larger than a hair it was moving the
needle round the gauge and indicating the ascent at the
rate of a thousand feet a minute.
And lo! the Aeroplane has almost reached the clouds!
But what's this? A sudden gust, and down sinks one wing
and up goes the other. ``Oh, my Horizontal Equivalent!''
despairingly call the Planes: ``it's eloping with the Lift,
and what in the name of Gravity will happen? Surely
there was enough scandal in the Factory without this, too!''
For the lift varies with the horizontal equivalent of the
planes, so that if the aeroplane tilts sideways beyond a certain
angle, the lift becomes less than the weight of the machine,
which must then fall. A fall in such a position is known as
a ``side-slip.''
But the ever-watchful Pilot instantly depresses one aileron,
elevating the other, with just a touch of the rudder to keep
on the course, and the Planes welcome back their precious
Lift as the Aeroplane flicks back to its normal position.
``Bit bumpy here under these clouds,'' is all the Pilot
says as he heads for a gap between them, and the next minute
the Aeroplane shoots up into a new world of space.
``My eye!'' ejaculates the Wind-screen, ``talk about a
view!'' And indeed mere words will always fail to express
the wonder of it. Six thousand feet up now, and look!
The sun is rising quicker than ever mortal on earth witnessed
its ascent. Far below is Mother Earth, wrapt in mists and
deep blue shadows, and far above are those light, filmy,
ethereal clouds now faintly tinged with pink And all
about great mountains of cloud, lazily floating in space.
The sun rises and they take on all colours, blending one
with the other, from dazzling white to crimson and deep
violet-blue. Lakes and rivers here and there in the enormous
expanse of country below refract the level rays of the sun
and, like so many immense diamonds, send dazzling shafts
of light far upwards. The tops of the hills now laugh to the
light of the sun, but the valleys are still mysterious dark
blue caverns, clowned with white filmy lace-like streaks of
vapour. And withal the increasing sense with altitude of
vast, clean, silent solitudes of space.
Lives there the man who can adequately describe this
Wonder? ``Never,'' says the Pilot, who has seen it many
times, but to whom it is ever new and more wonderful.
Up, up, up, and still up, unfalteringly speeds the Pilot
and his mount. Sweet the drone of the Engine and steady
the Thrust as the Propeller exultingly battles with the Drift.
And look! What is that bright silver streak all along
the horizon? It puzzled the Pilot when first he saw it,
but now he knows it for the Sea, full fifty miles away!
And on his right is the brightness of the Morn and the
smiling Earth unveiling itself to the ardent rays of the Sun;
and on his left, so high is he, there is yet black Night, hiding
innumerable Cities, Towns, Villages and all those places
where soon teeming multitudes of men shall awake, and by
their unceasing toil and the spirit within them produce
marvels of which the Aeroplane is but the harbinger.
And the Pilot's soul is refreshed, and his vision, now
exalted, sees the Earth a very garden, even as it appears
at that height, with discord banished and a happy time
come, when the Designer shall have at last captured Efficiency,
and the Man-who-takes-the-credit is he who has earned it,
and when kisses are the only things that go by favour.
Now the Pilot anxiously scans the Barograph, which is
an instrument much the same as the Altimeter; but in this
case the expansion of the vacuum box causes a pen to trace
a line upon a roll of paper. This paper is made by clockwork
to pass over the point of the pen, and so a curved line is
made which accurately registers the speed of the ascent in
feet per minute. No longer is the ascent at the rate of a
thousand feet a minute, and the Propeller complains to the
Engine, ``I'm losing my Revs. and the Thrust. Buck up
with the Power, for the Lift is decreasing, though the Weight
remains much the same.''
Quoth the Engine: ``I strangle for Air. A certain proportion,
and that of right density, I must have to one part
of Petrol, in order to give me full power and compression,
and here at an altitude of ten thousand feet the Air is only
two-thirds as dense as at sea-level. Oh, where is he who
will invent a contrivance to keep me supplied with Air of
right density and quality? It should not be impossible
within certain limits.''
``We fully agree,'' said the dying Power and Thrust. ``Only
maintain Us and you shall be surprised at the result. For
our enemy Drift decreases in respect of distance with the increase
of altitude and rarity of air, and there is no limit to the
speed through space if only our strength remains. And
with oxygen for Pilot and Passengers and a steeper pitch[[11]]
for the Propeller we may then circle the Earth in a day!''
[[11]] A propeller screws through the air, and the distance it advances
during one revolution, supposing the air to be solid, is known as the pitch.
The pitch, which depends upon the angle of the propeller blades, must be equal
to the speed of the aeroplane, plus the slip, and if, on account of the rarity
of the air the speed of the aeroplane increases, then the angle and pitch
should be correspondingly increased. Propellers with a pitch capable of being
varied by the pilot are the dream of propeller designers. For explanation of
``slip'' see Chapter IV. on propellers.
Ah, Reader, smile not unbelievingly, as you smiled but
a few years past. There may be greater wonders yet. Consider
that as the speed increases, so does the momentum
or stored-up force in the mass of the aeroplane become
terrific. And, bearing that in mind, remember that with
altitude gravity decreases. There may yet be literally other
worlds to conquer.[[12]]
[[12]] Getting out of my depth? Invading the realms of fancy? Well,
perhaps so, but at any rate it is possible that extraordinary speed through
space may be secured if means are found to maintain the impulse of the engine
and the thrust-drift efficiency of the propeller at great altitude.
Now at fifteen thousand feet the conditions are chilly
and rare, and the Pilot, with thoughts of breakfast far below,
exclaims, ``High enough! I had better get on with the
Test.'' And then, as he depresses the Elevator, the Aeroplane
with relief assumes its normal horizontal position.
Then, almost closing the Throttle, the Thrust dies away.
Now, the nose of the Aeroplane should sink of its own volition,
and the craft glide downward at flying speed, which is in
this case a hundred miles an hour. That is what should
happen if the Designer has carefully calculated the weight
of every part and arranged for the centre of gravity to be just
the right distance in front of the centre of lift. Thus is the
Aeroplane ``nose-heavy'' as a glider, and just so to a degree
ensuring a speed of glide equal to its flying speed. And the
Air Speed Indicator is steady at one hundred miles an hour,
and ``That's all right!'' exclaims the Pilot. ``And very
useful, too, in a fog or a cloud,'' he reflects, for then he can
safely leave the angle of the glide to itself, and give all his
attention, and he will need it all, to keeping the Aeroplane
horizontal from wing-tip to wing-tip, and to keeping it
straight on its course. The latter he will manage with the
rudder, controlled by his feet, and the Compass will tell him
whether a straight course is kept. The former he will control
by the Ailerons, or little wings hinged to the tips of the planes,
and the bubble in the Inclinometer in front of him must be
kept in the middle.
A Pilot, being only human, may be able to do two things
at once, but three is a tall order, so was this Pilot relieved
to find the Design not at fault and his craft a ``natural
glider.'' To correct this nose-heavy tendency when the
Engine is running, and descent not required, the centre
of Thrust is arranged to be a little below the centre of Drift
or Resistance, and thus acts as a counter-balance.
But what is this stream of bad language from the Exhaust
Pipe, accompanied by gouts of smoke and vapour?
The Engine, now revolving at no more than one-tenth its
normal speed, has upset the proportion of petrol to air,
and combustion is taking place intermittently or in the
Exhaust Pipe, where it has no business to be.
``Crash, Bang, Rattle----!----!----!'' and worse than
that, yells the Exhaust, and the Aeroplane, who is a gentleman
and not a box kite,[[13]] remonstrates with the severity
of a Senior Officer. ``See the Medical Officer, you young
Hun. Go and see a doctor. Vocal diarrhoea, that's your
complaint, and a very nasty one too. Bad form, bad for
discipline, and a nuisance in the Mess. What's your Regiment?
Special Reserve, you say? Humph! Sounds like
Secondhand Bicycle Trade to me!''
[[13]] Box-kite. The first crude form of biplane.
Now the Pilot decides to change the straight gliding
descent to a spiral one, and, obedient to the Rudder, the
Aeroplane turns to the left. But the Momentum (two tons
at 100 miles per hour is no small affair) heavily resents this
change of direction, and tries its level best to prevent it
and to pull the machine sideways and outwards from its
spiral course--that is, to make it ``side-skid'' outwards.
But the Pilot deflects the Ailerons and ``banks'' up the planes
to the correct angle, and, the Aeroplane skidding sideways
and outwards, the lowest surfaces of the planes press up against
the air until the pressure equals the centrifugal force of
the Momentum, and the Aeroplane spirals steadily downwards.
Down, down, down, and the air grows denser, and the
Pilot gulps largely, filling his lungs with the heavier air to
counteract the increasing pressure from without. Down
through a gap in the clouds, and the Aerodrome springs
into view, appearing no larger than a saucer, and the Pilot,
having by now got the ``feel'' of the Controls, proceeds
to put the Aeroplane through its paces. First at its Maximum
Angle, staggering along tail-down and just maintaining
horizontal flight; then a dive at far over flying speed, finishing
with a perfect loop; then sharp turns with attendant
vertical ``banks'' and then a wonderful switchback flight,
speeding down at a hundred and fifty miles an hour with
short, exhilarating ascents at the rate of two thousand feet
a minute!
All the parts are now working well together. Such
wires as were before in undue tension have secured relief
by slightly elongating their loops, and each one is now doing
its bit, and all are sharing the burden of work together.
The Struts and the Spars, which felt so awkward at first,
have bedded themselves in their sockets, and are taking
the compression stresses uncomplainingly.
The Control Cables of twisted wire, a bit tight before,
have slightly lengthened by perhaps the eighth of an inch,
and, the Controls instantly responding to the delicate touch
of the Pilot, the Aeroplane, at the will of its Master, darts
this way and that way, dives, loops, spirals, and at last, in
one long, magnificent glide, lands gently in front of its shed.
``Well, what result?'' calls the Flight-Commander to
the Pilot.
``A hundred miles an hour and a thousand feet a minute,''
he briefly replies.
``And a very good result too,'' says the Aeroplane, complacently,
as he is carefully wheeled into his shed.
That is the way Aeroplanes speak to those who love them
and understand them. Lots of Pilots know all about it,
and can spin you wonderful yarns, much better than this
one, if you catch them in a confidential mood--on leave,
for instance, and after a good dinner.
PART IV
'CROSS COUNTRY
The Aeroplane had been designed and built, and tested in
the air, and now stood on the Aerodrome ready for its first
'cross-country flight.
It had run the gauntlet of pseudo-designers, crank inventors,
press ``experts,'' and politicians; of manufacturers
keen on cheap work and large profits; of poor pilots who had
funked it, and good pilots who had expected too much of
it. Thousands of pounds had been wasted on it, many had
gone bankrupt over it, and others it had provided with safe
fat jobs.
Somehow, and despite every conceivable obstacle, it had
managed to muddle through, and now it was ready for its
work. It was not perfect, for there were fifty different
ways in which it might be improved, some of them shamefully
obvious. But it was fairly sound mechanically, had a little
inherent stability, was easily controlled, could climb a thousand
feet a minute, and its speed was a hundred miles an
hour. In short, quite a creditable machine, though of course
the right man had not got the credit.
It is rough, unsettled weather with a thirty mile an
hour wind on the ground, and that means fifty more or
less aloft. Lots of clouds at different altitudes to bother
the Pilot, and the air none to clear for the observation of
landmarks.
As the Pilot and Observer approach the Aeroplane the
former is clearly not in the best of tempers. ``It's rotten
luck,'' he is saying, ``a blank shame that I should have
to take this blessed 'bus and join X Reserve Squadron,
stationed a hundred and fifty miles from anywhere; and
just as I have licked my Flight into shape. Now some
slack blighter will, I suppose, command it and get the credit
of all my work!''
``Shut up, you grouser,'' said the Observer. ``Do you
think you're the only one with troubles? Haven't I been
through it too? Oh! I know all about it! You're from
the Special Reserve and your C.O. doesn't like your style
of beauty, and you won't lick his boots, and you were a bit
of a technical knut in civil life, but now you've jolly well
got to know less than those senior to you. Well! It's a
jolly good experience for most of us. Perhaps conceit won't
be at quite such a premium after this war. And what's
the use of grousing? That never helped anyone. So buck
up, old chap. Your day will come yet. Here's our machine,
and I must say it looks a beauty!''
And, as the Pilot approaches the Aeroplane, his face
brightens and he soon forgets his troubles as he critically
inspects the craft which is to transport him and the Observer
over the hills and far away. Turning to the Flight-Sergeant
he inquires, ``Tank full of petrol and oil?''
``Yes, sir,'' he replies, ``and everything else all correct.
Propeller, engine, and body covers on board, sir; tool kit
checked over and in the locker; engine and Aeroplane logbooks
written up, signed, and under your seat; engine revs.
up to mark, and all the control cables in perfect condition
and tension.''
``Very good,'' said the Pilot; and then turning to the
Observer, ``Before we start you had better have a look
at the course I have mapped out.
``A is where we stand and we have to reach B, a hundred
and fifty miles due North. I judge that, at the altitude
we shall fly, there will be an East wind, for although it is
not quite East on the ground it is probably about twenty
degrees different aloft, the wind usually moving round clockways
to about that extent. I think that it is blowing at the
rate of about fifty miles an hour, and I therefore take a line
on the map to C, fifty miles due West of A. The Aeroplane's
speed is a hundred miles an hour, and so I take a line of one
hundred miles from C to D. Our compass course will then
be in the direction A--E, which is always a line parallel to
C--D. That is, to be exact, it will be fourteen degrees off
the C--D course, as, in this part of the globe, there is that
much difference between the North and South lines on the
map and the magnetic North to which the compass needle
points. If the compass has an error, as it may have of a
few degrees, that, too, must be taken into account, and the
deviation or error curve on the dashboard will indicate it.
``The Aeroplane will then always be pointing in a direction
parallel to A--E, but, owing to the side wind, it will be actually
travelling over the course A--B, though in a rather
sideways attitude to that course.
``The distance we shall travel over the A--B course
in one hour is A--D. That is nearly eighty-seven miles,
so we ought to accomplish our journey of a hundred and
fifty miles in about one and three-quarter hours.
``I hope that's quite clear to you. It's a very simple
way of calculating the compass course, and I always do it
like that.''
``Yes, that's plain enough. You have drafted what
engineers call `a parallelogram of forces'; but suppose you
have miscalculated the velocity of the wind, or that it should
change in velocity or direction?''
``Well, that of course will more or less alter matters,''
replies the Pilot. ``But there are any number of good
landmarks such as lakes, rivers, towns, and railway lines.
They will help to keep us on the right course, and the compass
will, at any rate, prevent us from going far astray when
between them.''
``Well, we'd better be off, old chap. Hop aboard.''
This from the Observer as he climbs into the front seat
from which he will command a good view over the lower
plane; and the Pilot takes his place in the rear seat, and,
after making himself perfectly comfortable, fixing his safety
belt, and moving the control levers to make sure that they
are working freely, he gives the signal to the Engine Fitter
to turn the propeller and so start the engine.
Round buzzes the Propeller, and the Pilot, giving the
official signal, the Aeroplane is released and rolls swiftly
over the ground in the teeth of the gusty wind.
In less than fifty yards it takes to the air and begins
to climb rapidly upwards, but how different are the conditions
to the calm morning of yesterday! If the air were
visible it would be seen to be acting in the most extraordinary
manner; crazily swirling, lifting and dropping, gusts viciously
colliding--a mad phantasmagoria of forces!
Wickedly it seizes and shakes the Aeroplane; then tries
to turn it over sideways; then instantly changes its mind
and in a second drops it into a hole a hundred feet deep,
and if it were not for his safety belt the Pilot might find
his seat sinking away from beneath him.
Gusts strike the front of the craft like so many slaps in
the face; and others, with the motion of mountainous waves,
sometimes lift it hundreds of feet in a few seconds, hoping
to see it plunge over the summit in a death-dive--and so it
goes on, but the Pilot, perfectly at one with his mount and
instantly alert to its slightest motion, is skilfully and naturally
making perhaps fifty movements a minute of hand and feet;
the former lightly grasping the ``joy-stick'' which controls
the Elevator hinged to the tail, and also the Ailerons or little
wings hinged to the wing-tips; and the latter moving the
Rudder control-bar.
A strain on the Pilot? Not a bit of it, for this is his
Work which he loves and excels in; and given a cool head,
alert eye, and a sensitive touch for the controls, what
sport can compare with these ever-changing battles of
the air?
The Aeroplane has all this time been climbing in great
wide circles, and is now some three thousand feet above
the Aerodrome which from such height looks absurdly
small. The buildings below now seem quite squat; the
hills appear to have sunk away into the ground, and the
whole country below, cut up into diminutive fields, has
the appearance of having been lately tidied and thoroughly
spring-cleaned! A doll's country it looks, with tiny horses
and cows ornamenting the fields and little model motor-cars
and carts stuck on the roads, the latter stretching away
across the country like ribbons accidentally dropped.
At three thousand feet altitude the Pilot is satisfied
that he is now sufficiently high to secure, in the event of
engine failure, a long enough glide to earth to enable him
to choose and reach a good landing-place; and, being furthermore
content with the steady running of the engine, he
decides to climb no more but to follow the course he has
mapped out. Consulting the compass, he places the Aeroplane
on the A--E course and, using the Elevator, he gives
his craft its minimum angle of incidence at which it will
just maintain horizontal flight and secure its maximum
speed.
Swiftly he speeds away, and few thoughts he has now
for the changing panorama of country, cloud, and colour.
Ever present in his mind are the three great 'cross-country
queries. ``Am I on my right course? Can I see a good
landing-ground within gliding distance?'' And ``How is
the Engine running?''
Keenly both he and the Observer compare their maps
with the country below. The roads, khaki-coloured ribbons,
are easily seen but are not of much use, for there are so many
of them and they all look alike from such an altitude.
Now where can that lake be which the map shows so
plainly? He feels that surely he should see it by now,
and has an uncomfortable feeling that he is flying too far
West. What pilot is there indeed who has not many times
experienced such unpleasant sensation? Few things in the
air can create greater anxiety. Wisely, however, he sticks
to his compass course, and the next minute he is rewarded
by the sight of the lake, though indeed he now sees that the
direction of his travel will not take him over it, as should
be the case if he were flying over the shortest route to his
destination. He must have slightly miscalculated the velocity
or direction of the side-wind.
``About ten degrees off,'' he mutters, and, using the
Rudder, corrects his course accordingly.
Now he feels happier and that he is well on his way.
The gusts, too, have ceased to trouble him as, at this altitude,
they are not nearly so bad as they were near the ground
the broken surface of which does much to produce them;
and sometimes for miles he makes but a movement or two
of the controls.
The clouds just above race by with dizzy and uniform
speed; the country below slowly unrolls, and the steady
drone of the Engine is almost hypnotic in effect. ``Sleep,
sleep, sleep,'' it insidiously suggests. ``Listen to me and
watch the clouds; there's nothing else to do. Dream,
dream, dream of speeding through space for ever, and ever,
and ever; and rest, rest, rest to the sound of my rhythmical
hum. Droning on and on, nothing whatever matters. All
things now are merged into speed through space and a sleepy
monotonous d-d-r-r-o-o-n-n-e - - - - -.'' But the Pilot pulls
himself together with a start and peers far ahead in search
of the next landmark. This time it is a little country town.
red-roofed his map tells him, and roughly of cruciform shape;
and, sure enough, there in the right direction are the broken
outlines of a few red roofs peeping out from between the trees.
Another minute and he can see this little town, a fairy
town it appears, nestling down between the hills with its
red roofs and picturesque shape, a glowing and lovely contrast
with the dark green of the surrounding moors.
So extraordinarily clean and tidy it looks from such a
height, and laid out in such orderly fashion with perfectly
defined squares, parks, avenues, and public buildings, it
indeed appears hardly real, but rather as if it has this very
day materialized from some delightful children's book!
Every city and town you must know has its distinct
individuality to the Pilot's eye. Some are not fairy places
at all, but great dark ugly blots upon the fair countryside,
and with tall shafts belching forth murky columns of smoke
to defile clean space. Others, melancholy-looking masses
of grey, slate-roofed houses, are always sad and dispirited;
never welcoming the glad sunshine, but ever calling for leaden
skies and a weeping Heaven. Others again, little coquettes
with village green, white palings everywhere, bright gravel
roads, and an irrepressible air of brightness and gaiety.
Then there are the rivers, silvery streaks peacefully
winding far, far away to the distant horizon; they and the
lakes the finest landmarks the Pilot can have. And the
forests. How can I describe them? The trees cannot be
seen separately, but merge altogether into enormous irregular
dark green masses sprawling over the country, and sometimes
with great ungainly arms half encircling some town or village;
and the wind passing over the foliage at times gives the forest
an almost living appearance, as of some great dragon of olden
times rousing itself from slumber to devour the peaceful
villages which its arms encircle.
And the Pilot and Observer fly on and on, seeing these
things and many others which baffle my poor skill to describe--
things, dear Reader, that you shall see, and poets sing of,
and great artists paint in the days to come when the Designer
has captured Efficiency. Then, and the time is near, shall
you see this beautiful world as you have never seen it before,
the garden it is, the peace it breathes, and the wonder of it.
The Pilot, flying on, is now anxiously looking for the
railway line which midway on his journey should point
the course. Ah! There it is at last, but suddenly (and
the map at fault) it plunges into the earth! Well the writer
remembers when that happened to him on a long 'cross-
country flight in the early days of aviation. Anxiously
he wondered ``Are tunnels always straight?'' and with what
relief, keeping on a straight course, he picked up the line
again some three miles farther on!
Now at last the Pilot sees the sea, just a streak on the
north-eastern horizon, and he knows that his flight is two-
thirds over. Indeed, he should have seen it before, but
the air is none too clear, and he is not yet able to discern
the river which soon should cross his path. As he swiftly
speeds on the air becomes denser and denser with what he
fears must be the beginning of a sea-fog, perhaps drifting
inland along the course of the river. Now does he feel real
anxiety, for it is the DUTY of a Pilot to fear fog, his deadliest
enemy. Fog not only hides the landmarks by which he
keeps his course, but makes the control of the Aeroplane
a matter of the greatest difficulty. He may not realize
it, but, in keeping his machine on an even keel, he is
unconsciously balancing it against the horizon, and with the
horizon gone he is lost indeed. Not only that, but it also
prevents him from choosing his landing-place, and the
chances are that, landing in a fog, he will smash into a tree,
hedge, or building, with disastrous results. The best and
boldest pilot 'wares a fog, and so this one, finding the
conditions becoming worse and yet worse, and being forced to
descend lower and lower in order to keep the earth within
view, wisely decides to choose a landing-place while there is
yet time to do so.
Throttling down the power of the engine he spirals downwards,
keenly observing the country below. There are
plenty of green fields to lure him, and his great object is to
avoid one in which the grass is long, for that would bring
his machine to a stop so suddenly as to turn it over; or one
of rough surface likely to break the under-carriage. Now
is perfect eyesight and a cool head indispensable. He sees
and decides upon a field and, knowing his job, he sticks to
that field with no change of mind to confuse him. It is none
too large, and gliding just over the trees and head on to the
wind he skilfully ``stalls'' his machine; that is, the speed
having decreased sufficiently to avoid such a manoeuvre
resulting in ascent, he, by means of the Elevator, gives the
Aeroplane as large an angle of incidence as possible. and the
undersides of the planes meeting the air at such a large
angle act as an air-brake, and the Aeroplane, skimming
over the ground, lessens its speed and finally stops just at
the farther end of the field.
Then, after driving the Aeroplane up to and under the
lee of the hedge, he stops the engine, and quickly lashing
the joy-stick fast in order to prevent the wind from blowing
the controlling surfaces about and possibly damaging them,
he hurriedly alights. Now running to the tail he lifts it up
on to his shoulder, for the wind has become rough indeed
and there is danger of the Aeroplane becoming unmanageable.
By this action he decreases the angle at which the planes
are inclined to the wind and so minimizes the latter's effect
upon them. Then to the Observer, ``Hurry up, old fellow,
and try to find some rope, wire, or anything with which to
picket the machine. The wind is rising and I shan't be able
to hold the 'bus steady for long. Don't forget the wire-
cutters. They're in the tool kit.'' And the Observer rushes
off in frantic haste, before long triumphantly returning with
a long length of wire from a neighbouring fence. Blocking
up the tail with some debris at hand, they soon succeed,
with the aid of the wire, in stoutly picketing the Aeroplane
to the roots of the high hedge in front of it; done with much
care, too, so that the wire shall not fray the fabric or set up
dangerous bending-stresses in the woodwork. Their work
is not done yet, for the Observer remarking, ``I don't like
the look of this thick weather and rather fear a heavy rain-
storm,'' the Pilot replies, ``Well, it's a fearful bore, but the
first rule of our game is never to take an unnecessary risk,
so out with the engine and body covers.''
Working with a will they soon have the engine and the
open part of the body which contains the seats, controls,
and instruments snugly housed with their waterproof covers,
and the Aeroplane is ready to weather the possible storm.
Says the Observer, ``I'm remarkably peckish, and methinks
I spy the towers of one of England's stately homes
showing themselves just beyond that wood, less than a
quarter of a mile away. What ho! for a raid. What do
you say?''
``All right, you cut along and I'll stop here, for the
Aeroplane must not be left alone. Get back as quickly as
possible.''
And the Observer trots off, leaving the Pilot filling his
pipe and anxiously scrutinizing the weather conditions.
Very thick it is now, but the day is yet young, and he has
hopes of the fog lifting sufficiently to enable the flight to be
resumed. A little impatiently he awaits the return of his
comrade, but with never a doubt of the result, for the hospi-
tality of the country house is proverbial among pilots!
What old hand among them is there who cannot instance
many a forced landing made pleasant by such hospitality?
Never too late or too early to help with food, petrol, oil,
tools, and assistants. Many a grateful thought has the
writer for such kind help given in the days before the war
(how long ago they seem!), when aeroplanes were still more
imperfect than they are now, and involuntary descents
often a part of 'cross-country flying.
Ah! those early days! How fresh and inspiring they
were! As one started off on one's first 'cross-country flight,
on a machine the first of its design, and with everything
yet to learn, and the wonders of the air yet to explore; then
the joy of accomplishment, the dreams of Efficiency, the
hard work and long hours better than leisure; and what a
field of endeavour--the realms of space to conquer! And
the battle still goes on with ever-increasing success. Who
is bold enough to say what its limits shall be?
So ruminates this Pilot-Designer, as he puffs at his pipe,
until his reverie is abruptly disturbed by the return of the
Observer.
``Wake up, you AIRMAN,'' the latter shouts. ``Here's
the very thing the doctor ordered! A basket of first-class
grub and something to keep the fog out, too.''
``Well, that's splendid, but don't call me newspaper
names or you'll spoil my appetite!''
Then, with hunger such as only flying can produce, they
appreciatively discuss their lunch, and with many a grateful
thought for the donors--and they talk shop. They can't
help it, and even golf is a poor second to flight talk. Says
the Pilot, who must have his grievance, ``Just observe
where I managed to stop the machine. Not twenty feet
from this hedge! A little more and we should have been
through it and into Kingdom Come! I stalled as well as
one could, but the tail touched the ground and so I could
not give the Aeroplane any larger angle of incidence. Could
I have given it a larger angle, then the planes would have
become a much more effective air-brake, and we should
have come to rest in a much shorter distance. It's all the
fault of the tail. There's hardly a type of Aeroplane in
existence in which the tail could not be raised several feet,
and that would make all the difference. High tails mean
a large angle of incidence when the machine touches ground
and, with enough angle, I'll guarantee to safely land the
fastest machine in a five-acre field. You can, I am sure,
imagine what a difference that would make where forced
landings are concerned!'' Then rapidly sketching in his
notebook, he shows the Observer the following illustration:
``That's very pretty,'' said the Observer, ``but how
about Mechanical Difficulties, and Efficiency in respect of
Flight? And, anyway, why hasn't such an obvious thing
been done already?''
``As regards the first part of your question I assure
you that there's nothing in it, and I'll prove it to you as
follows----''
``Oh! That's all right, old chap. I'll take your word
for it,'' hurriedly replies the Observer, whose soul isn't tuned
to a technical key.
``As regards the latter part of your inquiry,'' went on
the Pilot, a little nettled at having such a poor listener,
``it's very simple. Aeroplanes have `just growed' like
Topsy, and they consequently contain this and many another
relic of early day design when Aeroplanes were more or less
thrown together and anything was good enough that could
get off the ground.''
``By Jove,'' interrupts the Observer, ``I do believe the
fog is lifting. Hadn't we better get the engine and body
covers off, just in case it's really so?''
``I believe you're right. I am sure those hills over there
could not be seen a few minutes ago, and look--there's
sunshine over there. We'd better hurry up.''
Ten minutes' hard work and the covers are off, neatly
folded and stowed aboard; the picketing wires are cast adrift,
and the Pilot is once more in his seat. The Aeroplane has
been turned to face the other end of the field, and, the Observer
swinging round the propeller, the engine is awake
again and slowly ticking over. Quickly the Observer climbs
into his seat in front of the Pilot, and, the latter slightly
opening the throttle, the Aeroplane leisurely rolls over the
ground towards the other end of the field, from which the
ascent will be made.
Arriving there the Pilot turns the Aeroplane in order to
face the wind and thus secure a quick ``get-off.'' Then he
opens the throttle fully and the mighty voice of the Engine
roars out ``Now see me clear that hedge!'' and the Aeroplane
races forward at its minimum angle of incidence. Tail
up, and with ever-increasing speed, it rushes towards the
hedge under the lee of which it has lately been at rest; and
then, just as the Observer involuntarily pulls back an imaginary
``joy-stick,'' the Pilot moves the real one and places the
machine at its best climbing angle. Like a living thing it
responds, and instantly leaves the ground, clearing the hedge
like a--well, like an Aeroplane with an excellent margin of
lift. Upwards it climbs with even and powerful lift, and the
familiar scenes below again gladden the eyes of the Pilot.
Smaller and more and more squat grow the houses and hills;
more and more doll-like appear the fields which are clearly
outlined by the hedges; and soon the country below is easily
identified with the map. Now they can see the river before
them and a bay of the sea which must be crossed or skirted.
The fog still lingers along the course of the river and between
the hills, but is fast rolling away in grey, ghost-like masses.
Out to sea it obscures the horizon, making it difficult to be
sure where water ends and fog begins, and creating a strange,
rather weird effect by which ships at a certain distance appear
to be floating in space.
Now the Aeroplane is almost over the river, and the
next instant it suddenly drops into a ``hole in the air.''
With great suddenness it happens, and for some two hundred
feet it drops nose-down and tilted over sideways; but the
Pilot is prepared and has put his craft on an even keel in
less time than it takes to tell you about it; for well he knows
that he must expect such conditions when passing over a
shore or, indeed, any well-defined change in the composition
of the earth's surface. Especially is this so on a hot and
sunny day, for then the warm surface of the earth creates
columns of ascending air, the speed of the ascent depending
upon the composition of the surface. Sandy soil, for instance,
such as borders this river produces a quickly ascending
column of air, whereas water and forests have not such a
marked effect. Thus, when our Aeroplane passed over the
shore of the river, it suddenly lost the lift due to the ascending
air produced by the warm sandy soil, and it consequently
dropped just as if it had fallen into a hole.
Now the Aeroplane is over the bay and, the sea being
calm, the Pilot looks down, down through the water, and
clearly sees the bottom, hundreds of feet below the surface.
Down through the reflection of the blue sky and clouds,
and one might think that is all, but it isn't. Only those
who fly know the beauties of the sea as viewed from above;
its dappled pearly tints; its soft dark blue shadows; the beautiful
contrasts of unusual shades of colour which are always
differing and shifting with the changing sunshine and the
ever moving position of the aerial observer. Ah! for some
better pen than mine to describe these things! One with
glowing words and a magic rhythm to express the wonders
of the air and the beauty of the garden beneath--the immensity
of the sea--the sense of space and of one's littleness
there--the realization of the Power moving the multitudes
below--the exaltation of spirit altitude produces--the joy of
speed. A new world of sensation!
Now the bay is almost crossed and the Aerodrome at B
can be distinguished.
On the Aerodrome is a little crowd waiting and watching
for the arrival of the Aeroplane, for it is of a new and improved
type and its first 'cross-country performance is of
keen interest to these men; men who really know something
about flight.
There is the Squadron Commander who has done some
real flying in his time; several well-seasoned Flight-
Commanders; a dozen or more Flight-Lieutenants; a
knowledgeable Flight-Sergeant; a number of Air Mechanics,
and, a little on one side and almost unnoticed, the
Designer.
``I hope they are all right,'' said someone, ``and that
they haven't had difficulties with the fog. It rolled up very
quickly, you know.''
``Never fear,'' remarked a Flight-Commander. ``I know
the Pilot well and he's a good 'un; far too good to carry on
into a fog.''
``They say the machine is really something out of the
ordinary,'' said another, ``and that, for once, the Designer
has been allowed full play; that he hasn't been forced to
unduly standardize ribs, spars, struts, etc., and has more
or less had his own way. I wonder who he is. It seems
strange we hear so little of him.''
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