The Aeroplane Speaks
H >>
H. Barber >> The Aeroplane Speaks
Pages:
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 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.
Pages:
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10