The Aeroplane Speaks | Page 7

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,''