The Aeroplane Speaks [4]
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
[[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