The Aeroplane Speaks | Page 5

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