The Aeroplane Speaks | Page 8

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