The Aeroplane Speaks [16]
air none to clear for the observation of landmarks.
As the Pilot and Observer approach the Aeroplane the former is clearly not in the best of tempers. ``It's rotten luck,'' he is saying, ``a blank shame that I should have to take this blessed 'bus and join X Reserve Squadron, stationed a hundred and fifty miles from anywhere; and just as I have licked my Flight into shape. Now some slack blighter will, I suppose, command it and get the credit of all my work!''
``Shut up, you grouser,'' said the Observer. ``Do you think you're the only one with troubles? Haven't I been through it too? Oh! I know all about it! You're from the Special Reserve and your C.O. doesn't like your style of beauty, and you won't lick his boots, and you were a bit of a technical knut in civil life, but now you've jolly well got to know less than those senior to you. Well! It's a jolly good experience for most of us. Perhaps conceit won't be at quite such a premium after this war. And what's the use of grousing? That never helped anyone. So buck up, old chap. Your day will come yet. Here's our machine, and I must say it looks a beauty!''
And, as the Pilot approaches the Aeroplane, his face brightens and he soon forgets his troubles as he critically inspects the craft which is to transport him and the Observer over the hills and far away. Turning to the Flight-Sergeant he inquires, ``Tank full of petrol and oil?''
``Yes, sir,'' he replies, ``and everything else all correct. Propeller, engine, and body covers on board, sir; tool kit checked over and in the locker; engine and Aeroplane logbooks written up, signed, and under your seat; engine revs. up to mark, and all the control cables in perfect condition and tension.''
``Very good,'' said the Pilot; and then turning to the Observer, ``Before we start you had better have a look at the course I have mapped out.
``A is where we stand and we have to reach B, a hundred and fifty miles due North. I judge that, at the altitude we shall fly, there will be an East wind, for although it is not quite East on the ground it is probably about twenty degrees different aloft, the wind usually moving round clockways to about that extent. I think that it is blowing at the rate of about fifty miles an hour, and I therefore take a line on the map to C, fifty miles due West of A. The Aeroplane's speed is a hundred miles an hour, and so I take a line of one hundred miles from C to D. Our compass course will then be in the direction A--E, which is always a line parallel to C--D. That is, to be exact, it will be fourteen degrees off the C--D course, as, in this part of the globe, there is that much difference between the North and South lines on the map and the magnetic North to which the compass needle points. If the compass has an error, as it may have of a few degrees, that, too, must be taken into account, and the deviation or error curve on the dashboard will indicate it.
``The Aeroplane will then always be pointing in a direction parallel to A--E, but, owing to the side wind, it will be actually travelling over the course A--B, though in a rather sideways attitude to that course.
``The distance we shall travel over the A--B course in one hour is A--D. That is nearly eighty-seven miles, so we ought to accomplish our journey of a hundred and fifty miles in about one and three-quarter hours.
``I hope that's quite clear to you. It's a very simple way of calculating the compass course, and I always do it like that.''
``Yes, that's plain enough. You have drafted what engineers call `a parallelogram of forces'; but suppose you have miscalculated the velocity of the wind, or that it should change in velocity or direction?''
``Well, that of course will more or less alter matters,'' replies the Pilot. ``But there are any number of good landmarks such as lakes, rivers, towns, and railway lines. They will help to keep us on the right course, and the compass will, at any rate, prevent us from going far astray when between them.''
``Well, we'd better be off, old chap. Hop aboard.'' This from the Observer
As the Pilot and Observer approach the Aeroplane the former is clearly not in the best of tempers. ``It's rotten luck,'' he is saying, ``a blank shame that I should have to take this blessed 'bus and join X Reserve Squadron, stationed a hundred and fifty miles from anywhere; and just as I have licked my Flight into shape. Now some slack blighter will, I suppose, command it and get the credit of all my work!''
``Shut up, you grouser,'' said the Observer. ``Do you think you're the only one with troubles? Haven't I been through it too? Oh! I know all about it! You're from the Special Reserve and your C.O. doesn't like your style of beauty, and you won't lick his boots, and you were a bit of a technical knut in civil life, but now you've jolly well got to know less than those senior to you. Well! It's a jolly good experience for most of us. Perhaps conceit won't be at quite such a premium after this war. And what's the use of grousing? That never helped anyone. So buck up, old chap. Your day will come yet. Here's our machine, and I must say it looks a beauty!''
And, as the Pilot approaches the Aeroplane, his face brightens and he soon forgets his troubles as he critically inspects the craft which is to transport him and the Observer over the hills and far away. Turning to the Flight-Sergeant he inquires, ``Tank full of petrol and oil?''
``Yes, sir,'' he replies, ``and everything else all correct. Propeller, engine, and body covers on board, sir; tool kit checked over and in the locker; engine and Aeroplane logbooks written up, signed, and under your seat; engine revs. up to mark, and all the control cables in perfect condition and tension.''
``Very good,'' said the Pilot; and then turning to the Observer, ``Before we start you had better have a look at the course I have mapped out.
``A is where we stand and we have to reach B, a hundred and fifty miles due North. I judge that, at the altitude we shall fly, there will be an East wind, for although it is not quite East on the ground it is probably about twenty degrees different aloft, the wind usually moving round clockways to about that extent. I think that it is blowing at the rate of about fifty miles an hour, and I therefore take a line on the map to C, fifty miles due West of A. The Aeroplane's speed is a hundred miles an hour, and so I take a line of one hundred miles from C to D. Our compass course will then be in the direction A--E, which is always a line parallel to C--D. That is, to be exact, it will be fourteen degrees off the C--D course, as, in this part of the globe, there is that much difference between the North and South lines on the map and the magnetic North to which the compass needle points. If the compass has an error, as it may have of a few degrees, that, too, must be taken into account, and the deviation or error curve on the dashboard will indicate it.
``The Aeroplane will then always be pointing in a direction parallel to A--E, but, owing to the side wind, it will be actually travelling over the course A--B, though in a rather sideways attitude to that course.
``The distance we shall travel over the A--B course in one hour is A--D. That is nearly eighty-seven miles, so we ought to accomplish our journey of a hundred and fifty miles in about one and three-quarter hours.
``I hope that's quite clear to you. It's a very simple way of calculating the compass course, and I always do it like that.''
``Yes, that's plain enough. You have drafted what engineers call `a parallelogram of forces'; but suppose you have miscalculated the velocity of the wind, or that it should change in velocity or direction?''
``Well, that of course will more or less alter matters,'' replies the Pilot. ``But there are any number of good landmarks such as lakes, rivers, towns, and railway lines. They will help to keep us on the right course, and the compass will, at any rate, prevent us from going far astray when between them.''
``Well, we'd better be off, old chap. Hop aboard.'' This from the Observer