Airspeed

“ It should be stressed that because of the high drag characteristics of the aircraft in the 40-degree flap configuration, high descent rates and airspeed reduction, in response to decreased thrust, can develop more rapidly than in the less sophisticated models and that this flight regime should be avoided close to the ground. ”

“ Station barometric pressure which when set in the altimeter allows for an altimeter reading of zero feet at the airport elevation. ↑ QNH – Local atmospheric pressure which when set in the altimeter allows for the appropriate mean sea level altitude reading at the airport elevation. ↑ The NASA VGH program is a continuing research project whereby recorded airspeed – acceleration – altitude data is collected for many different aircraft models and for different types of operation. ”

“ To alight with an airplane the pilot—supposing his descent to be voluntary and not compelled by accident or otherwise—surveys the country about him for a level field, big and clear enough for the machine to run off its momentum in a run of perhaps two hundred yards on its wheels. Then he gets up a good rate of speed, points the nose of the 'plane down at a sharp angle to the ground, cuts off the engine, and glides. The angle of the fall must be great enough for the force of gravity to keep up the speed. There is a minimum speed at which an airplane will remain subject to control. ”

“ Therefore, as long as the aeroplane rushes through the air at that or greater speed the thousands of cubic feet of air forced down beneath the wings deliver up a reaction that results in complete support. When an aircraft fails to move at that velocity it loses “flying speed” and falls to the earth. The net result of this reaction is called “lift,” and as long as the machine sweeps forward at that momentum it has lift. The engine, of course, must supply this forward movement, and when it stalls, the heavier-than-air machine must glide to a landing-place or fall perpendicular to the ground. ”

“ Oh, where is he who will invent a contrivance to keep me supplied with air of right density and quality? It should not be impossible within certain limits."
"We fully agree," said the dying Power and Thrust. "Only maintain Us and you shall be surprised at the result. For our enemy Drift decreases in respect of distance with the increase of altitude and rarity of air, and there is no limit to the speed through space if only our strength remains. And with oxygen for pilot and passengers and a steeper pitch11 [35] for the Propeller we may then circle the Earth in a day!" ”

“ The flying machine which will navigate successfully in a perfectly quiet atmosphere may be unseaworthy, or rather, unairworthy, when a wind springs up, or the shifting of the wind may spoil all the air pilot’s plans. To add to his troubles, the aviator must move among air currents which change and change again in a moment’s time. As we study the difficulties of air navigation we will appreciate, more than ever, the wonderful patience, skill, and daring of the successful aviators.
The action of the air currents had first to be carefully studied before flight became possible. ”

“ All airmen unite in declaring that even to the novice in an airplane there is none of that sense of dizziness or vertigo which so many people experience in looking down from high places. The flyer has no sense of motion. A speed of forty miles an hour and of one hundred miles are the same to him. As he looks down the earth seems to be slipping away from him, and moving by, tailwards, like an old-fashioned panorama being unwound.
Everything about the control of an airplane has to be learned mechanically. Once learned the aviator applies his knowledge intuitively. ”

“ If we assume some given value for the horse-power per unit weight, then a machine may be designed either to develop the highest flight speed possible or to obtain the greatest rate of altitude increase—i.e., vertical velocity. Any actual design is of the nature of a compromise; maximum flight speed is kept as high as possible consistently with obtaining a sufficient rapidity of ascent. The independent air fleet must be, without question, the master of the service machines whose destruction it is required to encompass, both in the matter of speed and climbing capacity. ”

“ Then there is the air speed indicator, which shows the speed of the plane in the air. This is necessary so that the engine is not over-speeded. A pilot never runs his plane at full speed as a general thing, because he’ll wear out his engine. He keeps it at about 80 per cent of its potential speed, which is a good safe margin. ”

“ On a clear night, however, with flambeaux, search-light flares, etc., a pilot has little trouble in landing, for [152] the straightaway can be as illuminated as it is in broad daylight. Nevertheless, when the aircraft is high in the sky, owing to the vast distances of infinite space, the speed at which an aeroplane moves, and the drift out of its regular course, due to the wind, it is often difficult for the flier to keep his bearings. ”

“ Regarding density, the pilot should know that for a low density he should theoretically get a high speed. As density decreases, high up in the air, the speed tends to increase, and moreover he gets more speed for the same amount of gasoline. Unfortunately, at an altitude the motor power falls off, so that nowadays the speed is not faster high up than low down; but when the motor builders succeed in designing their motors to give the same horsepower at 20,000 ft. as they do on the ground, airplanes will be able to reach terrific speed by doing their work above the clouds. ”

“ But the moment the plane is either augmented or retarded by favorable or unfavorable winds, the air-speed indicator becomes a very unreliable instrument for showing distances traveled: it practically only records the speed of the air pushed past the plane. It is like running at ten miles an hour with a pin-wheel in the hand on a perfectly calm day, and getting a certain velocity of revolutions of the wheel per minute. On another day one might stand still with the pin-wheel and permit the rush of a high velocity of wind to twirl it round with the same speed. ”

“ The direction and velocity of the wind must be carefully considered by the pilot in making any predetermined course or objective. The progress of the plane due to the pull of the propeller is primarily with reference to the air. If this is in motion the plane's ground speed and direction will be altered accordingly. In flying with or against the wind the ground speed is the sum or difference, respectively, of the plane's air speed (determined by an air speed indicator) and the speed of the wind. ”

“ What speed may we expect of an improved soaring-machine? and upon how gentle a decline can we hope to see it maintain its initial velocity? First, note the fact that with a dirigible aeroplane or soaring machine the rate of speed is practically a matter of choice and depends at the start upon the length of the first swoop. The limit of speed will probably be decided by the [13] strength of the machine and the breathing requirements of the aerial pilot. Let us consider a railroad train. Man has safely travelled at a rate of one hundred and twelve miles per hour. ”

“ The wings of the airplane, its propeller and its whole construction have been planned so that it can support itself best in the air when flying at a certain fixed speed. Suppose this speed for a certain type of airplane to be 150 miles per hour. The airplane cannot land while traveling at that rate, yet its speed while still in the air can only be diminished to a certain point with safety, and below that point it may not be able to sustain [166] itself in flight. The pilot must be able to land his machine without accident and without throttling his engine below this danger line ”

“ One salient fact is at once evident; the greater the horse-power available for a given engine weight the greater the advantage in the matter of speed in favour of the aeroplane; the highest speed of flight of an aeroplane attained to-day (through, i.e., relatively to, the air) is already more than twice that of which the fastest dirigible is capable. There is every prospect that its advantage in this respect will increase rather than diminish with the march of progress. ”

“ Of course, when an aviator is lost in the fog or above the clouds he needs to use all the instruments on board to find his position. For that purpose drift instruments are mounted on aircraft; those tell how much the air-currents, which have the same effect on aircraft as the tide has on a boat, have driven him off his course. A compass indicates the direction in which he is travelling, and other instruments show him whether his machine is climbing, diving, or “banking”; the aneroid barometer indicates the altitude. ”

“ By a greater efficiency in lifting surfaces and by reductions in the resistance a craft offers to its own passage through the air; by the provision of systems which will permit a pilot to reduce plane-area when his machine has gained altitude and he desires a maximum speed; by the equipping of craft with motors developing thousands of horse-power for a very low weight—by such means, and by a general improvement in design, it should be possible, eventually, to attain flying speeds of 150, 200, and even 250 miles an hour. ”

“ When the airplane was descending, the flying pilot would normally have reset the altitude selector to the next (lower) altitude target and moved the VERT SPEED (vertical speed) wheel to position the airplane in about a 1,000-feet-per-minute rate of descent to reach the next crossing altitude. The FD pitch command bars would move up and down to provide guidance to maintain the desired rate of descent. (In a precision approach, the command bars would provide guidance to maintain the glideslope; in nonprecision approaches, they provide guidance to maintain the desired vertical speed.) ”

“ At three thousand feet altitude the Pilot is satisfied that he is now sufficiently high to secure, in the event of engine failure, a long enough glide to earth to enable him to choose and reach a good landing-place; and, being furthermore content with the steady running of the engine, he decides to climb no more but to follow the course he has mapped out. Consulting the compass, he places the Aeroplane on the A–E course and, using the Elevator, he gives his craft its minimum angle of incidence at which it will just maintain horizontal flight and secure its maximum speed. ”

“ To shut off the engine at precisely the right moment, (p. 114) to choose an angle of descent that will secure the greatest speed and at the same moment bring you to your landing place, to change at the most favourable time from this angle to one that will bring you to the ground at the most gentle of obtuse angles, and to let your machine, weighing perhaps a ton, drop as lightly as a bird and run along the earth for several hundred feet before coming to a full stop, are all features of making a landing which the aviator has to master. ”

“ The flight of some of these birds has been measured. Four miles a minute or two hundred and forty miles an hour is not uncommon.”
The surprised manager made no comment.
“The mathematical possibilities of airship speed,” resumed Ned, “are based on height or altitude. The maximum of speed at or near sea level is no indication of what may be accomplished miles in the air. Let me explain. Say we have an airship such as the Ocean Flyer that can fly two hundred miles an hour near sea level where the air pressure is greatest.” ”

“ Speed change then requires that the pilot alter the angle of incidence simultaneously with the throttle; so there are two things to do, unlike the case of the automobile where only the throttle is altered.
Minimum Speed.—When, in slowing up an airplane, the angle of incidence reaches the 15° limit, no further decrease of speed is allowable; therefore, the critical angle determines the minimum limit of speed. If for any reason the machine exceeds the 15° limit, it must speed up to gain support; that is, the pilot has to increase angle and speed simultaneously instead of oppositely. ”

“ Maximum Speed.—Ordinarily, for moderate speeds, airplanes have a margin of power at which the throttle need not be opened wide; should speed be increased the resistance and horsepower required will increase steadily until the throttle is wide open and motor “full out;” this establishes the maximum speed of an airplane; there is no margin of power, no climb is possible. The only way to increase speed is to use the force of gravity in addition to the motor force. ”

“ Just as the navigator must know the sea, so the aviator must have a knowledge of the heavens and the basic principles of aerodynamics in order to become a successful pilot. Although the air is volatile like the water, the aviator flies through it as a fish moves through water. Therefore the aerial navigator must know enough about the medium through which he travels to know what to do in an emergency. ”

“ Invading the realms of fancy? Well, perhaps so, but at any rate it is possible that extraordinary speed through space may be secured if means are found to maintain the impulse of the engine and the thrust-drift efficiency of the propeller at great altitude. ”

“ Fighting planes with a speed of nine miles a minute are an actuality. A giant transport plane, capable of carrying 100 passengers, has flown across the continent in six hours. This means that a passenger may eat lunch in New York and dinner in California. It means that postwar air travelers will become accustomed to flying at the speed of our 1939 fighting planes. Air travelers soon will be crossing the country at a speed of eight miles a minute. ”