Aeroplanes and Dirigibles of War | Page 9

pressure against a plane is when it is in a horizontal position, because then the wind has no force against the surfaces, and the only effect on the drift is that which takes place when the wind strikes its forward edge.
Fig. 4. Normal Air Pressure
Fig. 5. Edge Resistance
HEAD RESISTANCE.--Fig. 5 shows such a plane, the only resistance being the thickness of the plane as at A. This is called head resistance, and on this subject there has been much controversy, and many theories, which will be considered under the proper headings.
If a plane is placed at an angle of 45 degrees the lift and the drift are the same, assumedly, because, if we were to measure the power required to drive it forwardly, it would be found to equal the weight necessary to lift it. That is, suppose we should hold a plane at that angle with a heavy wind blowing against it, and attach two pairs of scales to the plane, both would show the same pull.
Fig. 6. Measuring Lift and Drift
MEASURING LIFT AND DRIFT.--In Fig. 6, A is the plane, B the horizontal line which attaches the plane to a scale C, and D the line attaching it to the scale E. When the wind is of sufficient force to hold up the plane, the scales will show the same pull, neglecting, of course, the weight of the plane itself.
PRESSURE AT DIFFERENT ANGLES.--What every one wants to know, and a subject on which a great deal of experiment and time have been expended, is to determine what the pressures are at the different angles between the horizontal, and laws have been formulated which enable the pressures to be calculated.
DIFFERENCE BETWEEN LIFT AND DRIFT IN MOTION.--The first observation is directed to the differences that exist between the lift and drift, when the plane is placed at an angle of less than 45 degrees. A machine weighing 1000 pounds has always the same lift. Its mass does not change. Remember, now, we allude to its mass, or density.
We are not now referring to weight, because that must be taken into consideration, in the problem. As heretofore stated, when an object moves horizontally, it has less weight than when at rest. If it had the same weight it would not move forwardly, but come to rest.
When in motion, therefore, while the lift, so far as its mass is concerned, does not change, the drift does decrease, or the forward pull is less than when at 45 degrees, and the decrease is less and less until the plane assumes a horizontal position, where it is absolutely nil, if we do not consider head resistance.
TABLES OF LIFT AND DRIFT.--All tables of Lift and Drift consider only the air pressures. They do not take into account the fact that momentum takes an important part in the translation of an object, like a flying machine.
A mass of material, weighing 1000 pounds while at rest, sets up an enormous energy when moving through the air at fifty, seventy-five, or one hundred miles an hour. At the latter speed the movement is about 160 feet per second, a motion which is nearly sufficient to maintain it in horizontal flight, independently of any plane surface.
Such being the case, why take into account only the angle of the plane? It is no wonder that aviators have not been able to make the theoretical considerations and the practical demonstrations agree.
WHY TABLES OF LIFT AND DRIFT ARE WRONG.-- A little reflection will show why such tables are wrong. They were prepared by using a plane surface at rest, and forcing a blast of air against the plane placed at different angles; and for determining air pressures, this is, no doubt, correct. But it does not represent actual flying conditions. It does not show the conditions existing in an aeroplane while in flight.
To determine this, short of actual experiments with a machine in horizontal translation, is impossible, unless it is done by taking into account the factor due to momentum and the element attributable to the lift of the plane itself due to its impact against the atmosphere.
LANGLEY'S LAW.--The law enunciated by Langley is, that the greater the speed the less the power required to propel it. Water as a propelling medium has over seven hundred times more force than air. A vessel having, for instance, twenty horse power, and a speed of ten miles per hour, would require four times that power to drive it through the water at double the speed. The power is as the square of the speed.
With air the conditions are entirely different. The boat submergence in the water is practically the same, whether going ten or twenty miles an hour. The head resistance is the same, substantially, at all times in the case of the boat;