M.Goodall, A.Tagg British Aircraft before the Great War (Schiffer)

Журнал Flight

Flight, May 15, 1914.

THE WATSON ROCKING-WING AEROPLANE.

   IN connection with the competition organised by "L'Union pour La Securite en Aeroplanes," Mr. P. A. Watson, of Dundee, who has been experimenting with rocking-wing aeroplanes for a number of years, is at present demonstrating his latest type machine (No. 3) at Buc. We have asked Mr. Watson for a description of his machine, and he has sent us a copy of the explanation which, in accordance with the rules of the competition, he has given l'Union. The following extract from Mr. Watson's explanation of the principles of his machine will, we think, make it clear in what respect his aeroplane and the manner in which it is controlled differ from ordinary types.
   The machine (No. 3), as will be seen from the accompanying photographs, is of the tractor type, and is driven by a 40 h.p. Anzani engine, mounted in front of the wicker-work nacelle. The chassis, which is of the four-wheeled type, is very robust and provides a comparatively wide track. An outrigger formed by two tail booms carries at the rear a monoplane elevator and a small fixed vertical fin. It will be observed that no movable vertical rudder is fitted. Mounted on a very strong cabane formed by two pairs of inverted V struts, is the balancing plane, by means of which lateral equilibrium is maintained, and the action of which is explained by Mr. Watson in the following extract:-
   "The method of preserving lateral equilibrium invented by the Wright brothers has been slavishly followed, but this has probably been due to the fact that these gentlemen were the first to fly in a practical way. This does not prove, however, that they have not misled everybody as to the best means of preserving lateral equilibrium. It must be remembered that they began their experiments at Kittyhawk with the fixed intention of preserving lateral equilibrium by warping the wings, and when this means alone was found insufficient they never considered the possibility of using other means than warping, but looked for an addition to their warping wing machine and devised the vertically pivoted tail.
   "The Wright Brothers have stated, and it is well known, that if the angle of incidence of the lower wing is increased, its resistance is also increased, so that the fore and aft axis of the machine turns about its vertical axis, away from the line of flight, and the lower wing loses its velocity, unless this is prevented by the movement of a vertically pivoted tail. In the absence of a vertically pivoted tail the loss of velocity of the wing whose angle of incidence is increased, causes it to lose its support, and it descends while the other rises. Thus the vertically pivoted tail is proved to be necessary if lateral equilibrium is to be preserved by the warping of the wings. The absence in a bird of the vertically pivoted tail proves that warping of the wings is not the method employed by a bird to preserve lateral equilibrium.
   "The method by which a bird preserves its lateral equilibrium, and steers to right or left, is a beautiful method of flight. If a soaring bird is making a straight flight with its wings transversely in the horizontal and it wishes to steer to one side, it rocks its wings about a fore and aft axis by pulling one wing down and allowing the other to rise. It is able to do this because the centre of gravity of a bird is below its centre of support, and a pendulum thus exists. The force which this pendulum exerts if shifted from the natural position in which it hangs, provides a fulcrum in mid-air from which the wings can be rocked. Since the mass of the pendulum is considerable its inertia also helps in providing a fulcrum. When the wings are rocked out of the horizontal their lift has a component force pulling to one side of the line of flight. Now, when a body which is moving in a straight line is acted on by a constant force at right angles thereto, the body describes a circle. Therefore when the bird has rocked its wings it describes a circle.
   "It must be remembered that this beautifully balanced flight takes place without any attention on the part of the bird except that it controls the elevation (according to whether it wishes to ascend or descend or fly horizontally during the turn) and rocks its wings to that extent which it considers necessary to make a circle of the desired diameter. In fact the bird possesses a method of flight which takes care of itself and is controlled by two movements. The difficulty which caused Wilbur and Orville Wright to abandon this beautiful method of flight adopted by the bird was that considerable power is required to rock the whole surface of the wings in the manner of the bird.
   "A soaring bird has sufficient power to rock the whole wing surface quickly, since it employs for this purpose its strong flying muscles, but the pilot of an aeroplane has not sufficient power for this purpose. Thus the Wright brothers abandoned the perfect method of flight of the bird in favour of warping wings and a vertically pivoted tail, because with this latter method the pilot can preserve lateral equilibrium without having to exert so much power. Less power is required to warp or to control the ailerons than to rock the whole wing surface in the manner of a bird. The choice between one or the other of these methods of preserving lateral equilibrium is a choice between the perfect flight of the bird, which, however, has the disadvantage of requiring considerable power on the part of the pilot, and the method of preserving lateral equilibrium by controlling the angle of incidence of the wing tips, or the angle of incidence of the supplementary surfaces, a method which has the advantage of requiring small power on the part of the pilot, but which causes an excess of resistance on the surface which has the greater angle of incidence, and thus necessitates the vertically pivoted tail with its consequent disadvantages.
   "It remains to examine whether it is not possible to invent a method of preserving lateral equilibrium, which requires small power on the part of the pilot, and which does not increase the resistance of one side of the machine and thus does not necessitate the use of a vertically pivoted movable tail.
   "In the machine described, a supplementary aeroplane surface possessing a lifting effect is situated above the main aeroplane, and is attached to an upward extension of the frame of the machine. This supplementary surface can be rocked about a fore and aft axis with the exertion of small power on the part of the pilot, and when thus rocked it gives rise to a component side force similar to the side pull of the wings of a bird when they are rocked. This side pull is exerted on the upward extension of the frame of the machine, and thus controls the 'list' of the frame of the machine in the same way as a bird controls its 'list.' The main aeroplane is rigid with the frame, so that the rocking of the upper plane controls the rock of the main plane. The torque about the fore and aft axis of the machine depends on the distance between the centre of gravity of the machine, and the upper part of the upward extension of the frame where the supplementary aeroplane surface is situated. This surface may be of small area, and may still exert a sufficient torque about the fore and aft axis of the machine, if the upward extension of the frame is sufficiently long. It must be remembered that the pressure on the upper rocking wing is always balanced about the axle on which it rocks, so that the rocking does not require great power on the part of the pilot. On the other hand when wings are warped, the wing with the greater angle of incidence has the greater pressure, and considerable power is required on the part of the pilot because of this unbalanced pressure. By placing the supplementary aeroplane surface above the main aeroplane, and in making it to rock about a fore and aft axis, power is obtained with which to rock the main aeroplane surface. This is obtained without introducing any other force than the one required, that is to say the equilibrium of the aeroplane is left unaltered in every respect except that the 'list' is controlled. For instance, the relation between the resistance to the movement of advance, between the upper and lower parts of the machine, is not affected when the upper wing is rocked. When the main plane is rocked out of the 'horizontal' by the action of the supplementary plane, the machine makes a circular flight in the same way as a bird makes a circular flight. Thus the pilot can control the 'list,' and can steer to right or left as he desires. The resistance on one side of the machine is not increased when the main plane is rocked by the upper plane, since the main plane and the upper plane have everywhere the same angle of incidence. Thus there is never a tendency of the fore and aft axis of the machine to turn about the vertical axis, away from the line of flight. Therefore no movable vertically pivoted tail is required. Since there is no waiping of the wings, and since no vertically pivoted tail is required, movements to create an exact balance between the warp and the vertically pivoted tail are not required. Steering to right and left is caused solely by the rocking of the wings out of 'the horizontal.' Therefore the 'banking' is always just as much as the turn requires. If for any reason the machine acquires a 'list,' the pilot has only to rock the upper wing to correct this list, and if he desires to circle to right or left, again he has only to make one movement, namely, to rock the upper wing; the main plane is then rocked by the upper wing, and the circle is made without requiring any other attention on the part of the pilot, except that he controls the angle of incidence of both the upper and main plane, by means of the elevation rudder so as to make an ascent, a descent or a horizontal flight, taking care not to make a rock of the main plane too great for the power of the engine. If the turn becomes too quick, as may happen because of the tendency of the outer wing to rise and thus to increase the rock of the main plane, the pilot has only to rock the upper plane so that the upper part of the frame is pulled away from the centre of the circle. The main plane thus approaches more nearly to the horizontal and the circle increases in diameter.
   "My machine is almost 'fool-proof,' for, as has been shown, only one single movement must be made to preserve lateral equilibrium and to steer. This consists of a transverse movement of the lever. The elevator is controlled by a fore and aft movement of the same lever. The pilot, by rocking the upper plane, gradually rocks the main plane until the circular flight is being made as quickly as he desires, and the turn then takes place without requiring any other attention on the part of the pilot. In fact, this apparatus possesses the advantages of the bird's flight and requires little power on the part of the pilot. The equilibrium is natural compared to the forced equilibrium of the warping wing machine.
   "There is another difference between the machine described in the enclosed specification and the machine with warping wings, which is probably the greatest advantage of all possessed by the former. This is, that the warping of the wings and the movement of a vertically pivoted tail, because of their indirect action, that is to say because they depend on the speed of advance, preserve their power to restore the equilibrium, only if the aeroplane has sufficient speed to make the warping of the wings and the movement of the vertical tail effective. If the ordinary aeroplane has lost its speed of advance by being made to ascend too quickly, or if it begins to sideslip, no amount of warping of the wings and movement of the vertically pivoted tail will prevent a tendency to capsize laterally, and even in calm weather there is a tendency to capsize laterally if a single propeller is used and the engine is kept running, because of the torque of the engine acting on the machine.
   "On the other hand, the machine described in the enclosed specification may be made to preserve its lateral equilibrium, even if it has lost its speed of advance, because of the positive action of the upper plane in preserving lateral equilibrium. Thus if the machine has a 'list' to one side and has lost its speed of advance, so that it begins to descend, the upper wing, when rocked, is caught by the current of air caused by the descent, and the machine is 'righted.' In this case, the upper wing acts almost like a safety parachute, and not only 'rights' the machine but stops the descent."