Rocking Wings
Watson's full 1909 patent illustration showing the basis of the layout of his rocking wing aeroplanes. Note the distinctive layout of the Dutheil Chalmers engine. Although dated January 1 1909, this illustration was not delivered to the Patents Office until 24 July 1909; the earlier date is that on which the written patent was applied for. The Patent Office.
Although somewhat neglected by aviation historians, Preston Watson's aeronautical experiments are contemporary with those of better known British pioneers, such as Alliott Verdon Roe and Geoffrey de Havilland. In many ways Watson's experiments are of at least equal historic value today compared to those of his contemporaries, since his primary focus was developing an alternative means of controlling an aeroplane in flight - his "rocking wing" method of lateral control. Watson is known to have built three aeroplanes incorporating rocking wings, only two of which successfully flew under their own power; the first achieving powered hops of limited duration only.
From his unusual 1907 patent (Patent No.23, 553 of 1907, Watson’s flying machines), Watson reveals that he had been pondering means of lateral control for some time. On his whirling arm devices his solution to lateral control was by shifting ballast to either side, or, "...it can also be affected by rocking the wings transversely. Steering toward either side of the direction of flight... may be done by first shifting the ballast aft and, then either shifting the ballast to one side to which it is desired to turn, or rocking the wings toward that side."
In the 15 May 1914 issue of Flight magazine, Watson outlined the problem of adverse yaw, first encountered by the Wright brothers whilst flying their 1902 glider, and offered a solution as he saw it, revealing an insight into the origins of his thinking;
"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 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."
"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."
"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 a bird rocks its wings it describes a circle."
A reproduction of the Wright's 1902 glider at the Virginia Air and Space Museum. The first aircraft that was fully controllable about all three axes of movement, in the 1902 glider the Wrights first came across the phenomenon known as adverse yaw, when the up going wing in a turn stalls and causes the machine to yaw in the opposite direction of the turn. The Wrights called this "well digging", after a serious crash where Orville was injured. It was after this that they fitted hinged vertical surfaces to the glider. Author.
Regarding the Wrights' means of lateral control (wing warping), Watson claims that they, "...began their experiments at Kitty Hawk 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."
He theorised that the Wrights abandoned "the perfect method of flight of the bird" as he called it in favour of wing warping because of the considerable effort required to rock the whole surface of the wings in the manner described above. He then stated that, "less power is required to warp or to control the ailerons [Watson's italics] than to rock the wing surface in the manner of a bird."
"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 moveable tail."
It is likely that Watson’s second patent, Improvements in Flying Machines dated 1 January 1909 (Patent No.47 of 1909) was the first published description of Watson's rocking wing theory of lateral control, the function of which in a practicable sense is described by him as, "above [the main] plane...and carried by the frame of the machine is a rocking aeroplane...capable of rocking about a fore and aft central axle...”
“The pivot...is above the fore and aft central axis of the main plane and depending from the rocking plane and at right angles to it is a lever...fixed rigidly to such rocking plane. This lever is fixed in so far that it can tilt the plane...to one side or the other...” The actuation of which by the pilot induces the rocking motion of the wing.
When in flight the rocking wing functions in the following manner, "when the rocking aeroplane...is tilted out of the horizontal...by moving the lever...to one side, the normal pressure of the rocking aeroplane...is inclined out of the vertical and gives rise to a horizontal component pulling its axle...to one side relative to the line of flight.”
“The [aircraft is] thus caused to rotate about the line of flight, that is to say, the [rocking wing] becomes titled about the line of flight and out of the horizontal. The normal pressure of the [main plane] is thus inclined out of the vertical and gives rise to a horizontal component pulling the [aircraft] to one side of the line of flight."
To climb and descend in the aircraft, the vertically mounted lever, "...is moved fore and aft, thus causing the front edge of the rudder [tailplane, none of Watson's aeroplanes were fitted with a vertical rudder. The Wrights also initially referred to their horizontal stabilisers as horizontal rudders] to be moved downwards or upwards."
Because of the dual actuation of the control lever, "...the [rocking wing] and the [tailplane] can be moved so as to cause the machine to move up and down while at the same time moving to the one side or the other, that is to say that by simply moving the hand which actuates the lever in any desired direction and the trim altered."
Watson's declaration as a conclusion to the patent is in two points, as follows;
1) "In aeroplanes the use of a rocking plane situated on a higher level than the main plane, for preserving lateral stability and for steering right and left and controlled by a lever which also operates the horizontal rudder as described and illustrated on the drawings annexed."
2) "In aeroplanes the combination of a fixed main plane with an upper rocking plane as described and for the purposes set forthwith."
The centre section of Watson's first aeroplane in which he hoped to prove his theories in his 1909 patent. This was not to be however, and the aeroplane only achieved uncontrolled hops in his hands. Note the acute angle of the rocking wing. via Philip Jarrett.
Whilst undergoing flying training with the London and Provincial School at Hendon in 1915, Watson carried out stability experiments with one of the school's conventionally configured machines in flight to ascertain how they performed in comparison to his. Because his aircraft were not fitted with a rudder, he examined whether he could execute a turn without using one in a conventional aeroplane.
At an altitude of about 600 feet, he held the rudder centrally and moved the control stick to the left, then swiftly centralised it. "The machine immediately commenced a left-hand turn, as Mr Watson had anticipated", a contemporary account recorded. Thus satisfied, Watson then spoke to a Mr Kelly of the Beatty School, also at Hendon, who also carried out the same experiment in, "...a Wright machine... with equally convincing results, the machine easily steered merely by banking whilst holding the rudder central."
Despite Watson's firm belief in his system of control, however, the reality behind it, however ingenious, was that it was no more efficient that wing warping of the use of ailerons in its aerodynamic effect on an aeroplane in flight. Prompted by Charles Gibbs-Smith, when analysed by aerodynamic experts at the Royal Aeronautical Society in the late 1950s, it was found that the rocking wing had a significant disadvantage; it had the effect of a single combined aileron and rudder.
To execute a banked turn from flying straight and level, the rocking wing worked moderately effectively, but when the aeroplane's lateral equilibrium had been compromised, tipping the rocking wing in the opposite direction to the down-going wing to right itself had a tendency to yaw the aircraft in that direction. In effect, the rocking wing did not fully assist in correcting conditions of instability since the pilot had no means with which to induce or correct a yawing motion.
Another possible reason behind the rocking wing idea not progressing beyond Watson’s experiments was that it could only be applied to relatively light and small aircraft.
Had Preston Watson survived, it is possible that with continual experience flying his aeroplanes he would have thought up an ingenious solution to this problem. Although he would have had to forsake, in his mind, the biggest advantage of his system over contemporaries, the simplicity of operation of the rocking wing method (by a single control lever for pitch and roll), by perhaps adding another actuating device to adequately control his aeroplane.
Despite this however, the rocking wing means of lateral control as Watson proposed it, although it had no precedent in aviation's fledgling years, its influence and impact on history has proven to be negligible.
Next, read about Watson's aeroplanes: