RIGID STABLE AEROPLANES.

By L. Hargrave.

[With Four Drawings]

[Read before the Royal Society of New South Wales, December 1, 1909.]
(Note: Clicking on images will open a larger version of them)

The rapid progress of aeronautics is hampered and delayed by the want of a method of ensuring automatic longitudinal and transversal stability. To remove this obstacle I repeat or refer to such knowledge as has come under my notice, my own previously expressed views, and also describe and exhibit my last experiments and explain their novelty and utility.

We find that Dr. Thomas Young 1 proved in 1800, that a certain curved surface suspended by a thread approached an impinging air current, instead of receding from it. This surface was a reverse curve like Fig. 16, Plate XVII, this Journal, Vol. XXXI, 1897.

This curve has been worried over and tried by many kite and flying machine men with no appreciable success, or it would be used in all the flyers of to-day. Then there are my papers, " On the Cellular Kite, 2 and on "Aeronautics." 3 Then we have the all important article by W. R. Turnbull, on "Form and Stability of Aeroplanes." 4

A careful reading of the articles and matter referred to will make it clear that the road was paved with velvet and I had only to dance along it and make

(1) One section of a multiple planed flying machine with reverse curves and which possessed automatic stability.

(2) Design and make a suitable type of motor.

(3) Make a working model.

Figure 1

The scale drawing (Fig. 1) shows in every detail the method of combining two reverse curves so that they shall be permanently stable, not only longitudinally but transversely. It shows how rigidity of form is maintained without the use of diagonal ties of any sort. It shows how any number of sections may be united to support any weight. It shows that the limit of weight that the ordinary monoplane or biplane soon reaches, is easily passed by the substitution of arithmetical for geometrical progression in the proportions of the lifting areas. It shows the futility of applying reverse curves to the ordinary flying machines if they are rigidly attached thereto, because the combined inertia of motor, passengers, heavy struts, stays, etc., effectually masks and prevents the instant action of the light reverse curves in automatically adjusting themselves to every gust and tremor in the air.

Figure 2a

The type of motor most suitable for driving rigid stable aeroplanes is the two-stroke spring engine (Fig. 2a, b). This scale drawing shows two views of the first one I have made; it was designed to flap the four wings 120 degrees for each explosion. Numerous errors in the strength and proportion of its various parts cannot be altered without beginning anew. The sketch shows the wing arc had to be reduced to 90 degrees to suit the exhaust ports and compression space; it also shows how the main cranks and spring cranks are arranged so that the curve of the torque produced by the spring tension, shall, when plotted on the theoretical indicator diagram, fall about midway between the explosion and compression lines.

Figure 2b

This is the cycle of events. The wings are moved several times by hand to charge the crank chamber with mixture, which flows on through the external pipe and inlet valve to the compression space and cylinder. The hands are then withdrawn from the wings, and the springs at once flap the wings and in addition compress the cylinder full of mixture into the compression space, and also recharge the crank chamber. Contact is made, the compressed mixture explodes driving down the piston, flapping the wings, storing power in the springs for the up stroke, and compressing the mixture in the crank chamber. This is all, and it is repeated till there is a misfire or the effects of bad workmanship stop the engine.

Figure 3

The small working model (Fig. 3) shows an adaptation of means to ends, and is thought to be more significant and convincing than the tabulated results of an elaborate whirling machine would be at this particular juncture. You have seen here aeroplanes with absolutely no extensions fore and sit of their canvas, that maintain automatic stability both longitudinally and transversely under most trying circumstances. You have seen how the exact work of W. R. Turnbull was not of the slightest use to aeronautics till it could be combined with the other essentials of flying. You have observed that all flying machines that have been described previously embody scaffold-like structures forward or aft to hold movable surfaces requiring constant attention, and this fact alone indicates that the art as practised to-day is at the stage it was on April l2, 1890, as per our Journal of that date. You also understand, as a matter of pure mechanics, that the air is permeated with gusts and tremors of the most rapid and conflicting nature, and that the weight of a body that has to move through it and preserve a uniform aspect, must have a minimum of inertia so that it can instantly adapt itself readily to ever changing conditions. Common sense steps in here and says: Separate the parts you want to be mobile from the parts you want to be inert. You have seen the result, and I know many have the skill to apply it.

This is the very heart of the invention, and in the present state of the industry cannot fail to be understood. I am advised that it is, or was, patentable before if was exhibited here, but mature thought shows the perfect impossibility of collecting revenue from the consumers who are the practicers of the art I wish to advance and not to retard.

Figure 4

If the string and weight are swung without the rigid stable aeroplane, the string can only describe a blunt cone with the apex upwards. When the aeroplane is tied to the weight, the apex of the cone is downwards, indicating that the aeroplane at that velocity is lifting more than the weight. A great increase of velocity adds enormously to the weight on the aeroplane, as the weight is trying to flatten the inverted cone.

Used as kites, these rigid stable aeroplanes are superior to the very best cellular kites I can make; they are lighter, pull harder per square foot, attain a greater angle of elevation, and have fewer parts. When their qualities become known, the two-celled kite will be considered a, barbarism of the past. The ladder kite that was experimented with in 1897 (Fig. 4) is a very light and compact term of multiplane lifting surface. The twenty planes are 1 foot 5 1/3 inch square; they are spaced one foot apart. The two highest planes are strutted into the box form; the rest of the side surfaces are quite loose and only tightened by the lift of the planes. The best way to fly this kite is to lay it out on the ground in either of the dotted positions shown on the plan. Pull a little on the string that is not lying on the ground, thus squaring the rhomboidal shape of the kite, and it will at once assume the upright position. Similarly by pulling either string the kite will lay itself down without damage on the side that it is pulled. If you pull A the kite lies down at C. If you pull B it lies down at D. The kite, when on the ground, does not roll away to leeward as one might expect.


1. Progress in Flying Machines, by O. Chanute, p. 9.
2. This Journal, Aug. 5, 1896, p. 144.
3. Loc. cit., June 1, 1898, p. 55.
4. Scientific American Supplement, No 1726, Jan 30, 1909.
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