W. LeMaitre

“ The consequence is that an aeroplane which is safe enough while the propeller is exerting a tractive force of some 250 lbs., becomes, the moment this power is for any reason stopped, merely a shapeless construction at the mercy of the wind and the force of gravitation. It is true that most machines may be made to glide if the pilot is clever enough and quick enough to steer them into the proper gliding angle, but the machine that will naturally and by reason of its design assume its proper gliding angle when the propelling force is withdrawn, has not yet been built. ”

“ Considering that the propeller is the only means the aeroplane has of keeping in the air at all, the question arises: Is it possible to design a machine that will be stable to the extent of descending safely when the propeller stops, and that will yet be a good and speedy flyer? ”

“ THE LOW CENTRE OF GRAVITY.
The first thing that occurs to the investigator on the subject of stability is that nature offers us a sure means of keeping our machines upright by adopting the simple method of placing all the heavier parts at the bottom. In all other constructions we have adopted this plan with perfect success. In boats, yachts, cars, balloons, everything man uses in fact, the simplest, best and most obvious method of keeping a thing upright is to utilize the force of gravity, place the lighter or supporting parts above and the weight below, and the thing is done. ”

“ In constructing any sort of machine it is usual to first obtain the most important device and then to build up the accompanying parts to that. We have now succeeded in evolving the thing we set out to look for, i.e., a plane which will fly and lift with the minimum of head resistance, and which is absolutely stable laterally and longitudinally by reason of its construction and without any interference from the pilot or the employment of balancing devices of any description. ”

“ Since there is nothing new under the sun, it is useless to pretend that there is anything new in the design here advocated or the theories advanced. Both are rather the result of a commonsense consideration of the different points of all flying machines, natural and artificial, and an endeavour to select from the great number of good points those which seem most likely to blend together into a practical machine. ”

“ In reducing the span, however, we reduce the lifting surface of the machine. But on the other hand it must be remembered that the lifting efficiency is increased by increasing the speed. Lift is the product of supporting surface and speed. A small plane driven at a high speed will give as great a lift as a large plane driven at a low speed. Speed, again, is the difference between the propelling power and the head resistance, and we can increase the speed by decreasing the resistance. ”

“ The third point to be considered in the problem of speed is the resistance caused by the multitude of struts and wires, the body of the pilot, the tanks, engine, and all the other impedimenta projecting in all directions from the body of the aeroplane. It has occurred to our builders that if the whole of these things could be collected together and enclosed in a light covered-in car of a proper shape, the skin friction of such a car would be much less than the total head resistance offered by the different obstructions so covered. ”

“ To convert a high speed machine into a low speed machine means either variable surface area, variable camber, or variable angle of incidence. Any of these is possible, but the choice must be decided by simplicity of action. To spread extra wings when rising or landing is a cumbersome suggestion full of pitfalls and liable to accidents through the failure of mechanical [Pg 37] devices, which, experience shows, always have a way of failing at inopportune moments. ”

“ It is well known that all pendulum motion tends to damp out, and the shorter the pendulum the quicker it comes to rest. Hitherto the idea has been to shorten it vertically, [Pg 21] but the same effect exactly is obtained by shortening it horizontally, and the low centre of gravity remains to give stability. It was stated by some sapient objector to the low centre of gravity, that the pendulum motion once set up, increased till it turned the machine over. A pendulum which increased its swing at every stroke would be something new in the scientific world. ”

“ All flying machines will glide if put at the proper angle, and it [Pg 38] is the business of the pilot to attend to this when he stops the engine. But to glide with the same wing area as is used in flying, means to glide at the same rate. In order to descend slowly it is necessary to have more area. Is it possible to increase the area used for descent without interfering with the area used for flight? In the design we are engaged in considering, it is possible, and without any mechanical devices. There is a large space between the front plane and the back plane which is at present unused. ”

“ But the span is not the only factor in the speed problem. In the low speed machines at present in use we have found it necessary to curve the planes to get greater efficiency. This efficiency is also gained at the expense of head resistance, and it is already recognized that the higher the speed the less is the need of camber. This is the same problem over again. A high speed flat plane will give as much lift as a low speed cambered plane, and we gain in stability with every additional mile per hour. ”

“ The curious thing about it is that it does not seem to have occurred to our designers that if their pet design would not fly with the weight low, perhaps it might be possible to alter the design instead of altering the position of the centre of gravity, and so obtain what we are all looking for, a naturally stable machine that is yet sensitive to control. ”

“ To drive through the air at a high speed with a machine of 40 foot span is a practical impossibility, both because of the tremendous power it would require and also by reason of the great strength the plane must have to withstand the resistance of the air. ”

“ It is, then, quite possible to design a short span machine which shall be as efficient for lift as a long span machine, and which will have the advantage of possessing, by reason of its speed, much greater stability. ”

“ That is to say, its wings being started in a horizontal plane, would tend to keep in the same plane and would not easily tilt or sway out of it. Both these effects of natural law show that a high speed machine must be more stable than a low speed machine. How then are we to design a high speed machine?
Leaving aside the question of higher power, the first point that suggests itself is to lessen the head resistance. All fast things, boats, birds, arrows, even motor-cars, are made long and narrow. ”

“ It will be objected that a bird with its wings outspread is not long and narrow, but in the sense in which this illustration is meant, the bird’s wings, being merely its propelling apparatus, do not count, and when the bird is at its fastest, as in the swoop of a hawk or an [Pg 15] eagle, the wings are shut tightly to the body so as to offer no resistance to its lightning passage through the air. If we are to follow previous experience in Nature’s laws, our aeroplanes must be considerably reduced in span. ”

“ It is recognized on all hands that speed is a great factor in the problem of stability. To begin with, a machine going at high speed would be practically untouched by gusts of wind, different densities of air strata, holes in the air, etc. ”

“ Both on account of speed, and also on account of stability, with a low centre of gravity, we are forced in the direction of the short span machine. How are we to construct a machine with a span short enough to damp out swaying and yet with sufficient lifting surface to raise the machine and its load? ”

“ A model made on these lines will not need putting at any angle. It will assume its proper angle when left to itself by reason of its design and the way the weight is balanced between the supporting planes, and it will descend by partly gliding and partly parachuting at a steep angle but quite slowly. While, if the pilot so choose, he can, by raising the tail, increase the speed to a glide, which he can turn into a parachute action at any moment. ”

“ It may be objected that a bicycle does not do this, and this is true, but, on the other hand, the upsetting of a bicycle is a very small matter, whereas the tilting of an aeroplane mostly means sudden death to its occupant, and it is probable that if the same consequences followed the tilting of a bicycle, bicycles would soon have been made with four wheels. ”

“ It will be recognized that in the design here being gradually evolved, the great lifting surfaces of the ordinary machine have not been largely reduced, they have simply been broken up into several smaller surfaces, each of which retains its efficiency. ”

“ Olympia Show, in order to show the construction of a full-sized machine made to the design of the paper model. This has since been considerably simplified, though the broad lines have been retained, by doing away with the struts and supports at the rear. The whole of the back plane is now supported by two curved members, which start from the girder of the leading edge and curve down to the T-section longitudinals which form the rigid part of the chassis. These longitudinals and the skids end at the leading edge of the back plane and the laminated skids and wheels are placed there. ”

“ It follows, then, that we need not necessarily give up lifting power by reducing the span of the wings, since the shorter span gives greater speed, and the increase of efficiency by reason of the greater speed would go to make up for the loss of span. ”

“ And there is another advantage to be gained here, for if, at 40 miles per hour, the force of the wind is very seriously uncomfortable for the pilot, the position at such speeds as 70 or 100 miles per hour would be quite impossible. ”

“ The whole of this part of the machine is rigid and braced together by means of struts, though whether made of steel tube or timber, there must always, from the nature of the construction, be a certain amount of elasticity which makes for strength, a great [Pg 44] advantage over a construction braced rigidly by non-elastic wires, which snap instead of giving to a sudden strain. ”

“ To vary the camber of the planes is easier, but having decided on using flat planes it would be loss of strength to make these flexible, and an increase of mechanical complications to have to flex them. ”

“ The shock of landing is, therefore, taken first on the wheels, and should it be sufficiently heavy to cause the skids to touch the ground there is still the series of laminated wood springs to absorb any vibrations and prevent any possible shock to the car. ”