Progress on Construction of All-Metal Airplanes in 1927
LONG-DISTANCE records will be held in future by high-flyers in all-metal airplanes. So at least predicts Albert Lapoule, in an article contributed to La Revue des Vivants (Paris). In it he sets forth his reasons for this belief and explains in detail what it all may mean, and what modifications will be necessary in present practises. Recent attempts of French and American aviators, Mr. Lapoule reminds us, have made the question of long-distance flight one of present interest.
In 1920 Rateau established a formula for calculating the possible distance of flight as a function of the weight of the plane at its start and finish, the power of the screw, the fuel consumption of the motor and the shape of the wings. The results given by this formula have already been exceeded, we are told, because each of the elements that entered into it has been improved; and Breguet, who took up the problem again recently looked forward to the possibility of a maximum flight of 12,000 miles. We read further:
This depends only on the distance that can be traversed before the gasoline gives out, to which must be added the gliding distance after the motor stops running. The plane, in fact, finds itself, at the end of its course, at a height of five or six miles, and the gliding distance amounts to over eight times this height. This question of height takes on greater importance as the length of the flights increase. It is not improbable that very long flights will in future take place in the upper regions of the atmosphere. It is in this way that the Germans succeeded in the long-distance gun-fire that surprized us during the war. When we exceed six miles in height, the great obstacle to speed, which is air-resistance, considerably lessens. Three hundred miles an hour can be reached, and the trip from Paris to New York will require only twelve hours. Perhaps also aviators will then be less exposed to the atmospheric disturbances that have cost so many lives. We are unfortunately very far from this at present; and the Paris-Djask flight of Coste and Rignot was made between 5,000 and 9,000 feet. A height of 12,000 feet has been quite exceptional.
The problem is much more complex than for a projectile, for it involves a self-propelling machine carrying living beings. The fuel-supply of the motor in a rarefied atmosphere has received two solutions in France. The first is to adapt the air to the motor, by compressing it before admission, as in Rateau's turbo-compressor. The second fits the motor to the atmosphere by varying the course of the pistons in the cylinders. This has been practically realized by Louis Damblanc.
The transportation of human beings under such circumstances is a more delicate matter. Nothing prevents us from imagining an interior compartment, since Lindbergh traveled in one; it will be completely air-tight and will contain air at normal pressure. But for a long trip the air will have to be renewed with a compressor automatically regulated so as to keep the pressure in the cabin constant. Thus there will be no danger from leakage, through doorways, for instance.
In one way or another, the passengers must be kept supplied with the kind of air to which their lungs are accustomed. For the breathing of rarefied air involves serious trouble. Bayeux has studied in detail its effects on rabbits. They are of two kinds—modifications in the structure of the lung and in the composition of the blood. The way to prevent them is to keep the human motor, as well as the mechanical motor, supplied with air at the proper pressure.
Speed-measurements, we are told, have now been greatly facilitated by a newly invented instrument, the cine-mitrailleuse or "motion-gun," which registers on a photographic film the airplane itself, a frame fixt to the ground, and a chronometer. This enables the exact course of the plane to be plotted, and its velocity at any instant calculated. The writer goes on:
In the early days of aviation, and until recently, the only metal in a plane was in the motor. Wood was preferred elsewhere, for its lightness. But lately metallic alloys have assumed great importance, especially in motors. Steels of various kinds—tungsten, nickel, cobalt, chrome or silicon— enter into the fabrication of cylinders, valves and other parts. But besides this there has been a veritable revolution in the general use of light alloys for all parts of the airplane. Great progress has thus been possible for the motor. Five or six years ago an airplane motor of 250 horse-power weighed 900 pounds. To-day one of 500 horse-power weighs less than 1,100.
These light alloys all have an aluminum base. Magnesium which, altho it lacks fluidity, would be very interesting on account of its great lightness and relative strength, is still too costly to be much used. Aluminum, with 5 to 8 per cent. of copper, has replaced steel in cylinders and pistons. Still bettor is " alpax," an alloy of aluminum with 13 per cent. of silicon, known only for the last two or three years. For all pieces made of laminated metal—plates, tubes, propellers, etc.—duralumin is used—an alloy of aluminum containing copper, magnesium and silicon. After tempering and aging it acquires a resistance to rupture over four times as great as that of aluminum. It must be laminated, however, which restricts its use.
We have by no means exhausted the almost infinite combinations of the metallic alloys. What we are looking for is, first, increase of mechanical resistance, and next lightness. Again, alloys that resist corrosion well on land are often destroyed rapidly by the sea air, especially alloys of aluminum and magnesium. The remedy has been sought by electroplating or by using cellulose varnishes such as bakelite; but no definite solution has yet been reached.
We have, however, at the present time, a veritable scale of alloys fit for all needs. As soon as metal began to compete with wood, the latter had to give place, slowly perhaps, but surely. Metals are homogeneous, having well-defined properties which may be varied at will by insensible degrees. Their strength is greater. They admit of economy in manipulation. Pieces are interchangeable and easy to assemble.
Finally, resistance to the weather is better, except, perhaps, as has been said, in the case of salt air.
The Germans have clearly turned to entire-metal construction. This is the ease with the avions and hydra avions built by the Junkers, the Dormers and the Rohrbachs, all branches of the huge trust called the "Lufthansa."
With us, mixed construction is still often used—the body of the fuselage and the wings are of duralumin, the frame and fittings of wood. Still, we are beginning to build entirely of metal—such are the Breguet planes, piloted by Pelletier d'Oisy, Arrachart and Lemaitre. Except for the motor, they were of duralumin and alpax.
So wood is destined to be superseded more and more by metal in aero-construction, as has already taken place in ships. Of course we shall always prefer wood for the interior fittings, both of planes and vessels. The impression is warmer and softer, when one is in a wood-paneled compartment, than in a steel coffer. And besides, is it not a comfort for superstitious passengers to be able to "touch wood"?
Source: Literary Digest - November 5, 1927