American Planes: The Lessons of History
One of our foremost aircraft engineers, Grover Loening has been building airplanes since 1911. He was general manager of the Wright Company, Dayton, Ohio, 1913-1914; inventor of the strut-braced monoplane and Loening amphibian airplane; and was awarded the Distinguished Service Award in 1919 for the Loening two-seater fighting plane. He received the Collier Trophy in 1922 and the Wright Brothers Memorial Trophy in 1952. Mr. Loening speaks with authority and experience in this striking comparison of aircraft development here and in Europe.
To anyone who has been identified with the aviation industry for as long as three decades, and to anyone who is willing to admit our mistakes, it will seem at times as if our progress in heavier-than-air aviation had been less audacious than that of our European competitors, and that despite our initiative we were constantly held back by our consideration for regulations and for models which were already obsolete.
Right under our noses, today, are wrong trends, unrealized, and right trends, unappreciated, because we don't think things through. The turbojet engine, for example, could have been built and used thirty years ago. And why was it not? Because at that time we were thinking in terms of 100-mile-per-hour aircraft, and any designer would have known that the fuel consumption was prohibitive. None of us realized then that the jet engine immediately meant 600 miles per hour. And so we missed it.
Another thing that kept us from going ahead faster was the belief that engines and air frames are separate entities. A review of aircraft design clearly shows how much time and cost were consumed in trying to fit existing engines into air frames that were never designed for each other. The two are, after all, a unit, and—with the advent now of vertical flying—air-flow requirements around a wing from the jet engine gas generator source make the wing construction an intimate part of the power plant.
Some clear and not too pleasant lessons are to be learned from a reflective perusal of the more than half century in which we have developed our air travel. One is how often designers and constructors have failed to finish up what was started. As a result of discouraging initial troubles and "bugs"—often intensified by lack of foresight and interest on the part of the aircraft customers, military, industrial, and civilian—the continuity of effort required to achieve success petered out, and consequently highly desirable developments that had been started were abandoned, only to be revived years later,
Many a novel and significant idea or suggestion has lain on our doorstep for years, unappreciated. Let us look at a few examples:
Wing structure
In America, where flying was born, the biplane dominated our picture for almost twenty-five years, despite the obvious success of the monoplane in France and the fundamental correctness of its aerodynamics.
The Junkers low-wing, cantilever stressed-skin, all-metal monoplane, after its development in Germany in 1920, was brought over to this country and promptly ignored. It was not until William Stout developed the Ford planes many years later that we moved seriously into the stressed-skin metal structure. Fokker, during the early twenties, also chose the cantilever stressedskin, but used plywood covering (which could not take the weather).
Landing gears
In earlier years, landing gears started with skids, to which wheels were added; but the skids were left on, only to become the cause of many wrecks when they broke on hard landings. From the very beginning, wheels alone were, obviously, the correct solution. In Europe, Bleriot, and in America, Curtiss were unique in realizing this, and the practical three-wheel gear was constantly being demonstrated as successful and correct by the early Curtiss planes. But practically no one else saw this. Even Curtiss gave it up later.
It should have been obvious that retractable landing gears were desirable at the earliest date at which we reached a speed of 100 miles per hour, 1912. But not until the advent of the successful amphibian plane (which had to have its landing gear foldable) did we learn that retracting a landing gear and housing it were neither too complicated nor too heavy. Nevertheless, it was some six or eight years before retractable gears came into more general use.
Engine placement
On the early configurations in America, engines were to the side of, or behind, the aviator. The Wright design, translating twelve horsepower into effective enough thrust to fly eight hundred pounds, needed the two large geared-down propellers; in fact, this was one of the secrets of their success. But as more powerful engines came along, such as in the case of Curtiss' using his motorcycle engine, the gearing-down was not needed, but the engines were kept behind the pilot. It is curious that we should have done this in the United States, when in France the great early pioneers, Bleriot and others, from the start had tractor-type monoplanes, although Farman and Voisin also used pushers.
It was not until 1913 that America saw the Burgess tractor with Renault motor, the Glen Martin Model T, and the Curtiss N, which later became the ubiquitous JN-4 (the Curtiss Jenny). As far as the general industry is concerned, we waited four or five years before adopting the tractor-type airplane, which was to become practically universal as a land plane, even when later developed into multimotor models.
Enclosed bodies
The advent of the fuselage with enclosed seating was stimulated, of course, by the use of the tractor engine. But it is remarkable to note that the obvious further streamlining and closing in of the fuselage lagged for a few years. Nieuport, in his revolutionary little monoplane of 1910, which swept the field in competitive performance, practically started this vogue. But the enclosure of the aviators themselves in a cabin was very slow in coming, arid it was not really until some ten or fifteen years later that the majority of the aviators, including the military, discovered that they need not have their heads out in the open air in order to fly and permitted their prejudices against closed cabins to give way to the comforts that were immediately evident.
High-lift devices
Flaps and slots to slow down landing speeds or rather to permit higher cruising speeds and heavier loads without too great a landing penalty, were a long time coming—much too long.
Handley-Page and Lachmann in Europe and Orville Wright in this country were researching these high-lift aids in the twenties. In fact, it is not generally known that Orville Wright in 1923 patented the split flap. By 1926, Handley-Page slots had been applied to the British Moth plane with great success. The first such Moth was imported to this country by me and flown widely in the East. Still, many airplanes were being built, developed, and accepted with no thought of high-lift devices. Others worked on this addition to wing structures, notably Harlan Fowler. Then, in 1929, the Guggenheim Competition was held, specifically designed to advance airplanes that could land in smaller fields over obstacles without sacrifice of useful high speed.
The winner of that competition was the Curtiss Tanager, a very intelligent design that made full use of the then existing high-lift devices. Did all aircraft, the year following, adopt split flaps, or Fowler flaps, or Handley-Page slots that had been so successfully demonstrated? They did not. There was the usual opposition, criticism, and delay for several years more before this highly desirable development in aircraft wing structure came to its now universal fruition.
Even recently we have had a rather surprising example of delay in acceptance: the HelloCourier, developed in Boston by Koppen and Bollinger. A convincing demonstration of this STOL (steep take-off and landing) airplane, with its correct use of slots and flaps for higher lift, was witnessed more than seven years ago, and, despite the great need of our ground Army for a plane of this type, it is only recently that the Defense Department has become interested and ordered some.
Power plants
The Wrights designed their own engine for their own aircraft, and for its purpose, it was correct. In France, in the earlier days, most of the early power plants were derived from automobile or motorcycle sources. The first plane to fly in Europe, the Santos-Dumont, used a thirty-horsepower, two-cylinder Darracq motor. Before long—1909—the French developed the Gnome rotary air-cooled motor, which took over the field for several years in ever-increasing sizes and types and went into wide use in World War I.
In America we developed the Liberty motor, and in Germany also there was wide-development of water-cooled automobile types of upright engines. For an automobile this type of engine with crankshaft low was correct, but it was entirely wrong for aircraft.
From the beginning it was highly desirable for the crankshaft to be high, so as to provide pro-peller tip clearance, to keep the center of gravity low, and to enable the pilot to see over the engine. But it was not until 1924 that we finally saw the light and inverted the dry-sump Liberty engine in the configuration that it should have been in all along. Except for its successful use in the Loening amphibian, the change came almost too late, because the Liberty engine was shortly succeeded by the generally adopted radial air-cooled engine that developed from the pioneer work done by Charles Lawrance, the designer of Lindbergh's Wright Whirlwind engine.
Materials of construction
Materials of construction of aircraft have gone through many cycles. For several years after World War I and in spite of the Zeppelin duralumin development, aluminum was suspect as a structural material. The famous, specification 100-A of the Navy prohibited the use of aluminum in any structural part of aircraft. This is a pertinent example of how too rigid specifications, based on what was good practice in previous years, can prevent future development.
Today we face a similar situation in prohibitions against Fiberglas or plastic stressed structures because difficult, theoretically, to calculate and check the stressed condition. Yet plastics may well have as great a future in aircraft structures as dural stressed-skin monocoques and wing panels had thirty years ago. We hardly need to recapitulate how metal took over from wood and replaced a material that just could not stand the weathering difficulties of day-in, day-out air operation compared to aluminum alloy, so long-lasting and reliable. New alloys—titanium and others—are also beckoning alluringly, like Fiberglas, for a chance to show their worth. Also "sandwich" materials are most promising. Will we still be slow to pick up the ball?
The lesson one seems to gather from these and many other instances of long delays in acceptance is the unpleasant one that aviators' likes and dislikes were given too much weight, and hence discouraged the engineers from perfecting their developments. In retrospect, one finds that worthy developments were ignored or abandoned because they were politically unwise. Many a wing flutter that scared a test pilot condemned to utter oblivion an airplane that had structural or configuration features of great importance and advantage. Had the customer and the builder been patient or wise enough to work out such "bugs," success would have followed more quickly.
On the other side of the picture, many an airplane with little commercial or military value was used for years because the upholstery and the windshield were well worked out or because a lucky combination of slip stream and wing flow (totally unforeseen by the designer) gave unusually good control on landing, which pleased the pilot. Another personal prejudice revolved around ease of egress in case of accident.
As the years went on and there was a more scientific appraisal of new aircraft through test flying, other drags on development occurred, causing unnecessary time lags from the day of inception to the hardware-in-use stage. These delays were largely bureaucratic.
In 1926, the original Civil Aeronautics Act, reinforced by the later enactment of 1938, put the government into the position of passing judgment on the aircraft that the aviation industry wished to sell to the public and issuing certificates of airworthiness. We accepted this supervision unthinkingly, largely because of the supposed great risk that a gullible public would be subjected to by having offered to it all kinds of aircraft that would fall apart in the air.
And then the bureaucracy really got to work. The inspection and engineering staffs of the Civil Aeronautics organizations of the government had to grow with each page of more and more detailed specification that the law called for. But here is the fallacy: by necessity, such-specifications must specify last year's aircraft, because the writers of the specifications are not inventors or developers. Here is an example.
After World War II, in 1946, Robert Fulton designed and built in Connecticut an interesting new aircraft called the Airphibian, in which the body contained the engine. It was a perfectly operable small car from which the wings could be detached. Fulton never complained, but went through the Civil Aeronautics certification procedure. He was an expert designer and skillful builder. He would have had an immediate market from 1947 to 1950, but it was not until 1952 that he had managed finally to complete the Civil Aeronautics procedure. By the time he got his certificate, other developments in aviation had caused him to lose his market. The procedure had brought about practically no changes in the aircraft, but had changed many pages of Civil Aeronautics rules by waivers and allowances. Not all cases of CAA certification have been so bad as this, and recently there is much improvement—not in the law, but in the more liberal way the CAA and the FAA are interpreting their mandate.
Let us compare this experience with that of the automobile industry. The automobile in the hands of the public is fully as dangerous as aircraft, and yet there is no Washington government bureaucracy that requires each new model to have a "certificate of road-worthiness." To be sure, in the last fifty or sixty years, many automobiles have been discarded; some of them were badly built and dangerous, but the consumer, quickly found this out, and the death blow to the company's product was so strongly disciplinary that the companies which survived did so only by the most careful designing and the most exacting test procedures of their own, before the public could even get a look at their product. The states do a simple job of checking every car for safe conditions, but no design certification is thought of.
This is as it should be, and here is a lesson from the past that we could apply almost at once to small aircraft for use as private vehicles. Of course, huge air transports carrying more than a hundred passengers are comparable to ships, and some government and certification may be needed In this certification and inspection area, should not the insurance companies take a much greater role—as Lloyd's does in shipping? Let us think hard about any system that will get us away from the cumbersome governmental one our laws now call for.
Another bureaucratic drag on progress is in the system involved in what the Air Force calls "the Requirements Division." Here we are supposed to have the official requirements for new aircraft. For purely military requirments, such as the need to carry a larger gun or a different kind of bomb, this is fully justified. But it has unconsciously been extended by the Pentagon bureaucracy to cover too many broad features and types of aircraft. It is perfectly safe to say that, had the Junkers design been presented to a requirements division in 1920, the answer would have been: "We have no requirement for a low-wing stressed-skin all-metal aircraft."
Had an inventor appeared at the Requirements Division of the Air Force as recently as 1953 with an effective way to muffle the noise of aircraft power plants without sacrifice of performance, the bureaucratic system would have informed him: "There is no requirement for such a development." Intelligent and progressive officers sometimes alter these procedures on their own, and a new requirement is, in rare instances, created.
Russia seems to move more quickly in reaching hardware-in-use stage after early inception. As nearly as we can ascertain, the Russians do not use our system. This situation we had better study. Instead of a Requirements Division, perhaps we had better have a Stimulation Division.
We are at a disadvantage, however, operating in our private enterprise system, because the expenditures of government have to be substantiated, audited, and interminably reviewed, even to this day's unwarrantedly punitive renegotiation nonsense.
Let us now look at today's aircraft operation for some further lessons and possibly to anticipate some future troubles.
Today all aircraft can be spun and recovered with safety; forty years ago, this was not the case. As a matter of fact, up to 1913, the "spinning nose dive" or the deadly "spiral dive from air pockets" was the disheartening cause of accident after accident., At Dayton, in 1913, we witnessed a vital moment in airplane operation. This was when Orville Wright, so discouraged by the accidents that were happening to his exhibition fliers and to a whole series of Army fliers (Hazelhurst, Love, Kelly, and others), was determined to test out what was happening.
Before long he himself came back from a test flight smiling instead of grim, because he had discovered what a "spin" is and how to get out of it: namely, by pushing forward on the controls; and why so many aviators had been killed: namely, by pulling back on the controls at the wrong time.
Now, forty-six years later, when we fly through the sound barrier, we discover a brief moment when controls are reversed. And today also we are somewhat plagued by "pitch-up" in the control of supersonic aircraft. Recently a jet airliner suddenly dived 29,000 feet. Are these manifesta-tions of some new operational characteristic of swept-wing aircraft which may require controls other than those we have provided?
The operation of aircraft has become very complex, because of the constant addition of instruments: We have gone a long way from our first instruments—the string for sideslip, wire whistling for speed, and the railroad track for navigation! Are our present instruments the ones we should have? Has not the barometric altimeter caused us so many accidents that we should long ago have gone to something better? Our automatic pilots are all based on known flying procedures. What if the new types required some new controls of flying procedure, or crossed controls to prevent pitch-up or the swept--wing dive? It is exactly in such areas that we are much too complacent and ignore problems that should alert us more quickly to the utmost inquiry.
In 1917, Lawrence Sperry invented and demonstrated the turn-and-bank indicator. In 1934, the Army took on the airmail. Its planes did not have the turn-and-bank indicator as did the civilian planes. This one regrettable oversight was so serious in causing accidents that the cancellation of the Army's effort followed.
Noise
Noise abatement is now one of our most irritating problems, but we should know by now that abatement is not the answer to noise. The answer is to design a power plant with as much a fundamental limit on noise, in its original design, as there is today on its fuel consumption and weight. We can soundproof against internal noise rather well in a cabin, but external noise has made the airplane an undesirable neighbor, to the point that it has been ruled out in many places.
Airports
Literally billions of dollars are being spent on airports around the world. In too many instances, particularly in America, these are one-runway airports—in other words, one-track railroads. It is difficult to understand why this is so, when we stop to remember that whole squadrons of aircraft during the war (and even now) landed on reasonably wide runways within a few feet of each other at the same time, and similarly took off in formation. Why should not an airport have at least three runways in each direction, spaced possibly 300-feet on centers? It could then land aircraft three at the same time.
The hesitation on this is typical of our complacent thoughtlessness. There is no danger involved. Thousands of times a day the pilots of large transports land their planes accurately and within a few feet of the center line of runways.
Radio of course, has helped tremendously to bring about the era of practical civilian flying, and it still can be counted on to give us the things we need: simple collision-avoiding, close-reading radar with one-mile radius, not two hundred miles; direct-reading radio altimeters; more and better lighting of airports and runways. And in regard to all these instruments and landing aids using electronics one must not overlook the fact that visual line-of-sight above the horizon does not work for a low-flying airplane or helicopter, flying behind hills or buildings.
The jet plane development
Jet planes are not being developed in the same way in America as they are in Europe in one particularly prominent characteristic: the location of the jet engine. The Douglas DC-8 and Convair 880 have followed the lead of the Boeing 707, which naturally followed the lead of the B-47 and the B-52. Unfortunately, these leads seem to derive from the old position of piston engines in nacelles mounted outboard on the wings. Here we have a typical illustration of a lesson not learned. For a jet engine this is clearly not a good location. Jet engines are very light, so that the structural saving of spreading the weight over the wing is much less than in the case of the piston engine. Also there is no propeller clearance requirement. But the engines are now located so low that they will ingest any loose material on the runway with great risk to the delicate turbine engine interiors.
The outboard engine is so low that a tire or wheel failure on one side would come near to breaking it up on the ground, followed possibly by fire from the gas tanks above it. The position of the engine under the wings makes the wing a perfect sounding board to disturb the neighbors below, and the inboard engine is so located that its noise cone hits the rear of the fuselage, the result being almost unbearable. The builders and operators are aware of these features and are doing all they can still to give us excellent safety.
But in Europe, most of the newer commercial designers completely separate themselves from all piston engine concepts by placing the jet engines where they belong: above the wing and to the rear, mounted to the fuselage and leaving the wing with perfect aerodynamic cleanness. Maintenance also is improved by this location. The vertical-take-off concepts mentioned below may soften the impact of this questionable American design. Let us hope they do.
The lift plane: VTOL
The biggest revolution in the coming design of useful aircraft will be in the advent of the direct--lift airplane, sometimes awkwardly called VTOL (vertical take-off and landing).
After ten years of intensive research, resulting in several bookshelves full of excellent laboratory reports on how to make a fast airplane land vertically, it is only this year that we are beginning to show the needed interest and the beginnings of progress in this development. Boundary layer control is only one facet of this. Tilting wings, tilting jet engines, and other ways are being developed.
The helicopter does not quite fill the bill, simply because its speed is limited on account of the rotor configuration. Even if helicopters get up to a high cruising speed of 200 miles per hour, they will still at that time have to compete with fixed-wing aircraft of over twice that speed.
Now, throughout the history of aircraft development there is one lesson that stands out clearly, and that is that high speed is always the successful characteristic of any type of operation, even on the shortest ranges. Slow aircraft, no matter for what purposes, have never survived.
On the other hand, the airplane as we know it is a very deficient vehicle because it cannot slow down, hover, and back up, as every other vehicle can do. The penalty we pay for this characteristic—of having to keep going in order to keep up—is great. More skill is needed in operation. Prepared airports must be provided with preposterous runways of 10,000 and 15,000-foot length. As many as a hundred square miles of a airspace must be reserved for each jet plane while it awaits its turn to land on the one-track-railway airport. All because jets cannot slowdown below 180 miles per hour!
There are many objections to lift planes (VTOL) now being voiced. One is that the fuel consumption for vertical flying is utterly prohibitive. In the light of history, this belongs with the objections that were raised to monoplanes, to metal construction, and to slots and flaps.
A simple analysis will show quite quickly that while direct lift by jet will need three or four times the thrust of the existing jet engine configurations and will, therefore, use three times the fuel, the actual fuel used by the jet transport in taxiing out to the end of a long runway, waiting for clearance, making the long take-off run, then climbing to 1000 feet is, if anything, more than the direct-lift plane would use rising immediately from its pad at the loading ramp with all engines full-out to 1000 feet and then shutting off its lift engines.
Another argument in the same class as these old shibboleths concerns the additional 'weight involved in the extra jet engines for vertical thrust. Actually, vertical-lift capability means a much lighter landing gear; in fact, it might almost revert fifty-seven years back to the Wright skids, to an aircraft with practically no landing gear at all (just little rollers to push around the -rarnp), so that the weight of the extra jet engines that are needed for the vertical operation could be compensated for and would represent no more of a burden to the aircraft than did the landing gear itself. Originally, this represented 6 to 10 per cent of the empty weight of the aircraft, used only for a short while on landing and take-off and carried neatly folded in precious room in the body for thousands of miles in which it was utterly useless. Whereas the extra jet engines could, in a pinch, be used if the other power plants failed, or for quicker climb.
And with the ability to rise vertically and fly fast, the lift plane in smaller sizes (if not too noisy) would at last penetrate the open and fertile field of private vehicle aircraft—which has hardly even been touched, although we already lead the world in this field.
Immediately when we contemplate many different designs of aircraft for vertical lift and high speed, we find that the gas generator (the jet engine power plant) will most likely become an intimate part of the wing.
In 1926, Henry Ford visited an aircraft show in Detroit. As he was leaving, he turned and looked over the planes and said, with his usual finality and quickness: "Let me tell you, these things will never amount to anything until they use their power to land with." History will show that he was right.
The growth of air transport in the United States from nothing in 1920 to 24 billion passenger miles in 1958 is merely a beginning. We will shortly progress into supersonic flying, all over the world. Craft which will go to Europe in an hour and around the world in eight hours are on the drafting board. But there is much left to do to perfect our utilization of the air ocean in which we live. Tolerable noise, vibration, and acceleration must accompany supersonic flight. And greater safety!
We are becoming aware that speed is the raison d'être of flying, particularly in air transportation of passengers. Have we learned that the greatest comfort of all to a passenger is the notice that he has arrived? A supercomfortable seat does not balance a tediously slow aircraft.
Also one last thought, almost in metaphysics. History seems to show that anything man can clearly imagine eventually materializes into reality. In our travels and in the movements of ourselves and our goods, we are about to obsolete the wheel, just as the wheel and axle invention obsoleted the skid, some ten thousand years ago.