During the years immediately preceding the outbreak of war, a number of articles were written for various aviation and military magazines discussing the relative merits of flying boats and of large land-based airplanes. This discussion, like the air-cooled, 1iquid-coo1ed controversy, produced no real conclusion and was cut short by the war which welcomed anything that could fly. Flying boats like the Martin Mariner, the Consolidated Coronado, the Consolidated PBYs and various British types are in steady service and are giving a good account of themselves. At the same time, the Navy has turned enthusiastically to land-based Liberators. If the Army fails to use flying boats on occasion it is largely because we have fewer flying boats than land-based aircraft.
On the other hand there is the problem of private flying. Because of war training there are now at least one hundred thousand more Americans with pi1ot's licenses than there were three years ago. By the end of the war this number will have swollen to at least 250,000. Add to these the 750,000 men who failed to complete their military pilot training who can qualify for a civilian license and you have 1,000,000 brand new postwar pilots. Whatever helicopter production may or may not be, it is quite likely that the greater part of this million will forego the helicopter and will clamor for orthodox airplanes.
We can expect a mass demand for large-size passenger aircraft on the one hand and a mass demand for small private aircraft on the other. It may be said here that the question of flying boat and land-based aircraft efficiency does not affect the second kind of demand. But this comparison may arise for reasons which have little to do with flying. It is a question of airports and the money needed to build and to maintain them.
Much of the early discussion regarding large planes was concerned with questions of safety. It was claimed that land craft were essentially safer over land, while flying boats were less dangerous over water. This argument is now obsolete. A comprehensive survey made just before the war revealed so many sufficiently large bodies of water in the United States that transcontinental flights by flying boats can be considered quite safe. The war itself has produced additional proof. Consolidated has flown thousands of miles overland to deliver flying boats while land-based aircraft have been used extensively over long stretches of open water.
In engineering principles, flying boats and land planes of similar size and range Consolidated's Coronado and the Liberator for example offer little for pro-and-con comparison. According to Theodore P Hall, chief production engineer of Consolidated, the both planes cost about the same for fabrication, on a pound-for-pound basis. But the flying boat comes out some 20% heavier. Consequently, it consumes a comparably greater amount of gasoline. This produces the greatest cost of differential. At the same time, this aerodynamically "unclean" hull of a flying boat reduces the speed somewhat. However, Mr Hall declares "there is little use in comparing the planes as such, but only in relation to the job they are going to be called upon to do. Where high speed is essential and where suitable airports are available, I think it is safe to favor the landplane. On the other hand, when very high speed is not essential, and where there are no suitable airports, I think the flying boat can do the better job."
It should be emphasized that all foregoing remarks apply in production and in service. But what about planes of 200,000 pounds or larger? There can be little doubt that the flying boat will do better from the engineering point of view when growth has progressed to that point. In comparing all sizes up to the Coronado class, we find that flying boats are always heavier than land planes of equal size, power and load-carrying capacity. However, this weight difierential decreases proportionately as the overall plane size increases. If this is due to unalterable natural factors there must be a point at which flying boats become lighter than land planes. Then their only engineering drawback will be the aerodynamically inefficient hull.
Apparently, weight differentials do represent unchangeable natural factors. As size increases, the weight of the flying boat hull expressed as percentage of gross weight will decrease, the weight of the land-plane fuselage stays about the, same, but the weight of the landing gear of a craft changes rapidly. As plane size increases, undercarriage weight skyrockets. The reason is simply that structural weight in wheels and aerols increase at a much higher rate than the gear's carrying capacity. With currently available materials and equipment, the flying boat surpasses the land-based plane on this point well below the 100-ton level. Thus, it becomes the lighter and more efficient aircraft, despite its slow speed, when a gross weight of 200,000 pounds is reached.
This is an engineering plus factor but it is only part of the whole story. Let's look at the ground now and consider the airports. The equivalent of an "airport" for the flying boat, is a body of water with a certain minimum clear surface and depth. To determine this depth, the author contacted several flying boat manufacturers to learn the draft of various flying boat types. Glenn L Martin reported that the fully-loaded Martin 130, known familiarly as the China Clipper, has a draft of 37" while the Martin 156, the so-called Russian Clipper, has a draft of 42". Loaded takeoff runs are 2600' and 2900', respectively. Though non-committal on the length of the takeoff run "the time is from 30 to 50 seconds, depending on load, wind and water conditions" Boeing reported that their Model 314, Transatlantic Clipper, has a draft of 48" in calm water. Surprisingly a pontoon-equipped small Fairchild has a draft of 50", requires a takeoff run of about 2000'.
From these reports we may assume that existing marine planes, with the possible exception of Martin's Mars, could be launched from and landed on a body of water 4000' long, 75" deep. To build an airport with runways suitable for landplanes of the same weight, means considerable expenses. Water areas, on the other hand, which meet flying boat requirements are often available without cost. The cost of hangars would be the same for both plane types, while the cost of beaching gear and ramps necessary for marine operations is far less than runway constructions.
A survey made shortly before Pearl Harbor revealed that there were more marine sites available in the United States than there were airports and the marine sites were free-of-charge.
It seems, therefore, that large flying boats, even at a size still inferior to comparable landplanes on a weight basis, are much more versatile. Any lake, river, large reservoir and coastal area is a landing field for the flying boat. If it should be overloaded and should need a long takeoff run, the space is usually available at no extra expense. Maintenance is restricted to hangars and beaching gear.
In considering the expense of construction and maintenance for postwar flying, municipalities can expect lower costs with landing puddles than with airports, simply because so many suitable water areas exist. Even creating one may be cheaper under certain local conditions.
Private flying, too, may expect an economic lift from water bases. The figure of 50" for the pontoon-equipped Fairchild plane is high because this plane has pontoons. A small, three-passenger flying boat is unlikely to draw more than 12" under such conditions. Any flooded meadow will suffice for nonscheduled flights and the number of emergency landing puddles available in half of our states will be incredible. It is true, of course, that the small flying boat might cost a little more than a plane of the same weight-carrying capacity. It is also true that it may be of some ten or fifteen miles per hour less speedy. It may use a little more gasoline. But every important American city, with the possible exception of Indianapolis, has water areas suitable for take-off and landing right in the heart of the municipality. With elimination of auto travel to and from airports, necessarily located on the city's outskirts, the marine plane might well be faster in block-toblock flying time, cheaper in overall cost of operation. There will also be many more ports in emergencies.
Certainly, it will be much less expensive to create facilities for craft for which a few feet of water are a perfect port. The cost element will play a major role in deciding how big aviation can continue to be when the war is won.
This article was originally published in the June, 1944, issue of Air News magazine, vol 6, no 5, pp 18-19.
The original article includes 5 photos.
Photos credited to Glenn L Martin, Air News.