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Float Plane

Seaplanes are classified as flying boats or floatplanes. Flying boats land on their bellies in the water, and typically incorporate small floats called sponsons on their wings for roll stability while on the water. Float planes, on the other hand, typically feature a pair of large, parallel sausage-shaped floats attached to their undersides by struts. Floatplanes are generally high-wing, and thus easier to dock than flying boats, because their wings don't interfere with the dock. The float plane design also provides the flexibility of being able to mount floats on existing land plane designs. This flexibility saves time and money, because an entirely new airplane need not be designed--merely a means of attaching floats to an existing design.

Before the Wright brothers made their famous "first flight" on Dec. 12, 1903, another aviator named Samuel P. Langley attempted two powered flights launched from a houseboat in his Langley Aerodrome. These attempts occurred on Oct. 7 and Dec. 8, 1903. Unfortunately, both ended in premature water landings in the Potomac River. Sadly, Langley died in 1906 without again attempting flight. The Langley Aerodrome was consigned to storage, where it languished until 1914. During that year the Smithsonian Institute sponsored a study of its airworthiness. The Aerodrome was taken out of storage and shipped to the Curtiss factory at Hammonsport. Glenn Curtiss undertook its restoration, and made several modifications, including mounting it on floats. During the morning of May 29, 1914 Curtiss flew the Aerodrome 150 feet, and landed softly on the water. This was accomplished despite the addition of 350 pounds of weight, caused by the floats and their supports. Thus, it could be argued that the first aircraft design capable of engaging in controlled, powered flight, was a seaplane!

The Navy first investigated the possibilities of aviation for naval purposes in 1908 when Lieut. G.C. Sweet and Naval Constructor McIntee were detailed as observers for the test of the Wright plane at Fort Myer, Va. Lieutenant Sweet endeavored to stimulate interest in the subject of aviation and suggested the use of pontoons in this report to the Navy Department, but no action was taken thereon.

The use of a hydrodynamic step in a water hull for aircraft use is attributed by some to Glenn Curtiss. Early floatplanes designed by Curtiss had difficulty in becoming airborne, regardless of the amount of power applied or wing surface provided. It was discovered that the float or hull of the craft would tend to "stick" to the water surface due to the laminar flow of the water. The simple solution was to introduce a drag-inducing (and vortex generating) step at the rearward portion of hull or float to reduce or eliminate water adhesion and allow the craft to separate from the water flow. Unfortunately, this same step design also generates air vortices once the craft is airborne, thus contributing to aerodynamic drag.

Early aircraft utilized construction techniques resulting in high drag coefficients. Struts, wires, and braces in the airstream resulting in high drag designs. Thus, the amount of drag introduced by a hydrodynamic step contributed relatively little to the overall drag of the craft. However, modern aircraft are much more carefully designed to eliminate drag and have highly efficient aerodynamic designs. In such a design, a float or hull step may comprise a significant source of drag.

On November 14, 1910, the Curtiss Company representative, Eugene Ely, successfully flew a 50-horsepower Curtiss land-plane from a platform hastily built on the bow of the U.S.S. Birmingham at Hampton Roads, Va. On January 18, 1911, Mr. Ely, then attached to the Curtiss camp, at San Diego, made a successful landing with an airplane on the deck of the U.S.S. Pennsylvania lying in San Francisco harbor, and the next day he flew this plane from the deck on which he had landed.

During this same month, Glenn Curtiss and Lieutenant Ellyson perfected a hydroairplane attachment for airplanes. On January 26, 1911, Mr. Curtiss flew from the water at his San Diego base, landed alongside the U. S. S. Pennsylvania, was hoisted aboard ship, subsequently hoisted out again, and flew back to his camp. This performance, together with the previous feats of Mr. Ely, gave a very decided impetus to the development of naval aviation, not only in the US but in all the leading countries of the world.

Curtiss' hydroaeroplane was an airplane of conventional type in which the ordinary landing carriage of wheels and struts had been replaced by one of pontoons, or floats, and struts. Hydroaeroplanes possess the advantages, realtive to flying boats, of being somewhat faster for equal power, and of being somewhat more maneuverable in the air. As airplanes for fighting purposes they would also be superior since they would permit of better arrangement of guns for defensive or for offensive purposes. This latter, however, is probably true only of small craft, as on large ones it is possible to arrange guns so as to secure fire into all portions of the air.

Floatplanes may be equipped with retractable wheels, or landing gear, so as to afford the added versatility of being able to land on water or on a land runway. This type of floatplane is called an amphibian. Amphibians truly have the best of all worlds: they can land on any suitable land runway, and in addition they can land on any suitable water surface. This versatility permits a float plane to take off from a city airport, and land at its owner's lake out in the country. Amphibious floatplanes are commonly used to provision lake-side hunting and fishing camps, remote villages, and to transport patients from remote locations to hospitals.

An amphibian pilot must always be certain to have the retractable landing gear in the correct position when landing. Student floatplane pilots are taught to recite the mantras: "This is a LAND landing--gear checked DOWN" and "This is a WATER landing--gear checked UP". Making a land landing with the retractable landing gear erroneously retracted generally doesn't seriously damage the floats (although the runway surface could scrape them up some), or injure the floatplane occupants.

Making a water landing with the gear erroneously extended, however, is a horse of a different color. Landing in the water with gear extended could destroy the aircraft and seriously injure or kill its occupants. The reason is that on initial contact during landing, the floats are supposed to skim across the water on plane like water skis. As more weight put on the floats, the floatplane is supposed to gradually slow down without capsizing, until settling into displacement, where the entire aircraft weight is supported by the buoyancy of the floats.

If a floatplane's landing gear is in the extended position on initial contact with the water, the wheels tend to dig into the water, and slow the aircraft too quickly. This abrupt deceleration could hurl the aircraft over onto its nose, and the aircraft could literally dive nose first into the water. The abrupt stop could injure the occupants. In addition, an aircraft suddenly turned submarine, or floating inverted on its back in the water with its cabin submerged, poses significant drowning hazard.

Landing gear which retracts into a float is typically protected by gear doors which close after the gear has retracted. In land planes gear doors are installed to reduce drag, and therefore increase aircraft performance, principally speed aloft. In amphibians a more important reason for gear doors exists: to prevent water from entering the wheel well during water landings.

A typical float plane may land at 60 MPH. If the gear doors are open at that speed when the float initially contacts water, the wheel wells will immediately fill with water at high pressure urged into the wells by virtue of the speed of the airplane relative to the water. At high impact speeds water becomes a formidable force. Water landings with open gear doors have been known to result in the hull tearing open due to water pressure, hastening the airplane's sinking and the risk of occupant drowning and injury.

Even where the landing gear is correctly retracted during a water landing, if the gear doors should fail open, a similar result to a gear-down water landing may obtain: hull damage and sinking of the aircraft, with attendant hazard to its occupants. Thus, it would be desirable to provide a gear design incorporating gear doors which are sturdy and resistant to failure in the presence of water pressure during a water landing.

A number float retractable landing gear designs have been proposed. One design provides main landing gear which retracts rear-wards into the floats aft of the float step. The nose gear extends from the nose of the aircraft. Many light and ultra-light aircraft designs incorporate a high-wing mounted engine driving a pusher propeller, so the nose of such aircraft doesn't contain any structural re-enforcement (which it would if the engine were nose-mounted) onto which to attach the retractable nose gear. This re-enforcement must be added, increasing the aircraft weight and nose gear loading.

Another approach is to provide a pair of opposing gear doors mounted to the bottom of the float forward of the step. The hydrodynamic forces exerted on the float during water landings subjects these gear doors to high stresses, which may contribute to their failure. As noted above, gear door failure during water landings can have dire consequences, indeed.

Floatplanes may be equipped with retractable wheels, or landing gear, so as to afford the added versatility of being able to land on water or on a land runway. This type of floatplane is called an amphibian. Amphibians truly have the best of all worlds: they can land on any suitable land runway, and in addition they can land on any suitable water surface. This versatility permits a float plane to take off from a city airport, and land at its owner's lake out in the country. Amphibious floatplanes are commonly used to provision lake-side hunting and fishing camps, remote villages, and to transport patients from remote locations to hospitals.

An amphibian pilot must always be certain to have the retractable landing gear in the correct position when landing. Student floatplane pilots are taught to recite the mantras: "This is a LAND landing--gear checked DOWN" and "This is a WATER landing--gear checked UP". Making a land landing with the retractable landing gear erroneously retracted generally doesn't seriously damage the floats (although the runway surface could scrape them up some), or injure the floatplane occupants.

Making a water landing with the gear erroneously extended, however, is a horse of a different color. Landing in the water with gear extended could destroy the aircraft and seriously injure or kill its occupants. The reason is that on initial contact during landing, the floats are supposed to skim across the water on plane like water skis. As more weight put on the floats, the floatplane is supposed to gradually slow down without capsizing, until settling into displacement, where the entire aircraft weight is supported by the buoyancy of the floats.

If a floatplane's landing gear is in the extended position on initial contact with the water, the wheels tend to dig into the water, and slow the aircraft too quickly. This abrupt deceleration could hurl the aircraft over onto its nose, and the aircraft could literally dive nose first into the water. The abrupt stop could injure the occupants. In addition, an aircraft suddenly turned submarine, or floating inverted on its back in the water with its cabin submerged, poses significant drowning hazard.

Landing gear which retracts into a float is typically protected by gear doors which close after the gear has retracted. In land planes gear doors are installed to reduce drag, and therefore increase aircraft performance, principally speed aloft. In amphibians a more important reason for gear doors exists: to prevent water from entering the wheel well during water landings.

A typical float plane may land at 60 MPH. If the gear doors are open at that speed when the float initially contacts water, the wheel wells will immediately fill with water at high pressure urged into the wells by virtue of the speed of the airplane relative to the water. At high impact speeds water becomes a formidable force. Water landings with open gear doors have been known to result in the hull tearing open due to water pressure, hastening the airplane's sinking and the risk of occupant drowning and injury.

Lightweight aircraft which have been outfitted with twin pontoons for operation from lakes and rivers must be removed from the water during heavy winds or moderate wave action to prevent overturning or damage to the craft. Unlike most boats which are designed for relatively rough water, the pontoons for aircraft are designed as light and stream lined as possible so that the aircraft can fly as efficently as possible. This means that the pontoons are just barely able to keep a maximum loaded plane afloat. It is not uncommon for passengers loading and unloading to get their feet wet, even standing on a pontoon.

Because the pontoons are made from lightweight thin materials, dragging a seaplane up on a beach to get it out of the water often damages the very expensive pontoons. At present, there are no lifts which are suitable for lifting a light seaplane from the water, which are supported by stanchions driven into the lake or river bed. Present lifts which are designed for boats do not have the structure to support the pontoons yet enable the propeller to be free of obstructions.

Boat lifts have been found to be inadequate to meet the needs of seaplane owners who wish to quickly and easily lift these planes out of the water and launch them with the same ease and speed. The need for lifting ease and speed requirements may range from simple convenience to necessity in coping with difficult conditions induced by high waves, fast current or high winds. Further, the present boat lifts are capable of raising a boat only a few feet while many lakes and dams may periodically rise and fall five, ten or even fifteen or more feet due to hydroelectric power generation and re-generation by refilling the lake during off peak power generation hours. Rivers and flood control dams or sea coast waterways subject to tides can rise and fall several feet and render all but the largest lifts useless at low water conditions.

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Harper's Aircraft Book Why Aeroplanes Fly, how to Make Models, and All about Aircraft, Little and Big By Alpheus Hyatt Verrill



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