Aeronautics and astronautics – Landing gear – Water landing
Patent
1996-12-17
1999-06-22
Jordan, Charles T.
Aeronautics and astronautics
Landing gear
Water landing
244106, B64C 3502
Patent
active
059134933
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a seaplane hull and particularly to the form thereof.
By seaplane hull is meant an integral part of the fuselage of a flying boat or the floats on a floatplane. The design criteria of sponsons or floats mounted outboard on a flying boat which, arising from their displacement, commonly provide flying boats with lateral static stability, contrasts to the design criteria for seaplane hulls and this invention does not necessarily relate to their design.
Since the inception of seaplanes, hull development has revolved around the planing hull concept, so much so that the hydrodynamic form to achieve efficiency when in displacement mode, that is to say below planing speed, has been generally ignored. By combining aspects of design established in racing catamarans and passenger catamaran ferries and innovating to enable such hulls to achieve seaplane design criteria, a new, highly original and advantageous seaplane hull has now been developed.
In plan form, conventional hulls almost universally have a resemblance to an elongated rain-drop with a rounded bow and an afterbody trailing to a point. Though this form is aerodynamically very efficient, it is wholly unsuited to motion on the surface of water. It creates a large bow-wave which creates high drag, and the Coanda effect draws it powerfully down into the water preventing it from taking-off in addition to creating a powerful nose-up pitching tendency. This is in contrast to the comparatively sharp bows and fine bow entry angles of recent catamarans.
The object of conventional seaplane hull design has been to minimise these hydrodynamic penalties while incurring as mild structural and aerodynamic penalties as possible. To prevent the Coanda effect sucking the hull down into the water, hulls are generally fitted with a transverse abrupt "step" below the centre of gravity of the seaplane to separate the water flow from the hull. To enable them to climb over the bow wave, they feature hard edged forebody chines and powerful planing surfaces from the bow back to the step. The said forebody chines and the step are angled steeply across hydrodynamic and aerodynamic streamlines and create substantial vortices which both damage directional stability and create substantial drag. The result is undesirable qualities from the point of view of hydrodynamic loading and hydrodynamic resistance during take-off. They demand an aircraft with high power-to-weight ratio and result in limited payload capacity for a given size of aircraft.
Variable geometry hulls, hydrofoils, air blowing and other devices have been used to try and maintain a clean aerodynamic hull form. However, they all have limitations and add considerably to the weight and complexity of an aircraft. None of these attempted solutions have proved Certifiable and/or commercially viable though various ideas have been tested in prototype and experimental form.
Some improvements however have been demonstrated by the use of high length-to-beam ratio hulls and this was researched in some depth prior to 1950 and is well reported in "Development of High-speed Water-based Aircraft", by Earnest G Stout in the Journal of the Aeronautical Sciences Vol. 17 August 1950. This discusses tests on hulls with length/beam ratios of up to 12 though the advantages indicated were little exploited as there has since been little seaplane development work. The U.S. Navy's flying boat XP5Y-1 (first flown in 1950) had a length/beam ratio of 10. However, it had all the above-mentioned features of a conventional seaplane.
The top speeds of offshore racing multihulls and passenger catamarans approximately doubled in the 25 years to 1994. These hulls have also demonstrated major sea-keeping advantages, but despite the demonstration of the advantages of this type of hull, no seaplane has incorporated this type of design. The appropriate use of these types of hull for seaplanes is not obvious as there are two potentially problematic factors in their application to seaplanes. Firstly, they have a large wetted surface area at
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Dinh Tien
Jordan Charles T.
Warrior (Aero-Marine) Ltd.
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