Aeronautics and astronautics – Aircraft sustentation – Sustaining airfoils
Patent
1991-05-06
1993-05-04
Barefoot, Galen
Aeronautics and astronautics
Aircraft sustentation
Sustaining airfoils
B64C 916
Patent
active
052074005
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a flap assembly for an aerofoil, such as, for example, an aircraft wing.
The invention is particularly concerned with a flap assembly suitable for an aircraft having a variety of mission requirements, such as for example, a short take-off and landing.
It is conventional for commercial aircraft to be provided with single, double or triple slotted flaps that travel along curved tracks. Although this arrangement can provide near optimum flap positions for take-off and landing with small fairings posessing low-drag, the flap track supports are heavy and possess significant inherent in-service problems which arise mainly from the line contact of the heavily loaded rollers forming part of the flap assembly.
It is desirable to be able to provide a flap system having the aerodynamic characteristics of the track-guided flaps, particularly for aircraft which operate with a mix of mission requirements, such as short and long range, intermediate gross weight and short landing field lengths. It will be appreciated therefore, that a need arises for a flap system which possesses the desirable features of the track-guided flaps while avoiding some of their disadvantages.
It has been found that the type of flap arrangement suitable for an aircraft is determined by the following three basic mission requirements of the aircraft:
1. The length of landing field and maximum touch-down speed for the aircraft. These define the criteria of flap size for short to medium range aircraft having a high wing loading for operation from short runways, and include aircraft having a short take-off and landing run. It will be understood that for landing, the flap is fully extended thereby giving a maximum lift coefficient.
2. The maximum length of the take-off field or runway. This influences the flap arrangement particularly where there is a high thrust to weight ratio aircraft together with a requirement for a very short take-off field or runway.
3. The one-engine-out second segment climb gradient. To ensure safety, the certification authorities require a demonstration of aircraft climb capability with one engine inoperative. By "second segment" is meant that portion of the take-off process between thirty-five and four hundred feet above the take-off surface in which a specified minimum climb gradient shall be obtained. This requirement generally determines the flap configuration for twin and three engine aircraft having a high wing loading. In order to achieve the minimum climb gradient with one engine inoperative, the lift to drag ratio of the aircraft must be optimised. High lift to drag ratios may be achieved with high Fowler motion at low flap angles. Because the flap setting for take-off and second segment climb is usually the same, the take-off setting is influenced by both the take-off field or runway length and the second segment climb gradient.
Providing that the intermediate flap positions are not critical, the criteria for selecting the mechanism are; simplicity; high reliability and low cost, low load i.e. low weight; and compactness with a consequent low drag. However, in cases where there are stringent requirements for take-off field length, and one engine out second segment climb gradient, the intermediate flap positions are critical. In consequence, aircraft which have to fulfil these requirements, must have a flap system that provides very high Fowler motion at low flap angles, and in which most of the flap rotation occurs toward the end of the flap deployment to its downwardly extended position.
Consideration has therefore been given to providing a simple non-tracked flap mechanism which provides an adequate Fowler motion and requires a small flap support fairing having a low cruise drag.
A previously proposed flap track and roller mechanism has a so called cylindrical geometry, in which the amount of flap extension is uniform. This means that the linkage geometry has the same size for each span wise spaced flap extension mechanism. However, this cylindrical flap movement does not provide
REFERENCES:
patent: 2137879 (1938-11-01), Ksoll
patent: 3985319 (1976-10-01), Dean et al.
Barefoot Galen
Short Brothers PLC
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