Aeronautics and astronautics – Aircraft sustentation – Sustaining airfoils
Reexamination Certificate
2000-10-19
2002-07-23
Eldred, J. Woodrow (Department: 3644)
Aeronautics and astronautics
Aircraft sustentation
Sustaining airfoils
C244S04500R, C244S04500R, C244S130000, C244S201000
Reexamination Certificate
active
06422518
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an aircraft comprising a symmetry plane, two wings, a fuselage, a horizontal tail plane (HTP) and with means for a premature breakdown of a wing vortex pair behind the aircraft in flight, which pair is generated in the tip area of the wings, has a first spin direction and descends in the near field behind the aircraft.
The invention deals in particular with the premature breakdown of the wing vortex pair behind an aircraft in landing flight. However, it is also advisable to apply the invention to an aircraft in climbing or cruise flight.
BACKGROUND OF THE INVENTION
The wing vortices of the wing vortex pair are generated at an aircraft in flight by the rolling up of the vortex sheet shed from the wing tip area. The trailing vortices are particularly strong in landing approach. Especially with the advent of wide body aircraft the wing vortices, due to the trailing vortices they generate, are a hazard for other aircraft since the force of the wing vortices, which hereafter is called circulation, is essentially proportional to the weight of the respective aircraft. Hence, particularly heavy aircraft generate particularly strong wing vortices. Thus, the horizontal spacings between landing aircraft, that are necessary for air traffic safety, increase with the weight of the aircraft in front and are several nautical miles with the presently common wide body aircraft, such as Boeing type B-747. It is these large horizontal spacings for the avoidance of wake vortex encounters that prevent a marked increase in the passenger volumes per hour by even larger capacity aircraft since the admissible landing frequency of such larger aircraft further decreases with their increasing weight.
A method for a premature breakdown of wing vortex pairs is known from Ludwieg: “Vortex breakdown”, DLR-Report 70-40, 1970. The paper shows, that a vortex breaks down due to the Rayleigh-Ludwieg instability, if another vortex with an opposite rotation appears on its periphery. The condition that it appears on the periphery has been formulated by Steven C. Rennich et al.: “A Method for Accelerating the Destruction of Aircraft Wake Vortices”, AIAA 98-0667, 1998. This publication deals with theoretical models and calculations that are restricted to an external vortex pair as a wing vortex pair and an internal vortex pair with opposite spin direction as a interfering vortex pair. The basic assumption is that, under practical conditions, the external vortex pair is generated at the wing tips and the outside edges of the trailing and leading edge flaps while the internal vortex pair, due to the lift loss, occurs over the fuselage and at the inside edges of the landing flaps. Though a general observation is made that under practical conditions the entire vortex sheet should be considered, there is no reference to any specific further vortex sheets and vortex pairs. Regarding the internal vortex pair it is stated that its relative circulation and relative span in relation to the circulation and the span of the wing vortex pair have to be in a certain range so that the structure of the wing vortex pair can be destroyed due to as a result of the interaction with the interfering vortex pair behind the aircraft in flight. However, if the circulation of the interfering vortex pair is too high the interaction between the two single vortices of the interfering vortex pair is such that they escape to the above and thus the desired interaction, i.e. to destroy the structure of the wing vortices descending behind the aircraft, will not take place. No concrete actions are outlined to prevent the circulation of the interfering vortex pair from becoming too high. In addition, the consideration of the vortex sheets that are shed from the inside span area of an aircraft by only one interfering vortex pair is a very crude simplification since, for instance, vortex sheets that are shed from the aircraft near the horizontal tail plane have not yet rolled up into a defined vortex pair. A less crude simulation of the shed vortex sheets shows that the latter do not escape completely to the above as one interfering vortex but that parts of such already descend with the wing vortices while, according to Rennich et al., their total circulation should make them wholly escape above. Hence, the criterion proposed by Rennich and Lele is replaced by a criterion that is further described below and which considers the vortex sheets more profoundly than the criterion adopted by Rennich and Lele.
This invention is aimed at making use of the interfering vortex pair that is already existing at an aircraft in flight for a premature breakdown of the wing vortex pair to basically reduce its circulation.
SUMMARY OF THE INVENTION
Briefly described, this object is achieved by an aircraft comprising a symmetry plane, two wings, a fuselage, a horizontal tail plane and means for a premature breakdown of a wing vortex pair +/−&Ggr;
M
, which is generated in the wing tip area at an aircraft in flight, which has a first spin direction and which descends behind the aircraft, in that the means for said premature breakdown adjust the circulation &Ggr;
P
and the relative span b
P
— each related to the wing vortex pair—of an interfering vortex pair −/+&Ggr;
P
, which is generated between fuselage and wing tips without merging with the wing vortex pair already in the near field behind the wings, which has a second spin direction that is opposed to the first spin direction and which includes portions of both a fuselage vortex pair −/+&Ggr;
F
generated in the wing-fuselage junction area, and a tail plane vortex pair −/+&Ggr;
H
generated in the wing tip areas (
5
) of the horizontal tail plane (
4
), to appropriate values in order to retain the interfering vortex pair −/+&Ggr;
P
behind the aircraft within an altitude range of the descending wing vortices of the wing vortex pair.
This invention is based on the finding that the internal vortex pair which absorbs portions of the fuselage vortex and the tail plane vortex pairs, is particularly suited as an interfering vortex pair. The fuselage vortex pair is caused by the lift loss over the fuselage at the wing-fuselage junction area and always has a spin direction opposed to the wing vortex pair. The tail plane vortex pair is generated in the wing tip area of the horizontal tail plane which generates a downward lift in order to stabilize the desired angle of attack of the entire aircraft, so that also the tail plane vortex pair has a spin direction that is opposed to that of the wing vortex pair. Fuselage vortex pair and tail plane vortex pair merge into one internal vortex pair behind the aircraft. On the one hand the span between the two single interfering vortices of this interfering vortex pair is so small and, on the other, the distance to the wing vortex is so large that there is no risk for the merging of the interfering vortex pair with the wing vortex pair already in the near field behind the aircraft. Such a merging with the not yet aged wing vortex pair would cause a certain reduction of its circulation but not the desired premature breakdown of its structure. The reviewed interfering vortex pair with portions of the fuselage vortex and the tail plane vortex pairs typically has such a high circulation in the known wide body transport aircraft that, without a purposeful intervention, it would escape to the above from the area of the descending wing vortex pair due to the small span of its two opposed interfering vortices. As a counteraction the new method features an adjustment of the circulation and the relative span between said interfering vortex pairs to such values that the interfering vortex pair is retained in the altitude range of the descending wing vortices of the wing vortex pair. This means that the circulation of the naturally occurring interfering vortex pair with portions of the fuselage vortex and tail plane vortex pairs usually has to be reduced.
The use of winglets for said reduction can redu
Stuff Roland
Vollmers Heinrich
Duetsche Zentrum fur Luft- und Raumfahrt E.V.
Eldred J. Woodrow
Thomas Kayden Horstemeyer & Risley
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