Aeronautics and astronautics – Aircraft sustentation – Sustaining airfoils
Reexamination Certificate
2001-12-06
2004-05-04
Carone, Michael J. (Department: 3641)
Aeronautics and astronautics
Aircraft sustentation
Sustaining airfoils
C244S130000, C244S047000
Reexamination Certificate
active
06729577
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to supersonic aircraft, joined-wing aircraft and sonic boom reduction, separately and in combination, for long range supersonic cruise aircraft with reduced sonic boom loudness.
2. Description of Related Art
A number of prior patents and technical reports have individually described technologies for joined-wings, low supersonic drag and sonic boom minimization. Further design studies and actual supersonic aircraft revealed shortcomings that reduced and eliminated the perceived advantages of such designs. Although tandem and connected wing designs have been proposed in prior patents, such designs are unfavorable because the wing downwash on the following wing and pitch stability were not taken into account. Downwash created by one wing reduced the lifting efficiency of any nearby or following wing, requiring a greater angle-of-attack to generate the same lift. This reduction in lifting efficiency increased induced drag and reduced pitch stability. Trailing wings carried very little lift or often a down load to trim an aircraft with the center-of-gravity far enough forward for positive pitch stability. Current artificial stability technology allows the trailing wing lift to be slightly increased, but also increases development cost. Downwash is the main reason why biplane and canard airplanes were abandoned and now serve only in applications not primarily based on efficiency.
Additionally, prior patent designs were generally focused on subsonic applications rather than supersonic applications. Box-wings and tip-connected joined-wings claim vortex drag reductions as their primary improvement. However, the contribution of vortex drag to total drag and the vortex drag benefit of interconnection diminish as speed increases supersonically. Another important requirement of supersonic applications is the need to keep cross-sectional area distributions as low as possible and minimize second derivative changes, also known as area ruling, to reduce wave drag. Blunt and unswept wings, blunt connecting elements and superimposed connections have rapid cross-sectional area changes that produce high wave drag supersonically. Supersonic surfaces and bodies need to be sharp or swept greater than the Mach cone angle and need low thickness-to-chord ratios. The Mach cone angle is defined as the inverse cosine of 1/Mach, and is 60 degrees at Mach 2.
Finally, most prior patent designs that address sonic boom only reduce the sonic boom due to aircraft volume or use energy to alter boom pressures. Unfortunately, reducing the sonic boom due to volume results in a sonic boom due to lift that is typically stronger than the combined lift and volume boom. This counter-intuitive result occurs because the lift is concentrated in a length shorter than the vehicle length and the typical area ruled volume superimposes an expansion where the lift is located, mitigating the lift. As for energy techniques, the energy in the boom pressures is equivalent to the entire propulsion system output that balances them, suggesting impractical power requirements.
To help understand some of the benefits achieved in accordance with the present invention, the relevant shortcomings of prior designs, for the present supersonic application, are described below.
U.S. Pat. No. 1,264,037 to Emmons teaches a biplane aircraft with a sweptback forward wing connected to a sweptforward rear wing also connected to an additional mid-fuselage fin. The wings are connected by vertical struts, which cannot provide joined-wing
20
¢: in-plane stiffening or box-wing vortex induced drag reduction.
U.S. Pat. No. 1,453,830 to Coakley teaches multiple connected wings with dihedral for the lower wings and anhedral for the upper wings and vertical struts, creating a stiff structure that carries loads in-plane. However, it is only suitable for low speed flight having its connections superimposed, no wing sweep and an excess of bracing struts and wires.
U.S. Pat. No. 2,406,625 to Oglesby teaches multiple, unswept wings of alternating anhedral and dihedral connected at their tip to a common tube and connected at their root to a fuselage. This is recognized to form a truss arrangement, reducing wing loads.
However, the lack of sweep leads to a long tip-connecting tube that would have significant weight and friction drag. Multiple trailing wings have increasing drag due to increasing downwash.
U.S. Pat. No. 2,461,805 to Barker teaches dual wings and dual tails of differing height and tandem fore/aft position at their root and connected at their tips by an interconnecting structure that blends the forward tip into the aft tip. While this does carry loads in-plane, greatly increasing strength and rigidity, the interconnecting structure creates a large spanwise blockage of the flow at the tips unsuitable for compressible flow regimes (Mach>0.5) and creates redundant, closely-coupled surfaces increasing friction and interference drag.
U.S. Pat. No. 2,567,294 to Geraci teaches a tail-less bi-plane in a box-wing arrangement also with dual propeller box-prop arrangement. While there would be a vortex drag reduction, the wings are close causing high interference (downwash) and the vertical interconnecting structures cannot transfer loads in-plane for less strength and rigidity benefit. Further, both wings are highly sweptback, resulting in little torsional stiffness improvement leading to increased weight to resist flutter and aeroelastic elevon reversal. The interconnecting fins are also superimposed with the wings, creating increased area unsuited for compressible flow regimes.
U.S. Pat. No. 3,834,654 to Miranda teaches a box-wing with three relevant (to this patent) advantages. First, in having a rearwardly swept wing connected at the tip, by a vertical fin, to a forwardly swept wing, increased torsional stiffness eases aeroelastic problems. However, the box-wing is not claimed to resist lift loads in-plane, so it is more similar structurally to dual cantilevered wings. Second, reduced transonic and supersonic wave drag is attributed to the greater length over which the wing volume is spread. As a caveat, the patent notes that the superposition of wing/fin connections could increase shock strength and drag, and therefore, suggests: rounding the corners, adding the volume of a streamlined center body or using boundary layer control through suction, blowing or vortex generators. Third, the vertical separation of the wings theoretically makes possible a 40% induced drag reduction subsonically. Unfortunately, this improvement is greatly reduced with practical longitudinal stability requirements. A stable box-wing as shown requires a download from the aft wing to trim and current artificial stability systems would only allow a small upload, so trim drag and flight control system impacts must be considered when assessing benefits.
U.S. Pat. No. 3,942,747 to Wolkovitch teaches a canard swept back and up connected at its tip to an unswept wing, both canard and wing attached to a fuselage. The design is suited to a low speed, ultralight-type aircraft stressing simple construction and rugged design at the expense of performance. The design is in particular claimed suited to flexible lifting portions made material such as canvas.
U.S. Pat. No. 3,981,460 to Ratony teaches tip-joined, counter-swept wings with the upper wing being free from fuselage and vertical fin bracing, increasing load and wing weight. The acute angle and wing superposition at the tip results in high interference and wave drag in compressible flow regimes. Further, the short distance between the control surfaces and the center-of-gravity results in a large trimmed loss of flap lift and increase in drag. Finally, the preferred embodiment describes that elimination of the wing tip vortex eliminates sonic boom. Current theory attributes the formation of sonic boom to the (downward momentum imparted to the air to generate) lift and the volume disturbance. As this design shows no area ruling and a relatively short vehi
Carone Michael J.
Lockheed Martin Corporation
Semunegus L.
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