Swept-Forward Wings Design with Iwa Wings, the Frigatebird, for Better Solution Upgrade | Design Analysis and Configurations | Aspect Ratio Review

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A swept-forward wing is an aircraft wing configuration in which the quarter-chord line of the wing has a forward sweep. Typically, the leading-edge also sweeps forward.

Quarter-chord point - The point on the chord line at one quarter of the chord length behind the leading edge. Sweep back is usually quoted by the angle between the line of the quarter chord points and the normal to the aircraft fore and aft center lines.

However, this article is still under construction while i am concentrating all my effort to analyze and to arrange my other article "Trapezoidal Wings of Sukhoi Su-57 Design (should be) for 6th Generation Upgrade | Design Analysis and Design Configurations | Aspect Ratio Review". So stay tune and keep visiting my blog regularly  :-)

Swept-forward wings design might be a wing design and a wing configuration for 6th generation upgrade, as well as trapezoidal wings combined with LERX. That’s the necessity of re-arranging and re-building the swept-forward wings design in this article.

The iwa (or frigatebird) is the main idea of re-arranging the swept-forward wing in this article. It has the lowest wing loading of any bird, either has similar wing design and configuration with swept-forward wing. The iwa wing is perfect sample of swept-forward wing configuration, that I'm sure, can solve some problems in swept-forward wing as described.

Characteristics: The swept-forward configuration has a number of characteristics which increase as the angle of sweep increases.

Main spar location: The rearward location of the main wing spar would lead to a more efficient interior arrangement with more usable space.

Inward spanwise flow: Air flowing over any swept wing tends to move spanwise towards the rearmost end of the wing. On a rearward-swept wing this is outwards towards the tip, while on a forward-swept wing it is inwards towards the root. As a result, the dangerous tip stall condition of a rearward-swept design becomes a safer and more controllable root stall on a forward-swept design. This allows full aileron control despite loss of lift, and also means that drag-inducing leading-edge slots or other devices are not required.

With the air flowing inwards, wingtip vortices and the accompanying drag are reduced. Instead, the fuselage acts as a very large wing fence and, since wings are generally larger at the root, this raises the maximum lift coefficient allowing a smaller wing.

As a result, maneuverability is improved, especially at high angles of attack. At transonic speeds, shock waves build up first at the root rather than the tip, again helping ensure effective aileron control.

Yaw instability: One problem with the swept-forward design is that when a swept wing yaws sideways (moves about its horizontal axis), one wing retreats while the other advances. On a swept-forward design, this reduces the sweep of the rearward wing, increasing its drag and pushing it further back, increasing the amount of yaw and leading to directional instability. This can lead to a Dutch roll in reverse.

Aeroelasticity: One of the drawbacks of swept-forward wings is the increased chance of divergence, an aeroelastic consequence of lift force on swept-forward wings twisting the tip upwards under increased lift. On a forward-swept design, this causes a positive feedback loop that increases the angle of incidence at the tip, increasing lift and inducing further deflection, resulting in yet more lift and additional changes in wing shape. The effect of divergence increases with speed. The maximum safe speed below which this does not happen is the divergence speed of the aircraft.

Such an increase in tip lift under load causes the wing to tighten into turns and may result in a spiral dive from which recovery is not possible. In the worst case, the wing structure can be stressed to the point of failure.

At large angles of sweep and high speeds, in order to build a structure stiff enough to resist deforming yet light enough to be practicable, advanced materials such as carbon fiber composites are required. Composites also allow aeroelastic tailoring by aligning fibers to influence the nature of deformation to a more favorable shape, impacting stall and other characteristics.

Stall characteristics: Any swept wing tends to be unstable in the stall, since the rearward end stalls first causing a pitch-up force worsening the stall and making recovery difficult. This effect is more significant with sweep forward because the rearward end is the root and carries greater lift.

However, if the aeroelastic bending is sufficient, it can counteract this tendency by increasing the angle-of-attack at the wing tips to such an extent that the tips stall first and one of the main characteristics of the design is lost. Such a tip stall can be unpredictable, especially where one tip stalls before the other.

Composite materials allow aeroelastic tailoring, so that as the wing approaches the stall it twists as it bends, so as to reduce the angle of attack at the tips. This ensures that the stall occurs at the wing root, making it more predictable and allowing the ailerons to retain full control.

Design principles:

It is rather different to implement swept-forward wings configuration into the bases of modern aircraft design as described in my other article. Drawing a line of the wing, in general, begins at root of the wing, but for swept-forward wing begins at the tip of the wing, as well as angle 60 degrees needs different preparations and either treatments before used.

Begin with placing angle 60 degrees at 1.7 cm right from zero-point at horizontal line on the bases of modern aircraft design, make straight line from root of the angle 60 degrees along the horizontal line. And then make perpendicular line from tip of the angle, the perpendicular is equal to angle 60 degrees if measured from imaginary opposite of the angle, or equal to 30 degrees if measured from horizontal line. Configuration of the angle will perform 14.1 meters of wingspan. It will be main wingspan of Iwa wings. The wingspan is equal to 7.05 cm span of the wing on the right hand. Then continue marking the span to 7.35 and 7.65 cm on the right end of straight horizontal line. Make backward line from 7.05 and 7.35 to the horizontal line, while 7.65 will be final span of the wing and wingtip configuration. Finally connect every marked span on the wingtip with lean inward lines. The configuration of the marking span is a configuration called iwa wings the frigatebird, the swept-forward wing with advanced wingtip on the wings.

Main configuration and attention of this designing process is advanced wingtip of the iwa wing, where the lines on the wingtip will intersect and join with each other forming the iwa wing, the advanced wingtip. If the configuration is fulfilled, then angle of trailing-edge will be automatically formed sweep backward by 42 degrees from marked span 7.05 to the vertical line and the design compacted by itself. The Iwa wings configuration make all requirements of swept-forward wing design.

The iwa main wings has aspect ratio of span to root chord is about 0,75 which is equal to aspect ratio of highly swept trapezoidal wings. While overall iwa wings with advanced wingtip has the aspect ratio about 0.81. However, wingspan square formed by the aspect ratio extends downward not extends to the side. Meaning, the horizontal stability has been performed since the very first time the iwa wings is designed. The longer the root chord more stable the aircraft. The Iwa wings configuration make all requirements of swept-forward wing design. It fulfilled all aerodynamic characteristics and parameters.

The Iwa wing does not really need LERX since it has large number of wings area at the root. The Iwa just needs small LEX and canards behind the cockpit. LERX or LEX is required in any aircraft which function and configuration described in my previous article. The second LEX required in front of the wings because swept-forward wing is an inverted shape of conventional wing that structurally not strengthen. Any treatment on the wing is required for it to fly at supersonic speed. That is by placing imaginary LEX running forward the leading-edge of the wings. The LEX does not appear as aerodynamic surface or control surface, but appear as fuselage itself.

Length of nose as described in my previous article, is a flip horizontal copy of equilateral triangle formed by two angles 60 degrees, the two angles that stand side by side and meets at its perpendicular line. Copying the triangle results another equilateral triangle with two longer sides, in which shorter side stands at tip of the angle, and the longer side stands at vertical line. The side that standing at the vertical line will be length of nose. That is true design and configuration in length of nose. Mark the length of nose by making second straight horizontal line on it along the first straight horizontal line. At second straight horizontal line, then make angle 60 for second time at 1.7 cm right from its zero-point. Configuration of the second angle is similar to previous one. The angle will form into equilateral triangle that will become bases configuration for canards.

Canard is small wings in front of fuselage. It helps to provide longitudinal stability and appeared as control surfaces. In aerodynamic, canard is all-moveable fins that enable to move horizontal and even vertical axis. In iwa wings design, canard is flip horizontal copy of equilateral triangle formed by two angle 60 degrees. The triangle is then deflected backward. Then change the sweep of its trailing-edge from 30 degrees to 20 degrees.

The Iwa fuselage is then configured in such way to provide lifting body configurations.