Modern Aircraft Design of Sukhoi Su-27 (as should be) | Design Analysis and Aspect Ratio Review

Inspired by perfect design of Sukhoi Su-27 fighter aircraft, I study and analyze the design of the aircraft to find the advantages of the aircraft. I am very excited that Su-27 is an advance aircraft, compact in design, better in aerodynamic and super maneuverable. So in the basis of Sukhoi Su-27 design, I’d love to develop advanced design of aircraft for next generation fighter aircraft. Proper methodology is applied in designing an experimental aircraft design with many parameters as described. But don’t ask me if I graduated of Aviation or Aeronautical and even Aerospace. All my design is based on analysis how an aircraft design should be. My focus is to study and analyze perfect design of Sukhoi Su-27, the super maneuverable fighter, for 6th generation aircraft. I don’t have enough time to design new aircraft almost from the beginning. So the best way to develop new aircraft design is to analyze an existing aircraft design, find the advantages, and finally implement to develop the aircraft design. These are design analysis implemented to design layout. This acknowledge and effort, would like, could be useful to implement the advantages design of Sukhoi Su-27 to re-design Sukhoi Su-57 for upgrade to 6th generation. However, I imagine this experimental design would be a better specification of aircraft contract Indonesia – Russia. And finally to fix and solve some problems in experimental Su-47 swept forward wings. Wish Sukhoi Design Bureau would contact me on this experimental aircraft design.

New approach has been analyzed to determine proper methodology to design Sukhoi Su-27, begin with basic geometric descriptions which I call “The Bases of Modern Aircraft Design”. That is vertical line and horizontal line where both lines intersect and cross-meet with each other at one point, called zero-point, many say root. Vertical line and horizontal line similar to perpendicular and longitudinal axis of the aircraft design. From the zero-point, root of the aircraft design, then begin to draw a line of what aircraft to design. Due to aircraft design is symmetrically aligned, vertical line will help it aligned while horizontal line can be used to measure the alignment. And then continue to place an angle 60 degrees about 1.8 cm right from zero-point at horizontal line. Configuration of this angle will perform span of wing, LERX, and length of nose, even proper placement of many elements. This method provides compact design of the aircraft. Means if main configuration of the aircraft, span of wing for example, are changed, other elements will (be) change(d) and need to re-design. In other words, the configuration will affect overall elements and measurements, and the design automatically compacted by itself. So that one element to the others are unified and inseparable.

More on angle 60 degrees, configuration of the angle will perform one side of right-angled triangle. A right triangle is a triangle in which one angle is a right angle. The relation between the sides and angles of a right triangle is the basis for trigonometry. Implementing one side of right-angled triangle in aircraft design is main configuration to find proper methodology to design modern aircraft.

Creating geometric descriptions of a thing to be built, such as an aircraft, begins with a thought how a paper airplane can fly, or how a kite can fly. Thinking about it mainly based on a thought how birds above us flying wings spread out or folded, nothing holds them aloft but God.

As every line running and flow through the aircraft design square, many running upward or backward, even horizontally, and deflected to other side, the angle line will do so. Many of the lines might intersect and cross-meet with each other at certain point, as if it wants to point something idea. Talented designer(s) shall see the phenomenon as guide to design proper placement, shape, length and width of elements in aircraft design. Following and playing with running lines in aircraft design square is quite challenge.

Considering the aerodynamic principles as described, here are the elements of the general configuration of an aircraft needed to design, as following: wings, tail fins, number of engines, canards, and number of fins. All the elements must be compact in design, size, shape, placement, and many other parameters including definition, design principle, design characteristic, design analysis and implementation.

Wings Design :

A wing is a type of fin that produces lift while moving through the air or some other fluids. As such, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is expressed as its lift-to-drag ratio. The lift of a wing generated at given speed and angle of attack can be one to two orders of magnitude greater than the total drag on the wing. A high lift-to-drag ratio requires a significantly smaller thrust to propel the wings through the air at sufficient lift.

Aircraft wings are airfoils, the cross-sectional shape of a wing, which wings have a curve upper surface and a flatter lower surface making a cross-sectional shape, that create lift when moved rapidly through the air. Aircraft wings are shaped in such a way to split the oncoming airstream in front of the wing and to make air move faster over the top of the wing. When air move faster, the pressure of the air decreases. So the pressure on the top of the wing is less than the pressure on the bottom of the wing. The difference pressure creates a force on the wing that will lift wing up to the air.

These are laws of motion, proposed by Sir Isaac Newton, help to explain how plane can fly;

1.   if an object is not moving, it will not start moving by itself. If an object is moving, it will not stop or change direction unless something pushed it.

2.   object will move farther and faster when they are pushed harder.

3.   when object is pushed in one direction, there is always a resistance of the same size in the opposite direction.

An airfoil wing generates lift because it's both curved and tilted back, so the oncoming air is accelerated over the top surface and then forced downward. These create a region of low pressure directly above the wing, which generate lift. The wing's tilted angle force the air downward, and that also push the plane upward.

 Moving air has a force that will lift an aircraft up and down. Air has power to push and pull on aircraft. All things that fly, including aircrafts, need air to be manipulated into difference pressure on the wings to create lift force for the aircraft. Wings play key role on the lift by changing the direction and the pressure of the air. The amount of lifts generate lift force for the aircraft.

For a wing to produce lift, it must be oriented at a suitable angle of attack. When this occurs, the wing deflects the airflow downward as it passes the wing. Since the wing exerts a force on the air to change its direction, the air must also exert an equal and opposite force on the wing, resulting in different air pressures over the surface of the wing. A region of lower than-normal air pressure is generated over the top surface of the wing, with a higher pressure on the bottom of the wing. These air pressure differences can be measured directly using instrumentation or can be calculated from the airspeed distribution using basic physical principles such as Bernoulli's principle, which relates changes in air speed to changes in air pressure. It is possible to calculate lift from: the pressure differences, the different velocities of the air above and below the wing, or from the total momentum changed of the deflected air.

Four forces of flight work on flying aircraft :

-     lift – upward;

-     thrust – forward;

-     weight – downward;

-     drag – backward; 

Wingspan :

Wingspan of an aircraft is the distance from the tip of one wing to the tip of the other. The wingspan is always measured in a straight line, from wingtip to wingtip, independently of wing’s shape or sweep. In design, wingspan is formed by drawing line from root to its span, either straight or sweep.

How wingspan is measured? Let’s study the bases of aircraft design and analyze angle of 30 degrees at 1.8 cm right from zero point. It is 60 degrees of triangle at proper placement to begin aircraft design. I use trigonometry to analyze that can help to find angles and distances, and is used a lot in science, engineering and more.

Angle is often labeled as θ, and the three sides are then called :

Ÿ Adjacent: adjacent (next to) the angle θ

Ÿ Opposite: opposite the angle θ

Ÿ Hypotenuse: the longest side

The equation does not seem to solve the problem how to perform the span of wing. But let’s analyze more deeply.

Design principles of sweptback wings, the line of maximum chord is swept at an angle, usually backward. This increases the sweep of the leading-edge by 46 degrees, and decreases the sweep of the trailing-edge by 20 degrees. And at the same time to increase wingspan to 14.7 meters. The transition form, where the trailing-edge is straight, is equivalent to a cropped delta planform.

How do the configurations of angle 60 degrees result such measurement? To determine the configurations, firstly we need to define every single element, position and even deflection of running lines in square of aircraft design. Familiarization and talent about definition of the elements help designer(s) to build advanced aircraft design. The angle 60 degrees, for example, need to define correctly. Hypotenuse line, the longest side of angle 60 degrees, that intersects with vertical line will be called as root of the angle, while hypotenuse line that intersects with horizontal line called as chord. For useful simplification, here the angle 60 degrees placed at 1.8 cm right from zero point at horizontal line. From the root, make straight line along the horizontal line. And then make perpendicular line from hypotenuse at its chord. The perpendicular line is equal to 90 degrees if measured from the hypotenuse side, or equal to 60 degrees if measured from imaginary vertical line of the chord. And note that the straight horizontal line will intersect the perpendicular line at a certain point, called tip chord. If measured from root to tip, it will form 7.35 cm length. The value of 7.35 cm will be a span of wing at the right hand. Since span of left wing is the same as span of right wing, then wingspan is number of both span of left and right wing, which is equal to 14.7 meters of wingspan. This wingspan configuration exactly matches span of wings Sukhoi Su-27 Flanker.

The aspect ratio AR, one of parameters used in this analysis, is the ratio of the square of the wingspan b, to the projected wing area S, which is equal to the ratio of the span of wing b, to the standard mean chord SMC. While chord is the imaginary straight line joining the leading-edge and trailing-edge of an airfoil. The chord length is the distance between the trailing-edge and the point where the chord intersects the leading-edge. The point on the leading-edge used to define the chord may be either the surface point of minimum radius, or the surface point that maximizes chord length.

Aspect ratio and other features of the planform are often used to predict the aerodynamic efficiency of a wing because the lift-to-drag ratio increases with aspect ratio, improving the fuel economy in powered airplanes and the gliding angle of sailplanes.

As a useful simplification, an aircraft in flight can be imagined to affect a circular cylinder of air with a diameter equal to the wingspan. A large wingspan affects a large cylinder of air, and a small wingspan affects a small cylinder of air. A small air cylinder must be pushed down with a greater power (energy change per unit time) than a large cylinder in order to produce an equal upward force (momentum change per unit time). This is because giving the same momentum change to a smaller mass of air requires giving it a greater velocity change, and a much greater energy change because energy is proportional to the square of the velocity while momentum is only linearly proportional to the velocity. The aft-leaning component of this change in velocity is proportional to the induced drag, which is the force needed to take up that power at that airspeed.

The interaction between undisturbed air outside the cylinder of air, and the downward-moving cylinder of air occurs at the wingtips and can be seen as wingtip vortices. It is important to keep in mind that this is a drastic over simplification, and an airplane wing affects a very large area around itself. Although a long, narrow wing with a high aspect ratio, has aerodynamic advantages like better lift-to-drag-ratio there are several reasons why not all aircraft have high aspect wings: structural, maneuverability, etc.

Wings with larger aspect ratio generate lift with less drag and thus have greater flight efficiency. For example, an aspect ratio of 5.5 would be more efficient than an aspect ratio of 4. Fighter aircraft, in common, has aspect ratio ranging from 4 to 5.5.

Why high aspect ratio of wing is more efficient? Lift is created by a difference in pressure between the upper and lower surfaces of the wing. In all wings, some of the high pressure under the wing leaks around the wingtip creating a vortex and therefore, drag. A high aspect ratio wing is efficient because it reduces the formation of the vortex and associated drag.

In contrast, a low aspect ratio of wing allows the high pressure on the bottom of the wing to escape more easily, resulting in a larger vortex and greater drag.

The lift force of the wing is proportional to the area, so the heavier the aircraft the bigger the area must be. The area is the product of span times width (mean chord) of the wings.

So either a long, narrow wing or a shorter, broader wing will support the same mass. For efficient steady flight, the ratio span to chord, the aspect ratio, should be as high as possible. because this lowers the lift-induced drag associated with the inevitable wingtip vortices.

Wings Configuration :

The wing configuration of a fixed-wing aircraft (including both gliders and powered aeroplanes), is arrangement of lifting and related surfaces. And the aircraft design is often classified by its wings configuration.

Wings configuration vary to provide different flight characteristics. The particular design of the wings for any aircraft depends on several factors including the desired speed at takeoff, landing and in flight, the desired rate of climb, use of the aircraft, and including size and weight of the aircraft.

Modern high performances fighter aircrafts have one of three wings type: trapezoidal, sweptback wings and delta wings. In trapezoidal wings, the leading-edge sweeps back but the trailing-edge sweeps forward. In sweptback wings, both leading and trailer-edge are swept back. As for delta wing is a wing shaped in the form of equilateral triangle. Each type of wings have their own advantages and disadvantages. And what type of wings is to design depend on what aircraft flight characteristics to perform. The designers’ talents that will make it more advance than other type of wings, and superior than other competitor aircraft.

Wings of aircraft, both the trailing and the leading-edge may be curved or straight or one edge might be curved and the other straight. One or both edges of an aircraft wing can be tapered so that it is narrower at the tip. The wingtip can be pointed, rounded or square.

Aircraft wings may be attached at the bottom of the fuselage, mid-fuselage or at the top. They might extend perpendicular to the fuselage’s horizontal plain or can angle down or up slightly. This angle is called the wing dihedral angle and it affects the aircraft’s lateral stability.

A swept wing is a wing that angles either backward or occasionally forward from its root rather than in a straight sideways direction. The term “swept wing” is normally used to mean “swept back”. In design, sweep angle is normally measured by drawing a line from root to tip, typically 25% of the way back from the leading-edge, and comparing that with the perpendicular to the longitudinal axis of the aircraft. Typical sweep angles vary from 0 (zero) for a straight-wing aircraft to 45 degrees or more for fighters and other high speed designs.

Aircrafts wings are often of complete cantilever design. What this means is that they are built in such a way that they don’t require any external bracing. They are internally supported by structural members and the aircraft’s skin.

Sweptback wings are mostly associated with Sovyet design tradition. Sukhoi Su-27 that classified as heavy fighter fly at supersonic speed of 2.25 Mach number with two engines and twin fins. It has sweptback wings with leading-edge swept back by 42 degree while the trailer-edge swept back by 20 degrees, and equipped with LERX. Wingspan of Su-27 is 14.7 meters, length 21.9 meters, and height 5.9 meters.

Sweptback wings have very similar characteristics to trapezoidal wings; better performance at transonic speeds and during transition to and from supersonic conditions.

Compared with trapezoidal, sweptback wings have lower wings area and lower wings loading. In common, the aspect ratio of sweptback wings is better than trapezoidal wings.

The center of lift of sweptback wings lies between that trapezoidal and delta wings.

Tail(s) Design :

Tail is all-moveable fins that often referred to as stabilator. Aircraft stabilizer is an aerodynamic surface, typically including one or more moveable control surface, that provide longitudinal (pitch) and/or directional (yaw) stability and control. Longitudinal stability and control may be obtained with other wing configurations, including canard, tandem wing and tailless aircraft.

Horizontal stabilizer, many say tail fins or ventral fins, is used to maintain the aircraft in longitudinal balance. It exerts a vertical force in a distance so the summation of pitch moments about center of gravity is zero. The vertical force exerted by the stabilizer varies with flight conditions, in particular according to the aircraft lift coefficient and wing flaps deflection which both affect position of the center of pressure, and with the position of the aircraft center of gravity. Transonics flight makes special demands on horizontal stabilizers; when the local speed of the air over the wing reaches the speed of sound there is a sudden move aft of the center of pressure.

Vertical stabilizer, or fin(s) of an aircraft, are typically found on the aft end of the fuselage, and are intended to reduce side slip and provide direction stability. On aircraft, vertical stabilizer generally point upward. This upright mounting position has two major benefits: The drag of the stabilizer increases at speed, which creates a nose-up moment that helps to slow down the aircraft and prevent dangerous overspeed; and when the aircraft banks, the stabilizer produces lift which counters the banking moment and keeps the aircraft upright in the absence of control input. If the vertical stabilizer was mounted on the underside, it would produce a positive feedback whenever the aircraft dives or banks, which is inherently unstable. The trailing-end of the stabilizer is typically movable, and called the rudder; this allows the aircraft pilot to control yaw.

Tail fins is required in both trapezoidal dan sweptback wings. Delta wings do not require ventral fins instead of canards, a small wings in front of the aircraft. Canards will be described in leading-edge extension. Sukhoi Su-27 has unique tails design, beside horizontal fins (ventral fins) and vertical tail fins, it also has tail as should be.

Placement of ventral fins for sweptback wings is at straight line of wingspan; an imaginary line from wingtip to the other wingtip that meet with fuselage. There is tolerance 10 to 15 degrees for airplane due to fuselage length, but zero tolerance for fighter aircraft except for delta wings as it does not require ventral fins, but canards. 

As for vertical fins is pointed upward from aerodynamic center, the sweep of leading-edge of the fins equal to sweep of the wings. While the trailing-end of the stabilizer is typically moveable, and called the rudder. Commonly both leading and trailing-edge of vertical fins sweep back. As stabilizer, value of the aspect ratio is almost a half of the wing.

In sweptback wings, the aerodynamic center is at wingtip to wingtip of the leading-edge of the wings.

Sukhoi Su-27 has unique tail design, besides horizontal tail fins (ventral fins) and vertical fins, it also has tail as should be. Longer tail running far back from fuselage to maintain airflow around the fuselage. Mean chord of the tail measured from tip to tip of imaginary line of ventral fins to wingtip sweeps back along with angle of leading-edge of fins. That is length of the tail. Another secret of this tail is the aspect ratio of fuselage length to wingspan, which is reaching value of the golden ratio.

Leading-Edge eXtension :

A leading-edge extension (LEX) is a small extension to an aircraft wing surface, forward of the leading-edge. The primary reason for adding the extension is to improve the airflow at high angles of attack and low air speeds, to improve handling and delay the stall. A dogtooth can also improve airflow and reduce drag at higher speeds.

A leading-edge root extension (LERX) is a small fillet, typically roughly triangular in shape, running forward from the leading-edge of the wing root to a point along the fuselage. On a modern fighter aircraft, LERX induces controlled airflow over the wing at high angles of attack, so delaying the stall and consequent loss of lift. In cruising flight the effect of the LERX is minimal. However at high angles of attack, as often encountered in a dogfight or during take-off and landing, the LERX generates a high-speed vortex that attaches to the top of the wing. The vortex action maintains a smooth airflow over the wing surface well past the normal stall point at which the airflow would otherwise break up, thus sustaining lift at very high angles.

Leading-edge vortex controller (LEVCON) systems are a continuation of leading-edge root extension (LERX) technology, but with actuation that allows the leading-edge vortices to be modified without adjusting the aircraft's attitude. Otherwise they operate on the same principles as the LERX system to create lift augmenting leading-edge vortices during high angle of attack flight. This system has been incorporated in the Russian Sukhoi Su-57 and Indian HAL LCA Navy.

The LEVCON actuation ability also improve performance over the LERX system in other areas. When combined with the thrust vectoring controller (TVC), the aircraft controllability at extreme angles of attack is further increased, which assists in stunts which require supermaneuverability such as Pugachev's Cobra. Additionally, on the Sukhoi Su-57 the LEVCON system is used for increased departure-resistance in the event of TVC failure at a post-stall attitude. It can also be used for trimming the aircraft, and optimizing the lift to drag ratio during cruise.