Airbus A380 And Boeing 747

Airbus A380 and Boeing 747 are the new generation of aircraft for long haul and bulk passenger flights. The Airbus A380 holds 525 passengers whereas the Boeing 747 holds up to 452 passengers The feat of flying is a giant leap forward as well as flying with a huge passenger load. The project is to produce a conceptual design of a large civil aircraft using advanced computerised aircraft methods. The mission profile defined for this aircraft is long haul, matching the Airbus A380’s range of 15km [6]. Also, the aircraft to be designed is to carry 550 passengers, even more passengers than the Airbus A380. This can only be made possible by a number of criteria but the biggest problem comes from keeping the aircraft airborne under an increased passenger and structural load. The required lift for an increased load of this magnitude mainly comes from the combination of the lifting surfaces and lifting control surfaces of the wing.

Wings (SA)

Aircraft wing designers have drawn their inspiration from birds. Even in this day and age, engineers are still finding ways to improve design based on examples found in the ornithological (branch of zoology that deals with the study of birds) world [14].

Wings are airfoils that are attached to each side of the fuselage of an airplane and are the main lifting surfaces that support the airplane in flight [13]. Wings can be of different designs, sizes, and shapes. Different types of wings are used by manufacturers depending on the mission of the aircraft. A variety of wing shapes are shown in Fig.1. Each fulfils a certain need with respect to the expected performance for the particular airplane. Wings may be attached at the top, middle, or lower portion of the fuselage. Passenger airplanes usually have low wings. The number of wings on an aircraft can vary, for example airplanes with a single set of wings are called monoplanes and those with two sets are known as biplanes.[13] Fig.1: Examples of wing planform [12] Planform styles

Wings have evolved over the years from simpler designs as well as the Canard configuration (a configuration in which the span of the forward wing is substantially less than that of the main wing) and straight wings to futuristic designs such as oblique and morphed wings. The Canard configuration was founded by the Wright’s brothers where the tailplane is in front of the straight wing. Many years of research have been carried out to improve the aerodynamic efficiency and performance of wings in aircraft and evidence of this can be found in the more futuristic designs for aircraft. For example, the oblique wing is a wing of large span fitted about a pivot that rests on the top side of the fuselage and the wing can rotate about this pivot giving one side of the aircraft a forward swept wing and the other, an aft swept wing and vice versa. The varying sweep angle and configuration was the pinnacle point of research and development for this aircraft and was created to give the pilot more freedom into how the aircraft can be flown at different speeds. [8]

Variable sweep wings allow the aircraft to take advantage of the greater lift and handling qualities that come with straight wings during low speed phases such as takeoff and landing and can also benefit from the reduced drag and improved aerodynamic efficiency that comes with swept wings during high speed phases such as the cruise phase. However, this wing configuration is more likely to be found on high performance aircraft like military aircraft rather than transport maybe due to the unpleasant flying characteristics that come with the extreme wing sweep angles which could have discouraged transport aircraft designers from adopting this configuration in their designs. [8]

Evolution of aircraft wings (SA)

There were few large aircraft in the 1950’s. In those days, some aircraft’s wings were built by using wood instead of metal. One reason wing’s were built using wood is because there were a shortage of metal at that time [17]. This is due to various reasons.

One factor in favour of the wood wing was the quality of the ride in turbulence. The ride of a wood wing was better than a metal one. The quality of the ride in a metal wing was harsher and stiffer than the wood wing [17]. Also, the stall characteristics of the wood wing were much better than the metal ones. A disadvantage of wood wing was that it would have to be replaced early due to rot.

In1961, wings were no longer made of wood [11]. Instead metal wing was introduced. The reasons for this were for marketing aspects, that is, metal wing last longer than a wood one. People think of rot when they think of wood. When they think of Aluminium, they think it will last forever.

Morphed wing (SAJ and SA)

The morphed wing started as a conceptual design when then a prototype was eventually built to test the proposed idea. It works by using in-built shape memory alloy actuators which deforms into a different pre-proposed shape when heated. This new shape gives the wings a new set of aerodynamic characteristics adapting to different flight conditions or for a change in mission. [9]

Airbus is trying to use similar principles to morph aircraft wings to make them highly adaptable. A bird glides for maximum lift and folds its wings for reduced drag and this is the principle that is adopted from birds which made Airbus focus on wing planform.

Professor Meguid of University of Toronto believes the technology behind the UAV morphed wing design could eventually be applied to civil aircraft. Meguid also states that ‘some big airplane manufacturers are already interested in this technology and current research is being done to implement morphed wings [14].

On the other hand, Airbus senior manager of flight physics research, David Hills, disagrees with the idea of using morphed wing in commercial aircraft. He points out that unlike military aircraft, commercial airliners ‘do not need to drop like a stone’, therefore do not need morphed wings. [14]

Morphing aircraft are multi-role aircraft that change their external shape significantly to adapt to a changing mission environment during flight. This in turn creates superior system capabilities which are not possible without the shape changes of the wing. The objective of morphing activities is to develop high performance aircraft with wings designed to change shape and performance substantially during flight to create multiple-regime, aerodynamically-efficient and shape-changing aircraft.

Different Wing configurations (SAJ)

Braced wing

They are normally used in transonic aircraft designs just like the aircraft the group is designing. This truss braced wing configuration proved better than the normal cantilever because of its reduced fuel consumption and improved aerodynamic performance.

The configuration can be altered to maximise different performance criteria for example if minimum fuel emission is desired then the wings have a lower thickness-to-chord ratio (are a lot thinner) and if the maximisation of the lift to drag ratio is desired then the wings are in contrast a lot thicker.

The main desirable outcome from the use of having supporting truss wing configuration is the result of lower span wise bending moments for given loading. However, having this means a lighter wing structure, which results in needing an increased span (therefore greater lift to drag ratio), thinner wing and a reduced chord. The outcome is a more thin and slender looking wings that would therefore hold less fuel. If the wing could then in turn be designed with a high aspect ratio, it could minimise induced drag and as the wing is thinner, it will minimise the production of wave/form drag. [1]

However, this configuration is not desired because of its high wing.

Biplane Configuration (SAJ)

Having two wings on each side aligned vertically from each other, all wave drag that is caused by the thickness of airfoil is eliminated. However, at small angles of attack, the flow is similar to flat plate except for a small wave drag penalty. When the flow becomes choked, a lot of wave drag can be produced and this is controlled from the use of hinge slats.

However, this is not an ideal configuration for the transport aircraft to be designed as this configuration is mainly used in supersonic aircrafts, not transonic. [5]

Joint wing configuration (SAJ)

Joint wing configuration is when the tail is attached to the wing on both sides.

The advantage of this configuration is greater control when pitching the aircraft and that the tail provides adequate structural support of the wings. It also produces less drag and has an overall reduced structural weight compared to structural aircrafts of same span. Reduced structural weight is due to the tail acting like a truss in support of the wing and relieving bending moment.

Disadvantages of this configuration are that it needs a far greater wing span for it to cope with the take-off field length and constraints. [2] Also, with a greater wing span, there is greater drag and weight compared to conventional configurations as shown in Fig.10.

Therefore a conventional low wing cantilever design is preferred for the design of this aircraft.

Winglets (SAJ)

Winglets are the small vertical structures at the end of the wings to reduce the effects of “leakage” of flow from the under surface of the wing.

The effect of different taper ratios (SAJ)

Small taper ratios ensure that the wing is strong enough so that all vortex shedding ceases.

However, increasing the taper ratio will result in less induced drag so therefore, the aircraft can take advantage of a greater flight range from less drag, larger taper ratio.

Lower taper ratio wings are lower in weight but can hold an increased fuel volume.

So the preferred design of the wing will be to have a small taper ratio to keep the weight of the wing low without causing excessive variation in CL and stalling characteristics of the wing. [3]

Dihedral / Anhedral Angles (SA)

The dihedral angle, that is, the wing tip chord raised above the wing root chord, assists roll stability. Dihedral angle is normally between 2 and 3 degrees and rarely exceeds 5 degrees. The figure below shows the dihedral angle of a low-wing configuration. An advantage of a low-wing is it permits more ground clearance for the wing tip. The opposite of a dihedral angle is an anhedral angle. Anhedral angle lowers the wing tip with respect to the wing root and is typically associated with high-wing aircraft. (Aircraft Design, A. Kandu)

(a) Dihedral (midwing – low tail) (b) Anhedral (high-wing – T-tail)

Effects of dihedral angle (SA)

The dihedral angle affects the lateral stability of the aircraft. The greater the dihedral angle, the more stable it is during roll. However, having a small dihedral angle can mean that it is less stable, but it can increase the manoeuvrability.

When an aircraft is disturbed from upright position, that is, rolling, the aircraft sideslips towards the downgoing wing; the dihedral angle increases the angle of attack to lateral flow producing additional lift to restore straight and level flight. [4]

Leading edge strakes (SAJ)

Leading edge strakes is a component just in front of the wing and provides usable airflow over the wing at high angles of attack, delaying stall and consequently loss of lift.

LEXES, another abbreviation for the stakes are very highly swept lifting surfaces that generate high speed vortexes at high angles of attack and attaches itself to the top of the wing.

This is not really needed on a transport aircraft and is more apt for military aircraft which flies at high angles of attack at times and therefore not required. [4]

Wing size/ wing loading (SA)

Wing size or wing loading affects the following characteristics of an aircraft:

Take off / landing field length

Cruise performance (L/D)

Ride through turbulence

Weight of aircraft

Take off / landing field length (SA)

To achieve short field length, large wings (low wing loading) are better than small wings (high wing loading). The wing can be kept small by using flaps. Flaps provide the possibility to obtain high values of CLmax. Pilot uses flaps or slats to modify the shape and surface area of the wing to change its operating characteristics in flight. (Roskam, 1985)

Cruise performance (L/D) (SA)

To achieve cruise flight close to (L/D)max a high wing loading is needed so that the cruise lift coefficient can be close to that at (L/D)max.

Weight (SA)

The larger the wing area, the greater the weight of the wing and therefore the weight of the airplane.

High, Middle or Low wing (SA)

The choice of high, mid or low wing configuration depends on the mission of the airplane (passenger, cargo). Hence the type of airplane that is considered plays a vital role in deciding the vertical location of the wing.

Low wing (SA)

Low wing aircraft, as shown in Fig.14 are planes with the wing mounted below the main fuselage of the aircraft. Aerodynamically, there is not much difference between the two wing locations. [16]

Advantages (SA)

A Low wing aircraft provides superior visibility above and to the sides of the aircraft. The visibility advantage shows in turns when the pilot can see where the turn will go, even in a steep bank. On the other hand, a high wing aircraft will block the view in the direction of a turn. [16]

Low wing aircraft are thought to be easier to land in a crosswind. The reason for this is more to do where the landing gear is placed rather than its aerodynamics. On a low wing airplane, the gear is fixed and can be spaced wider apart than on a high wing airplane where the landing gear must be attached to the fuselage. Also, the landing gear of a low wing plane can be mounted straight up and down, which allows a more effective shock absorption system. [16]

Most planes carry fuel in the wings. The fuel ports of a low wing aircraft is easy to reach compare to a high wing aircraft. High wing airplanes require climbing up on the plane to re-fuel it.

Low wing aircraft uses (SA)

A low wing allows commercial jets to have the wing spar go through the fuselage below the passenger cabin. This leaves a lot of room in the passenger cabin with full headroom from front to back.

Low wing commercial jets have their engines mounted quite close to the ground. These planes need to fly and taxi on airports where the pavement is kept clean of any debris that could be sucked up by those big jet turbines. This is one reason why military cargo planes use a high wing design, to mount the engines higher off the ground. [16]

High wing (SA)

A high wing aircraft is when the wing is mounted above the fuselage. High wing is where the wing crosses the fuselage at the top.

Advantages (SA)

A high wing aircraft provides the best visibility below the aircraft. High wing airplane is also safer in a descent because it avoids the possibility of coming down on another aircraft, especially on approach to the airfield or in the traffic pattern.

Planform Tailoring (SA)

Many airplanes end up with significant planform irregularities. This is where the use of planform tailoring comes into play. Some reasons for using planform tailoring are: stall behaviour, pitching moment behaviour at high mach, aileron buzz and aerolastic behaviour. [Roskam, 1985]

To improve stall behaviour of wing, that is, delay stall to higher angle of attack, leading edge extensions and/or droop may be used.

Aileron buzz can occur if the wing sections at the aileron stations develop shocks close to the aileron hingeline. If the aileron is cable controlled then the aileron can develop a severe vibration which is known as aileron buzz. Such problems can be relieved by leading edge extensions.

References

Gur, O. (2010). Design optimisation of a truss braced wing transonic transport aircraft. Journal of aircraft. 47 (6), p1907-1917.

Gallman, J.W.. (1993). Optimisation of joint wing aircraft. Journal of aircraft. 30 (6), p897-907.

Ng, T.T.H.. (2002). Application of genetic algorithms to conceptual design of a micro air vehicle. Engineering applications of artificial intelligence. 15 (1), p439-445.

Roskam, J. (1985). Preliminary configuration design and integration of the propulison system. Kansas: Roskam avaition and engineering corporation. p141-162.

Kusunose, K.. (2011). Supersonic biplane – a review. Progress in Aerospace Sciences. 47 (1), p53-87.

Airbus A380 presentation.

Boeing 747 presentation.

Curry, M.. (2009). Past Projects – AD-1 Oblique Wing. Available: http://www.nasa.gov/centers/dryden/history/pastprojects/AD1/index.html. Last accessed 11th October 2012.

Stubbs, M.D. (2003). Kinematic Design and Analysis of a Morphing Wing. Virginia: Virginia Polytechnic Institute and State University. p1-72.

Tsai, D.. (2011). University of Washington Department of Aeronautics and Astronautics Senior Capstone Project 2011. Available: http://www.behance.net/gallery/Aerospace-Engineering-Senior-Capstone/1553987. Last accessed 11th October 2012.

http://www.mooneypilots.com/mapalog/woodwing.html

http://www.centennialofflight.gov/essay/Theories_of_Flight/airplane/TH2G5.htm

http://engg-learning.blogspot.co.uk/2011/03/introduction-to-aeroplane-airplane-is.html

http://www.flightglobal.com/news/articles/aircraft-engineers-look-to-bird-world-for-new-and-improved-wing-designs-345832/

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA479821

Airplanes: Low Wing Aircraft

http://www.acmp.com/blog/buyers-beware-mooney-m-20a-and-bellanca-cruiser.html

Wing Preliminary Calculations

Size and wing area (S)

Similar aircraft to the specifications we have made for our aircraft is the Airbus A380 and the Boeing 747.

Using the Roskam volumes, the aspect ratio of the Boeing 747 is 7.0 (Roskam, page 374) and 7.53 for the Airbus A380-100 (1).

The wing span of the Boeing 747-400 is 229ft and the airbus A380 has a wing span of 261ft 9in (1).

The reference wing area of the Boeing 747-400 is 6824 square feet and the reference wing area of the Airbus A380 is 9095 square feet (ft2)(1).

The takeoff weight for our proposed aircraft is around about 1300000lbs (1221267.35lbs or 553957.5516901kg). The wings of the aircraft generates most of the total lift of the aircraft so in order for the aircraft to take flight, the lift would at least have to equal the weight of the aircraft.

The lift equation is as follows:

The velocity can be calculated through the equation where a= the square root of the product of Gamma (1.4), R (287) and the Temperature. The cruise Mach number specified for this aircraft (A380) is 0.89.

The temperature at 35000ft, which is the cruising altitude proposed for this aircraft, is -54.23 Celsius which is 218.93 Kelvin.

Hence, a = √1.4 Ã- 287 Ã- 218.93 = 296.59

Therefore the V = 0.89 Ã- 296.59 = 263.97

The coefficient of lift for takeoff is 1.6 -2.2, for cruise it is 1.2-1.8 and for landing it is 1.8-2.8, so take the coefficient of lift to be 1.8.

The stall speed of an airbus A380 is 121kt (224 km/h) = 60.5 m/s and the 747X Stretch is 128kt (237 km/h) (1)

So, say the stall speed of the proposed aircraft should be 128kt, or 65.792m/s

Knot (kt)

m/s

1

0.51

ft2

m2

1

0.0929

Rearrange, the lift equation to make the wing area the subject:

=

The density of air is taken at sea level to be 1.225 kg/m3

50 kt = 25 m/s

Therefore, wing area = 553957.5516901/ 0.5 x 1.225 x 252 x 1.8 = 803.929 m2

Since the proposed aircraft is to be designed to carry more passengers than the airbus A380 and the Boeing 747-400, a larger wing span is proposed to create more lift, so b = 265ft.

The aspect ratio can be calculated by:

Aspect ratio= b2/S where S = Reference Wing Area and b = Wing Span

A (Aspect ratio) of A380 = 7.53 (550 passengers)

New A = 8 (an assumption based on having more passengers, 600)

Aspect ratio= b2/S= 280^2/6824=10.29

Sweep Angle

The sweep angle of the Boeing 747 is 37.5 degrees, the taper ratio is 0.25 and the dihedral angle is 7 degrees (Chapter 6, part II, page 146, Table 6.7, ROSKAM). In terms of the mission profile, size and configuration this aircraft is comparable to the A380.

The sweep angle of the A380 is 33.5 degrees and taper ratio is approximately 0.3. (http://www.dept.aoe.vt.edu/~mason/Mason_f/A380Hosder.pdf).

For the proposed aircraft, the sweep angle should be 30 degrees.

Thickness Ratio

the thickness ratio of the airbus a380 is 6%. (http://www.dept.aoe.vt.edu/~mason/Mason_f/A380Stephens.pdf)

The thickness ratio of the boeing 747 is

Airfoils

http://www.allstar.fiu.edu/aero/wing31.htm

http://www.allstar.fiu.edu/aero/images/pic3-1.gif

A deep camber should be used which gives high lift and low speeds. Suitable for transport planes.

http://www.allstar.fiu.edu/aero/images/fig18.gif

http://www.ae.illinois.edu/m-selig/ads/afplots/sc20610.gif

Airfoil for the wing root (http://www.ae.illinois.edu/m-selig/ads/afplots/sc20610.gif)

http://www.ae.illinois.edu/m-selig/ads/afplots/sc20606.gif

Airfoil of wing tip (http://www.ae.illinois.edu/m-selig/ads/afplots/sc20606.gif)

(6) Taper Ratio

The taper ratio of the Boeing 747 is 0.25

The taper ratio of the A380 is 0.3.

For the proposed aircraft, the taper ratio should be 0.25.

(7) Incidence Angle and Twist Angle

Incidence angle of the Boeing 747 is 2 degrees. (Roskam)

(8) Dihedral angle

The dihedral angle of the Boeing 747 is 7 degrees.

(9) Lateral control surface size and layout