Regional Aircraft Design Project(R831V)

Group 16Wing Lon See 2111037Josh Evens 2087805Max Grewar 2088759SeifAllah ElTayeb 2092091

Supervisor:John McIntyre 2019777

April 24, 2015

Contents

I Design Specification 3

1 Introduction 4

2 Market Research 52.1 Market Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.1.1 Competitor Market Outlook and Forecast Reports . . . . . . . . . . . . . . . . 52.1.2 Potential Routes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

II Aircraft Design 7

3 Fuselage and Empennage 83.1 Cabin Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.2 Multiple Utility Interior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.3 Empennage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.3.1 Empennage Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4 Aerodynamics 124.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124.2 Wing Configuration and Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124.3 Tailplane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144.4 Aerofoil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154.5 High Lift Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164.6 Wing Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164.7 Future Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.8 Performance Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

5 Propulsion 205.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205.2 Propulsion System Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

5.2.1 Turboprop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205.2.2 Turbojet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215.2.3 Turbofan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.3 Number of Engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235.4 Engine Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235.5 Engine Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245.6 Auxiliary Power Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

6 Landing Gear 266.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266.2 Ground Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276.3 Taxiing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286.4 Takeoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296.5 Retraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296.6 Deployment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306.7 Touchdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306.8 Braking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

6.9 Final Design and Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7 Aircraft CAD 33

8 Appendix 35

9 References 419.1 Landing Gear and Market Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41......Credits

Andrew McIntyre SupervisorWing Lon See, Fuselage and EmpennageJosh Evens, Aerodynamics, Weight and Range EstimationMax Grewar, PropulsionSeifAllah ElTayeb, Market Research, Landing Gear, Report Formatting(LaTeX)

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Part I

Design Specification

Chapter 1

Introduction

Objective The objective of this project is to design a regional aircraft that can competewith existent aircrafts through the improvement of some aspects which affects the perfor-mance, efficiency and economy of currently operational aircrafts.

Basic Design Requirements In order to meet the objectives the design must be able tomeet the following specifications:

Cabin

2 Pilots and 3 Flight Attendants

Maximum Payload: 12,000 kg

Stand-up Aisle Height: 2 m

Performance Parameters

Range: 2,500 km (IFR Reserves)

Full Fuel Payload: 10,000 kg

Maximum Speed: Mach 0.75 at 35,000 ft

Service Ceiling: 45,000 ft

Miscellaneous

Compliant with FAR Part 25 Certification requirements

Service Entry: 2018

Baseline Model Price: $14M

Operational Cost: $1 900 per hr

Average Fuel Price: $2.5 per gal (US)

Chapter 2

Market Research

2.1 Market Analysis

In order for the design to be competitive and appealing to customers, the market mustbe properly analysed in order to identify a gap which the aircraft can fill. Alternatively,existent models can be analysed to identify the aspects which can be improved, which aidsin prioritising the design of some elements which will form the aircrafts selling points.

2.1.1 Competitor Market Outlook and Forecast Reports

Given that the aerospace industry is particularly complex, a few manufacturers dominatemost of the market with big market shares. This is also due to the high cost of designresearch and development. Below is a survey of the major manufacturers forecast andoutlook reports which give an insight into the markets present and future.

Airbus

Airbus forecasts an increase of a 107% in the number of passenger aircrafts a figure thatsalmost the double of existent aircraft fleets, in addition to an increase of 65% increase indedicated freighters. Single-aisle aircrafts make up almost 70% of this forecasted increaseas the global middle class will almost double in size by 2033, stimulating the economyand making air travel more affordable and subject to even more traffic. Moreover, most ofthis traffic will come from the Asia-Pacific region which is currently undergoing fast pacedeconomic growth and increase in trade. It is also important to note that low maintenanceand fuel economy are becoming increasingly important for airlines as it increases theirprofits by reducing the running costs.

Boeing

As Airbuss main competitor Boeing has a major share in the global airliner market. Accord-ing to their report regional jets can be considered a niche market which comprises 6.77% ofthe future demand. The report also highlights the resilience of passenger traffic to changein relation to economic performance, growing annually. Cargo traffic on the other hand istied to economic performance as indicated by the slowdown in 2008 following the reces-sion, yet cargo traffic has been recovering since and growing at an average rate of 5%playing and increasingly important role in global supply chains.

Bombardier

Despite having a smaller share of the market, Bombardier still plays a major role in the re-gional jet and short-haul, single-aisle market. Bombardier expect a demand of 400 aircraftsin the 20-59 seat category and a significantly higher figure of 5,600 aircraft in the 60 to99 seat category. It is also important to note that one of the reports conclusions is thatemerging markets will be the main source of demand for new aircrafts in the coming 20years.

Embraer

According to South Americas biggest aircraft manufacturer, 70 to 90 seater planes are thefuture of and efficient hub and spoke air travel model. This is mainly due to the aircraftsoperating in emerging markets where population densities are low. The low number ofseats insures that the aircraft is constantly being used in an efficient manner where allseats are usually occupied. Similar to the previous reports, Embraers report highlightedthe important factor of a growing urban middle class. Moreover, it is mentioned that theAsia-Pacific regions economic growth and increasing liberalisation is creating a need formore frequent transportation and thus creating a secondary market that remains yet to besupplied with aircrafts.

2.1.2 Potential Routes

As a conclusion of the previously mentioned reports, Asia-Pacific is the region of potentialoperation. In addition, population census and population density data confirm the suitabilityof Asia-Pacific as the main marketing region for the aircraft. Potential routes were studiedin order to optimise the aircraft for operation on the Asia-Pacific region routes.

The region was surveyed for major airports in order to be able to calculate the maximumdesired range, as over-designing would result in decreasing the designs operational effi-ciency.Using the Haversine Law, the distance between all the mapped major hubs and Bangkokwas measured, and all were within range. This means that not only is it suitable for hub-spoke connections, but it can also serve hub-hub routes.

Figure 2.1: Map of major Asia-Pacific Hubs

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Part II

Aircraft Design

Chapter 3

Fuselage and Empennage

3.1 Cabin Layout

The Boeing 737 design was used to obtain the initial dimensions

Figure 3.1: Cross Section of B737 Cabin

Seat Capacity Number Of Rows Seat Width (m) Seat Abreast (m) Seat Arrangement Cabin Height (m) Cabin Width (m) Pitch (m) Aisle Width (m) Cabin Length (m)154 26 0.43 6 3-3 2.2 3.53 0.81 0.47 30.2

Our aircraft was based on current the successful civil aircraft Boeing 737. We let theseat capacity of our design decrease from 154 to 100.With the 100 seat capacity of aircraft (Np=100), we can calculate the number of abreastfor the design by using:

N =1

2N12p (3.1)

Where N is the number of seats abreast and Np is the number of passengers.From equation3.2 N is 5.

Then using:

Nr = 2N12p (3.2)

where Nr is the number of rows, we calculated Nr to be 20.We also estimated the cabin width, Wc usin equation 3.3

Wc WsN +WN (3.3)Here the the width of seat, width of aisle and number of aisle are denoted by Ws, W and Nrespectively. Wc is estimated to be 2.97m.

Similarly, the length of cabin Lc is proportional to the product of the seat pitch P and thenumber of rows, Nr .

Lc C3(PNr)1+ (3.4)Torenbeek (1982) suggests = 0.052 and the average of C3 for five seats abreast is 1.08(Sforza, 2014). This gave us an approximate cabin length, Lc of 19.88 m

Figure 3.2: Cross Section of our Cabin

Seat Capacity Number Of Rows Seat Width (m) Seat Abreast (m) Seat Arrangement Cabin Height (m) Cabin Width (m) Pitch (m) Aisle Width (m) Cabin Length (m)100 20 0.5 5 2-3 2.2 2.97 0.81 0.47 19.88

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3.2 Multiple Utility Interior

Our aim of our design is to increase the market competitiveness of the aircraft. The Boeing737 aircraft was designed for passenger. Therefore, this could be increased the use of theaircraft and let the design fit the seasonal demand.

A Modifiable Interior

It is noticed that cargo transportation is also a crucial application of aircraft. The Boeing737 variant can be exploited on both of passengers and cargo, it would not be restrictedfrom the seasonal requirement.

For the improvement of the upon design, firstly, the seats in the cabin we would select theremovable seats which can be used for the passenger aircraft and removed when it is forthe purpose of cargo. Then, the cargo module can be fitted into the cabin from the Afthatch. (pictured below)

3.3 Empennage

The tails are also a key element of stability, control and trim. The common tails are beingmostly used as conventional, t tail and cruciform tail.

Figure 3.3: Common Tail Sections

Cruciform Tail

The horizontal stabilisers are placed midway up the vertical stabiliser, giving the appear-ance of a cross when viewed from the front. The primary aim is to keep the horizontalstabilisers out of the engine wake or to prevent complex interference drag.

T-Tail

aThe horizontal stabiliser is positioned at the top of the vertical stabiliser. The horizontalstabiliser is then above the propeller flow, or prop wash, and the wing wake. Because thehorizontal stabiliser is more efficient, it can therefore be made both smaller and lighter.The placement of the horizontal stabiliser on top of the vertical stabiliser can also make thevertical stabiliser more aerodynamically efficient. By making the vertical stabiliser moreeffective, its size may be reduced.

Conventional Tail

It has one vertical stabiliser placed at the tapered tail section of the fuselage and onehorizontal stabiliser divided into two parts, one on each side of the vertical stabiliser. andthe conventional (lower) location for the horizontal stabiliser puts less stress on the vertical

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stabiliser. Therefore this arrangement provides adequate stability and the vertical stabilisercan be lighter.

3.3.1 Empennage Specification

Figure 3.4: B737 Front View, Showing Empennage

Eventually, we know the arrangement of conventional tail provides an adequate stabilityand lighter vertical stabiliser. In addition, most of the successful commercial aircrafts wouldadopt conventional tail, for instance, Boeing commercial airplanes ,Airbus. From thosesuccessful aircrafts, we think the answer is that sameness between the aircrafts is theresult of the typical design being the best compromise.

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Chapter 4

Aerodynamics

4.1 Introduction

For aerodynamics, we looked at a range of commercial aircraft wing designs to give us abrief idea of the qualities we would need for our wing. As with any aircraft design, it wasessential to do market research so we know what type of aircraft we are looking to design.Since we had decided to create a relatively small commercial plane (100 passengers), wethen had to look at certain wing designs which benefit this role.

Wing design is crucial in the development of any aircraft, as there are so many parametersthat could change the whole performance of the plane. For our wing design, we looked atcurrent commercial aircraft as a starting point, and then researched in to why these designsare so successful.

Figure 4.1: Boeing B737 Figure 4.2: Airbus A320

Comparing characteristics from the two most popular small commercial aircraft AS theBoeing 737 and the Airbus A320 AS we could compare our design to ensure that our air-craft would do well in the market. As our plane was based around efficiency, it was vitalthat we chose the most green and cost-effective wing.

4.2 Wing Configuration and Position

The chosen wing configuration was a low-wing configuration, as opposed to a high-wingconfiguration which is typically used for cargo aircraft. High-wing is useful for cargo trans-port because it allows the fuselage ground clearance to be smaller, enabling easy accessfor airport staff to add or remove the cargo from the aircraft. However, the high-wing con-figuration needs extra support because the wing bending moment is greater. This extraweight from the strut supports would prove unnecessary when the low-wing provides muchmore benefits.

Low wings are easier to maintain, favouring airline staff needs AS who have to check andmaintain the wings on a very regular basis. They also provide added landing stability whenthe landing gear is stored in the wings. High-winged aircraft store their landing gear in theirfuselage, which gives less stability because the wheels are much closer to the centre of theaircraft, as opposed to the low-wing aircraft where the wheels are far more separated. Also,from a safety perspective, the low-wing is desirable. In the unlikely event that our aircraftencounters a serious problem and is forced to land, assuming the pilot has successfullymanaged to land on a body of water which surrounds our hub airport, then the low wingwill keep much of the fuselage above the water for longer. This will provide the passengersand crew to exit the aircraft and use the wing as a temporary platform. Although it is highlyunlikely that such an event will happen, it is not impossible; therefore it is essential to makeour aircraft as safe as possible.

Figure 4.3: Wing Mounting Positions

Wing sweep depends on the role of the plane. For example, high-speed aircraft like fighterjets have a high-sweep angle, which gives them a low aspect ratio. This low aspect ratioprovides the jet with better rolling moment and therefore better manoeuvrability - essen-tial for fighter planes which engage in dogfights. However, our aircraft has a completelydifferent role, and a high aspect ratio was needed, and therefore a relatively small angle of25 sweep was used.

High aspect ratio provides an aircraft with stability, which is essential in a plane carryinglots of passengers. It also provides the aircraft with less induced drag, which in turn resultsin less fuel consumption. Induced drag is created from different air pressures at the tips ofthe wings, so a large, unswept wing with small a small tip chord produces less induced dragthan a swept wing with a large tip chord.

Winglets have also proved very successful in the fight for fuel-efficiency by also reducinginduced drag. This creates vortices much smaller than those produced by a wing tip withno device on it. Previously, there have been different shapes of winglet experimented,which could be added on to the ends of pre-existing wings; but some of these designs wereundesirable because they posed a threat of scraping along the ground from a low-wingaircraft in a rolling movement. Aviationpartners then developed what is now known as a"blended winglet". Blended winglets are now the most commonly used form of winglet asthey are they are the most effective, so our aircraft will have blended winglets. This willresult in a 3.5% fuel consumption decrease.

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Figure 4.4: Conventional Winglet Figure 4.5: Blended Winglet

4.3 Tailplane

The tailplane is a critical aspect of aircraft design because it highly influences the stabilityand control. Roughly 70% use the "conventional" arrangement, but this is less efficientthan the "T-tail". Since our aircraft design was geared towards creating a highly efficientplane, we went with the T-tail. The T-tail design raises the horizontal tail, which resultsin the tail avoiding wing wake and propwash. This reduces buffet on the tail, ultimatelyreducing fatigue on both the structure of the aircraft and the pilot, who has to work harderto control the aircraft.

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4.4 Aerofoil

Researching very successful aerofoils for current aircraft was difficult in some cases be-cause they are kept secret due to the highly competitive nature of the aviation industry.However, most typical commercial tend to use roughly the same aerofoil. We decided touse the NACA 0015. The symmetrical design is used because a cambered design is ineffi-cient in our specific role, which is transporting passengers in a low-speed cruising flight.

Figure 4.6: NACA0015

Figure 4.7: NACA0015 Aerofoil Characteristics at Various Reynolds Numbers

However, this aerofoil would not provide enough lift to allow the aircraft to take off and landon shorter runways. In order to increase the lift of the wing, high-lift devices were added.These devices alter the camber or chord of the wing in such a way that the lift produced bythe wing is significantly increased beyond the main aerofoils capabilities.

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4.5 High Lift Devices

Slats will be installed on to the aircraft wings. They are used to redirect the airflow to thewing, producing a laminar flow over the aerofoil. However, since they are only really effec-tive at high angles of attack, the slats will be retractable.

Slotted flaps are used to increase the camber of the wing, resulting in an increase in lift.Double slotted flaps are often used as they can create a smoother camber, further increas-ing the lift. Triple slotted flaps can be used, but due to the complexity of the mechanisms inthe flaps, they are hard to maintain and replace if necessary. Fowler flaps extend out fromthe edges of the wing, increasing the wing area, thus increasing the lift. We decided to usea double-slotted Fowler flap for our wings, in order to achieve the high lift that is neededfor take-off and landing.

Figure 4.8: Triple Slotted Fowler Flaps

Vortex generators will also be used on our wings. These are small vanes which stick outfrom the wing, and are spread out along the span off the wing. As well as an increase inthe planes stability, vortex generators also provide the aircraft with a higher rate of climb.This means that the plane has a shorter take-off run.

4.6 Wing Dimensions

As our plane was based on current successful commercial aircraft such as the Airbus A320or the Boeing B737, we used figures from these planes to get a rough idea of what ouraircraft should look like.

With a fuselage diameter or 2.51m (1m less than B737), I decided on using a span of34m (without winglets), and a reference wing area of 124m2. From here, we were able tocalculate the aspect ratio using equation 4.1

A =b2

S(4.1)

Where A = aspect ratiob = span (m)S = reference wing area (m2)

Which gave us A = 9.632.

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Assuming a taper ratio of 0.25, it was then possible to calculate the chord lengths at boththe root and the tip of the wing.

Croot =2.5

b(1 + )(4.2)

Where Croot = chord at root m = taper ration

Which gave Croot = 5.83 mThen using equation 4.3

Ctp = Croot (4.3)

Where Ctp is the chord at the tip of the wing (m), which worked out to be 1.46m.

Mean Aerodynamic Chord (m) was calculated using equation 4.4

MAC =2Croot

3(1 + + 2

1 + ) (4.4)

This worked out to be 4.08m.

PlaneSpan

[w/o winglets] (m) Fuselage Width (m)AspectRatio

TaperRatio Wing Area (m

2) MAC (m)

R831V 34 2.51 9.34 0.25 124 4.08B737 34.32 3.76 9.45 0.159 124.58 3.96A320 35.8 3.7 9.39 0.24 122.4 4

Our plane will also have a 6 dihedral angle. Dihedrals are very useful for the rolling stabilityof aircraft in the event of crosswinds, which cause sideslipping. The sideslip creates a rollingmovement in the aircraft, but the angle of the wing closest to the crosswind will create ahigher angle of attack, resulting in a counter-rolling movement, bring the aircraft back toequilibrium. This will be essential for the passengers who want a safe, stable flight, andalso the pilot who doesnAZt need to manually counteract the sideslip.

4.7 Future Technologies

As the battle for the most efficient aircraft continues, aviation companies will continueto develop technology which will reduce the amount of fuel needed, thus saving airlinesmoney on fuel as well as saving the planet. Here are some proposed future design conceptsfrom leading companies in the industry.

Flexfoil

Boston-based company FlexSys have designed a wing that has all of the high-lift devicesmerged in to it. This eliminates the need for complex mechanisms which are required forflaps and slots, by using a wing that has a variable geometry. This is achieved by integratinga series of sensors and actuators inside the structure of the wing, which then react anddeform the shape of the wing accordingly. FlexSys claim that their Flexfoil technology canreduce fuel consumption by 4-5% if installed on an existing wing, but claim a 12% fuelconsumption decrease if the wing is built with Flexfoil. Aerodynamic testing is taking placeat NASAs Dryden Flight Research Centre, and with applications not limited to aeronautics -the technology could be used for wind turbines or even boat rudders - this technology couldbe implemented in just a couple of years.

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Figure 4.9: Flexfoil

Hybrid Wing

The wings of these aircraft are "blended in" to the fuselage creating a whole body that canbe likened to a wing. Many developing technologies have been used in the design of thisaircraft, so much so that engineers have claimed that the aircraft uses half as much fuel asthe current aircraft of today. This 50% fuel consumption decrease is due to a new manufac-turing technique which creates aircraft components 25% lighter than current components,and also uses an ultra-high bypass ratio engine.

However, this aircraft is still in the development stage using smaller prototypes, and al-though new manufacturing processes will allow the full-size airframe to be much lighter, itis still in question whether or not this airframe will still be light enough. Also, the flat shapeof the aircraft will mean that some parts of the fuselage are right-angled, causing manyproblems if the cabin needs to be pressurised.

Advances in aircraft technology are more down materials, and the manufacturing processesused to create new components. Composite materials are being researched and developedto provide a material strong enough for the stress and pressures of flight, but to also belight enough to provide a high efficiency. NASA have said that although the Hybrid-Wingaircraft may take 20 years come to the market, the manufacturing technologies developedcould be used for future aircraft in as little as 8 years.

4.8 Performance Specifications

In order to execute the performance calculations, we had to firstly calculate the masses ofaircraft components. This was done by using the given design requirement weights, andadding them, on to each separate component weight, so we can obtain our maximum take-off weight (MTOW).

Maximum Payload: (12,000kg)Maximum Fuel: (10,000kg)

Using the properties of Aluminium 2024, our MTOW was estimated from the following:fuselage, two engines, wings and empennage, payload, fuel, landing gear, and avionics;giving us 47,988kg. Our empty weight (oe) is therefore 25,988kg. In comparison, theBoeing 737-300 has a MTOW of 49,900kg.

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Assuming a certain amount of fuel had been burned during take-off, and given our designrequirements, we were able to work out the lift and drag coefficients.

Mach No. (M):0.75Altitude (cruise):35,000ft

At 35,000ft the density is 0.011kg m3, and local speed of sound (a) is 295.4m s1.

Speed of our aircraft is given byV = M (4.5)

This gives us 221.55m s1.

Then, rearranging the lift equation to find the lift coefficient gives us:

CL =2L

V2S(4.6)

Where L = lift 441,450N

= air density (0.011kg m3)V = aircraft speed (221.5m s1)S = wing area (124m2)

Giving a CL of 13.18

From our engines cruise thrust, our drag is approximately equal to 23,887NUsing equation 4.7

CD =2D

V2S(4.7)

The drag coefficient, CD is calculated to be 0.714.

We can then work out the lift to drag ratio:

CL

CD=13.18

0.714= 18.8 (4.8)

In comparison, a Boeing 747 has a lift to drag ratio of 17 in cruise.

To calculate the range of our aircraft, we used the Brequet Range Equation:

Rnge =V

g

1

SFC

L

DlnMTOW

ETW(4.9)

Where V = flight speed (797.58km h1)g = gravitational acceleration (9.81m s2)SFC = specific fuel consumption (0.3 (estimated))L = lift(N)D = drag (N)MTOW = Maximum Takeoff Weight (47,988kg)ETW = Empty Weight (25,988kg)

This gave us a range of 3124.83km

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Chapter 5

Propulsion

5.1 Introduction

pro-pellere (latin): before or forward drive.

Aircraft engines provide the thrust needed to keep the aircraft flying. This is done by theengines propelling the aircraft through the air, this in turn creates airflow over the wings,providing lift.

Selecting the most useful and relevant aircraft power plant is crucial to our aircraft be-ing both cost effective and relevant to the job at hand. There were many choices thatneeded to be made when selecting propulsion these being; type of engine, engine position,number of engines and specific model chosen. There were three main different optionswhen it comes to selecting an engine for an aircraft, those being; Turboprop, Turbojet andTurbofan.

5.2 Propulsion System Comparison

5.2.1 Turboprop

Turboprop engines are comprised of (in their simplest form) an intake, compressor, com-bustion, turbine and propelling/exhaust nozzle as shown in figure 5.1. Drawn in throughthe intake, air is then compressed by the compressor before fuel is mixed in with the com-pressed air. This fuel and air mixture is then combusted in the combustion chamber, thecombustion gases then expand through the turbine. The majority of the power produced istransmitted to the propeller. The gases then are released to atmospheric pressure throughthe propelling nozzle.

Figure 5.1: Turboprop Engine Diagram

Turboprop engines are most often used for small commercial aircraft, they are also usedfor bush aircraft in remote areas of Australia, Africa, Canada and Alaska to name a few.

There are several advantages to using a turboprop engine, one of which is that turbopropengines consume two thirds less fuel per passenger than turbo fan aircraft when travellingat the same speed. Turboprop aircraft are also far quieter than a turbojet or turbofan equiv-alent. Turboprop engined aircraft are also used in airports that require a short take off andlanding distance.

However there are many disadvantages of turboprop engines that needed to be consid-ered. Whilst they are very fuel efficient, this is only at relatively low top speeds comparedto that of a turbofan or turbojet. The ceiling of operation is also far lower for a turbopropthan turbofan or turbojet, this would not be ideal as our international flights would be atrelatively high altitudes.

So when considering all of the points mentioned above, it was clear that turboprop wasnot ideal for our needs. Whilst they are very efficient at low altitude regional flights, ourflights are international flights that are at the longest over three and a half hours long.Although turboprops provide the ability to takeoff and land on short runways, this is not rel-evant to our needs as all airports we would be landing in are standard or large internationalairports. This as well as the fact that turboprops only fly at relatively low speeds makesthem unsuitable for our needs. Thus it was decided not to use turboprop engines for ouraircraft.

5.2.2 Turbojet

The Turbojet engine as shown in figure 5.2 is comprised of an air intake, followed by a com-pressor and combustion chamber, then turbine and exhaust nozzle. The turbojet is an airbreathing engine, almost exclusively used in aircraft. Thrust is generated by the engineby air being drawn in through the air intake before being compressed in the compressor.This compressed air is then heated and burned with fuel in the combustion chamber beforebeing passed through the turbine and accelerated out the exhaust. This provides the thrustneeded for flight.

Figure 5.2: Turbojet Engine Diagram

Turbojets were originally used quite often in smaller slower aircraft before the were grad-ually phased out and replaced with the more efficient turboprop engines. However evenin higher speed aircraft turbojets have been replaced by turbo fan engines which are moreefficient at similar speeds. The turbojets are also much louder than comparable sized tur-bofans.

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In terms of reasons why this particular type of engine was not chosen they were a few ma-jor down sides to choosing turbojets. As mentioned above they are unfavourable at bothlow and high speeds, this is due to inferior fuel efficiency when compared to prop enginesat low speeds and fan engines at high speeds. The desired speed for our aircraft will berelatively high, this means only turbofans or turbojets would be appropriate, however dueto the higher noise level and poorer fuel efficiency of the Turbojet it is not desirable for ourneeds.

5.2.3 Turbofan

Turbofan engines are very similar in design to turbojets, except from the additional bypassairflow, see figure 5.3 . This is achieved by placing a ducted fan in front of a turbojet engine,this creates two separate thrust forces to the engine. These two thrust values being thecore (jet) thrust and bypass thrust, when the bypass thrust is greater than the jet thrustthis is referred to as a high bypass engine, when the converse is true this is called a lowbypass engine. Most commercial aircraft in use these days feature high bypass turbofanengines. The ratio of mass flow of air in the bypass relative to the core is referred to as thebypass ratio (equation 5.1)

=mbypss

mcore(5.1)

Figure 5.3: Turbofan Engine Diagram

Turbofans in many ways are the ideal middle ground between turbojets and turboprops.While turboprops are ideal for low speed and pure jets are most useful at high airspeeds,turbofans are most effective and efficient in-between these two speeds. Around 500-1000km h1 (310-620mph) is the ideal operation speed of a turbofan engine, this being thespeed range of most commercial aircrafts makes turbofans an ideal choice for our aircraft.Figure 5.4 illustrates the ideal ranges for each engine in graph form in terms of propulsiveefficiency against airspeed.

Figure 5.4: Propulsive Efficiency against Speed

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In terms of benefits and drawbacks of using turbofans over the other two options it was clearthat turbofan was to be our choice of engine type. As shown in the above graph, turbofansare more efficient at our desired flight speeds. The 737 maximum speed is 544mph andcruise speed is around 480-510mph depending on model variant. Figure 5.4 clearly showsthat ducted fan engines are more efficient in the range from 0-500mph, this being therange of speeds our modified 737 will be operating in. Turbofans were also an attractiveoption due to the lower noise than comparable types of turbojets, this, when coupled withthe greater fuel efficiency, confirmed the turbofan as our choice of engine.

5.3 Number of Engines

Another key choice when deciding on our propulsion system was the number of engines tohave on our aircraft. There were two main options to choose from, either a twin engine orquad engine system. Four engine aircraft are mainly large commercial aircraft such as theBoeing 747 and Airbus A380. Therefore it makes more economic sense to choose just twoengines for our aircraft considering the size. The choice of two engines means less moneyspent on not just buying the engines but also fuel costs and repair costs. Modern twinengine aircraft often use turbofans with increased power, this provides a very steep initialclimb during take-off. This is also so that if an engine fails during take off the undamagedengine can provide sufficient thrust to take off steeply enough to avoid any obstacles in theflightpath.

5.4 Engine Placement

When it came to selecting engine positioning there were only two reasonable choices. Thefirst of which is tail mounted engines, however these are only ever used for small busi-ness or private style aircraft. This meant that below wing engine placement was to be ourchoice. Figure 5.5 shows an Airbus A320 (a similar sized aircraft to ours) with its twin en-gines mounted underneath the wings.

Placing the engines below the wings has long been the standard for modern airliners. Itallows for an uninterrupted airflow over the top of the wings which is one of the most cru-cial surfaces in terms of aerodynamics. This positioning also allows easy access for enginemaintenance whilst also reducing the noise heard by passengers in the cabin.

However the one major downside to under wing mounted engines is the increased chanceof foreign object damage or FOD. However instances like this are very rare. All enginesare also tested thoroughly to continue running and producing thrust after encountering aforeign object in the engine. This risk is far outweighed by the many benefits of under wingplacement.

Figure 5.5: Airbus A320 with under wing engine placement

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5.5 Engine Specification

Aircraft of similar size to our airliner such as the Boeing 737 and Airbus A320 use enginessuch as the CFM56 turbofan engine. The thrust force values produced by these similarlysized aircraft will be sufficient to provide lift for our aircraft.

The further the different series of CFM56 turbofans were researched, it was found that theyall have relatively similar performance values, thus it seemed wise to go with the older andtherefore cheaper CFM56-3 series of engines

Model Thrust Bypass Ratio Pressure Ratio Dry Weight

CFM56-3C-123,500lbf

100kN Alpha = 6 30.64301lbs1950kg

Figure 5.6: CFM56-3 Turbofan Engine

The CFM56-3 was designed for Boeing 737 second-generation: 300/400/500 aircraft. It isderived from the -2, the original CFM engine. This engine is in service all over the world withover 4500 still in use today. The fact that this series was designed specifically for Boeing737s makes it ideal for our airliners needs. The table below shows the key properties of thespecific model chosen, the CFM56-3C-1.

The CFM56-3C1 has a fan diameter of 60 inches (152cm), with the total length of the enginebeing 93 inches (236cm).

Takeoff Conditions (at sea level)

Max Take-off (lb) Airflow (lb/sec) Bypass Ratio

23500 638-710 6

In-flight Performance at 35,000ft & Mach 0.8

Maximum Climb Thrust (lb) Pressure Ratio at Maximum Climb Maximum Cruise Thrust (lb)

5540 30.6 5370

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5.6 Auxiliary Power Unit

Auxiliary Power Units (APU) are small devices which provide power for the aircraft whilst themain engines are off. They are found on most commercial aircraft and are of great benefit.

The main purpose of an APU is to generate power to start up the main engines of theaircraft. To do this the APU is first started usually by battery, once up to speed and runningthis power generated is then used as an ignition for the aircraft engines (CFM56-3C1s inour case). Once one engine has been started the APU is not needed as one engine can startthe other.

Model Specification

Model-APS 3200 APUBasic Dry Weight-308 lbs (140 kg)Altitude-Starts and Operates to 41,000 ft (12,500 m)Noise-Meets ICAO RequirementsKey Feature -Lowest Weight APU Option for theaA320 Family

The main benefit in our choice to have an APU installed is so that less ground assistance willbe needed in the various airports in which our aircraft will land and operate from. This willmean less reliance on outside assistance and therefore faster flight turnaround. APUs arealso used to run accessories in cabin when the engines are shut down. In the hot and oftenhumid climate of south-east Asia where we operate, Air conditioning whilst waiting at thegate will be a much needed feature for our passengers. The APU is also used for preflightchecks. During flight the APU is not needed as the main engines provide sufficient powerfor all systems on board. This APU is also ideal as it meets the maximum noise standardof ICAO (International Civil Aviation Organisation) of 305EPNdB (Effective Perceived NoiseLevel in Decibels).

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Chapter 6

Landing Gear

6.1 Introduction

The landing gear otherwise known as the undercarriage is an important part of almost allmodern aircrafts as it provides support for the airframe during ground interactions. Theusage of the landing gear during each flight can be summarised into 7 steps during whichthe landing gear must be able to perform as designed. These seven steps are: groundoperations, taxiing, takeoff, retraction, deployment, touchdown and braking.

The failure to perform any of the steps usually results in damage, financial losses andsometimes even casualties. As a result, potential emergencies must be taken into accountduring the design process.

Landing Gear Layouts The design process started with evaluating possible configura-tions and arrangements. Different arrangements have varying advantages and depend onthe intended utility of the aircraft. There are two main configurations used by aircrafts thatare intended to land on paved runways: tail dragger and tricycle.

Tail Dragger

Also referred to as the conventional configuration, the tail dragger usually has two mainwheels that are positioned ahead of the aircrafts center of gravity (along the fuselage) anda small wheel at the back to support the tail. This arrangement was commonly used bycommercial, freight and combat aircrafts during the early years of aviation and until the1960s. It is still used till today but only by smaller aircrafts. The conventional arrangementwas favoured as it kept parasitic drag to a minimum, provided more clearance for propelleraircrafts in addition to being easily replaced by skis to land on ice or snow. On the otherhand, the numerous disadvantages of using a conventional layout include poor forwardvisibility on ground, lack of manoeuvrability in high winds as a result of the aircrafts noseup attitude and inherent instability as the rear small wheel is used for steering. In thecase of a regional jet, the conventional layout is far from suitable as it lacks the requiredperformance, safety and reliability.

Tricycle

Essentially a reverse taildragger layout, the tricycle arrangement uses a steerable frontwheel and two or more wheels behind the center of gravity (along the fuselage). Commonlyused by modern airliners, the tricycle arrangement proved to be the optimum landing geararrangement for numerous reasons. To begin with, because the fuselages central axis isparallel to the ground, pilot visibility allows for spotting any ground obstacles and providesa field of vision wide enough to aid in avoiding incidents. In addition, as the wings sit ata negative angle of attack, manoeuvrability of the nose gear is enhanced and thus course

corrections are easier during takeoff and landing. The added control eases crosswind land-ings and is suitable for the flare stage that precedes landing. Disadvantages include heavyweight, high maintenance cost, and manufacturing complexity.

6.2 Ground Operation

Static Support The first test the landing gear must pass is supporting the airframe andall its payload when on the ground without collapsing or undergoing any significant ordamaging stresses. The sum of the forces on both the main and landing gear should supportthe aircrafts weight with full payload (including fuel).

FNG + FMG =W (6.1)

It is important to note that the nose gear is centered and that the main gears wheel aresymmetrically disposed relative to the fuselages centerline to insure that the port andstarboard force components are equal to avoid unbalance. The forces on the nose andmain gear are calculated given

FNG(c.o.goe NG) = FMG(c.o.goe MG) (6.2)This equation can be used to ensure quasi-static stability and balance during ground oper-ations to avoid the tail hitting the ground, or the plane tending to tip over. An additionalrequirement is that loading of the aircraft be carried out in a manner that moves the centerof gravity forward of the main gear, again to avoid stability and balance issues.

The wheelbase is also an important factor as it affects the load distribution. It is favourableto have most of the load on the main gear as it is structurally stronger and reliefs stress offthe fuselage. This is exhibited by the relationships

FNG =Woe(MG oe)

b(6.3)

FMG =Woe(oe NG)

b(6.4)

A survey of the most commonly used proportions for aircrafts that are either the samesize or bigger, revealed approximately similar positioning and dimensioning for the landinggear. Since aircrafts come in different dimensions it would only make sense to describe thepositioning of the nose and landing gear proportional to some other dimension. The centerof gravity is situated at approximately 45% of the fuselage length, the nose gear at 10%,and the main gear at approximately 50%. Bearing in mind that length of the wheelbaseb, is the difference between the positioning of the nose and main gear and therefore itis approximately 40% of the fuselage length. Substituting these numbers in equations 5.3and 5,4 showed that 10% of the force would be on the nose gear while the other 90% iscarried by the nose gear, which is ideal for the fuselage construction.

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6.3 Taxiing

Given that the landing gear sustains the aircraft while static and was designed with a safetyfactor that allows it to bear even more weight, taxiing is no different when it comes to load-ing. The only extra requirement for taxiing is steering, which can be done either throughthe control surfaces of the aircraft or being able to control the nose gear. As a benchmark,the circular turn radius is what can be used to compare the manoeuvrability of differentaircrafts. As a standard the landing gear track must not exceed half the runways width inorder to be able to execute a full 180turn.

In section 7.2.7 (Sforza) approximates the maximum achievable steering angle steer tobe 90 where = rctn t2b as shown in figure 6.1

Figure 6.1: Rotation path for aircraft with steerable nose gear

Although (Sforza) also cites that aircrafts like the B747, B777 and A380 use main gearsteering to limit the effects of tire scuffing during turns, it seemed unnecessary for thisdesign. All of the mentioned aircrafts are of significantly higher weight in comparison andthe addition of a main gear steering mechanism also means increased weight which isundesirable for fuel economy. Hence, nose gear steering will be adequate in this particularcase. In order to further enhance steering and taxiing, an electric actuator motor 1 isattached to the main gear to enable the aircraft to taxi at speeds of up to 30mph withjet engines running at idle. Powered by the APU, the independent electric drive allows forreduced fuel burning on the ground at the expense of extra weight. Major airport queuingtimes contribute to unnecessary fuel burning. In this context an independent drive train ismore economic and eco-friendly.

1refer to EGTS

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6.4 Takeoff

During takeoff rotation, the geometry and positioning of the landing gear are an essen-tial element of the airframes safety. Moreover, ease of manoeuvrability is necessary formaking course adjustments in case of any crosswinds that might move the aircraft off therunway.

As a result of limited runway distance, the aircraft must rotate as soon as the aircraftreaches VR in order to increase the angle of attack and achieve the maximum

CLCD

and liftoff the ground. This need for an increased angle of attack means that the tail must notstrike the ground to prevent damage to the airframe and friction that would increase thetime needed for takeoff. The takeoff geometry is shown in figure 6.2.

Figure 6.2: Takeoff geometry of an airliner

It was also considered while designing that there must be a safety margin to prevent anyincidents if the aircraft exceeds the desired angle of attack. The maximum compression ofthe main gear shock absorbers must be taken into account as well as it reduces the engineand tail clearances and thus an adequate safety margin must be taken into account,

6.5 Retraction

Smaller aircrafts with a fixed undercarriage like the Cessna 152 do not have to retract thelanding gear given its small size and the negligibility of the parasitic drag generated byconstant deployment. On the other hand, jet engine powered aircrafts can reach higherspeeds and reduce drag when the landing gear is retracted. This also increases the aero-dynamic efficiency,but it also means sacrificing precious cargo space as it must be stowedin the fuselage. The geometry was taking into account once again as it affects the safetyof the airframe.

Although almost all single-aisle, 70+ seats airliners have retracting landing gears, not allhave a stowage door otherwise known as a hubcap. Examples include the B737(shown infigure 6.3, EMB-170 and some variants of Bomabrdiers CRJ family. The absence of a doorsheds weight, saves space and doesnt interfere with the aerodynamics as much. Despite ofthe manufacturers choice to eliminate the door, the use of new light materials like carbonfibre and kevlar can be used as an alternative as the hubcap doesnt serve the structureas much as the aerodynamics. Carbon fibre and kevlar might be expensive material, butthey are probably the most suitable given their lightweight,ease of manufacturing and lowthickness.

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Figure 6.3: B737 Retracted Undercarraige

Clearances were also taken into account, as ageing tyres increase in size. A newlyinflated tyre will have a smaller diameter than one that has been in service, and thus, thewheel hub must be able to accommodate the maximum tyre diameter. Moreover, whenthe landing gear is no longer in contact with the ground, the tyres deform by increasing indiameter as the load is removed. This deformation was also taken into account when sizingthe wheel hub, so it fits with minimal clearance without getting caught or stuck.

6.6 Deployment

During final approach, pilots must deploy the landing gear to prepare for landing. The mainforce that both the nose and the landing gear must overcome is drag, and that is one of thefew cases in which increased weight of the landing gear is favourable. Increased weight inthis case exerts a downward force that reduces the needs for an extra mechanical force todeploy the landing gear into position.

Although not the norm, the landing gear must be able to deploy if any of the systems fail.As a result it the deployment arm was fitted with a high pressure nitrogen filled capsulethat explodes just like in automotive air bags. The rapid expansion of gas exerts enoughforce to help deploy the gear into position. After the capsule explodes a lock mechanisminsures that the landing gear remains in the right position perpendicular to the ground.

6.7 Touchdown

Upon making the final approach, the landing gear must be able to absorb the impact forcewithout collapsing in order to safely land the aircraft. Landing at angle is a factor that wasconsidered when determining the landing gears height to prevent a wing strike, as cross-winds can force pilots to yaw, resulting in undesired banking. This does not only increasethe chance of a wing strike, but it also increases the loading on the main gear as the loadis no more equally shared by the symmetrically disposed bogeys. Moreover, in order todissipate the impacts energy, cylinder filled with hydraulic fluid and nitrogen, commonlyknown as shock absorbers, are fixed to the landing strut. There are many important param-eters to consider when designing shock absorbers such as the cylinders internal diameter,external diameter, stroke length, gas pressure and maximum strength. This makes the useof tyres with high rated loads essential as it must be able to sustain the aircrafts weight.The different states of a shock absorber are shown in figure 6.4.

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Figure 6.4: A shock absorber in different states of compression

6.8 Braking

Tyre performance remains an important factor upon touching down as braking results inimmense friction which by return causes a rapid increase in temperature. There are manyrisks associated with this rapid increase in temperature including tire explosion, brake fail-ure or component damage. Another factor to take into consideration is the increased loadon the landing gear caused by the use of thrust reversers and a moment that is induced byusing spoilers and airbrakes.

6.9 Final Design and Specifications

The numbers listed in this sections are based on calculation methods used in (Sforza), andare a result of the design methodology previously mentioned in this chapter. Using litera-ture values and scaling was used where appropriate, as many of the dimensions depend onratios to function properly.The MATLAB Code that was used to calculate the final specifica-tions is available in the appendix.

All the requirements set by the FAR, in the aircraft subchapter C, Part 25, clauses 471to 519 and clauses 721 to 737 were checked against the design to make sure that it iscompliant and airworthy.

1datum is nose cone tip

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Positioning and Dimensioning 1

c.o.goe 46%

NG 12%

MG 52%

19.88m

b/ 0.40

b 7.95m

hoeb

0.18

t 4.65m

hoet

0.45

t2b

0.29

Loading (% Gross Weight)

FMG,st 85FNG,st 15FMG,m 127.5

FNG,m 27.5

Wheels & Tyres

dtyre,MG 46in.

dhee,MG 20in.

npys,MG 32

rated loadMG 20865 kg

dtyre,NG 30in.

dhee,NG 15in.

npys,NG 16

rated loadNG 6,504kg

Table 6.1: Landing Gear Specifications

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Chapter 7

Aircraft CAD

34

Chapter 8

Appendix

Aircraft Data (Sforza)

Aircraft hoe/ b b (m) b/ to (kg) t (m) t/2b b () hoe/ tB737-700 0.21 12.50 32.0 0.39 60328 5.71 0.227 12.8 0.463B737-800 0.18 17.37 38.1 0.46 70534 5.71 0.164 9.3 0.549B737-900 0.16 17.07 40.5 0.42 74389 5.71 0.166 9.4 0.481B787-8 0.19 22.86 55.8 0.41 219539 9.80 0.215 12.2 0.441B787-9 0.19 25.91 62.2 0.42 245167 9.80 0.190 10.8 0.500A320 0.23 12.80 37.5 0.34 73500 7.60 0.300 16.7 0.383E175 0.21 11.28 31.1 0.36 37500 4.11 0.182 10.3 0.577CRJ700 0.17 13.72 29.6 0.46 32999 5.72 0.209 11.8 0.406

Average 0.19 16.69 0.41 0.207 0.475

Table 8.1: Currently Operational Aircraft Specifications

Haversine MATLAB CODE

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39

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Chapter 9

References

9.1 Landing Gear and Market Research

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