DESIGN AND ANALYSIS OF THE KEEL BEAM

Transcription

1 ISTANBUL TECHNICAL UNIVERSITY FACULTY OF AERONAUTICS AND ASTRONAUTICS DESIGN AND ANALYSIS OF THE KEEL BEAM GRADUATION PROJECT Özgür KARALİ Department of Aeronautıcal Engineering Thesis Advisor: Prof. Dr. İbrahim ÖZKOL Anabilim Dalı : Herhangi Mühendislik, Bilim Programı : Herhangi Program JANUARY, 2019 i

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3 ISTANBUL TECHNICAL UNIVERSITY FACULTY OF AERONAUTICS AND ASTRONAUTICS DESIGN AND ANALYSIS OF THE KEEL BEAM GRADUATION PROJECT Özgür KARALİ Department of Aeronautical Engineering Thesis Advisor: Prof. Dr. İbrahim ÖZKOL Anabilim Dalı : Herhangi Mühendislik, Bilim Programı : Herhangi Program JANUARY, 2019 iii

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5 Özgür KARALİ, student of ITU Faculty of Aeronautics and Astronautics student ID , successfully defended the graduation entitled DESIGN AND ANALYSIS OF THE KEEL BEAM, which he prepared after fulfilling the requirements specified in the associated legislations, before the jury whose signatures are below. Thesis Advisor : Prof. Dr. Özgür KARALİ... İstanbul Technical University Jury Members : Prof. Dr. Metin Orhan KAYA... Technical University Dr. Özge ÖZDEMİR... İstanbul Technical University Date of Submission : 02 January 2012 Date of Defense : 14 January 2012 v

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7 7 To my family,

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9 FOREWORD First of all, I want to present my thanks to Mr. Prof. Dr. İbrahim ÖZKOL who supports to me when prepare this thesis. Also, I would like to thank Mr. Burhan ÇETİNKAYA, who helps the creating the outline, for consulting. Besides, I would like to thank all my friends and my family. January 2018 Özgür Karali 9

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11 Contents 1. Landing Gear Configurations Single Main Bicycle Tail-Gear Tricycle Quadricycle Multi-Bogey Releasable Rail Skid Seaplane Landing Device Human Leg Trade-Off Study Attachement Locations of the Landing Gear Fixed, Rectractable, or Seperable Landing Gear Components of Landing Gear Shock Absorber Rubber Shock Absorber Solid Spring Absorber Pneumatic Shock Absorbers Liquid Spring Oleo Pneumatic Shock Absorber Tires Brakes Sizing and Positioning of the Landing Gear Tail Gear Sizing and Positioning Nose Gear Sizing and Positioning The Sizing the Subsystems of the Landing Gear Tire Sizing Certification Requirements Design Requirements Shock Absorption Test Limit Drop Test

12 Ground Load Dynamic Tests Reserve Energy Absorption Drop Test Landing Gear Extension and Retraction System Wheels Tyres Brakes Basic Landing Loads for Tricycle Level Landing with Inclined Reactions Level Landing with Nose Wheel just Clear of Ground Tail Down Landing Basic Landing Loads for Tail-Gear Level Landing Tail Down Landing Nose Landing Load Calculations for a Example Aircraft Three Points Level Landing Braked Roll Supplementary Conditions for Nose Wheel Keel Beam, Frame and Bulkhead Initial Design Analyzes and Design Iterations Analysis of the Initial Design Analysis of the 0.8 mm Design Structures with Decreased Thickness More Detailed Design and Analyzes Final Design and Analysis Final Design of the Keel Beam Conclusion

13 ABBREVIATIONS CG CL Df Dr E.g. EASA FAA ft H i.e. in. K KE kg km L mm MPa MTOW n STOL Vf Vr : Center of Gravity : Lift coefficient : Drag load on the forward wheel : Drag load on the rear wheel : Example : European Aviation Safety Agency : Federal Aviation Administration : feet : Height : Example : inch : Drag load coefficient : Kinetic Energy : Kilogram : kilometer : Wing lift to the aero plane weight ratio : millimeter : Mega Pascal : Maximum take-off weight : Load Factor : Short take-off and landing : Vertical Load on the forward wheel : Vertical load on the rear wheel VS1 : Minimum steady flight speed for which the aircraft is still controllable in a specific configuration Vstall : Stall Velocity 13

14 W : Weight WW2 : World War 2 14

15 LIST OF TABLES Page Table 1.1 : Comparison Between Landing Gear (10:Best, 1:Worst)... 2 Table 1.2 : Comparison Between Fixed And Retractable Landing Gear... 4 Table 3.1 : Soıme Turn-Over Angle Table 3.2 : Statistical Tire Sizing Table 3.3 : Tire Data Table 3.4 : The Proper Pressure Values for the Tires Table 5.1: Load Table

16 LIST OF FIGURES Page Figure 1.1 : Single Main.... Error! Bookmark not defined. Figure 1.2 : U2 Aircraft Which Has Single Main... Error! Bookmark not defined. Figure 1.3 : Bicycle Configuration.... Error! Bookmark not defined. Figure 1.4 : AKS 21 Aircraft Which Using Bicycle Gear Configuration.Error! Bookmark not defined. Figure 1.5 : Tail-Gear... Error! Bookmark not defined. Figure 1.6 : Spitfire With Tail-Gear.... Error! Bookmark not defined. Figure 1.7 : Tricycle Configuration... Error! Bookmark not defined. Figure 1.8 : STOL CH 801 With Tricycle Landing GearError! Bookmark not defined. Figure 1.9 : Quadricycle Configuration.... Error! Bookmark not defined. Error! Reference source not found. B-52 Stratofortress Bomber AircraftError! Bookmark not defined. Error! Reference source not found. Multi-Bogey ConfigurationError! Bookmark not defined. Error! Reference source not found. Airbus A380 With Multi-BogeyError! Bookmark not defined. Figure 1.13 : Releasable Rail... Error! Bookmark not defined. Figure 1.14 : Some Helicopters Use Skid Configuration To Land Error! Bookmark not defined. Figure 1.15 : Bell 427 Helicopter... Error! Bookmark not defined. No table of figures entries found.figure 1.17 : Hang Glider Error! Bookmark not defined. No table of figures entries found.figure 1.19 : Robin DR400/120 Dauphin With Fixed Gear... Error! Bookmark not defined. No table of figures entries found.figure 2.2 : Rubber Absorber Error! Bookmark not defined. 16

17 No table of figures entries found.figure 2.4 : Solid Spring With Deflections Error! Bookmark not defined. No table of figures entries found.figure 2.6 : Oleo Types Error! Bookmark not defined. No table of figures entries found.figure 2.8 : Bias-Ply Tire Error! Bookmark not defined. No table of figures entries found.figure 2.10 : Boeing 737 Brake System / Carbon Brake... Error! Bookmark not defined. No table of figures entries found.figure 3.2 : Tail Gear Position Error! Bookmark not defined. No table of figures entries found.figure 3.4 : The Angle Between Vertical Axis And Leafspring... Error! Bookmark not defined. No table of figures entries found.figure 3.6 : The Clearence Values Of The Tricycle Configuration... Error! Bookmark not defined. No table of figures entries found.figure 3.8 : Propeller-Ground Clearence Of The Twin Engine Aircrafts... Error! Bookmark not defined. No table of figures entries found.figure 3.10 : Turn-Over Geometry Error! Bookmark not defined. No table of figures entries found.figure 3.12 : Typical 6-6 Size Type III Tire Error! Bookmark not defined. No table of figures entries found.figure 3.14 : The Foot Print of the Tire Error! Bookmark not defined. 17

18 No table of figures entries found.figure 4.1 : Level Landing with Inclined Reactions... Error! Bookmark not defined. No table of figures entries found.figure 4.3 : Tail Down Landing Error! Bookmark not defined. No table of figures entries found.figure 4.5 : Tail Down Landing Error! Bookmark not defined. No table of figures entries found.figure 5.2 : CG Distances Error! Bookmark not defined. No table of figures entries found.figure 5.4 : CG Distances for Level Landing Error! Bookmark not defined. No table of figures entries found.figure 5.6 : Braked Roll Error! Bookmark not defined. No table of figures entries found.figure 6.1 : General View of Our Design with Skin and Canopy... Error! Bookmark not defined. No table of figures entries found.figure 6.3 : General view of our design Error! Bookmark not defined. No table of figures entries found.figure 6.5 : Bulkheads and Frames Error! Bookmark not defined. No table of figures entries found.figure 7.1 : Von Misses Analysis Error! Bookmark not defined. No table of figures entries found. 18

19 DESIGN AND ANALYSIS OF THE KEEL BEAM SUMMARY This thesis includes genereal informations about the landing gears of the aircrafts. According to requirements, this thesis will give the point of view about the proper landing gear configuration selection. Also, the components of the landing gear will be detailed at this project. The various of these components will be clarified. The constraints will be mentioned when the landing gear designed for tricycle and tail-gear landing gear configurations. After that, certification requirements of landing gear will be explained based on CS 23. According these requirements, the loads on the nose wheel will be calculated. After that, initial design will be completed. Design is completed with Catia v5. Then, based on calculated loads, analyzes will be completed. Then, the design will be detailed. In this way, the final keel beam design is obtained. 19

20 KEEL BEAM TASARIMI VE ANALİZİ ÖZET Bu tezde iniş takımının çeşitli konfigürasyonlarına yer verilmiştir. Bir uçağaın gereksinimlerine göre uygun konfigürasyonlardan birini sağlamak adına bir trade-off çalışmasına bu tezde yer verilmiştir. Ayrıca iniş takımının çeşitli bileşenleri detaylıca açıklanmıştır bu tezde. Bu bileşenlerin çeşitlerinden bahsedilmiştir. Tricycle ve tail-gear iniş takımı konfigürasyonları için gerekli pervane ve yer clearance değerleri gerekli açı değerlerinden bu tezin konularından biri olmuştur. Ardından CS 23 kapsamına girebilen bir uçak için gerekli iniş takımı gereksinimleri bu tezde yer almaktadır. Yine CS -23 e göre temel iniş senaryoları için ön iniş takımna gelen yükler hesaplanmıştır. Ve bu değerler tablolanmıştır. Ardından ön gövde için başlangıç tasarımı yapılmıştır. Ardından hesaplanan yüklere göre bu tasarım analize sokulmuştur. Iterative bir yöntemle bu tasarım detaylandırılıp, son keel beam tasarımına ulaşılmıştır. 20

21 1. Landing Gear Configurations There are various landing gear configurations. The landing gear configuration must be decided among them to design landing gear. According to desires, proper the landing gear configuration is chosen. Several landing gear configurations are that; Sinle Main Bicycle Tail-Gear Tricycle or Nose-Gear Quadricycle Multi-Bogey Releasable Rail Skid Seaplane Landing Device Human Leg 1.1. Single Main Figure 1.1: Single Main Single Main is one of the simplest the landing gear configurations. It has one large main gear which is generally located in front of the CG, and one small gear is under the tail. Large main gear carries most of the load and weight. Both gears are in the aircraft symetrical plane. The large gear is near the CG; therefore, it carries most of the weight. On the other hand, the small gear is far from the CG. Sometimes, the main gear could locate aft of CG and the other one is located in front of the CG. At 21

22 that case, secondary gear is converted to a skid under the fuselage nose. Due to simlicity, majority of the sailplanes use this configuration. This configuration is fixed generally, so its height is very short. The aircrafts, which use this configuration, are not stable on the ground. Therefore, it could tip over one side (usually on wing tips), even it stays on the ground. Due to tipping on wing tips, the wing tips must be repaired regularly. The most important advantages of this configuration are simplicity and low weight. On the other hand, instability on the ground and longer take-off run because of limited take-off rotation, are two of disadvantages of this configuration Bicycle Figure 1.2: U2 Aircraft Which Has Single Main 22

23 Figure 1.3: Bicycle Configuration Bicycle gear has two main gears which have similar size. The CG is between them. To carry same load, two gears have same distance from the CG This configuration is not popular due to ground instability like single gear. However, it is simplicity and has low weight. Thus, some aircrafts, which have narrow fuselage and high wing configuration, use as a cheap configuration. Figure 1.4: AKS 21 Aircraft Which Using Bicycle Gear Configuration 1.3. Tail-Gear Figure 1.5: Tail-Gear 23

24 Tail-Gear configuration consists three wheels. Two of them forward of the aircraft CG and they are symetric according to aircraft axis. Therefore, they carry same load. These two wheels are main gear due to carrying most of the load. Thus, these wheels are bigger than other wheel which is under the tail. The main wheels is forward of the CG and they are close to CG. The other wheel is located under the tail so it is further from CG than main wheels. Thus, it could cary much smaller load. The main wheels carry 80-90% of the total load on this configuration. This configuration has a important plance on the aviation history because majority of the aircraft, during first 50 years of the aviation, use this configuration. However, 10% of the aircrafts are using tail-gear configuration nowadays. Sometimes, instead of tail wheel, a skid is used on this configuration to reduce drag. It is called as a taildragger. Most agricultural and some general aviation aircrafts have a tail-gear. Because the main gear is much larger and taller, the aircrafts which use tail-gear, are not level on the ground. Thus, passenger have to climb to floor. The tail of tail-gears aircrafts, must be lifted during the take-off because have high angle of attack during ground roll. It causes decreased pilot vision on the ground. Also, because the tail must be lifted during take-off, the runway of the aircrafts ire longer than aircrafts which have tricycle landing gear configuration. Due to three wheels, aircrafts are stable on the ground. Nevertheless, while aircrafts are maneuvering with high speed, it could tip over due to centrifugal force. This prblem could be handled by lowering taxi speed. However, if there are cross wind during landing, pilot sweat to control rudder of the aircraft. 24

25 Figure 1.6: Spitfire With Tail-Gear 1.4. Tricycle Figure 1.7: Tricycle Configuration Tricycle configuration is the most used landing gear configuration on the world. The aft wheels are the main gear due to carrying most load. The CG is the near-forward of the main gears. These two main gears are the same distance from the CG in the x and y axis. The other gear is located far-forward from the CG. Thus, this forward gear carry only 10-20% of the total load. Sometimes this configuration is called as a nose-gear. 25

26 There are a lot og general aviation and fighter aircraft which use tricycle configuration as a landing gear. Both main and nose gear have same height, so the aircrafts are level on the ground. However, the main gears generally have larger wheels to carry much larger load. Because the aircrafts are level of the ground, the floor could be flat for passengers and cargo loading. Also, the tricycle configuration is not only stable on the groundi but also it is stable during maneuver. Besides, when comared to tail-gear, this configuration provides more pilot view and shorter take-off run. Some aircrafts have two wheels on the nose gear to increase the safety. These aircrafts carry larger load on the nose gear. To handle it, instead of one large wheels, two small wheels on the nose are more appropriate. If, two small wheels uses on the nose gear instead of one large wheel, the drag will be reduce due to decreasing frontal area of the nose gear. Also, some aircrafts which use catapult launch mechanism, have two wheels on the nose gear. Although, the safety and performance of the aircraft increase, while the number of the wheels are increasing; the operating, manufacturing, and maintaining cost will be increased too. Another reason of the increasing number of the wheels is to fit the wheels volume to match to the retraction geometry inside the wing or fuselage. Generally, kg kg aircrafts two wheels per main strut are used. If the aircraft is very heavy like cargo aircraft Lockeed C-5 Galaxy ( kg MTOW), four wheels are used to spread out total load among the wheels. 26

27 1.5. Quadricycle Figure 1.8: STOL CH 801 With Tricycle Landing Gear Figure 1.9: Quadricycle Configuration This configuration consists of four wheels. Quadricycle configuration is similar to coniventional wheel system. Two of them are located in front of the CG and others located behind of the CG. If the distance between forward wheels and aft wheels from the CG is the same, all wheels carry same load. This situation causes aircraft to rotate during take-off and landing hardly. Therefore, the take-off run of the quadricycle aircrafts is longer than aircrafts which have tricycle configuration. Because the height of the quadricycle is lower, the floor level of the aircraft is low. Thanks to this, the loading and unloading will be easier on this configuration. Also, 27

28 it is very stable on the ground and during taxiing. Because of this properties, the quadricycle type landing gear is used on very high cargo or bomber aircrafts Multi-Bogey Figure 1.10: B-52 Stratofortress Bomber Aircraft Figure 1.11: Multi-Bogey Configuration Heavy aircrafts could have multiple gears. The multiple gears, which are more than four wheels, provide safety during landing and take-off. Tandem wheels are attached to aother structural component which name is Bogey with struts. Muti-bogey aircrafts are stable on the ground and during taxiing. 28

29 This landing gear configuration is the most expensive and most complex configuration for manufacturing. If the weight of the aircraft is beyond kg, multiple bogeys each with four to six wheels are used Releasable Rail Figure 1.12: Airbus A380 With Multi-Bogey Figure 1.13: Releasable Rail This configuration is used for aircrafts which do not land on the ground or sea. Rockets and missiles are the same category in terms of landing gear configuration. Take-off or launch gear usually consists of two to three fixed pieces. One piece is a T shape part. This is attached to mother vehicle to hold the vehicle while launched Skid Figure 1.14: Some Helicopters Use Skid Configuration To Land 29

30 Vertical take-off aircrafts do not need to taxiing. Therefore, the skid configuration could be considered to apply. The skid consists of three or four fixed centilever beam like truss structure. The beams are deflected outward when load is applied. This deflection behaves as a shock absorber which is not so efficient. However, this configuration is much simpler than regular landing gear. Basic beam deflection and bending stress equations are enough to calculate them. Besides, the fatigue loading and fatigue life are two important parameter to design skid landing configuration. They must be considered to predict skid endurance. Figure 1.15: Bell 427 Helicopter 1.9. Seaplane Landing Device Aircrafts, which is expected them landing or take-off on the water surface, includes some special landing gear configuration. This landing gear and fuselage shape is designed according to the some requirements. These are: Slipping Water-Impact Load Reduction Floating Lateral Static Stability 30

31 Figure 1.16: Water Landing Human Leg Human leg is used for only very light flying mechanism such as hang glider and paraglider. The usage area of the human leg is very limited as a landing mechanism due to human weaknesses. Figure 1.17: Hang Glider 31

32 No Trade-Off Study There are a lot of landing gear configurations which could be selected to apply. The best landing gear is the best fittable to our aircraft. To the decide this, the trade-off study must be done. Single Main Bicycle Quadricycle Tailgear Nosegear Multibogey 1 Cost Aircraft weight Manufacturability Take-off/landing run 5 Stability on the ground 6 Stability during taxi Table 1.1: Comparison Between Landing Gear (10:Best, 1:Worst) Human leg The trade-off study could be done according Table 1.1. As it seen, all landing gear configuration have a good properties and poor properties Attachement Locations of the Landing Gear After the landing gear configuration is selected, the landing gear atachments must be decided. The fuselage and the wing are the primary options for the attachments. The attachmenets affects the several design requirements like take-off and landing performance, cost etc. The main alternatives of the attachments; All struts / wheels are attached to the fuselage. For example, Boeing 747. Main gear is located to the wing, but the nose gear is located on the fuselage. E.g. Vickers VC10. Main gear are attached to the wing, when the tail gear is located on the fuselage. E.g. P-51 Mustang. 32

33 Main gears are attached to the nacelle, but the nose gear is located on the fuselage. E.g. Boeing B-47 Stratojet. In general, the expected attachment is that all struts are located on the fuselage. However, it could not be always possible. For instance, sometimes the fuslage is not wide enough Fixed, Rectractable, or Seperable Landing Gear After, the landing gear configuration and attachment are decided, it must be decide what to do with landing gear after take-off operation. There are four main alternatives; Landing gear is released after take-off. Landing gear hangs underneath the aircraft. (i.e. fixed) Landing gear is fully retracted inside aircraft. Landing gear is paritally retracted insdie aircraft. All of these options have some advantages and disadvantages. For instance, if the landing gear is released after the take-off, the aircraft do not land on the ground in general. Thus, this type landing gear is rarely used. Figure 1.18: The Jindivik Aircraft Releases The Landing Gear During Take-Off After take-off, the landing gear is dead weight on other three alternatives. The retracted landing gear is the best choice of them to get highest performance. 33

34 However, if the main aim is the reducing cost, the fixed gear will be the best choice. Therefore, the trade-off study should be made to get best solution. The trade off study could be made according to Table 1.2. No Item Fixed (non-retractable) Landing Gear Retractable Landing Gear 1 Cost Cheaper Expensive 2 Weight Lighter Heavier 3 Design Easier to design Harder to design 4 Manufacturing Easier to manufacture Harder to manufacture 5 Maintenance Easier to maintain Harder to maintain 6 Drag More drag Less drag 7 Aircraft performance Lower aircraft performance (e.g. maximum speed ) Higher aircraft performance (e.g. maximum speed) 8 Longitudinal stability More stable (stabilizing) Less stable (destabilizing) 9 Storing bay Does not require a bay Bay must be provided 10 Retraction system Does not require a retraction system Requires a retraction system 11 Fuel volume More available internal fuel volume Less available internal fuel volume 12 Aircraft structure Structure in un-interrupted Structural elements need reinforcement due to cutout Table 1.2: Comparison Between Fixed And Retractable Landing Gear 34

35 Figure 1.19: Robin DR400/120 Dauphin With Fixed Gear 2. Components of Landing Gear There are three main components of the landing gear. These are shock absorber, tires and brakes. Also, these components have various types. It will be clearified with a subtitle Shock Absorber During landing, the shock absorber have a improtant role due to requirements of the energy absorption. Therefore, the shock absorber affect the performance of the aircraft. Due to complexity of the shock absorber, it influences the total cost. The shock absrober provides the controlled landing. The landing will be diseaster without it, because the kinetic energy acts the aircraft. There are various types shock absorber. 35

36 Figure 2.1: Gear And Shock Absorbers Arrangments Rubber Shock Absorber This type shock absorbers is used in early aviation history. However, it is still used light aircrafts due to simplicity and low cost. Figure 2.2: Rubber Absorber 36

37 Figure 2.3: Rubber Absorber And İts Load-Deflection Graph Solid Spring Absorber A solid spring have flexible solid strut. Because the efficiency of this absorbers are significantly low, this type absorbers are not used in present day. Figure 2.4: Solid Spring With Deflections Pneumatic Shock Absorbers Pneumatic shock absorbers use the air to absorb the kinetic energy. Although, the oleo-pneumatic and the pneumatic have similar design, it is heavier, less efficient and less reliable. Therefore, it is not used today. 37

38 Liquid Spring It could be called as a Oil-type shock absorber. Dowty is developed this and it is used in WW2 firstly. Also, they are still used in aircrafts which have usually levered-suspension design.they are almost as efficiency and reliable as the oleo-pneumatic. Besides, they have low fatigue. However, it has some disadvantages. They are it affect from temperature due to volume changes of the liquid, it can be pressurized only while the aircraft is on jacks due to high pressure required, the high pressure should be protected, and the friction of this is high. Figure 2.5: Liquid Spring 38

39 Oleo Pneumatic Shock Absorber Oleo-Pneumatic Shock absorbers use the mixture of the rubber or solid steel or fluid spring with gas or oil. They have highest efficiency of all shock absorbers. Therefore, it uses with middle and large aircrafts. Figure 2.6: Oleo Types 39

40 Figure 2.7: The Efficiencies Between Shock Absorebers 2.2. Tires Tires have a important role during taxiing, landing and take-off. The static and dynamic loads are applied to tires. Therefore, the tires must be chosen according to this loading. The used tires in aircrafts must have higher strength and durability than the tires used in automobiles, because the loads are much higher than the applied loads of the automobiles during landing and take off. The tires encounter bar pressure; thus, they must endure this. Also, the take-off speed could reach 360 km/h speed. These constraints must be considered when it is designed. There are two basic type of the tires. These are bias ply and radial ply. Because the radial tires have longer life and less weight, the radial tires are preferred in aircrafts nowadays. 40

41 Figure 2.8: Bias-Ply Tire Figure 2.9: Radial-Ply Tire 2.3. Brakes A brake is another important part of the landing gear system. It provides to stop the aircrafts and control the speed during taxiing. The kinetic energy is converted into heat energy due to friction by the brakes. There are various type brake systems which is using on landing gears of the aircrafts. Single Disc Brakes Floating Disc Brakes Fixed-Disc Brakes Dual-Disc Brakes Multiple-Disc Brakes 41

42 Segmented Rotor-Disc Brakes Carbon Brakes Expander Tube Brakes The single brake systems could be used on the light aircrafts. They achieve effective braking with single disc. The dual disc brakes is used when the single disc could not provide enough friction. However, large and heavy aircrafts use the multiple disc brakes. Today, the carbon brakes, which is latest configuration of the multiple disc brakes, are not only the most efficient brake system but also the most expensive the brake configuration. Besides, the expander tube brakes are the different type brake configuration which is used in the 1930s-1950s. Figure 2.10: Boeing 737 Brake System / Carbon Brake 42

43 3. Sizing and Positioning of the Landing Gear There are a lot of configurations for the landing gears as mentioned at the first part. Two of them will size and position at this part. They will be tail-gear and tricycle (nose gear) configuration. Figure 3.1: Landing Gear Nomenclature 3.1. Tail Gear Sizing and Positioning There are some constraints when the tail gear is designed for aircraft. For instance, generally, the angle between the line from the main gear to the CG and vertical line of the main gear is between 15 o and 25 o. (Shown in Figure 3.2) Also, because of shock absorber deflection, the wheel motion should fall between the vertical line and 5 o. The tail gear should be located at the backmost position which do not create problem fot the structure. The ground angle is the angle between chord line of the airfoil and the line from the main gear to the tail gear. This angle should be 1 o -2 o less than the angle of the attack to get maximum lift coefficient. This angle generally is about 12 o. Also, the if 43

44 the the take-off angle is not smaller than landing angle, the situation, which is tail wheel touch the ground during takeoff rotation, will be critic for the aircraft. The spindle axis of the tail wheel should be inclined forward 5 o from the normal to the ground line in the taxiing position. The distance between spindle axis and the line from the wheel origin to the gorund should be 1/10 diameter of the wheel. The deflection area of the tail wheel must be within from the normal line of the ground to the 45 o line from the normal. However, the preferable angle of this 35 o. Also, the clearence values should be provided to healty conditions. The clearence between propeller and the ground sould be at the least 9 inches at the all conditions such as level,normal take-off, or taxiing attitude. The positive clearence must be provided during extreme condition like the tire is deflected completely. (Shown in Figure 3.3) Figure 3.2: Tail Gear Position 44

45 Figure 3.3: The Clearence With Deflected Tires Figure 3.4: The Angle Between Vertical Axis And Leafspring 3.2. Nose Gear Sizing and Positioning The nose gear configuration is more complex than tail gear. Its main gear should be located to near aft of the CG to carry most of the load. On the other hand, the nose gear is located as far forward of the CG. Generally, the nose gear carries the 10-20% of the total load. If this load increases, the aircraft could need high elevator down load to rotate the aircraft during take-off operations. Also, if the load on the nose gear is the too light, it causes another 45

46 problem that it makes steering deficiently. Approximately 15% of the load is the best load for nose gear at the static level attitude. If the load of the nose gear is lower than 10%, porpoising which is a slow oscillation in pitch could occur. The main gear location respect to CG is determined as follows: 1. The angle of attack (α) at CLmax is caluclated with flaps up. 2. Locate the most aft CG. 3. Draw a side view of the aircraft with the wing at the angle of attack α at CLmax. 4. The vertical line is drawn from CG, and from the tail skid a horizontal line is drawn. At least 1 inch cleareance should be provided between the tail skid and the ground. 5. The intersection of these two line is point A which is the middle of the tire contact area. 6. The statically deflected tire and absorber are drawn during the landing gear is drawn. 7. The compressed wheel positions could be drawn, after the stroke of the shock absorber is calculated. 8. The other clearence requirements could be seen in Figure 3.6. Figure 3.5: Tricycle Configuration 46

47 Between the propeller and the ground must be clearence value, which is at least 7 inches, according to FAR Part 23 when the landing gear is deflected at the most critic time. Also, the positive clearence must be provided between the propeller and the ground at the take-off operation with the critical tire defleated and its strut bottomed. It represent the most critic position of the aircraft for landing gear. Figure 3.6: The Clearence Values Of The Tricycle Configuration The clearence values must be provided for twin engines aircrafts too. Figure 3.7: Twin Engine Aircraft s Ground Clearence 47

48 Figure 3.8: Propeller-Ground Clearence Of The Twin Engine Aircrafts Also the overturning could be a problem for aircraft. If the direction of the resultant force is the outside of the contact line with the strut and tires deflected proportionately, when the free body diagram drew, the aircraft encounter with overturning. Figure 3.9: Free Body Diagram For The Overturning The tread and wheel is decided according to the turn-over angle. They affect the turn-over angle. It is determined as follows; 1- Firstly, the top view is drawn with the desired location of the nose wheel. Also the mosth CG position is shown. 48

49 2- Secondly, The side view is drawn with the shock absorbers and tires deflected and CG position. 3- The line is drawn from the nose wheel to the main wheel ( A to B line) and it is extends to the C point as Figure The perpendicular line, which is through the point C, to line A-B is drawn. 5- The paralel line to the A-B is drawn. This line also passes through the CG point. After that, the line segment is drawn from the A-B to the this line. The point D is obtained with intersection of these line. 6- From D point measure the height (h) of the CG obtained from the side view and obtained E point. 7- Between angle from the C to the E line segment to the from the C to the D line segment gives the turn-over angle (θ).it should have some values according to some situation. They are; a. It should be θ = 63 o for on smooth and hard surfaced runways. It is calculated based on the side friction coefficient is µ = 0.55 and assumption that the aircraft is slide sideways instead of tipping over. b. It should be θ = 55 o for typical general aviation aircraft. c. It should be θ = 50 o for aircraft which operates from rough land. The tread and wheel base could be increased to decrease the turnover angle. However, if the tread is very wide, the taxiing on narrow runways will be more difficult. 49

50 Figure 3.10: Turn-Over Geometry Also, the turnover angle is important for a tail gear. It could be checked with the same procedure and it should not exceed 63 o. Table 3.1: Soıme Turn-Over Angle 50

51 While the turn-over angle is calculating as a Table 3.1, some assumptions are made. The CG loaction is taken %25 of the mean aerodynamic chord because it is not know.also the height of the CG is estimated. However, while the aircrafts, which is marked with * symbol on the table, is calculating, the real values is used The Sizing the Subsystems of the Landing Gear Tire Sizing The tires is a rubber which cover the wheel. The main tires carry about 90% of the total load. If the aircraft uses the tricycle gear configuration, the nose gear carries the 10% of the total load. However, the dynamic loads during landing could be higher than this value. The statistical tire sizing could be used by engineers for early conceptual design. This statistical values could be used on the table 3.2. Table 3.2: Statistical Tire Sizing If the runway is rough, the calculated sizing values of the tires could be increased approximately 30%. The nose tires could be the % the size of the main tires for the tricycle landing gear configuration. On the other hand, the aft tire of the tail-gear aircrafts is about quarter to a third the size of the main tires. The design of the landing gear is completed, the tires is choosen from the manufacturer catalog, according to, our loading on the tires. The calculation of the tire sizing is the provided from followings; 51

52 Max Static Load = W N a B (Max Static Load) nose = W M f B (Min Static Load) nose = W M a B (Dynamic Braking Load) nose = 10HW gb (3.1) (3.2) (3.3) (3.4) Figure 3.11: Load Geometry of the Wheels The dynamic load on the nose tires could be calculated under 10 ft/s 2 deceleration with the 4.4 equation. It is assumed a braking coefficient (µ) is 0.3. This value could be used for classical hard runway. The nose gear should be carry load an optimum value. Therefore, the Ma/B value should be greater than Also, the Mf/B value should be less than This load value on the nose gear should be between 0.08 and 0.15 for optimum value. Also, after calculation of the load on the tires, the margin should be added. If the aircraft is transport category aircraft, this margin should be 7% based on FAR

53 Table 3.3: Tire Data The tables like Table 3.3 could be obtained from tire book of the tires manufacturers. The type III tires are used for piston engine aircrafts. They have low internal pressure and a wide tread. On the other hand, the most jet aircrafts use the type VII tires. They have the high internal pressure. It reduces the size of the tires. They could overcome the high landing speed. Also, there are the type VIII tires which have highest internal pressure. However, they are new design status. 53

54 Figure 3.12: Typical 6-6 Size Type III Tire Figure 3.13: Typical Size Type VIII Tire The tires should carry enough load with smallest size. They must carry calculated maximum load on the tire. (Ww) Therefore, especially for the nose tires, the dynamic load should be calculated as the static load calculation. The tires could be carry more the dynamic load than the static load. The type III tires could carry the dynamic load 1.4 times than the static load. On the other hand, the new design and the VII types tires catty 1.3 times than the static load. The selected tires must carry the calculated the dynamic and the static load. The Ww could be calculated as follows; W W = PA p (3.5) 54

55 A p = 2.3 wd( d 2 R r) (3.6) The WW is a carried load by the tires. The P is an inflation pressure. The contact area of the tires, which is called foot print, is Ap. The w is width, the d is a diameter and the Rr is a rolling radius of the tire. Figure 3.14: The Foot Print of the Tire The lower internal pressure provides longer life for the tires. Also, the tires are adversely affected by high internal pressure if they operate from soft or rough runway. Thus, the pressure of the tires should be reduced. Table 3.4: The Proper Pressure Values for the Tires Generally, the brake system is placed in the wheels. Therefore, when the diameter of the tires is selected, this condition also should be considered. 55

56 The brake system absorbs the kinetic energy. This kinetic energy could be calculated with 3.7 equation. KE braking = 1 2 W landing g 2 V stall (3.7) The landing weight is not same of the take-off weight. It could be considered as about %. The absorbed energy affects the wheel diameter. The affect could be seen at the figure The graph was made from statistical estimates. Figure 3.15: The Diameter of the Wheels According to Brake System 4. Certification Requirements The aircrafts must be certified, if they fly at international air space. This certification is provided by the authorities, such as EASA and FAA. The aircrafts are grouped according to size. The certification specifications are defined based on this grouping. The aircrafts, which are lighter than 5670 kg with less ten seat excluding 56

57 pilot seat(s), is certified with respect to CS-23 document. The landing gear and landing conditions are specified at this document for these aircrafts Design Requirements Shock Absorption Test Based on CS-23, the energy absorbation competence of the shock absorbers must be proven with the tests with landing and take-off loads or the analysis of the landing gear system with identical energy absorbation characteristics could be used for certification. The landing gear may not fail but it could yield in a test showing its reserve energy absorption capacity. The descent velocity at the test is 1.2 times higher than limit descent velocity. The wing lift assumes as equal to the weight of the aeroplane Limit Drop Test Limit drop test one of the requirements of the CS 23 for landing gear. This test must be completed with finished aeroplane. The free drop height is calculated with this formula: h(m) = ( Mg S ) (4.1) In spite of this formula, the height could not be above from 0.234m and not be less than 0.475m If the wing lift could be provided to test environment, the drop length is calculated following formula instead of 4.1. M e = M h+(1 L) d h+d (4.2) Me = The effective mass. (kg) h = Free drop height. (m) 57

58 d = deflection under impact of the tyre (at the approved inflation pressure)plus vertical component of the axle travel relative to the drop mass. (m) M = MM is mass for main gear. (kg) It equals to the static mass during the aeroplane at the level attitude. M = MT is mass for tail gear. (kg) It equals to the static mass with the aeroplane in the tail-down attitude. M = MN is mass for nose gear. (kg) It equals to the vertical component of the static reaction that would exist at the nose wheel. Assuming that the mass of the aeroplane acts at the center of gravity and exerts a force of 1 g downward and 0.33g forward. L = The assumed wing lift to aeroplane weight ratio. It could not be more than g = It is a gravitational acceleration. (m/s 2 ) During the drop test, the limit inertia load factor must be determined with using landing gear unit and applied landing loads which represent the landing conditions. The d value which is used for calculation of the effective weight, may not be above from the value which is obtained form the drop test. The limit inertia load factor is obtained with drop test with following formula; n = n j M e M + L (4.3) nj = The load factor which is obtained from the test ( that is, the acceleration (dv/dt) in g s recorded in the drop test) plus 1g. The value of the n could not be more than limit inertia load factor which is used in the landing conditions. 58

59 Ground Load Dynamic Tests According to various landing conditions, the requirements must be provided with drop test. The drop test meets limit drop test. However, the drop height will be 2.25 times higher than limit drop test or sufficient to develop 1.5 times the limit factor. The landing gear must be proven that it overcomes the critical conditions for all landing conditions Reserve Energy Absorption Drop Test If the reserve energy absorption requirements are provided at the shock absorption test, the drop weight may not be less than 1.44 times from the specified at the limit drop test. Also, if the wing lift is provided for, the units must be dropped with an effective mass equal to; M e = M ( h h+d ) (4.4) The other details for fround load dynamic test is same as limit drop test Landing Gear Extension and Retraction System The landing gear retracting mechanism and supporting structure must be designed for maximum flight load factor with the gear retracted. The friction, inertia, brake torque and air loads during retraction must be consider when the landing gear is designed. The design also overcomes at any airspeed up to 1.6 VS1 with flaps retracted and for any load factor for the flaps-extended condition The landing gear and retracting mechanism with the wheel well doors must withstand flight loads. Also, the landing gear must extend at any speed up to 1.6 VS1 with the flaps retracted. There must be the landing gear lock to keep the landing gear extended. It must be different from the using of hydraulic pressure. 59

60 For a landplane, there must be emergency operation. If there are probable failures in normal landing gear or in a power source which supply the power to the normal landing gea roperation system, the landing gear must extend as a emergency operation. The functionality of the retracting system must be tested. There must be position indicator for landing gear if the retractable landing gear is used. Also, there must be warning system for landing gear. If there is a equipment in the landing gear bay, this equipment must be designed and installed to minimise the damage Wheels The wheels must correspond the maximum static load rating of each wheel. While this load is calculating, the maximum weight and the critical location of the center of gravity must be considered. The maximum limit load rating of each wheel must be equal or higher than the radial limit load requirements of CS Tyres All landing gear wheels must have approved tyres. The selected tyres must be proper for maximum weight and critical center of gravity. The special constructed tyres must be marked which include the make, size, number of plies and identification of the proper tyre. Also, if the retractable landing gear is used on the aircraft, there must be a clearance between structure and tyres at the retracted position Brakes There must be brake system for the landing gear. The brake system must absorb the kinetic energy. To find requirements of the landing gear brake 60

61 system, the rational analysis must be provided for expected events during landing at the design landing weight. However, instead of rational analysis, the kinetic energy absorption requirements could be caluclated from the following formula: KE = MV2 2 N (4.5) KE = Kinetic energy per wheel (Joules); M = Mass at design landing weight (kg); V = Aeroplane speed in m/s. V must be not less than VSO, the power off stalling speed of the aeroplane at sea level, at the design landing weight, and in the landing configuration. N = Number of main wheel with brakes. The brakes must prevent the wheels from rolling at the paved runway. Besides, the brakes must prevent the movement of the aeroplane during locked. The pressure of the wheel braking system must not exceed the values, which is defined by manufacturer, during determination of the landing distance. If anti-skid device is used, it must be designed that when it failed, it must not cause the hazardous results like loss of braking ability or directional control of the aeroplane. Also, the rejected take-off brake kinetic energy capacity must be provided by rational analysis to formula 4.5. However, instead of aeroplane speed, the ground speed with the maximum value of the V1 is used at this formula Basic Landing Loads for Tricycle The landing loads are crucial for the landing gear system. If the landing loads could not be carried by the structure, the landing gear will fail. However, the landing loads 61

62 vary based on landing conditions. Therefore, the landing loads must be calculated according to different landing conditions Level Landing with Inclined Reactions To calculate the landing loads for this condition, the CG locations and the components of the resultant load at the CG must be clarified. If the vertical component of the landing load is indicated as a nw (n is a load factor), the fore and aft component of the load could be specified as a KnW. At this situation, K could be taken 0.25 for 1361kg or less. Also, K may be taken, 0.33 for 2722 kg or greater. The K value is calculated as a linear variation for other weights. Shock absorber deflection could be assumed 100% and the tyre deflection could be taken as a static. Thus, the main wheel loads could be found as follows; V r = (n L)W a d (4.6.) D r = KnW a d (4.7) Also, the loads on the nose wheel could be calculated. V f = (n L)W b d (4.8) D f = KnW b d (4.9) L: Wing lift to the aeroplane weight ratio n: Load Factor W: Weight of the aeroplane K: Drag load coefficient 62

63 Figure 4.1: Level Landing with Inclined Reactions Level Landing with Nose Wheel just Clear of Ground For this condition, the vertical component of the load at the CG, is the nw. Fore and aft components of the load is the KnW. When shock absorber deflection is 100% and the tyre deflection is static, the landing loads could be found with folowing formulas. For main wheel loads; V r = (n L)W (4.10) D r = KnW (4.11) For nose wheel, the loads are equal to zero for this condition. Figure 4.2: Level Landing with Nose Wheel Just Clear of Ground 63

64 Tail Down Landing The vertical component at the CG is nw for the tail down landing condition. The horizontal component of the load is the zero for this condition. Like other cases, the shock absorber deflection is 100% and the tyre deflection is static. According to these, the landing loads could be calculated. For main wheel loads; V r = (n L)W (4.12) Dr and nose wheel loads is equal to zero on this condition. Figure 4.3: Tail Down Landing 4.3. Basic Landing Loads for Tail-Gear Like Tricycle Gear configuration, the landing loads must be calculated for tail-gear configuration for different conditions Level Landing The vertical component of the load is nw and the horizontal component of the load is KnW at the CG for level landing condition. The shock absorber extension is 100% and the tyre deflection is only statically. At this situation, the landing loads could be calculated. V r = (n L)W (4.13) D r = KnW (4.14) Moreover, the laods of the tail wheel is equal to the zero. 64

65 Figure 4.4: Level Landing Tail Down Landing Another basic landing condition is the tail down landing for tail-gear configuration. At this condition, the vertical component at CG is nw. The horizontal component of the load is zero for this condition. The tyre deflection is static and the shock absorber deflection is %100. According to these, the loads are calculated with following formulas; For main wheel loads; V r = (n L)W b d (4.15) D r = 0 (4.16) For tail wheel loads; V f = (n L)W a d (4.17) D f = 0 (4.18) Figure 4.5: Tail Down Landing 65

66 5. Nose Landing Load Calculations for a Example Aircraft In this section, the nose loads will be computed for tricycle aircraft. There are not loads on the nose wheel at the all scenerio. Therefore, this chapter covers only three points level landing, braked roll landing and some supplementary conditions which are cause the force on the nose wheel. To calculate landing loads some distance must be clarifed. Therefore, some distance is taken by external sources. Figure 5.1: Given Distances Figure 5.2: CG Distances 66

67 Thus, the values of the a, b, d and h was getting ready. These values; a = 5086 mm b = 494 mm d = 5580 mm h = 2088 mm Also, some distances calculated to find level landing loads. Figure 5.3: Calculated Distances 67

68 Figure 5.4: CG Distances for Level Landing According to Catia sketch, the values of the a,b and d is found. These values; a = 4502 mm b = 911 mm d = 5412 mm The β value is taken according to CS-23. It says the value of K is taken as a 0.33 for higher than 2722 kg aircrafts. Also CS-23 says that the β is equal to arctan(k). So the β is found rad which equal to 18.3 degree. In addition of distance values, the weight values must be clarified. The weight is accepted as a 8100 kg. Also the ratio of the wing lift to aeroplane weight is accepted as a because based on CS-23, this ratio could not excess the Nose gear load factor is taken 3.52 because utility and military trainer aircrafts load factors are generally between scale. After all these assumptions and calculations, the loads on the wheels could be found Three Points Level Landing One of the landing scenario is three points level landing. In this scenario, three wheels contatct the ground. Therefore, the total weight spreads three wheels. The nose weheel is important for this project. Thus, the landing load on the nose wheel will be calculated as follows; 68

69 V f = (n L)W b d (5.1) D f = KnW b d (5.2) Figure 5.5: Level Landing The distances were calculated at the beginning section 5. Now the formulas will be calculated. V f = ( ) ( ) V f = N D f = ( ) D f = N 5.2. Braked Roll Braked roll is another landing scenario which causes the load on the nose wheel. This load could be calculated as follows; V f = (1.33 W ( b )) + (D d rtotal ( h )) (5.3) d The limit vertical load factor is defined as a To calculate Vf, Drtotal value should be found firstly. D rtotal = 0.8 V rtotal (5.4) 69

70 V rtotal = (1.33 W ( a )) /( d (h )) (5.5) d Figure 5.6: Braked Roll First of all, V rtotal value must be calculated; V rtotal = ( ( 5086 )) /( (2088 )) V rtotal = N After that D rtotal value could be found; D rtotal = N D rtotal = N Finally V f value could be calculated now; V f = ( ( 494 )) + ( (2088 )) V f = N 5.3. Supplementary Conditions for Nose Wheel When nose landing gear is designed, some additional loads must be calculated. The load on the nose wheel could be find as follows; 70

71 Figure 5.7: Level Position V f = (W ( b )) (5.6) d V f = ( ( )) V f = N Additional loads on the nose wheel could be divided as aft loads, forward loads and side loads. For aft loads, the vertical component (V faft ) is equal to "2.25 V f " and horizontal component is "0.8 V faft ". Thus; V faft = 2.25 V f (5.7) V faft = V faft = N D faft = 0.8 V faft (5.8) D faft = D faft = N For forward loads, the vertical component (V ffw ) is equal to "2.25 V f " and horizontal component is "0.4 V ffw ". V ffw = 2.25 V f (5.9) 71

72 V ffw = V ffw = N D ffw = 0.4 V ffw (5.10) D ffw = D ffw = N For side loads, the vertical component (V fs ) is equal to "2.25 V f " and horizontal component is "0.7 V fs ". However, this horizontal component acts to the y axis. The all other scenario horizontal components act to the x axis. (x axis to the tail from the spinner, y axis wing tip to the wing tip.) V fs = 2.25 V f (5.11) V fs = V fs = N D fs = 0.7 V fs (5.12) D fs = D fs = N NLG [N] and [Nmm] Fx Fy Fz Level landing 3p Level landing 2p Braked roll Supplementary conditions aft loads Supplementary conditions forward loads Supplementary conditions side loads Table 5.1: Load Table 72

73 6. Keel Beam, Frame and Bulkhead Initial Design At our case, the keel beam system with frames and bulkhead will carry the landing loads. Therefore, initial design is completed before the analyses. Figure 6.1: General View of Our Design with Skin and Canopy Figure 6.2: General View Skin without Canopy 73

74 Figure 6.3: General view of our design As it seen, the keel beams are located between bulkhead and frames. Also, 6 supporters half frames are located at the left and right side. Between the keel beams, the structure is stiffened with another beam. Besides, at the top of the frames the longerons are located. Between these longerons, the beam acts as a stiffener. In addition all of these, the connection point nose gear and keel beam could be seen at the Figure 6.3. The all structural parts are designated 2 mm web thickness for initial sizing. However, the skin of the design has 5 mm thickness. 74

75 Figure 6.4: Longeron In this design U profile is preferred for longerons. Figure 6.5: Bulkheads and Frames Except the most aft frame, all frames are partial due to keel beam continuity. The arms of the frame L profile; bottom side of the frames and bulkhead C profile. 75

76 Figure 6.6: Keel Beam The nose landing gear is connected at the pocket point which is seen at the Figure Analyzes and Design Iterations Before the analysis, the material must be selected. The Al 2024 T42 material is selected for our structure because it is proven for aircraft structures. The yield strength of this material is 261 MPa. To analyze the structure, some assumptions are accepted. For instance, the absorber affects are ignored and the strut direction is assumed as a same with load direction. The critical scenario is found for our case three points landing. Thus, the analyzes are performed based on this case Analysis of the Initial Design Von misses result for initial design which has 2 mm web thickness; 76

77 Displacement result for initial design; Figure 7.1: Von Misses Analysis Figure 7.2: Displacement Result Based on Von Misses analysis, the stress value is very low. 131 MPa < 261 MPa (Al 2024 T42 Yield Strength) 131 x 1.5 = 195 MPa (Multiplied by safety factor) After that, the thickness is reduced to 0.8 mm. 77

78 7.2. Analysis of the 0.8 mm Design Von Misses result for 0.8 mm thickness; Displacement result for 0.8 mm thickness; Figure 7.3: Von Misses Analysis Figure 7.4: Displacement Result According to Von Misses analysis, the stress value is lower than yield strength. 169 MPa < 261 MPa However, the safety must be provided. Therefore; 78

79 1.5 x 169 = MPa MPa < 261 MPa To decrease weight, all strucutres except bulkhead, aft frame and longerons, web thickness is reduced to 0.8 mm Structures with Decreased Thickness Figure 7.5: Von Misses Analysis Figure 7.6: Displacement Result 176 x 1.5 = 264 MPa 79

80 264 MPa > 261 MPa Thus, the structere must be more safe. To provide this, the design will be detailed More Detailed Design and Analyzes Figure 7.7: More Detailed Design At this design, the keel beam has various thickness. It has five different thikness. They are 30 mm, 15 mm, 7.5 mm, 3.5 mm and 0.8 mm. Bulkhead, aft frame and longerons 2 mm have thickness and others have 0.8 mm. Von Misses results of this design; 80

81 Figure 7.8: Von Misses Results Displacement results; Figure 7.9: Displacement Results 127 x 1.5 = MPa < 261 MPa It is over safe design. The thickness will be changed to obtain more weight structure. 81

82 7.5. Final Design and Analysis Figure 7.10: Final Design The design is improved with lightening holes and variable cape length. Von Misses results of this design; Figure 7.11: Von Misses Displacement results; 82

83 Figure 7.12: Displacement 134 x 1.5 = 201 MPa 201 MPa < 261 MPa It is at the safe side. Due to other loads, the gap could be necessary. 8. Final Design of the Keel Beam Figure 8.1: Final Keel Beam Design 83

84 It has variable thickness as seem at Figure Also, some pockets are opened due to reducing weight. This holes could be strenthen with doublers if it will be necessary. Figure 8.2: Top View of the Keel Beam As it seen at the Figure 7.12, the cap length is variable. The most length is 30 mm. Firstly, it decreases to 25 mm and then 20 mm. Figure 8.3: The Corner Radius and Decreasing Cap Length and Web Thickness 9. Conclusion In this thesis, firstly the landing gear configuratios were clarified. At this section, the tradeoff study was indicated. After that, the components of the landing gear are mentioned. Then, the constraints for sizin and positioning are specified when the landing gear are designed. After the constraints for sizing, the CS 23 requirements are specified. Then, to desing and analyzes the landing loads are calculated. As a final process, the design and analysez are completed with iterative procedures. The Excel is used for load calculations. The CS - 23 and Pazmany s book was be reference for these calculations. 84