Contents-

Introduction2

Specifications.3

Calculations4

Co-efficient of Lift..4 Co-efficient of Drag5

Velocity Stall...6

Thrust to Weight Ratio7

Aspect Ratio7

Wing Loading..8

Span Loading...8

Induced Drag...9

Parasite Drag.10

Wings and Control Surfaces11

Power Plant.13

Landing Gear..15

Systems17

Aircraft Structures19

References20

Introducing the LEARJET 60-

First taking to the skies on the 1st of June 1991 the Learjet 60 manufactured by Bombardier Aerospace, is the super slick medium sized business jet which exceeds all its competitors standards in safety, style, performance, cost and fuel efficiency. The aircraft is designed for two pilot operations and seats 8 passengers whilst also containing a bathroom facility and more than enough luggage storage. The 60, due to its Pratt and Whitney engines, has the ability to literally rocket its passengers and crew into the atmosphere with its staggering climb rate enabling it to reach its maximum cruise altitude of 41,000 feet in less than 13 minutes. This cruise altitude of 41,000 feet has always been the ancestral home of the Learjet and although many other business jets can now make this flight level the Learjet is still truly the quickest to get their. Despite this blistering speed the Learjet 60 makes considerably less noise than most other aircraft of its kind whilst also burning a reduced amount of fuel per hour.

Essentially this aircraft has been designed for those wishing not to be restricted by airport curfews but still make it to their destination in a short time period in the comfort of a full height cabin. The Learjet 60s ability to overshadow its competition comes down mainly due to the its aerodynamic designers use of NASA and Boeing Tranairs Computational Fluid Dynamics software ensuing a 4% reduction in drag. Hence it revolutionary jet like body as well as numerous technologically advanced components and systems has resulted in over 314 Learjet 60 aircraft being sold and operated across the globe.

Specifications-

Specifications-Learjet 60-

Basic Dimensions-Exterior Length-------------------------------Exterior Height:------------------------------Wing Span:------------------------------------Wing Area (Clean):--------------------------Cabin Length:---------------------------------Cabin Width:----------------------------------Cabin Height:---------------------------------17.80m 4.36m13.40m24.57m 5.39m 1.81m 1.74m

Weights- Max. Ramp Weight:--------------------------Max. Takeoff Weight:------------------------Max. Landing Weight:-----------------------Empty Weight:-------------------------------- Full Fuel Capacity Weight:-----------------10,773Kg10,659Kg 8,845Kg 6,641Kg 3,589Kg

Speeds-Take-Off:--------------------------------------Cruise:-----------------------------------------Landing:---------------------------------------281Km/h887Km/h252Km/h

Overall Performance- Altitude Ceiling:------------------------------Maximum Range:-----------------------------Rate of Climb:--------------------------------15,545m 4,440Km 4,500Ft/Min

Calculations-

(Acceleration due to gravity constant = 9.81m/s)

Co-efficient of Lift (CL)- Dimensionless co-efficient which relates to the lift generated by an aerofoil.

CL at Take-Off:(Sea Level, Max. Take-off Weight, Take-off velocity, Take-off Flaps Config.)

W = 10,659Kg x 9.81m/sP = 1.2256KgmV = 78m/sS = 32m

CL = 0.876 (3 dec. pl.)

CL at Cruise:(12,000m, Approx. cruise weight of 8757, cruise velocity 200m/s, no flaps)

W = 8757Kg x 9.81m/sP = 0.3106896 KgmV = 200m/sS = 24.6m

CL = 0.562 (3 dec. pl.)

CL at Landing:(Sea Level, landing velocity, landing flaps configuration)

W = 8000Kg x 9.81m/sP = 1.2256 KgmV = 70m/sS = 27m

CL = 0.933 (3 dec. pl.)

CL MAX Cruise:(12,000m, Approx. cruise weight, stall velocity, no flaps)

W = 8757Kg x 9.81m/sP = 0.3106896 KgmV = 55m/sS = 24.6m

CL Max = 7.431 (3 dec. pl.)

Co-efficient of Drag-A dimensionless co-efficient that represents the level of resistance obstructing an aircrafts movement through the air.

CD at Take-Off:(Sea level, full thrust, take-off velocity, take-off flaps config.)

T = 46,400NP = 1.2256 KgmV = 78m/sS = 32 m

CD = 0.389 (3 dec. pl.)

CD at Cruise:(12,000m 80% thrust, approx. cruise velocity, no flaps)

T = 37,120NP = 0.3106896 KgmV = 200m/sS = 24.6 m

CD = 0.243

CD at Landing:(Sea level, thrust at idle, landing velocity, landing flaps config.)

T = 11,600NP = 1.2256 KgmV = 70m/sS = 27 m

CD = 0.14

Velocity Stall-The speed at which the airfoil will no longer be travelling fast enough through the air to maintain lift and will hence stall.

(12,000m, approx cruise weight, no flaps)

W = 8757Kg x 9.81m/sP = 0.3106896 KgmS = 24.6mCLmax = 7.43

V stall = 55m/s

Thrust to Weight Ratio-

Take-Off Thrust to Weight:(Full thrust, max take-off weight)

T = 46,400NW = 10,659Kg

Thrust to Weight = 4.35N/Kg

Crusie Thrust to Weight:(80% thrust, approx. cruise weight)

T = 37, 120NW = 8757Kg

Thrust to Weight = 4.24N/Kg

Aspect Ratio-

Wing Span = 13.40mWing Area = 24.57m

Aspect Ratio = 7.31 (2 dec.pl)

Wing Loading-

Weight = 8757Kg (approx. cruise weight)Wing Area = 24.6m

Wing Loading = 355.97Kg/m

The Learjet 60s heavy wing loading ensures smooth flight even in turbulent areas allowing the most comfortable journey for its passengers.

Span Loading-

Wing Span = 13.40mWeight = 8757Kg

Span Loading = 653.507Kg/m (3 dec.pl.)

Induced Drag Cd(i)-

Induced Drag is caused by the aircrafts wings generation of lift. Hence this drag is generated by vortices which form on the tips of aircraft wings as the low pressure travelling over the top and high pressure underneath become joined rather than remaining separate. The greater a wings angle of attack the greater the amount of lift produced and hence more induced drag will result.

AR (Aspect Ratio) = 7.31e (Oswalds efficiency factor) = 0.75

K = 0.0581

Now sub K into:

K = 0.0581Cl = 0.562

Induced Drag Cd(i) = 0.018 (3 dec pl.)

Parasite Drag Cd(o)-

Parasite drag is made up of two main components, these being form and skin drag. Essentially these two causes of drag are the direct result of an aircrafts body travelling through a fluid which is air. Ultimately the resistance against the aircraft is dependant upon the speed and altitude at which the aircraft is travelling. Factors which can have a major impact upon parasite drag include control surface such as flaps, slats and speed brakes. When at cruise an aircrafts angle of attack is reduced and hence parasite drag has a greater impact upon the aircraft.

Cd = 0.243Cd(i) = 0.018

Cd(o) = 0.225 (3 dec pl.)

WINGS AND CONTROL SURFACES-

Fitting to its slick design the Learjet 60 features a swept back, cantilever (no bracing) wing structure ensuring optimum lift and minimal drag. The swept back nature of the 60s wings allow the aircraft to travel at high velocities as they suppress the effects of shockwaves generated when travelling at transonic speeds which would otherwise result in unwanted drag. This reduced drag at high speeds however, does result in the disadvantage and potentially dangerous lack of lift when travelling at low speeds. This situation is resolved by the Learjets fowler flaps situated on the wings trailing edge. As seen by the image unlike other flap types, these flaps originally deploy in a flat orientation before hinging downwards. This design enables the Learjet to deploy such flaps to an angle of 8 and hence increase wing surface area and lift produced without inducing excessive drag.

Another issue generated by the 60s swept back wing design is the inherent issue that the aircrafts wing tips will stall first before travelling inward. Such a scenario results in excessive difficulty to re-gain control of a stalling aircraft. The 60s engineers have combated such an issue through the implementation of stall fences. There are two such stall fences on each of the aircrafts wings and are visually obvious due to their protruding nature on the top surface of the wing as displayed by the image below. Such stall fences stop the essentially horizontal flow of air (when compared to the direction of flight) along the wing travelling in outboard direction caused by the aircrafts swept back wing design. Such span-wise air current is hence stopped and forced backwards by these stall fences reducing the ability for the aircrafts wing tips to stall first. The stall fences also eliminate the potential for this span-wise air flow to have an effect upon the Learjets ailerons located on the outboard section of the wing which could otherwise result in an inability to control the aircraft safely.

To further increase the lift efficiency of the aircraft, winglets are fitted to the tips of each wing. Such winglets dissipate the formation of vortices on wing tips, which are generated because as the wing narrows the high pressure air below the wing tends to curve over the top of the wing and hence results in unwanted induced drag and loss of lift.

As discussed previously the Learjet 60 features trailing edge fowler flaps which can be deployed by pilots to either induce drag and hence reduce speed upon landing or increase the surface area of the wing to increase lift on take-off. Outboard of the Learjets flaps are the aircrafts ailerons which are fixed to the main wing by a hinged mechanism. Such ailerons which control the roll of the aircraft are directed by the pilots control column and are then moved by a series of hydraulic actuators.

The final moveable surfaces upon the Learjets main wing are its spoilers. Once again these hinged sections are moved by hydraulic actuators and are vertically deployed from the wings surface to greatly induce drag and hence reduce speed during approach.

The Learjet 60s tail section or horizontal stabiliser is in a T shape and features two ventral fins pointing diagonally downwards below the stabiliser. These two ventral fins dubbed Delta Fins (circled in image) ensure aerodynamic stability whilst further improving safety by forcing the nose to pitch down if the aircraft were to stall. The 60s horizontal stabiliser is positioned high to ensure greater stability and control whilst also ensuring it is out of the way of the thrust being produced by the engines. The stabiliser also acts as the aircrafts elevator (responsible for changing pitch). Such elevator positioning is completed once again by hydraulic actuators and can be set to hold a certain angle by a pilots trim controller located on the centre pedestal, helping to reduce pilot fatigue. The rudder section of the aircraft comprises the rear portion of the vertical stabiliser. Once again it too is moved by hydraulic actuators which are originally directed by the pilots foot pedals resulting in the yaw of the aircraft.

Both the Learjet 60s main wing and horizontal stabiliser feature pneumatic de-ice boots. Essentially any ice build up upon the wings is cracked as these boots are inflated by turbine bleed air. To further ensure the 60 can be flown in even the worst icing conditions electronic wing heating mechanisms are also used to melt ice mainly on the inboard portion of the wing. This positioning of the electronic heating is due to the fact that cracking large pieces of ice with de-ice boots near the fuselage would result in such ice being digested by the aircrafts engines.

Power Plant-

The Learjet 60s power plant consists of two Pratt and Whitney model 305A turbofan engines mounted on the rear of the aircrafts fuselage. These Canadian built turbofan engines are the latest modern adaptation of the traditional gas turbine engine. Traditional gas turbine engines follow the simply suck, push, bang, blow procedure. That is, air is engulfed by the inlet fan blades (suck) before being compressed by a series of compressor blades rotating at varying velocities (push). This highly compressed air then passes through the combustion chamber where it is mixed with fuel and ignited in a controlled explosion (bang) to produce extremely hot exhaust gases. These exhaust gases then rapidly pass through the rear of the engine known as the turbine stage whilst spinning these turbines which in turn rotate a drive shaft powering the rotation of the original inlet fan blades and compressors. After passing through the turbines the exhaust gases drive out the rear of the engine and expand rapidly producing thrust in the opposite direction to which they travel.

The only difference to this form of engine and the turbofan engines on the Learjet 60 is that the original inlet fan is brought forward so that some of the incoming air bypasses the compression and combustion process (named secondary air stream in the diagram). Instead this low pressure air moves around the central core of the engine with the velocity generated from the inlet fan blades. This low pressure air then joins the high pressure air from the combustion chamber and is then released from the turbine through an hourglass shaped nozzle. This process is highly fuel efficient as approximately 85% of the air passes around the outside of the compression and combustion processes and is hence known as bypass air. The bypass ratio can therefore be described as the ratio of air that bypasses the central core of the engine compared to the amount of air that is compressed and combusted. The Learjet 60 boasts a bypass ratio of 4.3:1 helping to keep its engines highly fuel efficient because as such a large amount of air is bypass it only needs to be accelerated by a small amount in order to deliver a huge amount of thrust as the combusted exhaust gases.

This bypass air works further to silence the noise of the engines central core which is essential for the Learjets private business jet target market as it enables it to take-off outside airport curfews and ensure a more comfortable journey for its passengers. This has resulted in the Learjet 60 producing a mere 70.8dB of effective perceived noise on take-off and 87.7EPNdB on landing.

The Learjet 60s turbofan engines have the ability to produce 5,225 pounds of thrust each. However, Pratt and Whitney have flat-rated then (constrained their power output) to 4,600 pounds of thrust each. This action enables the power output of the engines to always remain at a constant level despite changes in atmospheric pressure and or temperature making then perfect for the Learjets high altitude operations. The Pratt and Whitney 305A turbofan engines also feature another innovation in turbofan engine technology known as the Full Authority Digital Engine Control System or FADEC. This technology enables further increases engine efficiency by constantly assessing and altering engine performance which in turn reduces pilot workload.

Through the implementation of all these engine performance technologies the Learjet 60s Pratt and Whitney 305A turbofan engines are able to see the aircraft operate at a maximum cruise altitude of 51,000 ft, travelling at a speed of 887km/hr for a maximum range of 4441km whilst only burning 203 gallons of jet fuel per hour.

Due to these impressive air speeds the Learjet 60 requires some powerful braking technologies which along with its dual rotor disc brakes include Rohr Thrust Reversers (pictured). These trust reversers work by opening two doors on the upper and low portion of each engine. The doors which are opened by hydraulic actuators see the direction of thrust made to become forward so that they oppose the direction of the landing aircraft. Hence the thrust is said to be reversed. Such an operation is undertaken by pilots after 4-6 seconds of touching down. Once the throttle is in the idle position pilots are able to activate the reverse thrust by raising the piggyback levers located on the top of the throttle. Ultimately thrust reversers are the most cost effective way to slow the aircraft after landing as they ensure less brake wear and tear which would otherwise result in more frequent part changes and associated maintenance.

In order to feed its two Pratt and Whitney engines the Learjet 60 has three fuel tanks located in each wing and one in the fuselage under the cabin floor. Together they have the capacity to hold 2799kg of fuel, enabling the aircraft to travel a maximum 4440 km. Despite this large fuel capacity the 60 is able to be re-fuelled in a little over 10 minutes due to its single point refuelling system. Single point refuelling sees a pressurised fuel hose having to be connected to the underside of only one of the aircrafts wings to re-fuel the entire aircraft. This works by opening all necessary valves resulting in fuel flowing between and filling all three tanks from once location. This system ensures cost efficiency by limiting turn around time and enabling the aircraft to quickly return to the air. It also works to maintain safety by reducing the amount of times a fuel hose must be connected/disconnected and hence reducing the likelihood of an accident during this process occurring.

Landing Gear-

The Learjet 60 features a retractable, tricycle design, landing gear system comprising of one wheel at the nose of the aircraft and a pair of wheels on either side of the fuselage, approximately in line with the inboard section of the aircrafts main wing. Such a tricycle design was primarily chosen due to its ability to allow braking pressure to be applied immediately after touching down ensuring the high speed flight of the 60 can be safely managed. This form of landing gear design also gives pilots greater visibility during ground operations as the nose is level with the ground rather than pointing skyward as is the case with tail-dragger aircraft.

Being a low wing aircraft the severity of damage that would occur if the aircraft where to enter a ground loop would be devastating. This issue was once again resolved through the implementation of the tricycle undercarriage design as this type of landing gear layout sees the aircrafts centre of gravity in front of the main gear insuring ground operation stability.

The main component responsible for the 60s ability to deliver a comfortable landing for its passengers are its Oleo Legs. These shock absorbers work as when placed under pressure they drive the piston connected to the tire upwards through a chamber of oil. Essentially the oil slows the pistons movement and hence takes all the downwards force of out the aircrafts tires during landing. As can be seen the pressure inside the oil chamber is directly related to different periods during flight. These Oleo Legs are supported by drag struts seen to run from the base of the Oleo Legs exposed piston diagonally to the inside of the gear door. The nose gear is attacked to such Oleo Legs through an L shaped bracket running down only the left hand side of the wheel.

Both the main and nose gear are retractable and when in such a position are covered by landing gear doors. The main gear retracts in a direction perpendicular to flight and lay flat with the wheels closest to the fuselage. The nose gear retracts with the wheel coming forward before being concealed by two hinged doors. Both the main and forward gear are held in their retracted positions with doors closed by a mechanical latch mechanism. Essentially by having retractable and concealed landing gear the Learjet 60 is able to promote fuel efficiency by reducing drag that would otherwise be generated by fixed landing gear.

To steer the Learjet once on the ground pilots use rudder input which results in an electrical signal being sent to the nose wheels electrically operated steering mechanism. At slow speeds this system enables the pilots to make up too 50 degree turns ensuring the aircraft can be parked accurately in a short time frame. Once the aircraft has exceeded 150km/hr during take-off however, nose gear steering is disabled and instead pilot pedal inputs are fed to the rudder. This ensures safety by reducing the risk of the aircraft straying off the runway during take-off by eliminating what would otherwise be violent turns if undertaken by the nose wheel at such speeds. The rudder instead enables pilots to steadily direct the aircraft down the runway making slight adjustments to its course.

Due to the high speed nature of the Learjet 60 strong braking technology is required to ensure the aircraft can be safely brought to a stop during landing and/or an aborted take-off. Engineers have therefore fitted the Learjet 60 with Dual Rotor/Disc Brakes effectively enabling double the braking capacity of an ordinary Rotor Brake. This system works as brake pads apply pressure to discs located on both sides of all the 60s fours main gear tyres, through a process similar to that illustrated. Like all brakes when applied the friction which effectively slows the aircraft also results in the production of heat. Combining both the use of reverse thrust and brakes therefore reduces the heat build up as less brake pressure is required without risking the inability to slow the aircraft.

The Learjet 60s main tyres are inflated to a pressure of 214 psi. This pressure is essential as it ensures that the landing gear isnt put under unnecessary pressure whilst also ensuring the braking effect isnt reduced and that the life time of the tire also isnt jeopardised. All these factors help to not only ensure safety but also cost efficiency. In order to ensure no Learjet is operated using an incorrect tire pressure engineers have permitted the use of a tire pressure remote sensor system by Crane Aerospace and Electronics. This system enables the tire pressure to be check and maintained on a hand-held device rather than manually, simply through the instillation of an electronically operated valve.

Systems-

Fitting with it super slick and technologically advanced style and performance the Learjet 60 is fitted with the latest in avionic system technology in the Pro Line 4 series by Rockwell Collins. This Pro Line system features four main 6 by 7 inch Air Data Computer Display Units featuring primary flight displays and navigational aids placed directly in front of each pilots view. This is combined with dual Computer display units placed on the pilots centre pedestal which features aircraft management systems including maintenance diagnostic and fuel management systems. This futuristic cockpit layout helps to reduce pilot workload by placing several different instruments onto one screen. To further reduced pilot workload and assist with navigation the 60 utilises an AC685A Learjet specific autopilot system guided by GPS technology. Communication between the Learjet 60, Air Traffic Control and other aircraft is enabled by two Collins VHF-422A radios. Engineers have ensured the safety on those on-board through the instillation of a Honeywells Enhanced Ground Proximity Warning System. This program uses the aircrafts speed, heading, altitude and position (provided by the Pitot-Static system) to ensure conflict does occur between the aircraft and terrain by comparing such indicators to the systems databases. The EGPWS fitted to the Learjet also include windshear detection technology ensuring the ability to land safely by giving pilots the most accurate and up-to-date wind forecasts. Maintaining a safe altitude is also made certain by the Collins ALT-55 Radio Altimeter on board. This system uses differences in the measurement of transmitted and reflected radio signals to accurately depict the altitude of the aircraft.

Safety is further ensured through the instillation of a version 7 Traffic Collision Avoidance System (TCAS). This program reduces the possibility of mid-air collisions by delivering heading and altitude changes to aircraft that are on a collision course with one another. As demonstrated by the diagram a region of dedicated airspace is issued to each TCAS equipped aircraft during its flight. The shape and size of this airspace is dependant upon the aircrafts heading, altitude and speed as these factors will impact upon the timeframe required for this aircraft to change its course. Course alterations are re-laid to Learjet pilots by both automated voice instruction as well as visual representation on the pilots primary flight display computers.

As well as other traffic, the Learjet 60 is able to avoid flying into any possibly dangerous weather due to its Collins WXR weather radar located in the nose of the aircraft. This weather radar works by comparing the size and frequency of the radio waves it emits too those that are reflected by places of precipitation in its path. A more severe weather system along the aircrafts flight path can be identified by a stronger radio wave reflection. Hence this enables Learjet 60 pilots to avoid such regions ensuring safety and passenger comfort.

Due to its maximum operating altitude of 51,000ft the 60 utilises a digital pressurisation system in order to ensure a safe and comfortable environment for both passengers and crew. This system automatically controls the volume of air being fed into the cabin from the engine compressors compared to that amount being released by the outlet valves.

Aircraft Structure-

The Learjet 60s fuselage is a semi-monocoque structure that comprises of stringers, frames and bulkheads to ensure the rigidity of the aircraft frame instead of simply relying upon the skin to do this task. Frames map of the skeleton shape of the aircrafts fuselage and are made of aluminium alloy. Attached to these frames and running the length of the aircraft are stringers constructed of the same material. These stringers provide the rigidity of the aircraft as they ensure it wont bend under various aerodynamic pressures. The skin of the aircraft is then riveted and bonded to these stringers and works to resist shear load. In areas of the fuselage where strenuous loads are found such as near the wings, engines and landing gear bulkheads are used. These bulkheads which are attached to both the aircrafts frame and stringers ensure the extra weight at these regions of the aircraft doesnt result in bending of the alloy.

Both the Learjets main wing and fin are also constructed mainly out of aluminium alloy which is connected to the structural front, centre and rear spars by rivets or bonding material. Stringers once again also run along the horizontal axis of the wing and are connected to these spars. These stringers offer further attachment location for the aircrafts skin whilst also providing some rigidity and mapping the shape of the aircrafts wings.

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