Unit 2 AE Review2.1 Material StructuresAerospace Materials

Commonly Used Aerospace Materialso Woodo Steelo Aluminum alloys

o Titanium alloyso Magnesium alloyso Nickel alloys

o Fiber-reinforced composites

Factors for Selecting Materialso Function

What is the component used for?o Material Properties

Strength to weight ratio Stiffness Toughness

Resistance to corrosion Fatigue and effects of

environmental heatingo Production

Machinability Availability and consistency of material

Stiffness is the ability of a material to resist deflection or stretching. Toughness is the work per unit volume required to fracture a material. Fatigue is the reduction of strength by repeated cyclic or random stress. Machinability is the way a material responds to specific machining techniques. Availability of both raw and processed material is affected by many factors, including: Cost of materials Quality control processes by the material producers Geopolitics (international relationships between trading partner countries) Cyclic Stresses

o Average commercial aircraft 30 year life cycle 60,000 Hours- 2,500 Days – 357 weeks – 6.85 Years 20,000 Flights- 667 flights per year 100,000 miles of taxiing- 4 times around the Earth’s circumference

Total average maintenance and service cost are double the original purchase price Flight Stresses

o Pressure differential fuselage to outside 0 kPa to 60 kPa (8.6 psi)

o Temperature differential ground to cruise Ground temp to -56 oC (-69 oF)

o Impact load of landing Landing gear now supports aircraft Wings flex from upward lift force to downward force of their own weight Tires accelerate from 0 kph to 400 kmph (this creates a puff of smoke)

Each flight subjects the aircraft to stresses similar to the ones listed below. The fuselage endures cyclic pressure cycles from ground level to inflight conditions which stress the aircraft from

a pressure differential of 0 kPa to 60 kPa (8.6 psi). On the ground inside and outside of the aircraft are equal to atmospheric pressure (~101.3 kPa or 14.7 psi). Inflight there is pressure differential between the outside pressure 18.7 kPa (2.8 psi) at a typical cruise altitude of 12,200 m (~40,000 ft) and the pressure inside the fuselage of 78.5 kPa (11.4 psi). The pressure inside the cabin is approximately that of 2,100 m (~6,900 ft), which is determined through the FAA aircraft certification process. Note that the fuselage is not maintained to be the same as ground level to reduce the fuselage pressure differential. The interior of the fuselage must be maintained at a pressure associated with an altitude below 10,000 ft (3,048 m); otherwise, the FAA requires supplemental oxygen to be supplied.

Unit 2 AE Review The aircraft is subjected to a thermal cycle of ground level (temperature at takeoff) to -56 oC (-69 oF) at a typical

cruise altitude of 12,200 m (~40,000 ft). Impact load of landing when landing gear cycles from no weight to supporting full weight of aircraft. Wings

support the weight of the aircraft during flight through lift (upward force) to downward force of supporting their own weight.

Landing gear tires accelerate from 0 kmph to 400 kmph (250 mph). This creates a puff of smoke as tires scrub the runway and accelerate to the landing speed.

Keep in Mindo Reducing material density reduces airframe weight and improves performance

Fuel efficiency Climb rate

G-force loading

o Material density reductions are 3 to 5 times more effective than increasing tensile strength, modulus, or impact resistance

Early Aircraft Built of Woodo Wright Brothers used Spruceo Widely availableo Uniform piece to pieceo Good strength to weight ratioo Different properties in different

directions o Easy fabrication and repair

o Sensitivity to moistureo Rot and insect damageo Natural product lower consistency than man-madeo Rarely used today in production aircrafto Used today in homebuilt and specialty, low-volume

productiono Chinese have selected oak for the heat shield of a

reentry vehicleo Spruce was an excellent product during the early days of aircraft manufacturing. Since then the progress

made in material engineering has provided more consistent and superior properties. Aerospace Materials – Metal Alloy

o Material Forms Sheet ˂ 0.250in.

Skin of fuselage, wings, control surfaces, etc. Plate ˃ 0.250in.

Machined into varying shapes and parts Forging – Material is plastically deformed by large compressive forces in closed dies

Produces high strength non-uniform cross sectional parts Extrusion – Material is forced through dies to create a uniform cross section

Uses include stiffeners and ribs Casting – Liquid material is solidified in a mold

Aerospace Materials – Aluminum Alloyo Cutting-edge (1920s-60s)o Most abundant metal in the earth’s crusto Pure aluminum is relatively softo The P-12 fighter, built for the U.S. Army in 1928, could hold a 500-pound bomb. It used bolted aluminum

tubing for the fuselage's inside structure rather than the typical welded steel tubing.o Currently most widely used materialo Readily formedo Moderate costo Excellent resistance to chemical corrosiono Excellent strength to weight ratioo Strength and stiffness are affected by:o Form

Sheet Plate

Bar Extrusion

Forging

o Heat treating and tempering

Unit 2 AE Review Stronger aluminum more brittle

o Ductility is the amount of plasticity that precedes failure.o Brittleness is a lack of ductility. This is often confused with lack of strength.o Most common alloy is 2024 (24ST)

93.5% aluminum, 4.4% copper, 1.5% manganese, and 0.6% magnesiumo High-strength applications – 7075 – 7050 – 7010

Zinc, magnesium, and coppero Sheet aluminum is clad with a thin layer of pure aluminum for corrosion protectiono Aluminum lithium

Same weight savings as composites but can be formed by standard techniques Aerospace Materials – Steel Alloy

o Steel is very cheap and easy to fabricateo First utilized in fuselage construction

Steel tubing replaced wire-braced wood constructiono Today’s applications: o High strength and fatigue resistance

Wing attachment fittingso High temperatures

Firewalls and engine mountso Alloy of iron and carbono Carbon adds strength to soft irono As carbon content increases, strength and brittleness increaseo Typical steel alloys are1% carbono Other common alloy materials –

Chromium, molybdenum, nickel, and cobalto Properties of steel are influenced by heat treating and temperingo Same alloy can have moderate strength and good ductility or high strength and brittleness, depending

on heat treatmento Materials temperature is raised to1400-1600 °F - The point at which carbon goes into solid solution with

the irono Ductility is the amount of plasticity that precedes failure.o Brittleness is a lack of ductility. This is often confused with lack of strength.

Aerospace Materials – Titaniumo Greater strength to weight ratio and stiffness than aluminum o Capable of sustaining temperatures almost as high as steelo Corrosion-resistanto Titanium parts manufactured complete with Wire EDM and Matsurra CNC mill. These parts are now on

the planet Mars as part of JPL's Mars Rovers.o Difficult to form o High forming temperatures and stresseso Seriously affected by any impuritieso Most impurity elements – Hydrogen, oxygen, and nitrogeno Higher fabrication costo Expensive – 5 to 10 times as much as aluminumo Most titanium alloys must be formed at temps over 1000F and at very high forming stresses. Mechanical

properties are seriously affected by any impurities that may be accidentally introduced during forming.o Extensively used in jet-engine componentso Lower-speed aircraft, high-stress airframe componentso Uses include landing gear beams and spindles for all moving tailso Super Plastic Forming/Diffusion Bonding (SPF/DB)

Unit 2 AE Reviewo Extreme temperature and pressure causes titanium to flow into the shape of the mold. o Separate pieces of titanium are diffusion-bonded at the same time, forming a joint that is

indistinguishable from the original metal Aerospace Materials – Magnesium

o Good strength to weight ratioo Tolerates high temperatureso Easily formed – Casting, forging, and machiningo Uses include engine mounts, wheels, control hinges, brackets, stiffeners, fuel tanks, and wingso Prone to corrosion – must have a protective finisho Flammableo Should not be used in areas that are difficult to inspect or where the protective finish could erode away

Aerospace Materials – High Temperature Nickel Alloyso Inconel, Rene 41, and Hastelloy o Suitable for hypersonic aircraft and reentry vehicleso Hastelloy is used primarily in engine partso Nickel alloy honeycomb sandwich is used for the stealth nozzles of the F-117o Heavier than aluminum and titaniumo Difficult to form

Aerospace Materials – Compositeso Mid 1960s and early 1970s o Empennages of the F-14 and F-15o In the mid-1960s and early 1970s, composites began being used. Their first production usage was on the

empennages of the F-14 and F-15.o Boron/epoxy – horizontal stabilizers, rudders, and vertical finso Mid-1970s carbon fibers

Carbon/epoxy speed brake o 1980s composite use expanded from 2% on the F15 to 27% on the AV-8B Harrier

Uses included wing (skins and substructure), forward fuselage, and horizontal stabilizero Modern fighters consist of 20% composite materialo 15-25% weight savings depending on structureo Boeing 787 uses upward of 50% composites and includes composite wing and fuselage

Aerospace Materials – Ceramico High temperature resistanceo Uses include engine exhaust nozzleso Space shuttle uses aluminum structure with heat-protective tiles

Material Properties and Forces Centroid Location

o Symmetrical Objects Centroid location is determined by an object’s line of symmetry.

Moment of Inertia (I) is a mathematical property of a cross section (measured in inches4) that gives important information about how that cross-sectional area is distributed about a centroidal axis.

Stiffness of an object related to its shape. In general, a higher moment of inertia produces a greater resistance to deformation.

Calculating the moment of inertia for a composite shape, such as an I-beam, is beyond the scope of this

presentation. The values of moment of inertia and cross-sectional area were given for purposes of comparison.

Unit 2 AE ReviewLead students to the observation that the beam’s stiffness is most influenced by the major cross-sectional area’s distance from the center of gravity.

Further analysis: o Both of these shapes are 2 in. wide x 4 in. tall, and both beams are comprised of the same material. The

I-beam’s flanges and web are 0.38 in. thick.o The moment of inertia for the rectangular beam is 10.67 in.4. Its area is 8 in.2.o The moment of inertia for the I-Beam is 6.08 in.4. Its area is 2.75 in.2. o The I-beam may be 43% less stiff than the rectangular beam, BUT it uses 66% less material.

Increasing the height of the I-beam by about 1 in. will make the moment of inertia for both of the shapes equal, but the I-beam will still use less material (61% less).

Composite shapes allow a weak material such as Styrofoam to act as a support for the stronger fiberglass material which is located farther away from the beam’s center of gravity. This design creates strong material that is lightweight

Modulus of Elasticity (E) The ratio of the increment of some specified form of stress to the increment of some specified form of strain. Also known as Young’s Modulus.

o E =  σϵ

Tension Stresso A body being stretchedo Applied load divided by cross-sectional area

o σ =  FA

o The shape of the cross section is not importanto Appropriate cross section is the smallest area in

the loaded part

Compressiono A body being squeezed

Strain

o ϵ =  δL0

Calculating Beam Deflectiono ΔMax = F L3/ 48 E I

Staticso The study of forces and their effects on a system in a state of rest or uniform motion

Equilibriumo Static equilibrium: A condition where there are no net external forces acting upon a particle or rigid

body and the body remains at rest or continues at a constant velocityo Translational equilibrium: The state in which there are no unbalanced forces acting on a body

oo Rotational equilibrium:o The state in which the sum of all clockwise moments equals the sum of all counterclockwise

moments about a pivot point

oo Moment = F x D

Truss Analysiso Primary truss loads – loads calculated with ideal assumptionso Used in welded steel-tube fuselages, piston-engine motor mounts, ribs, and landing gearo Engine Mount Example

Unit 2 AE Review Line of force is from the center of gravity of the engine Rigid connection from the fuselage and engine to the truss

Composites

Advantages of Compositeso Strength-to-weight ratioo Long lifeo Dampen vibrationo Easy to repair

o Easy to shapeo Tailored strength characteristicso No corrosion

Composite materials must have 2 basic parts:o Reinforcement (fiber)

Reinforcement provides the majority of strength.o Matrix (resin)

Matrix holds the reinforcement in a specific orientation, improves environmental properties, and provides some strength.

All composites MUST have an identifiable reinforcement and matrix. Common Composites

o Fiberglass – Most commono Graphite – Good strength-to-weight ratioo Kevlar – Toughest

o Boron – Strongesto Silicon Carbide – Ceramics reinforcement

Using Composites Safelyo Areas at risk:

Vision Liquids

o Resinso Solvents

o Initiators (MEKP)

Solidso Dust o Particles

Symptomso Watering eyeso Rednesso Swelling

o Itchingo Burning

Protection: These devices protect you from direct contact, but vapors may still have an effect.

o Chemical goggles o Glasses with side shields Dermal (skin)

Fibers Coatings Chemicals

o Resinso Solventso Mold release

Foams Dust Symptoms

3,200lbf3,200lbf3,200lbf3,200lbf3,200lbf3,200lbf3,200lbf3,200lbf3,200lbf3,200lbf3,200lbf3,200lbf3,200lbf3,200lbf3,200lbf

Unit 2 AE Reviewo Rednesso Rasho Itching

o Burningo Dry or cracking skin

Protectiono Cover your skino Gloves

o Latex (potential reaction)o Nitrileo Vinyl

Respiratory Fiber Selection Considerations

o Performance needso Cost

o Availability

Performance Considerationso Required strengtho Strength vs. cost ratioo Operating environment

Forces Engineering termSqueezing CompressionStretching TensionBending BendingSliding ShearTwisting Torsion

Type of Material

Strength in Tension

Strength in Compression

Cost Weight Pros and Cons Applications

Aluminum 3 2.5 9 2 Pros: Lightweight, doesn’t rust, strong in compression and tensionCons: Expensive

Airplane wings, boats, cars, skyscraper skin.

Steel 4 2 6.8 9 Pros: One of the strongest materials used in construction. Strong in tension and compression.Cons: Rusts, loses strength in extremely high temperatures.

Cables in suspension bridges, trusses, beams and columns in skyscrapers, and roller coasters.

Unit 2 AE Review

Based on your results, in which loading condition (tension or compression) are metals strongest?Metals perform best in tension.Even though steel is an exceptionally strong metal, why wouldn’t it be a good choice for use inside jet engines?The high temperatures inside of an aircraft engine would weaken the strength of steel.

Type of Material

Strength in Tension

Strength in Compression

Cost Weight Pros and Cons Applications

Plastic 3 3 9 1.5 Pros: Flexible, lightweight, long lasting, strong in compression and tension.Cons: Expensive

Umbrellas, inflatable roofs over sports arenas.

Based on your observations, would plastic be a suitable alternative to aluminum for airplanes, or steel for buildings? Why or why not?The plastic stretched very far before breaking. This would not be suitable to replace Aluminum because aircraft and building must maintain their shape to perform as it was designed.

CeramicsType of Material

Strength in Tension

Strength in Compression

Cost Weight Pros and Cons Applications

Brick 1 2.5 2.25

4 Pros: Cheap and strong in compressionCons: Heavy and weak in tension.

Walls of early skyscrapers and tunnels. Domes.

Based on your observations, in which method of loading (tension or compression) are ceramics strongest? In your opinion, why do you think ceramics behave this way?Ceramics are strongest when loaded in compression. The ceramic molecules are tightly packed so they are difficult to compress closer together. The molecular bonds are weak so they are weak in tension. Since ceramics can be so strong (and relatively inexpensive), why aren’t they used to make aircraft or other transportation machines? Why do we only seem them used in buildings or structures?Ceramics are heavy so they are not suitable for aircraft. Buildings rest on the ground so ceramics are suitable for their construction.Why wouldn’t brick be used to make the cables which hold up a suspension bridge?Cables require high tensile strength, but bricks have weak tensile strength.

CompositesType of Material

Strength in Tension

Strength in Compression

Cost Weight Pros and Cons Applications

Wood 2.5 1.5 1 4 Pros: Cheap, lightweight, moderately strong in compression and tension.Cons: Rots, swells and burns easily.

Bridges, houses, two and three story buildings, roller coasters.

Reinforced Concrete

2 3.5 4.5 6 Pros: Low cost, fireproof and weatherproof, molds to any shape, strong in compression and tension.Cons: Can crack as it cools and hardens.

Bridges, dams, domes, beams and columns in skyscrapers.

Unit 2 AE Review

Why were these materials strongest pulled along the rods and fibers?The steel rods and fibers are stronger than the base material so applying force along the length of the rods and fibers increase the overall strength. In your opinion, what would have happened if we would have pulled on the wood/reinforced concrete from the top and bottom instead of the sides? Why?The material would break with less applied force because the rods and fibers are only increasing the strength of short sections of the material.Click on the unreinforced concrete and perform a tension/compression test. How does adding the steel rods improve the strength of the concrete (and in which mode, tension or compression)? Explain.The unreinforced concrete breaks at 0.5 units in tension and 2.5 units in compression. The steel rods improve the tensile strength significantly and the compression strength slightly. As noted in the investigation, wood and reinforced concrete are relatively strong and inexpensive. Why don’t we use these particular composite materials to construct aircraft or other transportation vehicles?Concrete is heavy so it is not suitable for aircraft construction. Wood was used to construct early aircraft and some aircraft today. It was replaced in most aircraft construction because it is not as durable as metal and it burns more easily. The PBS Forces Lab is a resource designed to show qualitative comparisons between broad material categories. Engineers need accurate material properties to design safe and predictable products. These material properties were measured using stringent testing standards. These properties are published in sources for reference such as MatWeb http://www.matweb.com. Use this site or a similar site to find properties of the materials shown below.

Material Density or Specific Gravity

Tensile Strength (Yield)

Elongation at Break (if available)

Steel(AISI Type S14800 Stainless Steel condition A)

7.70 g/cc0.278 lb/in3

450 MPa65,300 psi

20.0 %

Aluminum(6061-T8)

2.70 g/cc0.0975 lb/in³

>= 276 MPa>= 40,000 psi

8.00 %

Plastic(PVC, Extruded)

0.549 - 1.85 g/cc0.0198 - 0.0668 lb/in³

1.90 - 57.4 MPa 20.0 - 720 %

Wood(American Sitka Spruce)

0.310 - 0.360 g/cc0.0112 - 0.0130 lb/in³

1.59 MPa230 psi (Ultimate)

n/a

Based on the information from the table rank the material for selection for an aircraft material choice for best strength to weight ratio. Use density as a substitute for weight. Show calculations.Aluminum, steel, American Sitka Spruce, then ABS.

RatioSteel=Tensile Strength

Density

RatioSteel=450MPa7.70 g/cc

RatioSteel=58.4 MPag /cc

RatioPVC=Tensile Strength

Density

RatioPVC=1.90MPa1.85 g /cc

RatioPVC=1.03 MPag /cc

Note: The values used reflect the most conservative ratio.

RatioAluminum=Tensile Strength

DensityRatioSpruce=

Tensile StrengthDensity

Unit 2 AE Review

RatioAluminum=276MPa2.70 g/cc

RatioAluminum=102.2 MPag /cc

RatioSpruce=1.59MPa

0.360 g/cc

RatioSpuce=4.42 MPag/cc

2.2 PropulsionReview of Newton’s Laws

• Law of inertia: Object in state of rest or uniform motion will continue unless acted upon by another force

• Acceleration of an object is proportional to net force acting on object and inversely proportional to object’s mass (F = ma)

• For every action force, there is an equal and opposite reaction force• Newton’s Third Law

• In Principles of Engineering you learned that forces act and react within structures• Aircraft are acted upon by forces• Four forces on airplane• Weight• Lift

• Drag• Thrust

• Aircraft is in steady flight when all forces are balanced• Aircraft accelerates in direction of strongest force when not balanced

• Weight• All mass of aircraft act toward center of Earth

• Aircraft frame• Fuel: Decreases during

flight

• Payload: Passengers and cargo

• Weight must be counteracted and balanced• Lift

• Opposes weight• Lift must equal weight for straight and level flight• Unbalanced lift and weight cause a body to ascend or descend• Lift is generated by air movement over wings

• Drag• Force that resists aircraft motion• Acts opposite of aircraft motion

• Thrust• Must equal drag for straight and level flight• Unbalance of drag and thrust causes slower or faster velocity• Propulsion system produces thrust

Aircraft Engines• Types of Propulsion Systems

• Propeller• Turbine (also called jet)• Ramjet

• Aircraft’s velocity compresses air• Newer form is supersonic combustion ramjet (scramjet) for speeds above mach

5• Rocket

• Fuel and oxygen burn very rapidly and are exploded and forced through nozzle

Unit 2 AE Review• Engine Categories

• Reciprocating (contains pistons)• Gasoline-powered

• Two stroke• Four stroke

• Diesel-powered (not typical in aircraft)• Turbine• Turbojet• Turbofan• Turboprop• Afterburning turbojet

• Engine Operations• All engines must perform four basic operations.

• Intake: Fuel and air must be brought into the engine• Compression: Fuel-air mixture must be compressed• Power: Fuel-air mixture must be ignited for the gases to provide engine power• Exhaust: Gases must be cleared for the next cycle

• Two Stroke Engine• Four operations occur in one revolution• Typically powers smaller engines

• Examples include ultralight aircraft, dirt bikes, lawn mowers, and generators• Compared to four stroke engines

• Typically more powerful• Higher fuel

consumption

• More noise

• Four Stroke Engine• Four operations occur in two revolutions• Typically found in automobiles and small aircraft• Compared to two stroke engines

• More fuel efficient • More quiet• Carburetor

• Mixes fuel and air for engine• Carburetor reduces cross-sectional area of air as it passes through• Air velocity increases and pressure lowers at reduction, creating a vacuum• Draws fuel into vacuum to mix with air• Bernoulli’s Law • Ps= Static pressure; ρ = Density; and V = Velocity.• Also called a Venturi effect• Carburetor only used on gasoline engines (unless fuel injected)• Icing can be a problem• Water vapor condenses in reduced air pressure• Heated air from engine prevents icing

• Turbojet• Simplest and earliest gas turbine• Air flows continuously through engine

• Intake• Compression

• Power (combustion)• Exhaust

• Large amounts of surrounding air are continuously brought into the engine inlet. In England they call this part the intake,

(P s+ρ v2

2 )1=(P s+

ρ v2

2 )2

ExhaustPower

CompressionIntake

Unit 2 AE Reviewwhich is probably a more accurate description, since the compressor pulls air into the engine. We have shown here a tube-shaped inlet, like one you would see on an airliner. But inlets come in many shapes and sizes depending on the aircraft's mission. At the rear of the inlet, the air enters the compressor. The compressor acts like many rows of airfoils, with each row producing a small jump in pressure. A compressor is like an electric fan; therefore, we must supply energy to turn the compressor. At the exit of the compressor, the air is at a much higher pressure than free stream. In the burner a small amount of fuel is combined with the air and ignited. In a typical jet engine, 100 pounds of air/sec is combined with only 2 pounds of fuel/sec. Most of the hot exhaust has come from the surrounding air. Once the hot exhaust leaves the burner, it is passed through the turbine. The turbine works like a windmill. Instead of needing energy to turn the blades to make the air flow, the turbine extracts energy from a flow of gas by making the blades spin in the flow. In a jet engine we use the energy extracted by the turbine to turn the compressor by linking the compressor and the turbine by the central shaft. The turbine takes some energy out of the hot exhaust, but the flow exiting the turbine is at a higher pressure and temperature than the free stream flow. The flow then passes through the nozzle which is shaped to accelerate the flow. Because the exit velocity is greater than the free stream velocity, thrust is created as described by the thrust equation. For a jet engine, the exit mass flow is nearly equal to the free stream mass flow, since very little fuel is added to the stream. The amount of mass flow is usually set by flow choking in the nozzle throat.

•• Turbofan

• Modern military and commercial aircraft• Combines best of high and low speed and altitude performance• Two airstreams

• Center core of air sent through process similar to basic turbojet• Some air passes around this center turbojet• Ratio of two streams is bypass ratio

• A turbofan engine is the most modern variation of the basic gas turbine engine. As with other gas turbines, there is a core engine. In the turbofan engine, the core engine is surrounded by a fan in the front and an additional turbine at the rear. The fan and fan turbine are composed of many blades, like the core compressor and core turbine, and are connected by an additional shaft also called turbo machinery. As with the core compressor and turbine, some of the fan blades turn with the shaft and some blades remain stationary. The fan shaft passes through the core shaft for mechanical reasons. This type of arrangement is called a two spool engine; one “spool" for the fan, one "spool" for the core. Some advanced engines have additional spools for sections of the compressor which provide for even higher compressor efficiency.

• How does a turbofan engine work? The incoming air is captured by the engine inlet. Some of the incoming air, colored blue on the figure, passes through the fan and continues on into the core compressor and then into the burner, where it is mixed with

Unit 2 AE Reviewfuel and combustion occurs. The hot exhaust passes through the core and fan turbines and then out the nozzle, as in a basic turbojet.

• Turbofan Bypass Ratios

•• High bypass ratio turbofan for

civilian aircraft

•• Low bypass ratio turbofan for

military aircraft

• Vflight < Vjet < Vturbojet

• Turbofan Operation

• Gas Turbine Engine• Compressor supplies high pressure air to the combustor where it is heated by burning

fuel• Flow leaving the combustor has a lot of energy• Thrust Producer

•• Shaft Power Producer

•

• The compressor supplies high pressure air to the combustor where it is heated by burning fuel. The flow leaving the combustor has a lot of energy.

• Some of the energy in the hot, high pressure air leaving the combustor is extracted by a high pressure turbine. The high pressure turbine turns this energy into rotating shaft power to turn the compressor.

• The gas energy left over after enough has been extracted to turn the compressor can be used as thrust or power.

• Purpose of a gas turbine engine is to generate thrust to propel an aircraft or to generate shaft power

• Thrust is a force generated by accelerating air• Thrust is rate of change of momentum• FN=W (v j−vo )=Net Thrust

•

W=Air Mass Flow(ms )• vo=Flight Velocity• v j=Jet Velocity

• Turboprop• Turbine engine (with power turbine) turns propeller

PRESSURE

Core turbineCore compressor

Core

BypassLPT 3

LPT 4

LPT 2LPT 1

Sparepressure

Accelerate, slow down, accelerate, slow down, at each stage Very fast core jet

Unit 2 AE Review• Propellers develop thrust by moving large mass of air through small change in

velocity• Used in low speed transport aircraft and small commuter aircraft• Turbo shaft is similar but drives a rotor for helicopters

• To move an airplane through the air, thrust is generated with some kind of propulsion system. Many low speed transport aircraft and small commuter aircraft use turboprop propulsion. On this page we will discuss some of the fundamentals of turboprop engines. The turboprop uses a gas turbine core to turn a propeller. Propellers develop thrust by moving a large mass of air through a small change in velocity. Propellers are very efficient and can use nearly any kind of engine to turn the prop. General aviation aircraft use an internal combustion engine to turn the propeller. In the turboprop, a gas turbine core is used. How does a turboprop engine work?

• There are two main parts to a turboprop propulsion system, the core engine and the propeller. The core is similar to a basic turbojet, which has a compressor, burner, and turbine. However, at the exit of the main turbine the hot exhaust gas is passed through an additional turbine, shown in green before entering the nozzle. Unlike a basic turbojet, most of the energy of the exhaust is used to turn this additional turbine. The turbine is attached to an additional drive shaft which passes through the core shaft and is connected to a gear box. The gear box is then connected to a propeller that produces most of the thrust. The exhaust velocity of the core is low and contributes little thrust because most of the energy of the core exhaust has gone into turning the drive shaft.

• Afterburning Turbojet• Most military fighter jet engines

(turbojet and turbofan) use afterburners

• Helps exceed drag close to sound barrier

• Nozzle extended and fuel injected in hot gases for extra thrust

• Inefficient burn uses a lot of fuel

• Gas Turbine Alternate Uses• Also used to power

• Racing cars• Ships• Electrical power

generators

• Natural gas pumping stations

• Engine Operation Similarity

• Engine Placement• Engine arrangements• Under wing

Intake Compression Ignition Expansion

Unit 2 AE Review• Engine weight close to lift generation• Reduces wing structure

• Rear-fuselage• Mixed under wing and rear fuselage

Rocket Propulsion• Types of Propulsion Systems

• Propeller• Turbine (also called jet)

• Ramjet and Scramjet• Rocket

• Rocket Propulsion• Produces thrust by ejecting stored matter• Rockets can be classified by propulsion

• Liquid• Solid

• Electric

• Other classifications• Expendable or reusable• Number of stages

• Size of payload• Manned or unmanned

• Rockets store their propellants onboard and they function in the vacuum of space where there is little air.

• Liquid and solid fuel rockets store fuel in the rocket and then oxidize (burn) their fuel to produce high pressure gases which create rocket thrust when vented out the end of the rocket. Exhaust and heat are byproducts of the oxidization. Electric propulsion uses a power supply to expel ionized particles.

• Liquid Fuel Rocket• Fuel mixed with oxidizer and burned• Gases escape out nozzle to generate thrust

•• Solid Fuel Rocket

• Fuel burned to generate gases• Gases escape out nozzle to generate thrust

•• Thrust Equation Derivation

Unit 2 AE Review

•• F=mVe+ (Pe−Po ) A• Two forces act together to create rocket thrust: mass ejection and expansion of the gas.• First consider gasses as they change from pressure Po to Pe• Pressure is force/area, so the resulting force on the rocket is proportional to the

pressure difference times the nozzle area: (Pe−Po ) A• The gas is flowing out with a mass flow rate m and velocity Ve.• The momentum of this gas is mVe• Force is proportional to the rate of change of momentum.• This results in a force for mass ejection given by:

•ddt

(mVe )=dmdtVe=mVe

• Impulse Equation Derivation

•• Use of Impulse Equation

• I=∫F (t)dt• Thrust force is a function of time.• Plotting the thrust as a function of time, you can integrate the values to find the area

under the curve.• This means you find the total area under the thrust vs. time curve to determine the total

impulse.• LoggerPro has an integrate function.

Area = Impulse (Ns)Thrust (N)

time(s)

Unit 2 AE Review• Model Rocket Flight Stages

•

• Model Rocket Engine Nomenclature

• Rocket Components and Design• Rocket Applications

• Bell X-1 first to exceed sound barrier

• Space launch vehicles

• Space shuttle• Military missiles• Space tourism

• Bell X-1 was the first supersonic flight. Chuck Yeager served as the test pilot. The X-1 was dropped from a bomber, the liquid propellants, alcohol, and liquid oxygen were mixed and burned to push the aircraft to reach a speed of mach 1.06.

• The space shuttle contains 67 rocket propulsion systems. The most noticeable ones are the two solid rocket boosters, SRB, which straddle the single large liquid oxygen and hydrogen rocket.

• Rocket Components

•• Rocket Stability

• Center of gravity ahead of center of pressure with respect to airflow along rocket

Delay Time(Seconds)

Average Thrust(Newtons)

Total ImpulseCode

(Newton-Seconds)

B6-4

Center of Pressure

Center of Gravity

Unit 2 AE Review

Space Propulsion

• Review of Newton’s Laws• Law of inertia• F = ma• For every action force, there is an equal and opposite reaction force

• Space is frictionless• Small forces result in movement

• Venting gas from spacecraft can cause spinning or undesired movement• Spacecraft frequently adjust direction with small pulses• Each pulse uses fuel• Ion Thruster

• Electric energy expels ions from nozzle• Efficient use of fuel and electrical power• Modern spacecraft to travel farther, faster, and cheaper than any other propulsion

technology currently available• Electric propulsion uses a power supply to expel ionized particles. The ions move at a

high velocity; however, they have little mass. The thrust is limited to travel within space and cannot carry a rocket into space from Earth.

• An ion propulsion system's efficient use of fuel and electrical power enable modern spacecraft to travel farther, faster, and cheaper than any other propulsion technology currently available. Ion thrusters are currently used for station-keeping on communication satellites and for main propulsion on deep space probes.

• Hall Thruster• Uses an electric field to accelerate ions• Uses radial magnetic field to generate an azimuthal Hall current• Hall thrusters use an electric field to accelerate ions, similar to Ion thrusters. Hall

thrusters utilize a radial magnetic field to generate an azimuthal Hall current. This current interacts with the radial magnetic field, producing a volumetric (j X B) accelerating force on the plasma.

• Solar Sail• Uses the sun's energy to enable travel• Bounces a stream of solar energy particles (photons) off of giant, reflective sails• Solar sail propulsion uses the Sun's energy to enable travel through space, much the

way wind pushes sailboats across water. The technology bounces a stream of solar energy particles called photons off of giant, reflective sails made of lightweight material

Unit 2 AE Review40 to 100 times thinner than a piece of writing paper. The continuous pressure provides sufficient thrust to perform maneuvers, such as hovering at a point in space and rotating the space vehicle's plane of orbit, which would require too much propellant for conventional rocket systems.

2.3 Human Factors and Flight Physiology• Human Factors

• Advances in technology have reduced demand for human input• Human input and decision making is often crucial at some level• Pilots and flight crews provide the human component to flight. It is critical that

aerospace designers as well as pilots and flight crews understand the limitations and capabilities of the human body, also called human factors, so that safety and efficiency are maximized at all times.

• Unmanned Ariel Vehicle, UAV, development has is eliminated the need for a human on board the aircraft and has reduced the need for human interaction on the ground.

• Flight Physiology• Pilots and the supporting flight crew provide the human dynamic for flight• The body and mind strengths and limitations impact the design and operation of aircraft

• Incidents and Accidents• More than 70% of aviation accidents and incidents are related to human factors• Most accidents occur as result of a series of incidents• The NTSB contains a wealth of factual information about aviation accidents.

• SHEL Model• Interrelationship between human factors and the aviation environment• SHEL

• S = Software• H = Hardware

• E = Environment• L = Liveware

• A model developed by Edwards and Hawkins of the International Civil Aviation Organization, ICAO, to provide a framework for safety management systems. Liveware is a component of the SHEL model. Liveware is also the central figure that each component will affect. Therefore if the pilot (liveware) has an issue, all systems are affected. If systems have issues, they affect the pilot (liveware).

• Liveware Failure: Incapacitation• Not able to perform at normal levels

• Sudden – Occurs in the moment without warning. A pilot collapse (heart attack, seizure, etc.) could be fatal. If a crew member is present, the first priority is to maintain flight.

• Subtle – Unnoticed by pilot or crew • Total – Completely incapacitated• Partial – Fatigued, sick, etc.• Distraction – Personal issues, control issues, etc.• Recognized or Unrecognized – Does the pilot recognize that an issue exists?

• Human Body System• A human body has multiple systems which impact aircraft and spacecraft design• Understanding these systems help Aerospace Engineers design safer vehicles

• Cardiovascular System

Unit 2 AE Review• Maintains an uninterrupted blood movement including oxygen, carbon dioxide,

nutrients, and waste• The heart pumps blood into arteries, capillaries, and then tissue and cells

• Central Nervous System• Collects, transfers and processes information with the brain and spinal cord• The brain controls physiological, mechanical, and mental functions through electrical

and biochemical signals. The spinal cord Bundle of nerves located in the spine that allow the signals transmitted from the brain to travel to other parts of the body. Nerves deliver information to and from the central nervous system and provide feedback to control breathing, digestion, heart rate, blood pressure, etc.

• Musculoskeletal System• Support bones• Allows for movement• The muscular and skeletal systems work together to move the human body. Muscles

contract, or shorten, and pull on bone to bring about movement. Muscles are connected to bones by tissue called tendons. Skeleton are made up of bones. Muscles pull on bone to bring about movement. Tendons link bone and muscle.

• Respiratory System• Exchange oxygen and carbon dioxide into and out of the blood stream through lungs

• Metabolic System• Allows all body systems to work together• Converts resources into substances, chemicals, and energy to support brain and body

activity• The metabolic system is comprised of the liver, gallbladder, kidneys, pancreas, thyroid.

• Vestibular System• Crucial for

• Balance • Sense of spatial orientation

• Impact on aviation• Helps to maintain

orientation• Can give confused

messages