Unit 2 AE Review
2.1 Material Structures
Aerospace Materials
 Commonly Used Aerospace Materials
o Wood
o Titanium alloys
o Fiber-reinforced composites
o Steel
o Magnesium alloys
o Aluminum alloys
o Nickel alloys
 Factors for Selecting Materials
o Function
 What is the component used for?
o Material Properties
 Strength to weight ratio
 Resistance to corrosion
 Stiffness
 Fatigue and effects of
 Toughness
environmental heating
o 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 Mind
o Reducing material density reduces airframe weight and improves performance
 Fuel efficiency
 G-force loading
 Climb rate
o Material density reductions are 3 to 5 times more effective than increasing tensile strength, modulus, or
impact resistance
Early Aircraft Built of Wood
o Wright Brothers used Spruce
o Rot and insect damage
o Widely available
o Natural product lower consistency than man-made
o Uniform piece to piece
o Rarely used today in production aircraft
o Good strength to weight ratio
o Used today in homebuilt and specialty, low-volume
o Different properties in different
production
directions
o Chinese have selected oak for the heat shield of a
o Easy fabrication and repair
reentry vehicle
o Sensitivity to moisture
o 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 Alloy
o Cutting-edge (1920s-60s)
o Most abundant metal in the earth’s crust
o Pure aluminum is relatively soft
o 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 material
o Readily formed
o Moderate cost
o Excellent resistance to chemical corrosion
o Excellent strength to weight ratio
o Strength and stiffness are affected by:
o Form
 Sheet
 Bar
 Forging
 Plate
 Extrusion
o Heat treating and tempering
Unit 2 AE Review
 Stronger aluminum more brittle
Ductility is the amount of plasticity that precedes failure.
Brittleness is a lack of ductility. This is often confused with lack of strength.
Most common alloy is 2024 (24ST)
 93.5% aluminum, 4.4% copper, 1.5% manganese, and 0.6% magnesium
o High-strength applications – 7075 – 7050 – 7010
 Zinc, magnesium, and copper
o Sheet aluminum is clad with a thin layer of pure aluminum for corrosion protection
o 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 fabricate
o First utilized in fuselage construction
 Steel tubing replaced wire-braced wood construction
o Today’s applications:
o High strength and fatigue resistance
 Wing attachment fittings
o High temperatures
 Firewalls and engine mounts
o Alloy of iron and carbon
o Carbon adds strength to soft iron
o As carbon content increases, strength and brittleness increase
o Typical steel alloys are1% carbon
o Other common alloy materials –
 Chromium, molybdenum, nickel, and cobalt
o Properties of steel are influenced by heat treating and tempering
o Same alloy can have moderate strength and good ductility or high strength and brittleness, depending
on heat treatment
o Materials temperature is raised to1400-1600 °F - The point at which carbon goes into solid solution with
the iron
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.
Aerospace Materials – Titanium
o Greater strength to weight ratio and stiffness than aluminum
o Capable of sustaining temperatures almost as high as steel
o Corrosion-resistant
o 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 stresses
o Seriously affected by any impurities
o Most impurity elements – Hydrogen, oxygen, and nitrogen
o Higher fabrication cost
o Expensive – 5 to 10 times as much as aluminum
o 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 components
o Lower-speed aircraft, high-stress airframe components
o Uses include landing gear beams and spindles for all moving tails
o Super Plastic Forming/Diffusion Bonding (SPF/DB)
o Extreme temperature and pressure causes titanium to flow into the shape of the mold.
o
o
o


Unit 2 AE Review
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 ratio
o Tolerates high temperatures
o Easily formed – Casting, forging, and machining
o Uses include engine mounts, wheels, control hinges, brackets, stiffeners, fuel tanks, and wings
o Prone to corrosion – must have a protective finish
o Flammable
o Should not be used in areas that are difficult to inspect or where the protective finish could erode away
Aerospace Materials – High Temperature Nickel Alloys
o Inconel, Rene 41, and Hastelloy
o Suitable for hypersonic aircraft and reentry vehicles
o Hastelloy is used primarily in engine parts
o Nickel alloy honeycomb sandwich is used for the stealth nozzles of the F-117
o Heavier than aluminum and titanium
o Difficult to form
Aerospace Materials – Composites
o Mid 1960s and early 1970s
o Empennages of the F-14 and F-15
o 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 fins
o 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 stabilizer
o Modern fighters consist of 20% composite material
o 15-25% weight savings depending on structure
o Boeing 787 uses upward of 50% composites and includes composite wing and fuselage
Aerospace Materials – Ceramic
o High temperature resistance
o Uses include engine exhaust nozzles
o 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.
Lead 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.
Unit 2 AE Review







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.
σ
o E= ϵ
Tension Stress
o A body being stretched
o Applied load divided by cross-sectional area
𝐹
o σ= 𝐴
Compression
o A body being squeezed
Strain
o



ϵ=
o
o
The shape of the cross section is not important
Appropriate cross section is the smallest area in
the loaded part
𝛿
𝐿0
Calculating Beam Deflection
o ΔMax = F L3/ 48 E I
Statics
o The study of forces and their effects on a system in a state of rest or uniform motion
Equilibrium
o 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 velocity
o Translational equilibrium: The state in which there are no unbalanced forces acting on a body
 F =0
 F =0
x
o
o
o
y
Rotational equilibrium:
The state in which the sum of all clockwise moments equals the sum of all counterclockwise
moments about a pivot point
M=0

o
o Moment = F x D
Truss Analysis
o Primary truss loads – loads calculated with ideal assumptions
o Used in welded steel-tube fuselages, piston-engine motor mounts, ribs, and landing gear
o Engine Mount Example
 Line of force is from the center of gravity of the engine
 Rigid connection from the fuselage and engine to the truss
Unit 2 AE Review
3,200lbf

Composites
 Advantages of Composites
o Strength-to-weight ratio
o Easy to shape
o Long life
o Tailored strength characteristics
o Dampen vibration
o No corrosion
o Easy to repair
 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 common
o Boron – Strongest
o Graphite – Good strength-to-weight ratio
o Silicon Carbide – Ceramics reinforcement
o Kevlar – Toughest
 Using Composites Safely
o Areas at risk:
 Vision
 Liquids
o Resins
o Initiators (MEKP)
o Solvents
 Solids
o Dust
o Particles
 Symptoms
o Watering eyes
o Itching
o Redness
o Burning
o Swelling
 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 Resins
o Solvents
o Mold release
 Foams
 Dust
 Symptoms
o Redness
o Burning
o Rash
o Dry or cracking skin
o Itching
Unit 2 AE Review

Protection
o Cover your skin
o Gloves
 Respiratory
Fiber Selection Considerations
o Performance needs
o Cost
Performance Considerations
o Required strength
o Strength vs. cost ratio
o Operating environment


Forces
Squeezing
Stretching
Bending
Sliding
Twisting
o
o
o
Latex (potential reaction)
Nitrile
Vinyl
o
Availability
Engineering term
Compression
Tension
Bending
Shear
Torsion
Type of
Material
Aluminum
Strength in
Tension
3
Strength in
Cost Weight
Compression
2.5
9
2
Steel
4
2
6.8
9
Pros and Cons
Applications
Pros: Lightweight, doesn’t rust,
strong in compression and tension
Cons: Expensive
Pros: One of the strongest
materials used in construction.
Strong in tension and
compression.
Cons: Rusts, loses strength in
extremely high temperatures.
Airplane wings,
boats, cars,
skyscraper skin.
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
Plastic
Strength in
Tension
3
Strength in
Compression
3
Cost
Weight
9
1.5
Pros and Cons
Applications
Pros: Flexible, lightweight, long Umbrellas, inflatable
lasting, strong in compression
roofs over sports
and tension.
arenas.
Cons: Expensive
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.
Ceramics
Type of
Material
Brick
Strength in
Tension
1
Strength in
Compression
2.5
Cost Weight
Pros and Cons
Applications
Pros: Cheap and strong in
Walls of early
compression
skyscrapers and
Cons: Heavy and weak in tension. 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.
Composites
Type of
Material
Wood
Reinforced
Concrete
2.25 4
Strength in
Tension
2.5
Strength in
Compression
1.5
Cost
Weight
Pros and Cons
Applications
1
4
Bridges, houses, two and
three story buildings,
roller coasters.
2
3.5
4.5
6
Pros: Cheap, lightweight,
moderately strong in
compression and tension.
Cons: Rots, swells and
burns easily.
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
Tensile Strength
Elongation at Break (if available)
Gravity
(Yield)
Steel
7.70 g/cc
450 MPa
20.0 %
3
(AISI Type S14800 Stainless 0.278 lb/in
65,300 psi
Steel condition A)
Aluminum
2.70 g/cc
>= 276 MPa
8.00 %
(6061-T8)
0.0975 lb/in³
>= 40,000 psi
Plastic
0.549 - 1.85 g/cc
1.90 - 57.4 MPa
20.0 - 720 %
(PVC, Extruded)
0.0198 - 0.0668 lb/in³
Wood
0.310 - 0.360 g/cc
1.59 MPa
n/a
(American Sitka Spruce)
0.0112 - 0.0130 lb/in³
230 psi (Ultimate)
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.
𝑇𝑒𝑛𝑠𝑖𝑙𝑒 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ
𝑇𝑒𝑛𝑠𝑖𝑙𝑒 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ
𝑅𝑎𝑡𝑖𝑜𝑆𝑡𝑒𝑒𝑙 =
𝑅𝑎𝑡𝑖𝑜𝑃𝑉𝐶 =
𝐷𝑒𝑛𝑠𝑖𝑡𝑦
𝐷𝑒𝑛𝑠𝑖𝑡𝑦
1.90 𝑀𝑃𝑎
450 𝑀𝑃𝑎
𝑅𝑎𝑡𝑖𝑜𝑃𝑉𝐶 = 1.85 𝑔/𝑐𝑐
𝑅𝑎𝑡𝑖𝑜𝑆𝑡𝑒𝑒𝑙 = 7.70 𝑔/𝑐𝑐
𝑀𝑃𝑎
𝑀𝑃𝑎
𝑅𝑎𝑡𝑖𝑜𝑃𝑉𝐶 = 1.03
𝑅𝑎𝑡𝑖𝑜𝑆𝑡𝑒𝑒𝑙 = 58.4
𝑔/𝑐𝑐
𝑔/𝑐𝑐
Note: The values used reflect the most conservative
ratio.
𝑅𝑎𝑡𝑖𝑜𝐴𝑙𝑢𝑚𝑖𝑛𝑢𝑚 =
𝑇𝑒𝑛𝑠𝑖𝑙𝑒 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ
𝐷𝑒𝑛𝑠𝑖𝑡𝑦
276 𝑀𝑃𝑎
𝑇𝑒𝑛𝑠𝑖𝑙𝑒 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ
𝐷𝑒𝑛𝑠𝑖𝑡𝑦
1.59 𝑀𝑃𝑎
𝑅𝑎𝑡𝑖𝑜𝐴𝑙𝑢𝑚𝑖𝑛𝑢𝑚 = 2.70 𝑔/𝑐𝑐
𝑅𝑎𝑡𝑖𝑜𝐴𝑙𝑢𝑚𝑖𝑛𝑢𝑚 = 102.2
𝑅𝑎𝑡𝑖𝑜𝑆𝑝𝑟𝑢𝑐𝑒 =
𝑅𝑎𝑡𝑖𝑜𝑆𝑝𝑟𝑢𝑐𝑒 = 0.360 𝑔/𝑐𝑐
𝑀𝑃𝑎
𝑔/𝑐𝑐
𝑅𝑎𝑡𝑖𝑜𝑆𝑝𝑢𝑐𝑒 = 4.42
𝑀𝑃𝑎
𝑔/𝑐𝑐
Unit 2 AE Review
2.2 Propulsion
Review 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
• Drag
• Lift
• 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
• Payload: Passengers and cargo
• Fuel: Decreases during flight
• 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
• Engine Categories
• Reciprocating (contains pistons)
• Gasoline-powered
• Two stroke
• Four stroke
• Diesel-powered (not typical in aircraft)
• Turbine
• Turbojet
• Turbofan
• Turboprop
Unit 2 AE Review
•
•
•
•
•
• 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
• More noise
• Higher fuel consumption
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
𝜌v 2
𝜌v 2
(𝑃𝑠 +
) = (𝑃𝑠 +
)
• Bernoulli’s Law
2 1
2 2
Exhaust
• Ps= Static pressure; ρ = Density; and V = Velocity.
Power
• Also called a Venturi effect
Compression
• Carburetor only used on gasoline engines (unless fuel injected)
Intake
• 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
• Power (combustion)
• Compression
• Exhaust
• Large amounts of surrounding air are continuously brought into the engine inlet. In England they call this
part the intake, which 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
Unit 2 AE Review
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 fuel 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
•
•
PRESSURE
•
•
•
•
High bypass ratio turbofan for civilian
aircraft
Vflight < Vjet < Vturbojet
Turbofan Operation
Low bypass ratio turbofan for military
aircraft
Core turbine
Core
compressor
Accelerate,
LPT 1
slow down,
LPT 2
accelerate,
slow down,
at each stage
Bypass
LPT 3
LPT 4
Spare
pressure
Very
fast core jet
Core
Unit 2 AE Review
•
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(v𝑗 − v𝑜 ) = 𝑁𝑒𝑡 𝑇ℎ𝑟𝑢𝑠𝑡
𝑚
• v𝑗 = 𝐽𝑒𝑡 𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦
• 𝑊 = 𝐴𝑖𝑟 𝑀𝑎𝑠𝑠 𝐹𝑙𝑜𝑤 ( )
𝑠
• v𝑜 = 𝐹𝑙𝑖𝑔ℎ𝑡 𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦
Turboprop
• Turbine engine (with power turbine) turns propeller
• 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
• Nozzle extended and fuel injected in hot gases for extra
and turbofan) use afterburners
thrust
• Helps exceed drag close to sound barrier
• Inefficient burn uses a lot of fuel
Gas Turbine Alternate Uses
• Also used to power
• Racing cars
• Electrical power generators
• Ships
• Natural gas pumping stations
•
•
•
Unit 2 AE Review
•
Engine Operation Similarity
Intake
Compression
Ignition
•
Expansion
Engine Placement
• Engine arrangements
• Under wing
• Engine weight close to lift generation
• Reduces wing structure
• Rear-fuselage
• Mixed under wing and rear fuselage
Rocket Propulsion
• Types of Propulsion Systems
• Propeller
• Ramjet and Scramjet
• Turbine (also called jet)
• Rocket
• Rocket Propulsion
• Produces thrust by ejecting stored matter
• Rockets can be classified by propulsion
• Liquid
• Electric
• Solid
• Other classifications
• Expendable or reusable
• Size of payload
• Number of stages
• 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
Unit 2 AE Review
•
•
Thrust Equation Derivation
•
•
•
•
•
•
𝐹 = 𝑚̇𝑉𝑒 + (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 𝑚̇ 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:
𝑑
𝑑𝑚
(𝑚𝑉𝑒) =
•
𝑉𝑒 = 𝑚̇𝑉𝑒
𝑑𝑡
𝑑𝑡
Impulse Equation Derivation
Thrust
(N)
Area = Impulse (Ns)
•
•
Use of Impulse Equation
• 𝐼 = ∫ 𝐹(𝑡) 𝑑𝑡
• Thrust force is a function of time.
time(s)
• 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.
Unit 2 AE Review
•
Model Rocket Flight Stages
•
•
Model Rocket Engine Nomenclature
Total Impulse
Code
Delay Time
(Newton-Seconds)(Seconds)
B6-4
•
•
•
Average Thrust
(Newtons)
Rocket Components and Design
• Rocket Applications
• Bell X-1 first to exceed sound barrier
• Military missiles
• Space launch vehicles
• Space tourism
• Space shuttle
• 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
Center of Gravity
Center of Pressure
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 40 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.
Unit 2 AE Review
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
• E = Environment
• H = Hardware
• 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
• 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
Unit 2 AE Review
•
•
•
•
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