Engineering mechanics and hydraulic

weight (aircraft)

force of gravity

Lift

upward force on wings . complicated phenomoen which can be explained through two principles

Lift (Bernoulli's Principle) (4 lines)

 the curved shape of the Wing causes 

↑ moving air =↓ pressure

↓ moving air =↑ pressure

= lift

Lift (Newton 3rd Law)

action of wing changing direction of downward air = in an equal and opposite upward force (lift).

Thrust (need, law and application of law)

necessary to overcome drag and maintain or increase speed.

Uses Newton's Third Law

action of air(hot gas) = in an equal and opposite forward force(jet goes forward)(thrust).

Drag

air resistance expeirenced by airplane

Total Drag

sum of all drag forces action on airplane

Induced Drag

total drag force associated with production of lift

Parasitic Drag

total drag force NOT associated with production of lift

Lift to drag ratio

Ratio of lift vs drag at any particular angle of attack

Typical training aricraft L/D Ratio and aspect (x, x)

12:1, 8

What changes built wing L/D Ratio

when building (wing design) in flight: angle of attack and extension of flaps

L/D basic formula

L/D = L(lift) /D(drag)

L/D formula with tan θ

tan θ = D/L

L/D = 1/tan θ

Effect of angle of attack

angle of attack determines angle between the wing and the oncoming relative airflow

Angle of attack & lifting force relationship and how this relationship stop

angle of attack higher = more lifiting force

angle of attack less = less lifting force

Up to a critical point then it stalls

3 types of Moments (PRY)

Pitching: Rotation about lateral axis

Rolling: Rotation about longitudinal axis

Yawing: Rotation about vertical axis

Elevator what is it and what does it do

Moveable surfacer at rear of plane which when changed, directly changes angle of attack.

1. If in question plane is level

2. If in question plane is straight constant level

1. & 2. weight = lift

2. thust = drag

Bernouli’s Principle & Connection to plane

increase in velocity of fluid = decrease in pressure

air acts like fluid for flow and pressure

Venturi effect

when fluid flows through a constriction,

velocity increases = pressure decreases

velocity decreases = pressure increases.

Airflow around plane (what does it depend on)

pattern of airflow around plane depends on shape

Streamline/laminar flow (molecule path & drag)

when molecules follow same path = least amount of drag

Turbulent flow

when suceeding molecules no longer follow streamline flow, point where air becomes turbulent = transition point

Point of seperation in Turbulent flow

when airflow cant follow contours,

point where it seperates = seperation point

3 types of aerofoils (f,c,cf)

flat: Breaks airflow. Increases Drag

Curved: Increased Lift, reduced drag compared to flat
curved, fat: More strength and space to store fuel compared to curved aerofoil.

3 types of Aerofoil Cross-section & effect (WC,S,S)

Well cambered:Increased lift but slow

Slender: Fast

Symmetrical: neutral pitching characteristics

Airframes forces

transfers lift to support aircraft while resisting lift,thrust/turbulence, ground support

Frames

They can be pinjointed or welded

Thinwalled vs Triangulated Truss

Truss is easiest and cheapest to repair, but not as failsafe as thin-walled tube.

Forces on beams (SS & CL)

simply supported: bending and shear

cantilever beams: tension, compression and bending stress

Forces on Thin-walled tubes

torsion & tensile stress

Forces & possible problems on wings

Static load, compression, stress corossion cracking

Forces on Fuselages

Bending stress, pressurisation & tension

Forces on Spars, frames, ribs

Loaded in bending stresses

3 considerations (LG,CS, V)

Landing gear: Either takes up space OR increases fuel and drag
Control surfaces: structural stiffness and must not fail
Vibrations: Must keep it acceptable so has to be dampened

5 Types of stresses on aircraft (TCTSB)

Tension: Pulling/stretching force

Compression: Pushing/reduction force

Torsion: twisting force; moments or torque

Shear: sliding one part over another

Bending: Combination of tension and compression

Piston Engines

horizontally opposed pistons which use dual independent ignition systems running in parallel

Piston Engine Uses

Light Aircraft

Turbojet engines

Follows brayton cycle of intake- compression - combustion - turbine . Then in engines - exhaust

Turbojet engine uses 3

High speed military aircraft, early commercial jets and supersonic jets

Tubroprop engines

Follows modified brayton cycle: intake- compression - combustion - turbine - power tubine and propellor.

Turboprop uses ( 3 description but still one thing)

Short haul, low-speed & alitude aircraft

Turbofan engine

same as turbojet but has additional fan stage

Tubrofan uses (4)

large commercial airliners, cargo planes, private jets and military aircraft

Ramjet

shape of enginer compresses air, fuel sprayed ignted gas goes out. has no moving parts and bad at takeoff/landing.

Ramjet uses

missiles and target drones

Scramjet

supersonic combustion ramjet; similar to ramjet but uses supersonic air instead

Scramjet uses

experimental aircraft and space planes

Rockets

air propellants are burned to form gas which is then expelled at extreme velocity. action of gas ejection - reaction of movement of rocket.

Can be liquid or solid

Rocket uses

military warheads and space flight

Pascal’s Principle

“if the pressure at any point in a liquid (or air), that is enclosed and at rest is changed, then the pressure at all points in the liquid changes by the same amount.”

Pascal’s Principle Formula

P=F1/A1 = F2/A2

Dynamic pressure & 2 key factors

pressure created by movement

speed of body relative to air.

density of air

Hydrostatic (Static) pressure key factor

The weight of air molecules above a point due to gravity.
Altitude

Hydrostatic vs direction

H: Acts equally in all directions
D: Acts in the direction of the relative wind (hitting the object).

Hydrostatic vs dynamic wall interaction

H: Acts perpendicular to the wall of a vessel
D: Exerts "extra" pressure above the ambient static level.

Dynamic pressure formula

½ρ V²

Where ρ (pronounced rho) is the air density and V is the relative airspeed of the body.

Hydrostatic pressure formula

P = ρgh

Altimeter

Instrument which has sealed wafer (aneroid capsule) inside which expands depending on atmospheric pressure which indicates height.

How does altimeter work

• As the plane climbs, atmospheric pressure drops. The sealed capsule expands.

• A mechanical linkage translates this expansion into the movement of needles on the dial which shows height

Pitot Tube

Measures speed using by comparing static pressure ( ambient pressure around plane) and stagnation pressure (air rammed into tube.

How does pitot tube work?

Difference between Total Pressure and Static Pressure = Dynamic Pressure.

This tells the pilot how fast they are moving through the air.

Actuating cylinder

converts hydraulic or fluid power into movement or mechanical power

Hydraulic System functions (3)

• Landing gear: Extending and retracting heavy wheels.

• Control surfaces: Moving flaps, ailerons, and rudders against high-speed wind resistance.

• Brakes: Providing the high force required to stop a landing aircraft.