ASCI 356: Exam 1 Review

stress

force applied

strain

Result of stress force

Tension (stressor)

a pulling force that stretches or attempts to pull a structural member apart (pressurizing)

Torsion (stressor)

a twisting force that acts around a structural member's longitudinal (lengthwise) axis

Compression (stressor)

a crushing or squeezing stress that tends to shorten, press together, or reduce the size of a structural member

sheer force (stressor)

a force acting parallel to a material's surface or cross-section, causing internal layers to slide past one another

Bending (force)

compression and tension forces applied together upon a structure

deformation

a change to the shape or form of a object/material

Elastic Deformation

deformation can be reversed

Plastic Deformation

object/material will never be original shape again

strongest geometric shape

circle

stress concentration

a location in an object where the stress is significantly greater than the surrounding region

Which Diagram is stress and which is strain

DeHavilland Comet

hidden metal fatigue to form and rapidly spread around sharp structural corners, leading to catastrophic mid-air fuselage failure

Truss Type Fuselage

rigid framework and frabric (wood to metal) only good for bending/compression and can't carry anything (INCLUDE IMAGE)

Flight Control Surface

actively steers the airplane

Stabilizer

keeps the aircraft steady and level (does not move)

Tapered Wing

Trapezoid shaped wings that are smaller and induce less drag on the aircraft

spars (false)

run the span of the wind (vertical)

ribs (false)

run from the bleeding to trailing edge of wing (horizontal)

cantilever wing

has sufficient internal support structures to keep it steady in its location, does not have any external support

Lamination (single cut pieces)

bonding multiple thin layers of a material to a structure, making it stronger. Has variable thicknesses depending on stress area

stress skin

transferring load concentration from one stress area to the rest of the aircraft (Skin → rivet → rib → stringers and spars)

Know how to label parts of wing

Know how to label parts of fuselage

bulkhead

a vertical structural partition or dividing wall built across the fuselage to separate different compartments, support the airframe, and maintain cabin pressure

frame/former

internal structural cross-members in an aircraft fuselage that establish its shape and support the outer skin

skin (fuselage term)

the outer covering of the fuselage that provides aerodynamics and protects internal structures from environmental forces

longeron (fuselage term)

a primary, continuous longitudinal structural member in an aircraft fuselage that runs lengthwise to carry major bending and axial loads

bulkhead (fuselage term)

a solid, upright wall or partition built inside an aircraft's fuselage

stringer (fuselage term)

a lightweight longitudinal structural member attached to the inside of an aircraft's skin and formers to reinforce the skin

C-172 Fuselage

All metal – semi-monocoque​

• Bulkheads, stringers, skin​

Front and rear carry-through spars​

• Front: 2 attachment points​

• Rear: 1 attachment on partial span spar​

4 engine mount stringers from door forward​

Externally braced wings​

Integral fuel tanks​

Vertical stabilizer has 1 spar​

Horizontal stabilizer has 2 spars​

Lead acid battery

• pink/red

• Used in most GA aircraft

• Most common

• Most affordable

• Easier to determine condition

Nickel Cadmium battery

• Typical in Turbine Powered aircraft​

• More Expensive​

• Can meet higher current demand​

• Can thermal runaway​ - low internal resistance

• Require bench testing​

• Steady voltage until “cliff”​

Lithium Ion battery

• new technology

• significant wieght reduction

• high energy storage

• reduced maintainance

• can thermal runway

• lots of heat and vapor issues

• unreliable when not in between 20 and 80 %

What are the three batteries and which line represents which

Refer to diagram

Battery Basics

• Converts chemical energy into electrical energy

• Only produces DC power

• batteries come with an ampere hour rating (current flow x time)

current flow

the movement of electrons through a conductor measures in ampperes.

rectifier

converts AC into DC power

inverter

converts DC into AC power

Factors affecting resistance

• Type of conductor material used​

• Length of conductor material​

• Cross-section of conductor material​

• Temperature of conductor material​

What type of energy does resistance make

heat and/or light

Types of resistance

• variable

• fixed

Voltage

Electrical pressure measured in volts. Most small aircraft use a 14-volt or 28-volt Direct Current (DC) system.

Conductors

conduct electrical current; have a few loosely bound electrons that will move​

Insulators

do not conduct electrical current very well; do not produce free electrons

ammeter

an instrument used to measure the amount of electrical current flowing through a circuit, measured in amperes (amps)

voltmeter

an instrument used to measure electrical pressure or potential difference between two points in a circuit, measured in volts

loadmeter

measures the total electrical current being generated by an aircraft's alternator or generator

relay

(usually a switch) Uses a small amount of to control a large amount of current​

open circuit

electrons are NOT flowing

closed circuit

electrons are flowing

AC Power

Current that flows back and forth in the circuit (alternating)

DC Power

Current that flows in one direction

loadshedding rules

• turn the things off that take the most energy (if it spins, lights up, or heats up, it takes a lot of power)

• do not turn anything off if you do not know what the consequence will be

• If still upright, start load shedding gradually

• If on fire or not staying upright, turn the entire electrical system off and add only what you need

4 ammeter cases

• slightly to right (+5 amps) = stable flying conditions, battery is charging

• slightly to left (-5 amps) = battery is not charging and is loosing power gradually

• all the way to right (+20 amps) = too much current in flowing into battery (bad regulator)

• all the way to left (-20 amps) = engine not working, plane on battery power (start loadshedding)

AC Electrical System Requirements for Aircraft

• 115 V

• 3-phase

• 400 hz

Amppere Hours Math Problems

Refer to class notes

Battery (electrical symbol)

fuse (electrical symbol)

relay (electrical symbol)

switch (electrical symbol)

rotary switch (electrical symbol)

Resistor (electrical symbol)

Constant Speed Drive (CSD)

• AC Generators need a faily consistent speed input

• CSD takes varying engine accessory gearbox output speeds and gives gen a constant input speed

Alternator

an engine-driven electrical component that converts mechanical energy into alternating current

Bus

a central electrical conductor or junction that distributes power from a source

Generator

an engine-driven machine that converts mechanical rotation into electrical energy

Inverter

an electrical component that converts direct current (DC) power from the aircraft's battery or generator into alternating current (AC)

Transformers

changes the voltage level of an existing AC power supply using electromagnetic induction

Switch

a specialized electrical or mechanical control device used to start, stop, or redirect current flow

C-172 Electrics

• 28-v dc electrical system​

• 24-volt battery​

• 60-amp alternator (belt driven)​

• 2 primary buses with (connected between them)

  • Essential bus​

  • Crossfeed bus​

• Standby battery

• Master switch = primary buses energized​

  • Each powers an avionics bus​

Hydraulic Actuators

transforms fluid pressure into mechnical force

• housing

• piston

• seals

Linear actuator

uses pressurized fluid to create straight-line push-and-pull motion

rotary actuator

a specialized mechanical or fluid-powered device that converts input energy into controlled rotational force, tansforming hydraulic pressure

single action actuator

operates under hydraulic or pneumatic pressure in only one direction, relying on an internal mechanical spring or external load to return the piston

double action actuator

uses hydraulic fluid or pneumatic pressure on both sides of a piston to power movement in two directions

Hydraulic Resevior

• A tank where hydraulic fluid is stored and returned​

• Replaces fluid lost through leakage​

• Servicing point​

• Overflow for fluid expansion​

• Place to purge air bubbles​​

Types of valves

Constant displacement pump

• Converts mechanical force into pressure.

• Moves an unchanging volume of fluid during every single rotation or stroke, no matter how high or low the system pressure gets

• Must incorperate pressure relief valve

Qualities of hydraulic oil

• well suited to transmit and distribute force

• Depending on the system the fluid requirements are different depending on:

  • System pressures​

  • Temperatures (inside & outside)​

  • Corrosion​

• Qualities that matter:

  • Low viscosity

  • Chemically stable

  • High flash point

Flow control valves

controls the speed and/or direction of fluid flow in the system

pressure relief valve

• open at a preset system pressure and route fluid away and/or back to reservoir​

• Prevents failure or rupture of other hydraulic components​

selector valve

• control the direction of movement of a hydraulic actuating cylinder or similar device

• The pilot valve receives the actual controlling input and then steers hydraulic fluid to the actuator

check valve

allows fluid to flow impeded in one direction, but prevents or restricts fluid flow in the other direction

proof pressure

the maximum safe pressure a device can handle without permanent damage or calibration shifts

ultimate pressure

the absolute limit where the component suffers structural rupture or catastrophic failure

closed center hydraulic system

• More used in aircraft because of instantaneous response​

• Faster​

• Always under continuous pressure​

• Pressure surges are greater​

• Not as smooth​

open center hydraulic system

• Because of less responsive, not used as much in aircraft​

• Slower​

• Not always under continuous pressure​

• Pressure surges are less​

• smoother

hydraulic system math

Input Force x Distance = Output Force x Distance​

components of basic hydraulic system

• Reservoir​

• Pump​

• Filter​

• selector valve​

• relief valve​

• actuator​

Examples of hydraulic systems

• Landing gear

• breaks

• propellers

Hydraulic heat exchanger

• Hot hydraulic fluid temps are used to preheat fuel​

• Cool fuel temps are used to remove heat from hydraulic fluid​

Label Selector Valve Diagram (Including the position each diagram is in)

DA-42 Hydraulic System

• Brakes​

  • Hydraulically actuated​

  • Individually controlled​

• Propeller​

  • Hydraulically controlled​

  • To DECREASE prop pitch, oil is pumped into the hub​

  • Prop governor has its own accumulator​

• Landing gear​

  • Electric gear pump may take 5-20 second to charge system from zero​

  • Powered by hydraulic pump​

  • Hydraulic valves are electrically actuated​

  • Hydraulic pressure “lock” keeps the landing gear retracted​

  • Hydraulic accumulator is part of twinstar hydraulic system​

Hydraulic Reservoir Functions

• A tank where hydraulic fluid is stored and returned​

• Replaces fluid lost through leakage​

• Servicing point​

• Overflow for fluid expansion​

• Place to purge air bubbles​

Types of Hydraulic Resevoirs

• Two types:​

  • Non-Pressurized​

    • Right-side up aircraft​

    • Fly in lower altitudes​

  • Pressurized​

    • Often found in airliners and mil aircraft

fill port (hydraulic pump)

A dedicated fluid entry point on a hydraulic pump or reservoir assembly

vent port (hydraulic resevoir)

allows the tank to breathe and maintain atmospheric or regulated pressure

baffles (hydraulic resevoir)

internal metal plates that prevent fluid sloshing, reduce turbulence, and separate air and heat from the hydraulic oil