AMT 287 Exam 2 (mine)

powerplants exam 2

the two main variables in the production of power

manifold absolute pressure (MAP) and RPM

relationship of MAP, RPM, and power

if one remains constant and another increases, the last will increase

factors affecting power

humidity, temperature, mixture, ambient pressure, friction loss, altitude effect, power settings

the effect of humidity on power _____ as temp _____

decreases; decreases

humidity effects become inconsequential at _______ altitudes

high

___ O2 molecules will be present in a cylinder full of ____ air so ____engine power can be expected from _____ air

more; cold; more; cold

general rule for temp and HP

for each 6 deg C below std, 1% more HP is produced; for each 6 deg C above std, 1% less HP is produced

if the throttle is fixed in the open position, MAP will vary with the amount of what?

ambient pressure and friction loss in the intake manifold

if the engine is not running, pressure in the intake manifold (MAP) will be ____ to ambient pressure

equal

ambient pressure decrease during climb

1 in of Hg per 1000 ft of alt

critical altitude

alt where the throttle is fully open in order to achieve the desired power setting

the desired power setting ____ be maintained above critical altitude

cannot

most normally aspirated reciprocating engines in GA a/c are designed to produce continuous power w/ economical operation and long life if operated at or below what % of their sea level rated power?

75%

100% power is only available when?

at sea level and full throttle

for any given % power and RPM, ____ manifold pressure is req’d to achieve the same power setting as altitude increases

less

most important rule for the pilot to follow with regards to engine operation

keep all operations within the limitations established by the manufacturer

when reducing power, reduce what first?

MAP

when increasing power, increase what first?

RPM

dieseling

engine running without ignition

keep what high during power changes?

RPM

superchargers

driven directly from the engine, using some of the power produced by the engine; compress the fuel:air mixture before it is mixed w/ the fuel

turbochargers

driven by the hot, high-velocity exhaust gasses that are being expelled from the engine

turbo-supercharger

an engine system that both boots the air pressure before the carburetor and further boots pressure of the fuel:air mixture

advantages of flying at high altitudes

• fly above icing conditions, turbulence, and high terrain

• utilize beneficial winds aloft

• enjoy a lower traffic density

• better speed

stage

each increase in the pressure of the air or fuel:air mixture in an induction system

types of engines that superchargers are found on

high-horsepower radial engines

main parts of a turbocharger

compressor assembly, exhaust gas turbine assembly, pump and bearing casing

how turbochargers derive their power

from the energy of engine exhaust gasses directed against some form or turbine

parts of a compressor assembly

impeller, diffuser, casing

impeller

gives the air high velocity

diffuser

direct the airflow and converts the high velocity of the air to high pressure

casing

where the air enters for the induction system

exhaust gas turbine assembly parts

turbine (bucket) wheel, nozzle box, butterfly valve (wastegate), and cooling cap

turbine wheel

driven by exhaust gasses and drives the compressor impeller

what drives the turbine wheel

exhaust gasses

nozzle box

collects and directs the exhaust gasses onto the turbine wheel

wastegate

regulates the amount of exhaust gasses directed to the turbine by the nozzle box; regulates the speed of the rotor

cooling cap

controls a flow of air for turbine cooling

manual wastegate control

vernier control in the cockpit connected by cable directly to the wastegate

automatic wastegate control

uses a pressure controller to control the wastegate

critical altitude for a given MAP setting is reached when the wastegate is

closed

further climb past critical altitude will result in what?

a reduction of MAP

in order to keep MAP from increasing above the desired setting during descent, what must the pilot do? (manual)

open the wastegate

when the wastegate is fully open, what is used for further MAP control?

the throttle

deck pressure

pressure between the discharge of the compressor and the engine throttle valve

ground boosted engine

engine that req’s MAP in excess of sea level pressure to produce its rated power

what do modern automatic turbocharger systems utilize to regulate the wastegate?

density controller and differential pressure controller

the position of the wastegate valve is controlled by what?

oil pressure

when oil pressure is increased, the position of the wastegate valve moves how?

closed

when oil pressure is decreased, the position of the wastegate valve moves how?

open

density controller

limits max MAP and prevents overboost by limiting the deck pressure while the a/c is below the turbocharger’s critical altitude

overboost

excessive MAP

what control device prevents overboost?

density controller

what control device reduces bootstrapping?

differential pressure controller

differential pressure controller

regulates the position of the wastegate valve to maintain a pre-set pressure differential across the throttle and reduces bootstrapping

bootstrapping

an indication of unregulated power change that results in the continual drift of manifold pressure

is bootstrapping detrimental to engine life?

no

overboost

a condition in which the MAP exceeds the limits prescribed for a particular engine; can cause serious damage

is overboost detrimental for an engine?

yes

overshoot

rapid movement of the throttle that can cause a certain amount of manifold pressure drift in a turbocharged engine

is overshoot fatal to an engine?

no

intercooler

cools the air in turbo-equipped induction systems after compression

electricity

the flow of electrons

electron

very small electrically charged particle that exists as a part of every atom

atom

the smallest particle of any matter that is able to exhibit the properties and characteristics of that matter

insulators

made of mat’ls which are composed of atoms that are tightly packed so that electrons cannot flow

conductors

mat’ls with loosely bound electrons so electrons can easily flow through them

electromotive force

the force which causes electrons to flow

resistance

opposition to electron flow

conventional current flow

positive to negative

electron flow

negative to positive

current

rate of electron flow

amp (unit)

measure of electron flow

voltage

electrical pressure

volt (unit)

unit of electrical pressure

two types of electricity

static and current

purpose of static electricity

rarely serves a useful purpose; more often a nuisance

static wicks

provide sharp points from which static charges are dissipated into the air before they can build up to a high potential on the control sfc

bonding straps

provide a low-resistance path between the control sfc and the a/c structure to prevent the buildup of a static charge on the control sfc

permeability

the measure of ease with which the lines of flux can travel through a mat’l or medium

two types of electromagnets

those with fixed cores and those with movable cores (solenoids and relays)

solenoids

electromagnets with movable cores

thermocouple

device for measuring temperature, consisting of two wires of different metals connected at two points

electrons will flow in a thermocouple made of dissimilar metals when

there is a temperature difference between the two junctions

piezoelectric

mat’l that when bent or deformed by a mechanical force, has an excess of electrons accumulate on one surface, leaving the opposite surface with a deficiency

piezoelectric effect

relating to or involving electric polarization resulting from the application of mechanical stress

Ohm’s Law

current that flows in a circuit is directly proportional to the voltage (pressure) that causes it, and inversely proportional to the resistance (opposition) in the circuit

which type of current is easier to generate in large quantities needed for homes and large transport a/c?

AC current

battery

a device composed of one or more cells in which chemical energy is converted into electric energy

parts of an aircraft electrical system

the electrical energy source, the circuit, and the active component

most commonly used storage battery for a/c

lead-acid battery

capacity

measure of a battery’s ability to produce a given amount of current for a specified time

ampere-hour

the amount of electricity that is put into/taken from a battery when a current of one ampere flows for one hour; expresses battery capacity

rated capacity

the battery’s ability to perform when it is new

actual battery capacity depends on

battery temperature, battery state of charge, and battery condition

battery condition is degraded by

age, service history, g forces applied

advantages of NiCd batteries

ability to accept high charge rates, discharge at equally high rates w/o voltage drop associated w/ lead-acid batteries, lower susceptibility to very low temps than lead-acid batteries

disadvantages of NiCd batteries

more expensive, req's more/more expensive maintenance, develops “memory” that must be erased, subject to thermal runaway, req’d more sophisticated monitoring systems

types of a/c NiCd batteries are used on

turbine engine a/c

thermal runaway

uncontrollable, self-heating state; battery accepts all of the charging current the source is capable of producing