Shadowing Practice: ATPL Instrumentation - Class 1: Temperature and Time - Learn English Speaking with Video
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If you're studying for your ATPLs and having a little bit of trouble with instrumentation, then this is the place to be.
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Over the next few months, we're going to be breaking down all the topics within the instrumentation subject, analysing them and hopefully making them make sense for you in time for the exam.
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Hi, I'm Grant and welcome to the first in a new series all about instrumentation.
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There's lots of different things that we can measure on board an aircraft, and analyse to make certain decisions about where we need to go,
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how high we need to fly and various other things.
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The most fundamental and easy to understand though is temperature and time.
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So we're going to start with them and slowly build up in complexity throughout the remainder of this course.
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We need to sense the temperature of various components
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so they don't overheat
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and we also need to sense the temperature of the air around us to make sure we know
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when to turn on any anti-ice systems and avoid any ice buildup.
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We can measure temperature in Celsius, Fahrenheit or even Kelvin.
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It doesn't really matter and the temperature probe will be calibrated to one of these
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and then it can convert it if necessary or can do the conversions manually just like I've got at the top here.
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So you've got Kelvin plus 273 equals Celsius.
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Celsius times 9 over 5 plus 32 equals the Fahrenheit.
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The simplest form of temperature sensor is to use a bi-metallic sensor.
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This is where we use two different metals spiraled together and
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when the temperature rises one metal will expand more than the other
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which basically unwinds the spiral and rotates a needle on a display.
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This is the sort of thing
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that you might use to measure air temperature on a small aircraft
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but you can't really measure the temperature of engine components
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and display the information in a useful place because this biometallic strip can only be so long.
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If you wanted to measure the temperature of the exhaust
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and you wanted the display in the cockpit you need a biometallic strip
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that went all the way to the back of the engine where the exhaust temperature was for example.
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So simple, robust, very easy to understand but not
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that useful for measuring some things but can be used in very simple applications.
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A resistance temperature detector relies on a metal that will change in resistance when heated.
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Four resistors are set up in this format essentially making a parallel circuit with a small battery outputting a consistent current.
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The values of these three resistors are known and then this one down here is the variable resistance one.
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As the resistance of this one changes it means
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that the voltage passing through this side of a parallel circuit
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measured at this point V2 will be different from the midpoint here at V1.
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This resistor setup is fairly common in electronics
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and it's called a wheat stone bridge if you're interested and want to look up more.
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Because there is a difference in voltage between the two midpoints it means
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that if we place a wire between point V1 and V2 we'll see that a current flows.
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We can then use that current flow to turn a dial on a display
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and the dial will turn based on how much resistance there is
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because of how much voltage difference there is and that resistance changes depending on how much temperature there is.
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So the temperature changes the resistance, changes the voltage, changes the voltage difference, turns the dial, gives us an effective display.
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It's a good setup
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and allows for the measurement of components from far away as all we need are longer wires to the display dial.
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It does however need a constant DC power supply to make it work.
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Thermocouples are used for very hot elements and work using a principle called Thermo-EMF, thermoelectromagnetic force.
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This is when a metal creates a small voltage or electromagnetic force
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when a temperature difference exists between two parts of the metal.
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Basically say this is a metal rod
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if it's hot over on the right hand side
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and cold over on the left hand side a small voltage is produced in this metal.
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Simple.
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In a thermocouple we use two different metals.
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We use metal one, let's just call it, and metal two in two sensing elements.
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We also have a reference cold temperature.
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This means we get a voltage difference produced when sensing a temperature which causes a current to flow.
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Essentially we use that thermal EMF, we've got a hot and a cold, a hot and a cold we get a voltage generated in metal one
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and a voltage generated in metal two because they're two different metals
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that means that we're going to have a voltage difference
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and then we do the same thing
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that we did in the resistance temperature detector
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and we hook up a dial and use the voltage difference and that current that's generated to turn the dial.
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These are very effective because we can measure components from very far away just like we did with the
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resistance temperature detector and it also doesn't need any power supply.
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The problem is they aren't hugely accurate
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so you wouldn't be using these for precision stuff
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but depending on the metals used for the thermocouples they can
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measure things at a very high temperature such as exhaust gas temperature in jet engines.
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Air temperature is one of the most important things to measure
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so that we can turn on any anti-icing systems when the temperature requires us to do so.
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In light aircraft
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that travel at low speed we tend to use a bi-metallic
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type of temperature probe with the end of the gauge poking out into the airflow
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and the dial giving us readings within the cockpit.
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It's simple and effective but we run into a problem when we start to go faster.
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Basically, as all the little particles in the air pass over the probe, they rub against it and create friction, causing the probe to heat up.
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This distorts the results and doesn't give us a true reading
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because we get this sort of kinetic heating effect whilst we're travelling through the air.
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We therefore measure something that we call a total air temperature, or TAT.
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and this is different from the actual air temperature which is the static air temperature
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or sometimes referred to as the outside air temperature so you get sat, oat and tat.
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That's a bit confusing and basically
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when we add friction to the static air temperature we then are going to be measuring the total air temperature.
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So how do we solve this problem?
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Well we use clever design.
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The most common type of probe and clever design that is used to get around this problem is called a Rosemount probe, which is I'm pretty sure a brand name,
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but this style with a little variation is all over the place on different aircraft.
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What happens in these probes is that air passes through this chamber past a small heater, which kind of seems a bit counter-intuitive,
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but it's there to stop any ice formation on the front of this probe.
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The venturi that follows the opening draws some of the air down into a sensing chamber
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while the heavier particles that are in the air like water
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or ice don't get drawn in and are free to pass by and they don't get sucked down into the sensing chamber.
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In the chamber a resistance type temperature probe detects the heat of the air
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before that air is dumped out the back of the probe.
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The separate chamber eliminates most of the effects of the anti-icing heaters in the probe entry
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and we can therefore get a reading for total air temperature
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that is accurate and isn't affected by any need to de-ice
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or anti-ice the probe
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and it also gets rid of all the particles in the air for a more accurate reading as well.
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It's important to note that this sort of probe will only work properly
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when it's moving through the air or has air moving through it.
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So when stationary, the air temperature readings will be way off and very, very high, especially if you've got the hot sun beating down on the probe, for example.
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So we've got our measure for true air temperature, but we want to know the outside air temperature or the static air temperature.
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What we do is we then use an equation
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or more specifically there'll be a little bit of electronics that does this calculation for you.
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The equation
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that we use is the static air temperature equals the total
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air temperature divided by 1 plus 3.2 times the recovery factor times the max squared.
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The equation has a few things to note.
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It must be used with Kelvin first of all,
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which confuses things because sometimes the recovery factor gets given the symbol k.
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And the recovery factor is essentially a measure of how efficient the probe is thermodynamically,
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as this equation is a thermodynamic expression, for how much heat is added to the air by the speed we are going through,
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hence the Mach number.
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So let's just put some numbers in this and talk through an example.
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So let's say we want to find out the outside air temperature, the static air temperature, and we have the following information.
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We've got a total air temperature is minus 40,
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that's what we measured, and we've got a recovery factor of 0.9
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and we've got a Mach number of 0.75 and we want to find out what is the
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static air temperature so the first thing we need to do is to convert it into Kelvin
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so we're going going to add 273 and
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that gives us an answer of 233 so 233 kelvin divided by 1 plus 0.2
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times 0.9 times 0.75 squared we'll just leave that in there for now
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and then I'll go away and do that on a calculator and see
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that we've got 233 divided by 1.10125 dot dot
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dot dot giving us a final answer in kelvin of 211.57 kelvin and if we wanted to convert that so let's
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just do it back over here so we've got 211.57 kelvin want to convert that back into
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um celsius so we take away 273
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and we get an answer so that's uh yes celsius is here that's going to give us minus 61.
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Yeah, 61.
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So we can see that the friction of us travelling through the air, we're going from minus 61 actual outside air temperature
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and we're adding about 20 degrees of friction to get us up to the total air temperature of minus 40.
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So it has a big effect whilst we're travelling at relatively high Mach numbers.
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In aviation, we measure things in UTC,
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universal time coordinate, which is a standardised time zone throughout the world.
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In the UK and parts of Europe, it is the same as the time in London, GMT, without daylight savings applied.
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And in other parts, it might be a few hours different from local, or even vastly different in places like New Zealand,
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where UTC is 12 hours different from local time.
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Basically, things can get confusing if you're referencing times to aviation related things like weather reports
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and arrival times which are all in UTC and then using your watch
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or phone which might be in local time especially
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when flying across different time zones with your phone maybe auto updating the time as you arrive in each place.
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So to save us and help us with
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that confusion we have a clock on the plane
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which is set to UTC time for referencing all these things like weather reports
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and arrival times etc and we call this the system clock.
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We use this as our time source when we are flying.
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These system clocks are the same as your wristwatch,
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usually a quartz based timekeeping device on smaller aircraft with larger aircraft having more complicated clocks with various features
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and they can use a GPS source to get an accurate time from the atomic clock
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on board the satellites up in space.
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They will also feature other things like a chrono which is a stopwatch used for timing short things.
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For example we need the engines to run at idle for
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at least three minutes before shutting them down after landing
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so we'd want to start the chrono shortly after landing to ensure we have achieved that three minute cool down time.
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We also have the elapsed time
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which we can use for longer timing typically for the time
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of pushback to the time of pulling back on stand again to get the block time of a flight, which is the flight time plus taxiing.
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Or we could use to record just the flight time by selecting it on just before take off
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and off just after landing.
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Another important use for an onboard system clock is to get
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an accurate measurement for how long the engine has been running and the the plane in general has been running.
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Engines have parts that need to be checked after a certain number of hours.
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So what we can do is we can manually record the startup
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and shutdown times in a tech log using the system clock
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and then we can get an accurate measurement of how long the engine has been running for
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and how often we need to service parts and
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when we need to service and check all of the components of the engine.
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Most aircraft will not rely on manually noting down the times though
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and they'll have a dedicated odometer that starts running when the engine starts and stops when the engine stops.
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This gives an accurate figure of how many hours the engine has been running for
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and it's kind of like the total mileage or total kilometreage odometer
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that you get on a car
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which gives an accurate figure of how long the engine has been on for
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and maintenance can be planned according to the figures on this odometer.
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In summary then you've got temperature sensing in a few different ways.
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Most simple is a bimetallic strip.
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You've got two different metals They untwine at different rates when heat is applied and the unspinning of one causes,
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faster than the other, causes a dial to move and we can measure temperature.
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Simple, but the biometallic strip limits how long it can be and how far away it can be from the source.
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You get resistive type elements that use a wheatstone bridge setup.
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the variable resistance reacts to heat and you'll get more or less heat and
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heat and more or less resistance according to that heat.
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You then get a voltage difference generated between each side of the Wheatstone bridge.
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That voltage difference creates a current that current can be used to turn a dial.
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They're good, they do rely on having a power source but it means that we can
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take this display and just attach some wires
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and send it to the cockpit away from the source of the temperature that we're measuring.
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You also get thermocouples which have the benefit of not needing power.
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They generate voltage when there's a temperature difference along their length.
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So it's going to be hot over here
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and it's going to be cold over here and that generates a voltage in this one metal, in this second metal,
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because it's a slightly different metal it means there's a slightly different voltage generated
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and we get two different voltages aka a voltage difference.
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Voltage difference means current can flow and we can use
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that flowing current to turn a dial which is proportional to the voltage difference and therefore proportional to the temperature
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and we get an accurate measurement of temperature in the cockpit.
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For air temperature sensing we generally on big aircraft use a rose mount probe.
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It's good because it means it's not going to
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ice up because there's heating elements here
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and then we draw air down into this sensing chamber
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and use a resistive type element to sense the temperature of the total air temperature
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and we get rid of all the particles of water
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and stuff in the air that might really affect and form this the result of the total air temperature.
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We then use electronics,
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we use an algorithm to calculate out what the static air temperature is compared to the total air temperature.
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The formula is static air temperature
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or outside air temperature equals the total air temperature divided by 1 plus 0.2 times the recovery factor times the Mach squared.
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These temperatures are in Kelvin.
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The recovery factor is a measurement of how efficient the resistive element
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and this system in general is and sometimes can be given the symbol k
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and then Mach is your Mach number
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which is going to be a measurement of how fast this air is flowing through the probe
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and how fast you're traveling through the air.
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So a few things to remember with this equation, but it's a good way of figuring out the outside air temperature versus the total air temperature.
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We also need to measure the time.
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Time is very easy to understand.
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It's UTC time, which is the universal worldwide time zone.
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Everything in aviation is referenced to UTC.
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So instead of using your watch where the local time might be vastly different to UTC,
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you can use the system clock which is always set to UTC for all aviation related things.
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And we can use accurate times from this to note down how long the engine's been running.
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And then we know how often we have to serve those parts and when we need to service those parts.
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Woordenschat en spreektips bij deze les
Deze video bevat 224 zinnen en 2982 woorden om na te spreken. Het gesproken deel duurt 19:11. De spreker praat in een natuurlijk tempo van ongeveer 155 woorden per minuut, dicht bij een alledaags gesprek. 82% van de woorden hoort bij de 3.000 meest gebruikte Engelse woorden; de rest kun je beter vooraf bekijken.
Belangrijke woorden in deze video
15 woorden uit de video die het leren waard zijn, met uitspraak en betekenis:
| Woord | Uitspraak | Betekenis |
|---|---|---|
| voltage zelfstandig naamwoord | /ˈvəʊltɪd͡ʒ/ | spanning |
| clock zelfstandig naamwoord | /klɑk/ | teller, kilometerteller |
| chamber zelfstandig naamwoord | /ˈt͡ʃeɪ̯mbɚ/ | slaapkamer |
| measurement zelfstandig naamwoord | /ˈmɛʒ.ə.mənt/ | meting |
| component zelfstandig naamwoord | /kəmˈpoʊ.nənt/ | onderdeel, component |
| equation zelfstandig naamwoord | /ɪˈkweɪ.ʒən/ | vergelijking |
| strip werkwoord | /ˈstɹɪp/ | strippen |
| aviation zelfstandig naamwoord | /ˌeɪ̯.viːˈeɪ̯.ʃən/ | luchtvaart |
| divide werkwoord | /dɪˈvaɪd/ | verdelen |
| minus | /ˈmaɪ.nəs/ | min |
| particle zelfstandig naamwoord | /ˈpɑɹtək(ə)l/ | deeltje, partikel |
| friction zelfstandig naamwoord | /ˈfɹɪkʃən/ | wrijving |
| wire zelfstandig naamwoord | /ˈwaɪɚ/ | draad |
| essentially bijwoord | /ɪˈsɛnʃəli/ | essentieel |
| rely werkwoord | /ɹɪˈlaɪ/ | rekenen op |
Phrasal verbs die je zult horen
| Woord | Uitspraak | Betekenis |
|---|---|---|
| find out werkwoord | ontdekken, onderzoeken | |
| break down werkwoord | stukgaan, kapot gaan | |
| cool down werkwoord | /kuːl ˈdaʊn/ | afkoelen, koelen |
| figure out werkwoord | uitvogelen, er achter komen | |
| go away werkwoord | weggaan | |
| hook up werkwoord | aansluiten | |
| look up werkwoord | /ˌlʊk ˈʌp/ | opkijken |
| take off werkwoord | uittrekken, afzetten |
Grammatica in deze video
De structuren die de spreker het meest gebruikt, met de exacte woorden uit de video:
| Structuur | In de video |
|---|---|
| Present perfect continuous have/has been + -ing — iets dat eerder begon en nog bezig is | has been running · engine's been running |
| Lijdende vorm be + voltooid deelwoord — het gaat om wat er gebeurt, niet om wie het doet | will be calibrated · are set · are known |
| Betrekkelijke bijzinnen who / which + zin — extra informatie over een persoon of ding | temperature which is · probe, which is · coordinate, which is |
| Present perfect have/has + voltooid deelwoord — iets uit het verleden dat nu nog telt | have achieved · has been |
Uitspraak om op te letten
De spreker gebruikt 46 samentrekkingen en verkorte vormen, zoals we're, we've, you're. Spreek ze kort uit, zoals je ze hoort.
- De “th”-klanken: thermal /ˈθɜːməl/, algorithm /ˈælɡəɹɪðm̩/, thermodynamic /ˌθɝmoʊdaɪˈnæmɪk/
- De klanken “sh” en “zh”: measurement /ˈmɛʒ.ə.mənt/, equation /ɪˈkweɪ.ʒən/, aviation /ˌeɪ̯.viːˈeɪ̯.ʃən/, friction /ˈfɹɪkʃən/, essentially /ɪˈsɛnʃəli/
- Lange woorden — let op de klemtoon: aviation /ˌeɪ̯.viːˈeɪ̯.ʃən/, essentially /ɪˈsɛnʃəli/, electronics /ɪˌlɛkˈtɹɑ.nɪks/, manually /ˈmænj(u)əliː/, universal /ˌjunəˈvɜɹs(ə)l/
Zo oefen je met deze video
- Luister de hele video één keer zonder te spreken en noteer de woorden die je niet kent.
- Begin op 0,75× snelheid, spreek zin voor zin na en ga terug naar normale snelheid zodra het makkelijk gaat.
- Neem jezelf op en vergelijk met het origineel; let daarbij op woorden als voltage, clock, chamber.
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