The Doppler Effect and Malaysian Flight 370

Posted by PITHOCRATES - March 26th, 2014

Technology 101

A Swan Pushes Waves Together in front of it and Pulls Waves Apart behind it as it Paddles across Water

Throw a stone in the water and what do you see?  Little circular ripples in the water moving away from and centered on where the stone broke the surface of the water.  These are waves.  Energy.  They are more intense the closer they are to the point of disturbance.  And become less intense the further they are from the point of disturbance.  So you’ll see larger circular ripples in the water closer to where the stone hit the water.  And smaller circular ripples at increasing radii from the point of impact.

You’ll see these little circular waves, too, when something else disturbs the surface of the water.  Like a swan.  Or a duck.  As they paddle their feet they move forward in the water.  Pushing the water out ahead them.  If you look closely you’ll see ripples bunched up in front of them.  And ripples spaced further apart behind them.  This is because of their movement towards the previous ripple.

These waves ripple through the water at the same speed (assuming the swan or duck is paddling at a constant speed).  So each ripple will travel the same distance at the same speed from the paddling bird.  But as the bird moves forward each subsequent wave in that direction is starting its journey at a point further along in that direction.  So one wave may have gotten to a point (let’s call it Point A) in the water 3 inches ahead of where the bird created it.  Since creating that wave the bird continued to paddle.  And created another wave.  This one created only 2 inches from Point A.  And then the bird created another wave at only 1 inch from Point A.  So subsequent waves are ‘catching up’ to previous waves.  Thus bunching the waves up in front of the bird.  While the bird is pushing these waves closer together the bird is traveling away from the waves behind it.  Stretching those waves further apart from each other.

A Guitar makes Sound by Vibrating the Soundboard in the Body of the Guitar

If you’ve ever played a guitar or watched someone play the guitar you’ve probably noticed how the sound changes depending on where the player fingers the string on the fingerboard (or fretboard).  If the player presses down on the string closer to the body of the guitar the note sounds higher.  If the player presses down on the string further away from the body of the guitar the note sounds lower.  Why?  Frequency.

A guitar makes sound by vibrating the soundboard in the body of the guitar.  The faster it vibrates the higher pitch the sound.  The slower it vibrates the lower pitch the sound.  The string vibrates back and forth a number of times each second.  The more it moves back and forth in one second the higher the frequency and the higher the pitch.  The fewer times it does the lower the frequency and the lower the pitch.  Thinner strings vibrate faster than thicker strings.  Shorter strings vibrate faster than longer strings.  So a typical guitar has 6 strings of various thickness stretched from the soundboard across the fingerboard.

The vibrating soundboard creates sound waves that move through the air.  Similar to a rock breaking the surface of the water.  As a guitar player fingers different notes on the fingerboard the soundboard vibrates at different frequencies.  Making music.  If you’re attending a small concert where a soloist is playing, say, Spanish Dance No. 2: Oriental by Enrique Granados you would hear the same beautiful music wherever you were sitting in the room.  The sound waves would be radiating throughout the room like the ripples created when a rock breaks the surface of the water.  However, if the soloist was moving like a swan through the water it would be a different story.

Using the Doppler Effect they determined Malaysian Airlines Flight 370 traveled the Southern Route

Ever listen to the sounds of cars and trucks traveling down a highway?  Maybe while visiting your aunt and uncle who live on a highway out in the country?  Did you notice that they had a higher-pitched sound when they approached you than when after they had passed you by?  The next time something noisy passes you by listen.  Especially if they’re blowing their horn.  It’ll go from a higher-pitched sound to a lower-pitched sound just as it passes you.  Why?  Think of the waves a swan makes gliding through the water.  Bunching waves closer together in front of it.  And stretching them further apart behind it.  The same thing happens with sound waves.  Austrian physicist Christian Doppler noted this in 1842.  Something we now call the Doppler Effect.

If a train is travelling down the track while blowing its horn it sounds the same aboard the train from the moment the engineer starts blowing it until he or she stops.  Just as the sound of a soloist playing Spanish Dance No. 2: Oriental sounds the same wherever you are in the room.  Because the distance between the source of the sound and the listener of the sound does not change.  But if you were standing stationary near the railroad track as the train traveled past you the frequency of the horn changes.  Because as it is approaching you it is pushing sound waves closer together.  Creating a higher frequency (or a higher-pitched sound).  As the train passes it is stretching those sound waves further apart.  Creating a lower frequency (or a lower-pitched sound).  This is the Doppler Effect.

When Malaysian Airlines Flight 370 shut off its transponder and ACARS (Aircraft Communications Addressing and Reporting System) stopped broadcasting the plane vanished.  But a satellite communicating with the airplane still ‘pinged’ the aircraft every hour of its remaining flight time.  And electronic handshake.  The satellite says, “Are you still there?”  And the plane responds, “Yes I am.”  No data was transmitted.  Only a sent and received signal.  Just a pulse of a constant frequency.  A ping.  But from those pings they could measure the time it took to send and receive those pings.  Which they could calculate distances between the satellite and the plane from.  Giving us the northern and southern possible routes as it traveled in an arc around the satellite.  But which way it went on that arc was a mystery.  Until they analyzed the frequencies of those pings.  And they detected a slight change in the frequencies.  Using the Doppler Effect they determined which side of the plane was bunching up the sound waves and what side of it was stretching them out.  And concluded the plane was traveling on the southern route.  Which is why all search efforts are now in the south Indian Ocean southeast from Australia.  Because, according to Christian Doppler, that’s the direction the plane flew.

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Snow Ski

Posted by PITHOCRATES - February 26th, 2014

Technology 101

Gravity and Speed keeps a Skier’s Skies in contact with the Mountain and Provides Control

The Winter Olympics have come and gone.  And if you are a big fan of the Winter Olympics you probably were somewhat disappointed.  Especially if you’re a fan of alpine skiing.  Because it was just too warm.  They have the Olympics in February for a reason.  Because February is a very cold month.  And the mountains have a couple of months of snow on them by February.  Allowing the snow groomers to do their magic.  And turn those mountains into hard sheets of ice.

Yes, ski racers ski on ice.  Not snow.  If you ever skied on a mountain where there was once an Olympic downhill racecourse you will see very steep slopes of ice.  If you ski slowly across the fall line of the slope at the top of the mountain you will slide further down hill than you ski across the slope.  With your ski edges sliding across the ice.  And about the only thing that will stop your ‘free-fall’ slide down that steep ice-covered slope is the loose snow on the sides of the slope.  But if you travel down this same slope at speeds around 70 mph your skies will carve into that ice.  Giving you great control.  If you have the skills of an Olympic downhill skier, that is.  If you’re not as skilled as a downhill racer then you shouldn’t try this.  Because if you fall at speed up there you can do some real damage to yourself.

Downhill skiers love that speed, though.  And will give themselves up completely to gravity.  And let it pull them down these steep, sheets of ice at breakneck speeds.  With nothing to keep them from flying off the mountain and breaking their necks but their skies.  As gravity and speed keeps their skies in contact with the mountain.  Giving them control to stay on their skies.  And carve their way down the mountain.  Literally.

When a Skier leans over on a Ski the Curved Edge of the Ski carves into the Snow or Ice and Turns the Skier

In alpine skiing there are 5 different races.  The downhill.  The super giant slalom (known as super G).  Giant slalom.  Slalom.  And combined.  Which is a combination of two ski races.  One downhill race and one slalom race.  The downhill is the straightest and fastest down the mountain.  The super G is a little more ‘turny’ and a little slower than downhill.   The giant slalom is more ‘turny’ and slower than Super G.  And the slalom is more ‘turny’ and slower than giant slalom.  The downhill is all about speed.  The turns aren’t that sharp.  While the slalom is all about the turns.  With speeds that aren’t that fast.

Each of these races requires different types of skies.  The downhill race needs long skies that will absorb the bumps of rough terrain without bouncing off.  And speed is more important than turning.  While slalom skies need shorter skies to make sharper turns.  And because they are shorter they may come off the snow as they bounce over rough terrain.  So they match the ski to the race.  And because of the requirements of downhill racing these skies are available only to professional skiers.  You will not find them in any sporting goods store.  As amateur and recreational skiers could not control them safely on steep sheets of ice at downhill speeds.

If you look at a ski lying on the ground you will see that it is narrower at the center where it attaches to the ski boot and wider at the tip and the tail.  And it goes from wide to narrow to wide in a continuous curve.  This curve is the side-cut radius.  This is what turns the ski.  When a skier leans over on the ski the curved edge of the ski carves into the snow or ice.  Turning the skier.  The more curved the side-cut radius the tighter turns it will allow.  So slalom skies are more curved in the side-cut radius than downhill skills.

The Winter Olympics are in February so Ski Racers can ski on Mountains that are Hard Sheets of Ice

Looking at a ski resting on a hard surface you will notice something else.  The center of the ski will be off that hard surface.  While the tip and the tail will be in contact with that surface.  This arch—or camber—of the ski helps to force the ski into contact with the snow when you place weight onto them.  Especially the steel edges when turning.  When a skier carves a turn he or she will literally carve that turn into the ice of the mountain.  In a clean turn the tail of the ski will follow the same groove carved by the tip.  With a minimum loss of speed.  If the tail slides out of this groove and carve its own groove it will slow the skier down.  And in downhill skiing where first and second place can be separated by one one-hundredth of a second one slight skid in a turn can be the difference between winning and coming in second.

As downhill skiers leave the starting gate they will take a couple of pushes with their ski poles to help gravity pull them down faster and then assume a tuck position.  To decrease their air drag.  As they approach a gate they will turn by leaning on their edges.  The sharper the turn the more they will lean onto to their edges to carve a tighter turn.  And the more speed they will lose.  Which is why racers will look for the best ‘line’ down the mountain.  One that minimizes sharp turns.  Once out of the turn they will release their edges and ski on the bottom of their skies.  Gaining speed.  They will absorb the rough terrain in their legs.  And fight the compression of the g-forces with their legs.  They lean into turns, release their edges, ride on the bottoms of their skis in the flats, lean on their edges, etc.  At speeds around 70 mph.  As they carve their way down a mountain of ice to cross the finish line in the shortest amount of time.

As spring approaches the ski resorts warm up.  Some people love this.  Spring skiing conditions.  Loose snow on the slopes but warming weather.  So warm that a lot of ski areas will have events like bikini races or lingerie races where girls will ski down the mountain half naked in the warming weather.  It can be a real party on the slopes.  But the skiing will be horrible.  The snow will be melting.  It will be wet.  Granular.  Pushed up into piles.  Making it easy to catch an edge and fall.  And difficult to build up any speed.  Which is why the Winter Olympics are in February.  In the coldest part of winter.  With a lot of snow frozen on the mountain.  And they typically don’t hold them in subtropical climates.  Where the average temperature in February is 50 degrees Fahrenheit.  Like in Sochi, Russia.  Where skiers had to deal with spring skiing conditions.  And varying conditions.  As the snow at the top of a run was different from the snow at the bottom of the run.  Despite the amount of chemicals they put on the snow to try and raise the melting temperature of the snow.  Making these Winter Games not as good as past Winter Games.  If you’re a fan of alpine skiing, that is.  Or prefer seeing cold winter vistas at the Winter Olympics.  And not people lying on the bare grass catching a suntan.

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Steam Locomotive

Posted by PITHOCRATES - November 13th, 2013

Technology 101

The Steam Locomotive was one of the Few Technologies that wasn’t replaced by a Superior Technology 

Man first used stone tools about two and a half million years ago.  We first controlled fire for our use about a million years ago.  We first domesticated animals and began farming a little over 10,000 years ago.  The Egyptians were moving goods by boats some 5,000 years ago.  The Greeks and Romans first used the water wheel for power about 2,500 years ago. The Industrial Revolution began about 250 years ago.  James Watt improved the steam engine about 230 years ago.  England introduced the first steam locomotive into rail service about 210 years ago. 

In the first half of the 1800s the United States started building its railroads.  Helping the North to win the Civil War.  And completing the transcontinental railroad in 1869.  By 1890 there were about 130,000 miles of track crisscrossing the United States.  With the stream locomotives growing faster.  And more powerful.  These massive marvels of engineering helped the United States to become the number one economic power in the world.  As her vast resources and manufacturing centers were all connected by rail.  These powerful steam locomotives raced people across the continent.  And pulled ever longer—and heavier—freight trains.

We built bigger and bigger steam locomotives.  That had the power to pull freight across mountains.  To race across the Great Plains.  And into our cities.  With the chugging sound and the mournful steam whistle filling many a childhood memories.  But by the end of World War II the era of steam was over.  After little more than a century.  Barely a blip in the historical record.  Yet it advanced mankind in that century like few other technological advances.   Transforming the Industrial Revolution into the Second Industrial Revolution.  Or the Technological Revolution.  That gave us the steel that built America.  Electric Power.  Mass production.  And the production line.  None of which would have happened without the steam locomotive.  It was one of the few technologies that wasn’t replaced by a superior technology.  For the steam locomotive was more powerful than the diesel-electric that replaced it.  But the diesel-electric was far more cost-efficient than the steam locomotive. Even if you had to lash up 5 diesels to do the job of one steam locomotive.

The Hot Gases from the Firebox pass through the Boiler Tubes to Boil Water into Steam

The steam engine is an external combustion engine.  Unlike the internal combustion engine the burning of fuel did not move a piston.  Instead burning fuel produced steam.  And the expansion energy in steam moved the piston.  The steam locomotive is a large but compact boiler on wheels.  At one end is a firebox that typically burned wood, coal or oil.  At the other end is the smokebox.  Where the hot gases from the firebox ultimately vent out into the atmosphere through the smokestack.  In between the firebox and the smokebox are a bundle of long pipes.  Boiler tubes.  The longer the locomotive the longer the boiler tubes. 

To start a fire the fireman lights something to burn with a torch and places it on the grating in the firebox.  As this burns he may place some pieces of wood on it to build the fire bigger.  Once the fire is strong he will start shoveling in coal.  Slowly but surely the fire grows hotter.  The hot gases pass through the boiler tubes and into the smokebox.  And up the smoke stack.  Water surrounds the boiler tubes.  The hot gases in the boiler tubes heat the water around the tubes.  Boiling it into steam.  Slowly but surely the amount of water boiled into steam grows.  Increasing the steam pressure in the boiler.  At the top of the boiler over the boiler tubes is a steam dome.  A high point in the boiler where steam under pressure collects looking for a way out of the boiler.  Turned up into the steam dome is a pipe that runs down and splits into two.  Running to the valve chest above each steam cylinder.  Where the steam pushes a piston back and forth.  Which connects to the drive wheels via a connecting rod.

When the engineer moves the throttle level it operates a variable valve in the steam dome.  The more he opens this valve the more steam flows out of the boiler and into the valve chests.  And the greater the speed.  The valve in the valve chest moved back and forth.  When it moved to one side it opened a port into the piston cylinder behind the piston to push it one way.  Then the valve moved the other way.  Opening a port on the other side of the piston cylinder to allow steam to flow in front of the piston.  To push it back the other way.  As the steam expanded in the cylinder to push the piston the spent steam exhausted into the smoke stack and up into the atmosphere.  Creating a draft that helped pull the hot gases from the firebox through the boiler tubes, into the smokebox and out the smoke stack.  Creating the chugging sound from our childhood memories.

The Challenger and the Big Boy were the Superstars of Steam Locomotives

To keep the locomotive moving required two things.  A continuous supply of fuel and water.  Stored in the tender trailing the locomotive.  The fireman shoveled coal from the tender into the firebox.  What space the coal wasn’t occupying in the tender was filled with water.  The only limit on speed and power was the size of the boiler.  The bigger the firebox the hotter the fire.  And the hungrier it was for fuel.  The bigger locomotives required a mechanized coal feeder into the firebox as a person couldn’t shovel the coal fast enough.  Also, the bigger the engine the greater the weight.  The greater the weight the greater the wear and tear on the rail.  Like trucks on the highway railroads had a limit of weight per axel.  So as the engines got bigger the more wheels there were ahead of the drive wheels and trailing the drive wheels.  For example, the Hudson 4-6-4 had two axels (with four wheels) ahead of the drive wheels.  Three axles (with 6 wheels) connected to the pistons that powered the train.  And two axels (with four wheels) trailing the drive wheels to help support the weight of the firebox.

To achieve ever higher speeds and power over grades required ever larger boilers.  For higher speeds used a lot of steam.  Requiring a huge firebox to keep boiling water into steam to maintain those higher speeds.  But greater lengths and heavier boilers required more wheels.  And more wheels did not turn well in curves.  Leading to more wear and tear on the rails.  Enter the 4-6-6-4 Challenger.  The pinnacle of steam locomotive design.  To accommodate this behemoth on curves the designers reintroduced the articulating locomotive.  They split up the 12 drive wheels of the then most powerful locomotive in service into two sets of 6.  Each with their own set of pistons.  While the long boiler was a solid piece the frame underneath wasn’t.  It had a pivot point.  The first set of drive wheels and the four wheels in front of them were in front of this pivot.  And the second set of drive wheels and the trailing 4 wheels that carried the weight of the massive boiler on the Challenger were behind this pivot.  So instead of having one 4-6-6-4 struggling through curves there was one 4-6 trailing one 6-4.  Allowing it to negotiate curves easier and at greater speeds.

The Challenger was fast.  And powerful.  It could handle just about any track in America.  Except that over the Wasatch Range between Green River, Wyoming and Ogden, Utah.  Here even the Challenger couldn’t negotiate those grades on its own.  These trains required double-heading.  Two Challengers with two crews (unlike lashing up diesels today where one crew operates multiple units from one cab).  And helper locomotives.  This took a lot of time.  And cost a lot of money.  So to negotiate these steep grades Union Pacific built the 4-8-8-4 articulated Big Boy.  Basically the Challenger on steroids.  The Big Boy could pull anything anywhere.  The Challenger and the Big Boy were the superstars of steam locomotives.  But these massive boilers on wheels required an enormous amount of maintenance.  Which is why they lasted but 20 years in service.  Replaced by tiny little diesel-electric locomotives.  That revolutionized railroading.  Because they were so less costly to maintain and operate.  Even if you had to use 7 of them to do what one Big Boy could do.

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Feedback Loop Control System

Posted by PITHOCRATES - October 30th, 2013

Technology 101

Living through Winters became easier with Thermostats

When man discovered how to make fire it changed where we could live.  We no longer had to follow the food south when winter came.  We could stay through the winter.  And build a home.  As long as we could store enough food for the winter.  And had fire to stay warm.  To prevent our dying from exposure to the cold.

There’s nothing like sitting around a campfire.  It’s warm.  And cozy.  In large part because it’s outside.  So the smoke, soot and ash stayed outside.  It wasn’t always like that, though.  We used to bring that campfire inside the home.  With a hole in the roof for the smoke.  And families slept around the fire.  Together.  Even as some fornicated.  To propagate the species.  But that wasn’t the worst part about living around an indoor campfire.

Your distance from the fire determined how hot or cold you were.  And it was very hot by it.  Not so hot away from it.  Especially with a hole in the roof.  Worst, everyone got colder as the fire burned out.  Meaning someone had to get up to start a new fire.  The hard way.  Creating an ember.  Using it to start some kindling burning.  Then adding larger sticks and branches onto the kindling until they started to burn.  Which was a lot harder than turning the thermostat to ‘heat’ at the beginning of the heating season and forgetting about it.  Then turning it to ‘off’ at the end of the heating season.

A Feedback Loop Control System measures the Output of a System and Compares it to a Desired Output

Replacing the indoor campfire with a boiler or furnace made life a lot simpler.  For with a supply of fuel (natural gas, fuel oil, electricity, etc.) the fire never burned itself out.  And you never had to get up to start a new one.  Of course, that created another problem.  Shutting it off.

Boilers and furnaces are very efficient today.  They produce a lot of heat.  And if you let them run all day long it would become like a hot summer day inside your house.  Something we don’t want.  Which is why we use air conditioners on hot summer days.  So heating systems can’t run all day long.  But we can’t keep getting up all night to turn it off when we’re too hot.  And turning it back on when we’re too cold.  Which is why we developed the feedback loop control system.

We did not develop the feedback loop control system for our heating systems.  Our heating systems are just one of many things we control with a feedback loop control system.  Which is basically measuring the output of a system and comparing it to a desired output.  For example, if we want to sleep under a cozy warm blanket we may set the ‘set-point’ to 68 degrees (on the thermostat).  The heating system will run and measure the actual temperature (at the thermostat) and compare it to the desired set-point.  That’s the feedback loop.  If the actual temperature is below the desired set-point (68 degrees in our example) the heat stays on.  Once the actual temperature equals the set-point the heat shuts off.

The Autopilot System includes Independent Control Systems for Speed, Heading and Altitude

Speed control on a car is another example of a feedback loop control system.  But this control system is a little more complex than a thermostat turning a heating system on and off.  As it doesn’t shut the engine off once the car reaches the set-point speed.  If it did the speed would immediately begin to fall below the set-point.  Also, a car’s speed varies due to terrain.  Gravity speeds the car when it’s going downhill.  And slows it down when it’s going uphill.  The speed controller continuously measures the car’s actual speed and subtracts it from the set-point.  If the number is negative the controller moves the vehicle’s throttle one way.  If it’s positive it moves the throttle in the other way.  The greater the difference the greater the movement.  And it keeps making these speed ‘corrections’ until the difference between the actual speed and the set-point is reduced to zero.

Though more complex than a heating thermostat the speed control on a car is pretty simple.  It has one input (speed).  And one output (throttle adjustment).  Now an airplane has a far more complex control system.  Often called just ‘autopilot’.  When it is actually multiple systems.  There is an auto-speed system that measures air speed and adjusts engine throttles.  There is a heading control system that measures the aircraft’s heading and adjusts the ailerons to adjust course heading.  There is an altitude control system that measures altitude and adjusts the elevators to adjust altitude.  And systems that measure and correct pitch and yaw.  Pilots enter set-points for each of these in the autopilot console.  And these control systems constantly measure actual readings (speed, heading and altitude) and compares them to the set-points in the autopilot console and adjusts the appropriate flight controls as necessary. 

Unlike a car or an airplane a building doesn’t move from point A to point B.  Yet they often have more complex control systems than autopilot systems on airplanes.  With thousands of inputs and outputs.  For example, in the summer there’s chilled water temperature, heating hot water temperature (for the summer boiler), supply air pressure, return air pressure, outdoor air pressure, indoor air pressure, outdoor temperature, outdoor humidity, indoor temperature (at numerous locations), indoor humidity, etc.  Thousands of inputs.  And thousands of outputs.  And unlike an airplane these are all integrated into one control system.  To produce a comfortable temperature in the building.  Maintain indoor air quality.  Keep humidity levels below what is uncomfortable and possibly damaging to electronic systems.  And prevent mold from growing.  But not keep it too dry that people suffer static sparks, dry eyes, dry nasal cavities that can lead to nose bleeds, dry and cracked skin, etc.  To prevent a blast of air hitting people when they open a door.  To keep the cold winter air from entering the building through cracks and spaces around doors and windows.  And a whole lot more.  Far more than the thermostat in our homes that turns our heating system on and off.

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Side Streets, Downtown Streets, Highways, Parkways and Freeways

Posted by PITHOCRATES - July 31st, 2013

Technology 101

In 20th Century our Subdivision Planners shifted from Automobile-Friendly to People-Friendly Designs

The automobile changed how we live.  Where once we crowded into crowded cites and worked close to where we lived today we don’t.  Instead choosing to live in sleepy suburbs.  Away from the noise and congestion of city life.  Where we can relax after work.  And on the weekend.  Enjoying a beer in the shade in our backyard.  Our little Shangri-La.  Come Monday morning, though, it’s back to the grind.  So we back our car out of the garage.  And drive out of our little residential community.

If you live in an older suburb that would be a drive down a straight road.  Running either north and south.  Or east and west.  Bringing you efficiently to a larger road.  That you can efficiently take to a larger road yet.  With a higher speed limit.  With many of us eventually taking that road to an onramp of an interstate freeway.  For that morning commute.  Quick.  And efficiently.  Thanks to our city and suburb planners making our cities and suburbs so automobile-friendly.

Soon everyone was driving so much that these roads got congested.  Including the ones in our sleepy little subdivisions.  With people racing down our side streets to get to those bigger roads.  Filling our little Shangri-La with the sounds of traffic.  And making it unsafe for our kids to ride their bicycles in the street.  Which is why somewhere around the middle of the 20th century our subdivision planners shifted from automobile-friendly to people-friendly.  Instead of grids of straight lines crossing other straight lines at neat right angles our roads in our subdivisions began to curve.  If you ever tried to cut through a subdivision and got so turned around that you ended up where you entered this is why.  To discourage people from driving through our sleepy little streets.  So we can relax with that beer in the shade.  And our kids can ride their bicycles safely in the streets in front of our homes.

Design Speed is the First Consideration when Designing a New Road

Cars are big and heavy.  Trucks are even bigger and heavier.  Yet millions of them safely share the same roads every day.  And few in a small car look twice at a semi truck and trailer stopped next to them at a traffic light.  Or give a second thought to an even bigger and heavier freight train crossing the road ahead of them while they sit at a railroad crossing.  All because of lines painted on the road.  Speed limit signs keeping us driving at the same speed.  And stop signs and traffic lights.  Which people observe.  And give the right-of-way to others.  While they wait their turn to proceed.  Except for trains.  They always have the right-of-way.  Because trains can’t stop as easily as a car or a truck.  And they pay a lot of money for that right-of-way.

As we left our neighborhoods and got onto the bigger roads and drove to the interstate freeway the speed limit got higher and higher.  And the faster large things go the more kinetic energy they build up.  Making it harder to stop.  And to control.  That’s why trains don’t stop for cars.  Cars stop for trains.  Emergency vehicles, like fire trucks and ambulances, get the right-of-way, too.  When we see their lights flashing and/or hear their sirens we pull to the curb and stop.  Because they’re speeding to an emergency and need a clear road.  But also because they are often traveling faster than the design speed of the road.

Yes, design speed.  Not the speed limit.  Two completely different things.  It’s the first consideration when designing a new road.  How fast will traffic travel?  Because everything follows from that.  Curves, grades, visibility, etc., these are all things that vary with speed.  Engineers will design a downtown street with a lot of vehicular and pedestrian traffic for lower speeds than they’ll design a country highway that connects two towns.  Also, lane width in a downtown street can be as narrow as 9 feet.  And they can have sidewalks adjacent to the curbs.  Allowing narrower streets for pedestrians to cross.  Freeways, on the other hand, have lanes that are 12 feet wide.  And have wide shoulders.  Because faster vehicles need more separation.  As they tend to waver across their lanes.  So this is another reason why we pull aside for emergency vehicles.  As they may approach or exceed the design speed of a road.  So we give them wider lanes by pulling over.  As well as giving them a less obstructive view of the road ahead.

The Modern Interstate Freeway System is Basically an Improved Parkway

Old 2-lane country highways had narrow lanes and narrow shoulders.  Making it easy to drift across the center line if distracted.  Or tired.  Into oncoming traffic.  If a person hugs the shoulder because he or she is nervous about fast-moving oncoming traffic they could drift over to the right.  Out of their lane.  And drop off of the shoulder.  Which could result in a loss of control.  Even a rollover accident.  And if you were stuck behind a slow-moving truck on a grade there was only one way around it.  Moving over into the lane of oncoming traffic.  And speeding up to get ahead of the truck before a car crashes head-on into you.  In fact, there used to be a passing lane.  A 3-lane highway with one lane traveling one direction.  One lane traveling in the other direction.  And a lane in the middle for passing.  Which worked well when only one person passed at a time.  But did not work so well when cars from each lane moved into the passing lane at the same time.  Running head-on into each other.  That’s why you won’t see a passing lane these days.  They are just too dangerous.

In the 20th century we started making roads for higher speeds.  Parkways.  The traffic travelling in either direction was separated by a median.  So you couldn’t drift into oncoming traffic.  There were no intersections.  Crossroads went over or under these parkways.  So traffic on the parkways didn’t have to stop.  They also had limited access.  On ramps and off ramps brought cars on and off, merging them into/out of moving traffic.  And unlike the old 2-lane country roads there were 2 lanes of traffic in each direction.  So if you wanted to pass someone you didn’t have to drive into oncoming traffic to go around a slower-moving vehicle.  And there was a paved shoulder.  So if a car had a flat tire they could limp onto the shoulder to change their tire.  Without interrupting the traffic on the parkway.  Of course, being on the shoulder of a parkway was not the safest place to be.  Especially if some distracted driver drifted onto the shoulder.  And crashed into your broken down car.

The modern interstate freeway system is basically an improved parkway.  They have wider lanes and wider shoulders.  Along the median and the outside right lane.  Instead of the typical Windsor Arch of the parkway they have bridges of concrete and steel.  Allowing greater spans over the roadway.  Keeping those shoulders wide even under the overpasses.  Grades are less steep.  And curves are less sharp.  Allowing little steering inputs at high speeds to control your vehicle.  Making for safer travel at even higher speeds.  And a much greater field of vision.  Even at night where there are no streetlights.  The road won’t change grade or curve so great beyond the length of your headlights.  Safely allowing a high speed even when you can’t see what’s up ahead.  Little things that you’ve probably never noticed.  But if you exit the interstate onto a curvy 2-lane highway with steep grades you will notice that you can’t drive at the same speed.  Especially at night.  In fact, you may drive well below the posted speed limit.  Because you can’t see the summit of the next hill.  Or the curve that takes you away from a sharp drop-off to a ravine below.  Like you find around ski resorts in the mountains.  The kind of highways you can’t wait to get off of and onto the safer interstate freeway system.  Especially in a driving snow storm.

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Air, Low Pressure, High Pressure, Lateen Sail, Flight, Wing, Lift, Drag, Leading Edge Slats, Trailing Edge Flaps and Angle of Attack

Posted by PITHOCRATES - October 10th, 2012

Technology 101

There’s more to Air than Meets the Eye even though it’s Invisible

When you take a shower have you noticed how the shower curtain pulls in towards you?  Have you ever wondered why it does this?  Here’s why.  Air has mass.  The water from the showerhead sends out a stream of water drops that also has mass.  So they fall to the floor of the shower.  Pushing air with it.  And pulling air behind it.  (Like drinking through a straw.  As you suck liquid out of the straw more liquid enters the straw.)  So you not only have a stream of water moving down alongside the shower curtain.  You also have a stream of air moving down alongside the shower curtain.

As the falling water sweeps away the air from the inside of the shower current it creates a low pressure there.  While on the outside of the curtain there is no moving water or air.  And, therefore, no change in air pressure.  But there is a higher pressure relative to the lower pressure on the inside of the shower curtain.  The low pressure inside pulls the curtain while the high pressure outside pushes it.  Causing the shower curtain to move towards you.

There’s more to air than meets the eye.  Even though it’s invisible.  It’s why we build modern cars aerodynamically to slice through large masses of invisible air that push back against cars trying to drive through it.  Making our engines work harder.  Consuming more gas.  And reducing our gas mileage.  While race cars will use spoilers to redirect that air up, forcing the weight of the car down on the tires.  To help the tires grip the road at higher speeds.  We even design skyscrapers to be aerodynamic.  To split the prevailing winds around the buildings to prevent large masses of air from slamming into the sides of buildings, minimizing the amount buildings sway back and forth.

We put the Engines on, and the Fuel in, the Wings to Counteract the Lifting Force on an Aircraft’s Wings

Air can be annoying.  Such as when the shower curtain sticks to your leg.  As it steals miles per gallon from your car.  When it shakes the building you’re in.  But it can also be beneficial.  As in early ship propulsion before the steam engine.  Large square-rigged sails that pushed ships along the prevailing winds.  And triangular lateen sails that allowed us to travel into the wind.  By zigzagging across the wind.  With the front edge of a lateen sail slicing into the wind.  The sail redirects the wind on one side of the sail to the rear of the boat that pushes the boat forward.  While the wind on the other side follows the curved sail creating a low pressure that pulls the boat forward.  Like the inside of that shower curtain.  Only with a lot more pulling force.

Harnessing the energy in wind let the world become a smaller place.  As people could travel anywhere in the world.  Of course, some of that early travel could take months.  And spending months on the open sea could be very trying.  And dangerous.  A lot of early ships were lost in storms.  Ran aground on some uncharted shoal.  Or simply got lost and ran out of drinking water and food.  Or fell to pirates.  So it took a hearty breed to travel the open seas under sail.  Of course today long-distant travel is a bit easier.  Because of another use for air.  Flight.

Like a lateen sail an aircraft wing splits the airflow above and below the wing.  And like the lateen sail an aircraft wing is curved.  The air pushes on the bottom of the wing creating a high pressure.  While the air passing over the curve of the top of the wing creates a low pressure.  Pulling the wing up.  In fact, it’s the wind passing over the top of the wing that does the lion’s share of lifting airplanes into the air.  The low pressure on top of the wing is so great that they put the engines on the wings, and the fuel in the wings, to counteract this lifting force.  To prevent the wings from curling up and snapping off of the plane.  Planes with tail-mounted engines have extra reinforcement in the wings to resist this bending force.  So those lifting forces only lift the plane.  And not curl the wing up until it separates from the plane.

To make Flying Safe at Slow Speeds they add Leading Edge Slats and Trailing Edge Flaps to the Wing

Sails can propel a ship because a ship floats on water.  The wind only propels a ship forward.  On an airplane the wind moving over the wings provides only lift.  It does not propel a plane forward.  Engines propel planes forward.  And it takes a certain amount of forward speed to make the air passing over the wings fast enough to create lift.  The faster the forward air speed the greater the lift.  Today jet engines let planes fly high and fast.  In the thin air where there is less drag.  That is, where the air has less mass pushing against the forward progress of the plane.  At these altitudes the big planes cruise in excess of 600 miles per hour.  Where these planes fly at their most fuel efficient.  But these big planes can’t land or take off at speeds in excess of 600 miles per hour.  In fact, a typical take-off speed for a 747-400 is about 180 miles per hour.  Give or take depending on winds and aircraft weight.  So how does a plane land and take off at speeds under 200 mph while cruising at speeds in excess of 600 mph?  By changing the shape of the wing.

We determine the amount of lift by the curvature and surface area of the wing.  The greater the curvature the greater the lift.  However, the greater the curvature the greater the drag.  And the greater the drag the more fuel consumed at higher speeds.  And the more stresses placed on the wing.  Also, current runways are about 2 miles long for the big planes.  That’s when they land and take off at speeds under 200 mph.  To land and take off at speeds around 600 mph would require much longer runways.  Which would be extremely costly.  And dangerous.  For anything traveling close to 600 mph on or near the ground would have a very small margin of error.  So to make flying safe and efficient they add leading edge slats to the front edge of the wing.  And trailing edge flaps to the back edge of the wing.  During cruise speeds both are fully retracted to reduce the curvature of the wing.  Allowing higher speeds.  At slower speeds they extend the slats and flaps.  Greatly increasing the curvature of the wing.  And the surface area.  Providing up to 80% more lift at these slower speeds.

At takeoff and landing pilots elevate the nose of the aircraft to increase the angle of attack of the wing.  Forcing more air under the wing to push the wing up.  And causing the air on top of the wing to turn farther away for its original direction of travel as it travels across the top of the up-tilted wing.  Creating greater lift.  And the ability to fly at slower speeds.  However, if the angle of attack it too great the smooth flow of air across the wing will break away from the wing surface and become turbulent.  The wing will not be able to produce lift.  So the wing will stall.  And the plane will fall out of the sky.  With the only thing that can save it being altitude.  For in a stall the aircraft will automatically push the stick forward to lower the nose.  To decrease the angle of attack of the wing.  Decrease drag.  And increase air speed.  If there is enough altitude, and the plane has a chance to increase speed enough to produce lift again, the pilot should be able to recover from the stall.  And most do.  Because most pilots are that good.  And aircraft designs are that good.  For although flying is the most complicated mode of travel it is also the safest mode of travel.  Where they make going from zero to 600 mph in a matter of minutes as routine as commuting to work.  Only safer.

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