Trucks, Trains, Ships and Planes

Posted by PITHOCRATES - August 21st, 2013

Technology 101

Big Over-the-Road Tractor Trailer Trucks have Big Wheels so they can have Big Brakes

If you buy a big boat chances are you have a truck or a big SUV to pull it.  For rarely do you see a small car pulling a large boat.  Have you ever wondered why?  A small car can easily pull a large boat on a level (or a near level) surface.  That’s not the problem.  The problem is stopping once it gets moving.  For that is a lot of mass.  Creating a lot of kinetic energy (one half of the mass times velocity squared).  Which is dissipated as heat as brake shoes or pads rub against the wheels.  This is why you need a big truck or SUV to pull a boat.  So you can stop it once it gets moving.

Big trucks and big SUVs have big wheels and big brakes.  Large areas where brake pads/shoes press against a rotating wheel.  All of which is heavy duty equipment.  That can grab onto to those wheels and slow them down.  Converting that kinetic energy into heat.  This is why the big over-the-road tractor trailer trucks have big wheels.  So they can have big enough brakes to stop that huge mass once it gets moving.  Without the brakes turning white hot and melting.  Properly equipped trucks can carry great loads.  Moving freight safely across our highways and byways.  But there is a limit to what they can carry.  Too much weight spread between too few axles will pound the road apart.  Which is why the state police weighs our trucks.  To make sure they have enough axles supporting the load they’re carrying.  So they don’t break up our roads.  And that they can safely stop.

It’s a little different with trains.  All train cars have a fixed number of axles.  But you will notice the size of the cars differ.  Big oversized boxcars carry a lot of freight.  But it’s more big than heavy.  Heavy freight, on the other hand, like coal, you will see in smaller cars.  So the weight they carry doesn’t exceed the permissible weight/axle.  If you ever sat at a railroad crossing as a train passed you’ve probably noticed that the rail moves as the train travels across.  Watch a section of rail the next time you’re stopped by a train.  And you will see the rail sink a little beneath the axle as it passes over.

If a Ship is Watertight and Properly Balanced it can be covered in Green Water and Rise back to the Surface

So the various sizes of train cars (i.e., rolling stock) keeps each car from being overloaded.  Unlike a truck.  Steel haulers and gravel trains (i.e., dump trucks) have numerous axles beneath the load they’re carrying.  But these axles are retractable.  For the more wheels in contact with the road the more fuel is needed to overcome the friction between the tires and the road.  And the more tires in contact with the road the more tire wear there is.  Tires and fuel are expensive.  So truckers like to have as few tires in contact with the road as possible.  When they’re running empty they will have as many of these wheels retracted up as possible.  Something you can’t do with a train.

That said, a train’s weight is critical for the safe operation of a train.  In particular, stopping a train.  The longer a train is the more distance it takes to stop.  It is hard to overload a particular car in the string of cars (i.e., consist) but the total weight tells engineers how fast they can go.  How much they must slow down for curves.  How much distance they need to bring a train to a stop.  And how many handbrakes to set to keep the train from rolling away after the pressure bleeds out of the train line (i.e., the air brakes).  You do this right and it’s safe sailing over the rails.  Ships, on the other hand, have other concerns when it comes to weight.

Ships float.  Because of buoyancy.  The weight of the load presses down on the water while the surface of the water presses back against the ship.  But where you place that weight in a ship makes a big difference.  For a ship needs to maintain a certain amount of freeboard.  The distance between the surface of the water and the deck.  Waves toss ships up and down.  At best you just want water spray splashing onto your deck.  At worst you get solid water (i.e., green water).  If a ship is watertight and properly balanced it can be covered in green water and rise back to the surface.  But if a ship is loaded improperly and lists to one side or is low in the bow it reduces freeboard.  Increases green water.  And makes it less likely to be able to safely weather bad seas.  The SS Edmund Fitzgerald sank in 1975 while crossing Lake Superior in one of the worst storms ever.  She was taking on water.  Increasing her weight and lowering her into the water.  Losing freeboard.  Had increasing amounts of green water across her deck.  To the point that a couple of monster waves crashed over her and submerged her and she never returned to the surface.  It happened so fast that the crew was unable to give out a distress signal.  And as she disappeared below the surface her engine was still turning the propeller.  Driving her into the bottom of the lake.  Breaking the ship in two.  And the torque of the spinning propeller twisting the stern upside down.

Airplanes are the only Mode of Transportation that has two Systems to Carry their Load

One of the worst maritime disasters on the Great Lakes was the sinking of the SS Eastland.  Resulting in the largest loss of life in a shipwreck on the Great Lakes.  In total 844 passengers and crew died.  Was this in a storm like the SS Edmund Fitzgerald?  No.  The SS Eastland was tied to the dock on the Chicago River.  The passengers all went over to one side of the ship.  And the mass of people on one side of the ship caused the ship to capsize.  While tied to the dock.  On the Chicago River.  Because of this shift in weight.  Which can have catastrophic results.  As it can on airplanes.  There’s a sad YouTube video of a cargo 747 taking off.  You then see the nose go up and the plane fall out of the sky.  Probably because the weight slid backwards in the plane.  Shifting the center of gravity.  Causing the nose of the plane to pitch up.  Which disrupted the airflow over the wings.  Causing them to stall.  And with no lift the plane just fell out of the sky.

Airplanes are unique in one way.  They are the only mode of transportation that has two systems to carry their weight.  On the ground the landing gear carries the load.  In the air the wings carry the load.  Which makes taking off and landing the most dangerous parts of flying.  Because a plane has to accelerate rapidly down the runway so the wings begin producing lift.  Once they do the weight of the aircraft begins to transfer from the landing gear to the wings.  Allowing greater speeds.  However, if something goes wrong that interferes with the wings producing lift the wings will be unable to carry the weight of the plane.  And it will fall out of the sky.  Back onto the landing gear.  But once the plane leaves the runway there is nothing the landing gear can gently settle on.  And with no altitude to turn or to glide back to a runway the plane will fall out of the sky wherever it is.  Often with catastrophic results.

A plane has a lot of mass.  And a lot of velocity.  Giving it great kinetic energy.  It takes long runways to travel fast enough to transfer the weight of the aircraft from the landing gear to the wings.  And it takes a long, shallow approach to land an airplane.  So the wheels touch down gently while slowly picking up the weight of the aircraft as the wings lose lift.  And it takes a long runway to slow the plane down to a stop.  Using reverse thrusters to convert that kinetic energy into heat.  Sometimes even running out of runway before bringing the plane to a stop.  No other mode of transportation has this additional complication of travelling.  Transferring the weight from one system to another.  The most dangerous part of flying.  Yet despite this very dangerous transformation flying is the safest mode of traveling.  Because the majority of flying is up in the air in miles of emptiness.  Where if something happens a skilled pilot has time to regain control of the aircraft.  And bring it down safely.


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High-Speed Train crashes in Spain because things moving at High Speeds on the Ground can be Very Dangerous

Posted by PITHOCRATES - July 27th, 2013

Week in Review

Trains are heavy.  Getting a train moving is one thing.  But getting it to stop is another.  Because heavy things moving fast have a lot of kinetic energy.  The energy of something in motion.  In classical mechanics we calculate the kinetic energy by multiplying one half of the mass times the velocity squared.  That last part is really important.  The velocity part.  For as the speed increases the kinetic energy increases by a far greater amount.  For example, a train increasing speed from 30 kilometers per hour (18 mph) to 190 kilometers per hour (114 mph) increases its speed by 533%.  But because we square the velocity the kinetic energy increases by 3,911%.   Making high-speed rail more dangerous than regular rail.  Because of the great amounts of kinetic energy involved.

Airplanes are very heavy.  They travel at great speeds.  And have great amounts of kinetic energy.  Which is why plane crashes or so horrific.  Anything with that amount of kinetic energy suddenly stopping dissipates that energy in great heat, noise and the explosion of solid parts.  But plane crashes, thankfully, are rare.  For when they are travelling at those great speeds they’re up in the air thousands of feet (or more) away from anything they can hit.  And if there is a malfunction they can fall safely though the sky (with enough altitude) until the pilots can recover the aircraft.  For airplanes have the best friend to high speed objects.  A lot of empty space all around them.  Not so with high-speed rail (see Driver in custody after 80 killed in Spain train crash by Teresa Medrano and Tracy Rucinski posted 7/25/2013 on Reuters).

The driver of a Spanish train that derailed, killing at least 80 people, was under police guard in hospital on Thursday after the dramatic accident which an official source said was caused by excessive speed.

The eight-carriage train came off the tracks, hit a wall and caught fire just outside the pilgrimage destination Santiago de Compostela in northwestern Spain on Wednesday night. It was one of Europe’s worst rail disasters…

Video footage from a security camera showed the train, with 247 people on board, hurtling into a concrete wall at the side of the track as carriages jack-knifed and the engine overturned…

El Pais newspaper said the driver told the railway station by radio after being trapped in his cabin that the train entered the bend at 190 kilometers per hour (120 mph). An official source said the speed limit on that stretch of twin track, laid in 2011, was 80 kph…

Investigators were trying to find out why the train was going so fast and why security devices to keep speed within permitted limits had not slowed the train…

Spain’s rail safety record is better than the European average, ranking 18th out of 27 countries in terms of railway deaths per kilometers traveled, the European Railway Agency said. There were 218 train accidents in Spain between 2008-2011, well below the EU average of 426 for the same period.

There are no rails to derail from in the air.  And no concrete walls to crash into.  Air travel requires no infrastructure between terminal points.  High-speed rail travel requires a very expensive, a very precise and a highly maintained infrastructure between terminal points.  As well as precise controls to keep the train from exceeding safe speeds.  Planes do, too.  But when you have thousands of feet of nothingness all around you there is time to make adjustments before something catastrophic happens.  Like derailing when speeding through a curve too fast.

Air travel is safer than high-speed rail travel.  Which is why when a plane crashes it’s big news.  Because it happens so rarely these days.  Thanks to good aircraft designs.  Good pilots.  And having thousands of feet of nothingness all around you when flying at speeds close to 950 kph (570 mph).  Unlike having a concrete wall just a few feet away from a train traveling at high speeds.

High-speed rail may work in France and Japan.  The only two rail lines to pay for themselves are in these countries.  But every other passenger rail line in the world needs a government subsidy.  Because the costs of a rail infrastructure are just so great.  Making high-speed rail more of a source of union jobs than an efficient means of transportation.  Which is why they are a fixture in countries with liberal governments.  Who subsidize the high cost of these union jobs with taxpayer money.  In exchange for votes in the next election.


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