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.


Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

Steam Locomotive, Diesel Electric Locomotive, Interstate Highway System, Airplane, Air Travel, Refined Petroleum Products and Pipelines

Posted by PITHOCRATES - March 21st, 2012

Technology 101

The Diesel Electric Locomotive could pull a Train Cross Country and into the Heart of a City with Minimal Pollution

The 1920s were transformative years.  The Roaring Twenties.  It’s when we moved from animal power to mechanical power.  From the horse and plow to the tractor.  From steam power to electric power.  From the telegraph to the telephone.  From the gas lamp to the electric light.  From crowded mass transit to the freedom of the automobile.  From manual labor to the assembly line. 

You can see a glimpse of that world in 1920’s Steam Train Journey Across the United States – Westward Ho!  The beginning of the modern city.  With modern street lighting.  Electric power and telephone overhead wiring.  Streets crowded with automobiles.  Tractors and mechanical harvesters on the farm.  And, of course, the steam locomotive.  Connecting distant cities.  Transferring the freight to feed the modern industrial economy.  And shipping the finished goods.  As well as all that food from the farm to our grocer’s shelves.  Proving the 1920s were vibrant economic times.  With real economic growth.  And not a speculative bubble.  For there was nothing speculative about all of this technology becoming a part of our way of life.

Of course the technology wasn’t perfect.  The coal-burning locomotives belched black smoke and ash wherever they went.  Which wasn’t all that bad in the open country where a train or two passed.  But it was pretty dangerous in tunnels.  Which had to be short lest they suffocated their passengers.  (One of the reasons why all subways use electric trains).  Making for some long and winding railroads in mountainous terrain.  To go around mountains instead of under them.  Slowing trains and increasing travel time.  And they were pretty unpleasant in the cities.  Where the several rail lines converged.  Bringing a lot of coal-burning locomotives together.  Creating a smoky haze in these cities.  And leaving a layer of ash everywhere.  The cleaner diesel-burning locomotives changed that.  The diesel electric locomotive could pull a train cross country and into the heart of a city with a minimal amount of pollution.  As long as they kept their engines from burning rich.  Which they would if they operated them with dirty air filters.  Reducing fuel efficiency by having the air-fuel mixture contain too much fuel.  And causing these engines to belch black smoke.  Similar to diesel trucks running with dirty air filters.

Airplanes can travel between Two Points in a Direct Line at Faster Speeds than a Train or Bus with Minimal Infrastructure

Trains shrunk our country.  Brought distant cities together.  Allowing people to visit anywhere in the continental United States.  And the railroads profited well from all of this travel.  Until two later developments.  One was the interstate highway system.  That transferred a lot of freight from the trains to trucks.  As well as people from trains to buses and cars.  And then air travel.  That transferred even more people from trains to airplanes.  This competition really weakening railroads’ profits.  And pretty much put an end to passenger rail.  For people used the interstate highway system for short trips.  And flew on the long ones.  Which was quicker.  And less expensive.  Primarily because airplanes flew over terrain that was costly to avoid.

Highways and railroads have to negotiate terrain.  They have to wind around obstacles.  Go up and down mountainous regions.  Cross rivers and valleys on bridges.  Travel under hilly terrain through tunnels.  And everywhere they go they have to travel on something built by man.  All the way from point A to point B.  Now trucks, buses and cars have an advantage here.  We subsidize highway travel with fuel taxes.  Trucking companies, bus lines and car owners didn’t have to build the road and infrastructure connecting point A to point B.  Like the railroads do.  The railroads had to supply that very extensive and very expensive infrastructure themselves.  Paid for by their freight rates and their passenger ticket sales.  And when there were less expensive alternatives it was difficult to sell your rates and fares at prices high enough to support that infrastructure.  Especially when that lower-priced alternative got you where you were going faster.  Like the airplane did.

Man had always wanted to fly.  Like a bird.  But no amount of flapping of man-made wings got anyone off the ground.  We’re too heavy and lacked the necessary breast muscles to flap anything fast enough.  Not to mention that if we could we didn’t have any means to stabilize ourselves in flight.  We don’t have a streamline body or tail feathers.  But then we learned we could create lift.  Not by flapping but my pushing a curved wing through the air.  As the air passes over this curved surface it creates lift.  Generate enough speed and you could lift quite a load with those wings.  Including people.  Cargo.  Engines.  And fuel.  Add in some control elements and we could stabilize this in flight.  A tail fin to prevent yawing (twisting left and right) from the direction of flight.  Like a weathercock turns to point in the direction of the wind.  And an elevator (small ‘wing’ at the tail of the plane) to control pitch (nose up and nose down).  Ailerons correct for rolling.  Or turn the plane by rolling.  By tipping the wings up or down to bank the airplane (to turn left the left aileron goes up and the right aileron goes down).  And using the elevator on the take-off roll to pitch the nose up to allow the plane to gain altitude.  And in flight it allows the plane to ascend or descend to different altitudes.  Put all of this together and it allows an airplane to travel between points A and B while avoiding all terrain.  In a direct line between these two points.  At a much faster speed than a train, bus or car can travel.  And the only infrastructure required for this are the airports at points A and B.  And the few en route air traffic controllers between points A and B. Which consisted of radar installations and dark rooms with people staring at monitors.  Communicating to the aircraft.  Helping them to negotiate the air highways without colliding into other aircraft.  And air travel took off, of course, in the 1920s.  The Roaring Twenties.  Those glorious transformative years.

Refined Petroleum Products have Large Concentrations of Energy and are the Only Fuel that allows Air Travel

The most expensive cost of flying is the fuel cost.  The costlier it is the costlier it is to fly.  Not so for the railroads.  Because their fuel costs aren’t the most expensive cost they have.  Maintaining their infrastructure is.  They can carry incredible loads cross country for a small price per unit weight.  Without swings in fuel prices eating into their profits.  Making them ideal to transfer very large and/or heavy loads over great distances.  Despite dealing with all the headaches of terrain.  For neither a plane nor a truck can carry the same volume a train can.  And heavier loads on a plane take far greater amounts of fuel.  This additional fuel itself adding a great amount of weight to the aircraft.  Thus limiting its flight distance.  Requiring refueling stops along the way.  Making it a very expensive way to transport heavy loads.  Which is why we ship coal on trains.  Not on planes.

Trains are profitable again.  But they’re not making their money moving people around.  Their money is in heavy freight.  Iron ore.  Coke.  And, of course, coal.  To feed the modern industrial economy.  Stuff too heavy for our paved roads.  And needed in such bulk that it would take caravans of trucks to carry what one train can carry.  But even trains can’t transport something in enough bulk to make it cost efficient.  Refined petroleum.  Gasoline.  Diesel.  And jet fuel.  For these we use pipelines.  From pipelines we load gas and diesel onto trucks and deliver it to your local gas station.  We run pipelines directly to the fuel racks in rail yards.   And run pipelines to our airports.  Where we pump jet fuel into onsite storage tanks in large fuel farms.  Which we then pump out in another set of pipelines to fueling hydrants located right at aircraft gates.

These refined petroleum products carry large concentrations of energy.  Are easy to transport in pipelines.  Are portable.  And are very convenient.  Planes and trains (as well as ships, busses and cars) can carry them.  Allowing them to travel great distances.  Something currently no renewable energy can do.  And doing without them would put an end to air travel.  Greatly increase the cost of rail transport (by electrifying ALL our tracks).  Or simply abandoning track we don’t electrify.  Making those far distant cities ever more distant.  And our traveling options far more limited than they were in the 1920s.  Turning the hands of time back about a hundred years.  Only we’ll have less.  And life will be less enjoyable.


Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,