Kerosene, Jet Fuel, Lockheed Constellation, Boeing 707, Boeing 747-400, Newton’s Third Law of Motion, Turbojet and Fan Jet

Posted by PITHOCRATES - October 3rd, 2012

Technology 101

The only way to make Flying Available to the General Public is to put as many People as Possible on an Airplane

Refined petroleum products have made our lives better.  We have gasoline to drive wherever we want.  We have diesel fuel to transport things on ships and trains like petroleum oil, iron ore, coal, food, medicine, smartphones, coffee, tea, wine, scotch whisky, bourbon whiskey, beer, fresh fish, sushi, etc.  Pretty much everything we buy at a store or a restaurant got there on something powered by diesel fuel.  And sometimes kerosene.  If it must travel fast.  And if it does then it finds itself on a jet aircraft.

Today aviation has shrunk the world.  We can order a new smartphone sitting on a shelf in California and have it the next day in New York.  We can even travel to distant countries.  Some in the time of a typical working day.  Some a half a day or longer.  When but a 100 years earlier it took a couple of weeks to cross the Atlantic Ocean.  While 200 years ago it took a couple of months.  We can travel anywhere.  And get there quickly.  Thanks to the jumbo jet.  And not just the super-rich.  Pretty much anyone today can afford to buy a plane ticket to travel anywhere in the world.  And one thing makes this possible.  The jet engine.

Airplanes are expensive.  So are airports, air traffic control and jet fuel.  Airlines pay for all of these costs one passenger at a time.  Their largest cost is their fuel cost.  The longer the flight the greater the cost.  So the only way to make flying available to the general public is to put as many people as possible on an airplane.  Dividing the total flying cost by the number of passengers on the airplane.  This is why we fly on jumbo jets for these longer flights.  Because there are more people to split the total costs.  Lowering the cost per ticket.  Before the jet engine, though, it was a different story.

The Boeing 747-400 can take up to 660 Passengers some 7,260 Miles at a Speed of 567 MPH

One of the last intercontinental propeller-driven airplanes was the Lockheed Constellation.  A plane with four (4) Wright R-3350-DA3 Turbo Compound 18-cylinder supercharged radial engines putting out 3,250 horsepower each.  Which is a lot considering today’s typical 6-cyclinder automobile engine is lucky to get 300 horsepower.  No, the horsepower of one of these engines is about what one modern diesel-electric locomotive produces.  So these are big engines.  With a total power equal to about four locomotives lashed up.  Which is a lot of power.  And what does that power allow the Constellation do?  Not much by today’s standards.

In its day the Lockheed Constellation was a technological wonder.  It could take up to 109 passengers some 5,500 miles at a speed of 340 mph.  No bus or train could match this.  Not to mention it could fly over the water.  Then came the age of the jet.  The Boeing 707 being the first largely successful commercial jetliner.  Which could take up to 189 passengers some 6,160 miles at a speed of 607 mph.  That’s 73.4% more passengers, a 78.5% faster speed and a 14.1% longer range.  Which is an incredible improvement over the Constellation.  But nothing compared to the Boeing 747-400.  Which can take up to 660 passengers (506% more than the Constellation and 249% more than the 707) some 7,260 miles at a speed of 567 mph.

Now remember, fuel is the greatest cost of aviation.  So let’s assume that a intercontinental flight costs a total of $75,000 for each plane flying the same route.  Dividing that cost by the number of passengers you get a ticket price of approximately $688, $397 and $114 for the Constellation, the 707 and the 747-400, respectively.  So you can see the advantage of packing in as many passengers as possible into an airplane to lower the cost of flying.  Which is why the jumbo jets fly the longest routes that consume the most fuel.  And why we no longer fly propeller-driven aircraft except on short routes to airports with short runways.  These engines just don’t have the power to get a plane off the ground with enough people to reduce the cost of flying to a price most people could afford.  Only the jet engine has that kind of power.

The Fan Jet is basically a Turbojet with a Large Fan in front of the Compressor

Newton’s Third Law of Motion states that for every action there is an equal and opposite reaction.  Think of a balloon you just blew up and are holding closed.  If you release your hold air will exit the balloon in one direction.  And the balloon will move in the opposite direction.  This is how a jet engine moves an aircraft.  Hot exhaust gases exit the engine in one direction.  Pushing the jet engine in the opposite direction.  And because the jet engines move the plane moves.  With the force of the jet engines transferred via their connection points to the aircraft.  The greater the speed of the gas exiting the jet the faster it will push a plane forward.

The jet engine gets that power from the continuous cycle of the jet engine.  Air enters one end, gets compressed, enters a combustion chamber, mixes with fuel (kerosene), ignites, expands rapidly and exits the other end.  The hot (3,632 degree Fahrenheit) and expanding gases pass through and spin a turbine.  Then exit the engine.  The turbine is connected to the compressor at the front of the engine.  So the exhaust gases spin the compressor that sucks air into the engine.  As the air passes through the compressor it compresses and heats up.  Then it enters the combustion chamber and joins fuel that is injected and burned continuously.  Sort of like pouring gas on a burning fire.  Only enormous amounts of compressed air and kerosene are poured onto a burning fire.  As this air-fuel mixture burns it rapidly expands.  And exits the combustion chamber faster than the air entered it.  And shoots a hot stream of jet gas out the tail pipe.  Which produces the loud noise of these turbojets.  This fast jet of air cuts through the surrounding air.  Resulting in a shear effect.  Which the next generation of jet engines, the fan jet, greatly reduces.

The fan jet is basically a turbojet with one additional feature.  A large fan in front of the compressor.  These are the big engines you see on the jumbo jets.  They add another turbine inside the jet that spins the fan at the front of the engine.  Which feeds some air into the compressor of what is basically a turbojet.  But a lot of the air this fan sucks in bypasses the turbojet core.  And blows directly out the back of the fan at high speed.  In fact, this bypass air provides about 75% of the total thrust of the fan jet.  Acting more like a propeller than a jet.  And as an added benefit this bypass air surrounds the faster exhaust of the jet thereby lessening the shear effect.  Making these larger engines pretty quiet.  In fact a DC-9, an MD-80, a 707 or a 727 with standard turbojets are much louder than a 747 with 4 fan jets at full power.  They’re quieter.  And they can push a lot more people through the air at incredible speeds over great distances at a reasonable price per passenger than any other aircraft engine.

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