Why doesn't the exhaust in a jet engine come out the front?

One thing to keep in mind when thinking about the flow of air through a jet engine is the "path of least resistance" concept. When you burn the fuel in a jet engine, the air and combusted fuel expand considerably. These exhaust gases are looking for a way out of the combustion chamber.

When they "look" forward toward the compressor, what they "see" is a wall of air at something like 10 times normal atmospheric pressure moving at several hundred miles per hour. When the gases "look" back toward the end of the engine, what they "see" is a nearly clear path toward normal atmospheric pressure. The only thing in the way is the turbine fan, and that is nothing. The path of least resistance is clearly toward the back of the engine, so that's where the gases go.

That is true in any jet engine that has a compressor. A Ram jet is essentially open at both ends, so it suffers from the problem you are suggesting. It actually has to be moving through the air at a fairly good clip before it will work. There has to be enough pressure in the incoming air to make the back of the engine the obvious path of least resistance.

In WWII, Germany used pulse jets in its V-1 missiles. These missiles were known as "buzz bombs" at the time. They actually had a valve like you suggest -- at the front of the engine was a set of shutters. These shutters would open to let in a slug of air, and then close. The engine would inject fuel into this slug of air and ignite it. With the flaps shut, the exhaust gases had only one way to go. Then the flaps would open and the cycle repeated. This allowed buzz bombs to start from a standing stop (unlike a Ram jet) without having the complexity of a compressor.

How much fuel does an international plane use for a trip?

A plane like a Boeing 747 uses approximately 1 gallon of fuel (about 4 liters) every second. Over the course of a 10-hour flight, it might burn 36,000 gallons (150,000 liters). According to Boeing's Web site, the 747 burns approximately 5 gallons of fuel per mile (12 liters per kilometer).

This sounds like a tremendously poor miles-per-gallon rating! But consider that a 747 can carry as many as 568 people. Let's call it 500 people to take into account the fact that not all seats on most flights are occupied. A 747 is transporting 500 people 1 mile using 5 gallons of fuel. That means the plane is burning 0.01 gallons per person per mile. In other words, the plane is getting 100 miles per gallon per person! The typical car gets about 25 miles per gallon, so the 747 is much better than a car carrying one person, and compares favorably even if there are four people in the car. Not bad when you consider that the 747 is flying at 550 miles per hour (900 km/h)!

How does a speedometer in an airplane work? How does a speedometer in an airplane Functions?

Airspeed is a measurement of the plane's speed relative to the air around it. The pitotairplanes (pronounced pee-toe) static tube system is an ingenious device used by and boats for measuring forward speed. The device is really a differential pressure gauge and was invented by Henri Pitot in 1732. An example of an air pressure gauge is a tire pressure gauge.

The open end of the pitot tube, usually mounted on a wing, faces toward the flow of air or water. The air speed indicator actually measures the difference between a static sensor not in the air stream and a sensor (pitot tube) in the air stream. When the airplane is standing still, the pressure in each tube is equal and the air speed indicator shows zero. The rush of air in flight causes a pressure differential between the static tube and the pitot tube. The pressure differential makes the pointer on the air speed indicator move. An increase in forward speed raises the pressure at the end of the pitot tube. In turn, the air pressure pushes against a flexible diaphragm that moves a connected mechanical pointer on the face of the indicator. The indicator is calibrated to compensate for winds in the air or the speed of the opposing current in the water. In airplanes, electronics also compensate for altitude and air temperature to make the air speed measurement accurate.

The following picture shows a direct reading air speed indicator for a hang glider. This instrument is for paragliding and ultra light aircraft and is also ideal for measuring wind speed for activities such as:

• Wind surfing
• Radio controlled model airplane flying

The difference between the static pressure and the pressure of the air rushing into the opening in the bottom of the tube causes the red indicator disc to rise, since the upward pressure in the tube is greater than the weight of the disc. Notice the slight taper in the design of the vertical tube. The red disc has a hole in the center for the slider rod to keep the disc level.

Photo courtesy Wills Wing, Inc. Air speed indicator

The air speed indicator fastens to the strut of a hang glider:

Photo courtesy Wills Wing, Inc. Air speed indicator mounted on a hang glider

Pitot tube devices and manometers are also used in commercial heating and air conditioning systems for duct air flow measurements.

Flight after the Cold War Timeline

January 12, 1984 The U.S. Marines get the first McDonnell Douglas AV-8B Harrier IIs, which will be used in the Persian Gulf War.

January 21, 1984 The Air Force successfully fires an ASAT (antisatellite) missile from an F-15 over the Pacific.

January 25, 1984 In his State of the Union address, President Ronald Reagan calls for building a space station.

Flight Pictures

Peter M. Bowers Collection
Voyager was an all-composite aircraft designed by Burt Rutan. His brother Dick Rutan made the first flight on June 22, 1984. See more pictures of flight.

February 3-11, 1984 Space Shuttle Challenger is launched. It tests the Manned Maneuvering Unit, in which astronaut Bruce McCandless orbits, untethered, around the shuttle.

February 24, 1984 The General Dynamics F-16XL is defeated by the McDonnell Douglas F-15E Strike Eagle in competition.

March 6, 1984 The comeback of lighter-than-air craft is signaled by the first flight of the British Airship Industries Skyship.

March 31, 1984 The last Avro Vulcan is removed from RAF service.

April 6-13, 1984 The Space Shuttle Challenger mission makes the first on-orbit satellite repair of Solar Max.

May 15, 1984 A consortium of Aeritalia/Aermacchi/EMBRAER creates the AMX close-support aircraft, which makes its first flight. On a subsequent flight 15 days later, it crashes, killing the pilot.

June 22, 1984 Voyager flies for the first time.

June 22, 1984 Virgin Airlines launches operations.

July 17-19, 1984 The 100th human space flight occurs with the launch of the Soviet Soyuz T-12.

July 25, 1984 Svetlana Savitskaya becomes the first woman to make a space walk, from Salyut 7.

August 4, 1984 European space flight exploration continues with the launch of Ariane 3 from French Guinea.

August 14, 1984 The last of 1,832 Boeing 727s is rolled out in Renton, Washington.

August 29, 1984 A Rockwell International B-1A crashes.

August 30, 1984 The Space Shuttle Discovery is launched on its maiden flight.

September 14-18, 1984 Joe Kittinger, famous for high-altitude parachute drops, makes the first nonstop solo balloon flight across the Atlantic.

October 5, 1984 The Space Shuttle Challenger is launched.

Peter M. Bowers Collection
The Rockwell B-1B bomber had one of the longest and most controversial development periods. After a rocky start, the swing-wing Mach 1.25 B-1B has done an outstanding job.

October 18, 1984 The Rockwell International B-1B makes its first flight. One hundred are ordered.

November 8-16, 1984 The Space Shuttle Discovery makes its second flight.

December 14, 1984 The Grumman X-29 technology demonstrator, with forward swept wings, makes its first flight.

January 24-27, 1985 The Space Shuttle Discovery conducts a classified defense assignment; military aviation has melded with space flight.

March 21, 1985 The RAF selects EMBRAER Tucano as its new basic trainer.

April 12-19, 1985 The Space Shuttle Discovery carries Senator Jake Garn into orbit.

April 29-May 6, 1985 The Space Shuttle Challenger launches with Spacelab 3.

May 29, 1985 The Soviet Union unveils the world's largest airplane, the Antonov An-124 heavy transport, at the Paris air show.

June 11, 1985 The Soviet Vega-1 spacecraft is sent to rendezvous with Halley's Comet.

June 17-24, 1985 The Space Shuttle Discovery is launched with two foreign astronauts, Patrick Baudry of France and Sulton Abdelazizi Al-Saud of Saudi Arabia.

July 29-August 6, 1985 The Space Shuttle Challenger is launched; it experiences the first major in-flight emergency of shuttle history when one main engine shuts down during ascent.

August 12, 1985 The world's worst aircraft disaster to date occurs when a Japan Air Lines Boeing 747 crashes into the mountains. Japan Air Lines later faults Boeing quality control for the accident.

August 18, 1985 The Japa­nese launch a space probe for a flyby of Halley's Comet.

August 27-September 3, 1985 Space Shuttle Discovery is launched; it deploys three satellites and repairs another.

September 10, 1985 The Lockheed C-5B Galaxy makes its first flight.

September 13, 1985 An ASAT missile fired from an F-15 successfully intercepts an orbiting satellite.

September 30, 1985 Italians acquire a new aircraft carrier for helicopters and VSTOL aircraft, the Giuseppe Garibaldi.

October 3-7, 1985 The Space Shuttle Atlantis is launched on its maiden flight; it sets a new shuttle altitude record with an orbit of 1,725,000 miles.

October 30-November 6, 1985 Space Shuttle Challenger is launched with German and Dutch astronauts as part of the largest (eight-member) crew in history.

November 15, 1985 The last independant general aviation manufacturer -- Cessna -- is purchased by General Dynamics.

November 26-December 3, 1985 Space Shuttle Atlantis is launched in an experiment with space station structures.

December 17, 1985 On the 82nd anniversary of the Wright Brothers flight, the Douglas DC-3 celebrates its 50th birthday. Approximately 400 are still in use.

December 28, 1985 The U.S. Pioneer 12 probe passes within 25,000,000 miles of Halley's Comet.

1986-1987 Flight Timeline

January 8, 1986 The first Lockheed C-5B transport is delivered to the Air Force.

January 12-18, 1986 Space Shuttle Columbia is launched.

January 24, 1986 The U.S. planetary spacecraft Voyager 2 makes a Uranus flyby (passes within 66,500 miles) and encounters moons and ring system, then is redirected toward Neptune.

Peter M. Bowers Collection
The Grumman X-29 was particularly valuable in testing the high angle of attack flight regimes. Germany had experimented with forward swept wings before, but not until the development of fly-by-wire and composite materials was further research rewarding.

January 28, 1986 The Space Shuttle Challenger blows up 72 seconds into liftoff; teacher Christa McAuliffe is on board. Seven astronauts perish; the Shuttle fleet is grounded for 30 months.

February 15, 1986 The futuristic Beech Starship 1 business aircraft makes its first flight.

March 9, 1986 Soviet comet probe Vega 2 observes Halley's Comet from a distance of 4,990 miles.

March 13-14, 1986 The European Space Agency's Giotto satellite flies within 335 miles of Halley's Comet.

April 14-15, 1986 The United States strikes Libya in retaliation for terrorist activities. Attacking aircraft include EF-111As and F-111s from the United Kingdom (France won't allow flight over its airspace), as well as Navy A-6s and A-7s.

July 1, 1986 The first close look at MiG-29 fighters occurs on a goodwill visit to Finland. The aircraft closely resembles the F-15 and has similar performance.

July 4, 1986 The Eurofighter, the Dassault-Breguet Rafale, makes its first flight.

July 10-14, 1986 On a test flight, the Voyager flies 11,336.9 miles nonstop, unrefueled.

July 11, 1986 Reports of the crash of the second Lockheed F-117A stealth fighter give rise to unfounded concerns that it is too unstable for pilots.

August 11, 1986 The Westland Lynx becomes the world's fastest production helicopter, flying at 249.09 miles per hour.

September 2, 1986 An unusual combination hot-air/helium balloon makes a record flight from Amsterdam to St. John, Newfoundland, in 50 hours, piloted by Henk and Evelyn Brink of the Netherlands.

September 23, 1986 The Piaggio Avanti twin turboprop makes its first flight; it is a potential competitor to the Beech Starship.

November 6, 1986 Forty-five people are killed in the crash of a Chinook helicopter near Scotland. It is the worst civilian helicopter crash in history.

November 30, 1986 The Fokker 100 twin-turboprop passenger liner makes its first flight.

December 4, 1986 The McDonnell Douglas MD-87, a smaller version of the older DC-9 airliner, makes its first flight.

December 11, 1986 The McDonnell Douglas F-15E Eagle, a combination air superiority/ground support fighter, makes its first flight.

December 14-23, 1986 Burt Rutan's specially designed Voyager makes the first nonstop, unrefueled circumnavigation of the world.

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Peter M. Bowers Collection
On July 4, 1987, a B-1B set four world records for speed, distance, and payload. The B-1B also has a tremendous conventional weapon capability.

January 21, 1987 Lois McCallan sets a human-powered record for women in MIT's Michelob Light Eagle.­

February 6-July 30, 1987 Soyuz TM-2 is launched; it uses a new automatic docking system to dock with space station Mir. The Soviet Union provides full television coverage.

February 6, 1987 The Aerospatial Super Puma helicopter flies.

February 19, 1987 The Boeing E-6A TACAMO relay aircraft makes its first flight.

February 22, 1987 The Airbus 320, with fly-by-wire system, makes its first flight.

March 1987 Patrice Fran­cheske makes the first microlight round-the-world flight.

April 26, 1987 The first prototype of the Saab JAS 39 Gripen is unveiled.

May 29, 1987 Mathias Rust lands a Cessna 172 in Red Square.

June 26, 1987 Richard Branson and Per Lindstrand cross the Atlantic by hot-air balloon for the first time. They reach 153 miles per hour in a jet stream.

September 30, 1987 A NASA report indicates that there are 18,400 trackable artificial objects in space.

October 9, 1987 The preproduction EH 101 helicopter makes its first flight.

November 19, 1987 Northrop is awarded a $2 billion contract to develop the B-2 stealth bomber.

November 29, 1987 A Korean Airlines Boeing 707 is blown up by a terrorist bomb.

December 29, 1987 Soviet cosmonaut Yuri Romanenko sets a new human space duration record of 326 days, 11 hours, and 38 minutes.

1988-1989 Flight Timeline

January 1988 The first Low Level Wind Shear Alert System is installed.

January 1988 Tupelov Blackjacks enter operational service with the Soviet Air Force.

January 29-30, 1988 A 747 SP sets a round-the-world record of 36 hours and 54 minutes.

February 8, 1988 The Department of Defense begins SDI (Star Wars) experimentation with the launch of the Delta 181.

Peter M. Bowers Collection
The Beech Starship made its first flight on February 15, 1986, a significant landmark in the history of general aviation.

March 1988 Germany revives a World War II idea of using the Sänger concept to "skip" a reusable aerospace plane through upper levels of atmosphere.

April 15, 1988 A modified Tupelov Tu-154, the first aircraft fueled by liquid hydrogen, flies for the first time.

April 16, 1988 The British Aerospace/McDonnell Douglas T-45A Goshawk trainer makes its first flight.

April 23, 1988 Smoking is banned on U.S. domestic airline flights.

May 23, 1988 The first Bell/Boeing V-22 Osprey prototype is rolled out.

May 27, 1988 The McDonnell Douglas F-4 Phantom celebrates the 30th anniversary of its first flight.

June 26, 1988 An Airbus Industries A320 airliner flies into the ground; questions are raised concerning the fly-by-wire concept.

July 3, 1988 An Airbus 300 of Iran Air is shot down by the guided missile cruiser USS Vincennes; there are 290 casualties.

July 7, 1988 The Soviet Phobos 1 spacecraft is launched to study Mars; communications are lost on August 29, 1989.

July 12, 1988 Phobos 2, the companion spacecraft to Phobos 1, is launched to study Mars, arriving on January 29, 1989.

August 17, 1988 President Zia of Pakistan is killed in the crash of a Lockheed C-130.

August 28, 1988 Three Aermacchi MB-339s from an Italian air demonstration team collide during an air show at Ramstein Air Base in Germany.

September 28, 1988 The Ilyushin Il-96 wide-body transport makes its first flight.

September 29, 1988 The Space Shuttle Discovery is launched in the first shuttle flight since the Challenger disaster.

November 5, 1988 Soviets unveil the Antonov An-225 Mriya transport. It is the largest aircraft in the world, weighing more than 1,000,000 pounds when fully loaded.

November 10, 1988 The U.S. Air Force confirms the existence of the Lockheed F-117 stealth fighter.

November 15, 1988 Soviets launch their counterpart to the Space Shuttle, the Buran; it is totally automatic, no humans are onboard. The program is later canceled.

November 22, 1988 The Northrop B-2A Spirit stealth bomber is rolled out.

December 2-6, 1988 The Space Shuttle Atlantis is launched on a classified defense mission.

December 9, 1988 The Saab JAS 39 Gripen multirole fighter makes its first flight.

December 15, 1988 The FAA issues a type certificate for the Airbus A320, the first fly-by-wire airliner.

December 21, 1988 Terrorists blow up a Pan Am 747 over Lockerbie, Scotland; 269 are killed.

January 2, 1989 The Tupelov Tu-204 makes its first flight.

January 4, 1989 Navy F-14A Tomcats shoot down two Libyan MiG-23s over international waters, which Libya claims as territorial.

January 10, 1989 The FAA requires the Traffic Alert and Collision Avoidance System on all airliners with more than 30 seats.

January 29, 1989 The Soviet Space probe Phobos 2 swings into orbit around Mars.

February 14, 1989 The first U.S. second-generation Nav­Star Global Positioning System (GPS) satellite is launched. It will be crucial in the Gulf War.

March 13-18, 1989 The Space Shuttle Discovery is launched; it deploys a
TDRS-D satellite.

March 24, 1989 The SDI satellite, Delta Star, is launched by the USAF.

May 4, 1989 The Magellan probe is launched by the Space Shuttle Atlantis. The probe arrives at Venus on August 10.

June 14, 1989 The USAF launches the first Titan IV.

July 17, 1989 The Northrop-Grumman B-2 stealth bomber makes its first flight.

July 19, 1989 A United DC-10 crashes while attempting an emergency landing; 107 perish.

August 8-13, 1989 The Space Shuttle Columbia is launched on a classified military mission.

August 22, 1989 Legendary Soviet aircraft designer Alex­ander Yakovlev dies at age 84.

August 25, 1989 Voyager 2 passes within 3,000 miles of Neptune.

September 14, 1989 The Bell-Boeing V-22 Osprey successfully transitions from helicopter mode to horizontal flight for the first time.

October 18, 1989 The Galileo probe to Jupiter is launched by the Space Shuttle Atlantis. The probe arrives at Jupiter in December 1999.

1990-1991 Flight Timeline

January 10, 1990 The McDonnell Douglas MD-11 makes its first flight.

January 23, 1990 Japan launches the Hiten (Muses A) satellite.

April 24-29, 1990 The Space Shuttle Discovery carries the Hubble Space Telescope into orbit.

August 2, 1990 Iraq seizes Kuwait.

September 6, 1990 A Boeing 747 becomes the new Air Force One.

Peter M. Bowers Collection
The EMBRAER firm was formed in 1969 and was an instant success with a wide variety of aircraft. The company expanded its range with the Tucano, a trainer originally intended for the Brazilian Air Force.

September 29, 1990 The Lockheed Martin YF-22 Raptor supersonic stealth fighter debuts.

October 29, 1990 Boeing gives the formal go-ahead for the 777, a twin-engine jet with a wider body than the 767. It is designed to compete with the Airbus A330 and A340.

November 9, 1990 Kansai Airport, built on a human-made island, becomes Japan's first 24-hour airport.

December 21, 1990 Famed aircraft designer Clarence L. "Kelly" Johnson dies at age 80. He designed the P-80, F-104, U-2, and SR-71.

1991 Mil-Brooke Helicopters in Miami becomes the support organization for Mil aircraft in North America.

January 15-19, 1991 Richard Branson and Per Lindstrand fly the first transpacific balloon flight, covering 6,700 miles.

January 17, 1991 Operation Desert Storm begins: The technology of modern warfare is unveiled.

February 13, 1991 The Swearingen SJ-30 small business jet makes its first flight.

February 27, 1991 The homebuilt Questair Venture sets three time-to-climb records.

April 23, 1991 Lockheed, Boeing, and General Dynamics are selected to build the F-22.

April 30, 1991 Boeing delivers the last 707 airframe, a Navy E-6A communications aircraft.

May 3, 1991 Robert Randolph's model airplane sets a duration record of 32 minutes and 9 seconds.

June 13, 1991 The Soviets display the MiG-31 and the Beriev A-40 at a Paris air show.

July 1991 The Beech T-1A Jayhawk makes its first flight.

July 16, 1991 The Falcon 900 B sets a distance record of 5,012 miles, flying from Paris to Houston.

July 22, 1991 Kari Castle sets the women's hang-gliding record with a flight of 208 miles.

August 12, 1991 Delta acquires most of Pan Am's operations.

September 15, 1991 The McDonnell Douglas C-17 makes its first flight.

October 25, 1991 The Airbus A340, the first European long-haul airliner in 30 years, makes its first flight.

December 4, 1991 Pan American World Airways makes their last flight after 64 years of operations.

1992-1993 Flight Timeline

March 23, 1992 Beechcraft (now part of Raytheon) delivers their 50,000th aircraft, a King Air 90B.

May 12, 1992 Lockheed Martin delivers the 2,000th C-130.

May 18, 1992 The first production McDonnell Douglas C-17 makes its first flight.

June 11, 1992 McDonnell Douglas delivers the 2,000th DC-9/MD-80/MD-90 series aircraft.

Warren M. Bodie Collection
Airbus threw down the gauntlet to Boeing's 747 and 777 aircraft with its A340 series of aircraft, which made its first flight on October 25, 1991. The later models of the A340 can carry up to 380 passengers over a 7,500 nautical mile range.

September 1992 The existence of the National Reconnaissance Office is declas­sified.

September 12, 1992 Dr. Mae C. Jemison becomes the first African American woman in space when she is launched onboard the Space Shuttle Endeavor.

September 25, 1992 NASA launches Mars Observer to study the Red Planet. Communication with the craft will be lost August 22, 1993.

November 2, 1992 The Airbus A330 335-passenger twin makes its first flight.

December 16, 1992 The McDonnell Douglas (Boeing) C-17 sets altitude records.

March 4, 1993 The Saab JAS 39B Gripen (a multirole aircraft) makes its first flight.

March 12, 1993 Lockheed acquires General Dynamics' Fort Worth division, the builder of the F-16.

June 8, 1993 The first Saab JAS 39 Grippen is handed over to the Swedish Air Force.

June 26, 1993 The NavStar Global Position System (GPS) satellite constellation is completed.

August 6, 1993 Sheila Widnall becomes Secretary of the U.S. Air Force.

August 17, 1993 NASA selects Boeing as its prime contractor for the International Space Station.

December 2-13, 1993 The Hubble's optical flaw is repaired by the Discovery Shuttle crew.

Flight after the Cold War

As the e­ighth decade of the twentieth century began, the world's political situation seemed to have stabilized. The Cold War contenders, the United States and the Soviet Union, though still armed to the teeth with enough weaponry to­ destroy civilization, were somehow becoming, if not friendly, at least not as overtly hostile. There were new players on the world scene -- Japan and a slowly unifying Europe and China -- but, for the most part, the main concern was that no war break out between the United States and the U.S.S.R.

The Soviet Union was continuing its long and outstanding series of space flights. Cosmonauts were spending lengthy periods in space, shuttling back and forth on their Soyuz vehicles as if they were space commuters. New Soviet aircraft were introduced, including advanced versions of the superb Sukhoi Su 27 and MiG-29, and Soviet vertical-lift fighters operated off a Soviet aircraft carrier. Then on December 25, 1991, the Soviet Union was split apart, dissolving like a cube of sugar in hot coffee. The communist system that had led the world in space, whose military might was renowned, never learned how to feed, clothe, or house its people, and, ultimately, the people spoke. Fortunately for the world, the Soviet Union went out with a whimper -- not with a nuclear bang.

Flight Pictures

Peter M. Bowers Collection
The Voyager aircraft was used by Jeana Yeager and Dick Rutan in their non-stop, round-the-world flight. See more pictures of flight.

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While the collapse of the Soviet Union might have been the defining event of the decade, it was only one of the many dramatic and exciting situations that kept people everywhere glued to their television sets as good and bad news poured forth.

Flight Timeline

Learn more about aviation events of the 1980s and 1990s, check out the Flight after the Cold War Timeline.

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On the good side, women achieved an ever increasing prominence in aerospace occupations. Captain Lynn Ripplemeyer flew a 747 across the Atlantic for People's Express. Sheila Widnall became the first female Secretary of the Air Force. Svetlana Savitskaya made the first EVA by a woman from the Salyut7/Soyuz T-12 for three hours. She was also the first woman to fly twice in space. The United States quickly countered when Sally Ride became the first American woman to go into space twice and Kathryn Sullivan made the first EVA by an American woman, both onboard the Space Shuttle Challenger.

The ebullient Jeana Yeager set a world record with Dick Rutan in their epochal nonstop, unrefueled flight around the world in the Voyager. But such progress was not without its costs. In a moment that remains etched in memory, the Space Shuttle Challenger blew up on January 28, 1986. Among the crew were veteran astronaut Judith Resnik and teacher Christa McAuliffe. Then, in 1991, Major Mari T. Rossi crashed in a Chinook helicopter, becoming the first American woman to die in aerial combat.

Aeronautical Progress

The speed of aeronautical progress accelerated as the world of flight eagerly seized upon computers, integrating them into every phase of air and space operations, from design to actual flying of air and spacecraft. The tremendous growth in computer technology was force-fed by the demand of aerospace companies, who pushed the envelope of computer development at a rate that no one would have believed and that ultimately benefitted everyone, including personal computer users.

United States Air Force Museum
The Lockheed F-117a Nighthawk is a ground attack airplane. Its unique design helps to minimize its radar profile.

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The Airbus Industrie A320 was a Computer Aided Design (CAD) and a Computer Aided Manufacture (CAM), and this would be the way of the future. Gone were wooden mock-ups and the absolute need for a prototype; with CAD/CAM the first aircraft made could be a production version, if desired.

Computers were also invaluable for the proliferation of simulators so lifelike they could be used for the transition training of airline and military crews. Simulators grew in importance as the cost of flying time went up; they would soon substitute for the actual use of aircraft for familiarization flying and flight checks.

Terrorism became more and more prevalent, with airliners being blown up on the ground and in the air. The most appalling incident was the destruction of Pan Am Flight 103 over Scotland on Dec­­ember 21, 1988. One decisive action against terrorists took place when President Ronald Reagan authorized Operation El Dorado Canyon, a swift strike by General Dynamics F-111s and Navy A-6 and A-7E aircraft that punished -- and reportedly terrorized -- Libya's Colonel Moammar Gadhafi.

In August 1990, Saddam Hussein sent his armies into Kuwait, annexing it as an Iraqi province. He next threatened Saudi Arabia, which was vulnerable to Iraq's military might. The United States led a U.N. force to intervene first with Operation Desert Shield and then to counterattack with Operation Desert Storm. Both operations revealed to the world the unprecedented might of the United States with conventional weapons. Stealth aircraft; precision-guided munitions; airborne command and control; and the use of space-based navigation, meteorological, communications, and intelligence systems overwhelmed the Iraqis.

The combination of Lockheed Martin F-117A Nighthawk stealth fighters and precision-guided munitions revealed, in real time, some of the most spectacular bombing results in history. All over the world, people watched in awe as crosshairs were aligned on a target -- the window of a bunker, the cockpit of a parked aircraft -- followed by a bomb dropping to strike the target. In the meantime, no Nighthawk was even hit by enemy fire.

Military Planes after Desert Storm

Many of those television sets watching the Persian Gulf War were in the Soviet Union, where both military and political leaders were forced to realize that the U.S.S.R. was no longer in any way competitive with the United States and, in its desperate economic situation, never could be again. This important factor hastened the Soviet Union's breakup and, perhaps more importantly, insured that it was a peaceful one.

Peter M. Bowers Collection
The B-1 Lancer was a supersonic bombing plane designed to replace the venerable B-52 Stratofortress.

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In the aftermath of Desert Storm, the United States did what it has always done -- it demobilized and stopped spending on defense. The three greatest air commands in history, SAC, TAC, and ADC were abolished, and in their place came the Air Mobility Command and Air Combat Command.

In the meantime, there was progress on many fronts, including the introduction of the Northrop Grumman B-2A Spirit stealth bomber and the new stealth fighter, the Lockheed Martin F-22 Raptor. Nor were foreign manufacturers idle, as France produced the Dassault-Breguet Rafale, Great Britain and Germany the Eurofighter, Israel the Lavi, and Sweden the Saab Gripen. The tilt-rotor Bell/Boeing V-22 Osprey flew, and a wave of huge aircraft company mergers began when Lockheed acquired the General Dynamics Military Aircraft Division and the following year merged with Martin Marietta to become Lockheed Martin.

Unfortunately, wars were not going away, they were going to become what was called "asymmetric," and the unfathomable world of terrorism would become the nemesis of the next decade.

How did FusionMan reach a speed of 186 mph in the air?

When the Roman poet Ovid (43 B.C.- c. A.D. 18) wrote his collection of mythical poems, "Metamorphoses," he included among it one of the most famous stories in history: The tale of Daedalus and his precocious son, Icarus. Although Ovid's account is considered to be the first written account of the myth, depictions of the story can be found on vases dating from the sixth century B.C.

­In the story, Daedalu­­s, a celebrated architect and in­ventor, is trying to escape the island of Crete with his son, where they've been imprisoned by King Minos for helping the hero Theseus slay the Minotaur, a half-bull, half-man creature locked up in a large labyrinth. Minos, unfortunately, controls the seas surrounding Crete, so Daedalus realizes the only way off the island is through the air. He fashions himself and Icarus a pair of feathered wings, which are glued on with wax. He also makes sure to warn Icarus not to fly too close to the sun, since the sun's heat would melt the wax, or too close to the sea, since the water below would dampen the wings and weigh him down.

Icarus, of course, gets too excited and proud of his flying, and does exactly what his father tells him not to do -- he flies too close to the sun, his wings melt and he plunges into the sea.

The age of the tale, along with the emphasis on human flight, illustrates how important the concept of flying is to us. The most exciting dreams we have are the ones in which we're flying, and our love of roller coasters and flying superheroes points toward our desire to move freely through the air. But we know it's just a simple daydream, right? Is it possible for winged flight, without the help of an airplane?

Fabrice Coffrini/AFP/Getty Images
How did this man manage to fly through the air at speeds of more than 180 mph?

A Swiss citizen who calls himself FusionMan has become a modern-day Daedalus -- not an Icarus -- by becoming the world's first person to fly with fitted wings attached to his back, reaching speeds as high as 186 mph (299 kph) in the air. But how did he do it? He certainly didn't use wax, right?

FusionMan and His Jet-powered Wings

First off, FusionMan isn't really FusionMan's real name. Although the name is catchy and appropriate, his given name is actually Yves Rossy. Born in Switzerland on Aug. 27, 1959, Rossy was a professional military pilot between the ages of 20 and 28 where he flew Hunter, Tiger F-5 and Mirage III planes and l­ogged more than 1,000 hours on a Mach 2 fighter jet. After his stint in the military he worked as a copilot on DC-9 and Boeing 747 planes for Swissair [source: Rossy].

Fabrice Coffrini/AFP/Getty Images
Swiss professional pilot Yves Rossy, better known as FusionMan, the world's first man to fly with fitted jet fuel powered wings strapped to his back, flies during his first official demonstration on May 14, 2008 over Bex, Switzerland.

Rossy clearly loves to fly, and he's practiced aerobatics, hang gliding, paragliding and skydiving. He's also quite the daredevil: Rossy's Web site lists him as a polysportsman, excelling in activities on land, water and in the air. So it isn't too surprising that after he left his job as a commercial pilot, he started work on a homemade pair of wings that would allow him to fly through the air horizontally at accelerated speeds.

He soon adopted the name FusionMan, and with his sponsors, which include Swiss watch company Hublot and the German jet engine company Jet Cat, he spent more than $190,000 on developing his futuristic set of wings. The foldable wings are constructed from carbon fiber, which make the material simultaneously light and strong, and are fitted with four kerosene-fueled jet engines that provide the acceleration.

Fabrice Coffrini/AFP/Getty Images
FusionMan didn't just fly in a straight line -- he used his body to change position, flying for five minutes over the Swiss Alps.

FusionMan can't take off from the ground by himself; instead, he's flown up 7,500 feet (2,286 meters) in an airplane, where he simply steps out wearing the wings. After a short freefall, the wings unfold and the jet engines kick in, allowing him to reach speeds of up to 186 mph (299 kph). He doesn't just fly horizontally, though; simply by using his body he can also dive, perform figure-eights and execute 360-degree barrel rolls.

The stuntman made his first successful flight over the Alps, soaring through the air for about five minutes, on May 15, 2008. Previous attempts hadn't fared so well: He nearly lost control of the wings during a jump in 2005 and couldn't access his parachute until he was only 1,500 feet (457 meters) above the ground, and damage to a previous set of wings in 2007 caused him to start over and build a newer prototype. FusionMan continues to look toward the future, however, and he plans to fly over the English Channel and the Grand Canyon.

How do they start jet engines on airplanes? How to start jet engines on airplanes?

Gas turbine engines come in many shapes and sizes. One type discussed in How turbine engines work includes a normal "jet" engine on an airplane. The hot gases produced by the burning fuel drive vanes in exactly the same way that wind turns a windmill. The vanes connect to a shaft that also spins the turbine's compressor. Another type of gas turbine engine, popular in tanks and helicopters, has one set of vanes for driving the compressor, as well as a separate set of vanes that drive the output shaft. In both of these types of engines, you need to get the main shaft spinning to start the engine.

This starting process normally uses an electric motor to spin the main turbine shaft. The motor is bolted to the outside of the engine and uses a shaft and gears to connect to the main shaft. The electric motor spins the main shaft until there is enough air blowing through the compressor and the combustion chamber to light the engine. Fuel starts flowing and an igniter similar to a spark plug ignites the fuel. Then fuel flow is increased to spin the engine up to its operating speed. If you have ever been at the airport and watched a big jet engine start up, you know that the blades start rotating slowly. The electric starter motor does that. Then you (sometimes) hear a pop and see smoke come out of the back of the engine. Then the engine spins up and starts producing thrust.

On smaller turbine engines (especially home-built models), another way to start the engine is to simply blow air through the air intake with a hair dryer or leaf blower. This technique has the same effect of getting air moving through the combustion chamber, but does not require the complexity or weight of an attached starter motor.

Besides the starter shaft, most big jet engines include another output shaft for driving things like electrical generators, air conditioning compressors, etc. needed to operate the plane and keep it comfortable. This shaft can connect to the main turbine shaft at the same point the starter does or elsewhere. Some jet airplanes have a separate turbine (sometimes in the tail cone of the plane) that does nothing but generate auxiliary power. It is more efficient to run this smaller turbine when the plane is sitting on the tarmac.

Where does your unclaimed luggage end up?

You've watched the luggage carousel spin around countless times. Your bag, however, has yet to show its generic navy blue face. It's gone -- one of the many bags "mishandled" by airlines annually. And although most baggage is returned to passengers within 24 hours, some languishes in airports and warehouses before carriers declare it officially lost. But where does the truly unclaimed luggage go? What happens to the wrinkle-proof suits, the much-regretted cameras and the occasional Egyptian artifact? They eventually end up in Scottsboro, Alabama, at the Unclaimed Baggage Center, where they're sold to the public at bargain-basement prices.

Jay Directo/AFP/Getty Images The moment of truth: Did the bags arrive? Airlines mishandle 7.34 out of every 1,000 bags. See more pictures of airports.

The Department of Transportation reports that airlines mishandle 7.34 out of every 1,000 bags [source: DOT]. Most carriers define a mishandled bag as delayed, lost, stolen or damaged. Passengers with delayed bags are relatively lucky: Their belongings are usually only a flight behind them. Even those with lost luggage usually see their bags again. Airlines spend a considerable amount of effort tracking down owners of unclaimed luggage -- they even use clues from inside the bag when the outer tags are gone. But some luggage, no matter how carefully the carrier tries to trace it, is irretrievably lost.

Airlines usually keep unclaimed luggage around the terminal where it was found for about five days before shipping it to a central warehouse. After about 60 days in storage, carriers donate the bags to charity or sell them to salvage.

The Unclaimed Baggage Center buys luggage from airlines with the contents site unseen. Clothing makes up about 60 percent of the millions of items that pass through the store annually. Cameras, electronics, sporting goods, jewelry, glasses, books and luggage help keep the constantly rotating shelves fully stocked. The Unclaimed Baggage Center founders, Doyle and Sue Owens, started their business by selling unclaimed Greyhound bus luggage in 1970. Now the store covers a city block and sells unclaimed cargo in addition to their staple of lost airline baggage.

So what makes people fly across the country to root through someone else's lost baggage? In the next section we'll learn about some unusual finds in Scottsboro and how you can avoid losing your own luggage.

Treasures of the Unclaimed Baggage Center

When a lost suitcase or backpack arrives at the Unclaimed Baggage Center, employees remove all clothing for laundering and search every zippered pocket and corner crevice for treasures. Their diligence pays: In addition to Egyptian artifacts from 1500 B.C. (which included a shrunken head), employees have uncovered a 40.95 carat emerald, a 5.8 carat diamond and a Muppet from the movie "Labyrinth."

Scott Olson/Getty Images To avoid losing your luggage, label your bags inside and out.

Some items are so valuable and unusual, you might wonder what happened to the person who lost them. The Unclaimed Baggage Center has returned an F-16 guidance system to the U.S. Navy and a space shuttle camera to NASA.

While the store keeps its stranger finds in a small museum, most items sell for 50-80 percent below retail value. The constantly changing stock makes the Unclaimed Baggage Center one of Alabama's major tourist destinations. The store donates what it can't sell -- giving clothing to the homeless and baby strollers to teen pregnancy centers.

Customers certainly get a good deal at the Unclaimed Baggage Center, but how much do airlines make from selling lost luggage? Although the store and carriers keep their negotiations private, the bargain prices suggest airlines receive very little. And, in fact, they start at a loss. Passengers with mishandled luggage on a domestic flight can file claims reports and receive up to $3,000 from the airline responsible. Do not, however, expect to receive the full amount. Airlines sometimes ask for receipts to back up claims and may refuse liability if you checked in late. The Montreal Convention determines liability for international trips originating in the United States or in other ratifying countries. The Convention limits liability to 1,000 "Special Drawing Rights," an international reserve asset that fluctuates based on several currencies.

To learn more about unclaimed luggage, baggage handling and airlines, carry on to the next page.

How to Keep Your Luggage Out of Scottsboro

• Don't overpack. Strained zippers are more likely to pop, spilling your favorite T-shirts on the tarmac and your souvenirs on the carousel.
• Label your luggage inside and out. Airlines can also use items like itineraries to help determine who you are.
• Pretend you're at school again: Put your name on smaller, easy-to-lose items like glasses cases and cameras.
• Mark your luggage with an identifying ribbon or tape.
• Prepare for the worst: Keep your money, prescriptions, travel documents and a change of underwear close to your person.
• And if you must bring your 40.95 carat emeralds and mummified falcons on vacation, don't check them!

How Hypersonic Planes Work? How Hypersonic Planes Functions?

NASA's experimental space plane, the X-43A, set a new speed record for aircraft on November 16, 2004. In the unmanned test flight, the plane reached Mach 10 -- 10 times the speed of sound, or about 6,600 miles (10,600 kilometers) per hour. This flight broke the previous speed record of Mach 7, set in March 2004 by the X-43A in a previous test flight.

Photo courtesy NASA The X-43A is the first aircraft to reach hypersonic speeds using an air-breathing engine.

What sets the X-43A apart from other rocket-powered aircraft is that it is powered by a scramjet engine. Instead of using onboard oxygen to combust the hydrogen fuel, the scramjet scoops up oxygen as it travels through the atmosphere. By eliminating the need for onboard oxygen, cutting the weight of the spacecraft, the X-43A could lead to cheaper Earth-to-orbit space travel.

In this article, we'll take a look at hypersonic planes and learn about their air-breathing engines.

Living On Air

The futuristic X-43A prototype looks like a flying surfboard. It’s thin, has a wingspan of 5 feet (1.5 m), measures 12 ft (3.7 m) long and 2 ft (0.61 m) thick and weighs 2,800 pounds (1,270 kg). But the most unique feature of the X-43A is its engine.

Photo courtesy NASA The dimensions and views of the X-43A

The best way to understand an X-43A’s air-breathing engine is to first look at a conventional rocket engine. A typical rocket engine is propelled by the combustion created when a liquid oxidizer and a hydrogen fuel are burned in a combustion chamber. These gases create a high-pressure, high-velocity stream of hot gases. These gases flow through a nozzle that further accelerates them to speeds of 5,000 to 10,000 mph (8,000 to 16,000 kph) and provides thrust. For more information on rocket engines, check out the article How Rockets Work.

The disadvantage of a conventional rocket engine is that it requires a lot of onboard oxygen. For example, the space shuttle needs 143,000 gallons of liquid oxygen, which weighs 1,359,000 pounds (616,432 kg). Without the liquid oxygen, the shuttle weighs a mere 165,000 pounds (74,842 kg).

An air-breathing engine requires no onboard oxygen. The X-43A scoops up oxygen as it flies through the atmosphere. In an Earth-to-orbit mission, the vehicle would store extra oxygen onboard, but less than what a space shuttle requires.

Image courtesy NASA The air-breathing engine system

The scramjet engine is a simple design with no moving parts. The X-43A craft itself is designed to be a part of the engine system: The front of the vehicle acts as the intake for the airflow, and the aft serves as the nozzle that accelerates the exhausted air.

Photo courtesy NASA Artist's concept of the X-43A in flight, with the scramjet engine firing

Combustion occurs in the engine only at supersonic speeds because the air has to be flowing at a high rate to be compressed. Rather than using a rotating compressor, like a turbojet engine does, the forward velocity and aerodynamics compress the air into the engine. Hydrogen fuel is then injected into the air stream, and the expanding hot gases from combustion accelerate the exhaust air to create tremendous thrust.

Taking Flight

As mentioned before, scramjet-powered aircraft don’t carry oxygen onboard. That means that they can’t lift off like conventional spacecraft. The X-43A requires a booster rocket to get it up to a hypersonic speed, at which point it is released and sent flying on its own. This rocket boost is necessary for the scramjet engine to work.

Photo courtesy NASA The X-43A attached to the Pegasus booster rocket

Here’s a rundown of how the X-43A test flights work:

1. The X-43A is attached to a Pegasus booster rocket.
2. The X-43A and booster rocket are carried up to about 20,000 feet (6,000 m) by a customized, B-52 aircraft.
3. The B-52 releases the launch vehicle.
4. The booster rocket accelerates to a speed of approximately Mach 5 and flies to an altitude of about 100,000 feet (30,500 m).
5. The X-43A separates from the booster rocket and flies under its own power and preprogrammed control.
6. The X-43A flies over the ocean for a few minutes before splashing down.

Image courtesy NASA

NASA officials say that the scramjet engine would be a major step forward for NASA and would arguably provide a safer, more flexible, less expensive way to get people and cargo to space.

What if we covered a city in a giant glass dome?

There's a very funny conversation that happens between Calvin and Hobbes in one of their comic strips. It goes like this:

Hobbes: A new decade is coming up.

Calvin: Yea, big deal! Humph. Where are the flying cars? Where are the moon colonies? Where are the personal robots and the zero gravity boots, huh? You call this a new decade?! You call this the future?? Ha! Where are the rocket packs? Where are the disintegration rays? Where are the floating cities?

Hobbes: Frankly, I'm not sure people have the brains to manage the technology they've got.

Calvin: I mean, look at this! We still have the weather?! Give me a break!

CALVIN AND HOBBES © Watterson. Reprinted with permission of UNIVERSAL PRESS SYNDICATE. All rights reserved.

People think about domed cities because, as Calvin points out, we haven't figured out a way to control the weather. If everywhere in the world could have weather like San Diego, it probably wouldn't be an issue. Unfortunately, in big cities like Buffalo, Minneapolis, New York and Chicago, the weather is decidedly NOT San Diego -- especially in the winter!

Digital Vision/Getty Images
A In a covered city, there would no longer be snow days, snow men or snowflakes.

The goal of a domed city is to take a large urban area and cover it so that:

• The temperature is the same year round.
• There's never any rain or snow to spoil picnics and weddings.
• The cancerous effects of the sun are eliminated during outdoor activities.

Small-scale Domed Cities

There have been lots of attempts to create domed cities on a very small scale. Consider these examples:

• The Mall of America near Minneapolis is a tiny city under glass. It contains about 80 acres of floor space (on 27 acres of ground) holding more than 500 stores, 80 restaurants and an indoor amusement park.
• Biosphere 2 is a giant, completely sealed lab covering 3.15 acres.
• The two Eden greenhouses in England are geodesic domes that together cover about 5 acres.
• Any dome stadium covers eight to 10 acres.

What if we were to expand on these projects in a massive way, moving up to city-size and covering somewhere on the order of 650 acres -- approximately a square mile? We're talking about taking a square parcel of land measuring approximately one mile on each side, or a circular piece of land measuring 1.13 miles in diameter, and completely covering it.

The Mall of America is like a mini city covered in glass.

The first question is what technology would we use to cover such a huge space. Here are three possibilities:

• The Mall of America uses typical mall construction technologies -- concrete and block walls, trusses, skylights, and so on. It's not very glamorous or inspiring architecture (there would be lots of supporting posts and walls in the city, rather than the dazzle of a mile-wide dome), but it is easy to imagine a construction process using these same techniques to cover a square mile.
• The Eden project uses a geodesic dome and hexagonal panels covered with multiple, inflatable layers of a very light plastic foil. The weight of the geodesic frame plus the hexagonal panels is about equal to the weight of the air contained inside the dome.
• The British Columbia Place Stadium is covered with a Teflon-coated fiberglass fabric held up by air pressure. The air pressure inside is only 0.03 psi higher than normal atmospheric pressure. Sixteen 100-horsepower fans provide the extra pressure.

In a project like covering a city with a dome, it may be that buildings form part of the structure for the dome. For example, six tall buildings at the center of the city could act as six pillars supporting the dome's center, with other buildings throughout the city acting as shorter pillars.

What would life be like?

Certainly, using the mall technology, and probably using either of the other two technologies, it's easy to create a protective shell covering a square mile. Here are some of the more interesting questions that would be raised if someone actually tried to do this:

How many people could live there?
We'll assume that the interior of the dome is developed at an average height of 10 stories. Some buildings will be higher, while some places in the city will be parks or otherwise undeveloped, working out to an average of 10 stories. That gives the city about 280,000,000 square feet of floor space. If you assume that the average person needs about 500 square feet of living space (pretty typical in suburban America), another 500 square feet of open space for things like hallways, walkways, parks, common areas, elevators, and so on, then this city could house almost 200,000 people. However, it's likely that real estate under the dome will be extremely valuable and that people will fit into much smaller spaces than they typically do today. In other words, the space occupied per person might total only 500 square feet. That would allow the city to hold more than half a million people.

2007 Photodisc
In a covered city, your legs might be the only form of transportation.

How much would it cost to build?
In today's dollars, space in a skyscraper costs something like $400 per square foot to build. The Eden greenhouses cost around of $400 per square foot too, so we'll use that number. The total cost for this project would be something on the order of $140 billion, or $250,000 per resident. That's not so unreasonable, when you think about it.

What will it cost to heat and cool this huge structure?
That's impossible to say because it depends on the type of construction, the location, and so on. However, it's interesting to note that the Mall of America doesn't have to spend money on heating, even though it's located in Minnesota. The lights and people provide plenty of heat. The problem will be cooling this massive structure, especially when the sun is shining. One way to solve this dilemma would be to locate the domed city in a very cold climate.

How will people get around?
The maximum distance between any two points in the city will be about one mile, meaning that a person can walk anywhere in a half-hour or less. Walking will be the primary, and possibly the only, means of transportation for the residents of the city. There will need to be some way to accommodate the movement of food and retail products into the city. Underground train systems or roads for trucks might be the best solution.

The thing that you come to understand after thinking about a domed city is that it's not such a far-fetched idea. There's a good chance that we will see such a city developed over the next decade or two. Finally, people will be able to plan their weekends without having to worry about the weather!

Why do those long, white clouds form behind jets flying high overhead?

The clouds that jets form on certain days are called condensation trails or contrails. Some days, the contrails will form thin lines that cross the entire sky. Other days they will be much shorter, and on some days there will be none at all.

A contrail forms because one of the components of jet engine exhaust is water. Jet fuel is made of carbon and hydrogen . When jet fuel burns with oxygen, most of the exhaust consists of CO₂ (carbon dioxide) and H₂O (water). The water is generally an invisible vapor.

When you exhale, your breath contains a great deal of invisible water vapor as well. You may have noticed that on certain days in the winter, your breath will form a cloud of condensation when you exhale. In the summer, however, you don't see your breath. Cold air can hold a lot less moisture than warm air, so in the winter, when the moisture in your breath hits the cold air, the moisture condenses into a visible cloud.

The same thing happens when a jet engine "exhales." If the temperature, winds and humidity in the upper atmosphere are right, long, white contrails form when the moisture in the exhaust condenses.

When an aerobatic plane flies upside down, how does the fuel get to the engine?

Gravity is one of those amazing things -- because it is constant, we take it completely for granted. For example, the fuel system in any normal car or airplane depends on gravity to position and move the fuel in the fuel tank. A high-wing monoplane like the one shown in How Airplanes Work would stall almost immediately if you tried to fly it upside down. Gravity draws the fuel from the fuel tanks (located inside the wings) down to the engine.

So how does an aerobatic plane that flies upside down and does loops get fuel from the gas tank to the engine? To answer this question, I spoke to Randy Henson, pilot of the aerobatic biplane shown below:

According to Randy, there are two techniques:

"The first is the flop tube design used in my airplane, a Pitts S-1T. The fuel tank is located in the fuselage in front of the pilot's knees, and inside of the tank is a flexible hose with a weight attached to the free end. When the plane is right side up, this hose, or flop tube, 'flops' to the bottom of the tank because of the weight and draws fuel from the bottom of the tank. When the plane is rolled to inverted, the weight causes to hose to flop to the top of the tank (which is really the bottom now) and draw fuel from there. This is really a cool design because it uses only one tank, and you have access to all the fuel in the tank whether you are right side up or inverted. This design is used on all the high-performance aerobatic airplanes with which I am familiar -- these planes all have a fuel tank in the fuselage.

"The second solution to the problem is the header tank. This is used in airplanes such as the Super Decathlon, a high-wing monoplane. In this type of plane the main fuel tanks are located in the wings, which are higher than the engine. In upright flight, the fuel has a gravity head to the suction of the engine-driven fuel pump (in planes like the Cessna 150, which does not have an inverted fuel system, you don't need a fuel pump -- the fuel is gravity-fed to the carb). For inverted flight, there is a small header tank near the pilot's feet. The header tank is connected to the main tanks in the wings; during upright flight, fuel from the wing tanks flows by gravity into the header tank until it is full. The header tank is connected to the suction side of the fuel pump -- when the plane is rolled inverted, the header tank is above the engine, and the fuel gravity flows from the header tank to the fuel pump. There is a check valve in the line connecting the main tank to the header tank; this prevents fuel from the header tank from draining back into the main tank when the plane is inverted. In the Decathlon, the header tank holds enough fuel for about two minutes of inverted flight.

"My plane and all of the more modern aerobatic planes I have seen are fuel injected. However, some of the older Pitts I have seen have a pressure carb, and it works in inverted flight. "