Piston engines

On the morning of Sunday, August 27, 1939, a gas turbine engine conceived by a young German physics student, Hans von Ohain, powered a Heinkel He 178 V1 on its first flight.

All previous aircraft had been powered by piston engines. Nearly every noteworthy aircraft performance improvement was the direct result of an engine improvement. Many of these engine improvements ranked among some of the greatest accomplishments of the first half of the Twentieth Century.

During the period between the World Wars, aircraft engines improved dramatically and made possible unprecedented progress in aircraft design. Engine development in those days, and to a large extent even today, is a very laborious, detailed process of building an engine, running it to destruction, analyzing what broke, designing a fix, and repeating the process. No product ever comes to market without some engineer(s) having spent many long, lonely, anxious hours perfecting that product. This is especially true of aircraft engines, which by their very nature push all the limits of ingenuity, materials, and manufacturing processes.

Just prior to World War II, engineers at both Pratt & Whitney and Curtiss-Wright worked feverishly to produce the first air-cooled engine capable of more than 2,000 horsepower. The efforts of both teams were nearly thwarted by severe vibration from unexpected sources. This is the story of how the Pratt & Whitney team, through hard labor and persistence, identified and solved the problems with vibration. The result was one of the most successful engines of all times - the R-2800.

Aviation fuel

Aviation fuel is a specialized type of petroleum-based fuel used to power aircraft. It is generally of a higher quality than fuels used in less critical applications such as heating or road transport, and often contains additives to reduce the risk of icing or explosion due to high temperatures, amongst other properties.

Most aviation fuels available for aircraft are kinds of gasoline used in engines with spark plugs i.e. piston engines and Wankel rotaries or fuel for jet turbine engines which is also used in diesel aircraft engines. Alcohol, alcohol mixtures and other alternative fuels may be used experimentally but are not generally available.

Avgas is sold in much lower volumes, but to many more individual aircraft, whereas Jet Fuel is sold in high volumes to large aircraft operated typically by airlines, military and large corporate aircraft.

The Convention on International Civil Aviation, which came into effect in 1947, exempted air fuels from tax. Australia and the USA oppose a worldwide levy on aviation fuel, but a number of other countries have expressed interest.

Aviation fuel is often dispensed from a tanker or bowser which is driven up to parked aeroplanes and helicopters. Some airports have pumps similar to filling stations that aircraft must taxi up to. Some airports also have permanent piping to parking areas for large aircraft.

Regardless of the method, aviation fuel is transferred to an aircraft via one of two methods: overwing and underwing. Overwing fuelling is used on smaller planes, helicopters, and all piston-engine aircraft. Overwing fuelling is similar to automobile fuelling — one or more fuel ports are opened and fuel is pumped in with a conventional pump. Underwing fuelling, also called single-point, is used on larger aircraft and for jet fuel exclusively. For single-point fuelling, a high-pressure hose is attached and fuel is pumped in at up to 50 PSI. Since there is only one attachment point, fuel distribution between tanks is either automated or it is controlled from a control panel at the fueling point or in the cockpit. As well, a dead man's switch is used to control fuel flow.

Because of the danger of confusing the fuel types, a number of precautions are taken to distinguish between AvGas and Jet Fuel beyond clearly marking all containers, vehicles, and piping. AvGas is treated with either a red, green, or blue dye, and is dispensed from nozzles with a diameter of 40 millimetres (49 millimetres in the USA). The aperture on fuel tanks of piston-engined aircraft cannot be greater than 60 millimetres in diameter. Jet Fuel is clear to straw in colour, and is dispensed from a special nozzle called a "J spout" that has a rectangular opening larger than 60 millimetres in diameter so as not to fit into AvGas ports. However, some jet and turbine aircraft, such as some models of the Astar helicopter, have a fueling port too small for the J spout and thus require a smaller nozzle to be installed in order to be refuelled efficiently.

Any fuelling operation can be very dangerous, and aviation fuelling has a number of unique characteristics which must be accommodated. As an aircraft flies through the air, it can accumulate a charge of static electricity. If this is not dissipated before fuelling, an electric arc can occur which may ignite fuel vapours. To prevent this, aircraft are electrically bonded to the fuelling apparatus before fuelling begins, and are not disconnected until fuelling is complete. Some regions require that the aircraft and/or fuel truck be grounded as well.

Aviation fuel can cause severe environmental damage, and all fuelling vehicles must carry equipment to control fuel spills. In addition, fire extinguishers must be present at any fuelling operation, and airport firefighting forces are specially trained and equipped to handle aviation fuel fires and spills. Aviation fuel must be checked daily and before every flight for contaminants such as water or dirt.

Many airlines now require that safety belts be left unfastened should passengers be aboard when refuelling happens.

Flying boats

A flying boat is a type of aircraft which uses its fuselage as a floating hull, generally stabilised on the water surface by underwing floats or stub projections. It is a specialised form of seaplane, an aircraft that is designed to take off and land on water utilising a carriage and pontoons that maintain the fuselage above water level.

Flying boats were among the largest aircraft of the first half of the 20th century. Their ability to alight on water allowed them to break free of the size constraints imposed by general lack of large, land-based runways, and also made them important for the rescue of downed pilots, a capability put to great use in world war II. Following World War II, their use gradually tailed off, with many of the roles taken over by land aircraft types. In the 21st century, flying boats maintain a few niche uses, such as for dropping water on forest fires and for air transport around archipelagos.

seaplanes

A seaplane is a fixed-wing aircraft designed to take off and land (or "alight") upon water. Seaplanes can be divided into separate categories such as float planes, flying boats, and amphibious aircraft ("amphibians").

These aircraft are occasionally called hydroplanes, based on usage in several Romance languages, which is rare in english.

• A floatplane has slender pontoons mounted under the fuselage. Two floats are common, but many floatplanes of World War II had a single float under the main fuselage and two small floats on the wings. Only the "floats" of a floatplane normally come into contact with water. The fuselage remains above water. Some small land aircraft can be modified to become float planes.
• In a flying boat, the main source of buoyancy is the fuselage, which acts like a ship's hull in the water. Most flying boats have small floats mounted on their wings to keep them stable.

The term "seaplane" is used by some to refer only to floatplanes (aircraft with floats as landing gear), with the flying boat being a distinct type of craft. This article treats both flying boats and floatplanes as types of seaplane.

An amphibious aircraft can take off and land both on conventional runways and water. A true seaplane can only take off and land on water. There are amphibious flying boats and amphibious floatplanes, as well as some hybrid designs, e.g., floatplanes with retractable floats. Modern production seaplanes are largely amphibious and of a floatplane design.

In the post war period the availability of large paved runways and the greatly expanded performance of land based planes meant that both commercial and military use of seaplanes was much reduced. Anti-Submarine Warfare was just as easily carried out with land based aircraft, which often had better performance, and Search and Rescue could more easily be carried out with helicopters, which had the advantages of being operated from smaller ships, and in higher sea states. The compromises that came from being able to float and rise again from the water caused excessive drag and added considerably to the weight of the aircraft. In commercial service this translated into increased costs, and for a military aircraft, into reduced warloads, speeds and ranges.

Only in specialized roles were they able to remain competitive, such as waterbombing, where their ability to quickly reload was a huge asset. A number of surplus WW2 seaplanes including the Consolidated Catalina and Martin Mars were initially used in this role but their advancing age has required a new specially designed aircraft in the form of the Canadair Waterbomber which operates alongside an entire air force of second-hand land-based bombers and transports.

The only amphibian aircraft produced for post war commercial usage was the Grumman Mallard which was designed as a true airliner, with modern technology and longer ranges, greater passenger and cargo loads. The Mallard saw production from 1946-1951. Only 59 were delivered, used mostly by corporations and some regional commuter carriers.

Life Aboard the Space Shuttle

orbiter must provide you with an environment similar to Earth. You must have air, food, water, and a comfortable temperature. The orbiter must also take away the wastes that your body produces (carbon dioxide, urine, feces) and protect you from fire. Let's look at these various aspects of the orbiter's life support system.

On board the space shuttle, you need to have the following:

• atmosphere similar to Earth
• carbon dioxide removed
• contaminating or trace gases removed
• normal humid environment

Our atmosphere is a mixture of gases (78 percent nitrogen, 21 percent oxygen, 1 percent other gases) at a pressure of 14 lbs/in² (1 atm) that we breathe in and out. The space shuttle must provide a similar atmosphere. To do this, the orbiter carries liquid oxygen and liquid nitrogen in two systems of pressurized tanks, which are located in the mid-fuselage (each system has two tanks for a total of four tanks). The cabin pressurization system combines the gases in the correct mixture at normal atmospheric pressure. While in orbit, only one oxygen-nitrogen system is used to pressurize the orbiter. During launch and landing, both systems of each gas are used.

Five loops of fans circulate the atmosphere. The circulated air picks up carbon dioxide, heat and moisture:

• Chemical carbon dioxide canisters remove carbon dioxide by reacting it with lithium hydroxide. These canisters are located in the lower deck of the crew compartment and changed every 12 hours.
• Filters and charcoal canisters remove trace odors, dust and volatile chemicals from leaks, spills and outgassing.
• A cabin heat exchanger in the lower deck cools the air and condenses the moisture, which collects in a slurper. Water from the slurper is moved with air to a fan separator, which uses centrifugal force to separate water from air. The air is recirculated and the
  water goes to a wastewater tank.

Besides air, water is the most important quantity aboard the orbiter. Water is made from liquid oxygen and hydrogen in the space shuttle's fuel cells (the fuel cells can make 25 lb (11 kg) of water per hour). The water passes through a hydrogen separator to eliminate any trapped hydrogen gas (excess hydrogen gas is dumped overboard). The water is then stored in four water storage tanks located in the lower deck. Each tank can hold 165 lb (75 kg). The water tanks are pressurized by nitrogen so that water can flow to the mid-deck for use by the crew. Drinkable water is then filtered to remove microbes and can be warmed or chilled through various heat exchangers depending upon the use (food preparation, consumption, personal hygiene). Excess water produced by the fuel cells gets routed to a wastewater tank and subsequently dumped overboard.

Outer space is an extremely cold environment and temperatures will vary drastically in different parts of the orbiter. You might think that heating the orbiter would be a problem. However, the electronic equipment generates more than enough heat for the ship. The problem is getting rid of the excess heat. So the temperature control system has to carry out two major functions:

• Distribute heat where it is needed on the orbiter (mid-fuselage and aft sections) so that vital systems do not freeze in the cold of space.
• Get rid of the excess heat.

To do this, the shuttle has two methods to handle temperature control:

• Passive methods - generally simple, handle small heat loads and require little maintenance
  • Insulating materials (blankets), surface coatings, paints - reduce heat loss through the walls of the various components just like your home insulation.
  • Electrical heaters - use electrically-heated wires like a toaster to heat various areas.
• Active methods - more complex, use fluid to handle large heat loads, require maintenance
  • Cold plates - metal plates that collect heat by direct contact with equipment or conduction
  • Heat exchangers - collect heat from equipment using fluid. The equipment radiates heat to a fluid (water, ammonia) which in turn passes heat on to freon. Both fluids are pumped and recirculated to remove heat.
  • Pumps, lines, valves - transport the collected heat from one area to another.
  • Radiators - located on the inside surfaces of the cargo bay doors that radiate the collected heat to outer space
  • Flash evaporator/ammonia boilers - these devices are located in the aft fuselage and transfer heat from Freon coolant loops overboard when cargo bay doors are closed or when cargo bay radiators are overloaded.
    • Flash evaporator
      1. Freon coolant loops wrap around an inner core.
      2. The evaporator sprays water on the heated core.
      3. The water evaporates removing heat.
      4. The water vapor is vented overboard.
    • Ammonia boiler
      1. Freon coolant loops pass through a tank of pressurized ammonia.
      2. Heat released from the freon causes the ammonia to boil.
      3. Ammonia vapor is dumped overboard.

The cabin heat exchanger also controls the cabin temperature. It circulates cool water to remove excess heat (cabin air is also used to cool electronic equipment) and transfers this heat to a Freon exchanger. The Freon then transfers the heat to other orbiter systems (e.g., cryogenic gas tanks, hydraulic systems) and radiates excess heat to outer space.

The orbiter has internal fluorescent floodlights that illuminate the crew compartment. The orbiter has external floodlights to illuminate the cargo bay. Finally, the control panels are lighted internally for easy viewing.

Food is stored on the mid-deck of the crew compartment. Food comes in several forms (dehydrated, low moisture, heat-stabilized, irradiated, natural and fresh). The orbiter has a galley-style kitchen module along the wall next to the entry hatch, which is equipped with the following:

• food storage compartments
• food warmers
• a food preparation area with warm and cold water outlets
• metal trays so the food packages and utensils do not float away

Like any home, the orbiter must be kept clean, especially in space when floating dirt and debris could present a hazard. Wastes are made from cleaning, eating, work and personal hygiene. For general housecleaning, various wipes (wet, dry, fabric, detergent and disinfectant), detergents, and wet/dry vacuum cleaners are used to clean surfaces, filters and the astronauts. Trash is separated into wet trash bags and dry trash bags, and the wet trash is placed in an evaporator that will remove the water. All trash bags are stowed in the lower deck to be returned to Earth for disposal. Solid waste from the toilet is compacted, dried and stored in bags where it is returned to Earth for disposal (burning). Liquid waste from the toilet goes to the wastewater tank where it is dumped overboard.

Fire is one of the most dangerous hazards in space. The orbiter has a Fire Detection and Suppression Subsystem that consists of the following:

• area smoke detectors on each deck
• smoke detectors in each rack of electrical equipment
• alarms and warning lights in each module
• non-toxic portable fire extinguishers (carbon dioxide-based)
• personal breathing apparatus - mask and oxygen bottle for each crew member

After a fire is extinguished, the atmosphere control system will filter the air to remove particulates and toxic substances.

History of the Space Shuttle

Near the end of the Apollo space program, NASA officials were looking at the future of the American space program. They were using one-shot, disposable rockets. What they needed was a reliable, less expensive rocket, perhaps one that was reusable. The idea of a reusable "space shuttle" that could launch like a rocket but land like an airplane was appealing and would be a great technical achievement.

NASA began design, cost and engineering studies on a space shuttle and many aerospace companies also explored the concepts. In 1972, President Nixon announced that NASA would develop a reusable space shuttle or space transportation system (STS). NASA decided that the shuttle would consist of an orbiter attached to solid rocket boosters and an external fuel tank and awarded the prime contract to Rockwell International.

At that time, spacecraft used ablative heat shields that would burn away as the spacecraft re-entered the Earth's atmosphere. However, to be reusable, a different strategy would have to be used. The designers of the space shuttle came up with an idea to cover the space shuttle with many insulating ceramic tiles that could absorb the heat of re-entry without harming the astronauts.

Remember that the shuttle was to fly like a plane, more like a glider, when it landed. A working orbiter was built to test the aerodynamic design, but not to go into outer space. The orbiter was called the Enterprise after the "Star Trek" starship. The Enterprise flew numerous flight and landing tests, where it was launched from a Boeing 747 and glided to a landing at Edwards Air Force Base in California.

Finally, after many years of construction and testing (i.e. orbiter,main engines, external fuel tank, solid rocket boosters), the shuttle was ready to fly. Four shuttles were made (Columbia, Discovery, Atlantis, Challenger). The first flight was in 1981 with the space shuttle Columbia, piloted by astronauts John Young and Robert Crippen. Columbia performed well and the other shuttles soon made several successful flights.

In 1986, the shuttle Challenger exploded in flight and the entire crew was lost. NASA suspended the shuttle program for several years, while the reasons for the disaster were investigated and corrected. After several years, the space shuttle flew again and a new shuttle, Endeavour, was built to replace Challenger in the shuttle fleet.

In 2003, while re-entering the Earth's atmosphere, the shuttle Columbia broke up over the United States. NASA grounded the space shuttle program after the accident and worked feverishly to make changes and return the shuttles to flight. In 2006, the shuttle Discovery lost foam from its external fuel tank. Once again, the program was grounded and scientists struggled to solve the problem. The Discovery launched twice in 2006, once in July and again in December. According to NASA, the July 2006 launch was the most photographed shuttle mission in history. The Atlantis launched in September 2006, after delays due to weather, a problem with the fuel cell and a faulty sensor reading.

While the space shuttles are a great technological advance, they are limited as to how much payload they can take into orbit. The shuttles are not the heavy lift vehicles like the Saturn V or the Delta rockets. The shuttle cannot go to high altitude orbits or escape the Earth's gravitational field to travel to the Moon or Mars. NASA is currently exploring new concepts for launch vehicles that are capable of going to the Moon and Mars.

How Space Shuttles Work

In its 26-year history, the space shuttle program has seen exhilarating highs and devastating lows. The fleet has taken astronauts on dozens of successful missions, resulting in immeasurable scientific gains. But this success has had a serious cost. In 1986, the Challenger exploded during launch. In 2003, the Columbia broke up during re-entry over Texas. Since the Columbia accident, the shuttles have been grounded pending redesigns to improve their safety. The 2005 shuttle Discovery was supposed to initiate the return to flight, but a large piece of insulating foam broke free from its external fuel tank, leaving scientists to solve the mystery and the program grounded once more until July 2006, when the Discovery and Atlantis both carried out successful missions.

In this article, we examine the monumental technology behind America's shuttle program, the mission it was designed to carry out, and the extraordinary efforts that NASA has made to return the shuttle to flight.

First, let's look at the parts of the space shuttle and a typical mission.

The space shuttle consists of the following major components:

• two solid rocket boosters (SRB) - critical for the launch
• external fuel tank (ET) - carries fuel for the launch
• orbiter - carries astronauts and payload

A typical shuttle mission is as follows:

• getting into orbit
  • launch - the shuttle lifts off the launching pad
  • ascent
  • orbital maneuvering burn
• orbit - life in space
• re-entry
• landing

A typical shuttle mission lasts seven to eight days, but can extend to as much as 14 days depending upon the objectives of the mission. Let's look at the stages of a mission one by one.