How Autopilot In An Aircraft Works? How Autopilot In An Aircraft Functions?

In 1931, American aviator Wiley Post flew his single-engine Lockheed Vega -- the "Winnie Mae" -- around the world in a record eight days, 15 hours and 51 minutes. Post had a navigator by the name of Harold Gatty to help him stay alert and fight fatigue on that historic flight. But when Post became the first person to fly solo around the world in 1933, he had to do everything without an extra pair of hands. The secret to his success, or at least one of his secrets, was a simple autopilot that steered the plane while he rested.

George Stroud/Express/Getty Images An early autopilot system in an Avro 19 plane, circa 1947. See more images of airplanes.

Today, autopilots are sophisticated systems that perform the same duties as a highly trained pilot. In fact, for some in-flight routines and procedures, autopilots are even better than a pair of human hands. They don't just make flights smoother -- they make them safer and more efficient.

In this article, we'll look at how autopilots work by examining their main components, how they work together -- and what happens if they fail.

Autopilots and Avionics

Automatic pilots, or autopilots, are devices for controlling spacecraft, aircraft, watercraft, missiles and vehicles without constant human intervention. Most people associate autopilots with aircraft, so that's what we'll emphasize in this article. The same principles, however, apply to autopilots that control any kind of vessel.

Image courtesy of Bill Harris

In the world of aircraft, the autopilot is more accurately described as the automatic flight control system (AFCS). An AFCS is part of an aircraft's avionics -- the electronic systems, equipment and devices used to control key systems of the plane and its flight. In addition to flight control systems, avionics include electronics for communications, navigation, collision avoidance and weather. The original use of an AFCS was to provide pilot relief during tedious stages of flight, such as high-altitude cruising. Advanced autopilots can do much more, carrying out even highly precise maneuvers, such as landing an aircraft in conditions of zero visibility.

Although there is great diversity in autopilot systems, most can be classified according to the number of parts, or surfaces, they control. To understand this discussion, it helps to be familiar with the three basic control surfaces that affect an airplane's attitude. The first are the elevators, which are devices on the tail of a plane that control pitch (the swaying of an aircraft around a horizontal axis perpendicular to the direction of motion). The rudder is also located on the tail of a plane. When the rudder is tilted to starboard (right), the aircraft yaws -- twists on a vertical axis -- in that direction. When the rudder is tilted to port (left), the craft yaws in the opposite direction. Finally, ailerons on the rear edge of each wing roll the plane from side to side.

Autopilots can control any or all of these surfaces. A single-axis autopilot manages just one set of controls, usually the ailerons. This simple type of autopilot is known as a "wing leveler" because, by controlling roll, it keeps the aircraft wings on an even keel. A two-axis autopilotthree-axis autopilot manages all three basic control systems: ailerons, elevators and rudder. manages elevators and ailerons. Finally, a

What are the basic parts of an autopilot that enable it to exert control over these surfaces? We'll explore the answer to that question in the next section.

Autopilot Parts

The heart of a modern automatic flight control system is a computer with several high-speed processors. To gather the intelligence required to control the plane, the processors communicate with sensors located on the major control surfaces. They can also collect data from other airplane systems and equipment, including gyroscopes, accelerometers, altimeters, compasses and airspeed indicators.

The processors in the AFCS then take the input data and, using complex calculations, compare it to a set of control modes. A control mode is a setting entered by the pilot that defines a specific detail of the flight. For example, there is a control mode that defines how an aircraft's altitude will be maintained. There are also control modes that maintain airspeed, heading and flight path.

The Invention of Autopilot Famous inventor and engineer Elmer Sperry patented the gyrocompass in 1908, but it was his son, Lawrence Burst Sperry, who first flight-tested such a device in an aircraft. The younger Sperry's autopilot used four gyroscopes to stabilize the airplane and led to many flying firsts, including the first night flight in the history of aviation. In 1932, the Sperry Gyroscope Company developed the automatic pilot that Wiley Post would use in his first solo flight around the world.

These calculations determine if the plane is obeying the commands set up in the control modes. The processors then send signals to various servomechanism units. A servomechanism, or servo for short, is a device that provides mechanical control at a distance. One servo exists for each control surface included in the autopilot system. The servos take the computer's instructions and use motors or hydraulics to move the craft's control surfaces, making sure the plane maintains its proper course and attitude.

Image courtesy Bill Harris

The above illustration shows how the basic elements of an autopilot system are related. For simplicity, only one control surface -- the rudder -- is shown, although each control surface would have a similar arrangement. Notice that the basic schematic of an autopilot looks like a loop, with sensors sending data to the autopilot computer, which processes the information and transmits signals to the servo, which moves the control surface, which changes the attitude of the plane, which creates a new data set in the sensors, which starts the whole process again. This type of feedback loop is central to the operation of autopilot systems. It's so important that we're going to examine how feedback loops work in the next section.

Autopilot Control Systems

An autopilot is an example of a control system. Control systems apply an action based on a measurement and almost always have an impact on the value they are measuring. A classic example of a control system is the negative feedback loop that controls the thermostat in your home. Such a loop works like this:

1. It's summertime, and a homeowner sets his thermostat to a desired room temperature -- say 78°F.
2. The thermostat measures the air temperature and compares it to the preset value.
3. Over time, the hot air outside the house will elevate the temperature inside the house. When the temperature inside exceeds 78°F, the thermostat sends a signal to the air conditioning unit.
4. The air conditioning unit clicks on and cools the room.
5. When the temperature in the room returns to 78°F, another signal is sent to the air conditioner, which shuts off.

It's called a negative feedback loop because the result of a certain action (the air conditioning unit clicking on) inhibits further performance of that action. All negative feedback loops require a receptor, a control center and an effector. In the example above, the receptor is the thermometer that measures air temperature. The control center is the processor inside the thermostat. And the effector is the air conditioning unit.

Image courtesy Bill Harris

Automated flight control systems work the same way. Let's consider the example of a pilot who has activated a single-axis autopilot -- the so-called wing leveler we mentioned earlier.

1. The pilot sets a control mode to maintain the wings in a level position.
2. However, even in the smoothest air, a wing will eventually dip.
3. Position sensors on the wing detect this deflection and send a signal to the autopilot computer.
4. The autopilot computer processes the input data and determines that the wings are no longer level.
5. The autopilot computer sends a signal to the servos that control the aircraft's ailerons. The signal is a very specific command telling the servo to make a precise adjustment.
6. Each servo has a small electric motor fitted with a slip clutch that, through a bridle cable, grips the aileron cable. When the cable moves, the control surfaces move accordingly.
7. As the ailerons are adjusted based on the input data, the wings move back toward level.
8. The autopilot computer removes the command when the position sensor on the wing detects that the wings are once again level.
9. The servos cease to apply pressure on the aileron cables.

This loop, shown above in the block diagram, works continuously, many times a second, much more quickly and smoothly than a human pilot could. Two- and three-axis autopilots obey the same principles, employing multiple processors that control multiple surfaces. Some airplanes even have autothrust computers to control engine thrust. Autopilot and autothrust systems can work together to perform very complex maneuvers.

Autopilot Failure

Autopilots can and do fail. A common problem is some kind of servo failure, either because of a bad motor or a bad connection. A position sensor can also fail, resulting in a loss of input data to the autopilot computer. Fortunately, autopilots for manned aircraft are designed as a failsafe -- that is, no failure in the automatic pilot can prevent effective employment of manual override. To override the autopilot, a crew member simply has to disengage the system, either by flipping a power switch or, if that doesn't work, by pulling the autopilot circuit breaker.

Some airplane crashes have been blamed on situations where pilots have failed to disengage the automatic flight control system. The pilots end up fighting the settings that the autopilot is administering, unable to figure out why the plane won't do what they're asking it to do. This is why flight instruction programs stress practicing for just such a scenario. Pilots must know how to use every feature of an AFCS, but they must also know how to turn it off and fly without it. They also have to adhere to a rigorous maintenance schedule to make sure all sensors and servos are in good working order. Any adjustments or fixes in key systems may require that the autopilot be tweaked. For example, a change made to gyro instruments will require realignment of the settings in the autopilot's computer.

The John F. Kennedy Jr. Crash
There has been much speculation about what caused the plane crash that killed John F. Kennedy Jr., along with his wife, Carolyn Bessette Kennedy, and her sister, Lauren Bessette, on July 16, 1999. Although the National Transportation Safety Board (NTSB) determined the probable cause of the accident to be pilot error due to spatial disorientation, some insist that a mechanical failure -- perhaps even a failure related to the autopilot -- contributed to the wreck.­

The plane, a Piper PA-32R-301, Saratoga II, N9253N, was equipped with a Bendix/King 150 Series Automatic Flight Control System, a two-axis autopilot that controlled pitch and roll. The investigation by the NTSB revealed that the autopilot had malfunctioned once or twice before the accident, turning the airplane to a new heading. The problem required that the autopilot be disengaged and then reengaged.

While such a problem with the autopilot could have contributed to the events leading to the wreck, it seems unlikely. In fact, some reports indicate that the autopilot had already been disengaged before the plane encountered problems.

Modern Autopilot Systems

Many modern autopilots can receive data from a Global Positioning System (GPS) receiver installed on the aircraft. A GPS receiver can determine a plane's position in space by calculating its distance from three or more satellites in the GPS network. Armed with such positioning information, an autopilot can do more than keep a plane straight and level -- it can execute a flight plan.

Digital Vision/Getty Images The newest autopilots can execute an entire flight plan.

Most commercial jets have had such capabilities for a while, but even ­smaller planes are incorporating sophisticated autopilot systems. New Cessna 182s and 206s are leaving the factory with the Garmin G1000 integrated cockpit, which includes a digital electronic autopilot combined with a flight director. The Garmin G1000 delivers essentially all the capabilities and modes of a jet avionics system, bringing true automatic flight control to a new generation of general aviation planes.

Wiley Post could have only dreamed of such technology back in 1933.

For more information about autopilots, check out the links on the next page.

Cruise Control -- Autopilot for Your Car
Autopilots aren't found only on airplanes. Ships have them, too, although they are often known by different names. Some captains refer to their ship's autopilot as "Metal Mike," a playful name that arose soon after Elmer Sperry invented the gyrocompass.

Others refer to the device as an "autohelmsman" because it assumes the role of helmsman, steering the ship efficiently with no human intervention. Even your car, if it's a later model, has an autopilot system. It's called cruise control, and it's another classic example of a control system. Cruise control automatically regulates the speed of your car using a feedback loop that involves a speed sensor and the car's accelerator.

How Black Box in an aircraft works? How Black Box in an aircraft functions?

On January 31, 2000, Alaska Airlines Flight 261 departed Puerto Vallarta, Mexico, heading for Seattle, WA, with a short stop scheduled in San Francisco, CA. Approximately one hour and 45 minutes into the flight, a problem was reported with the plane's stabilizer trim. After a 10-minute battle to keep the plane airborne, it plunged into the Pacific Ocean off the coast of California. All 88 people onboard were killed.

Photo courtesy U.S. Department of Defense The cockpit voice recorder from the downed Alaska Airlines Flight 261, held by the robotic arm of the remotely piloted vehicle that retrieved it

With any airplane crash, there are many unanswered questions as to what brought the plane down. Investigators turn to the airplane's flight data recorder (FDR) and cockpit voice recorder (CVR), also known as "black boxes," for answers. In Flight 261, the FDR contained 48 parameters of flight data, and the CVR recorded a little more than 30 minutes of conversation and other audible cockpit noises.

Following any airplane accident in the United States, safety investigators from the National Transportation Safety Board (NTSB) immediately begin searching for the aircraft's black boxes. These recording devices, which cost between $10,000 and $15,000 each, reveal details of the events immediately preceding the accident. In this article, we will look at the two types of black boxes, how they survive crashes, and how they are retrieved and analyzed.

Recording and Storage

The Wright Brothers pioneered the use of a device to record propeller rotations, according to documents provided by L-3 Communications. However, the widespread use of aviation recorders didn't begin until the post-World War II era. Since then, the recording medium of black boxes has evolved in order to record much more information about an aircraft's operation.

Although many of the black boxes in use today use magnetic tape, which was first introduced in the 1960s, airlines are moving to solid-state memory boards, which came along in the 1990s. Magnetic tape works like any tape recorder. The Mylar tape is pulled across an electromagnetic head, which leaves a bit of data on the tape.

Photo courtesy National Transportation Safety Board (NTSB) The magnetic tape inside the flight data recorder from EgyptAir Flight 990, which crashed on October 31, 1999

Black-box manufacturers are no longer making magnetic tape recorders as airlines begin a full transition to solid-state technology. Let's take a look at solid-state technology.

Solid-state Technology

Solid-state recorders are considered much more reliable than their magnetic-tape counterparts, according to Ron Crotty, a spokesperson for Honeywell, a black-box manufacturer. Solid state uses stacked arrays of memory chips, so they don't have moving parts. With no moving parts, there are fewer maintenance issues and a decreased chance of something breaking during a crash.

Data from both the CVR and FDR is stored on stacked memory boards inside the crash-survivable memory unit (CSMU). In recorders made by L-3 Communications, the CSMU is a cylindrical compartment on the recorder. The stacked memory boards are about 1.75 inches (4.45 cm) in diameter and 1 inch (2.54 cm) tall.

The memory boards have enough digital storage space to accommodate two hours of audio data for CVRs and 25 hours of flight data for FDRs.

Airplanes are equipped with sensors that gather data. There are sensors that detect acceleration, airspeed, altitude, flap settings, outside temperature, cabin temperature and pressure, engine performance and more. Magnetic-tape recorders can track about 100 parameters, while solid-state recorders can track more than 700 in larger aircraft.

All of the data collected by the airplane's sensors is sent to the flight-data acquisition unit (FDAU) at the front of the aircraft. This device often is found in the electronic equipment bay under the cockpit. The flight-data acquisition unit is the middle manager of the entire data-recording process. It takes the information from the sensors and sends it on to the black boxes.

Source: L-3 Communication Aviation Recorders Basic components and operation of an aviation recording system

Both black boxes are powered by one of two power generators that draw their power from the plane's engines. One generator is a 28-volt DC power source, and the other is a 115-volt, 400-hertz (Hz) AC power source. These are standard aircraft power supplies, according to Frank Doran, director of engineering for L-3 Communications Aviation Recorders.

Cockpit Voice Recorders

In almost every commercial aircraft, there are several microphones built into the cockpit to track the conversations of the flight crew. These microphones are also designed to track any ambient noise in the cockpit, such as switches being thrown or any knocks or thuds. There may be up to four microphones in the plane's cockpit, each connected to the cockpit voice recorder (CVR).

Photo courtesy L-3 Communication Aviation Recorders A solid-state recorder

Any sounds in the cockpit are picked up by these microphones and sent to the CVR, where the recordings are digitized and stored. There is also another device in the cockpit, called the associated control unit, that provides pre-amplification for audio going to the CVR. Here are the positions of the four microphones:

• Pilot's headset
• Co-pilot's headset
• Headset of a third crew member (if there is a third crew member)
• Near the center of the cockpit, where it can pick up audio alerts and other sounds

Most magnetic-tape CVRs store the last 30 minutes of sound. They use a continuous loop of tape that completes a cycle every 30 minutes. As new material is recorded, the oldest material is replaced. CVRs that used solid-state storage can record two hours of audio. Similar to the magnetic-tape recorders, solid-state recorders also record over old material.

Example: A Black Box Transcript

Final Words of Flight 261
CVR recordings can hold important clues to the cause of an accident. In the case of Alaska Airlines Flight 261, the conversations between the captain and his first officer pointed NTSB investigators to the plane's stabilizer. This is an excerpt taken from the official NTSB transcript of Flight 261, which crashed on January 31, 2000, off the coast of California. This excerpt contains an exchange between Captain Ted Thompson and First Officer William Tansky and the Los Angeles Route Traffic Control Center (LAX-CTR).

4:09:55 p.m.	Thompson: Center, Alaska two-sixty-one. We are, uh, in a dive here, and I've lost control, vertical pitch.
4:10:33	Thompson: Yea, we got it back under control here.
4:11:43	Tansky: Whatever we did is no good. Don't do that again...
4:11:44	Thompson: Yea, no, it went down. It went full nose down.
4:11:48	Tansky: Uh, it's a lot worse than it was?
4:11:50	Thompson: Yea. Yea. We're in much worse shape now.
4:14:12	Public address: Folks, we have had a flight-control problem up front here, we're working on it.
4:15:19	Flight 261 to LAX-CTR: L.A., Alaska two-sixty-one. We're with you, we're at twenty-two-five [22,500 feet]. We have a jammed stabilizer and we're maintaining altitude with difficulty...
4:15:36	LAX-CTR: Alaska two-sixty-one, L.A center. Roger, um, you're cleared to Los Angeles Airport via present position...
4:17:09	Flight attendant: Okay, we had like a big bang back there.
4:17:15	Thompson: I think the [stabilizer] trim is broke.
4:19:36	Extremely loud noise
4:19:43	Tansky: Mayday
4:19:54	Thompson: Okay, we are inverted, and now we gotta get it.
4:20:04	Thompson: Push, push, push...push the blue side up. Push...
4:20:14	Tansky: I'm pushing.
4:20:16	Thompson: Okay, now let's kick rudder. Left rudder, left rudder.
4:20:18	Tansky: I can't reach it.
4:20:20	Thompson: Okay. Right rudder, right rudder.
4:20:25	Thompson: Are we flying? We're flying, we're flying. Tell 'em what we're doing.
4:20:33	Tansky: Oh, yeah. Let me get...
4:20:38	Thompson: Gotta get it over again. At least upside down we're flying.
4:20:54	Thompson: Speedbrakes
4:20:55	Tansky: Got it.
4:20:56	Thompson: Ah, here we go.
4:20:57	End of recording

Flight Data Recorders

The flight data recorder (FDR) is designed to record the operating data from the plane's systems. There are sensors that are wired from various areas on the plane to the flight-data acquisition unit, which is wired to the FDR. When a switch is turned on or off, that operation is recorded by the FDR.

Photo courtesy National Transportation Safety Board (NTSB) The damaged flight data recorder from EgyptAir Flight 990

In the United States, the Federal Aviation Administration (FAA) requires that commercial airlines record a minimum of 11 to 29 parameters, depending on the size of the aircraft. Magnetic-tape recorders have the potential to record up to 100 parameters. Solid-state FDRs can record more than 700 parameters. On July 17, 1997, the FAA issued a Code of Federal Regulations that requires the recording of at least 88 parameters on aircraft manufactured after August 19, 2002.

Here are a few of the parameters recorded by most FDRs:

• Time
• Pressure altitude
• Airspeed
• Vertical acceleration
• Magnetic heading
• Control-column position
• Rudder-pedal position
• Control-wheel position
• Horizontal stabilizer
• Fuel flow

Solid-state recorders can track more parameters than magnetic tape because they allow for a faster data flow. Solid-state FDRs can store up to 25 hours of flight data. Each additional parameter that is recorded by the FDR gives investigators one more clue about the cause of an accident.

Built to Survive

In many airline accidents, the only devices that survive are the crash-survivable memory units (CSMUs) of the flight data recorders and cockpit voice recorders. Typically, the rest of the recorders' chassis and inner components are mangled. The CSMU is a large cylinder that bolts onto the flat portion of the recorder. This device is engineered to withstand extreme heat, violent crashes and tons of pressure. In older magnetic-tape recorders, the CSMU is inside a rectangular box.

Source: L-3 Communication Aviation Recorders

Using three layers of materials, the CSMU in a solid-state black box insulates and protects the stack of memory boards that store the digitized information. We will talk more about the memory and electronics in the next section. Here's a closer look at the materials that provide a barrier for the memory boards, starting at the innermost barrier and working our way outward:

• Aluminum housing - There is a thin layer of aluminum around the stack of memory cards.
• High-temperature insulation - This dry-silica material is 1 inch (2.54 cm) thick and provides high-temperature thermal protection. This is what keeps the memory boards safe during post-accident fires.
• Stainless-steel shell- The high-temperature insulation material is contained within a stainless-steel cast shell that is about 0.25 inches (0.64 cm) thick. Titanium can be used to create this outer armor as well.

Testing a CSMU

To ensure the quality and survivability of black boxes, manufacturers thoroughly test the CSMUs. Remember, only the CSMU has to survive a crash -- if accident investigators have that, they can retrieve the information they need. In order to test the unit, engineers load data onto the memory boards inside the CSMU. L-3 Communications uses a random pattern to put data onto every memory board. This pattern is reviewed on readout to determine if any of the data has been damaged by crash impact, fires or pressure.

There are several tests that make up the crash-survival sequence:

• Crash impact - Researchers shoot the CSMU down an air cannon to create an impact of 3,400 Gs (1 G is the force of Earth's gravity, which determines how much something weighs). At 3,400 Gs, the CSMU hits an aluminum, honeycomb target at a force equal to 3,400 times its weight. This impact force is equal to or in excess of what a recorder might experience in an actual crash.
• Pin drop - To test the unit's penetration resistance, researchers drop a 500-pound (227-kg) weight with a 0.25-inch steel pin protruding from the bottom onto the CSMU from a height of 10 feet (3 m). This pin, with 500-pounds behind it, impacts the CSMU cylinder's most vulnerable axis.
• Static crush - For five minutes, researchers apply 5,000 pounds per square-inch (psi) of crush force to each of the unit's six major axis points.
• Fire test - Researchers place the unit into a propane-source fireball, cooking it using three burners. The unit sits inside the fire at 2,000 degrees Fahrenheit (1,100 C) for one hour. The FAA requires that all solid-state recorders be able to survive at least one hour at this temperature.
• Deep-sea submersion - The CSMU is placed into a pressurized tank of salt water for 24 hours.
• Salt-water submersion - The CSMU must survive in a salt water tank for 30 days.
• Fluid immersion - Various CSMU components are placed into a variety of aviation fluids, including jet fuel, lubricants and fire-extinguisher chemicals.

During the fire test, the memory interface cable that attaches the memory boards to the circuit board is burned away. After the unit cools down, researchers take it apart and pull the memory module out. They restack the memory boards, install a new memory interface cable and attach the unit to a readout system to verify that all of the preloaded data is accounted for.

Black boxes are usually sold directly to and installed by the airplane manufacturers. Both black boxes are installed in the tail of the plane -- putting them in the back of the aircraft increases their chances of survival. The precise location of the recorders depends on the individual plane. Sometimes they are located in the ceiling of the galley, in the aft cargo hold or in the tail cone that covers the rear of the aircraft.

"Typically, the tail of the aircraft is the last portion of the aircraft to impact," Doran said. "The whole front portion of the airplane provides a crush zone, which assists in the deceleration of tail components, including the recorders, and enhances the likelihood that the crash-protected memory of the recorder will survive."

After a Crash

Although they are called "black boxes," aviation recorders are actually painted bright orange. This distinct color, along with the strips of reflective tape attached to the recorders' exteriors, help investigators locate the black boxes following an accident. These are especially helpful when a plane lands in the water. There are two possible origins of the term "black box": Some believe it is because early recorders were painted black, while others think it refers to the charring that occurs in post-accident fires.

Underwater Locator Beacon
In addition to the paint and reflective tape, black boxes are equipped with an underwater locator beacon (ULB). If you look at the picture of a black box, you will almost always see a small, cylindrical object attached to one end of the device. While it doubles as a handle for carrying the black box, this cylinder is actually a beacon.

Photo courtesy L-3 Communication Aviation Recorders A close-up of an underwater locator beacon

If a plane crashes into the water, this beacon sends out an ultrasonic pulse that cannot be heard by human ears but is readily detectable by sonar and acoustical locating equipment. There is a submergence sensor on the side of the beacon that looks like a bull's-eye. When water touches this sensor, it activates the beacon.

The beacon sends out pulses at 37.5 kilohertz (kHz) and can transmit sound as deep as 14,000 feet (4,267 m). Once the beacon begins "pinging," it pings once per second for 30 days. This beacon is powered by a battery that has a shelf life of six years. In rare instances, the beacon may get snapped off during a high-impact collision.

In the United States, when investigators locate a black box it is transported to the computer labs at the National Transportation Safety Board (NTSB). Special care is taken in transporting these devices in order to avoid any (further) damage to the recording medium. In cases of water accidents, recorders are placed in a cooler of water to keep them from drying out.

Photo courtesy U.S. Department of Defense U.S. Navy Lieutenant Junior Grade Jason S. Hall (right) watches as FBI Agent Duback (left) tags the cockpit voice recorder from EgyptAir Flight 990 on November 13, 1999.

"What they are trying to do is preserve the state of the recorder until they have it in a location where it can all be properly handled," Doran said. "By keeping the recorder in a bucket of water, usually it's a cooler, what they are doing is just keeping it in the same environment from which it was retrieved until it gets to a place where it can be adequately disassembled."

Retrieving Information

After finding the black boxes, investigators take the recorders to a lab where they can download the data from the recorders and attempt to recreate the events of the accident. This process can take weeks or months to complete. In the United States, black-box manufacturers supply the NTSB with the readout systems and software needed to do a full analysis of the recorders' stored data.

Photo courtesy L-3 Communication Aviation Recorders This portable interface can allow investigators quick access to the data on a black box.

If the FDR is not damaged, investigators can simply play it back on the recorder by connecting it to a readout system. With solid-state recorders, investigators can extract stored data in a matter of minutes. Very often, recorders retrieved from wreckage are dented or burned. In these cases, the memory boards are removed, cleaned up and a new memory interface cable is installed. Then the memory board is connected to a working recorder. This recorder has special software to facilitate the retrieval of data without the possibility of overwriting any of it.

A team of experts is usually brought in to interpret the recordings stored on a CVR. This group typically includes a representative from the airline, a representative from the airplane manufacturer, an NTSB transportation-safety specialist and an NTSB air-safety investigator. This group may also include a language specialist from the Federal Bureau of Investigation and, if needed, an interpreter. This board attempts to interpret 30 minutes of words and sounds recorded by the CVR. This can be a painstaking process and may take weeks to complete.

Both the FDR and CVR are invaluable tools for any aircraft investigation. These are often the lone survivors of airplane accidents, and as such provide important clues to the cause that would be impossible to obtain any other way. As technology evolves, black boxes will continue to play a tremendous role in accident investigations.

What's in store for Black Boxes?

According to L3 Communications, there are improvements on the horizon for black box technology. Reportedly, some form of cockpit video recorder will be developed. Such a recorder would be able to store video images in solid-state memory.

Other Uses for Black Box Technology
Currently, black boxes aren't just taking flight -- they're being grounded as well. Several automobile manufacturers are utilizing black box technology in their automobiles and a few have been doing so for quite some time. According to an article titled "Black boxes in GM cars increasingly help police after accidents" General Motors has been using black box technology for over a decade. The manufacturer has been installing a Sensing and Diagnostic Module (SDM) on thousands of its cars, including the Corvette. Furthermore, this article reports that "industry insiders say as many as a dozen other manufacturers install similar technology under different labels."

So, black box technology has moved from airplanes to automobiles -- where is it headed next? It could be on you. Right now it's just a prototype, but soon the SenseCam could provide you with an incredible amount of information about -- well, you!

Let's say you attended a crowded convention last month. Because you forgot your PDA, you were forced to scribble dozens of phone numbers and emails down on random cocktail napkins. You made plans with several colleagues, but much like the random napkins in the washing machine at home, your memory just didn't hold up. But, all would not be lost -- if you were wearing a SenseCam. According to its manufacturer, this badge-sized wearable camera reportedly captures up to 2000 VGA images within a 12-hour day and stores it in a 128Mbyte flash memory. So, most every scribbled note and every promised meeting would be recorded for you to look at later.

How Sonic Cruisers Will Work?

ride. If you want to take that kind of flight, you're going to have to stop at least once. There are many international and even shorter flights that require you to be herded through Getting from, say, New York to Sydney, Australia, is not a point-to-point, uninterrupted airplanehubs and make one or more stops before arriving at your destination.

All of that is about to change. In March 2001, Boeing released details of a new, delta-winged airplane, dubbed the Sonic Cruiser. This near-supersonic aircraft may be able to fly faster over extended ranges and allow passengers to spend less time in the air and at airports. Only the Concorde is faster than this new plane; but even the Concorde won't match the Sonic Cruiser's range.

Photo courtesy Boeing The Sonic Cruiser will shave one hour for every 3,000 miles flown.

Not a lot is known about this new aircraft, because Boeing is offering few details. In this article, you will learn why Boeing is planning to spend $10 billion on this new concept, how it will save you time and how it will get you to farther destinations than any other commercial aircraft.

Creating a New Look

While Boeing's major rival, Airbus, focuses on the 555-passenger A380 jumbo jet, Boeing is turning its attention to a smaller aircraft that will carry between 100 and 300 passengers and is more suited for non-stop, point-to-point service. The A380 is a behemoth of an aircraft that will be ready around 2006. It is designed to deal with the increased traffic to the high-traffic hub airports rather than point-to-point flights.

Photo courtesy Boeing Boeing is using new design elements, such as delta wings and canards, on the Sonic Cruiser.

Boeing consulted several major airlines that buy aircraft from Boeing and asked them what they wanted in a new airliner. Alan Mulally, Boeing Commercial Airplane president and CEO, said that most of them asked for an aircraft that could fly faster and higher over long ranges.

The result is the Sonic Cruiser. Boeing unveiled a one-fortieth-scale, 6-foot (1.8-m) model of the concept at the 2001 Paris Air Show. The aircraft will be the first major design change to commercial aircraft in decades. Here are the major design features of the Sonic Cruiser:

• Double delta wings - Delta wings are placed farther back on the plane than conventional wings. The Concorde has delta wings.
• Canards - These are the smaller, wing-like structures just behind the nose of the aircraft. Canards will give the plane more horizontal stability at high speeds.
• Aft-mounted engines - Reminiscent of the Blackbird SR-71 military aircraft, the engines are blended into the body of the wing. You will learn more about the Sonic Cruiser's engine in the next section.

Few details of the planes specific dimensions have been released, because Boeing engineers are likely to make more adjustments before moving beyond the drawing board. Boeing officials plan to hold additional meetings with airlines to determine the ideal size of the aircraft. The plane is expected to be ready for takeoff sometime between 2006 and 2008.

Flying at Near-Supersonic Speeds

One of the many unique features of the Sonic Cruiser is the placement of the twin engines. The plane's engine housing will be blended into the rear of the aircraft. This is in stark contrast to the under-the-wing engine configuration of most commercial airliners.

To push the Sonic Cruiser to 0.95 Mach and possibly faster, Boeing will initially install two 777-class engines in the Sonic Cruiser. (Mach is the speed of sound, or about 740 mph/1,190 kph). However, Boeing is not being specific about what type of 777 engines it will use. One example of such an engine is the Pratt & Whitney 4098, which generates 98,000 pounds (44,452 kg) of thrust. The Sonic Cruiser will probably be slightly smaller than a 777 aircraft, which seats 305 to 394 passengers. The lightened load, in addition to the plane's design, will allow it to travel at near-supersonic speeds.

The use of 777-class engines is likely a temporary fix until one of three major aircraft-engine makers -- Rolls Royce, General Electric or Pratt & Whitney - - develops an engine specific to the Sonic Cruiser's needs and configuration.

Traveling at 0.95 Mach, the Sonic Cruiser will be the second fastest commercial aircraft in the world, and 15 percent faster than most commercial aircraft. Only the Concorde, which flies faster than Mach 2, will be faster than the Cruiser. Boeing estimates that the Sonic Cruiser will shave one hour off of every 3,000 miles (4,828 km) traveled. The increased speed will get passengers to their destinations 20 percent faster.

Speed doesn't come cheap. While the Sonic Cruiser saves time, it uses significantly more fuel to do it. It's estimated that the Sonic Cruiser will burn anywhere from 15 percent to 20 percent more fuel than conventional aircraft. Boeing believes the added fuel cost will not be felt by the airlines. Boeing officials say that the operating costs for the aircraft will be equal to those of any other aircraft made around the same time.

Compare It Sonic Cruiser

• Speed - 0.95 Mach (703 mph/1131 kph)
• Engines - Twin 777-class
• Cruising Altitude - 40,000 feet (13,000 m)
• Range - 9,000 nautical miles (16,668 km)
• Seating - 100-300

Concorde

• Mach 2 (1,350 mph/2,172 kph)
• 4 Rolls Royce/Snecma Olympus 593 (18.7 tons/17 metric tons of thrust)
• 60,000 feet (18,300 m)
• 4,067 nautical miles (6,200 km)
• 100

747-400

• 0.84 Mach (560 mph/901 kph)
• 4 Pratt & Whitney PW4062 (63,300 lbs/26,945 kg of thrust)
• 35,000 feet (10,668 m)
• 7,325 nautical miles (13,570 km)
• 416-568

Almost Anywhere Non-stop

The whole point of flying is to get from one place to another quickly. But sometimes, air travel can get slowed by the numerous stops between destinations and the time spent waiting for the next flight. The Sonic Cruiser may be able to reduce those types of delays not only by travelling faster, but also by eliminating the need for a refueling stop.

Boeing said that the Sonic Cruiser could eventually connect cities thousands of miles apart via non-stop fights. If it fulfills its promise, the aircraft could have a range of about 9,000 nautical miles (16,668 km). Non-stop flights from Los Angeles to Singapore would be possible. The longer distances are achieved through using 777-class engines on a smaller aircraft, the new delta wings and increased fuel capacity.

Boeing has even suggested a potential range of 10,000 nautical miles (18,520 km) in later versions of the aircraft. If that were possible, you could get on a plane in New York and stay airborne until you arrived in Sydney, Australia. The trip, which takes about 21 hours today, would be reduced to 18 hours, and the need for a layover would be eliminated entirely.

One reason for developing the Sonic Cruiser is that it could help solve overcrowding in the skies by providing fast, point-to-point travel and avoiding the major hub airports. Craig Martin, a spokesperson for Boeing, said that Boeing envisions the air-travel industry becoming increasingly fragmented, with an increased demand for non-stop routes between smaller cities. The Sonic Cruiser will give airlines the ability to fulfill that demand.

While the Sonic Cruiser is expected to offer fast air travel, second only to the Concorde, passengers won't have to pay Concorde prices. The price of a transatlantic Concorde ticket is more than $5,000 and is based somewhat on the maintenance costs of the plane, but more so on the prestige of flying on it. The Sonic Cruiser would be a full-scale production plane and equivalent in cost to any conventional airplane. British Airways is even taking a look at the Sonic Cruiser, but hasn't committed to any plans to replace the recently beleaguered Concorde.

The Sonic Cruiser has received a lot of attention from the media and has created quite a buzz in the airline industry. Boeing has even said that it may starting taking orders for the aircraft in 2002. Yet, while the Sonic Cruiser opens up new possibilities for air travel, it is still just one concept on Boeing's drawing board. Only time will tell if this concept will fly.

How the Switchblade Plane Will Work? Theorey of Switchblade plane

Aircraft that can alter their wing configurations in mid-flight have been in development since World War II. With different wing positions allowing for greater efficiency and performance in various flight modes, these aircraft are more versatile than aircraft with fixed wings. Although a few models have made it into production, the limitations of engines, mechanics and computers have kept these aircraft from coming into widespread use. Now technology has finally caught up with the concept, and Northrop Grumman is in the process of building an unmanned shape-shifting plane: the Switchblade.

If you look at aircraft from World War I or World War II, you'll notice that the wings are almost always perpendicular to the fuselage, with only a few degrees of backwards sweep, if any. At the time, airplane engines couldn't propel the planes any faster than about 375 mph. At these low speeds, a perpendicular wing configuration allowed for maximum lift and maneuverability.

After World War II, the development of jet engines led to an enormous boost in aircraft speed. Traditional wing shapes weren't as efficient at high speeds (particularly supersonic speeds), so jet fighters began sporting tapered wings. The F-4 Phantom II is a good example of this type of wing profile. However, this increase in high-speed performance came with a trade-off -- the planes were not very effective or efficient at lower speeds.

Image courtesy U.S. Air Force A formation of F-4 Phantom II fighter aircraft

An aircraft that can alter its wing configuration in mid-flight has variable-wing geometry. This gives the plane the best possible performance characteristics at a given speed. The German Messerschmitt company first tested planes with variable wing geometry during World War II. The Messerschmitt P-1101's wings could be moved to different sweep angles, only while the plane was on the ground. Based on the Messerschmitt design, the U.S. developed a working test craft, the Bell X-5, which was slightly larger than the P-1101 and could change its wing-sweep angle while in flight.

This type of technology, also known as "swing wing," first appeared in a production aircraft in the late 1960s with the General Dynamics F-111. This plane had three different wing positions to give it maximum efficiency at all speeds. In fact, a variation of this plane, the FB-111A strategic bomber, carried the unofficial nickname "Switchblade." [ref].

Image courtesy U.S. Air Force The FB-111A strategic bomber never had an official name, but it was commonly called the "Switchblade."

Several other fighter jets used variable-geometry wings in the next few decades, including the Tornado and the F-14 Tomcat. The unswept wing position made these planes exceptionally maneuverable and easier to land on the short flight decks of aircraft carriers. However, the mechanisms required to make the wing movements function were complicated and heavy. They also took up a lot of space, cutting down on efficiency and payload. Swing wings were largely abandoned for more simplistic designs.

In the next section we'll look at the Switchblade plane design.

Switchblade Plane Design

Designers of planes with variable-geometry wings also had to consider agility. While sweeping the wings back made for more stable aircraft at high speeds, forward-swept wings allowed the aircraft to be exceptionally agile, an especially desirable characteristic for fighter aircraft. The German Ju-287 was the first aircraft with forward-swept wings, but the X-29 is the most well-known example [ref]. While this drastic configuration rendered the X-29 unstable, computers could control the aircraft with fly-by-wire flight control systems. The next swept-wing aircraft incorporated aspects of the previous designs.

Image courtesy NASA The X-29 featured one of the most unusual aircraft designs in history.

In the 1990s, Northrop Grumman tested variable-geometry wings on another plane with the "Switchblade" nickname. The Northrop Bird of Prey had three wing configurations:

• full-back position - The wings were perpendicular to the fuselage for low-speed flight.
• intermediate position - The wings were swept forward for exceptional maneuverability.
• full-forward position - The leading edge of the wings folded in against the fuselage, allowing the trailing edge to become the front of the wing for high speeds. This resulted in a triangular, or delta wing shape.

Image courtesy John MacNeill The Northrop Bird of Prey in full-back, intermediate and full-forward positions.

Patents for the variable-wing geometry are public knowledge, and there were reports of a test squadron flying these aircraft. Documents showing the existence of a Bird of Prey test craft were declassified, but this declassified craft did not incorporate "swing wing" technology. Details of the three-position "Switchblade" Bird of Prey remain classified.

The Defense Advanced Research Projects Agency (DARPA) is the Pentagon's high-tech military technology research branch. It has allocated $10.3 million to Northrop Grumman to develop a Switchblade preliminary design by late 2007. The company beat two other proposals for the design project, and work will proceed at Northrop Grumman's El Segundo, California headquarters. Northrop Grumman plans a scaled-down test model with a 40-foot wingspan for 2010, with a full-size, fully-functional Switchblade ready for flight in 2020. As the project moves into the scale and full-sized phases, costs will likely escalate into the billions of dollars.

Next, we'll look at how wing position affects a plane's performance and learn more about the Switchblade.

Wing Positions

Before we look at the specific technology involved in the design of this new Switchblade, we'll discuss exactly how the position of a plane's wings affect its performance.

Unswept wings are efficient at low speeds, providing a great amount of lift compared to the amount of induced drag exerted on the plane. Induced drag is essentially another component of the force that allows the plane to fly. As air flows around the wings, the resultant turning of the airflow deflects the plane up, counteracting gravity pulling the plane down toward the ground. However, some of that force also resists the plane's forward movement, resulting in drag. As speed increases, this drag becomes even more problematic. (You can learn more about lift and drag in How Airplanes Work.)

As an aircraft approaches and passes the speed of sound, shock waves form (pressure waves heard as a "sonic boom" by observers if the plane is supersonic). These waves create a second form of drag known as wave drag. When a shockwave forms, it changes the aerodynamic profile of the plane. Instead of a streamlined aircraft shape cutting smoothly through the air, this large pressure wave adds a bulky impediment that must be pushed through the air. It's sort of like running into the wind carrying a mattress. Unswept wings are very bad at dealing with wave drag.

Swept wings cut down on drag caused by turbulence at the wingtips. But the real advantage of swept wings comes in supersonic flight -- the configuration cuts down on wave drag by redistributing the shock waves along the plane's aerodynamic profile. They are ideal for these high-speed conditions. Unfortunately, they do not allow for heavy payloads at lower speeds. Swept wings are also inefficient and burn too much fuel to stay aloft, which reduces the range of the aircraft.

So why is the U.S. military bringing back variable-geometry wing technology? Technological advances mean better wing transition mechanisms, advanced wing shapes and computer systems that can control unstable aircraft. The Pentagon has identified a need for a plane that can remain aloft for long periods close to enemy territory, and then switch to a high-speed mode to rush in and deliver a blow before rushing back out at supersonic speeds. These two modes of flight require drastically different wing profiles for maximum efficiency. Northrop Grumman's new Switchblade is unlike any "swing wing" aircraft previously imagined.

Image courtesy Northrop Grumman The Switchblade flying at low speed will have long range and endurance capabilities.

In the next section we'll look at the Switchblade technology.

Switchblade Technology

This Switchblade is a flying wing with a pod attached underneath to carry the engines, surveillance equipment and weapons. It doesn't have fuselage, a tail, tail fins or other extraneous parts: it's literally one giant wing. For most of its mission, the Switchblade will cruise at high altitude for as long as 15 hours, waiting for the signal to strike. For that part of the mission, the wing will be perpendicular to the direction of flight, like a traditional aircraft. This will minimize fuel burn, and maximize the time aloft, much like a glider.

Image courtesy Northrop Grumman The Switchblade flying at high speed has the right wing swept forward and the left wing swept back.

When the time comes for a strike, the entire wing will pivot 60 degrees relative to the direction of flight. This will leave the right wing tip pointing forward, while the rest of the wing slants back. The resulting aerodynamic profile will be ideal for a high-speed assault -- in this case, up to Mach 2 for a distance of 2,500 miles. This type of pivoting wing is an oblique wing design. With the wing in the oblique position, supersonic shock waves disperse, rather than "piling up" in front of the craft and creating drag.

The Switchblade will have a 200-foot wingspan. The pod suspended beneath the wings will hold two advanced jet engines, cameras, flight computers and any missiles or bombs required for the mission. It won't have a cockpit, because it won't have a pilot. Flight control computers will handle all the flying because of the unstable wing configurations. This also prevents problems with pilot fatigue during extremely long missions.

For lots more information about the Switchblade project, flying wings and variable-wing geometry, check out the links on the next page.

Burt Rutan and the Oblique Wing The Switchblade is not the first attempt to develop an oblique wing aircraft. A NASA wind tunnel project conducted in 1979 showed that a pivoting wing could increase fuel efficiency at supersonic speeds by as much as 100 percent [ref]. Aircraft designer Burt Rutan developed a AD-1 oblique wing prototype that helped prove the viability of an oblique wing system. (Rutan is most famous for designing SpaceShipOne, the first privately owned and funded craft to carry a human into space.)

Image courtesy NASA The NASA Dryden AD-1 Oblique Wing

The AD-1 allowed the wing to pivot gradually as speed increased, always positioning it for maximum efficiency at the plane's present speed. NASA hoped that the technology could lead to a more efficient supersonic commercial transport. However, testing revealed that an aircraft became extremely unstable as the wing moved into an oblique position. A human pilot could not cope with the constant, minute adjustments necessary to maintain flight under these conditions. At the time, flight control computers were not sophisticated enough to manage it, either.

How Ejection Seats in aircrafts Work?

U.S. Air Force Captain Scott O'Grady was helping to enforce the no-fly zone over northern Bosnia on June 2, 1995, when a Bosnian-Serb surface-to-air missile (SAM) struck his F-16. With the plane disintegrating around him, O'Grady reached down between his knees and grabbed the pull handle of his ejection seat. After a loud bang caused by the canopy separating, O'Grady was blasted into the air along with his seat. Soon after, his parachute deployed and, like 90 percent of pilots who are forced to eject from their aircraft, O'Grady survived the ejection from his F-16. Following six days of evading capture and eating insects for survival, O'Grady was rescued.

Photo courtesy U.S. Air Force Ejecting from an aircraft is rare, but pilots sometimes have to resort to pulling the ejection handle to save their lives.

Ejecting from an aircraft moving at speeds greater than the speed of sound (mach 1: 750 miles per hour / 1,207 kph) can be very dangerous. The force of ejecting at those speeds can reach in excess of 20 Gs -- one G is the force of Earth's gravity. At 20 Gs, a pilot experiences a force equal to 20 times his or her body weight, which can cause severe injury and even death.
Most military aircraft, NASA research aircraft and some small commercial airplanes are equipped with ejection seats to allow pilots to escape from damaged or malfunctioning airplanes.

Take a Seat

It's important for many types of aircraft to have an ejection seat in case the plane is damaged in battle or during testing and the pilot has to bail out to save his or her life. Ejection seats are one of the most complex pieces of equipment on any aircraft, and some consist of thousands of parts. The purpose of the ejection seat is simple: To lift the pilot straight out of the aircraft to a safe distance, then deploy a parachute to allow the pilot to land safely on the ground.

Photo courtesy U.S. Department of Defense An ejection seat being removed from an F-15C Eagle

To understand how an ejection seat works, you must first be familiar with the basic components in any ejection system. Everything has to perform properly in a split second and in a specific sequence to save a pilot's life. If just one piece of critical equipment malfunctions, it could be fatal.

Ejection seats are placed into the cockpit and usually attach to rails via a set of rollers on the edges of the seat. During an ejection, these rails guide the seat out of the aircraft at a predetermined angle of ascent. Like any seat, the ejection seat's basic anatomy consists of the bucket, back and headrest. Everything else is built around these main components. Here are key devices of an ejection seat:

• Catapult
• Rocket
• Restraints
• Parachute

In the event of an ejection, the catapult fires the seat up the rails, the rocket fires to propel the seat higher and the parachute opens to allow for a safe landing. In some models, the rocket and catapult are combined into one device. These seats also double as restraint systems for the crewmembers both during an ejection and during normal operation.

Ejection seats are just one part of a larger system called the assisted egress system. "Egress" means "a way out" or "exit." Another part of the overall egress system is the plane's canopy, which has to be jettisoned prior to the ejection seat being launched from the aircraft. Not all planes have canopies. Those that don't will have escape hatches built into the roof of the plane. These hatches blow just before the ejection seat is activated, giving crewmembers an escape portal.

Photo courtesy U.S. Department of Defense A pilot prepares to pull down the face curtain that will launch the ejection seat up the track of the ejection-seat trainer.

Seats are activated through different methods. Some have pull handles on the sides or in the middle of the seat. Others are activated when a crew member pulls a face curtain down to cover and protect his or her face. In the next section, you will find out what happens once the seat is activated.

Ejection-seat Terms

• Bucket - This is the lower part of the ejection seat that contains the survival equipment.
• Canopy - This is the clear cover that encapsulates the cockpit of some planes; it is often seen on military fighter jets.
• Catapult - Most ejections are initiated with this ballistic cartridge.
• Drogue parachute - This small parachute is deployed prior to the main parachute; it designed to slow the ejection seat after exiting the aircraft. A drogue parachute in an ACES II ejection seat has a 5-foot (1.5-m) diameter. Others may be less than 2 feet (0.6 m) in diameter.
• Egress system - This refers to the entire ejection system, including seat ejection, canopy jettisoning and emergency life-support equipment.
• Environmental sensor - This is an electronic device that tracks the airspeed and altitude of the seat.
• Face curtain - Attached to the top of some seats, pilots pull this curtain down to cover his or her face from debris. This curtain also holds the pilot's head still during ejection.
• Recovery sequencer - This is the electronic device that controls the sequence of events during ejection.
• Rocket catapult - This is a combination of a ballistic catapult and an underseat rocket unit.
• Underseat rocket - Some seats have a rocket attached underneath to provide additional lift after the catapult lifts the crewmember out of the cockpit.
• Vernier rocket - Attached to a gyroscope, this rocket is mounted to the bottom of the seat and controls the seat's pitch.
• Zero-zero ejection - This is an ejection on the ground when the aircraft is at zero altitude and zero airspeed.

Bailing Out

When a crewmember lifts the pull handle or yanks the face curtain down on the ejection seat, it sets off a chain of events that propels the canopy away from the plane and thrusts the crewmember safely out. Ejecting from a plane takes no more than four seconds from the time the ejection handle is pulled. The exact amount of time depends on the seat model and the crewmember's body weight.

Photo courtesy Goodrich Corporation This ACES II ejection seat has a middle pull handle used to activate the ejection sequence.

Pulling the ejection handle on a seat sets off an explosive cartridge in the catapult gun, launching the ejection seat into the air. As the seat rides up the guide rails, a leg-restraint system is activated. These leg restraints are designed to protect the crewmember's legs from getting caught or harmed by debris during the ejection. An underseat rocket motor provides the force that lifts the crewmember to a safe height, and this force is not outside normal human physiological limitations, according to documents from Goodrich Corporation, a manufacturer of ejection seats used by the U.S. military and NASA.

Prior to the ejection system launching, the canopy has to be jettisoned to allow the crewmember to escape the cockpit. There are at least three ways that the canopy or ceiling of the airplane can be blown to allow the crewmember to escape:

• Lifting the canopy - Bolts that are filled with an explosive charge are detonated, detaching the canopy from the aircraft. Small rocket thrusters attached on the forward lip of the canopy push the transparency out of the way of the ejection path, according to Martin Herker, a former physics teacher who has written about ejection seats and maintains a Web site describing ejection seats. (Click here to go to Herker's site.)

• Shattering the canopy - To avoid the possibility of a crewmember colliding with a canopy during ejection, some egress systems are designed to shatter the canopy with an explosive. This is done by installing a detonating cord or an explosive charge around or across the canopy. When it explodes, the fragments of the canopy are moved out of the crewmember's path by the slipstream.

• Explosive hatches - Planes without canopies will have an explosive hatch. Explosive bolts are used to blow the hatch during an ejection.

The seat, parachute and survival pack are also ejected from the plane along with the crewmember. Many seats, like Goodrich's ACES II (Advanced Concept Ejection Seat, Model II), have a rocket motor fixed underneath the seat. After the seat and crewmember have cleared the cockpit, this rocket will lift the crewmember another 100 to 200 feet (30.5 to 61 m), depending on the crewmember's weight. This added propulsion allows the crewmember to clear the tail of the plane. As of January 1998, there had been 463 ejections worldwide using the ACES II system, according to the U.S. Air Force. More than 90 percent of those ejections were successful. There were 42 fatalities.

Photo courtesy NASA The parachutes opening on a Martin-Baker ejection seat during a test. The small parachute at the top is called the drogue parachute.

Once out of the plane, a drogue gun in the seat fires a metal slug that pulls a small parachute, called a drogue parachute, out of the top of the chair. This slows the person's rate of descent and stabilizes the seat's altitude and trajectory. After a specified amount of time, an altitude sensor causes the drogue parachute to pull the main parachute from the pilot's chute pack. At this point, a seat-man-separator motor fires and the seat falls away from the crewmember. The person then falls back to Earth as with any parachute landing.

Modes of Ejection
In the ACES II ejection seat produced by Goodrich Corporation, there are three possible ejection modes. The one used is determined by the aircraft's altitude and airspeed at the time of ejection. These two parameters are measured by the environmental sensor and recovery sequencer in the back of the ejection seat.

The environmental sensor senses the airspeed and altitude of the seat and sends data to the recovery sequencer. When the ejection sequence begins, the seat travels up the guide rails and exposes pitot tubes. Pitot tubes, named for physicist Henri Pitot, are designed to measure air-pressure differences to determine the velocity of the air. Data about the air flow is sent to the sequencer, which then selects from the three modes of ejections:

• Mode 1: low altitude, low speed - Mode 1 is for ejections at speeds of less than 250 knots (288 mph / 463 kph) and altitudes of less than 15,000 feet (4,572 meters). The drogue parachute doesn't deploy in mode 1.
• Mode 2: low altitude, high speed - Mode 2 is for ejections at speeds of more than 250 knots and altitudes of less than 15,000 feet.
• Mode 3: high altitude, any speed - Mode 3 is selected for any ejection at an altitude greater than 15,000 feet.

Timing an Ejection

• 0 seconds - Pilot pulls cord; canopy is jettisoned or shattered; catapult initiates, sending seat up rails.
• 0.15 seconds - Seat clears ejection rails at 50 feet (15 m) per second and is clear of surrounding cockpit; rocket catapult ignites; vernier motor fires to counteract any pitch changes; yaw motor fires, inducing slight yaw to assure man-seat separation. (Burn time of all motors equals 0.10 seconds.)
• 0.50 seconds - Seat has lifted to about 100 to 200 feet (30.5 to 61 m) from ejection altitude.
• 0.52 seconds - Seat-man-separator motor fires; cartridge fires to release crewmember and his equipment from seat; drogue gun fires parachute.
• 2.5 to 4 seconds - Main parachute is fully deployed.

Source: Goodrich Corporation

Physics of Ejecting

Ejecting from an airplane is a violent sequence of events that places the human body under an extreme amount of force. The primary factors involved in an aircraft ejection are the force and acceleration of the crewmember, according to Martin Herker, a former physics teacher. To determine the force exerted on the person being ejected, we have to look at Newton's second law of motion, which states that the acceleration of an object depends on the force acting upon it and the mass of the object.

Photo courtesy NASA An ejection seat is test-fired at NASA to analyze the seat's ability to perform a zero-altitude, zero-velocity ejection.

Newton's second law is represented as:

Force = Mass x Acceleration
(F=MA)

Regarding a crewmember ejecting from a plane, M equals his or her body mass plus the mass of the seat. A is equal to the acceleration created by the catapult and the underseat rocket.

Acceleration is measured in terms of G, or gravity forces. Ejecting from an aircraft is in the 5-G to 20-G range, depending on the type of ejection seat. As mentioned in the introduction, 1 G is equal to the force of Earth's gravity and determines how much we weigh. One G of acceleration is equal to 32 feet/second² (9.8 m/s²). This means that if you drop something off of a cliff, it will fall at a rate of 32 feet/second².

It's simple to determine the mass of the seat and the equipment attached to the seat. The pilot's mass is the largest variable. A 180-pound person normally feels 180 pounds of force being applied to him when standing still. In a 20-G impact, that same 180-pound person will feel 3,600 pounds of force being exerted. To learn more about force, click here.

"To determine the speed of the [ejection] seat at any point in time, one solves the Newton equation knowing the force applied and the mass of the seat/occupant system. The only other factors that are needed are the time of the force to be applied and the initial velocity present (if any)," writes Herker on his Web site describing the physics for understanding ejections. Herker provides this equation for determining the speed of the seat:

Speed = Acceleration x Time + Initial speed
V(f) = AT + V(i)

Initial speed refers to either the climb or the sink rate of the aircraft. It may also be determined by the initial step of the ejection process in a seat that combines an explosive catapult and an underseat rocket. The seat speed must be high enough to allow separation of the seat and person from the aircraft as quickly as possible in order to clear the entire aircraft.

The use of an ejection seat is always a last resort when an aircraft is damaged and the pilot has lost control. However, saving the lives of pilots is a higher priority than saving planes, and sometimes an ejection is required in order to save a life.

How the Aeroscraft Will Work

The Aeroscraft is a heavier-than-air vehicle currently in development for use in the near future -- a prototype should be finished by 2010. It will be able to haul massive amounts of cargo and transport hundreds of passengers in luxury with quiet, electric engines. It will also be able to take off and land without an airstrip. The Aeroscraft is sort of a hybrid -- it carries helium, like a blimp, but its shape provides lift, like an airplane. In this article, we'll see how the Aeroscraft flies and what it will be able to do.

Image courtesy Worldwide Aeros Corp. The Aeroscraft

Passenger travel and shipping by airship died out in the late 1930s, after the infamous Hindenburg disaster. Since then, lighter-than-air craft have been used mainly for advertising or to provide aerial views for television cameras. In recent years, several companies have been introducing safer, more efficient airships to the world. These companies include the Zeppelin Company, makers of the Hindenburg, and Worldwide Aeros Corp, designers of the Aeroscraft.

A lighter-than-air craft, such as an airship (or blimp), is filled with a gas, such as helium or hydrogen, which provides buoyancy. Buoyancy is the effect of something rising up in relation to a heavier substance surrounding it. Air is lighter than water, so if you fill an inflatable ball with air, it will float in a swimming pool. The same thing happens with helium or hydrogen -- they're both lighter than air. (To learn more about how blimps fly, check out How Blimps Work.) A regular airplane is much heavier than air, so lift must be provided by some other means. Lift is a force on a wing immersed in a moving fluid (in this case, air), and it acts perpendicular to the flow of the fluid. When the plane moves through the air at sufficient speed, the deflection of air creates lift. This is a very basic explanation; check out How Airplanes Work for more detail about how lift is created.

Image courtesy Worldwide Aeros Corp. The major parts of the Aeroscraft

The Aeroscraft combines elements of a lighter-than-air craft with those of an airplane. It holds 14 million cubic feet of helium, which negates about 60 percent of the craft's weight [ref]. When the Aeroscraft is at cruising speed, its aerodynamic shape, as well as canards (forward fins) and empennages (aft, or rear fins), provide the remaining lift. That's pretty impressive when you consider the Aeroscraft's size: 165 feet high, 244 feet wide and 647 feet long. That's about as long as two football fields. It will carry up to 400 tons of cargo over a range of 6,000 miles. With a top speed of 174 mph, it will be able to cross the U.S. in about 18 hours [ref].

Operating the Aeroscraft
The Aeroscraft can take off and land vertically using six turbofan jet engines, thanks to an emergent technology called Dynamic Buoyancy Management. This capability will allow it to fly to and from areas without an extensive transportation infrastructure. Once the craft reaches cruising altitude (around 8,000 feet), giant aft propellers will move it forward, and the Aeroscraft's aerodynamic shape will generate enough lift to keep it in the air. Hydrogen fuel cells or another form of environmentally friendly fuel will fuel the electric propellers. This means the Aeroscraft will be both efficient and quiet.

Image courtesy Worldwide Aeros Corp.

On the Aeroscraft, the four canards and two empennages will keep it stable and allow the pilot to make minor adjustments to keep it flying level. Outside conditions, such as wind and air pressure, will be measured along with weight distribution inside the craft. If all the passengers suddenly run to the port side of the craft to see something, the control system can compensate for that. Air from outside will be sucked into holding tanks, where it will be compressed and used as ballast.

All pilot control and avionics systems will use Fly-by-Light (FBL) technology. The pilot's commands are fed into a flight control processor and sent to the surface actuators via electrical signals transmitted along fiber optic cables. In Fly-by-Wire (FBW) Systems, wires must be shielded from electromagnetic frequency (EMF) interference, which results in additional weight, cost and maintenance. FBL is immune to EMF interference, such as lightning strikes. The FBL, flight control processor and flight control devices make up the Onboard Data Exchange Managing System (ODEMS). This system means that the flight is mostly automated, with the two-person crew monitoring the flight conditions to ensure safety.

The Aeroscraft does not require an extensive ground crew for either takeoff or landing. Its Air Cushion Take-off/Landing System (ACTLS), located on the belly of the aircraft, creates a vacuum to anchor it upon landing. The ACTLS reverses upon takeoff.

Next, we'll look at proposed uses for the Aeroscraft.

Aeroscraft Statistics

• Dimensions (feet): 165 high x 244 wide x 647 long (in meters, 50 x 74 x 197)
• Range: 6,000 miles (9,656 km)
• Cruising Speed: 174 mph (78 m/s)
• Altitude Range: 0 to 8,000 ft (0 to 2438 m)
• Payload: Up to 250 passengers or 400 tons (362,874 kg) of cargo

Proposed Uses

Designers envision the Aeroscraft operating like a luxury cruise ship that sails through the air instead of the ocean. Up to 250 passengers will travel in comfort and style, with sleeping quarters, restaurants, a casino and other amenities. The Aeroscraft will be able to cruise past scenic landmarks to give passengers a stunning view, even if the landmark is in the middle of a jungle. The passenger version is the Aeros-ML, which would have a smaller configuration, with room for about 120 passengers or 20 tons of cargo.

Image courtesy Worldwide Aeros Corp.

The Aeroscraft also has potential as a cargo ship. There are two versions for freight -- the Aeros-D4 and the Aeros-D8. Currently, time-sensitive cargo is usually shipped by land because shipping by airplane is cost-prohibitive and has weight limitations. But the Aeroscraft's cargo hold of two acres can accommodate 400 to 500 tons of cargo, and it can handle huge items that can't be disassembled, like oil rigs or huge pieces of factory machinery. It will be able to move them without disrupting traffic, and much more quickly than trucks can. Aeroscraft's designers think it will be able to do so at a competitive cost. It may even be able to carry "an entire store's worth of merchandise directly to a Wal-Mart" [ref].

Image courtesy Worldwide Aeros Corp.

That kind of cargo capacity interests the military as well. It could carry an entire company (100 to 200 troops), all of their equipment, all their support troops, fuel, rations, water and everything else the company would need to set up and go to work fighting a war, all in an aircraft that could drop them anywhere. Such a craft could revolutionize military logistics.

Worldswide Aeros was one of two companies to receive a $3 million preliminary design contract to design a vehicle for DARPA's Walrus program. DARPA (Defense Advanced Research Projects Agency) is the research and development arm of the U.S. Department of Defense. The Walrus program was created to develop a large heavier-than-air aircraft to deploy both military personnel and equipment. However, the project is currently without government funding, and DARPA's budget request for the 2007 fiscal year called to terminate Walrus at the end of this developmental phase "in keeping with congressional intent" [ref]. The company is still moving forward with its prototype development and plans to have it ready within 18 months.

Recently, the U.S. Air Force awarded Aeroscraft with a Phase I Small Business Innovative Research Program (SBIR) Award. This award "encourages small businesses to explore their technological potential and provides the incentive to profit from its commercialization" [ref]. Aeroscraft will use the award to develop high-altitude, near-space aircraft that can perform many of the same duties as Earth-orbiting spacecraft or satellites at a fraction of the cost.

The Aeroscraft Company also thinks their airship will be perfect for commuter flights. According to their Web site:

For short-haul markets, The Short Take-Off and Landing ("STOL") capability of Aeroscraft, its relatively low noise, and efficient fuel consumption (due to lower power levels) give the Aeroscraft power advantages. Aeroscraft will be comfortably competitive in short-haul markets, which have to date been largely uneconomical for traditional airliners. The airlines have largely abandoned service routes between 20 and 300 miles, but Aeroscraft could operate profitably in these markets, restore service between city centers and even minor airports, and work as a feeder to international airports and hubs.

Some other suggested uses:

• Agriculture and Environmental - An Aeroscraft could carry a huge amount of water to dump on a fire in a remote location. It could also deliver fertilizer and assist in identifying sources of pollution.
• Disaster relief - In the wake of a natural disaster, the lack of infrastructure can make it very difficult to bring in aid supplies in large quantities. The Aeroscraft could haul medical supplies, drinking water and food directly to the affected areas.

Worldwide Aeros plans to have a prototype Aeroscraft ready for testing by 2010. It's too early in the development stage to know how much it will cost to manufacture an Aeroscraft. However, the company claims that they will cost 30 percent less in capital costs and 50 percent less in maintenance costs than conventional aircraft [ref]. Two companies have already signed agreements to receive the first Aeroscrafts when it is ready for commercial production.

For lots more information on the Aeroscraft and related topics, check out the links on the next page.

Worldwide Aeros Corporation

Image courtesy Worldwide Aeros Corp. The Aerostat, a tethered balloon system made by Worldwide Aeros

The company now known as Worldwide Aeros Corporation started out at Aeros, Ltd., a small company founded in the Ukraine by Igor Pasternak. After growing up in the city of Lviv, Ukraine, Pasternak received a Masters degree in engineering from Lviv Politechnike. After achieving success with Aeros, Ltd. in developing and marketing lighter-than-air craft in Europe and Asia, Pasternak moved the company to New York in 1992. In 1994, they moved again, to California, where the company operates today. Worldwide Aeros Corp designs and manufactures blimps and other lighter-than-air craft for a wide variety of uses.