Electronic Design

New Modes Of Air transport Awaken A Slumbering Industry

New winds flowing through aviation hope to whirl some good in the direction of electronics designers in an industry segment that's seen little growth since the 1970s. If these trends continue apace, the entire air-traffic-control infrastructure will get a facelift.

The deregulation of the airline industry in 1978 led to an infrastructure based on large aircraft hauling hundreds of passengers at a time between hubs and dispersing them to their destinations via regional jets.

Airbus' 550-passenger A380 is the largest hub-to-hub craft to date. Boeing's 223-seat 787, announced at the end of April, is designed to serve the evolving "point-to-point" market. Planes such as Bombardier's 50-passenger Canada Regional Jet 900 and Embraer's 110-seat 195 handle shorter runs. Corporate jets range from the 18-passenger General Dynamics Gulfstream 550 to Cessna's six-passenger Citation CJ3.

Today, the climate is changing, one aspect being an onrush of smaller corporate aircraft dubbed very light jets, or VLJs (Fig. 1). Priced at a couple of million dollars or less and designed to be flown by a single pilot, the VLJ's appeal is boosted by a new fractional-ownership model. This setup relieves some of the burden corporations must otherwise handle when maintaining their own private fleets.

Under fractional ownership, the corporation owns as little as a 1/16 share, or 50 hours per year of one aircraft, but gains access to an entire fleet. This includes simultaneous access to more than one aircraft. For any given flight, the only passengers on the plane are company employees. Compared to sending execs to out-of-the-way locations via an airline cattle-car hub-to-hub flight, followed by waiting for connections on a regional jet, the fractional ownership holds lots of appeal. And nobody has to be wanded or take off their shoes to get to the plane.

The other part of the equation are the low-cost VLJs that make fractional ownership fleets attractive. The National Business Aircraft Association (NBAA) defines VLJs as jet aircraft weighing 10,000 pounds or less, certified for single-pilot operations. They also may feature advanced cockpit automation, automated engine and systems management, and integrated autoflight, autopilot, and flight-guidance systems.

Eclipse Aviation, the most aggressive promoter of VLJs, started taking orders in 2000 for an aircraft that was still on the drawing board. Today, three Eclipse 500 aircraft are flying and undergoing certification testing. Originally envisioned with modified Tomahawk missile engines, Eclipse switched to Pratt and Whitney PW610F engines last year. Still, the original sub-million-dollar price tag has only moved up to $1,175,000.

Cessna has been in the light-jet business for years with its Citation series. Its latest plane is the Citation Mustang. Priced at $2.29 million, this VLJ is more expensive than the Eclipse, but still a million bucks less than the cheapest production bizjet today. The prototype had its first flight in April. Two production Mustangs are scheduled to start the FAA certification test program later this year.

Earlier this year, Embraer announced plans for a new VLJ that's faster and has more seating—six to eight passengers—than the Eclipse or Mustang. It should be available in mid-2008.

Although none of these airplanes is in full production, Cessna and Eclipse have already received deposits for hundreds of orders. Presumably, when they achieve full production status, more eager buyers will line up.

At the other performance extreme from VLJs, there's the light sport aircraft (Fig. 2). Last year, the FAA approved the light sport aircraft proposal, opening the door to a class of general-aviation aircraft and pilot certificates between the recreational-pilot and private-pilot classes.

Light sport aircraft must stall at no more than 51 mph, cruise no faster than 138 mph, and weigh no more than 1320 lb (1430 lb for seaplanes). Also, they can't have more than two seats. They must have no more than one engine, fixed landing gear, and a fixed-pitch prop as well.

Sport pilots have less stringent training requirements than private pilots. Unlike private pilots who must undergo a physical exam with an FAA-recognized flight surgeon every six months to three years, depending on age and class of license, sport pilots need only a current driver's license to meet the medical requirements. (Medical issues constitute a vanishingly small component of in-flight accident causes for all classes of pilot.) Sport pilots can't fly at night, or when visibility is less than three miles, or over a solid cloud deck. And, they must have additional endorsements for flying where radio communication is required.

The new Sport Pilot rule supports flying purely for the joy of it, but at a higher level than the existing ultralight rules. This may spawn a resurgence of simple aircraft carrying basic instrumentation and radio gear. In fact, a number of rather efficient designs have sprung up from companies in Europe and Australia. As they take to the air, they will have to be integrated into the air traffic system.

Single-pilot corporate VLJs and light sport aircraft will make a significant impact. FAA documents show an existing base of only between 300,000 and 400,000 non-airline pilots in the U.S., flying a fleet of roughly 275,000 small planes. (The entire U.S. air-carrier fleet numbers fewer than 10,000 planes.)

As the airfleet expands, several key questions should interest electronics engineers. How will the air-traffic-control infrastructure handle the growth? Where will all of these airplanes take off and land? And what kind of support is it going to take from the design engineering community? If this is going to affect you, you'll need to get ready for some new systems. And like all good things that come from the government, they're identified by acronyms.

Replacing the array of round-face "steam-gauge" instruments that defined aircraft control panels from the 1930s on, a primary flight display (PFD) combines all pneumatic (airspeed, altitude, rate-of-climb), engine, radio (navigation and communications), and other displays on one or two video screens. The first civilian PFDs appeared in the airliners of the late 1980s. Today, with cheap and powerful embedded processing and flat-panel displays, they've migrated down to bizjets and even into single-engine trainers from Cessna and Diamond.

On the PFD, NASA's Highway in the Sky (HITS) technology plots a 3D "tunnel" along the flight path (Fig. 3). The tunnel appears as a series of green boxes superimposed over the terrain presentation on the PFD. Pilots simply "fly"an electronic representation of their airplane through the boxes all the way to their destination and down the glideslope (the angle between horizontal and the glide path of an aircraft) to the runway.

As an example of a PFD (although in this generation without the HITS boxes), Avidyne's Entegra system has two 10.7- by 8.5-in. flat screens (Fig. 4). One is called an electronic attitude direction indicator (EADI). The other is an electronic horizontal situation indicator (EHSI). The EADI displays the basic attitude display, consisting of a brown, earth-tone background with a blue sky above it. Superimposed on this are tape indicators for airspeed and altitude, plus trend indicators for airspeed, altitude, and heading. Inside the box is a solid-state gyro, heading, and air data system with plumbing for ram-air and static air-pressure inputs, which are the raw data for pressure-altitude, airspeed, and rate-of-climb information. Position information comes from a separate GPS system.

The wide area augmentation system (WAAS), which supplements all-satellite GPS coverage by providing higher precision in all axes, became available in the fall of 2000. It currently comprises 25 ground reference stations, two geostationary satellites, two master stations, and four uplink stations. WAAS detects errors in the basic GPS positioning service and broadcasts corrections via the two geostationary satellites.

Satellite-based instrumentation actually costs less than installing new versions of 1950s-era instrument-landing systems. Thus, the FAA is using WAAS to provide precision instrument-landing airport approaches to most airports in the country. (There's no need for a control tower for instrument approaches.)

Even with WAAS, GPS approaches don't allow ceilings and visibilities as low as conventional instrument approaches. However, a new constellation of GPS satellites that replace the present coarse/acquisition (C/A) code with a new code called L2/C will change things. The first of these satellites was supposed to launch this year, but the earliest projected date for full coverage is 2009.

As of March of this year, the FAA requires all turbine-powered aircraft with six or more passenger seats to be equipped with a terrain awareness and warning system (TAWS). Systems combine GPS position information with a terrain database that includes towers and man-made obstacles higher than 200 feet. A Class-A TAWS has a terrain display, while a Class B TAWS provides terrain warning via voice callouts.

The National Weather Service's next-generation radar (NEXRAD) is a network of Doppler radars that detect precipitation and some wind effects, such as the presence of wind-shear and microbursts, which make landing approaches dangerous. The information is processed and distributed by the government and various for-pay services via the Web and satellite radio.

Information from satellite radio now provides near-real-time weather imagery to the cockpit (Fig. 5). It's less expensive than onboard weather radar, and it provides more information than systems that merely detect nearby lightning strokes.

A new collision-avoidance technology, Automatic Dependent Surveillance-Broadcast (ADS-B), is now in developmental service along the U.S. East Coast. ADS-B uses GPS technology to send the aircraft's real-time position along with its call sign and ATC-assigned (air traffic control) transponder code once every second to other ADS-B-equipped aircraft.

As an adjunct to ADS-B, Traffic Information Service-Broadcast (TIS-B) sends out traffic information from ground-based air-traffic surveillance sensors, typically radar, to ADS-B-equipped aircraft. It reports all aircraft, not just those equipped with ADS-B. These systems are further supplemented by the Flight Information Services-Broadcast (FIS-B) system, which provides pilots and flight crews of properly equipped aircraft with a cockpit display of NEXRAD weather-radar data as well as textual weather forecasts and reports.

Full authority digital engine control (FADEC) refers to digital aircraft engine control. It dates back to the 1970s, when NASA and Pratt and Whitney flew the first experimental FADEC on an F-111 fighter. Later, P&W's PW2000 was the first civilian aircraft with FADEC. Based on throttle position and inputs from engine sensors, the FADEC system calculates and precisely controls the fuel flow rate to the engines for precise thrust.

Although originally a jet-engine control, FADEC has been applied to fuel-injected gasoline and diesel piston engines for aircraft. For gas-powered engines, Teledyne/Aerosance's FADEC system uses pulsed/timed fuel injection and variable spark timing to run the engine at peak efficiency. The only moving part is a valve in each fuel injector nozzle. Solid-state master power controllers (MPCs) replace the magnetos. The engine sensors provide cylinder head and exhaust-gas temperature data.

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