Engineers DRIVE a light aircraft revival

By Mark Allan Gottschalk; Anna Allen -- Design News, September 6, 1998

Picture yourself flying off to the office in the morning. You're clutching a mug of coffee in your right hand and steering a light aircraft with your left along a virtual road. This scenario isn't just some science fiction writer's vision of the future, but rather the expected results of design advancements in the general aviation industry. Like a phoenix rising from the ashes, general aviation is back. Nearly exterminated in the 1980's, the industry has recently seen a jump in research, development, and production activity perhaps unmatched in history. Around the world, engineers are on a mission to launch light aircraft design into the 21st century.

The life signs are appearing not a day too soon. Over the past 20 years, production of general aviation (GA) aircraft plunged 94%, from 17,811 in 1978 to just 1,132 in 1996. During this same time frame the cost of a single-engine aircraft as compared to the mean family income went from a factor of 2:1 to 4:1. The average light aircraft is 28 years old and incorporates antiquated flight deck layouts and piston propulsion technology from the 1950s and 1960s.

Yet, light aircraft account for a surprising 62% of the total flight hours, 37% of the miles, and 78% of the departures in the U.S.--figures that advocates hope to significantly increase by moving the popular air travel metaphor away from that of an air bus and closer to an air car.

To that end, NASA has made the revival of the general aviation industry a significant portion of one of the administration's "Three Pillars of Success." It has allocated more than $115 million to two government/industry collaborative efforts focused on the task. The largest of these is the Advanced General Aviation Technology Experiment (AGATE). Begun in 1994, the five-year program matches more than $60 million with 70 industry partners in an extraordinarily broad push to develop new technologies in several areas, including:

- Design and manufacturing

- Integrated flight systems

- Propulsion sensors and controls

The program's goals are highly ambitious. "We can create a small aircraft transportation system for the 21st century that delivers the ability to move about in the air at four or five times the speed of highways at the level of affordability we've come to expect from automobiles," says Bruce Holmes, NASA's AGATE program manager. "By 2001 we will have finished the essential technology ingredients for the industry to produce a first-generation AGATE plane; this should re-energize the marketplace."

AGATE is complemented by the General Aviation Propulsion (GAP) program, a four-year, $55-million effort launched in 1997 that targets the heart of every airplane: the engine. Two powerplants will emerge from GAP. At the high end is a low-cost turbofan being engineered by Williams Int'l (Walled Lake, MI). For entry-level GA aircraft, Teledyne Continental Motors (TCM) of Mobile, AL, is designing a two-stroke, compression-ignition piston engine that runs on Jet A/JP-8 or diesel fuel.

Both programs depict a future for the past 30 to 40 years pundits have insisted was just around the corner. The difference this time? Engineering experts say we are finally at the point where technology can deliver the vision.

Two factors are driving this potential sea change. The first is the plummeting price and soaring abundance of information, combined with ever-more-powerful and cheaper computing systems to process it. "The convergence right now of various information technologies will make it possible to operate a vehicle in three dimensions with much the same simplicity we've come to expect from operating a vehicle in two dimensions," says NASA's Holmes.

The second factor is the development of inexpensive, quiet, reliable, efficient powerplants. "If you look back at the aircraft industry, every major step in aircraft development was due to a major step in propulsion," says Leo Burkart, GAP program manager at NASA Lewis. "New engines alone won't reinvigorate the industry," he notes, "but a lack of new engines could prevent it."

Engines beget airplanes. At Williams Int'l, engineers are busy designing the engine they feel will bring jet propulsion to the masses. Called the FJX-2, it's a 14-inch diameter by 41-inch-long, barrel-shaped dynamo that weighs less than 100 lbs yet pumps out 700 lbs of thrust. Its 4:1 bypass ratio helps make it "the world's quietest jet engine by far," says Dr. Sam Williams, the company's chairman. But the real secret is its low cost.

Williams is shooting for an order-of-magnitude reduction in cost for a typical engine of this class. "We've got to take these from hundreds of thousands of dollars down to tens of thousands of dollars," says Burkart. The only reason the turbine engine is not the dominant form of propulsion in the light aircraft market today is that it costs too much, he explains. They've got pretty much everything else--high performance, low weight, and natural smoothness.

Engineers made cost reduction a primary design driver. Parts count is always an enemy, and they attacked it ruthlessly. "A small engine is not just a big engine scaled down," says Dr. Williams. "If it were, you'd have 10,000 parts." Though he won't reveal the exact number of components in the FJX-2, a small cruise missile engine produced by the company has about 600 parts.

Designers combined as many parts as possible into one. An example: the fan, instead of being an assembly of blades attached to a hub, is machined from a single titanium forging. Housings serve multiple purposes, combining several functions into one part.

Another target is the mechanical power takeoff. On a typical jet engine, the starter and mechanical power takeoff for things like the hydraulic system might account for as much as 20% of the overall engine cost. Williams Int'l is said to be developing an integral high-speed starter/generator, though the company won't confirm this.

The engine is aimed at single- and twin-engine four- to six-passenger aircraft capable of 350 to 400 knots. At the Experimental Aircraft Assn. convention in Oshkosh last year, the company flew an experimental twin-engine jet aircraft powered by FJX-1 turbofans developed previously by Williams Int'l. Called the V-JET II, the flight demonstrator was designed and produced by Scaled Composites (Mojave, CA), and the aircraft serves as a showcase for advanced aircraft structure technology.

The V-JET II's fuselage consists of just five parts. An example is the monolithic structure that begins at the pressure bulkhead in front of the rudder pedals and extends to the tail. It includes the windshield frames, door frames, bulkheads, longerons, wing mounts, and skin. It was formed in a single cure with no secondary bonds and no fasteners.

It's come a long way, but more work is necessary. "This only goes part of the way to what I would consider acceptable for mass production," says Burt Rutan, president of Scaled Composites. "We need a fuselage that is built by machine in 20 to 30 min; it will most likely be thermoplastic, not thermoset."

Piston progress. Regardless of Williams' ambition to make the turbine engine the only engine, the piston engine appears to have a healthy future. Aimed more at the entry-level airplane buyer are two designs that shun the leaded gasoline used by today's light aircraft. One is being developed by TCM, and the other by a small research and development firm called D-Starr Engineering (Shelton, CT). Uniquely, both are compression-ignition engines and, if successful, would be the first widespread use of this earliest of internal combustion methods.

Engineers have numerous incentives to design for heavier fuels such as JP-8, Jet-A, or diesel oil. Today, general aviation is the only application of leaded gasoline. Lead is an environmental hazard, and leaded fuel is not as readily available worldwide as jet fuel. The heavier fuels are also much less volatile and dangerous in an accident.

After fuel, significant design drivers included reducing noise, vibration, and harshness, and increasing durability and performance. NASA also challenged designers to cut cost by 50%.

TCM's design consists of a four-cylinder, two-stroke, horizontally opposed, liquid-cooled configuration, with turbocharged uniflo combustion, four exhaust valves per cylinder, and a high-pressure direct injection fuel system. A mono block design reduces part count substantially, contributing towards reduced cost, increased reliability, and projected time between overhaul of more than 3,000 hours. Output is expected to be about 200 hp.

Though TCM officials won't confirm the figures, industry experts say the engine displaces 241 cubic inches and weighs approximately 290 lbs. Two-stroke diesel engines normally require a supercharger for scavenging. "However, we believe that supercharging is not efficient at higher power output and we have added a turbocharger," explains TCM president Bryan Lewis in a written statement to Design News.

NASA officials say that the company has been working with Turbodyne (Woodland Hills, CA), a manufacturer of turbochargers augmented with electric motors that keep the turbocharger spinning when exhaust flow alone will not. If successful, this technology might allow TCM to eliminate the supercharger and its related drive assembly altogether.

Another interesting development, though not part of the General Aviation Propulsion program, D-STAR Engineering's motor is also a two-stroke compression ignition design. The company plans to create a family of engines ranging from two to six cylinders and 80 to 300 hp.

Anyone familiar with diesel truck engines know that they typically have high compression ratios necessitating a stout, heavy design. D-STAR's design trims about 20% of this weight by eliminating the valve train. "And we save another 20% because our combustion method doesn't require the engine structure to be as strong," says S. Paul Dev, the company's president.

In a typical diesel engine, fuel is injected into the hot, compressed air inside the cylinder for about 2 msec. At roughly 0.5 msec, the first droplets of fuel ignite like a bomb producing very high peak pressures and requiring a strong structure to contain it.

"Our objective was to reduce the compression ratio of the engine and to reduce this {combustion} delay period to get a lower starting pressure before combustion and a smaller increment in pressure from compression to combustion," says Dev. The patent-pending solution includes ceramic inserts that allow the engine to run very hot on the inside yet cool on the outside.

Also unusual is the engine's very short stroke and high operating rpm. The compression ratio is only about 16:1 vs. 24:1 for the typical diesel. This is combined with a proprietary breathing system that is claimed to have an efficiency of 89% as compared to the roughly 65-70% found in most two-stroke motorcycles. Says Dev, "The breathing system allows us to work with a very short stroke and actually get a higher efficiency than many conventional two-stroke engines, without using valves."

Cockpit contrivances. Under AGATE's Flight Systems work package, a series of companies are developing the cockpit of the future which will provide pilots with graphical, easy-to-interpret information on traffic, weather, and aircraft status.

"For years, it seems, we've had airplanes flying around in the sky, and in some cases, crashing," comments Ron Crotty, manager of public affairs at Allied Signal. "And in the vast majority of cases, pilot error gets the blame--which in most cases means being human. There are lots of traps out there that very good pilots fall into."

To assist pilots, Cirrus Design's (Duluth, MN) Panel 2000 will incorporate GPS navigation with small, low-cost, lightweight automotive sensors, and commercial, off-the-shelf multi-function cockpit graphical displays to present real and predictive virtual "highways in the sky."

"There's nothing really cosmic about this stuff," says Dean Vogel, VP of research and technology at Cirrus Design. "It's just that components have gotten smaller, lighter, and less expensive due to the juggernaut of the PC industry, and it's finally become economically possible for the small-aircraft industry to piggyback on the juggernaut."

Software plays a key role. "Typically, to certify software with the FAA, you have to start off with all source code, and be capable of testing all types of combo calls," says Vogel. He notes that using an operating system such as Windows NT to do this "is an extremely daunting task at the very least, if not impossible." Instead, engineers use open-source software so that they can control the source code and track modifications they make to it."

Weather watchers & traffic trackers. An initial application will be a simple moving-map display driven by GPS. Later, it will incorporate Storm Scope from BF Goodrich Avionics Systems (Grand Rapids, MI) to detect lightning. This device will help pilots avoid turbulence associated with lightning by overlaying the lightning information on top of the moving map display.

Eventually, engineers will add capabilities such as engine monitoring that could, for instance, alert the pilot to an oil-pressure problem. "All of these features conduct monitoring tasks that are very tedious for pilots to do," says Vogel. "It backs pilots up in a capable way, and at the same time reduces pilot workload."

Cirrus' Panel 2000 project also incorporates Data Link Weather from ARNAV (Puyallup, WA). The company will collect information from ground-based weather services, making it available for pilot viewing after only a slight delay.

Traffic information or CDTI (cockpit display of traffic information) can be data-linked to aircraft in a similar way. It will allow pilots to see the location of other aircraft and ground objects in relation to their current position.

Trimble/Avidyne will introduce the Trim View 500 at this year's Oshkosh Fly-In. The system includes a set of avionics with audio panels, IFR (Instrument Flight Rules), GPS receivers, communication and navigation radios, and transponders. Avidyne's Flight Situation Displays integrate moving map displays with airports, airways, and weather information, and offer an upgrade path to including topography, obstacles, and nearby traffic.

Trim View 500 will run Avidyne's software, be part of the Trim Line products, and run Avidyne applications. The map displays allow the pilot to watch the airplane fly along a VFR chart (road map), and IFR charts which simulate navigation information and radio stations. The system has been dubbed "Information Central" because of its ability to display information from many sources on a single screen.

While Cirrus Design chose open-source software, Avidyne has received FAA certification to use Microsoft's Windows NT operating system. "By taking an essentially off-the-shelf operating system, it is easier to write applications with the future in mind rather than having to write all the software from scratch," says Charles Gunderson, general manager at Trimble Avionics. For instance, to develop a weather radar, engineers simply have to create a hardware interface and write a Windows application to display the proper information.

Trim View runs on an industrial PC powered by an Intel Pentium 166 MHz computer, with a 5 1/2-inch color LCD display that's highly modified so pilots can read it in direct sunlight. The companies expect to have shipped a prototype of the product by the end of August.

Testing the goods. An AGATE Systems Standards Team is working on integrating useful weather controls into a Cessna T210 cockpit and testing the result. They are using ARNAV's 5200 Multi-Functional display (MFD) type-certified box that combines navigation and weather displays into a single display called the graphical pilot interface (GPI).

In tests, engineers restricted the pilots' vision so that only the instruments were visible. The results were interesting, to say the least. "We found that while the pilots were busy looking at maps, communicating with the towers, and so forth, the plane was actually deviating from altitude by several hundred feet," says John Carr, the flight test project leader. Without GPI, it took the pilots anywhere from 3 to 8 min to notice this deviation.

Weather displays provide the pilot with meteorology information updated at 10-minute intervals. "It's like looking at the weather channel up in the airplane," says Carr. Future plans call for sending icing and turbulence information and a predictive hazardous weather forecast. ARNAV is developing its own ground network that is 30% installed across the country.

NavRadio's (Denver, CO) contribution is an affordable, digital, datalink radio that has the potential for quickly communicating weather, clearance, flight planning, maintenance, and other data. It has enough capacity to bring national and regional aviation weather graphics into the cockpit of general aviation airplanes for display on computer screens.

"To have this technology be affordable enough for the single-engine market is a huge advancement," says Carr. "It is one thing to put a very expensive system into an airliner, but to be able to incorporate the technology at a reasonable price is remarkable."

Design challenges

- Cut the cost of light aircraft by one-half, while increasing performance, reliability, and safety.

- Decrease the potential for human error by designing new cockpits that minimize pilot workload.

- Upgrade existing aircraft with tomorrow's cockpits.