Each year TCM participates in the Oshkosh Air Show. The show provides a unique opportunity to visit with a large cross section of our customer base on a wide variety of subjects. One of the most commonly asked questions of TCM representatives each year at Oshkosh relates to the future of the piston powerplant for general aviation. Thanks in large part to the passage of the General Aviation Revitalization Act (GARA) of 1994 and the visionary leadership of NASA Administrator Dan Goldin, the future looks quite different today than only a few years ago.

It is the future which we are attempting to bring rapidly to reality through our NASA General Aviation Propulsion (GAP) program. In 1996 TCM was honored to be the recipient of a competitive award for the Internal Combustion (IC) element of this program. The NASA GAP program is designed to facilitate the development of a revolutionary IC powerplant for entry level general aviation aircraft. If all goes well, the prototype will be running by Oshkosh 1998 and headed for flight testing in late 1999.

The NASA GAP program is a forward thinking technology development program that was championed by NASA Administrator Dan Goldin. Through GAP and its counterpart, the NASA Advanced General Aviation Transport Experiment (AGATE) Program, NASA is encouraging the development and transfer to industry of world leading technologies to make general aviation an integral part of our country's future transportation infrastructure. Although the engine programs have received much attention, the total scope of NASA's efforts are leading the development of the data links and systems technologies that will bring the space age to general aviation.

To ensure the engine system integrates fully into this vision, the TCM GAP engine program includes a progressive six member industry team which includes airframe, engine controls, and propeller companies. TCM began design work on the new engine in April of 1997 and the project is now moving to detailed design of the prototype components.

In envisioning the next generation IC powerplant, the fundamental decision was to begin with a completely new core to maximize the use of modern and promising technology. The goals of the program were aggressive but obvious; dramatically lower acquisition cost, improved ease of operation, lower noise and vibration, low emissions, minimum maintenance, and extended engine life. Although we frequently refer to the engine as a "diesel", the fuel envisioned is Jet A, the fuel used to power today's turbine engines. Use of Jet A provides only a slight fuel cost advantage domestically, but solves the availability and cost issue in many international locations where gasoline aviation fuel is either not available, or prohibitively expensive.

Diesel engines are certainly not new and their durability in severe duty cycles are well established. The challenge is to realize that durability and performance potential at a total system weight and cost that can work in an aircraft. Not surprisingly, therefore, the majority of the technology challenge of the TCM GAP engine is to achieve a weight and a cost that is better than today's piston aircraft engines in a diesel cycle. To help meet these challenges, the design minimizes parts count and maximizes stiffness through the use of an advanced structural casting which encompasses many of today's individual parts such as cylinders, induction systems, coolant passages, push rod covers and lubrication systems.

"The TCM GAP engine integrates advanced technologies to improve engine capability."

To help meet the weight challenge, a two cycle configuration was selected. Noise and vibration will be improved through a direct drive propeller speed of only 2200 RPM and a cylinder firing frequency that is equal to an eight cylinder automobile engine. When coupled with the development of improved engine mounts and vibration isolators, the engine holds great promise for smoothness. To help meet the reliability and performance targets, four valves per cylinder are used. The engine is designed to be much like your automotive unit from a service standpoint; no major maintenance of the powerplant is expected throughout its planned operational life.

The new engine is a modular design that can eventually cover a wide variety of horsepower. The prototype technology demonstrator is a four cylinder engine that provides 200 horsepower at a fuel specific of .36. To meet the performance goals of the program, the engine is both lightly supercharged and turbocharged and can be expected to hold sea level power through approximately 12,000 feet. Six and eight cylinder variations could provide growth to almost 500 horsepower.

To shorten the overall design and development cycle, the latest in computerized design technology is being employed.

"Advanced computer design tools are being used in the TCM GAP design. The unique rod arrangement of the engine is shown in this computer 3D image."

Control of the engine will be with a single lever control, eventually supplemented with electronics. Liquid cooling and the diesel cycle eliminate the need for leaning. The low output speed of 2200 RPM allows continuous operation at that speed during takeoff, climb and cruise. Electronic displays and diagnostics are an integral part of the ultimate engine package. Perhaps the day will come when you can down load your engines history through a link with your TCM Link Aviator Services package.

When could this radically new powerplant be available in a production aircraft? We think in about four years if all were to go extremely well. Although we would all like to see earlier availability of this revolutionary step in internal combustion powerplants, the challenges to develop any new engine to production levels are significant. A meaningful evaluation of the suitability and timing for this technology to move to production can be expected within the next two years. The good news is that with the support of the congress in passing GARA and the leadership of NASA, we are at long last moving forward to meet these challenges.

As the NASA GAP program progresses, look for press releases and bulletins on the TCM Link System and our Internet site.